Make sure transitioned arrays efficiently call builtin Array functions

src/ia32/macro-assembler-ia32.cc

Index: src/ia32/macro-assembler-ia32.cc
diff --git a/src/ia32/macro-assembler-ia32.cc b/src/ia32/macro-assembler-ia32.cc
index 3356e818922d0ccce2967e4cd2bf6a586917663d..97abf0b0c9110f69b3b7e3d3c542a63aba3f5613 100644
--- a/src/ia32/macro-assembler-ia32.cc
+++ b/src/ia32/macro-assembler-ia32.cc
@@ -1,4 +1,4 @@
-// Copyright 2011 the V8 project authors. All rights reserved.
+// Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
@@ -490,12 +490,38 @@ void MacroAssembler::StoreNumberToDoubleElements(
 void MacroAssembler::CheckMap(Register obj,
                               Handle<Map> map,
                               Label* fail,
-                              SmiCheckType smi_check_type) {
+                              SmiCheckType smi_check_type,
+                              MapCheckMode mode) {
   if (smi_check_type == DO_SMI_CHECK) {
     JumpIfSmi(obj, fail);
   }
+
+  Label success;
   cmp(FieldOperand(obj, HeapObject::kMapOffset), Immediate(map));
+  if (mode == ALLOW_ELEMENT_TRANSITION_MAPS) {
+    bool ignore;
+    Map* transitioned_double_map =
+        map->LookupElementsTransitionMap(FAST_DOUBLE_ELEMENTS, &ignore);
+    ASSERT(transitioned_double_map == NULL ||
+           map->elements_kind() == FAST_SMI_ONLY_ELEMENTS);
+    Map* transitioned_fast_element_map =
+        map->LookupElementsTransitionMap(FAST_ELEMENTS, &ignore);
+    ASSERT(transitioned_fast_element_map == NULL ||
+           map->elements_kind() != FAST_ELEMENTS);
+    if (transitioned_fast_element_map != NULL) {
+      j(equal, &success);
+      cmp(FieldOperand(obj, HeapObject::kMapOffset),
+          Immediate(Handle<Map>(transitioned_fast_element_map)));
+    }
+
+    if (transitioned_double_map != NULL) {
+      j(equal, &success);
+      cmp(FieldOperand(obj, HeapObject::kMapOffset),
+          Immediate(Handle<Map>(transitioned_double_map)));
+    }
+  }
   j(not_equal, fail);
+  bind(&success);
 }