[Bug tree-optimization/112628] `~a < -a` can be optimized to `a != 0` for unsigned types

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112628

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
For signed, it is just true.

That is:
```
int f(int a)
{
  return (~a) < -a;
}
int f0(int a)
{
  return (a) > ~(-a);
}
```
Are the same.

In fact we can optimize even more:
```
int feq(int a)
{
  return (~a) == -a;
}
```
is always false for both signed and unsigned types.

So we just do `~a CMP -a` -> `(a - 1) CMP a` for all types.

Which is what we do for: `/* Fold ~X op ~Y as Y op X.  */`

So it is just
```
/* Fold ~X op -Y as (~(-Y)) op X. or `(Y-1) op X`  */
(for cmp (simple_comparison)
 (simplify
  (cmp:c (bit_not @0) (negative @1))
  (cmp (plus @1 { build_minus_one_cst (TREE_TYPE (@0)); }) @0)))
```