https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126286
Bug ID: 126286
Summary: [17 Regression] 4% slowdown of milc on Zen2 since
r17-2354-g10f6223d833874
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
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=288.70.0
there was a 4% exec time slowdown of the milc SPEC 2006
benchmark when compiled with -Ofast -march=native -g -flto=128 with PGO on an
Zen2 machine. I bisected it to r17-2354-g10f6223d833874.
10f6223d833874199e17226fbb0c562b69a1e72f is the first 'bad' commit
commit 10f6223d833874199e17226fbb0c562b69a1e72f
Author: Dylan Rees <[email protected]>
Date: Mon Jul 13 09:57:18 2026 +0000
middle-end: Eliminate redundant scalar duplication at different vector
widths
This is a regression against GCC 16. See the comparison
here:
https://lnt.opensuse.org/db_default/v4/SPEC/graph?plot.0=321.70.0&plot.1=306.70.0&plot.2=342.70.0&plot.3=271.70.0&plot.4=394.70.0&plot.5=410.70.0&plot.6=768.70.0&plot.7=924.70.0&plot.8=1040.70.0&plot.9=1197.70.0&plot.10=1492.70.0&plot.11=288.70.0&;
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)
