Eagerly follow transitions to existing maps while json parsing.

src/objects-inl.h

Index: src/objects-inl.h
diff --git a/src/objects-inl.h b/src/objects-inl.h
index 7e0ba9f1000a7246277e82bf52ff2ae2e0be0668..c09bfc169358c5a13090c7048fec8e6d12eb76dc 100644
--- a/src/objects-inl.h
+++ b/src/objects-inl.h
@@ -1414,6 +1414,40 @@ MaybeObject* JSObject::ResetElements() {
 }
 
 
+MaybeObject* JSObject::AddFastPropertyUsingMap(Map* map) {
+  int size =

[danno, 2012/10/17 13:54:23]

As discussed, please convert this into something a little more readable.

[Toon Verwaest, 2012/10/17 14:03:40]

Done.

+      map->NumberOfOwnDescriptors() -
+      map->inobject_properties() +
+      map->unused_property_fields();
+  if (properties()->length() == size) {
+    set_map(map);
+    return this;
+  }
+  FixedArray* new_properties;
+  MaybeObject* maybe_properties = properties()->CopySize(size);
+  if (!maybe_properties->To(&new_properties)) return maybe_properties;
+  set_properties(new_properties);
+  set_map(map);
+  return new_properties;
+}
+
+
+bool JSObject::TryTransitionToField(String* key) {

[danno, 2012/10/17 13:54:23]

This should only be called by handlified code, it should be clear from API.

[Toon Verwaest, 2012/10/17 14:03:40]

Done.

+  Map* own_map = map();
+  if (!own_map->HasTransitionArray()) return false;
+  TransitionArray* transitions = own_map->transitions();
+  int transition = transitions->Search(key);
+  if (transition == TransitionArray::kNotFound) return false;
+  PropertyDetails target_details = transitions->GetTargetDetails(transition);
+  if (target_details.type() != FIELD) return false;
+  if (target_details.attributes() != NONE) return false;
+  Handle<JSObject> self(this);
+  Handle<Map> target(transitions->GetTarget(transition));
+  JSObject::AddFastPropertyUsingMap(self, target);
+  return true;
+}
+
+
 ACCESSORS(Oddball, to_string, String, kToStringOffset)
 ACCESSORS(Oddball, to_number, Object, kToNumberOffset)