Fix Map::AsArray to properly iterate over the backing store

src/api.cc

Index: src/api.cc
diff --git a/src/api.cc b/src/api.cc
index 2695b3e0955677790388bd907b7e29a4f6e79717..9ed18887a903ece61fb55877f6777850fa492ecf 100644
--- a/src/api.cc
+++ b/src/api.cc
@@ -6367,14 +6367,18 @@ Local<Array> Map::AsArray() const {
   LOG_API(isolate, "Map::AsArray");
   ENTER_V8(isolate);
   i::Handle<i::OrderedHashMap> table(i::OrderedHashMap::cast(obj->table()));
-  int size = table->NumberOfElements();
-  int length = size * 2;
+  int length = table->NumberOfElements() * 2;
   i::Handle<i::FixedArray> result = factory->NewFixedArray(length);
-  for (int i = 0; i < size; ++i) {
-    if (table->KeyAt(i)->IsTheHole()) continue;
-    result->set(i * 2, table->KeyAt(i));
-    result->set(i * 2 + 1, table->ValueAt(i));
+  int capacity = table->UsedCapacity();
+  int result_index = 0;
+  for (int i = 0; i < capacity; ++i) {
+    i::Object* key = table->KeyAt(i);
+    if (key->IsTheHole()) continue;

[Camillo Bruni, 2016/05/10 06:50:59]

nit: IsTheHole in a loop is rather slow, keep a local hole around for direct
comparison is a bit faster ;)

[adamk, 2016/05/10 17:19:24]

Done, and added a DisallowHeapAllocation for good measure.

+    result->set(result_index++, key);
+    result->set(result_index++, table->ValueAt(i));
   }
+  DCHECK_EQ(result_index, result->length());
+  DCHECK_EQ(result_index, length);
   i::Handle<i::JSArray> result_array =
       factory->NewJSArrayWithElements(result, i::FAST_ELEMENTS, length);
   return Utils::ToLocal(result_array);