Introduce FieldIndex to unify and abstract property/field offset

src/objects-inl.h

Index: src/objects-inl.h
diff --git a/src/objects-inl.h b/src/objects-inl.h
index 5f58306ec22d41b4dd98ba8303c00b06b6c5a656..cd61ab52b92a657d66eaef1d2b759e3123584d0d 100644
--- a/src/objects-inl.h
+++ b/src/objects-inl.h
@@ -17,6 +17,7 @@
 #include "src/objects.h"
 #include "src/contexts.h"
 #include "src/conversions-inl.h"
+#include "src/field-index-inl.h"
 #include "src/heap.h"
 #include "src/isolate.h"
 #include "src/heap-inl.h"
@@ -1945,29 +1946,22 @@ void JSObject::SetInternalField(int index, Smi* value) {
 // Access fast-case object properties at index. The use of these routines
 // is needed to correctly distinguish between properties stored in-object and
 // properties stored in the properties array.
-Object* JSObject::RawFastPropertyAt(int index) {
-  // Adjust for the number of properties stored in the object.
-  index -= map()->inobject_properties();
-  if (index < 0) {
-    int offset = map()->instance_size() + (index * kPointerSize);
-    return READ_FIELD(this, offset);
+Object* JSObject::RawFastPropertyAt(FieldIndex index) {
+  if (index.is_inobject()) {
+    return READ_FIELD(this, index.offset());
   } else {
-    ASSERT(index < properties()->length());
-    return properties()->get(index);
+    return properties()->get(index.outobject_array_index());
   }
 }
 
 
-void JSObject::FastPropertyAtPut(int index, Object* value) {
-  // Adjust for the number of properties stored in the object.
-  index -= map()->inobject_properties();
-  if (index < 0) {
-    int offset = map()->instance_size() + (index * kPointerSize);
+void JSObject::FastPropertyAtPut(FieldIndex index, Object* value) {
+  if (index.is_inobject()) {
+    int offset = index.offset();
     WRITE_FIELD(this, offset, value);
     WRITE_BARRIER(GetHeap(), this, offset, value);
   } else {
-    ASSERT(index < properties()->length());
-    properties()->set(index, value);
+    properties()->set(index.outobject_array_index(), value);
   }
 }
 
@@ -4076,7 +4070,7 @@ int Map::pre_allocated_property_fields() {
 int Map::GetInObjectPropertyOffset(int index) {
   // Adjust for the number of properties stored in the object.
   index -= inobject_properties();
-  ASSERT(index < 0);
+  ASSERT(index <= 0);
   return instance_size() + (index * kPointerSize);
 }