Reapply r18377 it was reverted due to the unrelated bug it surfaced.

runtime/vm/flow_graph_type_propagator.h

Index: runtime/vm/flow_graph_type_propagator.h
diff --git a/runtime/vm/flow_graph_type_propagator.h b/runtime/vm/flow_graph_type_propagator.h
new file mode 100644
index 0000000000000000000000000000000000000000..c68a4ff40932856eb5975b505ae45eef0e534e39
--- /dev/null
+++ b/runtime/vm/flow_graph_type_propagator.h
@@ -0,0 +1,77 @@
+// Copyright (c) 2013, 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.
+
+#ifndef VM_FLOW_GRAPH_TYPE_PROPAGATOR_H_
+#define VM_FLOW_GRAPH_TYPE_PROPAGATOR_H_
+
+#include "vm/flow_graph.h"
+#include "vm/intermediate_language.h"
+
+namespace dart {
+
+class FlowGraphTypePropagator : public FlowGraphVisitor {
+ public:
+  explicit FlowGraphTypePropagator(FlowGraph* flow_graph);
+
+  void Propagate();
+
+ private:
+  void PropagateRecursive(BlockEntryInstr* block);
+
+  void VisitValue(Value* value);
+
+  virtual void VisitJoinEntry(JoinEntryInstr* instr);
+  virtual void VisitCheckSmi(CheckSmiInstr* instr);
+  virtual void VisitCheckClass(CheckClassInstr* instr);
+
+  // Current reaching type of the definition. Valid only during dominator tree
+  // traversal.
+  CompileType* TypeOf(Definition* def);
+
+  // Mark definition as having given compile type in all dominated instructions.
+  void SetTypeOf(Definition* def, CompileType* type);
+
+  // Mark definition as having given class id in all dominated instructions.
+  void SetCid(Definition* value, intptr_t cid);
+
+  void AddToWorklist(Definition* defn);
+  Definition* RemoveLastFromWorklist();
+
+  FlowGraph* flow_graph_;
+
+  // Mapping between SSA values and their current reaching types. Valid
+  // only during dominator tree traversal.
+  GrowableArray<CompileType*> types_;
+
+  // Worklist for fixpoint computation.
+  GrowableArray<Definition*> worklist_;
+  BitVector* in_worklist_;
+
+  // RollbackEntry is used to track and rollback changed in the types_ array
+  // done during dominator tree traversal.
+  struct RollbackEntry {
+   public:

[Florian Schneider, 2013/02/13 15:39:18]

struct has default public members, so you could save a line here.

[Vyacheslav Egorov (Google), 2013/02/13 16:18:46]

changed to class.

+    // Default constructor needed for the container.
+    RollbackEntry()

[Florian Schneider, 2013/02/13 15:39:18]

Strange line breaks. Maybe all in one line?

[Vyacheslav Egorov (Google), 2013/02/13 16:18:46]

I wanted it to match the next constructor.

+        : index_(), type_() {
+    }
+
+    RollbackEntry(intptr_t index, CompileType* type)
+        : index_(index), type_(type) {
+    }
+
+    intptr_t index() const { return index_; }
+    CompileType* type() const { return type_; }
+
+   private:
+    intptr_t index_;
+    CompileType* type_;
+  };
+
+  GrowableArray<RollbackEntry> rollback_;
+};
+
+}  // namespace dart
+
+#endif  // VM_FLOW_GRAPH_TYPE_PROPAGATOR_H_