[Bug tree-optimization/114539] New: `__builtin_add_overflow(unsigned, b, &r); r < b` where b is a CST is not optimized to using the overflow

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114539

            Bug ID: 114539
           Summary: `__builtin_add_overflow(unsigned, b, &r); r  < b`
                    where b is a CST is not optimized to using the
                    overflow
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Keywords: 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 f(unsigned v, unsigned tt)
{
 unsigned r;
 unsigned t = __builtin_add_overflow(v, tt, &r);
 return (r < tt) == t;
}


bool f1(unsigned v, unsigned tt)
{
 tt = 3;
 unsigned r;
 unsigned t = __builtin_add_overflow(v, tt, &r);
 return (r < tt) == t;
}
```

f is able to be optimized to 1 but f1 is not due to the `r < 3` being Canonical
form being `r <= 2` (or in the case of 1, `r == 0`).

I found this while looking into PR 114538 if we change things slightly.