After a dynamic call, refine the receiver type by looking at the potential targets of that call.

sdk/lib/_internal/compiler/implementation/types/simple_types_inferrer.dart

Index: sdk/lib/_internal/compiler/implementation/types/simple_types_inferrer.dart
===================================================================
--- sdk/lib/_internal/compiler/implementation/types/simple_types_inferrer.dart	(revision 22031)
+++ sdk/lib/_internal/compiler/implementation/types/simple_types_inferrer.dart	(working copy)
@@ -96,28 +96,6 @@
   bool get isDone => constructorsToVisitCount == 0;
 }
 
-/**
- * A sentinel type mask class used by the inferrer for the give up
- * type, and the dynamic type.
- */
-class SentinelTypeMask extends TypeMask {
-  final String name;
-
-  SentinelTypeMask(this.name) : super(null, 0, false);
-
-  bool operator==(other) {
-    return identical(this, other);
-  }
-
-  TypeMask nullable() {
-    throw 'Unsupported operation';
-  }
-
-  bool get isNullable => true;
-
-  String toString() => '$name sentinel type mask';
-}
-
 final OPTIMISTIC = 0;
 final RETRY = 1;
 final PESSIMISTIC = 2;
@@ -261,8 +239,8 @@
    * Sentinel used by the inferrer to notify that it does not know
    * the type of a specific element.
    */
-  final TypeMask dynamicType = new SentinelTypeMask('dynamic');
-  bool isDynamicType(TypeMask type) => identical(type, dynamicType);
+  TypeMask dynamicType;
+  bool isDynamicType(TypeMask type) => type == dynamicType;
 
   TypeMask nullType;
   TypeMask intType;
@@ -543,6 +521,9 @@
         rawTypeOf(backend.functionImplementation));
     typeType = new TypeMask.nonNullExact(
         rawTypeOf(backend.typeImplementation));
+
+    dynamicType = new TypeMask.subclass(
+        rawTypeOf(compiler.objectClass));
   }
 
   dump() {
@@ -1187,7 +1168,6 @@
    * [secondType].
    */
   TypeMask computeLUB(TypeMask firstType, TypeMask secondType) {
-    assert(secondType != null);
     if (firstType == null) {
       return secondType;
     } else if (isDynamicType(secondType)) {
@@ -1590,6 +1570,7 @@
       inferrer.recordType(variable, locals.locals[variable]);
     });
 
+    locals.update(elements[node], inferrer.functionType);
     return inferrer.functionType;
   }
 
@@ -2078,6 +2059,19 @@
           : new TypedSelector(receiver, selector);
       updateSelectorInTree(node, selector);
     }
+   
+    // If the receiver of the call is a local, we may know more about
+    // its type by refining it with the potential targets of the
+    // calls. 
+    if (node.asSend() != null
+        && node.asSend().receiver != null
+        && Elements.isLocal(elements[node.asSend().receiver])) {
+      Element element = elements[node.asSend().receiver];
+      TypeMask refinedMask = new TypeMask.refineWith(
+          locals.use(element), selector, compiler);
+      locals.update(element, refinedMask);
+    }
+
     return inferrer.registerCalledSelector(
         node, selector, receiver, outermostElement, arguments,
         constraint, inLoop);