Make objects embedded in optimized code weak.

src/mark-compact.cc

Index: src/mark-compact.cc
diff --git a/src/mark-compact.cc b/src/mark-compact.cc
index 263de4878fcbc83661a57d70183df2166b04860a..4de8d690734c50c0f09701ef8407cf2a1ec94d34 100644
--- a/src/mark-compact.cc
+++ b/src/mark-compact.cc
@@ -92,10 +92,8 @@ class VerifyMarkingVisitor: public ObjectVisitor {
 
   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());
     }
   }
@@ -432,9 +430,8 @@ void MarkCompactCollector::CollectGarbage() {
 #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();
@@ -495,7 +492,7 @@ void MarkCompactCollector::VerifyMarkbitsAreClean() {
 }
 
 
-void MarkCompactCollector::VerifyWeakEmbeddedMapsInOptimizedCode() {
+void MarkCompactCollector::VerifyWeakEmbeddedObjectsInOptimizedCode() {
   HeapObjectIterator code_iterator(heap()->code_space());
   for (HeapObject* obj = code_iterator.Next();
        obj != NULL;
@@ -503,7 +500,7 @@ void MarkCompactCollector::VerifyWeakEmbeddedMapsInOptimizedCode() {
     Code* code = Code::cast(obj);
     if (code->kind() != Code::OPTIMIZED_FUNCTION) continue;
     if (WillBeDeoptimized(code)) continue;
-    code->VerifyEmbeddedMapsDependency();
+    code->VerifyEmbeddedObjectsDependency();
   }
 }
 
@@ -1481,7 +1478,7 @@ class MarkCompactMarkingVisitor
     // 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);
@@ -2116,6 +2113,8 @@ void MarkCompactCollector::MarkRoots(RootMarkingVisitor* visitor) {
   // 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();
@@ -2156,6 +2155,16 @@ void MarkCompactCollector::MarkImplicitRefGroups() {
 }
 
 
+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
@@ -2523,7 +2532,8 @@ void MarkCompactCollector::ClearNonLiveReferences() {
     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()));
     }
   }
 
@@ -2537,6 +2547,30 @@ void MarkCompactCollector::ClearNonLiveReferences() {
       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());
+      }
+    }
+  }
 }
 
 
@@ -2602,9 +2636,9 @@ void MarkCompactCollector::ClearNonLiveMapTransitions(Map* map,
 }
 
 
-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;
@@ -2620,7 +2654,6 @@ void MarkCompactCollector::ClearAndDeoptimizeDependentCode(Map* map) {
     }
     entries->clear_at(i);
   }
-  map->set_dependent_code(DependentCode::cast(heap()->empty_fixed_array()));
 }
 
 
@@ -3459,6 +3492,12 @@ void MarkCompactCollector::EvacuateNewSpaceAndCandidates() {
   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(