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

src/full-codegen/mips/full-codegen-mips.cc

Index: src/full-codegen/mips/full-codegen-mips.cc
diff --git a/src/full-codegen/mips/full-codegen-mips.cc b/src/full-codegen/mips/full-codegen-mips.cc
index 1018cbdefad6dbded8c97ad4a7503a9bba7909a8..f0865ff333be0cfc299c46abeb564e04d52dc2b6 100644
--- a/src/full-codegen/mips/full-codegen-mips.cc
+++ b/src/full-codegen/mips/full-codegen-mips.cc
@@ -527,7 +527,7 @@ 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_) __ Branch(false_label_);
   } else if (lit->IsTrue() || lit->IsJSObject()) {
@@ -4298,8 +4298,8 @@ void FullCodeGenerator::EmitLiteralCompareTypeof(Expression* expr,
     __ LoadRoot(at, Heap::kFalseValueRootIndex);
     Split(eq, v0, Operand(at), if_true, if_false, fall_through);
   } else if (String::Equals(check, factory->undefined_string())) {
-    __ LoadRoot(at, Heap::kUndefinedValueRootIndex);
-    __ Branch(if_true, eq, v0, Operand(at));
+    __ LoadRoot(at, Heap::kNullValueRootIndex);
+    __ Branch(if_false, eq, v0, Operand(at));
     __ JumpIfSmi(v0, if_false);
     // Check for undetectable objects => true.
     __ lw(v0, FieldMemOperand(v0, HeapObject::kMapOffset));