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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/109925] New: Wrong code at -O2 on x86_64-linux-gnu since
 GCC-12
Date: Sun, 21 May 2023 15:02:02 +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=3D109925

            Bug ID: 109925
           Summary: Wrong code at -O2 on x86_64-linux-gnu since GCC-12
           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: ---

For the following code, gcc trunk emits wrong code at -O2.

Compiler explorer: https://godbolt.org/z/hcnaxoPaP

$ cat a.c
int printf(const char *, ...);
int a, c, f;
int main() {
  int g[2];
  c =3D 0;
  for (; c < 2; c++) {
    {
      char h[20];
      char *b =3D h;
      int d =3D 48, e =3D 0;
      while (d && e < 5)
        b[e++] =3D d /=3D 10;
      f =3D e;
    }
    g[f - 2 + c] =3D 0;
  }
  for (;;) {
    for (; a <=3D 4; a++)
      if (g[0])
        break;
    break;
  }
  printf("%d\n", a);
}
$
$ gcc-tk -O0 a.c && ./a.out
5
$ gcc-tk -O2 a.c && ./a.out
0
$ gcc-tk -v
Using built-in specs.
COLLECT_GCC=3D/zdata/shaoli/compilers/ccbuilder-compilers/gcc-f211757f6fa95=
15e3fd1a4f66f1a8b48e500c9de/bin/gcc
COLLECT_LTO_WRAPPER=3D/zdata/shaoli/compilers/ccbuilder-compilers/gcc-f2117=
57f6fa9515e3fd1a4f66f1a8b48e500c9de/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-f211757f6fa9515e=
3fd1a4f66f1a8b48e500c9de
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 14.0.0 20230521 (experimental) (GCC)
$=