dart2js cps: Avoid deep recursion using trampolines and basic blocks.

pkg/compiler/lib/src/cps_ir/mutable_ssa.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.mutable_ssa;
 
 import 'cps_ir_nodes.dart';
 import 'optimizers.dart';
 
 /// Determines which mutable variables should be rewritten to phi assignments
 /// in this pass.
 ///
 /// We do not rewrite variables that have an assignment inside a try block that
 /// does not contain its declaration.
 class MutableVariablePreanalysis extends RecursiveVisitor {
   // Number of try blocks enclosing the current position.
   int currentDepth = 0;
 
   /// Number of try blocks enclosing the declaration of a given mutable
   /// variable.
   ///
   /// All mutable variables seen will be present in the map after the analysis.
   Map<MutableVariable, int> variableDepth = <MutableVariable, int>{};
 
   /// Variables with an assignment inside a try block that does not contain
   /// its declaration.
   Set<MutableVariable> hasAssignmentInTry = new Set<MutableVariable>();
 
-  void visitLetHandler(LetHandler node) {
+  @override
+  Expression traverseLetHandler(LetHandler node) {
+    push(node.handler);
     ++currentDepth;
-    visit(node.body);
-    --currentDepth;
-    visit(node.handler);
+    pushAction(() => --currentDepth);
+    return node.body;
   }
 
   void processLetMutable(LetMutable node) {
     variableDepth[node.variable] = currentDepth;
   }
 
   void processSetMutable(SetMutable node) {
     MutableVariable variable = node.variable.definition;
     if (currentDepth > variableDepth[variable]) {
       hasAssignmentInTry.add(variable);
@@ skipping 201 matching lines @@
 class VariableItem extends StackItem {}
 
 /// Represents a yet unprocessed continuation together with the
 /// environment in which to process it.
 class ContinuationItem extends StackItem {
   final Continuation continuation;
   final Map<MutableVariable, Primitive> environment;
 
   ContinuationItem(this.continuation, this.environment);
 }