Add fast path for FastProperty objects in JSON.stringify.

src/json-stringifier.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 542 matching lines @@
 BasicJsonStringifier::Result BasicJsonStringifier::SerializeJSObject(
     Handle<JSObject> object) {
   HandleScope handle_scope(isolate_);
   Result stack_push = StackPush(object);
   if (stack_push != SUCCESS) return stack_push;
   if (object->IsJSGlobalProxy()) {
     object = Handle<JSObject>(
                  JSObject::cast(object->GetPrototype()), isolate_);
     ASSERT(object->IsGlobalObject());
   }
-  bool has_exception = false;
-  Handle<FixedArray> contents =
-      GetKeysInFixedArrayFor(object, LOCAL_ONLY, &has_exception);
-  if (has_exception) return EXCEPTION;
+
   Append('{');
   bool comma = false;
-  for (int i = 0; i < contents->length(); i++) {
-    Object* key = contents->get(i);
-    Handle<String> key_handle;
-    Handle<Object> property;
-    if (key->IsString()) {
-      key_handle = Handle<String>(String::cast(key), isolate_);
-      property = GetProperty(object, key_handle);
-    } else {
-      ASSERT(key->IsNumber());
-      key_handle = factory_->NumberToString(Handle<Object>(key, isolate_));
-      uint32_t index;
-      if (key->IsSmi()) {
-        property = Object::GetElement(object, Smi::cast(key)->value());
-      } else if (key_handle->AsArrayIndex(&index)) {
-        property = Object::GetElement(object, index);
+
+  if (object->HasFastProperties() &&
+      !object->HasIndexedInterceptor() &&
+      !object->HasNamedInterceptor() &&
+      object->elements() == isolate_->heap()->empty_fixed_array()) {
+    Handle<DescriptorArray> descs(
+        object->map()->instance_descriptors(), isolate_);
+    int num_desc = object->map()->NumberOfOwnDescriptors();
+    Handle<Map> map(object->map());
+    bool map_changed = false;
+    for (int i = 0; i < num_desc; i++) {
+      Handle<String> key(descs->GetKey(i), isolate_);
+      PropertyDetails details = descs->GetDetails(i);
+      if (details.IsDontEnum() || details.IsDeleted()) continue;
+      Handle<Object> property;
+      if (details.type() == FIELD && !map_changed) {
+        property = Handle<Object>(
+            object->FastPropertyAt(descs->GetFieldIndex(i)), isolate_);
       } else {
+        property = GetProperty(object, key);
+      }
+      if (property.is_null()) return EXCEPTION;
+      Result result = SerializeProperty(property, comma, key);
+      if (!comma && result == SUCCESS) comma = true;
+      if (result >= EXCEPTION) return result;
+      if (*map != object->map()) map_changed = true;
+    }
+  } else {
+    bool has_exception = false;
+    Handle<FixedArray> contents =
+        GetKeysInFixedArrayFor(object, LOCAL_ONLY, &has_exception);
+    if (has_exception) return EXCEPTION;
+
+    for (int i = 0; i < contents->length(); i++) {
+      Object* key = contents->get(i);
+      Handle<String> key_handle;
+      Handle<Object> property;
+      if (key->IsString()) {
+        key_handle = Handle<String>(String::cast(key), isolate_);
         property = GetProperty(object, key_handle);
+      } else {
+        ASSERT(key->IsNumber());
+        key_handle = factory_->NumberToString(Handle<Object>(key, isolate_));
+        uint32_t index;
+        if (key->IsSmi()) {
+          property = Object::GetElement(object, Smi::cast(key)->value());
+        } else if (key_handle->AsArrayIndex(&index)) {
+          property = Object::GetElement(object, index);
+        } else {
+          property = GetProperty(object, key_handle);
+        }
       }
+      if (property.is_null()) return EXCEPTION;
+      Result result = SerializeProperty(property, comma, key_handle);
+      if (!comma && result == SUCCESS) comma = true;
+      if (result >= EXCEPTION) return result;
     }
-    if (property.is_null()) return EXCEPTION;
-    Result result = SerializeProperty(property, comma, key_handle);
-    if (!comma && result == SUCCESS) comma = true;
-    if (result >= EXCEPTION) return result;
   }
+
   Append('}');
   StackPop();
   current_part_ = handle_scope.CloseAndEscape(current_part_);
   return SUCCESS;
 }
 
 
 void BasicJsonStringifier::ShrinkCurrentPart() {
   ASSERT(current_index_ < part_length_);
   if (current_index_ == 0) {
@@ skipping 160 matching lines @@
       SerializeString_<false, char>(flat.ToAsciiVector(), object);
     } else {
       SerializeString_<false, uc16>(flat.ToUC16Vector(), object);
     }
   }
 }
 
 } }  // namespace v8::internal
 
 #endif  // V8_JSON_STRINGIFIER_H_