https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115025
Bug ID: 115025
Summary: prime computation performance regression, x86, between
gcc-14 and gcc-13 on skylake platform
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 58163
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=58163&action=edit
reproducer source code
I'm seeing a ~7% performance regression in gcc-14 compared to gcc-13, using gcc
on Ubuntu 24.04 computing prime numbers:
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:~$ CFLAGS="" gcc-13 -O2 reproducer-prime.c -lm
cking@skylake:~$ ./a.out
473.04 prime ops per sec
cking@skylake:~$ CFLAGS="" gcc-14 -O2 reproducer-prime.c -lm
cking@skylake:~$ ./a.out
439.86 prime ops per sec
Attached is the reproducer. Note that the use of
__attribute__((optimize("-O3"))) and/or __builtin_expect((x), 0) does not
affect the performance regression.
The original issue appeared when regression testing stress-ng cpu prime number
stressor [1]. I've managed to extract the attached reproducer from the original
code (see attached).
Attached are the reproducer C source and disassembled object code.
References: [1]
https://github.com/ColinIanKing/stress-ng/blob/master/stress-cpu.c
