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* [Bug target/115071] New: performance regression, x86, between gcc-14 and gcc-13 using -O3 and _Pragma("GCC unroll 4") on skylake
@ 2024-05-13 14:31 colin.king at intel dot com
2024-05-13 14:34 ` [Bug target/115071] " colin.king at intel dot com
` (3 more replies)
0 siblings, 4 replies; 5+ messages in thread
From: colin.king at intel dot com @ 2024-05-13 14:31 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115071
Bug ID: 115071
Summary: performance regression, x86, between gcc-14 and gcc-13
using -O3 and _Pragma("GCC unroll 4") on skylake
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: colin.king at intel dot com
Target Milestone: ---
Created attachment 58191
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=58191&action=edit
reproducer source code
I'm seeing a ~15% performance regression in gcc-14 compared to gcc-13, using
gcc on Ubuntu 24.04:
Versions:
gcc version 13.2.0 (Ubuntu 13.2.0-23ubuntu4)
gcc version 14.0.1 20240412 (experimental) [master r14-9935-g67e1433a94f]
(Ubuntu 14-20240412-0ubuntu1)
cking@skylake:~$ gcc-13 reproducer-bitonicsort.c -O2
cking@skylake:~$ ./a.out
duration: 5.71 seconds, count = 1119566602
cking@skylake:~$ gcc-14 reproducer-bitonicsort.c -O2
cking@skylake:~$ ./a.out
duration: 6.56 seconds, count = 1119566602
The original issue appeared when regression testing stress-ng bitonic sorting
stressor [1]. I've managed to extract the attached reproducer from the original
code (see attached).
Salient point to focus on:
1. The issue is also dependant on the use of _Pragma("GCC unroll 4")
2. The issue is also dependant on the use of __attribute__((optimize("-O3")))
by use of the OPTIMIZE3 macro in the example.
Attached are the reproducer C source and disassembled object code.
References:
[1] https://github.com/ColinIanKing/stress-ng/blob/master/stress-bitonicsort.c
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug target/115071] performance regression, x86, between gcc-14 and gcc-13 using -O3 and _Pragma("GCC unroll 4") on skylake
2024-05-13 14:31 [Bug target/115071] New: performance regression, x86, between gcc-14 and gcc-13 using -O3 and _Pragma("GCC unroll 4") on skylake colin.king at intel dot com
@ 2024-05-13 14:34 ` colin.king at intel dot com
2024-05-13 14:34 ` colin.king at intel dot com
` (2 subsequent siblings)
3 siblings, 0 replies; 5+ messages in thread
From: colin.king at intel dot com @ 2024-05-13 14:34 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115071
--- Comment #1 from Colin Ian King <colin.king at intel dot com> ---
Created attachment 58192
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=58192&action=edit
gcc-13 disassembly
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug target/115071] performance regression, x86, between gcc-14 and gcc-13 using -O3 and _Pragma("GCC unroll 4") on skylake
2024-05-13 14:31 [Bug target/115071] New: performance regression, x86, between gcc-14 and gcc-13 using -O3 and _Pragma("GCC unroll 4") on skylake colin.king at intel dot com
2024-05-13 14:34 ` [Bug target/115071] " colin.king at intel dot com
@ 2024-05-13 14:34 ` colin.king at intel dot com
2024-05-15 6:38 ` haochen.jiang at intel dot com
2024-05-16 1:49 ` [Bug target/115071] [14/15 regression] " sjames at gcc dot gnu.org
3 siblings, 0 replies; 5+ messages in thread
From: colin.king at intel dot com @ 2024-05-13 14:34 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115071
--- Comment #2 from Colin Ian King <colin.king at intel dot com> ---
Created attachment 58193
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=58193&action=edit
gcc-14 disassembly
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug target/115071] performance regression, x86, between gcc-14 and gcc-13 using -O3 and _Pragma("GCC unroll 4") on skylake
2024-05-13 14:31 [Bug target/115071] New: performance regression, x86, between gcc-14 and gcc-13 using -O3 and _Pragma("GCC unroll 4") on skylake colin.king at intel dot com
2024-05-13 14:34 ` [Bug target/115071] " colin.king at intel dot com
2024-05-13 14:34 ` colin.king at intel dot com
@ 2024-05-15 6:38 ` haochen.jiang at intel dot com
2024-05-16 1:49 ` [Bug target/115071] [14/15 regression] " sjames at gcc dot gnu.org
3 siblings, 0 replies; 5+ messages in thread
From: haochen.jiang at intel dot com @ 2024-05-15 6:38 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115071
Haochen Jiang <haochen.jiang at intel dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |haochen.jiang at intel dot com
--- Comment #3 from Haochen Jiang <haochen.jiang at intel dot com> ---
I could not reproduce the regression. For me, it is:
[haochenj@shgcc101 pr115071]$ ./13.exe
duration: 7.09 seconds, count = 1119566602
[haochenj@shgcc101 pr115071]$ ./trunk.exe
duration: 4.97 seconds, count = 1119566602
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug target/115071] [14/15 regression] performance regression, x86, between gcc-14 and gcc-13 using -O3 and _Pragma("GCC unroll 4") on skylake
2024-05-13 14:31 [Bug target/115071] New: performance regression, x86, between gcc-14 and gcc-13 using -O3 and _Pragma("GCC unroll 4") on skylake colin.king at intel dot com
` (2 preceding siblings ...)
2024-05-15 6:38 ` haochen.jiang at intel dot com
@ 2024-05-16 1:49 ` sjames at gcc dot gnu.org
3 siblings, 0 replies; 5+ messages in thread
From: sjames at gcc dot gnu.org @ 2024-05-16 1:49 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115071
Sam James <sjames at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|--- |14.2
^ permalink raw reply [flat|nested] 5+ messages in thread
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2024-05-13 14:31 [Bug target/115071] New: performance regression, x86, between gcc-14 and gcc-13 using -O3 and _Pragma("GCC unroll 4") on skylake colin.king at intel dot com
2024-05-13 14:34 ` [Bug target/115071] " colin.king at intel dot com
2024-05-13 14:34 ` colin.king at intel dot com
2024-05-15 6:38 ` haochen.jiang at intel dot com
2024-05-16 1:49 ` [Bug target/115071] [14/15 regression] " sjames at gcc dot gnu.org
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