[Bug tree-optimization/127444] New: `x sCMP -x` should be simplified into x sCMP 0

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=127444

            Bug ID: 127444
           Summary: `x sCMP -x` should be simplified into x sCMP 0
           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(int x)
{
    return x < -x;
}
```

This can be convert into `x < 0`.
And this is true for all signed comparisons too.

We already have a pattern for EQ:
```
/* -x == x -> x == 0 */
(for cmp (eq ne)
 (simplify
  (cmp:c @0 (negate @0))
   (if (ANY_INTEGRAL_TYPE_P (TREE_TYPE (@0))
        && !TYPE_OVERFLOW_WRAPS (TREE_TYPE(@0)))
    (cmp @0 { build_zero_cst (TREE_TYPE(@0)); }))))
```

For `>`, this can be done even for wrapping values but still for signed only.