[Bug tree-optimization/81554] New: [8 Regression] 25% performance regression in Himeno benchmark

[kristerw at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81554

            Bug ID: 81554
           Summary: [8 Regression] 25% performance regression in Himeno
                    benchmark
           Product: gcc
           Version: 8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: kristerw at gcc dot gnu.org
  Target Milestone: ---

Created attachment 41831
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=41831&action=edit
The Himeno benchmark

The Himeno benchmark from the Phoronix test suite lost 25% of its performance
by r248771 that fixed PR 66313 ("Unsafe factorization of a*b+a*c").

The benchmark is attached, can be compiled as
  gcc -O3 himenobmtxpa.c
and run as
  ./a.out s

I see 15% slowdown when the benchmark is compiled as "-O3" and 25% if compiled
as "-O3 -march=native" on a Broadwell CPU.