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From: "fkastl at suse dot cz" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/113847] New: [14 Regression] 10% slowdown of
 462.libquantum on AMD Ryzen 7700X and Ryzen 7900X
Date: Fri, 09 Feb 2024 09:24:35 +0000
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: target
X-Bugzilla-Version: 14.0
X-Bugzilla-Keywords: missed-optimization, needs-bisection
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D113847

            Bug ID: 113847
           Summary: [14 Regression] 10% slowdown of 462.libquantum on AMD
                    Ryzen 7700X and Ryzen 7900X
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Keywords: missed-optimization, needs-bisection
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: fkastl at suse dot cz
  Target Milestone: ---
              Host: x86_64-linux
            Target: x86_64-linux

As seen here

https://lnt.opensuse.org/db_default/v4/SPEC/graph?plot.0=3D956.210.0

between commits

g:d826596acb02edf4

and

g:23cd2961bd2ff635

there is about 10% slowdown of execution time of the 2006SPEC 462.libquantum
benchmark.

The test is run with -O2 and lto on an AMD Ryzen 7700X.

I also reproduced the slowdown on a AMD Ryzen 7900X machine. However I wasn=
't
able to reproduce the slowdown on an AMD EPYC machine - also Zen4
microarchitecture. So I suppose this slowdown occurs only on Zen4 Ryzen CPU=
s or
is maybe even more specific.

I'm not sure if we want to do anything about this. The same slowdown on the
same machine has already happened once, see pr112547. The benchmark results
eventually returned to the original values.=