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| author | Jonathan Wakely <jwakely@redhat.com> | 2016-01-13 19:07:21 +0000 |
|---|---|---|
| committer | Jonathan Wakely <redi@gcc.gnu.org> | 2016-01-13 19:07:21 +0000 |
| commit | 260936f29d63bb0cebfd624804c915e528aea575 (patch) | |
| tree | 71bba69fcc54ed2e710937d7b5b9304f6c25f93f /gcc | |
| parent | 398d6febaf20997eedb94bec295e50bd7fc6ed82 (diff) | |
| download | gcc-260936f29d63bb0cebfd624804c915e528aea575.zip gcc-260936f29d63bb0cebfd624804c915e528aea575.tar.gz gcc-260936f29d63bb0cebfd624804c915e528aea575.tar.bz2 | |
Clarify __atomic_compare_exchange effects
* doc/extend.texi (__atomic Builtins): Clarify compare_exchange
effects.
From-SVN: r232341
Diffstat (limited to 'gcc')
| -rw-r--r-- | gcc/ChangeLog | 5 | ||||
| -rw-r--r-- | gcc/doc/extend.texi | 13 |
2 files changed, 12 insertions, 6 deletions
diff --git a/gcc/ChangeLog b/gcc/ChangeLog index ae3afde..a759568 100644 --- a/gcc/ChangeLog +++ b/gcc/ChangeLog @@ -1,3 +1,8 @@ +2016-01-13 Jonathan Wakely <jwakely@redhat.com> + + * doc/extend.texi (__atomic Builtins): Clarify compare_exchange + effects. + 2016-01-13 Richard Henderson <rth@redhat.com> PR tree-opt/68964 diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi index 8122c4c..b85c34c 100644 --- a/gcc/doc/extend.texi +++ b/gcc/doc/extend.texi @@ -9559,17 +9559,18 @@ This compares the contents of @code{*@var{ptr}} with the contents of @code{*@var{expected}}. If equal, the operation is a @emph{read-modify-write} operation that writes @var{desired} into @code{*@var{ptr}}. If they are not equal, the operation is a @emph{read} and the current contents of -@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 +@code{*@var{ptr}} are written into @code{*@var{expected}}. @var{weak} is true +for weak compare_exchange, which may fail spuriously, and false for +the strong variation, which never fails spuriously. Many targets only offer the strong variation and ignore the parameter. When in doubt, use the strong variation. -True is returned if @var{desired} is written into -@code{*@var{ptr}} and the operation is considered to conform to the +If @var{desired} is written into @code{*@var{ptr}} then true is returned +and memory is affected according to the memory order specified by @var{success_memorder}. There are no restrictions on what memory order can be used here. -False is returned otherwise, and the operation is considered to conform +Otherwise, false is returned and memory is affected according to @var{failure_memorder}. This memory order cannot be @code{__ATOMIC_RELEASE} nor @code{__ATOMIC_ACQ_REL}. It also cannot be a stronger order than that specified by @var{success_memorder}. @@ -9678,7 +9679,7 @@ 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), 0)) +if (__atomic_always_lock_free (sizeof (long long), 0)) @end smallexample @end deftypefn |