[Bug tree-optimization/91207] New: Wrong code with -O3

[vsevolod.livinskij at frtk dot ru]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91207

            Bug ID: 91207
           Summary: Wrong code with -O3
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: vsevolod.livinskij at frtk dot ru
  Target Milestone: ---

GCC produces wrong code with -O3.

Reproducer:

#include <stdio.h>

long long a;
int b[92][32];
unsigned int c, d;

void e(long long *f, int p2) { *f = p2; }

int main() {
  for (int i = 6; i <= 20; d = i++)
    for (int j = 6; j <= 91; j++) {
      for (int k = 16; k <= 31;k++)
        b[j][k] ^= 7;
      c *= d;
    }

  for (int i = 0; i < 21; ++i)
    for (int j = 0; j < 32; ++j)
      e(&a, b[i][j]);

  printf("%llu\n", a);
}

Error:
>$ gcc -O0 repr.c ; ./a.out
7
>$ gcc -O3 repr.c ; ./a.out
0

GCC version is 10.0.0 (Revision: 273580)