https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126373
Bug ID: 126373
Summary: [17 Regression] 12% slowdown of milc on Zen3 since
r17-2478-g3adb3325954177
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=474.70.0
there was a 12% exec time slowdown of the milc SPEC 2006
benchmark when compiled with -Ofast -march=native -g -flto=128 PGO on an Zen3
machine. I bisected it to r17-2478-g3adb3325954177.
3adb3325954177939d59031055fc08a81ae21be3 is the first bad commit
commit 3adb3325954177939d59031055fc08a81ae21be3
Author: Richard Biener <[email protected]>
Date: Wed Jul 15 11:33:50 2026 +0200
Improve BB vectorization of reductions
This is a regression against GCC 16. See the comparison
here:
https://lnt.opensuse.org/db_default/v4/SPEC/graph?plot.0=551.70.0&plot.1=526.70.0&plot.2=559.70.0&plot.3=478.70.0&plot.4=510.70.0&plot.5=496.70.0&plot.6=736.70.0&plot.7=884.70.0&plot.8=1030.70.0&plot.9=1142.70.0&plot.10=1470.70.0&plot.11=474.70.0&;
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)
