Add CPS IR transformation to make the JavaScript backend specific semantics explicit in the tree.

pkg/compiler/lib/src/cps_ir/shrinking_reductions.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.
 
 part of dart2js.optimizers;
 
 /**
  * [[ShrinkingReducer]] applies shrinking reductions to CPS terms as described
  * in 'Compiling with Continuations, Continued' by Andrew Kennedy.
  */
 class ShrinkingReducer implements Pass {
   _RedexVisitor _redexVisitor;
   Set<_ReductionTask> _worklist;
 
   static final _DeletedNode _DELETED = new _DeletedNode();
 
   /// Applies shrinking reductions to root, mutating root in the process.
   void rewrite(FunctionDefinition root) {
     if (root.isAbstract) return;
 
     _worklist = new Set<_ReductionTask>();
     _redexVisitor = new _RedexVisitor(_worklist);
 
     // Set all parent pointers.
-    new _ParentVisitor().visit(root);
+    new ParentVisitor().visit(root);
 
     // Sweep over the term, collecting redexes into the worklist.
     _redexVisitor.visitFunctionDefinition(root);
 
     // Process the worklist.
     while (_worklist.isNotEmpty) {
       _ReductionTask task = _worklist.first;
       _worklist.remove(task);
       _processTask(task);
     }
@@ skipping 250 matching lines @@
       }
       Node parent = cont.parent;
       if (parent is LetCont && _isDeadCont(parent)) {
         worklist.add(new _ReductionTask(_ReductionKind.DEAD_CONT, parent));
       }
     }
   }
 }
 
 /// Traverses the CPS term and sets node.parent for each visited node.
-class _ParentVisitor extends RecursiveVisitor {
+class ParentVisitor extends RecursiveVisitor {
 
   processFunctionDefinition(FunctionDefinition node) {
     node.body.parent = node;
     node.parameters.forEach((Parameter p) => p.parent = node);
   }
 
   // Expressions.
 
   processLetPrim(LetPrim node) {
     node.primitive.parent = node;
@@ skipping 77 matching lines @@
   processContinuation(Continuation node) {
     node.body.parent = node;
     node.parameters.forEach((Parameter param) => param.parent = node);
   }
 
   // Conditions.
 
   processIsTrue(IsTrue node) {
     node.value.parent = node;
   }
+
+  // JavaScript specific nodes.
+
+  processIdentical(Identical node) {
+    node.left.parent = node;
+    node.right.parent = node;
+  }
 }
 
 class _ReductionKind {
   final String name;
   final int hashCode;
 
   const _ReductionKind(this.name, this.hashCode);
 
   static const _ReductionKind DEAD_VAL = const _ReductionKind('dead-val', 0);
   static const _ReductionKind DEAD_CONT = const _ReductionKind('dead-cont', 1);
@@ skipping 26 matching lines @@
   }
 
   String toString() => "$kind: $node";
 }
 
 /// A dummy class used solely to mark nodes as deleted once they are removed
 /// from a term.
 class _DeletedNode extends Node {
   accept(_) => null;
 }