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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/114894] New: `a == 0 ? 0 : a * b` -> `a * b`
 likewise for `a & b`
Date: Tue, 30 Apr 2024 06:18:04 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 14.0
X-Bugzilla-Keywords: missed-optimization
X-Bugzilla-Severity: enhancement
X-Bugzilla-Who: pinskia at gcc dot gnu.org
X-Bugzilla-Status: UNCONFIRMED
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X-Bugzilla-Priority: P3
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D114894

            Bug ID: 114894
           Summary: `a =3D=3D 0 ? 0 : a * b` -> `a * b` likewise for `a & b`
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: enhancement
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pinskia at gcc dot gnu.org
  Target Milestone: ---

Take:
```
int fmul(int a, int b)
{
        int c =3D a * b;
        int d =3D a !=3D 0;
        return c & -d;
}

int fand(int a, int b)
{
        int c =3D a & b;
        int d =3D a !=3D 0;
        return c & -d;
}

```

These should just optimize to: `return a * b;` and `return a & b;`.

Currently we get:
```
  c_4 =3D a_2(D) * b_3(D);
  _1 =3D a_2(D) !=3D 0;
  _6 =3D _1 ? c_4 : 0;
...

  c_4 =3D a_2(D) & b_3(D);
  _1 =3D a_2(D) !=3D 0;
  _6 =3D _1 ? c_4 : 0;
```

For:
```

int fmul1(int a, int b)
{
        int c =3D a * b;
        if (a !=3D 0)
          return c;
        return 0;
}


int fand1(int a, int b)
{
        int c =3D a & b;
        if (a !=3D 0)
          return c;
        return 0;
}
```

It is not until phiopt4 we are able to remove the conditional.=