Don't set a propagate type if the variable has already the same static type.

pkg/analyzer/lib/src/generated/element.dart

 // Copyright (c) 2014, 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.
 
 // This code was auto-generated, is not intended to be edited, and is subject to
 // significant change. Please see the README file for more information.
 
 library engine.element;
 
 import 'dart:collection';
@@ skipping 6320 matching lines @@
         typeArguments.length != typeParameters.length) {
       return supertype;
     }
     return supertype.substitute2(typeArguments, typeParameters);
   }
 
   @override
   List<TypeParameterElement> get typeParameters => element.typeParameters;
 
   @override
-  bool operator ==(Object object) =>
-      internalEquals(object, new HashSet<ElementPair>());
+  bool operator ==(Object object) {
+    if (identical(object, this)) {

[Brian Wilkerson, 2015/03/03 14:53:49]

I'm not sure why this logic needs to be duplicated (both here and in
internalEquals).

[scheglov, 2015/03/03 15:02:17]

Here we have a chance to check quickly without creating a HashSet instance, e.g.
"int == int".
In internalEquals we short circuit equals for type used in other types, e.g.
"int" in "List<int> == List<int>"

+      return true;
+    }
+    return internalEquals(object, new HashSet<ElementPair>());
+  }
 
   @override
   void appendTo(StringBuffer buffer, Set<DartType> visitedTypes) {
     if (!visitedTypes.add(this)) {
       buffer.write(name == null ? '...' : name);
       return;
     }
     buffer.write(name);
     int argumentCount = typeArguments.length;
     if (argumentCount > 0) {
@@ skipping 72 matching lines @@
   @override
   MethodElement getMethod(String methodName) => MethodMember.from(
       (element as ClassElementImpl).getMethod(methodName), this);
 
   @override
   PropertyAccessorElement getSetter(String setterName) => PropertyAccessorMember
       .from((element as ClassElementImpl).getSetter(setterName), this);
 
   @override
   bool internalEquals(Object object, Set<ElementPair> visitedElementPairs) {
+    if (identical(object, this)) {
+      return true;
+    }
     if (object is! InterfaceTypeImpl) {
       return false;
     }
     InterfaceTypeImpl otherType = object as InterfaceTypeImpl;
     return (element == otherType.element) &&
         TypeImpl.equalArrays(
             typeArguments, otherType.typeArguments, visitedElementPairs);
   }
 
   @override
@@ skipping 4639 matching lines @@
     // void <: void (by reflexivity)
     // bottom <: void (as bottom is a subtype of all types).
     // void <: dynamic (as dynamic is a supertype of all types)
     return identical(type, this) || type.isDynamic;
   }
 
   @override
   VoidTypeImpl substitute2(
       List<DartType> argumentTypes, List<DartType> parameterTypes) => this;
 }