Use weak cells in dependent code.

src/heap/mark-compact.cc

 // 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.
 
 #include "src/v8.h"
 
 #include "src/base/atomicops.h"
 #include "src/base/bits.h"
 #include "src/code-stubs.h"
 #include "src/compilation-cache.h"
@@ skipping 283 matching lines @@
 
 
 void MarkCompactCollector::CollectGarbage() {
   // Make sure that Prepare() has been called. The individual steps below will
   // update the state as they proceed.
   DCHECK(state_ == PREPARE_GC);
 
   MarkLiveObjects();
   DCHECK(heap_->incremental_marking()->IsStopped());
 
+  // ClearNonLiveReferences can deoptimize code in dependent code arrays.
+  // Process weak cells before so that weak cells in dependent code
+  // arrays are cleared or contain only live code objects.
+  ProcessAndClearWeakCells();
+
   if (FLAG_collect_maps) ClearNonLiveReferences();
 
-  ProcessAndClearWeakCells();
 

[Hannes Payer (out of office), 2015/02/12 12:19:47]

remove one more newline

[ulan, 2015/02/12 12:55:51]

Done.

   ClearWeakCollections();
 
   heap_->set_encountered_weak_cells(Smi::FromInt(0));
 
 #ifdef VERIFY_HEAP
   if (FLAG_verify_heap) {
     VerifyMarking(heap_);
   }
 #endif
 
   SweepSpaces();
 
 #ifdef VERIFY_HEAP
-  if (heap()->weak_embedded_objects_verification_enabled()) {
-    VerifyWeakEmbeddedObjectsInCode();
-  }
+  VerifyWeakEmbeddedObjectsInCode();
   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;
   } else {
@@ skipping 1617 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);
 
-  MarkWeakObjectToCodeTable();
-
   // 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::MarkWeakObjectToCodeTable() {
-  HeapObject* weak_object_to_code_table =
-      HeapObject::cast(heap()->weak_object_to_code_table());
-  if (!IsMarked(weak_object_to_code_table)) {
-    MarkBit mark = Marking::MarkBitFrom(weak_object_to_code_table);
-    SetMark(weak_object_to_code_table, 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() {
   Map* filler_map = heap_->one_pointer_filler_map();
   while (!marking_deque_.IsEmpty()) {
     HeapObject* object = marking_deque_.Pop();
     // Explicitly skip one word fillers. Incremental markbit patterns are
     // correct only for objects that occupy at least two words.
@@ skipping 298 matching lines @@
   for (HeapObject* obj = map_iterator.Next(); obj != NULL;
        obj = map_iterator.Next()) {
     Map* map = Map::cast(obj);
 
     if (!map->CanTransition()) continue;
 
     MarkBit map_mark = Marking::MarkBitFrom(map);
     ClearNonLivePrototypeTransitions(map);
     ClearNonLiveMapTransitions(map, map_mark);
 
-    if (map_mark.Get()) {
-      ClearNonLiveDependentCode(map->dependent_code());
-    } else {
-      ClearDependentCode(map->dependent_code());
+    if (!map_mark.Get()) {
+      have_code_to_deoptimize_ |=
+          map->dependent_code()->MarkCodeForDeoptimization(
+              isolate(), DependentCode::kWeakCodeGroup);
       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());
-    }
-  }
-
-  // Iterate over allocation sites, removing dependent code that is not
-  // otherwise kept alive by strong references.
-  Object* undefined = heap()->undefined_value();
-  for (Object* site = heap()->allocation_sites_list(); site != undefined;
-       site = AllocationSite::cast(site)->weak_next()) {
-    if (IsMarked(site)) {
-      ClearNonLiveDependentCode(AllocationSite::cast(site)->dependent_code());
-    }
-  }
-
-  if (heap_->weak_object_to_code_table()->IsHashTable()) {
-    WeakHashTable* table =
-        WeakHashTable::cast(heap_->weak_object_to_code_table());
-    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 (key->IsCell() && !IsMarked(key)) {
-        Cell* cell = Cell::cast(key);
-        Object* object = cell->value();
-        if (IsMarked(object)) {
-          MarkBit mark = Marking::MarkBitFrom(cell);
-          SetMark(cell, mark);
-          Object** value_slot = HeapObject::RawField(cell, Cell::kValueOffset);
-          RecordSlot(value_slot, value_slot, *value_slot);
-        }
-      }
-      if (IsMarked(key)) {
-        if (!IsMarked(value)) {
-          HeapObject* obj = HeapObject::cast(value);
-          MarkBit mark = Marking::MarkBitFrom(obj);
-          SetMark(obj, mark);
-        }
-        ClearNonLiveDependentCode(DependentCode::cast(value));
-      } else {
-        ClearDependentCode(DependentCode::cast(value));
-        table->set(key_index, heap_->the_hole_value());
-        table->set(value_index, heap_->the_hole_value());
-        table->ElementRemoved();
-      }
+  WeakHashTable* table = heap_->weak_object_to_code_table();
+  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 (WeakCell::cast(key)->cleared()) {
+      have_code_to_deoptimize_ |=
+          DependentCode::cast(value)->MarkCodeForDeoptimization(
+              isolate(), DependentCode::kWeakCodeGroup);
+      table->set(key_index, heap_->the_hole_value());
+      table->set(value_index, heap_->the_hole_value());
+      table->ElementRemoved();
     }
   }
 }
 
 
 void MarkCompactCollector::ClearNonLivePrototypeTransitions(Map* map) {
   int number_of_transitions = map->NumberOfProtoTransitions();
   FixedArray* prototype_transitions = map->GetPrototypeTransitions();
 
   int new_number_of_transitions = 0;
@@ skipping 151 matching lines @@
   if (to_trim <= 0) return;
   heap_->RightTrimFixedArray<Heap::FROM_GC>(descriptors->GetEnumCache(),
                                             to_trim);
 
   if (!descriptors->HasEnumIndicesCache()) return;
   FixedArray* enum_indices_cache = descriptors->GetEnumIndicesCache();
   heap_->RightTrimFixedArray<Heap::FROM_GC>(enum_indices_cache, to_trim);
 }
 
 
-void MarkCompactCollector::ClearDependentCode(DependentCode* entries) {
-  DisallowHeapAllocation no_allocation;
-  DependentCode::GroupStartIndexes starts(entries);
-  int number_of_entries = starts.number_of_entries();
-  if (number_of_entries == 0) return;
-  int g = DependentCode::kWeakCodeGroup;
-  for (int i = starts.at(g); i < starts.at(g + 1); i++) {
-    // If the entry is compilation info then the map must be alive,
-    // and ClearDependentCode shouldn't be called.
-    DCHECK(entries->is_code_at(i));
-    Code* code = entries->code_at(i);
-    if (IsMarked(code) && !code->marked_for_deoptimization()) {
-      DependentCode::SetMarkedForDeoptimization(
-          code, static_cast<DependentCode::DependencyGroup>(g));
-      code->InvalidateEmbeddedObjects();
-      have_code_to_deoptimize_ = true;
-    }
-  }
-  for (int i = 0; i < number_of_entries; i++) {
-    entries->clear_at(i);
-  }
-}
-
-
-int MarkCompactCollector::ClearNonLiveDependentCodeInGroup(
-    DependentCode* entries, int group, int start, int end, int new_start) {
-  int survived = 0;
-  for (int i = start; i < end; i++) {
-    Object* obj = entries->object_at(i);
-    DCHECK(obj->IsCode() || IsMarked(obj));
-    if (IsMarked(obj) &&
-        (!obj->IsCode() || !WillBeDeoptimized(Code::cast(obj)))) {
-      if (new_start + survived != i) {
-        entries->set_object_at(new_start + survived, obj);
-      }
-      Object** slot = entries->slot_at(new_start + survived);
-      RecordSlot(slot, slot, obj);
-      survived++;
-    }
-  }
-  entries->set_number_of_entries(
-      static_cast<DependentCode::DependencyGroup>(group), survived);
-  return survived;
-}
-
-
-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.
-  for (int g = 0; g < DependentCode::kGroupCount; g++) {
-    int survived = ClearNonLiveDependentCodeInGroup(
-        entries, g, starts.at(g), starts.at(g + 1), new_number_of_entries);
-    new_number_of_entries += survived;
-  }
-  for (int i = new_number_of_entries; i < number_of_entries; i++) {
-    entries->clear_at(i);
-  }
-}
-
-
 void MarkCompactCollector::ProcessWeakCollections() {
   GCTracer::Scope gc_scope(heap()->tracer(),
                            GCTracer::Scope::MC_WEAKCOLLECTION_PROCESS);
   Object* weak_collection_obj = heap()->encountered_weak_collections();
   while (weak_collection_obj != Smi::FromInt(0)) {
     JSWeakCollection* weak_collection =
         reinterpret_cast<JSWeakCollection*>(weak_collection_obj);
     DCHECK(MarkCompactCollector::IsMarked(weak_collection));
     if (weak_collection->table()->IsHashTable()) {
       ObjectHashTable* table = ObjectHashTable::cast(weak_collection->table());
@@ skipping 55 matching lines @@
 
 void MarkCompactCollector::ProcessAndClearWeakCells() {
   HeapObject* undefined = heap()->undefined_value();
   Object* weak_cell_obj = heap()->encountered_weak_cells();
   while (weak_cell_obj != Smi::FromInt(0)) {
     WeakCell* weak_cell = reinterpret_cast<WeakCell*>(weak_cell_obj);
     // We do not insert cleared weak cells into the list, so the value
     // cannot be a Smi here.
     HeapObject* value = HeapObject::cast(weak_cell->value());
     if (!MarkCompactCollector::IsMarked(value)) {
-      weak_cell->clear();
+      // Cells for new-space objects embedded in optimized code are wrapped in
+      // WeakCell and put into Heap::weak_object_to_code_table.
+      // Such cells do not have any strong references but we want to keep them
+      // alive as long as the cell value is alive.
+      // TODO(ulan): remove this once we remove Heap::weak_object_to_code_table.
+      if (value->IsCell()) {
+        Object* cell_value = Cell::cast(value)->value();
+        if (cell_value->IsHeapObject() &&
+            MarkCompactCollector::IsMarked(HeapObject::cast(cell_value))) {
+          // Resurrect the cell.
+          MarkBit mark = Marking::MarkBitFrom(value);
+          SetMark(value, mark);
+          Object** slot = HeapObject::RawField(value, Cell::kValueOffset);
+          RecordSlot(slot, slot, *slot);
+          slot = HeapObject::RawField(weak_cell, WeakCell::kValueOffset);
+          RecordSlot(slot, slot, *slot);
+        } else {
+          weak_cell->clear();
+        }
+      } else {
+        weak_cell->clear();
+      }
     } else {
       Object** slot = HeapObject::RawField(weak_cell, WeakCell::kValueOffset);
-      heap()->mark_compact_collector()->RecordSlot(slot, slot, value);
+      RecordSlot(slot, slot, *slot);
     }
     weak_cell_obj = weak_cell->next();
     weak_cell->set_next(undefined, SKIP_WRITE_BARRIER);
   }
   heap()->set_encountered_weak_cells(Smi::FromInt(0));
 }
 
 
 void MarkCompactCollector::AbortWeakCells() {
   Object* undefined = heap()->undefined_value();
@@ skipping 825 matching lines @@
   HeapObjectIterator js_global_property_cell_iterator(
       heap_->property_cell_space());
   for (HeapObject* cell = js_global_property_cell_iterator.Next(); cell != NULL;
        cell = js_global_property_cell_iterator.Next()) {
     if (cell->IsPropertyCell()) {
       PropertyCell::BodyDescriptor::IterateBody(cell, &updating_visitor);
     }
   }
 
   heap_->string_table()->Iterate(&updating_visitor);
-  updating_visitor.VisitPointer(heap_->weak_object_to_code_table_address());
-  if (heap_->weak_object_to_code_table()->IsHashTable()) {
-    WeakHashTable* table =
-        WeakHashTable::cast(heap_->weak_object_to_code_table());
-    table->Iterate(&updating_visitor);
-    table->Rehash(heap_->isolate()->factory()->undefined_value());
-  }
 
   // Update pointers from external string table.
   heap_->UpdateReferencesInExternalStringTable(
       &UpdateReferenceInExternalStringTableEntry);
 
   EvacuationWeakObjectRetainer evacuation_object_retainer;
   heap()->ProcessAllWeakReferences(&evacuation_object_retainer);
 
   // Collects callback info for handles that are pending (about to be
   // collected) and either phantom or internal-fields.  Releases the global
   // handles.  See also PostGarbageCollectionProcessing.
   isolate()->global_handles()->CollectAllPhantomCallbackData();
 
   // Visit invalidated code (we ignored all slots on it) and clear mark-bits
   // under it.
   ProcessInvalidatedCode(&updating_visitor);
 
   heap_->isolate()->inner_pointer_to_code_cache()->Flush();
 
   slots_buffer_allocator_.DeallocateChain(&migration_slots_buffer_);
   DCHECK(migration_slots_buffer_ == NULL);
+
+  // The hashing of weak_object_to_code_table is no longer valid.
+  heap()->weak_object_to_code_table()->Rehash(
+      heap()->isolate()->factory()->undefined_value());
 }
 
 
 void MarkCompactCollector::MoveEvacuationCandidatesToEndOfPagesList() {
   int npages = evacuation_candidates_.length();
   for (int i = 0; i < npages; i++) {
     Page* p = evacuation_candidates_[i];
     if (!p->IsEvacuationCandidate()) continue;
     p->Unlink();
     PagedSpace* space = static_cast<PagedSpace*>(p->owner());
@@ skipping 834 matching lines @@
   SlotsBuffer* buffer = *buffer_address;
   while (buffer != NULL) {
     SlotsBuffer* next_buffer = buffer->next();
     DeallocateBuffer(buffer);
     buffer = next_buffer;
   }
   *buffer_address = NULL;
 }
 }
 }  // namespace v8::internal