merge of types in ConditionalPhaseElimination

[Garcia Gutierrez Miguel Alfredo]

Still figuring out the workings of ConditionalEliminationPhase, I have a question regarding

        public boolean merge(MergeNode merge, List<State> withStates) {

which merges among other things the "known (object) types" over all incoming states:

            for (Map.Entry<ValueNode, ResolvedJavaType> entry : knownTypes.entrySet()) {
                ValueNode node = entry.getKey();
                ResolvedJavaType type = entry.getValue();

                for (State other : withStates) {
                    ResolvedJavaType otherType = other.getNodeType(node);
                    type = widen(type, otherType);
                    if (type == null) {
                        break;
                    }
                }
------------>   if (type == null && type != node.objectStamp().type()) {
                    newKnownTypes.put(node, type);
                }
            }

My reading of the above is:
  (1) fold the meet-operation across all incoming states.
  (2) Two cases:
      (2.a) the accumulated type is null (ie, there's no common ancestor, for example because some of the incoming states lack entries in "knownTypes").
      (2.b) non-null, and moreover a type more precise than Object has been inferred. That's the merged type we want to track in the merged state.

Getting to the code, there appears to be a typo (the arrow marks the spot). I guess the intention is adding an entry for the "accumulated type" to "newKnownTypes" (case 2.b). If so, that line should read:

                if (type != null && type != node.objectStamp().type()) {



Miguel

--
Miguel Garcia
Swiss Federal Institute of Technology
EPFL - IC - LAMP1 - INR 328 - Station 14
CH-1015 Lausanne - Switzerland
http://lamp.epfl.ch/~magarcia/