Free one bit in Map by removing unused retaining counter.

src/objects-inl.h

 // 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.
 //
 // Review notes:
 //
 // - The use of macros in these inline functions may seem superfluous
 // but it is absolutely needed to make sure gcc generates optimal
 // code. gcc is not happy when attempting to inline too deep.
 //
@@ skipping 4736 matching lines @@
 
 
 void Map::set_new_target_is_base(bool value) {
   set_bit_field3(NewTargetIsBase::update(bit_field3(), value));
 }
 
 
 bool Map::new_target_is_base() { return NewTargetIsBase::decode(bit_field3()); }
 
 
-void Map::set_counter(int value) {
-  set_bit_field3(Counter::update(bit_field3(), value));
+void Map::set_construction_counter(int value) {
+  set_bit_field3(ConstructionCounter::update(bit_field3(), value));
 }
 
 
-int Map::counter() { return Counter::decode(bit_field3()); }
+int Map::construction_counter() {
+  return ConstructionCounter::decode(bit_field3());
+}
 
 
 void Map::mark_unstable() {
   set_bit_field3(IsUnstable::update(bit_field3(), true));
 }
 
 
 bool Map::is_stable() {
   return !IsUnstable::decode(bit_field3());
 }
@@ skipping 1382 matching lines @@
 
 
 void JSFunction::CompleteInobjectSlackTrackingIfActive() {
   if (has_initial_map() && initial_map()->IsInobjectSlackTrackingInProgress()) {
     initial_map()->CompleteInobjectSlackTracking();
   }
 }
 
 
 bool Map::IsInobjectSlackTrackingInProgress() {
-  return counter() >= Map::kSlackTrackingCounterEnd;
+  return construction_counter() != Map::kNoSlackTracking;
 }
 
 
 void Map::InobjectSlackTrackingStep() {
   if (!IsInobjectSlackTrackingInProgress()) return;
-  int counter = this->counter();
-  set_counter(counter - 1);
+  int counter = construction_counter();
+  set_construction_counter(counter - 1);
   if (counter == kSlackTrackingCounterEnd) {
     CompleteInobjectSlackTracking();
   }
 }
 
 
 Code* JSFunction::code() {
   return Code::cast(
       Code::GetObjectFromEntryAddress(FIELD_ADDR(this, kCodeEntryOffset)));
 }
@@ skipping 1680 matching lines @@
 #undef WRITE_INT64_FIELD
 #undef READ_BYTE_FIELD
 #undef WRITE_BYTE_FIELD
 #undef NOBARRIER_READ_BYTE_FIELD
 #undef NOBARRIER_WRITE_BYTE_FIELD
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_OBJECTS_INL_H_