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extend.texi (x86 transactional memory intrinsics): Reorganize discussion of _xbegin.

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2015-02-27  Sandra Loosemore  <sandra@codesourcery.com>

	gcc/
	* doc/extend.texi (x86 transactional memory intrinsics):
	Reorganize discussion of _xbegin.  Clarify that the return
	value is a bit mask.  Expand example and move to end of section.

From-SVN: r221068
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Sandra Loosemore 2015-02-27 13:59:29 -05:00 committed by Sandra Loosemore
parent 9c78ecc2e6
commit 8eba66e880
2 changed files with 46 additions and 17 deletions

6
gcc/ChangeLog

@ -1,3 +1,9 @@
2015-02-27 Sandra Loosemore <sandra@codesourcery.com>
* doc/extend.texi (x86 transactional memory intrinsics):
Reorganize discussion of _xbegin. Clarify that the return
value is a bit mask. Expand example and move to end of section.
2015-02-26 Jakub Jelinek <jakub@redhat.com>
Aldy Hernandez <aldyh@redhat.com>

57
gcc/doc/extend.texi

@ -17274,24 +17274,11 @@ and suitable fallback code always needs to be supplied.
Start a RTM (Restricted Transactional Memory) transaction.
Returns @code{_XBEGIN_STARTED} when the transaction
started successfully (note this is not 0, so the constant has to be
explicitly tested). If the transaction aborts, all side-effects
are undone and an abort code is returned. There is no guarantee
any transaction ever succeeds, so there always needs to be a valid
fallback path.
@end deftypefn
explicitly tested).
@smallexample
#include <immintrin.h>
if ((status = _xbegin ()) == _XBEGIN_STARTED) @{
... transaction code...
_xend ();
@} else @{
... non transactional fallback path...
@}
@end smallexample
If the transaction aborts, the return value is one of:
If the transaction aborts, all side-effects
are undone and an abort code encoded as a bit mask is returned.
The following macros are defined:
@table @code
@item _XABORT_EXPLICIT
@ -17309,6 +17296,11 @@ Transaction abort due to a debug trap.
Transaction abort in an inner nested transaction.
@end table
There is no guarantee
any transaction ever succeeds, so there always needs to be a valid
fallback path.
@end deftypefn
@deftypefn {RTM Function} {void} _xend ()
Commit the current transaction. When no transaction is active this faults.
All memory side-effects of the transaction become visible
@ -17325,6 +17317,37 @@ The @var{status} is an 8-bit constant; its value is encoded in the return
value from @code{_xbegin}.
@end deftypefn
Here is an example showing handling for @code{_XABORT_RETRY}
and a fallback path for other failures:
@smallexample
#include <immintrin.h>
int n_tries, max_tries;
unsigned status = _XABORT_EXPLICIT;
...
for (n_tries = 0; n_tries < max_tries; n_tries++)
@{
status = _xbegin ();
if (status == _XBEGIN_STARTED || !(status & _XABORT_RETRY))
break;
@}
if (status == _XBEGIN_STARTED)
@{
... transaction code...
_xend ();
@}
else
@{
... non-transactional fallback path...
@}
@end smallexample
@noindent
Note that, in most cases, the transactional and non-transactional code
must synchronize together to ensure consistency.
@node Target Format Checks
@section Format Checks Specific to Particular Target Machines