https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90056
Bug ID: 90056
Summary: 548.exchange2_r regressions on AMD Zen
Product: gcc
Version: 9.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: jamborm at gcc dot gnu.org
CC: hubicka at gcc dot gnu.org, marxin at gcc dot gnu.org
Blocks: 26163
Target Milestone: ---
Host: x86_64-linux
Target: x86_64-linux
As of revision 270053, the 548.exchange2_r benchmark from SPEC 2017
INTrate suite suffered a number of smaller regressions on AMD Zen
CPUs:
- At -O2, it is 4.5% slower than when compiled with GCC 7
- At -Ofast, it is 4.7% slower than when compiled with GCC 8
- At -Ofast -march=native -mutine=native, this difference is 6.9%
- At -Ofast and native tuning, it is 6% slower with PGO than
without it.
According to
https://lnt.opensuse.org/db_default/v4/SPEC/spec_report/options the
last regression on a different Ryzen CPU is 6.8 and PGO+LTO is 8.2%
slower than just native -Ofast.
Bisecting does not help much because the performance of the benchmark
has varied a lot. For example in September there was no PGO
regression but only because the non-PGO executable was equally slow.
I only have data from February from an Intel machine, but there I only
saw the native -Ofast regression, but it might have gone away
meanwhile.
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)
