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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/110141] New: Wrong code at -O2 on x86_64-linux-gnu
Date: Tue, 06 Jun 2023 12:00:34 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D110141

            Bug ID: 110141
           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: ---

For the following code, gcc since 12 emits the wrong code at -O2.

Compiler explorer: https://godbolt.org/z/reGo6jqGK

$ cat a.c
int printf(const char *, ...);
int h, i =3D 1, m;
int *j =3D &i, *k =3D &i, *l;
short n(short b, short c, int d) {
  short e[] =3D {71, c, c, 40, 28, 57, 3, 8, 79, 19, c};
  int f =3D d, a =3D b;
  short *g =3D e;
  while (f > 1) {
    a +=3D *g++;
    f -=3D 2;
  }
  a +=3D *g -=3D 255;
  return a;
}
int fn2() {
  h =3D 0;
  for (;; h =3D 5) {
    int o[4];
    m =3D 0;
    for (; m < 4; m++)
      o[n(6, 7, 19) - 70 + m] =3D 6;
    if (h) {
      for (;;) {
        int p =3D 0;
        if (*k)
          break;
        l =3D &p;
      }
      *j =3D o[0];
      return 0;
    }
  }
}
int main() {
  fn2();
  printf("%d\n", i);
}
$
$ gcc-tk -O0 a.c && ./a.out
6
$ gcc-tk -O2 a.c && ./a.out
0
$=