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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/112113] New: wrong code at -O3 on
 x86_64-linux-gnu
Date: Sat, 28 Oct 2023 06:11:16 +0000
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X-Bugzilla-Component: tree-optimization
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D112113

            Bug ID: 112113
           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 recent regression.

Compiler Explorer: https://godbolt.org/z/vaY9GEnrz


[549] % 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/14.0.0/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 14.0.0 20231028 (experimental) (GCC)=20
[550] %=20
[550] % gcctk -O2 small.c; ./a.out
[551] %=20
[551] % gcctk -O3 small.c
small.c: In function =E2=80=98main=E2=80=99:
small.c:3:29: warning: iteration 1 invokes undefined behavior
[-Waggressive-loop-optimizations]
    3 |   for (int b =3D 0; b < 33; b +=3D 3) {
      |                           ~~^~~~
small.c:3:21: note: within this loop
    3 |   for (int b =3D 0; b < 33; b +=3D 3) {
      |                   ~~^~~~
[552] % ./a.out
Aborted
[553] %=20
[553] % cat small.c
volatile int a;
int main() {
  for (int b =3D 0; b < 33; b +=3D 3) {
    if (b > 31)
      a++;
  }
  if (a !=3D 0)
    __builtin_abort();
  return 0;
}=