In-object double fields unboxing (for 64-bit only).

src/hydrogen.cc

Index: src/hydrogen.cc
diff --git a/src/hydrogen.cc b/src/hydrogen.cc
index a87d623790e0007198cd6bf08ca20a1662606154..df9b3f8f252c0b7b21df290235019f196f42e760 100644
--- a/src/hydrogen.cc
+++ b/src/hydrogen.cc
@@ -5799,7 +5799,8 @@ HInstruction* HOptimizedGraphBuilder::BuildLoadNamedField(
   }
 
   HObjectAccess access = info->access();
-  if (access.representation().IsDouble()) {
+  if (access.representation().IsDouble() &&
+      (!FLAG_unbox_double_fields || !access.IsInobject())) {
     // Load the heap number.
     checked_object = Add<HLoadNamedField>(
         checked_object, static_cast<HValue*>(NULL),
@@ -5831,7 +5832,8 @@ HInstruction* HOptimizedGraphBuilder::BuildStoreNamedField(
   HObjectAccess field_access = info->access();
 
   HStoreNamedField *instr;
-  if (field_access.representation().IsDouble()) {
+  if (field_access.representation().IsDouble() &&
+      (!FLAG_unbox_double_fields || !field_access.IsInobject())) {
     HObjectAccess heap_number_access =
         field_access.WithRepresentation(Representation::Tagged());
     if (transition_to_field) {
@@ -11004,7 +11006,8 @@ void HOptimizedGraphBuilder::BuildEmitInObjectProperties(
       Representation representation = details.representation();
       HInstruction* value_instruction;
 
-      if (representation.IsDouble()) {
+      if (representation.IsDouble() &&
+          (!FLAG_unbox_double_fields || !access.IsInobject())) {
         // Allocate a HeapNumber box and store the value into it.
         HValue* heap_number_constant = Add<HConstant>(HeapNumber::kSize);
         // This heap number alloc does not have a corresponding