https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120941
Bug ID: 120941
Summary: [16 Regression] 20-40% slowdown of 519.lbm_r on Zen2
since r16-1644-gaba3b9d3a48a07
Product: gcc
Version: 16.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: pheeck at gcc dot gnu.org
CC: hjl 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=287.477.0
there was a 40% exec time slowdown (on another machine I measured only 24%) of
527.cam4_r SPEC 2017 benchmark when run with -Ofast -march=native -flto on an
AMD Zen2 machine.
I bisected it to r16-1644-gaba3b9d3a48a07.
aba3b9d3a48a0703fd565f7c5f0caf604f59970b is the first bad commit
commit aba3b9d3a48a0703fd565f7c5f0caf604f59970b
Author: H.J. Lu <hjl.to...@gmail.com>
Date: Fri May 9 07:17:07 2025 +0800
x86: Extend the remove_redundant_vector pass
Extend the remove_redundant_vector pass to handle vector broadcasts from
constant and variable scalars. When broadcasting from constants and
function arguments, we can place a single widest vector broadcast at
entry of the nearest common dominator for basic blocks with all uses
since constants and function arguments aren't changed. For broadcast
from variables with a single definition, the single definition is
replaced with the widest broadcast.
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)
