[Bug tree-optimization/116700] New: `(A > PZ) ? ABS(A) : PZ` -> `MAX(A, PZ)` where PZ is known to be non-negative

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116700

            Bug ID: 116700
           Summary: `(A > PZ) ? ABS(A) : PZ` -> `MAX(A, PZ)` where PZ is
                    known to be non-negative
           Product: gcc
           Version: 15.0
            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:
```
int f(unsigned char a, int b, int c)
{
  int t = a;
  if (c > t)  t = (c > 0 ? c : -c);
  return t;
}

int f1(unsigned char a, int b, int c)
{
  int t = a;
  if (c > t)  return (c > 0 ? c : -c);
  return t;
}
```

This should be caught in phiopt1 as being `MAX_EXPR((int)a, c)`. Note for -O2
it is almost caught except VRP does not do copyprop sometimes when it reduces
ABS(c) to c. -O1 is not caught at all even though we know that t is
non-negative.