[Bug tree-optimization/117572] Missing optimization after SCCP due to rewriting for overflow

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117572

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
After adding a hack like:
```
(simplify
 (minus (plus:c @2 (convert ADDR_EXPR@0)) (convert @1))
 (if (tree_nop_conversion_p (type, TREE_TYPE (@0)))
  (with { poly_int64 diff; }
   (if (ptr_difference_const (@0, @1, &diff))
    (plus @2 { build_int_cst_type (type, diff); })))))
(simplify
 (minus (plus:c @2 (convert @0)) (convert ADDR_EXPR@1))
 (if (tree_nop_conversion_p (type, TREE_TYPE (@0)))
  (with { poly_int64 diff; }
   (if (ptr_difference_const (@0, @1, &diff))
    (plus @2 { build_int_cst_type (type, diff); })))))
```


For the original testcase we get:
```
  _386 = (sizetype) &o;
  _390 = _386 + 2;
  h_391 = (char *) _390;
  h_392 = h_391 + 1;
  _394 = h_392 - &o;
  _395 = (int) _394;
```

Seems like h_391 could be optimized to just:
`&o p+ 2 ` . 
Which means _395 is just 3.

Filed that as PR 117601.