[Bug tree-optimization/21513] [4.0/4.1/4.2 Regression] __builtin_expect getting in the way of uninitialized warnings

["bonzini at gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #5 from bonzini at gnu dot org  2005-12-17 10:27 -------
Well, another work around should probably be (untested)

Confirmed, reduced testcase:
void f(void*);
void *g(void);

void _aie_malloc(unsigned int size)
{
   void *aie_memory_heap_ptr;
   if (__builtin_expect(size != 0, true)
     {
       aie_memory_heap_ptr = g();
       if (__builtin_expect (aie_memory_heap_ptr != 0, 1))
         f(aie_memory_heap_ptr);
     }
}

This could be fixed also by folding __builtin_expect of &&, ||, and = like
this:

  __b_e (a && b, 1) => __b_e (a, 1) && __b_e (b, 1)
  __b_e (a && b, 0) => a && __b_e (b, 0)
  __b_e (a || b, 1) => a || __b_e (b, 1)
  __b_e (a || b, 0) => __b_e (a, 0) || __b_e (b, 0)
  __b_e (x, y) => (save_expr (x), __b_e (save_expr (x), y)) (*)

(*) when x has side effects

This could even produce better code (I remember a bug about worse code produced
when putting complex expression within __builtin_expect, but it might be
resolved as of now).


-- 

bonzini at gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bonzini at gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21513