Make objects embedded in optimized code weak.

src/mark-compact.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 74 matching lines @@
     for (Object** current = start; current < end; current++) {
       if ((*current)->IsHeapObject()) {
         HeapObject* object = HeapObject::cast(*current);
         CHECK(heap_->mark_compact_collector()->IsMarked(object));
       }
     }
   }
 
   void VisitEmbeddedPointer(RelocInfo* rinfo) {
     ASSERT(rinfo->rmode() == RelocInfo::EMBEDDED_OBJECT);
-    if (!FLAG_weak_embedded_maps_in_optimized_code || !FLAG_collect_maps ||
-        rinfo->host()->kind() != Code::OPTIMIZED_FUNCTION ||
-        !rinfo->target_object()->IsMap() ||
-        !Map::cast(rinfo->target_object())->CanTransition()) {
+    if (!Code::IsWeakEmbeddedObject(rinfo->host()->kind(),
+                                    rinfo->target_object())) {
       VisitPointer(rinfo->target_object_address());
     }
   }
 
  private:
   Heap* heap_;
 };
 
 
 static void VerifyMarking(Heap* heap, Address bottom, Address top) {
@@ skipping 316 matching lines @@
 
   if (!FLAG_collect_maps) ReattachInitialMaps();
 
 #ifdef DEBUG
   if (FLAG_verify_native_context_separation) {
     VerifyNativeContextSeparation(heap_);
   }
 #endif
 
 #ifdef VERIFY_HEAP
-  if (FLAG_collect_maps && FLAG_weak_embedded_maps_in_optimized_code &&
-      heap()->weak_embedded_maps_verification_enabled()) {
-    VerifyWeakEmbeddedMapsInOptimizedCode();
+  if (heap()->weak_embedded_maps_verification_enabled()) {

[Hannes Payer (out of office), 2013/10/01 13:13:50]

This property should be renamed to weak_embedded_objects_verification_enabled

[ulan, 2013/10/01 14:50:29]

Can we instead rename the method to
VerifyWeakEmbeddedMapsAndObjectsInOptimizedCode()?
Renaming of the property triggers renaming of
NoWeakEmbeddedMapsVerificationScope, which makes many lines longer than 80. :)

[Hannes Payer (out of office), 2013/10/02 12:21:47]

I think object is general enough to also reflect maps.
What about renaming the method to VerifyWeakEmbeddedObjectsInOptimizedCode()?
The scope and the field should not be called *Map* anymore, we need a shorter
name for that. Anything that is generic enough is fine with me.

[ulan, 2013/10/02 12:36:49]

Done.

+    VerifyWeakEmbeddedObjectsInOptimizedCode();
   }
   if (FLAG_collect_maps && FLAG_omit_map_checks_for_leaf_maps) {
     VerifyOmittedMapChecks();
   }
 #endif
 
   Finish();
 
   if (marking_parity_ == EVEN_MARKING_PARITY) {
     marking_parity_ = ODD_MARKING_PARITY;
@@ skipping 40 matching lines @@
 
   LargeObjectIterator it(heap_->lo_space());
   for (HeapObject* obj = it.Next(); obj != NULL; obj = it.Next()) {
     MarkBit mark_bit = Marking::MarkBitFrom(obj);
     CHECK(Marking::IsWhite(mark_bit));
     CHECK_EQ(0, Page::FromAddress(obj->address())->LiveBytes());
   }
 }
 
 
-void MarkCompactCollector::VerifyWeakEmbeddedMapsInOptimizedCode() {
+void MarkCompactCollector::VerifyWeakEmbeddedObjectsInOptimizedCode() {
   HeapObjectIterator code_iterator(heap()->code_space());
   for (HeapObject* obj = code_iterator.Next();
        obj != NULL;
        obj = code_iterator.Next()) {
     Code* code = Code::cast(obj);
     if (code->kind() != Code::OPTIMIZED_FUNCTION) continue;
     if (WillBeDeoptimized(code)) continue;
-    code->VerifyEmbeddedMapsDependency();
+    code->VerifyEmbeddedObjectsDependency();
   }
 }
 
 
 void MarkCompactCollector::VerifyOmittedMapChecks() {
   HeapObjectIterator iterator(heap()->map_space());
   for (HeapObject* obj = iterator.Next();
        obj != NULL;
        obj = iterator.Next()) {
     Map* map = Map::cast(obj);
@@ skipping 957 matching lines @@
         JSWeakCollection::kTableOffset);
     BodyVisitorBase<MarkCompactMarkingVisitor>::IteratePointers(
         map->GetHeap(),
         object,
         JSWeakCollection::kTableOffset + kPointerSize,
         object_size);
 
     // Mark the backing hash table without pushing it on the marking stack.
     Object* table_object = weak_collection->table();
     if (!table_object->IsHashTable()) return;
-    ObjectHashTable* table = ObjectHashTable::cast(table_object);
+    WeakHashTable* table = WeakHashTable::cast(table_object);
     Object** table_slot =
         HeapObject::RawField(weak_collection, JSWeakCollection::kTableOffset);
     MarkBit table_mark = Marking::MarkBitFrom(table);
     collector->RecordSlot(table_slot, table_slot, table);
     if (!table_mark.Get()) collector->SetMark(table, table_mark);
     // Recording the map slot can be skipped, because maps are not compacted.
     collector->MarkObject(table->map(), Marking::MarkBitFrom(table->map()));
     ASSERT(MarkCompactCollector::IsMarked(table->map()));
   }
 
@@ skipping 614 matching lines @@
 
 
 void MarkCompactCollector::MarkRoots(RootMarkingVisitor* visitor) {
   // Mark the heap roots including global variables, stack variables,
   // etc., and all objects reachable from them.
   heap()->IterateStrongRoots(visitor, VISIT_ONLY_STRONG);
 
   // Handle the string table specially.
   MarkStringTable(visitor);
 
+  MarkWeakObjectToCode(visitor);
+
   // There may be overflowed objects in the heap.  Visit them now.
   while (marking_deque_.overflowed()) {
     RefillMarkingDeque();
     EmptyMarkingDeque();
   }
 }
 
 
 void MarkCompactCollector::MarkImplicitRefGroups() {
   List<ImplicitRefGroup*>* ref_groups =
@@ skipping 20 matching lines @@
     }
 
     // Once the entire group has been marked, dispose it because it's
     // not needed anymore.
     delete entry;
   }
   ref_groups->Rewind(last);
 }
 
 
+void MarkCompactCollector::MarkWeakObjectToCode(RootMarkingVisitor* visitor) {

[Hannes Payer (out of office), 2013/10/01 13:13:50]

Visitor is not needed for this function.

[ulan, 2013/10/01 14:50:29]

Done.

+  HeapObject* weak_object_to_code =
+      HeapObject::cast(heap()->weak_object_to_code());
+  if (!IsMarked(weak_object_to_code)) {
+    MarkBit mark = Marking::MarkBitFrom(weak_object_to_code);
+    SetMark(weak_object_to_code, mark);
+  }
+}
+
+
 // Mark all objects reachable from the objects on the marking stack.
 // Before: the marking stack contains zero or more heap object pointers.
 // After: the marking stack is empty, and all objects reachable from the
 // marking stack have been marked, or are overflowed in the heap.
 void MarkCompactCollector::EmptyMarkingDeque() {
   while (!marking_deque_.IsEmpty()) {
     HeapObject* object = marking_deque_.Pop();
     ASSERT(object->IsHeapObject());
     ASSERT(heap()->Contains(object));
     ASSERT(Marking::IsBlack(Marking::MarkBitFrom(object)));
@@ skipping 347 matching lines @@
       // Since it survived the GC, reattach it now.
       JSFunction::cast(map->constructor())->shared()->AttachInitialMap(map);
     }
 
     ClearNonLivePrototypeTransitions(map);
     ClearNonLiveMapTransitions(map, map_mark);
 
     if (map_mark.Get()) {
       ClearNonLiveDependentCode(map->dependent_code());
     } else {
-      ClearAndDeoptimizeDependentCode(map);
+      ClearAndDeoptimizeDependentCode(map->dependent_code());
+      map->set_dependent_code(DependentCode::cast(heap()->empty_fixed_array()));
     }
   }
 
   // Iterate over property cell space, removing dependent code that is not
   // otherwise kept alive by strong references.
   HeapObjectIterator cell_iterator(heap_->property_cell_space());
   for (HeapObject* cell = cell_iterator.Next();
        cell != NULL;
        cell = cell_iterator.Next()) {
     if (IsMarked(cell)) {
       ClearNonLiveDependentCode(PropertyCell::cast(cell)->dependent_code());
     }
   }
+
+  if (heap_->weak_object_to_code()->IsHashTable()) {
+    WeakHashTable* table = WeakHashTable::cast(heap_->weak_object_to_code());
+    uint32_t capacity = table->Capacity();
+    for (uint32_t i = 0; i < capacity; i++) {
+      uint32_t key_index = table->EntryToIndex(i);
+      Object* key = table->get(key_index);
+      if (!table->IsKey(key)) continue;
+      uint32_t value_index = table->EntryToValueIndex(i);
+      Object* value = table->get(value_index);
+      if (IsMarked(key)) {
+        if (!IsMarked(value)) {
+          HeapObject* obj = HeapObject::cast(value);
+          MarkBit mark = Marking::MarkBitFrom(obj);
+          SetMark(obj, mark);
+        }
+        ClearNonLiveDependentCode(DependentCode::cast(value));
+      } else {
+        ClearAndDeoptimizeDependentCode(DependentCode::cast(value));
+        table->set(key_index, heap_->the_hole_value());
+        table->set(value_index, heap_->the_hole_value());
+      }
+    }
+  }
 }
 
 
 void MarkCompactCollector::ClearNonLivePrototypeTransitions(Map* map) {
   int number_of_transitions = map->NumberOfProtoTransitions();
   FixedArray* prototype_transitions = map->GetPrototypeTransitions();
 
   int new_number_of_transitions = 0;
   const int header = Map::kProtoTransitionHeaderSize;
   const int proto_offset = header + Map::kProtoTransitionPrototypeOffset;
@@ skipping 45 matching lines @@
   // Follow back pointer, check whether we are dealing with a map transition
   // from a live map to a dead path and in case clear transitions of parent.
   bool current_is_alive = map_mark.Get();
   bool parent_is_alive = Marking::MarkBitFrom(parent).Get();
   if (!current_is_alive && parent_is_alive) {
     parent->ClearNonLiveTransitions(heap());
   }
 }
 
 
-void MarkCompactCollector::ClearAndDeoptimizeDependentCode(Map* map) {
+void MarkCompactCollector::ClearAndDeoptimizeDependentCode(
+    DependentCode* entries) {
   DisallowHeapAllocation no_allocation;
-  DependentCode* entries = map->dependent_code();
   DependentCode::GroupStartIndexes starts(entries);
   int number_of_entries = starts.number_of_entries();
   if (number_of_entries == 0) return;
   for (int i = 0; i < number_of_entries; i++) {
     // If the entry is compilation info then the map must be alive,
     // and ClearAndDeoptimizeDependentCode shouldn't be called.
     ASSERT(entries->is_code_at(i));
     Code* code = entries->code_at(i);
 
     if (IsMarked(code) && !code->marked_for_deoptimization()) {
       code->set_marked_for_deoptimization(true);
       have_code_to_deoptimize_ = true;
     }
     entries->clear_at(i);
   }
-  map->set_dependent_code(DependentCode::cast(heap()->empty_fixed_array()));
 }
 
 
 void MarkCompactCollector::ClearNonLiveDependentCode(DependentCode* entries) {
   DisallowHeapAllocation no_allocation;
   DependentCode::GroupStartIndexes starts(entries);
   int number_of_entries = starts.number_of_entries();
   if (number_of_entries == 0) return;
   int new_number_of_entries = 0;
   // Go through all groups, remove dead codes and compact.
@@ skipping 818 matching lines @@
        cell = js_global_property_cell_iterator.Next()) {
     if (cell->IsPropertyCell()) {
       PropertyCell::BodyDescriptor::IterateBody(cell, &updating_visitor);
     }
   }
 
   // Update the head of the native contexts list in the heap.
   updating_visitor.VisitPointer(heap_->native_contexts_list_address());
 
   heap_->string_table()->Iterate(&updating_visitor);
+  updating_visitor.VisitPointer(heap_->weak_object_to_code_address());
+  if (heap_->weak_object_to_code()->IsHashTable()) {
+    WeakHashTable* table = WeakHashTable::cast(heap_->weak_object_to_code());
+    table->Iterate(&updating_visitor);
+    table->Rehash(heap_->undefined_value());
+  }
 
   // Update pointers from external string table.
   heap_->UpdateReferencesInExternalStringTable(
       &UpdateReferenceInExternalStringTableEntry);
 
   if (!FLAG_watch_ic_patching) {
     // Update JSFunction pointers from the runtime profiler.
     heap()->isolate()->runtime_profiler()->UpdateSamplesAfterCompact(
         &updating_visitor);
   }
@@ skipping 843 matching lines @@
   while (buffer != NULL) {
     SlotsBuffer* next_buffer = buffer->next();
     DeallocateBuffer(buffer);
     buffer = next_buffer;
   }
   *buffer_address = NULL;
 }
 
 
 } }  // namespace v8::internal