Correctly handle clearing of deprecated field types.

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 <iomanip>
 #include <sstream>
 
 #include "src/v8.h"
 
 #include "src/accessors.h"
@@ skipping 2371 matching lines @@
                                     new_field_type,
                                     isolate)->NowIs(old_field_type));
     return;
   }
 
   // Determine the field owner.
   Handle<Map> field_owner(map->FindFieldOwner(modify_index), isolate);
   Handle<DescriptorArray> descriptors(
       field_owner->instance_descriptors(), isolate);
   DCHECK_EQ(*old_field_type, descriptors->GetFieldType(modify_index));
+  bool old_field_type_was_cleared =
+      old_field_type->Is(HeapType::None()) && old_representation.IsHeapObject();
 
-  // Determine the generalized new field type.
-  new_field_type = Map::GeneralizeFieldType(
-      old_field_type, new_field_type, isolate);
+  // Determine the generalized new field type. Conservatively assume type Any
+  // for cleared field types because the cleared type could have been a
+  // deprecated map and there still could be live instances with a non-
+  // deprecated version of the map.
+  new_field_type =
+      old_field_type_was_cleared
+          ? HeapType::Any(isolate)
+          : Map::GeneralizeFieldType(old_field_type, new_field_type, isolate);
 
   PropertyDetails details = descriptors->GetDetails(modify_index);
   Handle<Name> name(descriptors->GetKey(modify_index));
 
   Handle<Object> wrapped_type(WrapType(new_field_type));
   field_owner->UpdateFieldType(modify_index, name, new_representation,
                                wrapped_type);
   field_owner->dependent_code()->DeoptimizeDependentCodeGroup(
       isolate, DependentCode::kFieldTypeGroup);
 
@@ skipping 14645 matching lines @@
                                                CompilationInfo* info) {
   Handle<DependentCode> codes = DependentCode::InsertCompilationInfo(
       handle(cell->dependent_code(), info->isolate()),
       DependentCode::kPropertyCellChangedGroup, info->object_wrapper());
   if (*codes != cell->dependent_code()) cell->set_dependent_code(*codes);
   info->dependencies(DependentCode::kPropertyCellChangedGroup)->Add(
       cell, info->zone());
 }
 
 } }  // namespace v8::internal