[runtime] Add fast path to update LookupIterator in simple cases

src/lookup.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/lookup.h"
 
 #include "src/bootstrapper.h"
 #include "src/deoptimizer.h"
 #include "src/elements.h"
 #include "src/isolate-inl.h"
@@ skipping 148 matching lines @@
   DCHECK(state_ == DATA || state_ == ACCESSOR);
   DCHECK(HolderIsReceiverOrHiddenPrototype());
 
   Handle<JSObject> holder = GetHolder<JSObject>();
 
   if (IsElement()) {
     ElementsKind kind = holder_map_->elements_kind();
     ElementsKind to = value->OptimalElementsKind();
     if (IsHoleyElementsKind(kind)) to = GetHoleyElementsKind(to);
     to = GetMoreGeneralElementsKind(kind, to);
-    JSObject::TransitionElementsKind(holder, to);
-    holder_map_ = handle(holder->map(), isolate_);
+
+    if (kind != to) {
+      JSObject::TransitionElementsKind(holder, to);
+      holder_map_ = handle(holder->map(), isolate_);
+    }
 
     // Copy the backing store if it is copy-on-write.
     if (IsFastSmiOrObjectElementsKind(to)) {
       JSObject::EnsureWritableFastElements(holder);
     }
 
+    if (kind == to) return;
+
   } else {
     if (holder_map_->is_dictionary_map()) return;
     holder_map_ =
         Map::PrepareForDataProperty(holder_map_, descriptor_number(), value);
+
+    if (holder->map() == *holder_map_) {
+      // Update the property details if the representation was None.
+      if (representation().IsNone()) {
+        property_details_ = holder_map_->instance_descriptors()->GetDetails(
+            descriptor_number());
+      }
+      return;
+    }
   }
 
   JSObject::MigrateToMap(holder, holder_map_);
   ReloadPropertyInformation();
 }
 
 
 void LookupIterator::ReconfigureDataProperty(Handle<Object> value,
                                              PropertyAttributes attributes) {
   DCHECK(state_ == DATA || state_ == ACCESSOR);
@@ skipping 65 matching lines @@
   }
 }
 
 
 void LookupIterator::ApplyTransitionToDataProperty() {
   DCHECK_EQ(TRANSITION, state_);
 
   Handle<JSObject> receiver = GetStoreTarget();
   if (receiver->IsJSGlobalObject()) return;
   holder_ = receiver;
-  holder_map_ = transition_map();
+  Handle<Map> transition = transition_map();
+  bool simple_transition = transition->GetBackPointer() == receiver->map();
+  holder_map_ = transition;
   JSObject::MigrateToMap(receiver, holder_map_);
-  ReloadPropertyInformation();
+
+  if (simple_transition) {
+    int number = transition->LastAdded();
+    number_ = static_cast<uint32_t>(number);
+    property_details_ = transition->GetLastDescriptorDetails();
+    state_ = DATA;
+  } else {
+    ReloadPropertyInformation();
+  }
 }
 
 
 void LookupIterator::Delete() {
   Handle<JSReceiver> holder = Handle<JSReceiver>::cast(holder_);
   if (IsElement()) {
     Handle<JSObject> object = Handle<JSObject>::cast(holder);
     ElementsAccessor* accessor = object->GetElementsAccessor();
     accessor->Delete(object, number_);
   } else {
@@ skipping 390 matching lines @@
     // Fall through.
     default:
       return NOT_FOUND;
   }
   UNREACHABLE();
   return state_;
 }
 
 }  // namespace internal
 }  // namespace v8