https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95034
--- Comment #7 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Andrew Pinski from comment #6)
> 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
> ...
Or we could support what we do for casts for `~` and push the ~ outside of the
if statement to see if that improves the phi-opt.
That is get:
```
bool f(bool a, bool b)
{
bool t = a | b;
bool t1;
if (t) t1 = a & b; else t1 = 1;
return !t1;
}
```
Which is already known how to optimized to `t1 = a == b;`
