[Bug tree-optimization/114894] New: `a == 0 ? 0 : a * b` -> `a * b` likewise for `a & b`

["pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114894

            Bug ID: 114894
           Summary: `a == 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 = a * b;
        int d = a != 0;
        return c & -d;
}

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

```

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

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

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

For:
```

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


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

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