[Bug tree-optimization/127485] VRP misses that if the difference between two values is non-zero then the two values are different

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=127485

Drea Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2026-09-26
             Status|RESOLVED                    |NEW
         Resolution|FIXED                       |---

--- Comment #3 from Drea Pinski <pinskia at gcc dot gnu.org> ---
This is not fully fixed.
For my original testcase nothing is registered:
```
Folding statement: diff_4 = x_2(D) - y_3(D);
Not folded
Folding statement: if (diff_4 > 1)

Visiting conditional with predicate: if (diff_4 > 1)
```

For a slightly modified testcase:
```
unsigned fu(unsigned x, unsigned y)
{
  unsigned diff = x - y;
  if (diff >= 1)
   ;
  else
    __builtin_unreachable ();
  if (x == y) diff ++ ;
  return diff;
}

signed fs(signed x, signed y)
{
  signed diff = x - y;
  if (diff != 0)
   ;
  else
    __builtin_unreachable ();
  if (x == y) diff ++ ;
  return diff;
}
```

Only == is registered on one edge but != is not registered on the other edge:
```
Folding statement: if (diff_4 != 0)
 Registering value_relation (x_2(D) == y_3(D)) on (2->3)
```