Ensure we update attributes in CopyGeneralizeFieldRepresentation

src/objects.cc

 // Copyright 2013 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.
 
 #include "src/v8.h"
 
 #include "src/accessors.h"
 #include "src/allocation-site-scopes.h"
 #include "src/api.h"
 #include "src/arguments.h"
@@ skipping 2321 matching lines @@
   int length = descriptors->number_of_descriptors();
   for (int i = 0; i < length; i++) {
     descriptors->SetRepresentation(i, Representation::Tagged());
     if (descriptors->GetDetails(i).type() == FIELD) {
       descriptors->SetValue(i, HeapType::Any());
     }
   }
 
   // Unless the instance is being migrated, ensure that modify_index is a field.
   PropertyDetails details = descriptors->GetDetails(modify_index);
-  if (store_mode == FORCE_FIELD && details.type() != FIELD) {
+  if (store_mode == FORCE_FIELD &&
+      (details.type() != FIELD || details.attributes() != attributes)) {
+    int field_index = details.type() == FIELD ? details.field_index()
+                                              : new_map->NumberOfFields();
     FieldDescriptor d(handle(descriptors->GetKey(modify_index), isolate),
-                      new_map->NumberOfFields(),
-                      attributes,
-                      Representation::Tagged());
+                      field_index, attributes, Representation::Tagged());
     descriptors->Replace(modify_index, &d);
-    int unused_property_fields = new_map->unused_property_fields() - 1;
-    if (unused_property_fields < 0) {
-      unused_property_fields += JSObject::kFieldsAdded;
+    if (details.type() != FIELD) {
+      int unused_property_fields = new_map->unused_property_fields() - 1;
+      if (unused_property_fields < 0) {
+        unused_property_fields += JSObject::kFieldsAdded;
+      }
+      new_map->set_unused_property_fields(unused_property_fields);
     }
-    new_map->set_unused_property_fields(unused_property_fields);
+  } else {
+    ASSERT(details.attributes() == attributes);
   }
 
   if (FLAG_trace_generalization) {
     HeapType* field_type = (details.type() == FIELD)
         ? map->instance_descriptors()->GetFieldType(modify_index)
         : NULL;
     map->PrintGeneralization(stdout, reason, modify_index,
                         new_map->NumberOfOwnDescriptors(),
                         new_map->NumberOfOwnDescriptors(),
                         details.type() == CONSTANT && store_mode == FORCE_FIELD,
@@ skipping 14632 matching lines @@
 #define ERROR_MESSAGES_TEXTS(C, T) T,
   static const char* error_messages_[] = {
       ERROR_MESSAGES_LIST(ERROR_MESSAGES_TEXTS)
   };
 #undef ERROR_MESSAGES_TEXTS
   return error_messages_[reason];
 }
 
 
 } }  // namespace v8::internal