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

src/full-codegen/arm/full-codegen-arm.cc

Index: src/full-codegen/arm/full-codegen-arm.cc
diff --git a/src/full-codegen/arm/full-codegen-arm.cc b/src/full-codegen/arm/full-codegen-arm.cc
index d9bbbc08b3e83b3f00bcab762b94be3bf84193bb..5ca37f7e678c2a11bb5326f188c58ea5d3265161 100644
--- a/src/full-codegen/arm/full-codegen-arm.cc
+++ b/src/full-codegen/arm/full-codegen-arm.cc
@@ -537,7 +537,7 @@ 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_) __ b(false_label_);
   } else if (lit->IsTrue() || lit->IsJSObject()) {
@@ -4299,8 +4299,8 @@ void FullCodeGenerator::EmitLiteralCompareTypeof(Expression* expr,
     __ CompareRoot(r0, Heap::kFalseValueRootIndex);
     Split(eq, if_true, if_false, fall_through);
   } else if (String::Equals(check, factory->undefined_string())) {
-    __ CompareRoot(r0, Heap::kUndefinedValueRootIndex);
-    __ b(eq, if_true);
+    __ CompareRoot(r0, Heap::kNullValueRootIndex);
+    __ b(eq, if_false);
     __ JumpIfSmi(r0, if_false);
     // Check for undetectable objects => true.
     __ ldr(r0, FieldMemOperand(r0, HeapObject::kMapOffset));