https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126515
Bug ID: 126515
Summary: [17 Regression] 5% slowdown of dealII on Zen5 since
r17-2654-gfb0838bc1073aa
Product: gcc
Version: 17.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: jmelcr at gcc dot gnu.org
CC: rguenth at gcc dot gnu.org
Blocks: 26163
Target Milestone: ---
Host: x86_64-suse-linux
Target: x86_64-suse-linux
Build: x86_64-suse-linux
As seen here
https://lnt.opensuse.org/db_default/v4/SPEC/graph?plot.0=1239.140.0
there was a 5% exec time slowdown of the dealII SPEC 2006
benchmark when compiled with -O2 -g -flto=128 PGO on an Zen5
machine. I bisected it to r17-2654-gfb0838bc1073aa.
fb0838bc1073aa5f22ec38e0cca2d70d625c6d71 is the first bad commit
commit fb0838bc1073aa5f22ec38e0cca2d70d625c6d71
Author: Richard Biener <[email protected]>
Date: Wed Jul 15 10:37:57 2026 +0200
Support two-lane vector BB reductions without target support
This is a regression against GCC 16. See the comparison
here:
https://lnt.opensuse.org/db_default/v4/SPEC/graph?plot.0=1259.140.0&plot.1=1324.140.0&plot.2=1292.140.0&plot.3=1355.140.0&plot.4=1549.140.0&plot.5=1239.140.0&;
Referenced Bugs:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=26163
[Bug 26163] [meta-bug] missed optimization in SPEC (2026, 2k17, 2k and 2k6 and
95)
