Implement Harmony semantics for typeof null (behind a flag).

src/x64/lithium-codegen-x64.cc

 // Copyright 2011 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:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 3990 matching lines @@
     __ testb(FieldOperand(input, Map::kBitFieldOffset),
              Immediate(1 << Map::kIsUndetectable));
     final_branch_condition = zero;
 
   } else if (type_name->Equals(heap()->boolean_symbol())) {
     __ CompareRoot(input, Heap::kTrueValueRootIndex);
     __ j(equal, true_label);
     __ CompareRoot(input, Heap::kFalseValueRootIndex);
     final_branch_condition = equal;
 
+  } else if (FLAG_harmony_typeof && type_name->Equals(heap()->null_symbol())) {
+    __ CompareRoot(input, Heap::kNullValueRootIndex);
+    final_branch_condition = equal;
+
   } else if (type_name->Equals(heap()->undefined_symbol())) {
     __ CompareRoot(input, Heap::kUndefinedValueRootIndex);
     __ j(equal, true_label);
     __ JumpIfSmi(input, false_label);
     // Check for undetectable objects => true.
     __ movq(input, FieldOperand(input, HeapObject::kMapOffset));
     __ testb(FieldOperand(input, Map::kBitFieldOffset),
              Immediate(1 << Map::kIsUndetectable));
     final_branch_condition = not_zero;
 
   } else if (type_name->Equals(heap()->function_symbol())) {
     __ JumpIfSmi(input, false_label);
     __ CmpObjectType(input, FIRST_CALLABLE_SPEC_OBJECT_TYPE, input);
     final_branch_condition = above_equal;
 
   } else if (type_name->Equals(heap()->object_symbol())) {
     __ JumpIfSmi(input, false_label);
-    __ CompareRoot(input, Heap::kNullValueRootIndex);
-    __ j(equal, true_label);
+    if (!FLAG_harmony_typeof) {
+      __ CompareRoot(input, Heap::kNullValueRootIndex);
+      __ j(equal, true_label);
+    }
     __ CmpObjectType(input, FIRST_NONCALLABLE_SPEC_OBJECT_TYPE, input);
     __ j(below, false_label);
     __ CmpInstanceType(input, LAST_NONCALLABLE_SPEC_OBJECT_TYPE);
     __ j(above, false_label);
     // Check for undetectable objects => false.
     __ testb(FieldOperand(input, Map::kBitFieldOffset),
              Immediate(1 << Map::kIsUndetectable));
     final_branch_condition = zero;
 
   } else {
@@ skipping 144 matching lines @@
   RegisterEnvironmentForDeoptimization(environment);
   ASSERT(osr_pc_offset_ == -1);
   osr_pc_offset_ = masm()->pc_offset();
 }
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64