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

sdk/lib/_internal/compiler/implementation/universe/universe.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library universe;
 
 import '../closure.dart';
 import '../elements/elements.dart';
 import '../dart2jslib.dart';
 import '../dart_types.dart';
@@ skipping 73 matching lines @@
     return hasMatchingSelector(invokedSetters[member.name], member, compiler);
   }
 
   bool hasFieldGetter(Element member, Compiler compiler) {
     return fieldGetters.contains(member);
   }
 
   bool hasFieldSetter(Element member, Compiler compiler) {
     return fieldSetters.contains(member);
   }
+
+  bool onlyReachesFinalFields(Selector getterSelector, Compiler compiler) {
+    assert(getterSelector.isGetter());
+    Selector setterSelector = new Selector.setterFrom(getterSelector);
+    if (getterSelector.mask != null) {
+      setterSelector = new TypedSelector(getterSelector.mask, setterSelector);
+    }
+
+    bool hasInvokedSetter = invokedSetters[setterSelector.name] != null
+        && !invokedSetters[setterSelector.name].isEmpty;
+
+    Iterable<Element> targets =
+        compiler.world.allFunctions.filter(setterSelector);
+    for (Element target in targets) {
+      assert(!target.isAbstractField());
+      // Final fields have been filtered out.
+      assert(!target.modifiers.isFinal());
+      if (target.isNative()) return false;
+      if (!target.isField()) return false;
+      if (hasInvokedSetter) return false;
+    }
+    return true;
+  }
 }
 
 class SelectorKind {
   final String name;
   const SelectorKind(this.name);
 
   static const SelectorKind GETTER = const SelectorKind('getter');
   static const SelectorKind SETTER = const SelectorKind('setter');
   static const SelectorKind CALL = const SelectorKind('call');
   static const SelectorKind OPERATOR = const SelectorKind('operator');
@@ skipping 29 matching lines @@
 
   Selector.getter(SourceString name, LibraryElement library)
       : this(SelectorKind.GETTER, name, library, 0);
 
   Selector.getterFrom(Selector selector)
       : this(SelectorKind.GETTER, selector.name, selector.library, 0);
 
   Selector.setter(SourceString name, LibraryElement library)
       : this(SelectorKind.SETTER, name, library, 1);
 
+  Selector.setterFrom(Selector selector)
+      : this(SelectorKind.SETTER, selector.name, selector.library, 1);
+
   Selector.unaryOperator(SourceString name)
       : this(SelectorKind.OPERATOR,
              Elements.constructOperatorName(name, true),
              null, 0);
 
   Selector.binaryOperator(SourceString name)
       : this(SelectorKind.OPERATOR,
              Elements.constructOperatorName(name, false),
              null, 1);
 
@@ skipping 295 matching lines @@
     //   bar() => foo(); // The call to 'foo' is a typed selector.
     // }
     if (element.getEnclosingClass().isClosure()) {
       return appliesUntyped(element, compiler);
     }
 
     if (!mask.canHit(element, this, compiler)) return false;
     return appliesUntyped(element, compiler);
   }
 }