https://gcc.gnu.org/bugzilla/show_bug.cgi?id=122585
Bug ID: 122585
Summary: [16 Regression] 4-5% slowdown of 433.milc on AMD zen4
since r16-4469-gd6986e06db5eeb
Product: gcc
Version: 16.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: pheeck at gcc dot gnu.org
CC: rguenth at gcc dot gnu.org
Blocks: 26163
Target Milestone: ---
Host: x86_64-linux
Target: x86_64-linux
As seen here
https://lnt.opensuse.org/db_default/v4/SPEC/graph?plot.0=1109.70.0
there was a 4-5% exec time slowdown of the 433.milc SPEC 2006
benchmark when compiled with -O2 -march=x86-64-v3 -flto -fprofile-use on an AMD
Zen4 machine. I bisected it to r16-4469-gd6986e06db5eeb.
commit d6986e06db5eeb797344d86bd3ef9b0654606bbd
Author: Richard Biener <[email protected]>
AuthorDate: Fri Oct 17 15:12:11 2025 +0200
Commit: Richard Biener <[email protected]>
CommitDate: Fri Oct 17 16:03:28 2025 +0200
tree-optimization/122308 - apply LIM after unroll-and-jam
Just like with loop interchange, unroll-and-jam can leave invariant
stmts in the inner loop from outer loop stmts inbetween the two
inner loop copies. Do a per-function invariant motion when we
applied unroll-and-jam. This avoids failed dataref analysis
and fallback to gather/scatter during vectorization.
PR tree-optimization/122308
* gimple-loop-jam.cc (tree_loop_unroll_and_jam): Do LIM
after applying unroll-and-jam.
* gcc.dg/vect/vect-pr122308.c: New testcase.
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)
