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

src/full-codegen/x87/full-codegen-x87.cc

Index: src/full-codegen/x87/full-codegen-x87.cc
diff --git a/src/full-codegen/x87/full-codegen-x87.cc b/src/full-codegen/x87/full-codegen-x87.cc
index 4540d19a6a34a4679c9c53b289f8040e9ac23561..3c019b8c6e13a604232325bc14d06f0c343009b2 100644
--- a/src/full-codegen/x87/full-codegen-x87.cc
+++ b/src/full-codegen/x87/full-codegen-x87.cc
@@ -490,7 +490,7 @@ void FullCodeGenerator::TestContext::Plug(Handle<Object> lit) const {
                                           true,
                                           true_label_,
                                           false_label_);
-  DCHECK(!lit->IsUndetectableObject());  // There are no undetectable literals.
+  DCHECK(lit->IsNull() || lit->IsUndefined() || !lit->IsUndetectableObject());
   if (lit->IsUndefined() || lit->IsNull() || lit->IsFalse()) {
     if (false_label_ != fall_through_) __ jmp(false_label_);
   } else if (lit->IsTrue() || lit->IsJSObject()) {
@@ -4227,8 +4227,8 @@ void FullCodeGenerator::EmitLiteralCompareTypeof(Expression* expr,
     __ cmp(eax, isolate()->factory()->false_value());
     Split(equal, if_true, if_false, fall_through);
   } else if (String::Equals(check, factory->undefined_string())) {
-    __ cmp(eax, isolate()->factory()->undefined_value());
-    __ j(equal, if_true);
+    __ cmp(eax, isolate()->factory()->null_value());
+    __ j(equal, if_false);
     __ JumpIfSmi(eax, if_false);
     // Check for undetectable objects => true.
     __ mov(edx, FieldOperand(eax, HeapObject::kMapOffset));