[Bug tree-optimization/125756] New: nonnegative < (typeof nonnegative)(nonnegative != 0) is false

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=125756

            Bug ID: 125756
           Summary: nonnegative < (typeof nonnegative)(nonnegative != 0)
                    is false
           Product: gcc
           Version: 16.0
            Status: UNCONFIRMED
          Keywords: easyhack, missed-optimization
          Severity: enhancement
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pinskia at gcc dot gnu.org
  Target Milestone: ---

Take:
```
bool f1(unsigned short aa)
{
  int a = aa;
  bool t = a != 0;
  int tu = t;
  return a < tu;
}
bool f(unsigned short a)
{
  bool t = a != 0;
  unsigned short tu = t;
  return a < tu;
}
```
These both should just be optimized to 0 but currently is not due to this
pattern:
```
(simplify
 (lt:c @0 (convert (ne @0 integer_zerop)))
 (if (TYPE_UNSIGNED (TREE_TYPE (@0)))
  { constant_boolean_node (false, type); }))
```

Only checking TYPE_UNSIGNED rather than checking if @0 is nonnegative.