[Bug tree-optimization/112472] New: (trunc)copysign((extend)x, CST) is not optimized to just copysign(x, CST')

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112472

            Bug ID: 112472
           Summary: (trunc)copysign((extend)x, CST) is not optimized to
                    just copysign(x, CST')
           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:
```
float f(float a, float b)
{
        return (float)__builtin_copysign(a,-3.0);
}
```

This should be optimized to just:
```
_tmp = .COPYSIGN(a, -1.0)
return _tmp;
```

The pattern for that does this for the non-constant second argument case is:
```
/* Simplify (trunc)copysign ((extend)x, (extend)y) to copysignf (x, y),
   x,y is float value, similar for _Float16/double.  */
(for copysigns (COPYSIGN_ALL)
 (simplify
  (convert (copysigns (convert@2 @0) (convert @1)))
   (if (optimize
       && !HONOR_SNANS (@2)
       && types_match (type, TREE_TYPE (@0))
       && types_match (type, TREE_TYPE (@1))
       && TYPE_PRECISION (type) < TYPE_PRECISION (TREE_TYPE (@2))
       && direct_internal_fn_supported_p (IFN_COPYSIGN,
                                          type, OPTIMIZE_FOR_BOTH))
    (IFN_COPYSIGN @0 @1))))

```

We should be able to handle (convert @1) as a constant ...