[Bug tree-optimization/128521] New: `x ord x` can be treated as `x ord CST` when combining with `x CMP CST`

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=128521

            Bug ID: 128521
           Summary: `x ord x` can be treated as `x ord CST` when combining
                    with `x CMP CST`
           Product: gcc
           Version: 17.0
            Status: UNCONFIRMED
          Keywords: easyhack, missed-optimization
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pinskia at gcc dot gnu.org
  Target Milestone: ---

Take:
```
int f(double x)
{
  int t = !__builtin_isunordered(x, x);
  int t1 = x > 1.0;
  return t1 & t;
}

int f1(double x, double y)
{
  int t = !__builtin_isunordered(x, 1.0);
  int t1 = x > 1.0;
  return t1 & t;
}
```

For non-trapping (though the trapping case is different and I am too lazy to
figure out a testcase for it), these 2 should produce the same code but does
not currently as we don't treat `x ord x` as the same as `x ord CST` and don't
combine the two.  The same is true of unord.