[Bug tree-optimization/114539] `__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

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|unassigned at gcc dot gnu.org      |pinskia at gcc dot 
gnu.org
             Status|UNCONFIRMED                 |ASSIGNED
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=114538
   Last reconfirmed|                            |2024-04-01
     Ever confirmed|0                           |1

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
This is the current pattern that matches the non-CST case:
```
/* Testing for overflow is unnecessary if we already know the result.  */
/* A - B > A  */
(for cmp (gt le)
     out (ne eq)
 (simplify
  (cmp:c (realpart (IFN_SUB_OVERFLOW@2 @0 @1)) @0)
  (if (TYPE_UNSIGNED (TREE_TYPE (@0))
       && types_match (TREE_TYPE (@0), TREE_TYPE (@1)))
   (out (imagpart @2) { build_zero_cst (TREE_TYPE (@0)); }))))
/* A + B < A  */
(for cmp (lt ge)
     out (ne eq)
 (simplify
  (cmp:c (realpart (IFN_ADD_OVERFLOW:c@2 @0 @1)) @0)
  (if (TYPE_UNSIGNED (TREE_TYPE (@0))
       && types_match (TREE_TYPE (@0), TREE_TYPE (@1)))
   (out (imagpart @2) { build_zero_cst (TREE_TYPE (@0)); }))))
```

Mine for GCC 15.