[svn-r7373] add TODOs for BG optimization opportunities

No reviewer.

src/include/mpihandlemem.h

@@ -313,6 +313,8 @@ typedef OPA_int_t MPIU_Handle_ref_count;
  * It is also assumed that any object being reference counted via these macros
  * will have a valid value in the handle field, even if it is
  * HANDLE_SET_KIND(0, HANDLE_KIND_INVALID) */
+/* TODO profile and examine the assembly that is generated for this if() on Blue
+ * Gene (and elsewhere).  We may need to mark it unlikely(). */
 #define MPIU_Object_add_ref(objptr_)                           \
     do {                                                       \
         int handle_kind_ = HANDLE_GET_KIND((objptr_)->handle); \

src/include/mpiimpl.h

@@ -369,6 +369,9 @@ void *MPIU_Handle_indirect_init( void *(**)[], int *, int, int, int, int );
 int MPIU_Handle_free( void *((*)[]), int );
 */
 /* Convert Handles to objects for MPI types that have predefined objects */
+/* TODO examine generated assembly for this construct, it's probably suboptimal
+ * on Blue Gene.  An if/else if/else might help the compiler out.  It also lets
+ * us hint that one case is likely(), usually the BUILTIN case. */
 #define MPID_Getb_ptr(kind,a,bmsk,ptr)                                  \
 {                                                                       \
    switch (HANDLE_GET_KIND(a)) {                                        \