[Bug tree-optimization/95034] Failure to convert xor pattern (made out of or+and) to xor

["pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95034

--- Comment #6 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
So after phiopt2 we end up with:
```
  _1 = a_3(D) | b_4(D);
  if (_1 != 0)
    goto <bb 3>; [50.00%]
  else
    goto <bb 4>; [50.00%]

  <bb 3> [local count: 536870912]:
  _5 = a_3(D) & b_4(D);
  _7 = ~_5;

  <bb 4> [local count: 1073741824]:
  # iftmp.0_2 = PHI <_7(3), 0(2)>
```

Phi-opt does not support more than one statement inside the middle BB so it
does nothing here.

But if we rewrite it such that the 2 statements were not inside the middle BB
by phiopt2, we get the xor as expected.
That is:
```
bool f(bool a, bool b)
{
  bool c = a | b;
  bool d = a & b;
  d = !d;
  return c ? d : false;
}
```
Will produce:
```
  _8 = a_3(D) ^ b_4(D);
  return _8;
```
From the phiopt2 dump:
```
Folded into the sequence:
_8 = a_3(D) ^ b_4(D);
```

I wonder if we could support more than 1 statement in the middle BBs iff the
resulting simplifications only reference one SSA_NAME of the statements max ...