A reduced testcase from https://codeforces.com/blog/entry/97433

$ cat test.c
int z = 5;
int a[6] = {0, 0, 0, 0, 0, 1};
int main() {
  for (int x = 5; x; x--)
    for (int y = z; y >= x; y--)
      a[y - x] += a[y];
  if (a[0] != 7)
    __builtin_abort ();
  return 0;
}

$ gcc-7.3.0 -O3 test.c && ./a.out

$ gcc-8.3.0 -O3 test.c && ./a.out
Aborted

$ gcc-9.3.0 -O3 test.c && ./a.out
Aborted

$ gcc-9.4.1 -O3 test.c && ./a.out
Aborted

$ gcc-10.3.0 -O3 test.c && ./a.out

Only GCC versions 8.x and 9.x are affected and the bug is triggered by "-O3" or "-O1 -ftree-vectorize" optimization option.