Use type propagation to eliminate store barriers.

runtime/vm/intermediate_language.h

 // Copyright (c) 2012, 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_INTERMEDIATE_LANGUAGE_H_
 #define VM_INTERMEDIATE_LANGUAGE_H_
 
 #include "vm/allocation.h"
 #include "vm/ast.h"
 #include "vm/growable_array.h"
@@ skipping 343 matching lines @@
   // Returns true if the value represents constant null.
   virtual bool BindsToConstantNull() const = 0;
 
   // Assert if BindsToConstant() is false, otherwise returns constant.
   virtual const Object& BoundConstant() const = 0;
 
   // Reminder: The type of the constant null is the bottom type, which is more
   // specific than any type.
   bool CompileTypeIsMoreSpecificThan(const AbstractType& dst_type) const;
 
+  // Compile time constants, Bool, Smi and Nulls do not need to update
+  // the store buffer.
+  bool NeedsStoreBuffer() const;
+
   virtual bool Equals(Value* other) const = 0;
 
   virtual Value* CopyValue() = 0;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(Value);
 };
 
 
 // Functions defined in all concrete computation classes.
@@ skipping 2949 matching lines @@
   ForwardInstructionIterator* current_iterator_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(FlowGraphVisitor);
 };
 
 
 }  // namespace dart
 
 #endif  // VM_INTERMEDIATE_LANGUAGE_H_