https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115192
Bug ID: 115192
Summary: GCC 14.1.0 -O3 miscompilation on x86-64 (loops with
vectors and scalars)
Product: gcc
Version: 14.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: jukka.suomela at aalto dot fi
Target Milestone: ---
Created attachment 58268
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=58268&action=edit
Preprocessed source code
It seems that GCC 14.1.0 with -O3 mis-compiles the attached code on x86-64. The
key element seems to be loops that involve both arrays of vector types and
arrays of scalar types.
This is the expected output:
$ g++-14 -Wall -Wextra -O2 test.cc -o test && ./test
0.000000 0.000000
3.000000 3.000000
9.000000 9.000000
This is the unexpected output that we got with -O3:
$ g++-14 -Wall -Wextra -O3 test.cc -o test && ./test
0.000000 0.000000
3.000000 3.000000
6.000000 6.000000
I have attached the preprocessed source code produced by the following command,
and I will attach also the full compiler output that I got:
g++-14 -v -save-temps -Wall -Wextra -O3 test.cc -o test
Compiler: GNU C++17 (Homebrew GCC 14.1.0) version 14.1.0
(x86_64-apple-darwin21), compiled by GNU C version 14.1.0, GMP version 6.3.0,
MPFR version 4.2.1, MPC version 1.3.1, isl version isl-0.26-GMP, Target:
x86_64-apple-darwin21.6.0.
This is GCC on Intel-macOS from Homebrew, but we originally noticed the problem
in Intel-Linux, so it doesn't seem to be specific to macOS or Homebrew.
However, I wasn't able to reproduce the bug on Apple M3, so it might be
specific to x86-64.
