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

src/x64/full-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 3953 matching lines @@
     __ CmpObjectType(rax, FIRST_NONSTRING_TYPE, rdx);
     __ j(above_equal, if_false);
     __ testb(FieldOperand(rdx, Map::kBitFieldOffset),
              Immediate(1 << Map::kIsUndetectable));
     Split(zero, if_true, if_false, fall_through);
   } else if (check->Equals(isolate()->heap()->boolean_symbol())) {
     __ CompareRoot(rax, Heap::kTrueValueRootIndex);
     __ j(equal, if_true);
     __ CompareRoot(rax, Heap::kFalseValueRootIndex);
     Split(equal, if_true, if_false, fall_through);
+  } else if (FLAG_harmony_typeof &&
+             check->Equals(isolate()->heap()->null_symbol())) {
+    __ CompareRoot(rax, Heap::kNullValueRootIndex);
+    Split(equal, if_true, if_false, fall_through);
   } else if (check->Equals(isolate()->heap()->undefined_symbol())) {
     __ CompareRoot(rax, Heap::kUndefinedValueRootIndex);
     __ j(equal, if_true);
     __ JumpIfSmi(rax, if_false);
     // Check for undetectable objects => true.
     __ movq(rdx, FieldOperand(rax, HeapObject::kMapOffset));
     __ testb(FieldOperand(rdx, Map::kBitFieldOffset),
              Immediate(1 << Map::kIsUndetectable));
     Split(not_zero, if_true, if_false, fall_through);
   } else if (check->Equals(isolate()->heap()->function_symbol())) {
     __ JumpIfSmi(rax, if_false);
     STATIC_ASSERT(LAST_CALLABLE_SPEC_OBJECT_TYPE == LAST_TYPE);
     __ CmpObjectType(rax, FIRST_CALLABLE_SPEC_OBJECT_TYPE, rdx);
     Split(above_equal, if_true, if_false, fall_through);
   } else if (check->Equals(isolate()->heap()->object_symbol())) {
     __ JumpIfSmi(rax, if_false);
-    __ CompareRoot(rax, Heap::kNullValueRootIndex);
-    __ j(equal, if_true);
+    if (!FLAG_harmony_typeof) {
+      __ CompareRoot(rax, Heap::kNullValueRootIndex);
+      __ j(equal, if_true);
+    }
     __ CmpObjectType(rax, FIRST_NONCALLABLE_SPEC_OBJECT_TYPE, rdx);
     __ j(below, if_false);
     __ CmpInstanceType(rdx, LAST_NONCALLABLE_SPEC_OBJECT_TYPE);
     __ j(above, if_false);
     // Check for undetectable objects => false.
     __ testb(FieldOperand(rdx, Map::kBitFieldOffset),
              Immediate(1 << Map::kIsUndetectable));
     Split(zero, if_true, if_false, fall_through);
   } else {
     if (if_false != fall_through) __ jmp(if_false);
@@ skipping 227 matching lines @@
   __ jmp(rdx);
 }
 
 
 #undef __
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64