2016-01-20 Martin Sebor <msebor@redhat.com>
PR c/52291
* extend.texi (__sync Builtins): Clarify the semantics aof
__sync_fetch_and_OP built-ins on pointers.
(__atomic Builtins): Same.
===================================================================
@@ -9262,8 +9262,11 @@ work on multiple types.
The definition given in the Intel documentation allows only for the use of
the types @code{int}, @code{long}, @code{long long} or their unsigned
-counterparts. GCC allows any integral scalar or pointer type that is
-1, 2, 4 or 8 bytes in length.
+counterparts. GCC allows any scalar type that is 1, 2, 4 or 8 bytes in
+size other than the C type @code{_Bool} or the C++ type @code{bool}.
+Operations on pointer operands are performed as if the operands were
+of the @code{uintptr_t} type. That is, they are not scaled by the size
+of the type to which the pointer points.
These functions are implemented in terms of the @samp{__atomic}
builtins (@pxref{__atomic Builtins}). They should not be used for new
@@ -9309,7 +9312,11 @@ accessible variables should be protected
@findex __sync_fetch_and_xor
@findex __sync_fetch_and_nand
These built-in functions perform the operation suggested by the name, and
-returns the value that had previously been in memory. That is,
+returns the value that had previously been in memory. That is, operations
+on integer operands have the following semantics. Operations on pointer
+operands are performed as if the operands were of the @code{uintptr_t}
+type. That is, they are not scaled by the size of the type to which
+the pointer points.
@smallexample
@{ tmp = *ptr; *ptr @var{op}= value; return tmp; @}
@@ -9335,7 +9342,9 @@ as @code{*ptr = ~(tmp & value)} instead
@findex __sync_xor_and_fetch
@findex __sync_nand_and_fetch
These built-in functions perform the operation suggested by the name, and
-return the new value. That is,
+return the new value. That is, operations on integer operands have
+the following semantics. Operations on pointer operands are performed as
+if the operands were of the @code{uintptr_t} type. That is, they are not
+scaled by the size of the type to which the pointer points.
@smallexample
@{ *ptr @var{op}= value; return *ptr; @}
@@ -9592,7 +9601,9 @@ pointer.
@deftypefnx {Built-in Function} @var{type} __atomic_or_fetch (@var{type} *ptr, @var{type} val, int memorder)
@deftypefnx {Built-in Function} @var{type} __atomic_nand_fetch (@var{type} *ptr, @var{type} val, int memorder)
These built-in functions perform the operation suggested by the name, and
-return the result of the operation. That is,
+return the result of the operation. Operations on pointer operands are
+performed as if the operands were of the @code{uintptr_t} type. That is,
+they are not scaled by the size of the type to which the pointer points.
@smallexample
@{ *ptr @var{op}= val; return *ptr; @}
@@ -9610,7 +9621,10 @@ type. It must not be a Boolean type. A
@deftypefnx {Built-in Function} @var{type} __atomic_fetch_or (@var{type} *ptr, @var{type} val, int memorder)
@deftypefnx {Built-in Function} @var{type} __atomic_fetch_nand (@var{type} *ptr, @var{type} val, int memorder)
These built-in functions perform the operation suggested by the name, and
-return the value that had previously been in @code{*@var{ptr}}. That is,
+return the value that had previously been in @code{*@var{ptr}}. Operations
+on pointer operands are performed as if the operands were of
+the @code{uintptr_t} type. That is, they are not scaled by the size of
+the type to which the pointer points.
@smallexample
@{ tmp = *ptr; *ptr @var{op}= val; return tmp; @}