Don't emit a write barrier when storing a known old space value.

Review URL: http://codereview.chromium.org/6072009

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@6120 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/hydrogen-instructions.h

@@ -1769,6 +1769,8 @@ class HConstant: public HInstruction {
 
   Handle<Object> handle() const { return handle_; }
 
+  bool InOldSpace() const { return !Heap::InNewSpace(*handle_); }
+
   virtual bool EmitAtUses() const { return !representation().IsDouble(); }
   virtual void PrintDataTo(StringStream* stream) const;
   virtual HType CalculateInferredType() const;
@@ -2687,6 +2689,12 @@ class HLoadKeyedGeneric: public HLoadKeyed {
 };
 
 
+static inline bool StoringValueNeedsWriteBarrier(HValue* value) {
+  return !value->type().IsSmi() &&
+      !(value->IsConstant() && HConstant::cast(value)->InOldSpace());
+}
+
+
 class HStoreNamed: public HBinaryOperation {
  public:
   HStoreNamed(HValue* obj, Handle<Object> name, HValue* val)
@@ -2704,6 +2712,10 @@ class HStoreNamed: public HBinaryOperation {
   HValue* value() const { return OperandAt(1); }
   void set_value(HValue* value) { SetOperandAt(1, value); }
 
+  bool NeedsWriteBarrier() const {
+    return StoringValueNeedsWriteBarrier(value());
+  }
+
   DECLARE_INSTRUCTION(StoreNamed)
 
  protected:
@@ -2784,6 +2796,10 @@ class HStoreKeyed: public HInstruction {
   HValue* key() const { return OperandAt(1); }
   HValue* value() const { return OperandAt(2); }
 
+  bool NeedsWriteBarrier() const {
+    return StoringValueNeedsWriteBarrier(value());
+  }
+
   DECLARE_INSTRUCTION(StoreKeyed)
 
  protected:
@@ -2803,10 +2819,6 @@ class HStoreKeyedFastElement: public HStoreKeyed {
     SetFlag(kChangesArrayElements);
   }
 
-  bool NeedsWriteBarrier() const {
-    return !value()->type().IsSmi();
-  }
-
   virtual Representation RequiredInputRepresentation(int index) const {
     // The key is supposed to be Integer32.
     return (index == 1) ? Representation::Integer32()

src/ia32/lithium-ia32.cc

@@ -1939,7 +1939,7 @@ LInstruction* LChunkBuilder::DoStoreKeyedGeneric(HStoreKeyedGeneric* instr) {
 
 
 LInstruction* LChunkBuilder::DoStoreNamedField(HStoreNamedField* instr) {
-  bool needs_write_barrier = !instr->value()->type().IsSmi();
+  bool needs_write_barrier = instr->NeedsWriteBarrier();
 
   LOperand* obj = needs_write_barrier
       ? UseTempRegister(instr->object())