Implement class id checks as a separate instruction and add a local CSE optimization pass.

runtime/vm/flow_graph_optimizer.h

Index: runtime/vm/flow_graph_optimizer.h
===================================================================
--- runtime/vm/flow_graph_optimizer.h	(revision 10885)
+++ runtime/vm/flow_graph_optimizer.h	(working copy)
@@ -14,8 +14,8 @@
 
 class FlowGraphOptimizer : public FlowGraphVisitor {
  public:
-  explicit FlowGraphOptimizer(const FlowGraph& flow_graph)
-      : FlowGraphVisitor(flow_graph.reverse_postorder()) {}
+  FlowGraphOptimizer(const FlowGraph& flow_graph, bool use_ssa)
+      : FlowGraphVisitor(flow_graph.reverse_postorder()), use_ssa_(use_ssa) {}
   virtual ~FlowGraphOptimizer() {}
 
   void ApplyICData();
@@ -46,6 +46,8 @@
 
   bool TryInlineInstanceMethod(BindInstr* instr, InstanceCallComp* comp);
 
+  bool use_ssa_;
+
   DISALLOW_COPY_AND_ASSIGN(FlowGraphOptimizer);
 };
 
@@ -107,6 +109,21 @@
   DISALLOW_COPY_AND_ASSIGN(FlowGraphTypePropagator);
 };
 
+
+class LocalCSE : public ValueObject {
+ public:
+  explicit LocalCSE(const FlowGraph& flow_graph)
+      : blocks_(flow_graph.reverse_postorder()) { }
+
+  void Optimize();
+
+ private:
+  const GrowableArray<BlockEntryInstr*>& blocks_;
+
+  DISALLOW_COPY_AND_ASSIGN(LocalCSE);
+};
+
+
 }  // namespace dart
 
 #endif  // VM_FLOW_GRAPH_OPTIMIZER_H_