Free one bit in Map by removing unused retaining counter.

src/objects.cc

 // Copyright 2013 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 <sstream>
 
@@ skipping 8801 matching lines @@
   result->set_bit_field2(map->bit_field2());
   int new_bit_field3 = map->bit_field3();
   new_bit_field3 = OwnsDescriptors::update(new_bit_field3, true);
   new_bit_field3 = NumberOfOwnDescriptorsBits::update(new_bit_field3, 0);
   new_bit_field3 = EnumLengthBits::update(new_bit_field3,
                                           kInvalidEnumCacheSentinel);
   new_bit_field3 = Deprecated::update(new_bit_field3, false);
   if (!map->is_dictionary_map()) {
     new_bit_field3 = IsUnstable::update(new_bit_field3, false);
   }
-  new_bit_field3 = Counter::update(new_bit_field3, kRetainingCounterStart);
+  new_bit_field3 =
+      ConstructionCounter::update(new_bit_field3, kNoSlackTracking);
   result->set_bit_field3(new_bit_field3);
   return result;
 }
 
 
 Handle<Map> Map::Normalize(Handle<Map> fast_map, PropertyNormalizationMode mode,
                            const char* reason) {
   DCHECK(!fast_map->is_dictionary_map());
 
   Isolate* isolate = fast_map->GetIsolate();
@@ skipping 3253 matching lines @@
 
   // Visitor id might depend on the instance size, recalculate it.
   map->set_visitor_id(Heap::GetStaticVisitorIdForMap(map));
 }
 
 
 void Map::CompleteInobjectSlackTracking() {
   // Has to be an initial map.
   DCHECK(GetBackPointer()->IsUndefined());
 
-  DCHECK_GE(counter(), kSlackTrackingCounterEnd - 1);
-  set_counter(kRetainingCounterStart);
+  set_construction_counter(kNoSlackTracking);
 
   int slack = unused_property_fields();
   TransitionArray::TraverseTransitionTree(this, &GetMinInobjectSlack, &slack);
   if (slack != 0) {
     // Resize the initial map and all maps in its transition tree.
     TransitionArray::TraverseTransitionTree(this, &ShrinkInstanceSize, &slack);
   }
 }
 
 
@@ skipping 1150 matching lines @@
 
 void Map::StartInobjectSlackTracking() {
   DCHECK(!IsInobjectSlackTrackingInProgress());
 
   // No tracking during the snapshot construction phase.
   Isolate* isolate = GetIsolate();
   if (isolate->serializer_enabled()) return;
 
   if (unused_property_fields() == 0) return;
 
-  set_counter(Map::kSlackTrackingCounterStart);
+  set_construction_counter(Map::kSlackTrackingCounterStart);
 }
 
 
 void SharedFunctionInfo::ResetForNewContext(int new_ic_age) {
   code()->ClearInlineCaches();
   // If we clear ICs, we need to clear the type feedback vector too, since
   // CallICs are synced with a feedback vector slot.
   ClearTypeFeedbackInfo();
   set_ic_age(new_ic_age);
   if (code()->kind() == Code::FUNCTION) {
@@ skipping 5815 matching lines @@
   if (cell->value() != *new_value) {
     cell->set_value(*new_value);
     Isolate* isolate = cell->GetIsolate();
     cell->dependent_code()->DeoptimizeDependentCodeGroup(
         isolate, DependentCode::kPropertyCellChangedGroup);
   }
 }
 
 }  // namespace internal
 }  // namespace v8