[Bug tree-optimization/126751] New: (int)(((unsigned)a) + CST) should be simplified into a + CST if a+CST is known not to overflow in int

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126751

            Bug ID: 126751
           Summary: (int)(((unsigned)a) + CST) should be simplified into a
                    + CST if a+CST is known not to overflow in int
           Product: gcc
           Version: 17.0
            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
            Blocks: 126710
  Target Milestone: ---

Noticed for PR 126710 but I thought it would be a good idea to split out:
```
int f(unsigned  t)
{
  int a = __builtin_clzg(t,32); // range is [0,32]
  unsigned b = a;
  b -= 10; // [-10, 22] no overflow in signed integer
  a = b;
  return a;
}
```


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126710
[Bug 126710] missed ifcvt optimization with clz