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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/115661] New: wrong code at -O{2,3} on
 x86_64-linux-gnu
Date: Wed, 26 Jun 2024 10:06:48 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D115661

            Bug ID: 115661
           Summary: wrong code at -O{2,3} 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: ---

This appears to be a recent regression as it doesn't reproduce with 14.1.

Compiler Explorer: https://godbolt.org/z/1dneGGoTE

[517] % 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 20240626 (experimental) (GCC)=20
[518] %=20
[518] % gcctk -O0 small.c; ./a.out
[519] % gcctk -O2 small.c
[520] % ./a.out
0
[521] % cat small.c
int printf(const char *, ...);
int a, b[6], c =3D 2, d, e =3D 446984904, *g, h, *i =3D &b[5];
int *m() {
  int *f =3D &c;
  if (d < 6)
    return &b[5];
  return f;
}
void n() {
  int j;
  for (; a < 1; a++)
    for (j =3D 0; j < 1; j++) {
      g =3D m();
      int k =3D *g;
      if (k) {
        int l =3D (3504049682 + e) & 3504049682;
        h =3D ~(k * l) * 7455084268;
        if (h > -1436818931) {
          printf("0\n");
          continue;
        }
        return;
      }
    }
}
int main() {
  *i =3D 1;
  n();
  return 0;
}=