[heap] Notify GC on potentially unsafe object layout changes.

src/objects.cc

 // Copyright 2015 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/objects.h"
 
 #include <cmath>
 #include <iomanip>
 #include <memory>
 #include <sstream>
@@ skipping 3257 matching lines @@
     case kDouble: return "d";
     case kInteger32: return "i";
     case kHeapObject: return "h";
     case kExternal: return "x";
     default:
       UNREACHABLE();
       return NULL;
   }
 }
 
+bool Map::TransitionRemovesTaggedField(Map* target) {
+  int inobject = GetInObjectProperties();
+  int target_inobject = target->GetInObjectProperties();
+  for (int i = target_inobject; i < inobject; i++) {
+    FieldIndex index = FieldIndex::ForPropertyIndex(this, i);
+    if (!IsUnboxedDoubleField(index)) return true;
+  }
+  return false;
+}
+
+bool Map::TransitionChangesTaggedFieldToUntaggedField(Map* target) {
+  int inobject = GetInObjectProperties();
+  int target_inobject = target->GetInObjectProperties();
+  int limit = Min(inobject, target_inobject);
+  for (int i = 0; i < limit; i++) {
+    FieldIndex index = FieldIndex::ForPropertyIndex(target, i);

[Igor Sheludko, 2017/02/21 10:22:25]

This will work only if target is a non-dictionary map...

[Igor Sheludko, 2017/02/21 10:36:37]

Please ignore my comments.

+    if (!IsUnboxedDoubleField(index) && target->IsUnboxedDoubleField(index)) {
+      return true;
+    }
+  }
+  return false;
+}
+
+bool Map::TransitionRequiresSynchronizationWithGC(Map* target) {
+  return TransitionRemovesTaggedField(target) ||

[Igor Sheludko, 2017/02/21 10:22:25]

... if a slow map does not contain inobject space then the first predicate will
return false and the second predicate will get a slow map as a target.

+         TransitionChangesTaggedFieldToUntaggedField(target);
+}
+
 bool Map::InstancesNeedRewriting(Map* target) {
   int target_number_of_fields = target->NumberOfFields();
   int target_inobject = target->GetInObjectProperties();
   int target_unused = target->unused_property_fields();
   int old_number_of_fields;
 
   return InstancesNeedRewriting(target, target_number_of_fields,
                                 target_inobject, target_unused,
                                 &old_number_of_fields);
 }
@@ skipping 230 matching lines @@
     int target_index = new_descriptors->GetFieldIndex(i) - inobject;
     if (target_index < 0) target_index += total_size;
     array->set(target_index, *value);
   }
 
   // From here on we cannot fail and we shouldn't GC anymore.
   DisallowHeapAllocation no_allocation;
 
   Heap* heap = isolate->heap();
 
+  heap->NotifyObjectLayoutChange(*object, no_allocation);
+
   // Copy (real) inobject properties. If necessary, stop at number_of_fields to
   // avoid overwriting |one_pointer_filler_map|.
   int limit = Min(inobject, number_of_fields);
   for (int i = 0; i < limit; i++) {
     FieldIndex index = FieldIndex::ForPropertyIndex(*new_map, i);
     Object* value = array->get(external + i);
     // Can't use JSObject::FastPropertyAtPut() because proper map was not set
     // yet.
     if (new_map->IsUnboxedDoubleField(index)) {
       DCHECK(value->IsMutableHeapNumber());
@@ skipping 94 matching lines @@
                       PropertyCellType::kNoCell);
     dictionary = NameDictionary::Add(dictionary, key, value, d);
   }
 
   // Copy the next enumeration index from instance descriptor.
   dictionary->SetNextEnumerationIndex(real_size + 1);
 
   // From here on we cannot fail and we shouldn't GC anymore.
   DisallowHeapAllocation no_allocation;
 
+  Heap* heap = isolate->heap();
+  heap->NotifyObjectLayoutChange(*object, no_allocation);
+
   // Resize the object in the heap if necessary.
   int new_instance_size = new_map->instance_size();
   int instance_size_delta = map->instance_size() - new_instance_size;
   DCHECK(instance_size_delta >= 0);
 
   if (instance_size_delta > 0) {
-    Heap* heap = isolate->heap();
     heap->CreateFillerObjectAt(object->address() + new_instance_size,
                                instance_size_delta, ClearRecordedSlots::kYes);
     heap->AdjustLiveBytes(*object, -instance_size_delta);
   }
 
   // We are storing the new map using release store after creating a filler for
   // the left-over space to avoid races with the sweeper thread.
   object->synchronized_set_map(*new_map);
 
   object->set_properties(*dictionary);
@@ skipping 16423 matching lines @@
       // depend on this.
       return DICTIONARY_ELEMENTS;
     }
     DCHECK_LE(kind, LAST_ELEMENTS_KIND);
     return kind;
   }
 }
 
 }  // namespace internal
 }  // namespace v8