[Bug tree-optimization/116998] New: [15 Regression] 5% slowdown of 400.perlbench on AMD Zen3/4 since r15-3986-g3e1bd6470e4deb

[pheeck at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116998

            Bug ID: 116998
           Summary: [15 Regression] 5% slowdown of 400.perlbench on AMD
                    Zen3/4 since r15-3986-g3e1bd6470e4deb
           Product: gcc
           Version: 15.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pheeck at gcc dot gnu.org
                CC: rguenth at gcc dot gnu.org
            Blocks: 26163
  Target Milestone: ---
              Host: x86_64-pc-linux-gnu
            Target: x86_64-pc-linux-gnu

As seen here

https://lnt.opensuse.org/db_default/v4/SPEC/graph?plot.0=956.10.0
https://lnt.opensuse.org/db_default/v4/SPEC/graph?plot.0=469.10.0

there was a ~5% exec time slowdown of the 400.perlbench SPEC 2006 benchmark
when run with -O2 -flto on AMD Zen3/4 machines (maybe also on other Zen
microarchs).  I bisected the slowdown to r15-3986-g3e1bd6470e4deb (Cc-ing
richi).

See comparison with other branches here:

https://lnt.opensuse.org/db_default/v4/SPEC/graph?plot.0=938.10.0&plot.1=999.10.0&plot.2=971.10.0&plot.3=1010.10.0&plot.4=956.10.0&;


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=26163
[Bug 26163] [meta-bug] missed optimization in SPEC (2k17, 2k and 2k6 and 95)