[Bug target/84481] New: 429.mcf with -O2 regresses by ~6% and ~4%, depending on tuning, on Zen compared to GCC 7.2

["jamborm at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84481

            Bug ID: 84481
           Summary: 429.mcf with -O2 regresses by ~6% and ~4%, depending
                    on tuning, on Zen compared to GCC 7.2
           Product: gcc
           Version: 8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jamborm at gcc dot gnu.org
  Target Milestone: ---

Our friends at AMD reported that, compared to gcc 7.2, 429.mcf is
about 6% slower when compiled with just -O2 with trunk and run on Zen
CPU, which I can confirm.  I have managed to bisect this to Honza's
r255395.

The benchmark also regresses compared to gcc 7.2 with -O2
-march=native -mtune=native, by over 4% but I was not able to pin this
down to a single commit.