e742722f76
This patch adds support for an -Oz command line option, aggressively optimizing for size at the expense of performance. GCC's current -Os provides a reasonable balance of size and performance, whereas -Oz is probably only useful for code size benchmarks such as CSiBE. Or so I thought until I read in https://news.ycombinator.com/item?id=25408853 that clang's -Oz sometimes outperforms -O[23s]; I suspect modern instruction decode stages can treat "pushq $1; popq %rax" as a short uop encoding. Instead of introducing a new global variable, this patch simply abuses the existing optimize_size by setting its value to 2. The only change in behaviour is the tweak to the i386 backend implementing the suggestion in PR target/32803 to use a short push/pop sequence for loading small immediate values (-128..127) on x86, matching the behaviour of LLVM. On x86_64, the simple function: int foo() { return 25; } currently generates with -Os: foo: movl $25, %eax // 5 bytes ret With the proposed -Oz, it generates: foo: pushq $25 // 2 bytes popq %rax // 1 byte ret On CSiBE, this results in a 0.94% improvement (3703513 bytes total down to 3668516 bytes). 2021-12-18 Roger Sayle <roger@nextmovesoftware.com> gcc/ChangeLog PR target/32803 * common.opt (Oz): New command line option. * doc/invoke.texi: Document the new -Oz option. * lto-wrapper.c (merge_and_complain, append_compiler_options): Treat OPT_Oz as synonymous with OPT_Os. * optc-save-gen.awk: Increase maximum value of optimize_size to 2. * opts.c (default_options_optimization) [OPT_Oz]: Handle OPT_Oz just like OPT_Os, except set opt->x_optimize_size to 2. (common_handle_option): Skip OPT_Oz just like OPT_Os. * config/i386/i386.md (*movdi_internal): Use a push/pop sequence for suitable SImode TYPE_IMOV moves when optimize_size > 1. (*movsi_internal): Likewise. gcc/testsuite/ChangeLog PR target/32803 * gcc.target/i386/pr32803.c: New test case. |
||
|---|---|---|
| c++tools | ||
| config | ||
| contrib | ||
| fixincludes | ||
| gcc | ||
| gnattools | ||
| gotools | ||
| include | ||
| INSTALL | ||
| intl | ||
| libada | ||
| libatomic | ||
| libbacktrace | ||
| libcc1 | ||
| libcody | ||
| libcpp | ||
| libdecnumber | ||
| libffi | ||
| libgcc | ||
| libgfortran | ||
| libgo | ||
| libgomp | ||
| libiberty | ||
| libitm | ||
| libobjc | ||
| liboffloadmic | ||
| libphobos | ||
| libquadmath | ||
| libsanitizer | ||
| libssp | ||
| libstdc++-v3 | ||
| libvtv | ||
| lto-plugin | ||
| maintainer-scripts | ||
| zlib | ||
| .dir-locals.el | ||
| .gitattributes | ||
| .gitignore | ||
| ABOUT-NLS | ||
| ar-lib | ||
| ChangeLog | ||
| ChangeLog.jit | ||
| ChangeLog.tree-ssa | ||
| compile | ||
| config-ml.in | ||
| config.guess | ||
| config.rpath | ||
| config.sub | ||
| configure | ||
| configure.ac | ||
| COPYING | ||
| COPYING.LIB | ||
| COPYING.RUNTIME | ||
| COPYING3 | ||
| COPYING3.LIB | ||
| depcomp | ||
| install-sh | ||
| libtool-ldflags | ||
| libtool.m4 | ||
| ltgcc.m4 | ||
| ltmain.sh | ||
| ltoptions.m4 | ||
| ltsugar.m4 | ||
| ltversion.m4 | ||
| lt~obsolete.m4 | ||
| MAINTAINERS | ||
| Makefile.def | ||
| Makefile.in | ||
| Makefile.tpl | ||
| missing | ||
| mkdep | ||
| mkinstalldirs | ||
| move-if-change | ||
| multilib.am | ||
| README | ||
| symlink-tree | ||
| test-driver | ||
| ylwrap | ||
This directory contains the GNU Compiler Collection (GCC). The GNU Compiler Collection is free software. See the files whose names start with COPYING for copying permission. The manuals, and some of the runtime libraries, are under different terms; see the individual source files for details. The directory INSTALL contains copies of the installation information as HTML and plain text. The source of this information is gcc/doc/install.texi. The installation information includes details of what is included in the GCC sources and what files GCC installs. See the file gcc/doc/gcc.texi (together with other files that it includes) for usage and porting information. An online readable version of the manual is in the files gcc/doc/gcc.info*. See http://gcc.gnu.org/bugs/ for how to report bugs usefully. Copyright years on GCC source files may be listed using range notation, e.g., 1987-2012, indicating that every year in the range, inclusive, is a copyrightable year that could otherwise be listed individually.