Ensure slow properties for simple {__proto__:null} literals.

src/ast/ast.cc

Index: src/ast/ast.cc
diff --git a/src/ast/ast.cc b/src/ast/ast.cc
index 5b98e3165447f69f292b898139d85d8ab5161b6c..8e847c4c86e20e049093f2d2d155b4f28d033421 100644
--- a/src/ast/ast.cc
+++ b/src/ast/ast.cc
@@ -490,7 +490,7 @@ void ObjectLiteral::AssignFeedbackSlots(FeedbackVectorSpec* spec,
     ObjectLiteral::Property* property = properties()->at(property_index);
 
     Expression* value = property->value();
-    if (property->kind() != ObjectLiteral::Property::PROTOTYPE) {
+    if (!property->IsPrototype()) {
       if (FunctionLiteral::NeedsHomeObject(value)) {
         property->SetSlot(spec->AddStoreICSlot(language_mode));
       }
@@ -512,7 +512,7 @@ void ObjectLiteral::CalculateEmitStore(Zone* zone) {
   for (int i = properties()->length() - 1; i >= 0; i--) {
     ObjectLiteral::Property* property = properties()->at(i);
     if (property->is_computed_name()) continue;
-    if (property->kind() == ObjectLiteral::Property::PROTOTYPE) continue;
+    if (property->IsPrototype()) continue;
     Literal* literal = property->key()->AsLiteral();
     DCHECK(!literal->IsNullLiteral());
 
@@ -534,8 +534,7 @@ void ObjectLiteral::CalculateEmitStore(Zone* zone) {
 
 
 bool ObjectLiteral::IsBoilerplateProperty(ObjectLiteral::Property* property) {
-  return property != NULL &&
-         property->kind() != ObjectLiteral::Property::PROTOTYPE;
+  return property != NULL && !property->IsPrototype();
 }
 
 void ObjectLiteral::InitDepthAndFlags() {
@@ -550,6 +549,9 @@ void ObjectLiteral::InitDepthAndFlags() {
   for (int i = 0; i < properties()->length(); i++) {
     ObjectLiteral::Property* property = properties()->at(i);
     if (!IsBoilerplateProperty(property)) {
+      // __proto__:null at the first position has no side-effects and is set

[adamk, 2017/03/13 18:10:44]

Why do you say "first position"? The placement of the null proto isn't
important, I don't think.

+      // directly on the boilerplate.
+      if (property->IsNullPrototype()) continue;
       is_simple = false;
       continue;
     }