[Bug tree-optimization/118658] `(a | CST)` -> a if we know that a already contains all bits of CST set

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118658

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Note like PR 118660 implementing this optimization gets in the way.
That is take:
```
unsigned short f(unsigned a)
{
  if ((a & 3) != 3) return a | 1;
  return a | 1;
}

```
Afterwards we get:
```
  <bb 2> [local count: 1073741824]:
  _1 = a_5(D) & 3;
  _6 = (short unsigned int) a_5(D);
  if (_1 != 3)
    goto <bb 3>; [50.00%]
  else
    goto <bb 4>; [50.00%]

  <bb 3> [local count: 536870912]:
  _7 = _6 | 1;

  <bb 4> [local count: 1073741824]:
  # _4 = PHI <_7(3), _6(2)>
```