Optimization of some packed array cases.

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index 128902f93afefbc2cea441bbccc487d2538f0743..9ed5310b5c9bd8253446234e270a8d6ea26dd952 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -10023,6 +10023,12 @@ void JSObject::GetElementsCapacityAndUsage(int* capacity, int* used) {
       // Fall through.
     case FAST_SMI_ELEMENTS:
     case FAST_ELEMENTS:
+      if (FLAG_packed_arrays && IsJSArray()) {

[Jakob Kummerow, 2012/06/12 12:50:44]

This flag check isn't necessary, as we can't have PACKED elements kinds without
the flag anyway. Same below.

[danno, 2012/06/12 15:38:14]

Done.

+        *capacity = backing_store_base->length();
+        *used = Smi::cast(JSArray::cast(this)->length())->value();
+        break;
+      }
+      // Fall through if packing is not guaranteed.
     case FAST_HOLEY_SMI_ELEMENTS:
     case FAST_HOLEY_ELEMENTS:
       backing_store = FixedArray::cast(backing_store_base);
@@ -10039,6 +10045,12 @@ void JSObject::GetElementsCapacityAndUsage(int* capacity, int* used) {
       break;
     }
     case FAST_DOUBLE_ELEMENTS:
+      if (FLAG_packed_arrays && IsJSArray()) {
+        *capacity = backing_store_base->length();
+        *used = Smi::cast(JSArray::cast(this)->length())->value();
+        break;
+      }
+      // Fall through if packing is not guaranteed.
     case FAST_HOLEY_DOUBLE_ELEMENTS: {
       FixedDoubleArray* elms = FixedDoubleArray::cast(elements());
       *capacity = elms->length();