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From: "jamborm at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug target/101935] New: 538.imagick_r LTO -Ofast regression on Zen2
 and Kabylake caused by r12-2666-g29f0e955c97
Date: Mon, 16 Aug 2021 12:42:33 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D101935

            Bug ID: 101935
           Summary: 538.imagick_r LTO -Ofast regression on Zen2 and
                    Kabylake caused by r12-2666-g29f0e955c97
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jamborm at gcc dot gnu.org
                CC: hjl at gcc dot gnu.org
            Blocks: 26163
  Target Milestone: ---
              Host: x86_64-linux
            Target: x86_64-linux

When compiled with -flto -Ofast -march=3Dnative, the benchmark
538.imagick_r is about 28% slower on AMD zen2 machines (see
https://lnt.opensuse.org/db_default/v4/SPEC/graph?plot.0=3D287.507.0 )
and about 18% slower on Intel Kabylake (see
https://lnt.opensuse.org/db_default/v4/SPEC/graph?plot.0=3D11.507.0 )

I have independently reproduced the regression on a zen2-based desktop
and bisected it down to commit r12-2666-g29f0e955c97 (x86: Update
piecewise move and store).


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=
)=