Adding ElementsAccessor::Pop

src/builtins.cc

Index: src/builtins.cc
diff --git a/src/builtins.cc b/src/builtins.cc
index 4e30fb55f0f1d7ee5f9dd577069f041b7b8f78e5..d50d6d7157f9b34bd0d3b01efd036fbd038b60b9 100644
--- a/src/builtins.cc
+++ b/src/builtins.cc
@@ -209,7 +209,7 @@ inline bool GetSloppyArgumentsLength(Isolate* isolate, Handle<JSObject> object,
 }
 
 
-bool PrototypeHasNoElements(PrototypeIterator* iter) {
+inline bool PrototypeHasNoElements(PrototypeIterator* iter) {
   DisallowHeapAllocation no_gc;
   for (; !iter->IsAtEnd(); iter->Advance()) {
     if (iter->GetCurrent()->IsJSProxy()) return false;
@@ -386,13 +386,21 @@ BUILTIN(ArrayPop) {
     return CallJsIntrinsic(isolate, isolate->array_pop(), args);
   }
 
-  uint32_t new_length = len - 1;
-  Handle<Object> element;
-  ASSIGN_RETURN_FAILURE_ON_EXCEPTION(
-      isolate, element, Object::GetElement(isolate, array, new_length));
-
-  JSArray::SetLength(array, new_length);
-  return *element;
+  Handle<Object> result;
+  if (IsJSArrayFastElementMovingAllowed(isolate, JSArray::cast(*receiver))) {

[Camillo Bruni, 2015/08/31 07:45:50]

Using this separate branch I gain roughly 50% speedup on a tight pop loop.

+    // Fast Elements Path
+    result = array->GetElementsAccessor()->Pop(array, elms_obj);
+    if (result->IsTheHole()) {

[Igor Sheludko, 2015/08/31 14:08:03]

I think hole handling should be in elements.cc and it's only necessary for holy
arrays (see usages of IsHoleyElementsKind(kind()) ).

[Camillo Bruni, 2015/08/31 14:41:35]

Makes sense.

+      result = isolate->factory()->undefined_value();

[Camillo Bruni, 2015/08/28 14:08:11]

I am not fully convinced about this branch myself. But I think this is the only
value that has to be converted for a FastElements Array.

+    }
+  } else {
+    // Use Slow Lookup otherwise
+    uint32_t new_length = len - 1;
+    ASSIGN_RETURN_FAILURE_ON_EXCEPTION(
+        isolate, result, Object::GetElement(isolate, array, new_length));
+    JSArray::SetLength(array, new_length);
+  }
+  return *result;
 }