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From: "jamborm at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/107499] New: 433.milc regressed by 6-8% on
 zen3 at -O2 -flto
Date: Tue, 01 Nov 2022 17:27:45 +0000
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X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 12.0
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107499

            Bug ID: 107499
           Summary: 433.milc regressed by 6-8% on zen3 at -O2 -flto
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jamborm at gcc dot gnu.org
                CC: rguenth at gcc dot gnu.org
            Blocks: 26163
  Target Milestone: ---
              Host: x86_64-linux
            Target: x86_64-linux

LNT reports a 8.5% regression of 433.milc when compiled with -O2 -flto
on a zen3 machine:

https://lnt.opensuse.org/db_default/v4/SPEC/graph?plot.0=3D469.70.0

On a similar machine I reproduced it as a 6.5% regression and bisected
it to 19295e8607d (tree-optimization/100756 - niter analysis and
folding).

Possibly related, possibly not:

- An intel machine results show something which might be a 2%
  regression around the same time at -O2 -flto -march=3Dnative.
  See https://lnt.opensuse.org/db_default/v4/SPEC/graph?plot.0=3D790.70.0=20

- In the same time-frame there is also a 5% performance drop on zen2
  with -Ofast -flto -march=3Dnative, but those results have been rather
  flaky in the past (see PR 101296):
  https://lnt.opensuse.org/db_default/v4/SPEC/graph?plot.0=3D289.70.0

- there is a 11% regression reported on the same zen3 machine when
  using O2 flto -march=3Dnative but either I cannot reproduce it or it
  does not seem to be caused by the same commit.  I'll wait for more
  LNT results before investigating.  See
  https://lnt.opensuse.org/db_default/v4/SPEC/graph?plot.0=3D465.70.0


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D26163
[Bug 26163] [meta-bug] missed optimization in SPEC (2k17, 2k and 2k6 and 95=
)=