dart2js cps: Maintain parent pointers instead of recomputing them.

pkg/compiler/lib/src/cps_ir/redundant_phi.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.
 
 library dart2js.cps_ir.redundant_phi_elimination;
 
 import 'cps_ir_nodes.dart';
 import 'optimizers.dart';
 
 /// Eliminate redundant phis from the given [FunctionDefinition].
 ///
 /// Phis in this case are [Continuations] together with corresponding
 /// [InvokeContinuation]s. A [Continuation] parameter at position i is redundant
 /// if for all [InvokeContinuation]s, the parameter at position i is identical
 /// (except for feedback). Redundant parameters are removed from the
 /// continuation signature, all invocations, and replaced within the
 /// continuation body.
-class RedundantPhiEliminator extends RecursiveVisitor implements Pass {
+class RedundantPhiEliminator extends TrampolineRecursiveVisitor implements Pass {
   String get passName => 'Redundant phi elimination';
 
   final Set<Continuation> workSet = new Set<Continuation>();
 
   @override
   void rewrite(FunctionDefinition root) {
-    // Set all parent pointers.
-    new ParentVisitor().visit(root);
-
     // Traverse the tree once to build the work set.
     visit(root);
 
     // Process each continuation one-by-one.
     while (workSet.isNotEmpty) {
       Continuation cont = workSet.first;
       workSet.remove(cont);
 
       if (cont.isReturnContinuation) {
         continue; // Skip function return continuations.
@@ skipping 160 matching lines @@
 /// Returns the LetCont that now binds [continuation].
 LetCont _makeUniqueBinding(Continuation continuation) {
   LetCont letCont = continuation.parent;
   if (letCont.continuations.length == 1) return letCont;
   letCont.continuations.remove(continuation);
   LetCont newBinding = new LetCont(continuation, null);
   continuation.parent = newBinding;
   newBinding.insertBelow(letCont);
   return newBinding;
 }