[TypeFeedbackVector] Root literal arrays in function literals slots

src/objects-inl.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
 // Review notes:
 //
 // - The use of macros in these inline functions may seem superfluous
 // but it is absolutely needed to make sure gcc generates optimal
 // code. gcc is not happy when attempting to inline too deep.
 //
@@ skipping 3476 matching lines @@
 void LiteralsArray::set(int index, Object* value, WriteBarrierMode mode) {
   FixedArray::set(index, value, mode);
 }
 
 
 LiteralsArray* LiteralsArray::cast(Object* object) {
   SLOW_DCHECK(object->IsLiteralsArray());
   return reinterpret_cast<LiteralsArray*>(object);
 }
 
+bool LiteralsArray::needs_feedback_vector() const {
+  return get(kVectorIndex)->IsUndefined(this->GetIsolate());
+}
 
 TypeFeedbackVector* LiteralsArray::feedback_vector() const {
-  if (length() == 0) {
+  if (length() == 0 || needs_feedback_vector()) {
     return TypeFeedbackVector::cast(
-        const_cast<FixedArray*>(FixedArray::cast(this)));
+        this->GetIsolate()->heap()->empty_type_feedback_vector());
   }
+
   return TypeFeedbackVector::cast(get(kVectorIndex));
 }
 
 
 void LiteralsArray::set_feedback_vector(TypeFeedbackVector* vector) {
   if (length() <= kVectorIndex) {
     DCHECK(vector->length() == 0);
     return;
   }
   set(kVectorIndex, vector);
@@ skipping 3106 matching lines @@
   // context based on the state change.
   if (!was_optimized && is_optimized) {
     context()->native_context()->AddOptimizedFunction(this);
   }
   if (was_optimized && !is_optimized) {
     // TODO(titzer): linear in the number of optimized functions; fix!
     context()->native_context()->RemoveOptimizedFunction(this);
   }
 }
 
+bool JSFunction::needs_literals_array() const {
+  SharedFunctionInfo* shared = this->shared();
+
+  return literals() == shared->GetIsolate()->heap()->empty_literals_array() &&
+         (shared->feedback_metadata()->slot_count() > 0 ||
+          shared->num_literals() > 0);
+}
 
 Context* JSFunction::context() {
   return Context::cast(READ_FIELD(this, kContextOffset));
 }
 
 
 JSObject* JSFunction::global_proxy() {
   return context()->global_proxy();
 }
 
@@ skipping 1797 matching lines @@
 #undef WRITE_INT64_FIELD
 #undef READ_BYTE_FIELD
 #undef WRITE_BYTE_FIELD
 #undef NOBARRIER_READ_BYTE_FIELD
 #undef NOBARRIER_WRITE_BYTE_FIELD
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_OBJECTS_INL_H_