[Bug tree-optimization/126964] New: [17 Regression] 4-5% slowdown of tonto of Zen{2,3,4,5} since r17-3342-gf3943597388db4

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126964

            Bug ID: 126964
           Summary: [17 Regression] 4-5% slowdown of tonto of Zen{2,3,4,5}
                    since r17-3342-gf3943597388db4
           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: jvdelisle 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=476.230.0

there was a 5% exec time slowdown of the tonto SPEC 2006
benchmark when compiled with -Ofast -march=native -g -flto=128 on an Zen 3
machine. I bisected it to r17-3342-gf3943597388db4.

f3943597388db4846386b6d5a18d33ebf80ea96c is the first 'bad' commit
commit f3943597388db4846386b6d5a18d33ebf80ea96c
Author: Jerry DeLisle <[email protected]>
Date:   Mon Aug 10 09:37:01 2026 -0700

    fortran: [PR53800] Wrong copy-in/out with array actual to TARGET dummy

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

https://lnt.opensuse.org/db_default/v4/SPEC/graph?plot.0=542.230.0&plot.1=529.230.0&plot.2=558.230.0&plot.3=482.230.0&plot.4=511.230.0&plot.5=494.230.0&plot.6=738.230.0&plot.7=889.230.0&plot.8=1029.230.0&plot.9=1140.230.0&plot.10=1471.230.0&plot.11=476.230.0&

There were numerous tonto regressions in the same timeframe with various
options on various machines:

4% on Zen 2 with -Ofast -march=native -g -flto=128:
https://lnt.opensuse.org/db_default/v4/SPEC/graph?plot.0=289.230.0

4% on Zen 2 with -Ofast -march=native -g -flto=128 PGO:
https://lnt.opensuse.org/db_default/v4/SPEC/graph?plot.0=288.230.0

4% on Zen 3 with -Ofast -march=native -g -flto=128 PGO:
https://lnt.opensuse.org/db_default/v4/SPEC/graph?plot.0=474.230.0

4% on Zen 4 with -Ofast -march=native -g -flto=128:
https://lnt.opensuse.org/db_default/v4/SPEC/graph?plot.0=992.230.0

5% on Zen 4 with -Ofast -march=native -g -flto=128 PGO:
https://lnt.opensuse.org/db_default/v4/SPEC/graph?plot.0=991.230.0

4% on Zen 5 with -Ofast -march=native -g -flto=128:
https://lnt.opensuse.org/db_default/v4/SPEC/graph?plot.0=1284.230.0

5% on Zen 5 with -Ofast -march=native -g -flto=128 PGO:
https://lnt.opensuse.org/db_default/v4/SPEC/graph?plot.0=1283.230.0


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)