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* [Bug target/48227] New: "rep ret" generated for -march=core2
@ 2011-03-22 9:10 zuxy.meng at gmail dot com
2011-04-01 19:21 ` [Bug target/48227] " pinskia at gcc dot gnu.org
` (4 more replies)
0 siblings, 5 replies; 6+ messages in thread
From: zuxy.meng at gmail dot com @ 2011-03-22 9:10 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48227
Summary: "rep ret" generated for -march=core2
Product: gcc
Version: 4.5.4
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
AssignedTo: unassigned@gcc.gnu.org
ReportedBy: zuxy.meng@gmail.com
gcc 4.5 will use "rep; ret" for K8, Athlon, AMDFam10, Core2, and
generic. Looking into the change history, we can see that gcc has padded
returns for Core2 ever since Core2 support was added here:
http://gcc.gnu.org/ml/gcc-patches/2006-11/msg00860.html
It is suspected
that Vlad just copied the generic tunings for Core2, and didn't notice
that there was no particular reason to pad returns for Core2.
^ permalink raw reply [flat|nested] 6+ messages in thread* [Bug target/48227] "rep ret" generated for -march=core2
2011-03-22 9:10 [Bug target/48227] New: "rep ret" generated for -march=core2 zuxy.meng at gmail dot com
@ 2011-04-01 19:21 ` pinskia at gcc dot gnu.org
2011-04-02 0:55 ` ian at airs dot com
` (3 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: pinskia at gcc dot gnu.org @ 2011-04-01 19:21 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48227
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target| |x86_64-linux-gnu
--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> 2011-04-01 19:20:52 UTC ---
A good question is does it make a difference in actual performance numbers, it
might still make a positive difference. Until someone tries it out and sees
the difference in performance, I am going to say we should keep it.
^ permalink raw reply [flat|nested] 6+ messages in thread* [Bug target/48227] "rep ret" generated for -march=core2
2011-03-22 9:10 [Bug target/48227] New: "rep ret" generated for -march=core2 zuxy.meng at gmail dot com
2011-04-01 19:21 ` [Bug target/48227] " pinskia at gcc dot gnu.org
@ 2011-04-02 0:55 ` ian at airs dot com
2011-04-06 13:42 ` zuxy.meng at gmail dot com
` (2 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: ian at airs dot com @ 2011-04-02 0:55 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48227
--- Comment #2 from Ian Lance Taylor <ian at airs dot com> 2011-04-02 00:55:40 UTC ---
If it doesn't make a difference in performance, we should get rid of it, so
that we can save a byte of code.
^ permalink raw reply [flat|nested] 6+ messages in thread* [Bug target/48227] "rep ret" generated for -march=core2
2011-03-22 9:10 [Bug target/48227] New: "rep ret" generated for -march=core2 zuxy.meng at gmail dot com
2011-04-01 19:21 ` [Bug target/48227] " pinskia at gcc dot gnu.org
2011-04-02 0:55 ` ian at airs dot com
@ 2011-04-06 13:42 ` zuxy.meng at gmail dot com
2011-12-15 23:23 ` pinskia at gcc dot gnu.org
2021-12-29 4:12 ` pinskia at gcc dot gnu.org
4 siblings, 0 replies; 6+ messages in thread
From: zuxy.meng at gmail dot com @ 2011-04-06 13:42 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48227
--- Comment #3 from Zuxy <zuxy.meng at gmail dot com> 2011-04-06 13:42:21 UTC ---
(In reply to comment #1)
> A good question is does it make a difference in actual performance numbers, it
> might still make a positive difference. Until someone tries it out and sees
> the difference in performance, I am going to say we should keep it.
Actually GCC since 4.6 has stopped generating 'rep ret' for all Intel CPUs.
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug target/48227] "rep ret" generated for -march=core2
2011-03-22 9:10 [Bug target/48227] New: "rep ret" generated for -march=core2 zuxy.meng at gmail dot com
` (2 preceding siblings ...)
2011-04-06 13:42 ` zuxy.meng at gmail dot com
@ 2011-12-15 23:23 ` pinskia at gcc dot gnu.org
2021-12-29 4:12 ` pinskia at gcc dot gnu.org
4 siblings, 0 replies; 6+ messages in thread
From: pinskia at gcc dot gnu.org @ 2011-12-15 23:23 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48227
--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> 2011-12-15 23:18:35 UTC ---
/* X86_TUNE_PAD_RETURNS */
m_CORE2I7 | m_AMD_MULTIPLE | m_GENERIC,
So we still do it for Core2 i7.
^ permalink raw reply [flat|nested] 6+ messages in thread* [Bug target/48227] "rep ret" generated for -march=core2
2011-03-22 9:10 [Bug target/48227] New: "rep ret" generated for -march=core2 zuxy.meng at gmail dot com
` (3 preceding siblings ...)
2011-12-15 23:23 ` pinskia at gcc dot gnu.org
@ 2021-12-29 4:12 ` pinskia at gcc dot gnu.org
4 siblings, 0 replies; 6+ messages in thread
From: pinskia at gcc dot gnu.org @ 2021-12-29 4:12 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=48227
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |RESOLVED
Resolution|--- |FIXED
Target Milestone|--- |8.0
See Also| |https://gcc.gnu.org/bugzill
| |a/show_bug.cgi?id=81616
--- Comment #6 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
/* X86_TUNE_PAD_RETURNS: Place NOP before every RET that is a destination
of conditional jump or directly preceded by other jump instruction.
This is important for AND K8-AMDFAM10 because the branch prediction
architecture expect at most one jump per 2 byte window. Failing to
pad returns leads to misaligned return stack. */
DEF_TUNE (X86_TUNE_PAD_RETURNS, "pad_returns",
m_ATHLON_K8 | m_AMDFAM10)
Core2 issue was Fixed by r0-125351 for 4.9.0.
GCC 8 removed it even for generic by r8-5077.
So all fixed.
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2021-12-29 4:12 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
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2011-03-22 9:10 [Bug target/48227] New: "rep ret" generated for -march=core2 zuxy.meng at gmail dot com
2011-04-01 19:21 ` [Bug target/48227] " pinskia at gcc dot gnu.org
2011-04-02 0:55 ` ian at airs dot com
2011-04-06 13:42 ` zuxy.meng at gmail dot com
2011-12-15 23:23 ` pinskia at gcc dot gnu.org
2021-12-29 4:12 ` pinskia at gcc dot gnu.org
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