[runtime] Speed up allocating instances in the runtime by having a quick-check...

[runtime] Speed up allocating instances in the runtime by having a quick-check for inobject slack tracking.

This speeds up
https://github.com/kpdecker/six-speed/blob/master/tests/object-assign/object-assign.es5
by over 5%.

Review URL: https://codereview.chromium.org/1690923002

Cr-Commit-Position: refs/heads/master@{#33917}

src/heap/heap.cc

@@ -3446,7 +3446,6 @@ void Heap::InitializeJSObjectBody(JSObject* obj, Map* map, int start_offset) {
   if (start_offset == map->instance_size()) return;
   DCHECK_LT(start_offset, map->instance_size());
 
-  Object* filler;
   // We cannot always fill with one_pointer_filler_map because objects
   // created from API functions expect their internal fields to be initialized
   // with undefined_value.
@@ -3456,15 +3455,17 @@ void Heap::InitializeJSObjectBody(JSObject* obj, Map* map, int start_offset) {
 
   // In case of Array subclassing the |map| could already be transitioned
   // to different elements kind from the initial map on which we track slack.
-  Map* initial_map = map->FindRootMap();
-  if (initial_map->IsInobjectSlackTrackingInProgress()) {
-    // We might want to shrink the object later.
-    filler = Heap::one_pointer_filler_map();
+  bool in_progress = map->IsInobjectSlackTrackingInProgress();
+  Object* filler;
+  if (in_progress) {
+    filler = one_pointer_filler_map();
   } else {
-    filler = Heap::undefined_value();
+    filler = undefined_value();
   }
   obj->InitializeBody(map, start_offset, Heap::undefined_value(), filler);
-  initial_map->InobjectSlackTrackingStep();
+  if (in_progress) {
+    map->FindRootMap()->InobjectSlackTrackingStep();
+  }
 }
 
 

src/objects.cc

@@ -9310,8 +9310,6 @@ Handle<Map> Map::RawCopy(Handle<Map> map, int instance_size) {
   if (!map->is_dictionary_map()) {
     new_bit_field3 = IsUnstable::update(new_bit_field3, false);
   }
-  new_bit_field3 =
-      ConstructionCounter::update(new_bit_field3, kNoSlackTracking);
   result->set_bit_field3(new_bit_field3);
   return result;
 }
@@ -9398,6 +9396,7 @@ Handle<Map> Map::CopyNormalized(Handle<Map> map,
 
   result->set_dictionary_map(true);
   result->set_migration_target(false);
+  result->set_construction_counter(kNoSlackTracking);
 
 #ifdef VERIFY_HEAP
   if (FLAG_verify_heap) result->DictionaryMapVerify();
@@ -12713,6 +12712,7 @@ static void ShrinkInstanceSize(Map* map, void* data) {
   map->SetInObjectProperties(map->GetInObjectProperties() - slack);
   map->set_unused_property_fields(map->unused_property_fields() - slack);
   map->set_instance_size(map->instance_size() - slack * kPointerSize);
+  map->set_construction_counter(Map::kNoSlackTracking);
 
   // Visitor id might depend on the instance size, recalculate it.
   map->set_visitor_id(Heap::GetStaticVisitorIdForMap(map));
@@ -12723,8 +12723,6 @@ void Map::CompleteInobjectSlackTracking() {
   // Has to be an initial map.
   DCHECK(GetBackPointer()->IsUndefined());
 
-  set_construction_counter(kNoSlackTracking);
-
   int slack = unused_property_fields();
   TransitionArray::TraverseTransitionTree(this, &GetMinInobjectSlack, &slack);
   if (slack != 0) {
@@ -13316,6 +13314,7 @@ MaybeHandle<Map> JSFunction::GetDerivedMap(Isolate* isolate,
 
       JSFunction::SetInitialMap(function, map, prototype);
       map->SetConstructor(*constructor);
+      map->set_construction_counter(Map::kNoSlackTracking);
       map->StartInobjectSlackTracking();
       return map;
     }

src/objects.h

@@ -5584,7 +5584,11 @@ class Map: public HeapObject {
   // Builtins::kJSConstructStubGeneric stub.
   // This counter is used for in-object slack tracking.
   // The in-object slack tracking is considered enabled when the counter is
-  // non zero.
+  // non zero. The counter only has a valid count for initial maps. For
+  // transitioned maps only kNoSlackTracking has a meaning, namely that inobject
+  // slack tracking already finished for the transition tree. Any other value
+  // indicates that either inobject slack tracking is still in progress, or that
+  // the map isn't part of the transition tree anymore.
   class ConstructionCounter : public BitField<int, 29, 3> {};
   static const int kSlackTrackingCounterStart = 7;
   static const int kSlackTrackingCounterEnd = 1;