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

pkg/compiler/lib/src/tree_ir/tree_ir_tracer.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 tree_ir_tracer;
 
 import 'dart:async' show EventSink;
 import '../tracer.dart';
 import 'tree_ir_nodes.dart';
 
@@ skipping 74 matching lines @@
   visitRethrow(Rethrow node) {
     _addStatement(node);
   }
 
   visitUnreachable(Unreachable node) {
     _addStatement(node);
   }
 
   visitBreak(Break node) {
     _addStatement(node);
-    blocks.last.addEdgeTo(breakTargets[node.target]);
+    if (breakTargets.containsKey(node.target)) {
+      blocks.last.addEdgeTo(breakTargets[node.target]);
+    }
   }
 
   visitContinue(Continue node) {
     _addStatement(node);
     blocks.last.addEdgeTo(continueTargets[node.target]);
   }
 
   visitIf(If node) {
     _addStatement(node);
     Block thenTarget = new Block();
@@ skipping 161 matching lines @@
 
   visitRethrow(Rethrow node) {
     printStatement(null, "rethrow");
   }
 
   visitUnreachable(Unreachable node) {
     printStatement(null, "unreachable");
   }
 
   visitBreak(Break node) {
-    printStatement(null, "break ${collector.breakTargets[node.target].name}");
+    Block block = collector.breakTargets[node.target];
+    String name = block != null ? block.name : '<missing label>';
+    printStatement(null, "break $name");
   }
 
   visitContinue(Continue node) {
     printStatement(null,
         "continue ${collector.continueTargets[node.target].name}");
   }
 
   visitIf(If node) {
     String condition = expr(node.condition);
     String thenTarget = collector.substatements[node.thenStatement].name;
@@ skipping 283 matching lines @@
       String prefix = v.element == null ? 'v' : '${v.element.name}_';
       while (name == null || _usedNames.contains(name)) {
         name = "$prefix${_counter++}";
       }
       _names[v] = name;
       _usedNames.add(name);
     }
     return name;
   }
 }