deps: backport rehash strings after deserialization

Original commit messages:
a2ab1353f6
  [snapshot] Rehash strings after deserialization.

  See https://goo.gl/6aN8xA

  Bug: v8:6593
  Change-Id: Ic8b0b57195d01d41591397d5d45de3f0f3ebc3d9
  Reviewed-on: https://chromium-review.googlesource.com/574527
  Reviewed-by: Camillo Bruni <cbruni@chromium.org>
  Reviewed-by: Jakob Gruber <jgruber@chromium.org>
  Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
  Commit-Queue: Yang Guo <yangguo@chromium.org>
  Cr-Commit-Position: refs/heads/master@{#46732}

182caaf4a9
  Do not track transitions for built-in objects.

  Objects created during bootstrapping do not need
  a transition tree except for elements kind transitions.

  Bug: v8:6596
  Change-Id: I237b8b2792f201336e1c9731c815095dd06bc182
  Reviewed-on: https://chromium-review.googlesource.com/571750
  Reviewed-by: Igor Sheludko <ishell@chromium.org>
  Commit-Queue: Yang Guo <yangguo@chromium.org>
  Cr-Commit-Position: refs/heads/master@{#46693}

Fixes: https://github.com/nodejs/node/issues/14171
PR-URL: https://github.com/nodejs/node/pull/14345
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Ali Ijaz Sheikh <ofrobots@google.com>

configure

@@ -425,12 +425,12 @@ parser.add_option('--without-perfctr',
 # Dummy option for backwards compatibility
 parser.add_option('--with-snapshot',
     action='store_true',
-    dest='with_snapshot',
+    dest='unused_with_snapshot',
     help=optparse.SUPPRESS_HELP)
 
 parser.add_option('--without-snapshot',
     action='store_true',
-    dest='unused_without_snapshot',
+    dest='without_snapshot',
     help=optparse.SUPPRESS_HELP)
 
 parser.add_option('--without-ssl',
@@ -815,7 +815,7 @@ def configure_node(o):
   cross_compiling = (options.cross_compiling
                      if options.cross_compiling is not None
                      else target_arch != host_arch)
-  want_snapshots = 1 if options.with_snapshot else 0
+  want_snapshots = not options.without_snapshot
   o['variables']['want_separate_host_toolset'] = int(
       cross_compiling and want_snapshots)
   o['variables']['want_separate_host_toolset_mkpeephole'] = int(
@@ -962,7 +962,7 @@ def configure_v8(o):
   o['variables']['v8_optimized_debug'] = 0  # Compile with -O0 in debug builds.
   o['variables']['v8_random_seed'] = 0  # Use a random seed for hash tables.
   o['variables']['v8_promise_internal_field_count'] = 1 # Add internal field to promises for async hooks.
-  o['variables']['v8_use_snapshot'] = b(options.with_snapshot)
+  o['variables']['v8_use_snapshot'] = 'false' if options.without_snapshot else 'true'
   o['variables']['v8_trace_maps'] = 1 if options.trace_maps else 0
   o['variables']['node_use_v8_platform'] = b(not options.without_v8_platform)
   o['variables']['node_use_bundled_v8'] = b(not options.without_bundled_v8)

deps/v8/include/v8-version.h

@@ -11,7 +11,7 @@
 #define V8_MAJOR_VERSION 5
 #define V8_MINOR_VERSION 9
 #define V8_BUILD_NUMBER 211
-#define V8_PATCH_LEVEL 38
+#define V8_PATCH_LEVEL 39
 
 // Use 1 for candidates and 0 otherwise.
 // (Boolean macro values are not supported by all preprocessors.)

deps/v8/src/api.cc

@@ -601,6 +601,9 @@ StartupData SnapshotCreator::CreateBlob(
     isolate->heap()->SetSerializedGlobalProxySizes(*global_proxy_sizes);
   }
 
+  // We might rehash strings and re-sort descriptors. Clear the lookup cache.
+  isolate->descriptor_lookup_cache()->Clear();
+
   // If we don't do this then we end up with a stray root pointing at the
   // context even after we have disposed of the context.
   isolate->heap()->CollectAllAvailableGarbage(
@@ -642,11 +645,15 @@ StartupData SnapshotCreator::CreateBlob(
   // Serialize each context with a new partial serializer.
   i::List<i::SnapshotData*> context_snapshots(num_additional_contexts + 1);
 
+  // TODO(6593): generalize rehashing, and remove this flag.
+  bool can_be_rehashed = true;
+
   {
     // The default snapshot does not support embedder fields.
     i::PartialSerializer partial_serializer(
         isolate, &startup_serializer, v8::SerializeInternalFieldsCallback());
     partial_serializer.Serialize(&default_context, false);
+    can_be_rehashed = can_be_rehashed && partial_serializer.can_be_rehashed();
     context_snapshots.Add(new i::SnapshotData(&partial_serializer));
   }
 
@@ -654,10 +661,12 @@ StartupData SnapshotCreator::CreateBlob(
     i::PartialSerializer partial_serializer(
         isolate, &startup_serializer, data->embedder_fields_serializers_[i]);
     partial_serializer.Serialize(&contexts[i], true);
+    can_be_rehashed = can_be_rehashed && partial_serializer.can_be_rehashed();
     context_snapshots.Add(new i::SnapshotData(&partial_serializer));
   }
 
   startup_serializer.SerializeWeakReferencesAndDeferred();
+  can_be_rehashed = can_be_rehashed && startup_serializer.can_be_rehashed();
 
 #ifdef DEBUG
   if (i::FLAG_external_reference_stats) {
@@ -666,8 +675,8 @@ StartupData SnapshotCreator::CreateBlob(
 #endif  // DEBUG
 
   i::SnapshotData startup_snapshot(&startup_serializer);
-  StartupData result =
-      i::Snapshot::CreateSnapshotBlob(&startup_snapshot, &context_snapshots);
+  StartupData result = i::Snapshot::CreateSnapshotBlob(
+      &startup_snapshot, &context_snapshots, can_be_rehashed);
 
   // Delete heap-allocated context snapshot instances.
   for (const auto& context_snapshot : context_snapshots) {

deps/v8/src/bootstrapper.cc

@@ -644,6 +644,8 @@ Handle<JSFunction> Genesis::GetThrowTypeErrorIntrinsic(
     DCHECK(false);
   }
 
+  JSObject::MigrateSlowToFast(function, 0, "Bootstrapping");
+
   return function;
 }
 
@@ -1385,6 +1387,8 @@ void Genesis::InitializeGlobal(Handle<JSGlobalObject> global_object,
     sloppy_function_map_writable_prototype_->SetConstructor(*function_fun);
     strict_function_map_writable_prototype_->SetConstructor(*function_fun);
     class_function_map_->SetConstructor(*function_fun);
+
+    JSObject::MigrateSlowToFast(function_fun, 0, "Bootstrapping");
   }
 
   {
@@ -2204,6 +2208,8 @@ void Genesis::InitializeGlobal(Handle<JSGlobalObject> global_object,
       info->set_length(1);
       native_context()->set_promise_reject_shared_fun(*info);
     }
+
+    JSObject::MigrateSlowToFast(promise_fun, 0, "Bootstrapping");
   }
 
   {  // -- R e g E x p

deps/v8/src/flag-definitions.h

@@ -987,6 +987,8 @@ DEFINE_BOOL(abort_on_stack_overflow, false,
 DEFINE_BOOL(randomize_hashes, true,
             "randomize hashes to avoid predictable hash collisions "
             "(with snapshots this option cannot override the baked-in seed)")
+DEFINE_BOOL(rehash_snapshot, true,
+            "rehash strings from the snapshot to override the baked-in seed")
 DEFINE_INT(hash_seed, 0,
            "Fixed seed to use to hash property keys (0 means random)"
            "(with snapshots this option cannot override the baked-in seed)")

deps/v8/src/heap/heap.cc

@@ -5546,14 +5546,7 @@ bool Heap::SetUp() {
 
   // Set up the seed that is used to randomize the string hash function.
   DCHECK(hash_seed() == 0);
-  if (FLAG_randomize_hashes) {
-    if (FLAG_hash_seed == 0) {
-      int rnd = isolate()->random_number_generator()->NextInt();
-      set_hash_seed(Smi::FromInt(rnd & Name::kHashBitMask));
-    } else {
-      set_hash_seed(Smi::FromInt(FLAG_hash_seed));
-    }
-  }
+  if (FLAG_randomize_hashes) InitializeHashSeed();
 
   for (int i = 0; i < static_cast<int>(v8::Isolate::kUseCounterFeatureCount);
        i++) {
@@ -5591,6 +5584,14 @@ bool Heap::SetUp() {
   return true;
 }
 
+void Heap::InitializeHashSeed() {
+  if (FLAG_hash_seed == 0) {
+    int rnd = isolate()->random_number_generator()->NextInt();
+    set_hash_seed(Smi::FromInt(rnd & Name::kHashBitMask));
+  } else {
+    set_hash_seed(Smi::FromInt(FLAG_hash_seed));
+  }
+}
 
 bool Heap::CreateHeapObjects() {
   // Create initial maps.

deps/v8/src/heap/heap.h

@@ -994,6 +994,9 @@ class Heap {
   // without actually creating any objects.
   bool SetUp();
 
+  // (Re-)Initialize hash seed from flag or RNG.
+  void InitializeHashSeed();
+
   // Bootstraps the object heap with the core set of objects required to run.
   // Returns whether it succeeded.
   bool CreateHeapObjects();

deps/v8/src/js/array.js

@@ -1334,6 +1334,8 @@ var unscopables = {
   keys: true,
 };
 
+%ToFastProperties(unscopables);
+
 %AddNamedProperty(GlobalArray.prototype, unscopablesSymbol, unscopables,
                   DONT_ENUM | READ_ONLY);
 

deps/v8/src/objects.cc

@@ -8823,7 +8823,13 @@ void Map::TraceAllTransitions(Map* map) {
 
 void Map::ConnectTransition(Handle<Map> parent, Handle<Map> child,
                             Handle<Name> name, SimpleTransitionFlag flag) {
-  if (!parent->GetBackPointer()->IsUndefined(parent->GetIsolate())) {
+  Isolate* isolate = parent->GetIsolate();
+  // Do not track transitions during bootstrap except for element transitions.
+  if (isolate->bootstrapper()->IsActive() &&
+      !name.is_identical_to(isolate->factory()->elements_transition_symbol())) {
+    return;
+  }
+  if (!parent->GetBackPointer()->IsUndefined(isolate)) {
     parent->set_owns_descriptors(false);
   } else {
     // |parent| is initial map and it must keep the ownership, there must be no
@@ -16779,6 +16785,9 @@ template class Dictionary<UnseededNumberDictionary,
                           UnseededNumberDictionaryShape,
                           uint32_t>;
 
+template void
+HashTable<GlobalDictionary, GlobalDictionaryShape, Handle<Name> >::Rehash(Handle<Name> key);
+
 template Handle<SeededNumberDictionary>
 Dictionary<SeededNumberDictionary, SeededNumberDictionaryShape, uint32_t>::New(
     Isolate*, int at_least_space_for, PretenureFlag pretenure,

deps/v8/src/snapshot/deserializer.cc

@@ -121,6 +121,8 @@ void Deserializer::Deserialize(Isolate* isolate) {
   LOG_CODE_EVENT(isolate_, LogCodeObjects());
   LOG_CODE_EVENT(isolate_, LogBytecodeHandlers());
   LOG_CODE_EVENT(isolate_, LogCompiledFunctions());
+
+  if (FLAG_rehash_snapshot && can_rehash_) Rehash();
 }
 
 MaybeHandle<Object> Deserializer::DeserializePartial(
@@ -151,6 +153,9 @@ MaybeHandle<Object> Deserializer::DeserializePartial(
   // changed and logging should be added to notify the profiler et al of the
   // new code, which also has to be flushed from instruction cache.
   CHECK_EQ(start_address, code_space->top());
+
+  if (FLAG_rehash_snapshot && can_rehash_) RehashContext(Context::cast(root));
+
   return Handle<Object>(root, isolate);
 }
 
@@ -177,6 +182,63 @@ MaybeHandle<HeapObject> Deserializer::DeserializeObject(Isolate* isolate) {
   }
 }
 
+// We only really just need HashForObject here.
+class StringRehashKey : public HashTableKey {
+ public:
+  uint32_t HashForObject(Object* other) override {
+    return String::cast(other)->Hash();
+  }
+
+  static uint32_t StringHash(Object* obj) {
+    UNREACHABLE();
+    return String::cast(obj)->Hash();
+  }
+
+  bool IsMatch(Object* string) override {
+    UNREACHABLE();
+    return false;
+  }
+
+  uint32_t Hash() override {
+    UNREACHABLE();
+    return 0;
+  }
+
+  Handle<Object> AsHandle(Isolate* isolate) override {
+    UNREACHABLE();
+    return isolate->factory()->empty_string();
+  }
+};
+
+void Deserializer::Rehash() {
+  DCHECK(can_rehash_);
+  isolate_->heap()->InitializeHashSeed();
+  if (FLAG_profile_deserialization) {
+    PrintF("Re-initializing hash seed to %x\n",
+           isolate_->heap()->hash_seed()->value());
+  }
+  StringRehashKey string_rehash_key;
+  isolate_->heap()->string_table()->Rehash(&string_rehash_key);
+  SortMapDescriptors();
+}
+
+void Deserializer::RehashContext(Context* context) {
+  DCHECK(can_rehash_);
+  for (const auto& array : transition_arrays_) array->Sort();
+  Handle<Name> dummy = isolate_->factory()->empty_string();
+  context->global_object()->global_dictionary()->Rehash(dummy);
+  SortMapDescriptors();
+}
+
+void Deserializer::SortMapDescriptors() {
+  for (const auto& address : allocated_maps_) {
+    Map* map = Map::cast(HeapObject::FromAddress(address));
+    if (map->instance_descriptors()->number_of_descriptors() > 1) {
+      map->instance_descriptors()->Sort();
+    }
+  }
+}
+
 Deserializer::~Deserializer() {
 #ifdef DEBUG
   // Do not perform checks if we aborted deserialization.
@@ -367,6 +429,16 @@ HeapObject* Deserializer::PostProcessNewObject(HeapObject* obj, int space) {
             string->resource()));
     isolate_->heap()->RegisterExternalString(string);
   }
+  if (FLAG_rehash_snapshot && can_rehash_ && !deserializing_user_code()) {
+    if (obj->IsString()) {
+      // Uninitialize hash field as we are going to reinitialize the hash seed.
+      String* string = String::cast(obj);
+      string->set_hash_field(String::kEmptyHashField);
+    } else if (obj->IsTransitionArray() &&
+               TransitionArray::cast(obj)->number_of_entries() > 1) {
+      transition_arrays_.Add(TransitionArray::cast(obj));
+    }
+  }
   // Check alignment.
   DCHECK_EQ(0, Heap::GetFillToAlign(obj->address(), obj->RequiredAlignment()));
   return obj;

deps/v8/src/snapshot/deserializer.h

@@ -39,7 +39,8 @@ class Deserializer : public SerializerDeserializer {
         external_reference_table_(NULL),
         deserialized_large_objects_(0),
         deserializing_user_code_(deserializing_user_code),
-        next_alignment_(kWordAligned) {
+        next_alignment_(kWordAligned),
+        can_rehash_(false) {
     DecodeReservation(data->Reservations());
   }
 
@@ -62,6 +63,8 @@ class Deserializer : public SerializerDeserializer {
     attached_objects_.Add(attached_object);
   }
 
+  void SetRehashability(bool v) { can_rehash_ = v; }
+
  private:
   void VisitPointers(Object** start, Object** end) override;
 
@@ -117,6 +120,15 @@ class Deserializer : public SerializerDeserializer {
   // snapshot by chunk index and offset.
   HeapObject* GetBackReferencedObject(int space);
 
+  // Rehash after deserializing an isolate.
+  void Rehash();
+
+  // Rehash after deserializing a context.
+  void RehashContext(Context* context);
+
+  // Sort descriptors of deserialized maps using new string hashes.
+  void SortMapDescriptors();
+
   // Cached current isolate.
   Isolate* isolate_;
 
@@ -144,11 +156,15 @@ class Deserializer : public SerializerDeserializer {
   List<AccessorInfo*> accessor_infos_;
   List<Handle<String> > new_internalized_strings_;
   List<Handle<Script> > new_scripts_;
+  List<TransitionArray*> transition_arrays_;
 
   bool deserializing_user_code_;
 
   AllocationAlignment next_alignment_;
 
+  // TODO(6593): generalize rehashing, and remove this flag.
+  bool can_rehash_;
+
   DISALLOW_COPY_AND_ASSIGN(Deserializer);
 };
 

deps/v8/src/snapshot/partial-serializer.cc

@@ -15,7 +15,9 @@ PartialSerializer::PartialSerializer(
     v8::SerializeEmbedderFieldsCallback callback)
     : Serializer(isolate),
       startup_serializer_(startup_serializer),
-      serialize_embedder_fields_(callback) {
+      serialize_embedder_fields_(callback),
+      rehashable_global_dictionary_(nullptr),
+      can_be_rehashed_(true) {
   InitializeCodeAddressMap();
 }
 
@@ -24,7 +26,7 @@ PartialSerializer::~PartialSerializer() {
 }
 
 void PartialSerializer::Serialize(Object** o, bool include_global_proxy) {
-  if ((*o)->IsContext()) {
+  if ((*o)->IsNativeContext()) {
     Context* context = Context::cast(*o);
     reference_map()->AddAttachedReference(context->global_proxy());
     // The bootstrap snapshot has a code-stub context. When serializing the
@@ -32,14 +34,18 @@ void PartialSerializer::Serialize(Object** o, bool include_global_proxy) {
     // and it's next context pointer may point to the code-stub context.  Clear
     // it before serializing, it will get re-added to the context list
     // explicitly when it's loaded.
-    if (context->IsNativeContext()) {
-      context->set(Context::NEXT_CONTEXT_LINK,
-                   isolate_->heap()->undefined_value());
-      DCHECK(!context->global_object()->IsUndefined(context->GetIsolate()));
-      // Reset math random cache to get fresh random numbers.
-      context->set_math_random_index(Smi::kZero);
-      context->set_math_random_cache(isolate_->heap()->undefined_value());
-    }
+    context->set(Context::NEXT_CONTEXT_LINK,
+                 isolate_->heap()->undefined_value());
+    DCHECK(!context->global_object()->IsUndefined(context->GetIsolate()));
+    // Reset math random cache to get fresh random numbers.
+    context->set_math_random_index(Smi::kZero);
+    context->set_math_random_cache(isolate_->heap()->undefined_value());
+    DCHECK_NULL(rehashable_global_dictionary_);
+    rehashable_global_dictionary_ =
+        context->global_object()->global_dictionary();
+  } else {
+    // We only do rehashing for native contexts.
+    can_be_rehashed_ = false;
   }
   VisitPointer(o);
   SerializeDeferredObjects();
@@ -104,6 +110,8 @@ void PartialSerializer::SerializeObject(HeapObject* obj, HowToCode how_to_code,
     }
   }
 
+  if (obj->IsHashTable()) CheckRehashability(obj);
+
   // Object has not yet been serialized.  Serialize it here.
   ObjectSerializer serializer(this, obj, &sink_, how_to_code, where_to_point);
   serializer.Serialize();
@@ -152,5 +160,14 @@ void PartialSerializer::SerializeEmbedderFields() {
   sink_.Put(kSynchronize, "Finished with embedder fields data");
 }
 
+void PartialSerializer::CheckRehashability(HeapObject* table) {
+  DCHECK(table->IsHashTable());
+  if (!can_be_rehashed_) return;
+  // We can only correctly rehash if the global dictionary is the only hash
+  // table that we deserialize.
+  if (table == rehashable_global_dictionary_) return;
+  can_be_rehashed_ = false;
+}
+
 }  // namespace internal
 }  // namespace v8

deps/v8/src/snapshot/partial-serializer.h

@@ -23,6 +23,8 @@ class PartialSerializer : public Serializer {
   // Serialize the objects reachable from a single object pointer.
   void Serialize(Object** o, bool include_global_proxy);
 
+  bool can_be_rehashed() const { return can_be_rehashed_; }
+
  private:
   void SerializeObject(HeapObject* o, HowToCode how_to_code,
                        WhereToPoint where_to_point, int skip) override;
@@ -31,9 +33,15 @@ class PartialSerializer : public Serializer {
 
   void SerializeEmbedderFields();
 
+  void CheckRehashability(HeapObject* table);
+
   StartupSerializer* startup_serializer_;
   List<JSObject*> embedder_field_holders_;
   v8::SerializeEmbedderFieldsCallback serialize_embedder_fields_;
+  GlobalDictionary* rehashable_global_dictionary_;
+  // Indicates whether we only serialized hash tables that we can rehash.
+  // TODO(yangguo): generalize rehashing, and remove this flag.
+  bool can_be_rehashed_;
   DISALLOW_COPY_AND_ASSIGN(PartialSerializer);
 };
 

deps/v8/src/snapshot/snapshot-common.cc

@@ -41,6 +41,7 @@ bool Snapshot::Initialize(Isolate* isolate) {
   Vector<const byte> startup_data = ExtractStartupData(blob);
   SnapshotData snapshot_data(startup_data);
   Deserializer deserializer(&snapshot_data);
+  deserializer.SetRehashability(ExtractRehashability(blob));
   bool success = isolate->Init(&deserializer);
   if (FLAG_profile_deserialization) {
     double ms = timer.Elapsed().InMillisecondsF();
@@ -62,6 +63,7 @@ MaybeHandle<Context> Snapshot::NewContextFromSnapshot(
       ExtractContextData(blob, static_cast<int>(context_index));
   SnapshotData snapshot_data(context_data);
   Deserializer deserializer(&snapshot_data);
+  deserializer.SetRehashability(ExtractRehashability(blob));
 
   MaybeHandle<Object> maybe_context = deserializer.DeserializePartial(
       isolate, global_proxy, embedder_fields_deserializer);
@@ -98,7 +100,7 @@ void ProfileDeserialization(const SnapshotData* startup_snapshot,
 
 v8::StartupData Snapshot::CreateSnapshotBlob(
     const SnapshotData* startup_snapshot,
-    const List<SnapshotData*>* context_snapshots) {
+    const List<SnapshotData*>* context_snapshots, bool can_be_rehashed) {
   int num_contexts = context_snapshots->length();
   int startup_snapshot_offset = StartupSnapshotOffset(num_contexts);
   int total_length = startup_snapshot_offset;
@@ -111,6 +113,8 @@ v8::StartupData Snapshot::CreateSnapshotBlob(
 
   char* data = new char[total_length];
   memcpy(data + kNumberOfContextsOffset, &num_contexts, kInt32Size);
+  int rehashability = can_be_rehashed ? 1 : 0;
+  memcpy(data + kRehashabilityOffset, &rehashability, kInt32Size);
   int payload_offset = StartupSnapshotOffset(num_contexts);
   int payload_length = startup_snapshot->RawData().length();
   memcpy(data + payload_offset, startup_snapshot->RawData().start(),
@@ -143,6 +147,13 @@ int Snapshot::ExtractNumContexts(const v8::StartupData* data) {
   return num_contexts;
 }
 
+bool Snapshot::ExtractRehashability(const v8::StartupData* data) {
+  CHECK_LT(kRehashabilityOffset, data->raw_size);
+  int rehashability;
+  memcpy(&rehashability, data->data + kRehashabilityOffset, kInt32Size);
+  return rehashability != 0;
+}
+
 Vector<const byte> Snapshot::ExtractStartupData(const v8::StartupData* data) {
   int num_contexts = ExtractNumContexts(data);
   int startup_offset = StartupSnapshotOffset(num_contexts);

deps/v8/src/snapshot/snapshot.h

@@ -73,7 +73,7 @@ class Snapshot : public AllStatic {
 
   static v8::StartupData CreateSnapshotBlob(
       const SnapshotData* startup_snapshot,
-      const List<SnapshotData*>* context_snapshots);
+      const List<SnapshotData*>* context_snapshots, bool can_be_rehashed);
 
 #ifdef DEBUG
   static bool SnapshotIsValid(v8::StartupData* snapshot_blob);
@@ -81,14 +81,16 @@ class Snapshot : public AllStatic {
 
  private:
   static int ExtractNumContexts(const v8::StartupData* data);
+  static bool ExtractRehashability(const v8::StartupData* data);
   static Vector<const byte> ExtractStartupData(const v8::StartupData* data);
   static Vector<const byte> ExtractContextData(const v8::StartupData* data,
                                                int index);
 
   // Snapshot blob layout:
   // [0] number of contexts N
-  // [1] offset to context 0
-  // [2] offset to context 1
+  // [1] rehashability
+  // [2] offset to context 0
+  // [3] offset to context 1
   // ...
   // ... offset to context N - 1
   // ... startup snapshot data
@@ -96,8 +98,10 @@ class Snapshot : public AllStatic {
   // ... context 1 snapshot data
 
   static const int kNumberOfContextsOffset = 0;
+  // TODO(yangguo): generalize rehashing, and remove this flag.
+  static const int kRehashabilityOffset = kNumberOfContextsOffset + kInt32Size;
   static const int kFirstContextOffsetOffset =
-      kNumberOfContextsOffset + kInt32Size;
+      kRehashabilityOffset + kInt32Size;
 
   static int StartupSnapshotOffset(int num_contexts) {
     return kFirstContextOffsetOffset + num_contexts * kInt32Size;

deps/v8/src/snapshot/startup-serializer.cc

@@ -16,7 +16,8 @@ StartupSerializer::StartupSerializer(
     : Serializer(isolate),
       clear_function_code_(function_code_handling ==
                            v8::SnapshotCreator::FunctionCodeHandling::kClear),
-      serializing_builtins_(false) {
+      serializing_builtins_(false),
+      can_be_rehashed_(true) {
   InitializeCodeAddressMap();
 }
 
@@ -75,6 +76,8 @@ void StartupSerializer::SerializeObject(HeapObject* obj, HowToCode how_to_code,
     accessor_infos_.Add(info);
   }
 
+  if (obj->IsHashTable()) CheckRehashability(obj);
+
   // Object has not yet been serialized.  Serialize it here.
   ObjectSerializer object_serializer(this, obj, &sink_, how_to_code,
                                      where_to_point);
@@ -184,5 +187,17 @@ bool StartupSerializer::RootShouldBeSkipped(int root_index) {
          serializing_immortal_immovables_roots_;
 }
 
+void StartupSerializer::CheckRehashability(HeapObject* table) {
+  DCHECK(table->IsHashTable());
+  if (!can_be_rehashed_) return;
+  // We can only correctly rehash if the four hash tables below are the only
+  // ones that we deserialize.
+  if (table == isolate_->heap()->empty_slow_element_dictionary()) return;
+  if (table == isolate_->heap()->empty_properties_dictionary()) return;
+  if (table == isolate_->heap()->weak_object_to_code_table()) return;
+  if (table == isolate_->heap()->string_table()) return;
+  can_be_rehashed_ = false;
+}
+
 }  // namespace internal
 }  // namespace v8

deps/v8/src/snapshot/startup-serializer.h

@@ -29,6 +29,8 @@ class StartupSerializer : public Serializer {
 
   int PartialSnapshotCacheIndex(HeapObject* o);
 
+  bool can_be_rehashed() const { return can_be_rehashed_; }
+
  private:
   class PartialCacheIndexMap {
    public:
@@ -68,12 +70,18 @@ class StartupSerializer : public Serializer {
   // roots. In the second pass, we serialize the rest.
   bool RootShouldBeSkipped(int root_index);
 
+  void CheckRehashability(HeapObject* hashtable);
+
   bool clear_function_code_;
   bool serializing_builtins_;
   bool serializing_immortal_immovables_roots_;
   std::bitset<Heap::kStrongRootListLength> root_has_been_serialized_;
   PartialCacheIndexMap partial_cache_index_map_;
   List<AccessorInfo*> accessor_infos_;
+  // Indicates whether we only serialized hash tables that we can rehash.
+  // TODO(yangguo): generalize rehashing, and remove this flag.
+  bool can_be_rehashed_;
+
   DISALLOW_COPY_AND_ASSIGN(StartupSerializer);
 };
 

deps/v8/src/transitions-inl.h

@@ -106,7 +106,6 @@ int TransitionArray::SearchName(Name* name, int* out_insertion_index) {
 }
 
 
-#ifdef DEBUG
 bool TransitionArray::IsSpecialTransition(Name* name) {
   if (!name->IsSymbol()) return false;
   Heap* heap = name->GetHeap();
@@ -115,7 +114,6 @@ bool TransitionArray::IsSpecialTransition(Name* name) {
          name == heap->elements_transition_symbol() ||
          name == heap->strict_function_transition_symbol();
 }
-#endif
 
 
 int TransitionArray::CompareKeys(Name* key1, uint32_t hash1, PropertyKind kind1,

deps/v8/src/transitions.cc

@@ -551,5 +551,47 @@ int TransitionArray::Search(PropertyKind kind, Name* name,
   if (transition == kNotFound) return kNotFound;
   return SearchDetails(transition, kind, attributes, out_insertion_index);
 }
+
+void TransitionArray::Sort() {
+  DisallowHeapAllocation no_gc;
+  // In-place insertion sort.
+  int length = number_of_transitions();
+  for (int i = 1; i < length; i++) {
+    Name* key = GetKey(i);
+    Map* target = GetTarget(i);
+    PropertyKind kind = kData;
+    PropertyAttributes attributes = NONE;
+    if (!IsSpecialTransition(key)) {
+      PropertyDetails details = GetTargetDetails(key, target);
+      kind = details.kind();
+      attributes = details.attributes();
+    }
+    int j;
+    for (j = i - 1; j >= 0; j--) {
+      Name* temp_key = GetKey(j);
+      Map* temp_target = GetTarget(j);
+      PropertyKind temp_kind = kData;
+      PropertyAttributes temp_attributes = NONE;
+      if (!IsSpecialTransition(temp_key)) {
+        PropertyDetails details = GetTargetDetails(temp_key, temp_target);
+        temp_kind = details.kind();
+        temp_attributes = details.attributes();
+      }
+      int cmp =
+          CompareKeys(temp_key, temp_key->Hash(), temp_kind, temp_attributes,
+                      key, key->Hash(), kind, attributes);
+      if (cmp > 0) {
+        SetKey(j + 1, temp_key);
+        SetTarget(j + 1, temp_target);
+      } else {
+        break;
+      }
+    }
+    SetKey(j + 1, key);
+    SetTarget(j + 1, target);
+  }
+  DCHECK(IsSortedNoDuplicates());
+}
+
 }  // namespace internal
 }  // namespace v8

deps/v8/src/transitions.h

@@ -190,15 +190,17 @@ class TransitionArray: public FixedArray {
   void TransitionArrayVerify();
 #endif
 
+  void Sort();
+
 #ifdef DEBUG
   bool IsSortedNoDuplicates(int valid_entries = -1);
   static bool IsSortedNoDuplicates(Map* map);
   static bool IsConsistentWithBackPointers(Map* map);
+#endif
 
   // Returns true for a non-property transitions like elements kind, observed
   // or frozen transitions.
   static inline bool IsSpecialTransition(Name* name);
-#endif
 
   // Constant for denoting key was not found.
   static const int kNotFound = -1;

deps/v8/test/cctest/heap/test-heap.cc

@@ -6609,5 +6609,26 @@ HEAP_TEST(Regress5831) {
   CHECK(chunk->NeverEvacuate());
 }
 
+UNINITIALIZED_TEST(ReinitializeStringHashSeed) {
+  // Enable rehashing and create an isolate and context.
+  i::FLAG_rehash_snapshot = true;
+  for (int i = 1; i < 3; i++) {
+    i::FLAG_hash_seed = 1337 * i;
+    v8::Isolate::CreateParams create_params;
+    create_params.array_buffer_allocator = CcTest::array_buffer_allocator();
+    v8::Isolate* isolate = v8::Isolate::New(create_params);
+    {
+      v8::Isolate::Scope isolate_scope(isolate);
+      CHECK_EQ(1337 * i,
+               reinterpret_cast<i::Isolate*>(isolate)->heap()->HashSeed());
+      v8::HandleScope handle_scope(isolate);
+      v8::Local<v8::Context> context = v8::Context::New(isolate);
+      CHECK(!context.IsEmpty());
+      v8::Context::Scope context_scope(context);
+    }
+    isolate->Dispose();
+  }
+}
+
 }  // namespace internal
 }  // namespace v8

deps/v8/test/cctest/test-serialize.cc

@@ -2547,6 +2547,51 @@ TEST(SnapshotCreatorIncludeGlobalProxy) {
   delete[] blob.data;
 }
 
+UNINITIALIZED_TEST(ReinitializeStringHashSeedNotRehashable) {
+  DisableAlwaysOpt();
+  i::FLAG_rehash_snapshot = true;
+  i::FLAG_hash_seed = 42;
+  i::FLAG_allow_natives_syntax = true;
+  v8::StartupData blob;
+  {
+    v8::SnapshotCreator creator;
+    v8::Isolate* isolate = creator.GetIsolate();
+    {
+      v8::HandleScope handle_scope(isolate);
+      v8::Local<v8::Context> context = v8::Context::New(isolate);
+      v8::Context::Scope context_scope(context);
+      // Create dictionary mode object.
+      CompileRun(
+          "var a = {};"
+          "a.b = 1;"
+          "a.c = 2;"
+          "delete a.b;");
+      ExpectInt32("a.c", 2);
+      creator.SetDefaultContext(context);
+    }
+    blob =
+        creator.CreateBlob(v8::SnapshotCreator::FunctionCodeHandling::kClear);
+  }
+
+  i::FLAG_hash_seed = 1337;
+  v8::Isolate::CreateParams create_params;
+  create_params.array_buffer_allocator = CcTest::array_buffer_allocator();
+  create_params.snapshot_blob = &blob;
+  v8::Isolate* isolate = v8::Isolate::New(create_params);
+  {
+    // Check that no rehashing has been performed.
+    CHECK_EQ(42, reinterpret_cast<i::Isolate*>(isolate)->heap()->HashSeed());
+    v8::Isolate::Scope isolate_scope(isolate);
+    v8::HandleScope handle_scope(isolate);
+    v8::Local<v8::Context> context = v8::Context::New(isolate);
+    CHECK(!context.IsEmpty());
+    v8::Context::Scope context_scope(context);
+    ExpectInt32("a.c", 2);
+  }
+  isolate->Dispose();
+  delete[] blob.data;
+}
+
 TEST(SerializationMemoryStats) {
   FLAG_profile_deserialization = true;
   FLAG_always_opt = false;

deps/v8/test/mjsunit/regress/regress-5902.js

@@ -58,6 +58,5 @@ assertEquals(
       'Error.prototype',
       'EvalError.prototype', 'RangeError.prototype', 'ReferenceError.prototype',
       'SyntaxError.prototype', 'TypeError.prototype', 'URIError.prototype',
-      'Map', 'Map.prototype.constructor', 'Set', 'Set.prototype.constructor'
     ],
     log);