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From: "shaohua.li at inf dot ethz.ch" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/110702] New: Wrong code at -O1 on x86_64-linux-gnu
 (regression since GCC-12.2)
Date: Mon, 17 Jul 2023 13:26:16 +0000
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: c
X-Bugzilla-Version: 14.0
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D110702

            Bug ID: 110702
           Summary: Wrong code at -O1 on x86_64-linux-gnu (regression
                    since GCC-12.2)
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: shaohua.li at inf dot ethz.ch
  Target Milestone: ---

This looks like a regression since GCC-12.2.

Compiler explorer: https://godbolt.org/z/655af97j7

$ cat a.c
int printf(const char *, ...);
int a, b, c, d;
long e[9][7][4];
void f() {
  for (; a >=3D 0; a--) {
    b =3D 0;
    for (; b <=3D 3; b++) {
      c =3D 0;
      for (; c <=3D 3; c++) {
        int *g =3D &d;
        *g =3D e[0][0][b] | e[a][b][a];
      }
    }
  }
}
int main() {
  f();
  printf("%d\n", a);
}
$
$ gcc-tk -O0 a.c && ./a.out
-1
$ gcc-tk -O1 a.c && ./a.out
0
$
$ gcc-tk -v
Using built-in specs.
COLLECT_GCC=3Dgcc-tk
COLLECT_LTO_WRAPPER=3D/zdata/shaoli/compilers/ccbuilder-compilers/gcc-322d1=
7ae51ea0137167424e0018d7fa355948f9f/libexec/gcc/x86_64-pc-linux-gnu/14.0.0/=
lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../configure --disable-multilib --disable-bootstrap
--enable-languages=3Dc,c++
--prefix=3D/zdata/shaoli/compilers/ccbuilder-compilers/gcc-322d17ae51ea0137=
167424e0018d7fa355948f9f
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 14.0.0 20230711 (experimental) (GCC)=20
$=