[Bug tree-optimization/126710] missed ifcvt optimization with clz

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126710

--- Comment #2 from Drea Pinski <pinskia at gcc dot gnu.org> ---
Reduced testcase for the post removal of the casts:
```
int f(unsigned a)
{
    if (a == 0) return 32;
    unsigned t = a>>1;
    if (t)
      return __builtin_clzg(t, 32) - 1;
    return 31;
}
```