Make maps in monomorphic IC stubs 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 431 matching lines @@
   if (!FLAG_collect_maps) ReattachInitialMaps();
 
 #ifdef DEBUG
   if (FLAG_verify_native_context_separation) {
     VerifyNativeContextSeparation(heap_);
   }
 #endif
 
 #ifdef VERIFY_HEAP
   if (heap()->weak_embedded_objects_verification_enabled()) {
-    VerifyWeakEmbeddedObjectsInOptimizedCode();
+    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;
@@ 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::VerifyWeakEmbeddedObjectsInOptimizedCode() {
+void MarkCompactCollector::VerifyWeakEmbeddedObjectsInCode() {
   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 (!code->is_optimized_code() && !code->is_weak_stub()) continue;
     if (WillBeDeoptimized(code)) continue;
     code->VerifyEmbeddedObjectsDependency();
   }
 }
 
 
 void MarkCompactCollector::VerifyOmittedMapChecks() {
   HeapObjectIterator iterator(heap()->map_space());
   for (HeapObject* obj = iterator.Next();
        obj != NULL;
@@ skipping 2046 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->dependent_code());
+      ClearDependentCode(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()) {
@@ skipping 34 matching lines @@
         }
       }
       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));
+        ClearDependentCode(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();
@@ skipping 49 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(
+void MarkCompactCollector::ClearDependentICList(Object* head) {
+  Object* current = head;
+  Object* undefined = heap()->undefined_value();
+  while (current != undefined) {
+    Code* code = Code::cast(current);
+    if (IsMarked(code)) {
+      ASSERT(code->is_weak_stub());
+      IC::InvalidateMaps(code);
+    }
+    current = code->next_code_link();
+    code->set_next_code_link(undefined);
+  }
+}
+
+
+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;
-  for (int i = 0; i < number_of_entries; i++) {
+  int g = DependentCode::kWeakICGroup;
+  if (starts.at(g) != starts.at(g + 1)) {
+    int i = starts.at(g);
+    ASSERT(i + 1 == starts.at(g + 1));
+    Object* head = entries->object_at(i);
+    ClearDependentICList(head);
+  }
+  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 ClearAndDeoptimizeDependentCode shouldn't be called.
+    // and ClearDependentCode 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);
       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;
+  if (group == DependentCode::kWeakICGroup) {
+    // Dependent weak IC stubs form a linked list and only the head is stored
+    // in the dependent code array.
+    if (start != end) {
+      ASSERT(start + 1 == end);
+      Object* old_head = entries->object_at(start);
+      MarkCompactWeakObjectRetainer retainer;
+      Object* head = VisitWeakList<Code>(heap(), old_head, &retainer, true);
+      entries->set_object_at(new_start, head);
+      Object** slot = entries->slot_at(new_start);
+      RecordSlot(slot, slot, head);
+      // We do not compact this group even if the head is undefined,
+      // more dependent ICs are likely to be added later.
+      survived = 1;
+    }
+  } else {
+    for (int i = start; i < end; i++) {
+      Object* obj = entries->object_at(i);
+      ASSERT(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 group_number_of_entries = 0;
-    for (int i = starts.at(g); i < starts.at(g + 1); i++) {
-      Object* obj = entries->object_at(i);
-      ASSERT(obj->IsCode() || IsMarked(obj));
-      if (IsMarked(obj) &&
-          (!obj->IsCode() || !WillBeDeoptimized(Code::cast(obj)))) {
-        if (new_number_of_entries + group_number_of_entries != i) {
-          entries->set_object_at(
-              new_number_of_entries + group_number_of_entries, obj);
-        }
-        Object** slot = entries->slot_at(new_number_of_entries +
-                                         group_number_of_entries);
-        RecordSlot(slot, slot, obj);
-        group_number_of_entries++;
-      }
-    }
-    entries->set_number_of_entries(
-        static_cast<DependentCode::DependencyGroup>(g),
-        group_number_of_entries);
-    new_number_of_entries += group_number_of_entries;
+    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(tracer_, GCTracer::Scope::MC_WEAKCOLLECTION_PROCESS);
   Object* weak_collection_obj = encountered_weak_collections();
@@ skipping 631 matching lines @@
     MarkBit mark_bit = Marking::MarkBitFrom(code);
     if (Marking::IsWhite(mark_bit)) return;
 
     invalidated_code_.Add(code);
   }
 }
 
 
 // Return true if the given code is deoptimized or will be deoptimized.
 bool MarkCompactCollector::WillBeDeoptimized(Code* code) {
-  return code->marked_for_deoptimization();
+  return code->is_optimized_code() && code->marked_for_deoptimization();
 }
 
 
 bool MarkCompactCollector::MarkInvalidatedCode() {
   bool code_marked = false;
 
   int length = invalidated_code_.length();
   for (int i = 0; i < length; i++) {
     Code* code = invalidated_code_[i];
 
@@ skipping 1101 matching lines @@
   while (buffer != NULL) {
     SlotsBuffer* next_buffer = buffer->next();
     DeallocateBuffer(buffer);
     buffer = next_buffer;
   }
   *buffer_address = NULL;
 }
 
 
 } }  // namespace v8::internal