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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/114999] New: `a - b == b - a` -> `a == b`
Date: Thu, 09 May 2024 00:11:17 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 15.0
X-Bugzilla-Keywords: missed-optimization
X-Bugzilla-Severity: enhancement
X-Bugzilla-Who: pinskia at gcc dot gnu.org
X-Bugzilla-Status: UNCONFIRMED
X-Bugzilla-Resolution: 
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: pinskia at gcc dot gnu.org
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D114999

            Bug ID: 114999
           Summary: `a - b =3D=3D b - a` -> `a =3D=3D b`
           Product: gcc
           Version: 15.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: enhancement
          Priority: P3
         Component: tree-optimization
          Assignee: pinskia at gcc dot gnu.org
          Reporter: pinskia at gcc dot gnu.org
  Target Milestone: ---

Take:
```
int f(int a, int b, int c)
{
        c =3D a - b;
        int d =3D -c;
        int t =3D  c =3D=3D d;
        int t1 =3D c =3D=3D 0;
        return t =3D=3D t1;
}
```

This is not able to optimize to 1 as we don't detect that `a - b` and `b - =
a`
are negative of each other.

```
(for cmp (eq ne)
 (simplify
  (cmp:c @0 (negate @0))
```

needs to be improved.=