[Bug tree-optimization/126917] New: [17 Regression] 4% slowdown of namd_r on Zen2 since r17-3220-g5e63fb58f84e3c

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126917

            Bug ID: 126917
           Summary: [17 Regression] 4% slowdown of namd_r on Zen2 since
                    r17-3220-g5e63fb58f84e3c
           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=297.447.0

there was a 4% exec time slowdown of the namd_r SPEC 2017
benchmark when compiled with -O2 -march=native -g on an Zen2
machine. I bisected it to r17-3220-g5e63fb58f84e3c.

5e63fb58f84e3ce19cb336710f69094ecbd4b63d is the first 'bad' commit
commit 5e63fb58f84e3ce19cb336710f69094ecbd4b63d
Author: Richard Biener <[email protected]>
Date:   Wed Jul 15 15:33:31 2026 +0200

    tree-optimization/126028 - vector placement and live lane extracts

This is a regression against GCC 16. See the comparison
here:

https://lnt.opensuse.org/db_default/v4/SPEC/graph?plot.0=324.447.0&plot.1=311.447.0&plot.2=348.447.0&plot.3=280.447.0&plot.4=400.447.0&plot.5=416.447.0&plot.6=779.447.0&plot.7=930.447.0&plot.8=1068.447.0&plot.9=1211.447.0&plot.10=1525.447.0&plot.11=297.447.0&


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)