[Bug target/101935] New: 538.imagick_r LTO -Ofast regression on Zen2 and Kabylake caused by r12-2666-g29f0e955c97

[jamborm at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101935

            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=native, 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=287.507.0 )
and about 18% slower on Intel Kabylake (see
https://lnt.opensuse.org/db_default/v4/SPEC/graph?plot.0=11.507.0 )

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=26163
[Bug 26163] [meta-bug] missed optimization in SPEC (2k17, 2k and 2k6 and 95)