Ensure newly allocated empty Arrays are transitioned to FAST_ELEMENT

src/bootstrapper.cc

Index: src/bootstrapper.cc
diff --git a/src/bootstrapper.cc b/src/bootstrapper.cc
index d1bf975fb5fb7f225e0ce4283a1e3c8b804e1633..7d65e09635584ecca524cf8ba3f87ef3004c8da2 100644
--- a/src/bootstrapper.cc
+++ b/src/bootstrapper.cc
@@ -892,9 +892,8 @@ void Genesis::InitializeGlobal(Handle<GlobalObject> inner_global,
             static_cast<PropertyAttributes>(DONT_ENUM | DONT_DELETE));
 
     // Cache the fast JavaScript array map
-    global_context()->set_js_array_map(array_function->initial_map());
-    global_context()->js_array_map()->set_instance_descriptors(
-        *array_descriptors);
+    Map* initial_map = array_function->initial_map();
+    initial_map->set_instance_descriptors(*array_descriptors);
     // array_function is used internally. JS code creating array object should
     // search for the 'Array' property on the global object and use that one
     // as the constructor. 'Array' property on a global object can be
@@ -1637,7 +1636,7 @@ bool Genesis::InstallNatives() {
     MaybeObject* maybe_map =
         array_function->initial_map()->CopyDropTransitions();
     Map* new_map;
-    if (!maybe_map->To<Map>(&new_map)) return maybe_map;
+    if (!maybe_map->To<Map>(&new_map)) return false;
     new_map->set_elements_kind(FAST_ELEMENTS);
     array_function->set_initial_map(new_map);
 
@@ -1736,17 +1735,15 @@ bool Genesis::InstallNatives() {
     initial_map->set_prototype(*array_prototype);
 
     // Update map with length accessor from Array and add "index" and "input".
-    Handle<Map> array_map(global_context()->js_array_map());
-    Handle<DescriptorArray> array_descriptors(
-        array_map->instance_descriptors());
-    ASSERT_EQ(1, array_descriptors->number_of_descriptors());
-
     Handle<DescriptorArray> reresult_descriptors =
         factory()->NewDescriptorArray(3);
-
     DescriptorArray::WhitenessWitness witness(*reresult_descriptors);
 
-    reresult_descriptors->CopyFrom(0, *array_descriptors, 0, witness);
+    JSFunction* array_function = global_context()->array_function();
+    Handle<DescriptorArray> array_descriptors(
+        array_function->initial_map()->instance_descriptors());
+    int index = array_descriptors->SearchWithCache(heap()->length_symbol());
+    reresult_descriptors->CopyFrom(0, *array_descriptors, index, witness);
 
     int enum_index = 0;
     {
@@ -2324,6 +2321,11 @@ Genesis::Genesis(Isolate* isolate,
     isolate->counters()->contexts_created_from_scratch()->Increment();
   }
 
+  Handle<Context> context = global_context();
+  context->set_untransitioned_js_array_map(
+      context->array_function()->initial_map());
+  context->set_fast_array_element_bias(0);

[Jakob Kummerow, 2012/01/04 20:55:17]

I have a weak preference to use "Smi::FromInt(0)" here, just to make it clear
what the "0" is.

+
   // Initialize experimental globals and install experimental natives.
   InitializeExperimentalGlobal();
   if (!InstallExperimentalNatives()) return;