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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 tree-optimization/111422] New: Wrong code at -O3 on
 x86_64-linux-gnu
Date: Fri, 15 Sep 2023 07:42:05 +0000
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 14.0
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X-Bugzilla-Who: shaohua.li at inf dot ethz.ch
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D111422

            Bug ID: 111422
           Summary: Wrong code at -O3 on x86_64-linux-gnu
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: shaohua.li at inf dot ethz.ch
  Target Milestone: ---

gcc at -O3 produced the wrong code.

Compiler explorer: https://godbolt.org/z/3b4v478TG

$ cat a.c
int printf(const char *, ...);
int a, b;
int *c =3D &b;
unsigned d;
char e;
int f=3D1;
int i(int k, char *l) {
  if (k < 6)
    return a;
  l[0] =3D l[1] =3D l[k - 1] =3D 8;
  return 0;
}
int m(int k) {
  char g[11];
  int h =3D i(k, g);
  return h;
}
int main() {
  for (; b < 8; b =3D b + 1)
    ;
  int j;
  int *n[8];
  j =3D 0;
  for (;18446744073709551608U + m(*c) + *c + j < 2; j++){
    n[j] =3D &f;
  }
  for (; e <=3D 4; e++)
    d =3D *n[0] =3D=3D f;
  printf("%d\n", d);
}
$
$ gcc -O0 a.c && ./a.out
1
$ gcc -O3 a.c && ./a.out
Segmentation fault
$ gcc -O3 -fwrapv a.c && ./a.out=20
Segmentation fault
$ gcc -fsanitize=3Daddress,undefined a.c && ./a.out
1
$=