diff options
author | Andrew MacLeod <amacleod@redhat.com> | 2012-02-10 18:37:18 +0000 |
---|---|---|
committer | Andrew Macleod <amacleod@gcc.gnu.org> | 2012-02-10 18:37:18 +0000 |
commit | 9ac1504be01a543e183091558f1b146a0d7ee25a (patch) | |
tree | c56b1419ca20bae69d8b297f4dcf8e9310ee9e06 /gcc/doc/extend.texi | |
parent | 877fb4507b254f536cbe3aa19e346092e0bf2661 (diff) | |
download | gcc-9ac1504be01a543e183091558f1b146a0d7ee25a.zip gcc-9ac1504be01a543e183091558f1b146a0d7ee25a.tar.gz gcc-9ac1504be01a543e183091558f1b146a0d7ee25a.tar.bz2 |
re PR c/52190 (question about atomic intrinsics -- test and documentation vary -- please clarify)
2012-02-10 Andrew MacLeod <amacleod@redhat.com>
PR c/52190
* doc/extend.texi : Update comments for __atomic_compare_exchange and
__atomic_{is,always}_lock_free.
From-SVN: r184112
Diffstat (limited to 'gcc/doc/extend.texi')
-rw-r--r-- | gcc/doc/extend.texi | 26 |
1 files changed, 17 insertions, 9 deletions
diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi index e821041..a131c91 100644 --- a/gcc/doc/extend.texi +++ b/gcc/doc/extend.texi @@ -7146,7 +7146,10 @@ This built-in function implements an atomic compare and exchange operation. This compares the contents of @code{*@var{ptr}} with the contents of @code{*@var{expected}} and if equal, writes @var{desired} into @code{*@var{ptr}}. If they are not equal, the current contents of -@code{*@var{ptr}} is written into @code{*@var{expected}}. +@code{*@var{ptr}} is written into @code{*@var{expected}}. @var{weak} is true +for weak compare_exchange, and false for the strong variation. Many targets +only offer the strong variation and ignore the parameter. When in doubt, use +the strong variation. True is returned if @code{*@var{desired}} is written into @code{*@var{ptr}} and the execution is considered to conform to the @@ -7242,27 +7245,32 @@ All memory orders are valid. @end deftypefn -@deftypefn {Built-in Function} bool __atomic_always_lock_free (size_t size) +@deftypefn {Built-in Function} bool __atomic_always_lock_free (size_t size, void *ptr) -This built-in function returns true if objects of size bytes will always -generate lock free atomic instructions for the target architecture. -Otherwise false is returned. +This built-in function returns true if objects of @var{size} bytes will always +generate lock free atomic instructions for the target architecture. +@var{size} must resolve to a compile time constant and the result also resolves to compile time constant. -size must resolve to a compile time constant. +@var{ptr} is an optional pointer to the object which may be used to determine +alignment. A value of 0 indicates typical alignment should be used. The +compiler may also ignore this parameter. @smallexample -if (_atomic_always_lock_free (sizeof (long long))) +if (_atomic_always_lock_free (sizeof (long long), 0)) @end smallexample @end deftypefn -@deftypefn {Built-in Function} bool __atomic_is_lock_free (size_t size) +@deftypefn {Built-in Function} bool __atomic_is_lock_free (size_t size, void *ptr) -This built-in function returns true if objects of size bytes will always +This built-in function returns true if objects of @var{size} bytes will always generate lock free atomic instructions for the target architecture. If it is not known to be lock free a call is made to a runtime routine named @code{__atomic_is_lock_free}. +@var{ptr} is an optional pointer to the object which may be used to determine +alignment. A value of 0 indicates typical alignment should be used. The +compiler may also ignore this parameter. @end deftypefn @node Object Size Checking |