[Bug target/126516] New: [17 Regression] 9% slowdown of calculix on Zen3 since r17-2723-g3f2b3eced0f827

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126516

            Bug ID: 126516
           Summary: [17 Regression] 9% slowdown of calculix on Zen3 since
                    r17-2723-g3f2b3eced0f827
           Product: gcc
           Version: 17.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jmelcr at gcc dot gnu.org
                CC: liuhongt 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=464.170.0

there was a 9% exec time slowdown of the calculix SPEC 2006
benchmark when compiled with -O2 -march=native -g on an Zen3
machine. I bisected it to r17-2723-g3f2b3eced0f827.

3f2b3eced0f8278fa335b1337a98b96df3ea062e is the first bad commit
commit 3f2b3eced0f8278fa335b1337a98b96df3ea062e
Author: liuhongt <[email protected]>
Date:   Mon Jul 6 20:14:01 2026 -0700

    i386: Prefer shorter fold-left reduction chains

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

https://lnt.opensuse.org/db_default/v4/SPEC/graph?plot.0=552.170.0&plot.1=530.170.0&plot.2=564.170.0&plot.3=479.170.0&plot.4=513.170.0&plot.5=495.170.0&plot.6=859.170.0&plot.7=886.170.0&plot.8=1037.170.0&plot.9=1155.170.0&plot.10=1476.170.0&plot.11=464.170.0&


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)