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From: "zhendong.su at inf dot ethz.ch" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/115347] New: wrong code at -O3 on
 x86_64-linux-gnu
Date: Tue, 04 Jun 2024 19:13:21 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D115347

            Bug ID: 115347
           Summary: wrong code at -O3 on x86_64-linux-gnu
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: zhendong.su at inf dot ethz.ch
  Target Milestone: ---

It appears to be a regression from 11.*, affecting 12.* and later.

Compiler Explorer: https://godbolt.org/z/PY985hnff

[510] % gcctk -v
Using built-in specs.
COLLECT_GCC=3Dgcctk
COLLECT_LTO_WRAPPER=3D/local/suz-local/software/local/gcc-trunk/libexec/gcc=
/x86_64-pc-linux-gnu/15.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../gcc-trunk/configure --disable-bootstrap
--enable-checking=3Dyes --prefix=3D/local/suz-local/software/local/gcc-trunk
--enable-sanitizers --enable-languages=3Dc,c++ --disable-werror --enable-mu=
ltilib
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 15.0.0 20240604 (experimental) (GCC)=20
[511] %=20
[511] % gcctk -O2 small.c; ./a.out
[512] % gcctk -O3 small.c
[513] % ./a.out
Aborted
[514] % cat small.c
struct a {
  int b;
  int c;
} d, e[2];
int f, g, h;
int main() {
  for (; f < 1; f++) {
    for (h =3D 0; h < 2; h++) {
      d =3D e[f];
      g =3D e[1].c;
      e[f].c =3D 1;
    }
  }
  if (d.c !=3D 1)
    __builtin_abort();
  return 0;
}=