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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/111319] New: Wrong code at -O2 on x86_64-linux-gnu
Date: Thu, 07 Sep 2023 07:38:40 +0000
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X-Bugzilla-Version: 14.0
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D111319

            Bug ID: 111319
           Summary: Wrong code at -O2 on x86_64-linux-gnu
           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: ---

The executable produced by gcc -O2 would crash. Not sure if there is UB in =
the
code or not as `h` has not been dereferenced after `h--`.

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

$ cat a.c
int printf(const char *, ...);
int a, b =3D 5, c, d;
int e[2] =3D {0, 0};
int i() {
  int f =3D 0;
  int g[2] =3D {1, f};
  int *h =3D g;
  h--;
  if (!b)
    while (h >=3D &c =3D=3D 1)
      h--;
  h++;
  d =3D *h;
  return d;
}
int main() {
  if (e[i()])
    e[0] =3D 0;
  printf("%d\n", a);
}
$
$ gcc -O2 a.c && ./a.out
Segmentation fault
$=