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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/95034] Failure to convert xor pattern (made
 out of or+and) to xor
Date: Wed, 23 Aug 2023 02:16:53 +0000
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X-Bugzilla-Component: tree-optimization
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X-Bugzilla-Keywords: easyhack, missed-optimization
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D95034

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

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

  <bb 4> [local count: 1073741824]:
  # iftmp.0_2 =3D 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 =3D a | b;
  bool d =3D a & b;
  d =3D !d;
  return c ? d : false;
}
```
Will produce:
```
  _8 =3D a_3(D) ^ b_4(D);
  return _8;
```
>From the phiopt2 dump:
```
Folded into the sequence:
_8 =3D 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=
 ...=