dart2js cps: Fix performance issues in optimization passes.

pkg/compiler/lib/src/cps_ir/shrinking_reductions.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.shrinking_reductions;
 
 import 'cps_ir_nodes.dart';
 import 'optimizers.dart';
 
 /**
  * [ShrinkingReducer] applies shrinking reductions to CPS terms as described
  * in 'Compiling with Continuations, Continued' by Andrew Kennedy.
  */
 class ShrinkingReducer extends Pass {
   String get passName => 'Shrinking reductions';
 
-  Set<_ReductionTask> _worklist;
+  List<_ReductionTask> _worklist;
 
   static final _DeletedNode _DELETED = new _DeletedNode();
 
   /// Applies shrinking reductions to root, mutating root in the process.
   @override
   void rewrite(FunctionDefinition root) {
-    _worklist = new Set<_ReductionTask>();
+    _worklist = new List<_ReductionTask>();
     _RedexVisitor redexVisitor = new _RedexVisitor(_worklist);
 
     // Set all parent pointers.
     new ParentVisitor().visit(root);
 
     // Sweep over the term, collecting redexes into the worklist.
     redexVisitor.visit(root);
 
     // Process the worklist.
     while (_worklist.isNotEmpty) {
-      _ReductionTask task = _worklist.first;
-      _worklist.remove(task);
+      _ReductionTask task = _worklist.removeLast();
       _processTask(task);
     }
   }
 
   /// Removes the given node from the CPS graph, replacing it with its body
   /// and marking it as deleted. The node's parent must be a [[InteriorNode]].
   void _removeNode(InteriorNode node) {
     Node body           = node.body;
     InteriorNode parent = node.parent;
     assert(parent.body == node);
@@ skipping 346 matching lines @@
     if (current.parent is! InvokeContinuation) return false;
     InvokeContinuation invoke = current.parent;
     if (invoke.continuation.definition != continuation) return false;
     current = current.next;
   }
   return true;
 }
 
 /// Traverses a term and adds any found redexes to the worklist.
 class _RedexVisitor extends RecursiveVisitor {
-  final Set<_ReductionTask> worklist;
+  final List<_ReductionTask> worklist;
 
   _RedexVisitor(this.worklist);
 
   void processLetPrim(LetPrim node) {
     if (_isDeadVal(node)) {
       worklist.add(new _ReductionTask(_ReductionKind.DEAD_VAL, node));
     }
   }
 
   void processContinuation(Continuation node) {
@@ skipping 25 matching lines @@
   }
 }
 
 /// Traverses a deleted CPS term, marking nodes that might participate in a
 /// redex as deleted and adding newly created redexes to the worklist.
 ///
 /// Deleted nodes that might participate in a reduction task are marked so that
 /// any corresponding tasks can be skipped.  Nodes are marked so by setting
 /// their parent to the deleted sentinel.
 class _RemovalVisitor extends RecursiveVisitor {
-  final Set<_ReductionTask> worklist;
+  final List<_ReductionTask> worklist;
 
   _RemovalVisitor(this.worklist);
 
   void processLetPrim(LetPrim node) {
     node.parent = ShrinkingReducer._DELETED;
   }
 
   void processContinuation(Continuation node) {
     node.parent = ShrinkingReducer._DELETED;
   }
@@ skipping 267 matching lines @@
   }
 
   String toString() => "$kind: $node";
 }
 
 /// A dummy class used solely to mark nodes as deleted once they are removed
 /// from a term.
 class _DeletedNode extends Node {
   accept(_) => null;
 }