RFR: Simpler obj equals barrier for C2

[Roman Kennke]

Am 12.09.2018 um 10:22 schrieb Roland Westrelin:
> 
>> http://cr.openjdk.java.net/~rkennke/c2-obj-eq-barrier/webrev.02/
> 
> LibraryCallKit::inline_native_subtype_check() needs the mem phi that you
> removed.
> 
> Roland.
> 

Would it also require the memphi if we pulled up the
resolve_for_obj_equals() to right after we got the args? E.g. something
like:

  args[0] = argument(0);
  args[1] = argument(1);
  access_resolve_for_obj_equals(args[0], args[1]);

?

Roman