[Bug target/94400] New: 531.deepsjeng_r is 7% slower at -O2 -march=znver2 than GCC 9

[jamborm at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94400

            Bug ID: 94400
           Summary: 531.deepsjeng_r is 7% slower at -O2 -march=znver2 than
                    GCC 9
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jamborm at gcc dot gnu.org
                CC: hubicka at gcc dot gnu.org
            Blocks: 26163
  Target Milestone: ---
              Host: x86_64-linux
            Target: x86_64-linux

When compiled with -O2 -march=native and run on an AMD Zen2 CPU,
531.deepsjeng_r runs about 7% slower.  This can be bisected to a
single commit:

commit a9a4edf0e71bbac9f1b5dcecdcf9250111d16889
Author: Jan Hubicka <hubicka@ucw.cz>
Date:   Sat Nov 30 22:25:24 2019 +0100

    Update max_bb_count in execute_fixup_cfg

            * tree-cfg.c (execute_fixup_cfg): Update also max_bb_count when
            scaling happen.

    From-SVN: r278879

Surprisingly, I cannot see a similar problem on an Intel Cascade Lake
server CPU, but I have confirmed the above on two different Rome
systems (one running SLES, one openSUSE Tumbleweed).


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)