Revert "Create a fast path to get migration target when updating map"

This reverts commit c285380ca8.

Reason for revert: Lots of dcheck failures on GPU bots, e.g.:
https://ci.chromium.org/p/v8/builders/luci.v8.ci/Win%20V8%20FYI%20Release%20(NVIDIA)/1997
https://ci.chromium.org/p/v8/builders/luci.v8.ci/Linux%20V8%20FYI%20Release%20(NVIDIA)/2770

Original change's description:
> Create a fast path to get migration target when updating map
> 
> During map updating, store the pointer to new map in the
> raw_transitions slot of the old map that is deprecated from map
> transition tree. Thus, we can get the migration target directly
> instead of TryReplayPropertyTransitions when updating map.
> 
> This can improve Speedometer2.0 Elm-TodoMVC case by ~5% on ATOM
> Chromebook and ~9% on big-core Ubuntu.
> 
> Change-Id: I56f9ce5183bbdd567b964890f623ef0ceed9b7db
> Reviewed-on: https://chromium-review.googlesource.com/1233433
> Commit-Queue: Shiyu Zhang <shiyu.zhang@intel.com>
> Reviewed-by: Igor Sheludko <ishell@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#56303}

TBR=ishell@chromium.org,shiyu.zhang@intel.com

Change-Id: I9b268d662cfa3a7fec577468eafe6570389252bc
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/1253104
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56305}

src/map-updater.cc

@@ -170,7 +170,6 @@ Handle<Map> MapUpdater::Update() {
   if (FindTargetMap() == kEnd) return result_map_;
   ConstructNewMap();
   DCHECK_EQ(kEnd, state_);
-  TransitionsAccessor(isolate_, old_map_).SetMigrationTarget(*result_map_);
   return result_map_;
 }
 

src/objects-printer.cc

@@ -2386,7 +2386,6 @@ void TransitionsAccessor::PrintTransitions(std::ostream& os) {  // NOLINT
   switch (encoding()) {
     case kPrototypeInfo:
     case kUninitialized:
-    case kMigrationTarget:
       return;
     case kWeakRef: {
       Map* target = Map::cast(raw_transitions_->GetHeapObjectAssumeWeak());

src/objects.cc

@@ -4882,25 +4882,6 @@ Handle<Map> Map::ReconfigureElementsKind(Isolate* isolate, Handle<Map> map,
   return mu.ReconfigureElementsKind(new_elements_kind);
 }
 
-namespace {
-
-Map* SearchMigrationTarget(Isolate* isolate, Map* old_map) {
-  DisallowHeapAllocation no_allocation;
-  DisallowDeoptimization no_deoptimization(isolate);
-
-  Map* target = old_map;
-  do {
-    target = TransitionsAccessor(isolate, target, &no_allocation)
-                 .GetMigrationTarget();
-  } while (target != nullptr && target->is_deprecated());
-  SLOW_DCHECK(target == nullptr ||
-              Map::TryUpdateSlow(isolate, old_map) == nullptr ||
-              Map::TryUpdateSlow(isolate, old_map) == target);
-  return target;
-}
-}  // namespace
-
-// TODO(ishell): Move TryUpdate() and friends to MapUpdater
 // static
 MaybeHandle<Map> Map::TryUpdate(Isolate* isolate, Handle<Map> old_map) {
   DisallowHeapAllocation no_allocation;
@@ -4908,22 +4889,6 @@ MaybeHandle<Map> Map::TryUpdate(Isolate* isolate, Handle<Map> old_map) {
 
   if (!old_map->is_deprecated()) return old_map;
 
-  Map* target_map = SearchMigrationTarget(isolate, *old_map);
-  if (target_map != nullptr) {
-    return handle(target_map, isolate);
-  }
-
-  Map* new_map = TryUpdateSlow(isolate, *old_map);
-  if (new_map == nullptr) return MaybeHandle<Map>();
-  TransitionsAccessor(isolate, *old_map, &no_allocation)
-      .SetMigrationTarget(new_map);
-  return handle(new_map, isolate);
-}
-
-Map* Map::TryUpdateSlow(Isolate* isolate, Map* old_map) {
-  DisallowHeapAllocation no_allocation;
-  DisallowDeoptimization no_deoptimization(isolate);
-
   // Check the state of the root map.
   Map* root_map = old_map->FindRootMap(isolate);
   if (root_map->is_deprecated()) {
@@ -4932,21 +4897,23 @@ Map* Map::TryUpdateSlow(Isolate* isolate, Map* old_map) {
     DCHECK(constructor->initial_map()->is_dictionary_map());
     if (constructor->initial_map()->elements_kind() !=
         old_map->elements_kind()) {
-      return nullptr;
+      return MaybeHandle<Map>();
     }
-    return constructor->initial_map();
+    return handle(constructor->initial_map(), constructor->GetIsolate());
   }
-  if (!old_map->EquivalentToForTransition(root_map)) return nullptr;
+  if (!old_map->EquivalentToForTransition(root_map)) return MaybeHandle<Map>();
 
   ElementsKind from_kind = root_map->elements_kind();
   ElementsKind to_kind = old_map->elements_kind();
   if (from_kind != to_kind) {
     // Try to follow existing elements kind transitions.
     root_map = root_map->LookupElementsTransitionMap(isolate, to_kind);
-    if (root_map == nullptr) return nullptr;
+    if (root_map == nullptr) return MaybeHandle<Map>();
     // From here on, use the map with correct elements kind as root map.
   }
-  return root_map->TryReplayPropertyTransitions(isolate, old_map);
+  Map* new_map = root_map->TryReplayPropertyTransitions(isolate, *old_map);
+  if (new_map == nullptr) return MaybeHandle<Map>();
+  return handle(new_map, isolate);
 }
 
 Map* Map::TryReplayPropertyTransitions(Isolate* isolate, Map* old_map) {
@@ -5028,10 +4995,6 @@ Map* Map::TryReplayPropertyTransitions(Isolate* isolate, Map* old_map) {
 // static
 Handle<Map> Map::Update(Isolate* isolate, Handle<Map> map) {
   if (!map->is_deprecated()) return map;
-  Map* target_map = SearchMigrationTarget(isolate, *map);
-  if (target_map != nullptr) {
-    return handle(target_map, isolate);
-  }
   MapUpdater mu(isolate, map);
   return mu.Update();
 }

src/objects/map.h

@@ -632,7 +632,6 @@ class Map : public HeapObject {
   // is found.
   static MaybeHandle<Map> TryUpdate(Isolate* isolate,
                                     Handle<Map> map) V8_WARN_UNUSED_RESULT;
-  static Map* TryUpdateSlow(Isolate* isolate, Map* map) V8_WARN_UNUSED_RESULT;
 
   // Returns a non-deprecated version of the input. This method may deprecate
   // existing maps along the way if encodings conflict. Not for use while

src/transitions-inl.h

@@ -65,7 +65,6 @@ Name* TransitionsAccessor::GetKey(int transition_number) {
   switch (encoding()) {
     case kPrototypeInfo:
     case kUninitialized:
-    case kMigrationTarget:
       UNREACHABLE();
       return nullptr;
     case kWeakRef: {
@@ -119,7 +118,6 @@ Map* TransitionsAccessor::GetTarget(int transition_number) {
   switch (encoding()) {
     case kPrototypeInfo:
     case kUninitialized:
-    case kMigrationTarget:
       UNREACHABLE();
       return nullptr;
     case kWeakRef:

src/transitions.cc

@@ -21,12 +21,9 @@ void TransitionsAccessor::Initialize() {
   } else if (raw_transitions_->GetHeapObjectIfStrong(&heap_object)) {
     if (heap_object->IsTransitionArray()) {
       encoding_ = kFullTransitionArray;
-    } else if (heap_object->IsPrototypeInfo()) {
-      encoding_ = kPrototypeInfo;
     } else {
-      DCHECK(map_->is_deprecated());
+      DCHECK(heap_object->IsPrototypeInfo());
-      DCHECK(heap_object->IsMap());
+      encoding_ = kPrototypeInfo;
-      encoding_ = kMigrationTarget;
     }
   } else {
     UNREACHABLE();
@@ -51,7 +48,6 @@ bool TransitionsAccessor::HasSimpleTransitionTo(Map* map) {
       return raw_transitions_->GetHeapObjectAssumeWeak() == map;
     case kPrototypeInfo:
     case kUninitialized:
-    case kMigrationTarget:
     case kFullTransitionArray:
       return false;
   }
@@ -216,7 +212,6 @@ Map* TransitionsAccessor::SearchTransition(Name* name, PropertyKind kind,
   switch (encoding()) {
     case kPrototypeInfo:
     case kUninitialized:
-    case kMigrationTarget:
       return nullptr;
     case kWeakRef: {
       Map* map = Map::cast(raw_transitions_->GetHeapObjectAssumeWeak());
@@ -269,7 +264,6 @@ Handle<String> TransitionsAccessor::ExpectedTransitionKey() {
   switch (encoding()) {
     case kPrototypeInfo:
     case kUninitialized:
-    case kMigrationTarget:
     case kFullTransitionArray:
       return Handle<String>::null();
     case kWeakRef: {
@@ -436,7 +430,6 @@ int TransitionsAccessor::NumberOfTransitions() {
   switch (encoding()) {
     case kPrototypeInfo:
     case kUninitialized:
-    case kMigrationTarget:
       return 0;
     case kWeakRef:
       return 1;
@@ -447,18 +440,6 @@ int TransitionsAccessor::NumberOfTransitions() {
   return 0;  // Make GCC happy.
 }
 
-void TransitionsAccessor::SetMigrationTarget(Map* migration_target) {
-  DCHECK(map_->is_deprecated());
-  ReplaceTransitions(MaybeObject::FromObject(migration_target));
-}
-
-Map* TransitionsAccessor::GetMigrationTarget() {
-  if (encoding() == kMigrationTarget) {
-    return map_->raw_transitions()->cast<Map>();
-  }
-  return nullptr;
-}
-
 void TransitionArray::Zap(Isolate* isolate) {
   MemsetPointer(
       data_start() + kPrototypeTransitionsIndex,
@@ -493,8 +474,7 @@ void TransitionsAccessor::SetPrototypeTransitions(
 
 void TransitionsAccessor::EnsureHasFullTransitionArray() {
   if (encoding() == kFullTransitionArray) return;
-  int nof =
+  int nof = encoding() == kUninitialized ? 0 : 1;
-      (encoding() == kUninitialized || encoding() == kMigrationTarget) ? 0 : 1;
   Handle<TransitionArray> result = isolate_->factory()->NewTransitionArray(nof);
   Reload();  // Reload after possible GC.
   if (nof == 1) {
@@ -517,7 +497,6 @@ void TransitionsAccessor::TraverseTransitionTreeInternal(
   switch (encoding()) {
     case kPrototypeInfo:
     case kUninitialized:
-    case kMigrationTarget:
       break;
     case kWeakRef: {
       Map* simple_target =

src/transitions.h

@@ -106,14 +106,6 @@ class TransitionsAccessor {
   void PutPrototypeTransition(Handle<Object> prototype, Handle<Map> target_map);
   Handle<Map> GetPrototypeTransition(Handle<Object> prototype);
 
-  // During the first-time Map::Update and Map::TryUpdate, the migration target
-  // map could be cached in the raw_transitions slot of the old map that is
-  // deprecated from the map transition tree. The next time old map is updated,
-  // we will check this cache slot as a shortcut to get the migration target
-  // map.
-  void SetMigrationTarget(Map* migration_target);
-  Map* GetMigrationTarget();
-
 #if DEBUG || OBJECT_PRINT
   void PrintTransitions(std::ostream& os);
   static void PrintOneTransition(std::ostream& os, Name* key, Map* target);
@@ -133,7 +125,6 @@ class TransitionsAccessor {
   enum Encoding {
     kPrototypeInfo,
     kUninitialized,
-    kMigrationTarget,
     kWeakRef,
     kFullTransitionArray,
   };

test/cctest/test-field-type-tracking.cc

@@ -78,14 +78,6 @@ static Handle<AccessorPair> CreateAccessorPair(bool with_getter,
   return pair;
 }
 
-// Check cached migration target map after Map::Update() and Map::TryUpdate()
-static void CheckMigrationTarget(Isolate* isolate, Map* old_map, Map* new_map) {
-  Map* target = TransitionsAccessor(isolate, handle(old_map, isolate))
-                    .GetMigrationTarget();
-  if (!target) return;
-  CHECK_EQ(new_map, target);
-  CHECK_EQ(Map::TryUpdateSlow(isolate, old_map), target);
-}
 
 class Expectations {
   static const int MAX_PROPERTIES = 10;
@@ -715,7 +707,6 @@ static void TestGeneralizeField(int detach_property_at_index,
   // Update all deprecated maps and check that they are now the same.
   Handle<Map> updated_map = Map::Update(isolate, map);
   CHECK_EQ(*new_map, *updated_map);
-  CheckMigrationTarget(isolate, *map, *updated_map);
 }
 
 static void TestGeneralizeField(const CRFTData& from, const CRFTData& to,
@@ -976,11 +967,9 @@ TEST(GeneralizeFieldWithAccessorProperties) {
   // Update all deprecated maps and check that they are now the same.
   Handle<Map> updated_map = Map::Update(isolate, map);
   CHECK_EQ(*active_map, *updated_map);
-  CheckMigrationTarget(isolate, *map, *updated_map);
   for (int i = 0; i < kPropCount; i++) {
     updated_map = Map::Update(isolate, maps[i]);
     CHECK_EQ(*active_map, *updated_map);
-    CheckMigrationTarget(isolate, *maps[i], *updated_map);
   }
 }
 
@@ -1071,7 +1060,6 @@ static void TestReconfigureDataFieldAttribute_GeneralizeField(
   // Update deprecated |map|, it should become |new_map|.
   Handle<Map> updated_map = Map::Update(isolate, map);
   CHECK_EQ(*new_map, *updated_map);
-  CheckMigrationTarget(isolate, *map, *updated_map);
 }
 
 // This test ensures that trivial field generalization (from HeapObject to
@@ -1382,7 +1370,6 @@ struct CheckDeprecated {
     // Update deprecated |map|, it should become |new_map|.
     Handle<Map> updated_map = Map::Update(isolate, map);
     CHECK_EQ(*new_map, *updated_map);
-    CheckMigrationTarget(isolate, *map, *updated_map);
   }
 };
 
@@ -1841,7 +1828,6 @@ static void TestReconfigureElementsKind_GeneralizeField(
   // Update deprecated |map|, it should become |new_map|.
   Handle<Map> updated_map = Map::Update(isolate, map);
   CHECK_EQ(*new_map, *updated_map);
-  CheckMigrationTarget(isolate, *map, *updated_map);
 
   // Ensure Map::FindElementsKindTransitionedMap() is able to find the
   // transitioned map.
@@ -2353,11 +2339,9 @@ static void TestGeneralizeFieldWithSpecialTransition(TestConfig& config,
   // Update all deprecated maps and check that they are now the same.
   Handle<Map> updated_map = Map::Update(isolate, map);
   CHECK_EQ(*active_map, *updated_map);
-  CheckMigrationTarget(isolate, *map, *updated_map);
   for (int i = 0; i < kPropCount; i++) {
     updated_map = Map::Update(isolate, maps[i]);
     CHECK_EQ(*active_map, *updated_map);
-    CheckMigrationTarget(isolate, *maps[i], *updated_map);
   }
 }
 
@@ -2639,7 +2623,6 @@ struct FieldGeneralizationChecker {
     CHECK_NE(*map1, *map2);
     Handle<Map> updated_map = Map::Update(isolate, map1);
     CHECK_EQ(*map2, *updated_map);
-    CheckMigrationTarget(isolate, *map1, *updated_map);
 
     expectations2.SetDataField(descriptor_, attributes_, constness_,
                                representation_, heap_type_);