[Bug tree-optimization/126138] New: `fp0 == fp1 || fp0 CMP fp1` can be combined always even with trapping

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126138

            Bug ID: 126138
           Summary: `fp0 == fp1 || fp0 CMP fp1` can be combined always
                    even with trapping
           Product: gcc
           Version: 17.0
            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 (double i, double j)
{
  return (i == j) || (i < j);
}
```

This can be optimized to `i <= j` as Nan will cause (i == j) to return false so
you will always get the trapping expression `i < j`.

I have a patch for fold. But it seems not working for ifcombine which I need to
figure out why still.

The same is true with:
```
int g(double i, double j)
{
  return (i != j) && (i < j);
}
```