Mark maps having a hidden prototype rather than maps of hidden prototypes.

src/x87/builtins-x87.cc

Index: src/x87/builtins-x87.cc
diff --git a/src/x87/builtins-x87.cc b/src/x87/builtins-x87.cc
index a710dd3646be7cbee0a4e62e8adbff2bf83912c7..602471771c5a4222b75f32d93e4cf8ff1b627650 100644
--- a/src/x87/builtins-x87.cc
+++ b/src/x87/builtins-x87.cc
@@ -2689,14 +2689,12 @@ static void CompatibleReceiverCheck(MacroAssembler* masm, Register receiver,
   // Load the next prototype.
   __ bind(&next_prototype);
   __ mov(receiver, FieldOperand(receiver, HeapObject::kMapOffset));
-  __ mov(receiver, FieldOperand(receiver, Map::kPrototypeOffset));
-  // End if the prototype is null or not hidden.
-  __ CompareRoot(receiver, Heap::kNullValueRootIndex);
-  __ j(equal, receiver_check_failed);
-  __ mov(scratch0, FieldOperand(receiver, HeapObject::kMapOffset));
-  __ test(FieldOperand(scratch0, Map::kBitField3Offset),
+  __ test(FieldOperand(receiver, Map::kBitField3Offset),
           Immediate(Map::IsHiddenPrototype::kMask));

[Camillo Bruni, 2016/02/08 13:24:09]

missed ::HasHiddenPrototype

   __ j(zero, receiver_check_failed);
+
+  __ mov(receiver, FieldOperand(receiver, Map::kPrototypeOffset));
+  __ mov(scratch0, FieldOperand(receiver, HeapObject::kMapOffset));
   // Iterate.
   __ jmp(&prototype_loop_start, Label::kNear);