[Bug gcov-profile/90364] 521.wrf_r is 8-17% slower with PGO at -Ofast and native march/mtune

[jamborm at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90364

Martin Jambor <jamborm at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|2019-05-06 00:00:00         |2020-3-30
            Summary|521.wrf_r is 9.5 % slower   |521.wrf_r is 8-17% slower
                   |with PGO on Zen CPUs at     |with PGO at -Ofast and
                   |-Ofast and native           |native march/mtune
                   |march/mtune                 |

--- Comment #9 from Martin Jambor <jamborm at gcc dot gnu.org> ---
The problem still persists accross the board, causing:

- 17% regression against non-PGO on AMD Zen2 CPU,
-  8% regression against non-PGO on AMD Zen1 CPU, and
- 12% regression against non-PGO on Intel Cascade Lake server CPU.

All of the above is at -Ofast -march=native, by the way, at just -O2
(and generic -march) PGO actually helps by 25-27% on all three
systems, so I would double check before blaming specinvoke (though of
course it might be the culprit).