https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94375
Bug ID: 94375
Summary: 548.exchange2_r run time is 8-18% worse than GCC 9 at
-Ofast -march=native
Product: gcc
Version: 10.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: jamborm at gcc dot gnu.org
Blocks: 26163
Target Milestone: ---
Host: x86_64-linux
Target: x86_64-linux
When compiled with trunk revision 26b3e568a60 and options -Ofast
-march=native -mtune=native, SPEC 2017 INTrate benchmark
548.exchange2_r runs 19% slower on AMD Zen2 and 12% slower on Intel
Cascade Lake than when built with GCC 9.2.
It appears that the main culprit is the vectorizer, switching it off
recovers the performance - it is in fact even some 4% better than GCC
9 on AMD).
Side note: with --param ipa-cp-eval-threshold=1 --param
ipa-cp-unit-growth=80 one can exchange that is 25% faster yet but that
is a different issue.
This started happening in the autumn but not exactly at one point, as
the following table of run-times relative to GCC 9.2 shows.
Revision: time
------------------------- ----
d82f38123b5 (Nov 14 2019) 117%
d9adca6e663 (Nov 5 2019) 117%
bf037872d3c (Oct 24 2019) 101%
77ef339456f (Oct 14 2019) 118%
38a734350fd (Oct 3 2019) 100%
d469a71e5a0 (Sep 23 2019) 101%
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)
