Mark null and undefined as undetectable, and use it to handle abstract equality comparison in the g…

src/mips64/macro-assembler-mips64.h

Index: src/mips64/macro-assembler-mips64.h
diff --git a/src/mips64/macro-assembler-mips64.h b/src/mips64/macro-assembler-mips64.h
index 03e535d55e56bc169e6ab13abbb16b572a29e7db..ce72ba207ffa6f3c8afcfd3bd18f1713c76233b3 100644
--- a/src/mips64/macro-assembler-mips64.h
+++ b/src/mips64/macro-assembler-mips64.h
@@ -1132,6 +1132,11 @@ class MacroAssembler: public Assembler {
                      Register map,
                      Register type_reg);
 
+  void GetInstanceType(Register object_map, Register object_instance_type) {
+    lbu(object_instance_type,
+        FieldMemOperand(object_map, Map::kInstanceTypeOffset));
+  }
+
   // Check if a map for a JSObject indicates that the object has fast elements.
   // Jump to the specified label if it does not.
   void CheckFastElements(Register map,