dart2js cps: Maintain parent pointers instead of recomputing them.

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

 // Copyright (c) 2015, 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.scalar_replacement;
 
 import 'optimizers.dart';
 
 import 'dart:collection' show Queue;
 
 import '../closure.dart' show
@@ skipping 30 matching lines @@
 
   final dart2js.InternalErrorFunction _internalError;
   final World _classWorld;
 
   ScalarReplacer(dart2js.Compiler compiler)
       : _internalError = compiler.internalError,
         _classWorld = compiler.world;
 
   @override
   void rewrite(FunctionDefinition root) {
-    // Set all parent pointers.
-    new ParentVisitor().visit(root);
     ScalarReplacementVisitor analyzer =
         new ScalarReplacementVisitor(_internalError, _classWorld);
     analyzer.analyze(root);
     analyzer.process();
   }
 }
 
 /**
  * Do scalar replacement of aggregates on instances. Since scalar replacement
  * can create new candidiates, iterate until all scalar replacements are done.
  */
-class ScalarReplacementVisitor extends RecursiveVisitor {
+class ScalarReplacementVisitor extends TrampolineRecursiveVisitor {
 
   final dart2js.InternalErrorFunction internalError;
   final World classWorld;
   ScalarReplacementRemovalVisitor removalVisitor;
 
   Primitive _current = null;
   Set<Primitive> _allocations = new Set<Primitive>();
   Queue<Primitive> _queue = new Queue<Primitive>();
 
   ScalarReplacementVisitor(this.internalError, this.classWorld) {
@@ skipping 110 matching lines @@
 
     // Delete [allocation] since that might 'free' another scalar replacement
     // candidate by deleting the last non-field-access.
     deleteLetPrimOf(allocation);
   }
 
   /// Replaces [old] with [primitive] in [old]'s parent [LetPrim].
   void replacePrimitive(Primitive old, Primitive primitive) {
     LetPrim letPrim = old.parent;
     letPrim.primitive = primitive;
+    primitive.parent = letPrim;
   }
 
   void deleteLetPrimOf(Primitive primitive) {
     assert(primitive.hasNoUses);
     LetPrim letPrim = primitive.parent;
     letPrim.remove();
     deletePrimitive(primitive);
   }
 
   void deletePrimitive(Primitive primitive) {
@@ skipping 21 matching lines @@
   }
 
   void visitCreateBox(CreateBox node) {
     enqueue(node);
   }
 }
 
 
 /// Visit a just-deleted subterm and unlink all [Reference]s in it.  Reconsider
 /// allocations for scalar replacement.
-class ScalarReplacementRemovalVisitor extends RecursiveVisitor {
+class ScalarReplacementRemovalVisitor extends TrampolineRecursiveVisitor {
   ScalarReplacementVisitor process;
 
   ScalarReplacementRemovalVisitor(this.process);
 
   processReference(Reference reference) {
     process.reconsider(reference.definition);
     reference.unlink();
   }
 }