dart2js cps: Maintain parent pointers instead of recomputing them.

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

Index: pkg/compiler/lib/src/cps_ir/insert_refinements.dart
diff --git a/pkg/compiler/lib/src/cps_ir/insert_refinements.dart b/pkg/compiler/lib/src/cps_ir/insert_refinements.dart
index afea3976dee6bb0de887eee47d1d8de6b271ba79..4dded8d127ae2879f6b16268224d4c7815cb0735 100644
--- a/pkg/compiler/lib/src/cps_ir/insert_refinements.dart
+++ b/pkg/compiler/lib/src/cps_ir/insert_refinements.dart
@@ -5,7 +5,6 @@
 library cps_ir.optimization.insert_refinements;
 
 import 'optimizers.dart' show Pass;
-import 'shrinking_reductions.dart' show ParentVisitor;
 import 'cps_ir_nodes.dart';
 import '../types/constants.dart';
 import '../constants/values.dart';
@@ -23,7 +22,7 @@ import 'type_mask_system.dart';
 ///
 /// Refinement nodes are inserted after a method invocation to refine the
 /// receiver to the types that can respond to the given selector.
-class InsertRefinements extends RecursiveVisitor implements Pass {
+class InsertRefinements extends TrampolineRecursiveVisitor implements Pass {
   String get passName => 'Insert refinement nodes';
 
   final TypeMaskSystem types;
@@ -34,7 +33,6 @@ class InsertRefinements extends RecursiveVisitor implements Pass {
   InsertRefinements(this.types);
 
   void rewrite(FunctionDefinition node) {
-    new ParentVisitor().visit(node);
     visit(node.body);
   }
 
@@ -80,6 +78,7 @@ class InsertRefinements extends RecursiveVisitor implements Pass {
   /// Enqueues [cont] for processing in a context where [refined] is the
   /// current refinement for its value.
   void pushRefinement(Continuation cont, Refinement refined) {
+    refined.value.parent = refined;

[Kevin Millikin (Google), 2015/10/05 12:04:37]

Is this necessary here?  It looks like the constructor for Refinement sets
value.parent appropriately and pushRefinement is always passed a newly
constructed Refinement.

[asgerf, 2015/10/12 13:18:32]

You're right, done.

     Primitive value = refined.effectiveDefinition;
     Primitive currentRefinement = refinementFor[value];
     pushAction(() {
@@ -121,7 +120,8 @@ class InsertRefinements extends RecursiveVisitor implements Pass {
     } else {
       // Filter away receivers that throw on this selector.
       TypeMask type = types.receiverTypeFor(node.selector, node.mask);
-      pushRefinement(cont, new Refinement(receiver, type));
+      Refinement refinement = new Refinement(receiver, type);
+      pushRefinement(cont, refinement);
     }
   }