[Bug tree-optimization/123038] [16 Regression] ICE at O3 during GIMPLE pass: vect

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=123038

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Reduced:
```
unsigned char f(int b) {
  for (int a = 0; a < 10; a += 1)
    b = __builtin_ffs(b);
  return b;
}
```