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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/110919] [14 Regression] Dead Code Elimination
 Regression at -O3 since r14-1691-gbc5a2c2e793
Date: Sun, 20 Aug 2023 18:36:23 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D110919

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
           Assignee|unassigned at gcc dot gnu.org      |pinskia at gcc dot =
gnu.org

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
After reassoc1 we have:


  _19 =3D _6 =3D=3D iftmp.1_8;
  _3 =3D iftmp.1_8 ^ 1;
  _21 =3D (_Bool) _3;
  _23 =3D _6 !=3D 0;
  _10 =3D _19 & _23;
  _5 =3D _10 & _21;


Which is: (_6 !=3D 0) & (_6 =3D=3D iftmp.1_8) But since we know that iftmp.=
1_8 only
has 2 values, we could optimize this to: (_6 =3D=3D 1) & (iftmp.1_8 =3D=3D =
1)


Reduced testcase:
```
_Bool f(int a, int b)
{
  b &=3D 1;
  _Bool t =3D a =3D=3D b;
  int c =3D b^1;
  _Bool d =3D c;
  _Bool e =3D a;
  _Bool g =3D t & d;
  _Bool h =3D g & e;
  return h;
}
```
This should return false always.

So something like:
(simplify
 (bit_and:c (eq:c @0 @1) (ne:c @0 INTEGER_CST@2))
 (if (has_two_value_range (@1))
  (with {
     tree other_value =3D ...;
   }
   (bit_and (eq @0 { other_value; }) (eq @1 { other_value; }))
  )
 )
)=