[builtins] Remove superfluous fixed array allocation

src/builtins.cc

 // Copyright 2012 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/builtins.h"
 
 #include "src/api.h"
 #include "src/api-natives.h"
 #include "src/arguments.h"
 #include "src/base/once.h"
@@ skipping 1834 matching lines @@
 // ES6 section 19.1.2.14 Object.keys ( O )
 BUILTIN(ObjectKeys) {
   HandleScope scope(isolate);
   Handle<Object> object = args.atOrUndefined(isolate, 1);
   Handle<JSReceiver> receiver;
   ASSIGN_RETURN_FAILURE_ON_EXCEPTION(isolate, receiver,
                                      Object::ToObject(isolate, object));
 
   Handle<FixedArray> keys;
   int enum_length = receiver->map()->EnumLength();
-  if (enum_length != kInvalidEnumCacheSentinel) {
+  if (enum_length != kInvalidEnumCacheSentinel &&
+      JSObject::cast(*receiver)->elements() ==
+          isolate->heap()->empty_fixed_array()) {

[Camillo Bruni, 2016/02/12 13:04:21]

Maybe add a HasNoElements helper at some point?

     DCHECK(receiver->IsJSObject());
-    Handle<JSObject> js_object = Handle<JSObject>::cast(receiver);
-    DCHECK(!js_object->HasNamedInterceptor());
-    DCHECK(!js_object->IsAccessCheckNeeded());
-    DCHECK(!js_object->map()->has_hidden_prototype());
-    DCHECK(js_object->HasFastProperties());
-    if (js_object->elements() == isolate->heap()->empty_fixed_array()) {
-      keys = isolate->factory()->NewFixedArray(enum_length);
-      if (enum_length != 0) {
-        Handle<FixedArray> cache(
-            js_object->map()->instance_descriptors()->GetEnumCache());
-        keys = isolate->factory()->CopyFixedArrayUpTo(cache, enum_length);
-      }
+    DCHECK(!JSObject::cast(*receiver)->HasNamedInterceptor());
+    DCHECK(!JSObject::cast(*receiver)->IsAccessCheckNeeded());
+    DCHECK(!receiver->map()->has_hidden_prototype());
+    DCHECK(JSObject::cast(*receiver)->HasFastProperties());
+    if (enum_length == 0) {
+      keys = isolate->factory()->empty_fixed_array();
+    } else {
+      Handle<FixedArray> cache(
+          receiver->map()->instance_descriptors()->GetEnumCache());
+      keys = isolate->factory()->CopyFixedArrayUpTo(cache, enum_length);

[Camillo Bruni, 2016/02/12 13:04:21]

This pattern probably as well... GetEnumCacheCopy ;)

     }
-  }
-
-  if (keys.is_null()) {
+  } else {
     ASSIGN_RETURN_FAILURE_ON_EXCEPTION(
         isolate, keys,
         JSReceiver::GetKeys(receiver, OWN_ONLY, ENUMERABLE_STRINGS,
                             CONVERT_TO_STRING));
   }
   return *isolate->factory()->NewJSArrayWithElements(keys, FAST_ELEMENTS);
 }
 
 BUILTIN(ObjectValues) {
   HandleScope scope(isolate);
@@ skipping 2496 matching lines @@
 BUILTIN_LIST_C(DEFINE_BUILTIN_ACCESSOR_C)
 BUILTIN_LIST_A(DEFINE_BUILTIN_ACCESSOR_A)
 BUILTIN_LIST_H(DEFINE_BUILTIN_ACCESSOR_H)
 BUILTIN_LIST_DEBUG_A(DEFINE_BUILTIN_ACCESSOR_A)
 #undef DEFINE_BUILTIN_ACCESSOR_C
 #undef DEFINE_BUILTIN_ACCESSOR_A
 
 
 }  // namespace internal
 }  // namespace v8