[Bug tree-optimization/126367] New: [17 Regression] 6% slowdown of milc on Zen4 since r17-2163-ge754b70fe5470b

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126367

            Bug ID: 126367
           Summary: [17 Regression] 6% slowdown of milc on Zen4 since
                    r17-2163-ge754b70fe5470b
           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: hjl.tools at gmail dot com, 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=991.70.0

there was a 6% exec time slowdown of the milc SPEC 2006
benchmark when compiled with -Ofast -march=native -g -flto=128 with PGO on an
Zen4
machine. I bisected it to r17-2163-ge754b70fe5470b.

e754b70fe5470b975d31887fa5647f1c92d6522d is the first bad commit
commit e754b70fe5470b975d31887fa5647f1c92d6522d
Author: H.J. Lu <[email protected]>
Date:   Tue Apr 7 23:16:38 2026 +0800

    x86: Rewrite ix86_find_max_used_stack_alignment

This <is (not)> a regression against GCC 16. See the comparison
here:

https://lnt.opensuse.org/db_default/v4/SPEC/graph?plot.0=945.70.0&plot.1=989.70.0&plot.2=974.70.0&plot.3=1011.70.0&plot.4=1148.70.0&plot.5=1574.70.0&plot.6=991.70.0&


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)