[Bug tree-optimization/127600] New: wrong code at -O{2,3}

[kyuwoncho18 at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=127600

            Bug ID: 127600
           Summary: wrong code at -O{2,3}
           Product: gcc
           Version: 17.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: kyuwoncho18 at gmail dot com
  Target Milestone: ---

### Reproducer
#include <stdio.h>
int f (int *a, int n)
{
  int last = -1;
  int j = 1;
  for (int i = 0; i < n; i++)
    {
      if (a[i])
        last = j;
      j = -j;
    }
  return last;
}

int
main (void)
{
  int a[16] = { 0, 0, 0, 0, 0, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0 };
  printf ("%d\n", f (a, 16));
  return 0;
}

Stdout:
-O0/1/s: 1
-O2/3: -1

https://gcc.godbolt.org/z/dcKvjfP98