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re PR web/79738 (Documentation for __attribute__((const)) slightly misleading)

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2018-11-25  Sandra Loosemore  <sandra@codesourcery.com>

	PR web/79738

	gcc/
	* doc/extend.texi (Common Function Attributes): Clarify that
	functions with "const" attribute can read const global variables.

From-SVN: r266445
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Sandra Loosemore 2018-11-25 20:38:00 -05:00 • committed by Sandra Loosemore
parent 47e53bb646
commit 721b7fd257
2 changed files with 15 additions and 6 deletions
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gcc/ChangeLog
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@ -1,3 +1,9 @@
2018-11-25 Sandra Loosemore <sandra@codesourcery.com>
PR web/79738
* doc/extend.texi (Common Function Attributes): Clarify that
functions with "const" attribute can read const global variables.
2018-11-26 Alan Modra <amodra@gmail.com>
* config/rs6000/rs6000.h (OBJECT_PEF, TARGET_MACOS): Delete.

15
gcc/doc/extend.texi
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@ -2521,11 +2521,13 @@ are automatically detected and this attribute is ignored.
Many functions do not examine any values except their arguments, and
have no effects except to return a value. Calls to such functions lend
themselves to optimization such as common subexpression elimination.
The presence of the @code{const} attribute on a function declaration
allows GCC to emit more efficient code for some calls to the function.
The @code{const} attribute imposes greater restrictions on a function's
definition than the similar @code{pure} attribute below because it prohibits
the function from reading global variables. Consequently, the presence of
the attribute on a function declaration allows GCC to emit more efficient
code for some calls to the function. Decorating the same function with
definition than the similar @code{pure} attribute below because it
additionally prohibits the function from reading memory except for
constant global variables. Decorating the same function with
both the @code{const} and the @code{pure} attribute is diagnosed.
@cindex pointer arguments
@ -3315,8 +3317,9 @@ depending on volatile memory or other system resource, that may change between
two consecutive calls (such as @code{feof} in a multithreading environment).
The @code{pure} attribute imposes similar but looser restrictions on
a function's defintion than the @code{const} attribute: it allows the
function to read global variables. Decorating the same function with
a function's definition than the @code{const} attribute: @code{pure}
allows the function to read any non-volatile memory, not just
constant global variables. Decorating the same function with
both the @code{pure} and the @code{const} attribute is diagnosed.
Because a @code{pure} function cannot have any side effects it does not
make sense for such a function to return @code{void}. Declaring such