Use shorter write-barrier filtering sequence when value is known to be non-smi.

runtime/vm/intermediate_language.h

 // 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_INTERMEDIATE_LANGUAGE_H_
 #define VM_INTERMEDIATE_LANGUAGE_H_
 
 #include "vm/allocation.h"
 #include "vm/ast.h"
 #include "vm/growable_array.h"
@@ skipping 2819 matching lines @@
         && (emit_store_barrier_ == kEmitStoreBarrier);
   }
 
   virtual void PrintOperandsTo(BufferFormatter* f) const;
 
   virtual bool CanDeoptimize() const { return false; }
 
   virtual bool HasSideEffect() const { return true; }
 
  private:
+  bool CanValueBeSmi() const {
+    const intptr_t cid = value()->Type()->ToNullableCid();
+    // Write barrier is skipped for nullable and non-nullable smis.
+    ASSERT(cid != kSmiCid);
+    return (cid == kDynamicCid);
+  }
+
   const Field& field_;
   const StoreBarrierType emit_store_barrier_;
 
   DISALLOW_COPY_AND_ASSIGN(StoreInstanceFieldInstr);
 };
 
 
 class GuardFieldInstr : public TemplateInstruction<1> {
  public:
   GuardFieldInstr(Value* value,
@@ skipping 1818 matching lines @@
   ForwardInstructionIterator* current_iterator_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(FlowGraphVisitor);
 };
 
 
 }  // namespace dart
 
 #endif  // VM_INTERMEDIATE_LANGUAGE_H_