dart2js cps: Redundant join elimination.

pkg/compiler/lib/src/cps_ir/cps_ir_nodes.dart

 // Copyright (c) 2013, 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 dart2js.ir_nodes;
 
 import '../constants/values.dart' as values show ConstantValue;
 import '../dart_types.dart' show DartType, InterfaceType, TypeVariableType;
 import '../elements/elements.dart';
 import '../io/source_information.dart' show SourceInformation;
 import '../types/types.dart' show TypeMask;
@@ skipping 110 matching lines @@
   /// Unlinks this reference from the list of occurrences.
   void unlink() {
     if (previous == null) {
       assert(definition.firstRef == this);
       definition.firstRef = next;
     } else {
       previous.next = next;
     }
     if (next != null) next.previous = previous;
   }
+
+  /// Changes the definition referenced by this object and updates
+  /// the reference chains accordingly.
+  void changeTo(Definition<T> newDefinition) {
+    unlink();
+    previous = null;
+    definition = newDefinition;
+    next = definition.firstRef;
+    if (next != null) next.previous = this;
+    definition.firstRef = this;
+  }
 }
 
 /// Evaluates a primitive and binds it to variable: `let val x = V in E`.
 ///
 /// The bound value is in scope in the body.
 ///
 /// During one-pass construction a LetPrim with an empty body is used to
 /// represent the one-hole context `let val x = V in []`.
 class LetPrim extends Expression implements InteriorNode {
   Primitive primitive;
@@ skipping 1288 matching lines @@
   const RemovalVisitor();
 
   processReference(Reference reference) {
     reference.unlink();
   }
 
   static void remove(Node node) {
     (const RemovalVisitor()).visit(node);
   }
 }