[snapshot] Continue splitting up Deserializer

Another pure refactoring CL. This extracts methods used only by Deserializer
subclasses.

Bug: v8:6624
Change-Id: Ib4dd7cdc591dff217e282e68a490c8c7129b9c96
Reviewed-on: https://chromium-review.googlesource.com/602188
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47211}

src/snapshot/code-serializer.cc

@@ -194,7 +194,7 @@ MaybeHandle<SharedFunctionInfo> CodeSerializer::Deserialize(
     return MaybeHandle<SharedFunctionInfo>();
   }
 
-  ObjectDeserializer deserializer(&scd, false);
+  ObjectDeserializer deserializer(&scd);
   deserializer.AddAttachedObject(source);
   Vector<const uint32_t> code_stub_keys = scd.CodeStubKeys();
   for (int i = 0; i < code_stub_keys.length(); i++) {
@@ -265,7 +265,7 @@ MaybeHandle<FixedArray> WasmCompiledModuleSerializer::DeserializeWasmModule(
     return nothing;
   }
 
-  ObjectDeserializer deserializer(&scd, true);
+  ObjectDeserializer deserializer(&scd);
   deserializer.AddAttachedObject(isolate->native_context());
 
   MaybeHandle<String> maybe_wire_bytes_as_string =

src/snapshot/deserializer.cc

@@ -33,25 +33,9 @@ void Deserializer::DecodeReservation(
   for (int i = 0; i < kNumberOfPreallocatedSpaces; i++) current_chunk_[i] = 0;
 }
 
-void Deserializer::FlushICacheForNewIsolate() {
-  DCHECK(!deserializing_user_code_);
-  // The entire isolate is newly deserialized. Simply flush all code pages.
-  for (Page* p : *isolate_->heap()->code_space()) {
-    Assembler::FlushICache(isolate_, p->area_start(),
-                           p->area_end() - p->area_start());
-  }
-}
-
-void Deserializer::FlushICacheForNewCodeObjectsAndRecordEmbeddedObjects() {
-  DCHECK(deserializing_user_code_);
-  for (Code* code : new_code_objects_) {
-    // Record all references to embedded objects in the new code object.
-    isolate_->heap()->RecordWritesIntoCode(code);
-
-    if (FLAG_serialize_age_code) code->PreAge(isolate_);
-    Assembler::FlushICache(isolate_, code->instruction_start(),
-                           code->instruction_size());
-  }
+void Deserializer::RegisterDeserializedObjectsForBlackAllocation() {
+  isolate_->heap()->RegisterDeserializedObjectsForBlackAllocation(
+      reservations_, &deserialized_large_objects_, &allocated_maps_);
 }
 
 bool Deserializer::ReserveSpace() {
@@ -83,126 +67,6 @@ void Deserializer::Initialize(Isolate* isolate) {
            SerializedData::GetExtraReferences(external_reference_table_));
 }
 
-void Deserializer::Deserialize(Isolate* isolate) {
-  Initialize(isolate);
-  if (!ReserveSpace()) V8::FatalProcessOutOfMemory("deserializing context");
-  // No active threads.
-  DCHECK_NULL(isolate_->thread_manager()->FirstThreadStateInUse());
-  // No active handles.
-  DCHECK(isolate_->handle_scope_implementer()->blocks()->is_empty());
-  // Partial snapshot cache is not yet populated.
-  DCHECK(isolate_->partial_snapshot_cache()->is_empty());
-  // Builtins are not yet created.
-  DCHECK(!isolate_->builtins()->is_initialized());
-
-  {
-    DisallowHeapAllocation no_gc;
-    isolate_->heap()->IterateStrongRoots(this, VISIT_ONLY_STRONG_ROOT_LIST);
-    isolate_->heap()->IterateSmiRoots(this);
-    isolate_->heap()->IterateStrongRoots(this, VISIT_ONLY_STRONG);
-    isolate_->heap()->RepairFreeListsAfterDeserialization();
-    isolate_->heap()->IterateWeakRoots(this, VISIT_ALL);
-    DeserializeDeferredObjects();
-    FlushICacheForNewIsolate();
-    RestoreExternalReferenceRedirectors(&accessor_infos_);
-  }
-
-  isolate_->heap()->set_native_contexts_list(
-      isolate_->heap()->undefined_value());
-  // The allocation site list is build during root iteration, but if no sites
-  // were encountered then it needs to be initialized to undefined.
-  if (isolate_->heap()->allocation_sites_list() == Smi::kZero) {
-    isolate_->heap()->set_allocation_sites_list(
-        isolate_->heap()->undefined_value());
-  }
-
-  // Issue code events for newly deserialized code objects.
-  LOG_CODE_EVENT(isolate_, LogCodeObjects());
-  LOG_CODE_EVENT(isolate_, LogBytecodeHandlers());
-  LOG_CODE_EVENT(isolate_, LogCompiledFunctions());
-
-  isolate_->builtins()->MarkInitialized();
-
-  // If needed, print the dissassembly of deserialized code objects.
-  // Needs to be called after the builtins are marked as initialized, in order
-  // to display the builtin names.
-  PrintDisassembledCodeObjects();
-
-  if (FLAG_rehash_snapshot && can_rehash_) Rehash();
-}
-
-MaybeHandle<Object> Deserializer::DeserializePartial(
-    Isolate* isolate, Handle<JSGlobalProxy> global_proxy,
-    v8::DeserializeEmbedderFieldsCallback embedder_fields_deserializer) {
-  Initialize(isolate);
-  if (!ReserveSpace()) {
-    V8::FatalProcessOutOfMemory("deserialize context");
-    return MaybeHandle<Object>();
-  }
-
-  AddAttachedObject(global_proxy);
-
-  DisallowHeapAllocation no_gc;
-  // Keep track of the code space start and end pointers in case new
-  // code objects were unserialized
-  OldSpace* code_space = isolate_->heap()->code_space();
-  Address start_address = code_space->top();
-  Object* root;
-  VisitRootPointer(Root::kPartialSnapshotCache, &root);
-  DeserializeDeferredObjects();
-  DeserializeEmbedderFields(embedder_fields_deserializer);
-
-  isolate->heap()->RegisterDeserializedObjectsForBlackAllocation(
-      reservations_, &deserialized_large_objects_, &allocated_maps_);
-
-  // There's no code deserialized here. If this assert fires then that's
-  // 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);
-}
-
-MaybeHandle<HeapObject> Deserializer::DeserializeObject(Isolate* isolate) {
-  Initialize(isolate);
-  if (!ReserveSpace()) {
-    return MaybeHandle<HeapObject>();
-  } else {
-    deserializing_user_code_ = true;
-    HandleScope scope(isolate);
-    Handle<HeapObject> result;
-    {
-      DisallowHeapAllocation no_gc;
-      Object* root;
-      VisitRootPointer(Root::kPartialSnapshotCache, &root);
-      DeserializeDeferredObjects();
-      FlushICacheForNewCodeObjectsAndRecordEmbeddedObjects();
-      result = Handle<HeapObject>(HeapObject::cast(root));
-      isolate->heap()->RegisterDeserializedObjectsForBlackAllocation(
-          reservations_, &deserialized_large_objects_, &allocated_maps_);
-    }
-    CommitPostProcessedObjects(isolate);
-    return scope.CloseAndEscape(result);
-  }
-}
-
-void Deserializer::Rehash() {
-  DCHECK(can_rehash_);
-  isolate_->heap()->InitializeHashSeed();
-  isolate_->heap()->string_table()->Rehash();
-  isolate_->heap()->weak_object_to_code_table()->Rehash();
-  SortMapDescriptors();
-}
-
-void Deserializer::RehashContext(Context* context) {
-  DCHECK(can_rehash_);
-  for (const auto& array : transition_arrays_) array->Sort();
-  context->global_object()->global_dictionary()->Rehash();
-  SortMapDescriptors();
-}
-
 void Deserializer::SortMapDescriptors() {
   for (const auto& address : allocated_maps_) {
     Map* map = Map::cast(HeapObject::FromAddress(address));
@@ -266,81 +130,28 @@ void Deserializer::DeserializeDeferredObjects() {
   }
 }
 
-void Deserializer::DeserializeEmbedderFields(
-    v8::DeserializeEmbedderFieldsCallback embedder_fields_deserializer) {
-  if (!source_.HasMore() || source_.Get() != kEmbedderFieldsData) return;
-  DisallowHeapAllocation no_gc;
-  DisallowJavascriptExecution no_js(isolate_);
-  DisallowCompilation no_compile(isolate_);
-  DCHECK_NOT_NULL(embedder_fields_deserializer.callback);
-  for (int code = source_.Get(); code != kSynchronize; code = source_.Get()) {
-    HandleScope scope(isolate_);
-    int space = code & kSpaceMask;
-    DCHECK(space <= kNumberOfSpaces);
-    DCHECK(code - space == kNewObject);
-    Handle<JSObject> obj(JSObject::cast(GetBackReferencedObject(space)),
-                         isolate_);
-    int index = source_.GetInt();
-    int size = source_.GetInt();
-    byte* data = new byte[size];
-    source_.CopyRaw(data, size);
-    embedder_fields_deserializer.callback(v8::Utils::ToLocal(obj), index,
-                                          {reinterpret_cast<char*>(data), size},
-                                          embedder_fields_deserializer.data);
-    delete[] data;
-  }
+StringTableInsertionKey::StringTableInsertionKey(String* string)
+    : StringTableKey(ComputeHashField(string)), string_(string) {
+  DCHECK(string->IsInternalizedString());
 }
 
-void Deserializer::PrintDisassembledCodeObjects() {
-#ifdef ENABLE_DISASSEMBLER
-  if (FLAG_print_builtin_code) {
-    Heap* heap = isolate_->heap();
-    HeapIterator iterator(heap);
-    DisallowHeapAllocation no_gc;
-
-    CodeTracer::Scope tracing_scope(isolate_->GetCodeTracer());
-    OFStream os(tracing_scope.file());
-
-    for (HeapObject* obj = iterator.next(); obj != NULL;
-         obj = iterator.next()) {
-      if (obj->IsCode()) {
-        Code::cast(obj)->Disassemble(nullptr, os);
-      }
-    }
-  }
-#endif
+bool StringTableInsertionKey::IsMatch(Object* string) {
+  // We know that all entries in a hash table had their hash keys created.
+  // Use that knowledge to have fast failure.
+  if (Hash() != String::cast(string)->Hash()) return false;
+  // We want to compare the content of two internalized strings here.
+  return string_->SlowEquals(String::cast(string));
 }
 
-// Used to insert a deserialized internalized string into the string table.
-class StringTableInsertionKey : public StringTableKey {
- public:
-  explicit StringTableInsertionKey(String* string)
-      : StringTableKey(ComputeHashField(string)), string_(string) {
-    DCHECK(string->IsInternalizedString());
-  }
-
-  bool IsMatch(Object* string) override {
-    // We know that all entries in a hash table had their hash keys created.
-    // Use that knowledge to have fast failure.
-    if (Hash() != String::cast(string)->Hash()) return false;
-    // We want to compare the content of two internalized strings here.
-    return string_->SlowEquals(String::cast(string));
-  }
-
-  MUST_USE_RESULT Handle<String> AsHandle(Isolate* isolate) override {
-    return handle(string_, isolate);
-  }
-
- private:
-  uint32_t ComputeHashField(String* string) {
-    // Make sure hash_field() is computed.
-    string->Hash();
-    return string->hash_field();
-  }
+Handle<String> StringTableInsertionKey::AsHandle(Isolate* isolate) {
+  return handle(string_, isolate);
+}
 
-  String* string_;
-  DisallowHeapAllocation no_gc;
-};
+uint32_t StringTableInsertionKey::ComputeHashField(String* string) {
+  // Make sure hash_field() is computed.
+  string->Hash();
+  return string->hash_field();
+}
 
 HeapObject* Deserializer::PostProcessNewObject(HeapObject* obj, int space) {
   if (deserializing_user_code()) {
@@ -415,26 +226,6 @@ HeapObject* Deserializer::PostProcessNewObject(HeapObject* obj, int space) {
   return obj;
 }
 
-void Deserializer::CommitPostProcessedObjects(Isolate* isolate) {
-  StringTable::EnsureCapacityForDeserialization(
-      isolate, new_internalized_strings_.length());
-  for (Handle<String> string : new_internalized_strings_) {
-    StringTableInsertionKey key(*string);
-    DCHECK_NULL(StringTable::LookupKeyIfExists(isolate, &key));
-    StringTable::LookupKey(isolate, &key);
-  }
-
-  Heap* heap = isolate->heap();
-  Factory* factory = isolate->factory();
-  for (Handle<Script> script : new_scripts_) {
-    // Assign a new script id to avoid collision.
-    script->set_id(isolate_->heap()->NextScriptId());
-    // Add script to list.
-    Handle<Object> list = WeakFixedArray::Add(factory->script_list(), script);
-    heap->SetRootScriptList(*list);
-  }
-}
-
 HeapObject* Deserializer::GetBackReferencedObject(int space) {
   HeapObject* obj;
   SerializerReference back_reference =

src/snapshot/deserializer.h

@@ -39,9 +39,6 @@ class Deserializer : public SerializerDeserializer {
   void SetRehashability(bool v) { can_rehash_ = v; }
 
  protected:
-  // This section is temporary while the deserializer is being refactored into
-  // {object,partial,object}-deserializer.h.
-
   // Create a deserializer from a snapshot byte source.
   template <class Data>
   Deserializer(Data* data, bool deserializing_user_code)
@@ -58,30 +55,37 @@ class Deserializer : public SerializerDeserializer {
     DecodeReservation(data->Reservations());
   }
 
-  // Deserialize the snapshot into an empty heap.
-  void Deserialize(Isolate* isolate);
+  void Initialize(Isolate* isolate);
+  bool ReserveSpace();
+  void DeserializeDeferredObjects();
+  void RegisterDeserializedObjectsForBlackAllocation();
 
-  // Deserialize a single object and the objects reachable from it.
-  MaybeHandle<Object> DeserializePartial(
-      Isolate* isolate, Handle<JSGlobalProxy> global_proxy,
-      v8::DeserializeEmbedderFieldsCallback embedder_fields_deserializer);
+  // This returns the address of an object that has been described in the
+  // snapshot by chunk index and offset.
+  HeapObject* GetBackReferencedObject(int space);
 
-  // Deserialize an object graph. Fail gracefully.
-  MaybeHandle<HeapObject> DeserializeObject(Isolate* isolate);
+  // Sort descriptors of deserialized maps using new string hashes.
+  void SortMapDescriptors();
+
+  Isolate* isolate() const { return isolate_; }
+  SnapshotByteSource* source() { return &source_; }
+  List<Code*>& new_code_objects() { return new_code_objects_; }
+  List<AccessorInfo*>* accessor_infos() { return &accessor_infos_; }
+  List<Handle<String>>& new_internalized_strings() {
+    return new_internalized_strings_;
+  }
+  List<Handle<Script>>& new_scripts() { return new_scripts_; }
+  List<TransitionArray*>& transition_arrays() { return transition_arrays_; }
+  bool deserializing_user_code() const { return deserializing_user_code_; }
+  bool can_rehash() const { return can_rehash_; }
 
  private:
   void VisitRootPointers(Root root, Object** start, Object** end) override;
 
   void Synchronize(VisitorSynchronization::SyncTag tag) override;
 
-  void Initialize(Isolate* isolate);
-
-  bool deserializing_user_code() { return deserializing_user_code_; }
-
   void DecodeReservation(Vector<const SerializedData::Reservation> res);
 
-  bool ReserveSpace();
-
   void UnalignedCopy(Object** dest, Object** src) {
     memcpy(dest, src, sizeof(*src));
   }
@@ -94,17 +98,6 @@ class Deserializer : public SerializerDeserializer {
     next_alignment_ = static_cast<AllocationAlignment>(alignment);
   }
 
-  void DeserializeDeferredObjects();
-  void DeserializeEmbedderFields(
-      v8::DeserializeEmbedderFieldsCallback embedder_fields_deserializer);
-
-  void FlushICacheForNewIsolate();
-  void FlushICacheForNewCodeObjectsAndRecordEmbeddedObjects();
-
-  void CommitPostProcessedObjects(Isolate* isolate);
-
-  void PrintDisassembledCodeObjects();
-
   // Fills in some heap data in an area from start to end (non-inclusive).  The
   // space id is used for the write barrier.  The object_address is the address
   // of the object we are writing into, or NULL if we are not writing into an
@@ -118,19 +111,6 @@ class Deserializer : public SerializerDeserializer {
   // Special handling for serialized code like hooking up internalized strings.
   HeapObject* PostProcessNewObject(HeapObject* obj, int space);
 
-  // This returns the address of an object that has been described in the
-  // 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_;
 
@@ -156,11 +136,11 @@ class Deserializer : public SerializerDeserializer {
   List<HeapObject*> deserialized_large_objects_;
   List<Code*> new_code_objects_;
   List<AccessorInfo*> accessor_infos_;
-  List<Handle<String> > new_internalized_strings_;
-  List<Handle<Script> > new_scripts_;
+  List<Handle<String>> new_internalized_strings_;
+  List<Handle<Script>> new_scripts_;
   List<TransitionArray*> transition_arrays_;
 
-  bool deserializing_user_code_;
+  const bool deserializing_user_code_;
 
   AllocationAlignment next_alignment_;
 
@@ -170,6 +150,22 @@ class Deserializer : public SerializerDeserializer {
   DISALLOW_COPY_AND_ASSIGN(Deserializer);
 };
 
+// Used to insert a deserialized internalized string into the string table.
+class StringTableInsertionKey : public StringTableKey {
+ public:
+  explicit StringTableInsertionKey(String* string);
+
+  bool IsMatch(Object* string) override;
+
+  MUST_USE_RESULT Handle<String> AsHandle(Isolate* isolate) override;
+
+ private:
+  uint32_t ComputeHashField(String* string);
+
+  String* string_;
+  DisallowHeapAllocation no_gc;
+};
+
 }  // namespace internal
 }  // namespace v8
 

src/snapshot/object-deserializer.cc

@@ -4,6 +4,66 @@
 
 #include "src/snapshot/object-deserializer.h"
 
+#include "src/assembler-inl.h"
+#include "src/isolate.h"
+#include "src/objects.h"
+#include "src/snapshot/code-serializer.h"
+
 namespace v8 {
-namespace internal {}  // namespace internal
+namespace internal {
+
+MaybeHandle<HeapObject> ObjectDeserializer::Deserialize(Isolate* isolate) {
+  Initialize(isolate);
+  if (!ReserveSpace()) return MaybeHandle<HeapObject>();
+
+  DCHECK(deserializing_user_code());
+  HandleScope scope(isolate);
+  Handle<HeapObject> result;
+  {
+    DisallowHeapAllocation no_gc;
+    Object* root;
+    VisitRootPointer(Root::kPartialSnapshotCache, &root);
+    DeserializeDeferredObjects();
+    FlushICacheForNewCodeObjectsAndRecordEmbeddedObjects();
+    result = Handle<HeapObject>(HeapObject::cast(root));
+    RegisterDeserializedObjectsForBlackAllocation();
+  }
+  CommitPostProcessedObjects();
+  return scope.CloseAndEscape(result);
+}
+
+void ObjectDeserializer::
+    FlushICacheForNewCodeObjectsAndRecordEmbeddedObjects() {
+  DCHECK(deserializing_user_code());
+  for (Code* code : new_code_objects()) {
+    // Record all references to embedded objects in the new code object.
+    isolate()->heap()->RecordWritesIntoCode(code);
+
+    if (FLAG_serialize_age_code) code->PreAge(isolate());
+    Assembler::FlushICache(isolate(), code->instruction_start(),
+                           code->instruction_size());
+  }
+}
+
+void ObjectDeserializer::CommitPostProcessedObjects() {
+  StringTable::EnsureCapacityForDeserialization(
+      isolate(), new_internalized_strings().length());
+  for (Handle<String> string : new_internalized_strings()) {
+    StringTableInsertionKey key(*string);
+    DCHECK_NULL(StringTable::LookupKeyIfExists(isolate(), &key));
+    StringTable::LookupKey(isolate(), &key);
+  }
+
+  Heap* heap = isolate()->heap();
+  Factory* factory = isolate()->factory();
+  for (Handle<Script> script : new_scripts()) {
+    // Assign a new script id to avoid collision.
+    script->set_id(isolate()->heap()->NextScriptId());
+    // Add script to list.
+    Handle<Object> list = WeakFixedArray::Add(factory->script_list(), script);
+    heap->SetRootScriptList(*list);
+  }
+}
+
+}  // namespace internal
 }  // namespace v8

src/snapshot/object-deserializer.h

@@ -10,19 +10,22 @@
 namespace v8 {
 namespace internal {
 
+class SerializedCodeData;
+
 // Deserializes the object graph rooted at a given object.
 // Currently, the ObjectDeserializer is only used to deserialize code objects
 // and compiled wasm modules.
-class ObjectDeserializer : public Deserializer {
+class ObjectDeserializer final : public Deserializer {
  public:
-  template <class Data>
-  ObjectDeserializer(Data* data, bool deserializing_user_code)
-      : Deserializer(data, deserializing_user_code) {}
+  explicit ObjectDeserializer(const SerializedCodeData* data)
+      : Deserializer(data, true) {}
 
   // Deserialize an object graph. Fail gracefully.
-  MaybeHandle<HeapObject> Deserialize(Isolate* isolate) {
-    return DeserializeObject(isolate);
-  }
+  MaybeHandle<HeapObject> Deserialize(Isolate* isolate);
+
+ private:
+  void FlushICacheForNewCodeObjectsAndRecordEmbeddedObjects();
+  void CommitPostProcessedObjects();
 };
 
 }  // namespace internal

src/snapshot/partial-deserializer.cc

@@ -4,6 +4,75 @@
 
 #include "src/snapshot/partial-deserializer.h"
 
+#include "src/heap/heap-inl.h"
+#include "src/snapshot/snapshot.h"
+
 namespace v8 {
-namespace internal {}  // namespace internal
+namespace internal {
+
+MaybeHandle<Object> PartialDeserializer::Deserialize(
+    Isolate* isolate, Handle<JSGlobalProxy> global_proxy,
+    v8::DeserializeEmbedderFieldsCallback embedder_fields_deserializer) {
+  Initialize(isolate);
+  if (!ReserveSpace()) V8::FatalProcessOutOfMemory("PartialDeserializer");
+
+  AddAttachedObject(global_proxy);
+
+  DisallowHeapAllocation no_gc;
+  // Keep track of the code space start and end pointers in case new
+  // code objects were unserialized
+  OldSpace* code_space = isolate->heap()->code_space();
+  Address start_address = code_space->top();
+  Object* root;
+  VisitRootPointer(Root::kPartialSnapshotCache, &root);
+  DeserializeDeferredObjects();
+  DeserializeEmbedderFields(embedder_fields_deserializer);
+
+  RegisterDeserializedObjectsForBlackAllocation();
+
+  // There's no code deserialized here. If this assert fires then that's
+  // 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);
+}
+
+void PartialDeserializer::DeserializeEmbedderFields(
+    v8::DeserializeEmbedderFieldsCallback embedder_fields_deserializer) {
+  if (!source()->HasMore() || source()->Get() != kEmbedderFieldsData) return;
+  DisallowHeapAllocation no_gc;
+  DisallowJavascriptExecution no_js(isolate());
+  DisallowCompilation no_compile(isolate());
+  DCHECK_NOT_NULL(embedder_fields_deserializer.callback);
+  for (int code = source()->Get(); code != kSynchronize;
+       code = source()->Get()) {
+    HandleScope scope(isolate());
+    int space = code & kSpaceMask;
+    DCHECK(space <= kNumberOfSpaces);
+    DCHECK(code - space == kNewObject);
+    Handle<JSObject> obj(JSObject::cast(GetBackReferencedObject(space)),
+                         isolate());
+    int index = source()->GetInt();
+    int size = source()->GetInt();
+    // TODO(yangguo,jgruber): Turn this into a reusable shared buffer.
+    byte* data = new byte[size];
+    source()->CopyRaw(data, size);
+    embedder_fields_deserializer.callback(v8::Utils::ToLocal(obj), index,
+                                          {reinterpret_cast<char*>(data), size},
+                                          embedder_fields_deserializer.data);
+    delete[] data;
+  }
+}
+
+void PartialDeserializer::RehashContext(Context* context) {
+  DCHECK(can_rehash());
+  for (const auto& array : transition_arrays()) array->Sort();
+  context->global_object()->global_dictionary()->Rehash();
+  SortMapDescriptors();
+}
+
+}  // namespace internal
 }  // namespace v8

src/snapshot/partial-deserializer.h

@@ -13,19 +13,23 @@ namespace internal {
 
 // Deserializes the context-dependent object graph rooted at a given object.
 // Currently, the only use-case is to deserialize native contexts.
-// The PartialDeserializer is not expected to any deserialize code objects.
-class PartialDeserializer : public Deserializer {
+// The PartialDeserializer is not expected to deserialize any code objects.
+class PartialDeserializer final : public Deserializer {
  public:
-  explicit PartialDeserializer(SnapshotData* data)
+  explicit PartialDeserializer(const SnapshotData* data)
       : Deserializer(data, false) {}
 
   // Deserialize a single object and the objects reachable from it.
   MaybeHandle<Object> Deserialize(
       Isolate* isolate, Handle<JSGlobalProxy> global_proxy,
-      v8::DeserializeEmbedderFieldsCallback embedder_fields_deserializer) {
-    return DeserializePartial(isolate, global_proxy,
-                              embedder_fields_deserializer);
-  }
+      v8::DeserializeEmbedderFieldsCallback embedder_fields_deserializer);
+
+ private:
+  void DeserializeEmbedderFields(
+      v8::DeserializeEmbedderFieldsCallback embedder_fields_deserializer);
+
+  // Rehash after deserializing a context.
+  void RehashContext(Context* context);
 };
 
 }  // namespace internal

src/snapshot/startup-deserializer.cc

@@ -4,6 +4,97 @@
 
 #include "src/snapshot/startup-deserializer.h"
 
+#include "src/assembler-inl.h"
+#include "src/heap/heap-inl.h"
+#include "src/snapshot/snapshot.h"
+
 namespace v8 {
-namespace internal {}  // namespace internal
+namespace internal {
+
+void StartupDeserializer::Deserialize(Isolate* isolate) {
+  Initialize(isolate);
+  if (!ReserveSpace()) V8::FatalProcessOutOfMemory("StartupDeserializer");
+
+  // No active threads.
+  DCHECK_NULL(isolate->thread_manager()->FirstThreadStateInUse());
+  // No active handles.
+  DCHECK(isolate->handle_scope_implementer()->blocks()->is_empty());
+  // Partial snapshot cache is not yet populated.
+  DCHECK(isolate->partial_snapshot_cache()->is_empty());
+  // Builtins are not yet created.
+  DCHECK(!isolate->builtins()->is_initialized());
+
+  {
+    DisallowHeapAllocation no_gc;
+    isolate->heap()->IterateStrongRoots(this, VISIT_ONLY_STRONG_ROOT_LIST);
+    isolate->heap()->IterateSmiRoots(this);
+    isolate->heap()->IterateStrongRoots(this, VISIT_ONLY_STRONG);
+    isolate->heap()->RepairFreeListsAfterDeserialization();
+    isolate->heap()->IterateWeakRoots(this, VISIT_ALL);
+    DeserializeDeferredObjects();
+    FlushICacheForNewIsolate();
+    RestoreExternalReferenceRedirectors(accessor_infos());
+  }
+
+  isolate->heap()->set_native_contexts_list(isolate->heap()->undefined_value());
+  // The allocation site list is build during root iteration, but if no sites
+  // were encountered then it needs to be initialized to undefined.
+  if (isolate->heap()->allocation_sites_list() == Smi::kZero) {
+    isolate->heap()->set_allocation_sites_list(
+        isolate->heap()->undefined_value());
+  }
+
+  // Issue code events for newly deserialized code objects.
+  LOG_CODE_EVENT(isolate, LogCodeObjects());
+  LOG_CODE_EVENT(isolate, LogBytecodeHandlers());
+  LOG_CODE_EVENT(isolate, LogCompiledFunctions());
+
+  isolate->builtins()->MarkInitialized();
+
+  // If needed, print the dissassembly of deserialized code objects.
+  // Needs to be called after the builtins are marked as initialized, in order
+  // to display the builtin names.
+  PrintDisassembledCodeObjects();
+
+  if (FLAG_rehash_snapshot && can_rehash()) Rehash();
+}
+
+void StartupDeserializer::FlushICacheForNewIsolate() {
+  DCHECK(!deserializing_user_code());
+  // The entire isolate is newly deserialized. Simply flush all code pages.
+  for (Page* p : *isolate()->heap()->code_space()) {
+    Assembler::FlushICache(isolate(), p->area_start(),
+                           p->area_end() - p->area_start());
+  }
+}
+
+void StartupDeserializer::PrintDisassembledCodeObjects() {
+#ifdef ENABLE_DISASSEMBLER
+  if (FLAG_print_builtin_code) {
+    Heap* heap = isolate()->heap();
+    HeapIterator iterator(heap);
+    DisallowHeapAllocation no_gc;
+
+    CodeTracer::Scope tracing_scope(isolate()->GetCodeTracer());
+    OFStream os(tracing_scope.file());
+
+    for (HeapObject* obj = iterator.next(); obj != NULL;
+         obj = iterator.next()) {
+      if (obj->IsCode()) {
+        Code::cast(obj)->Disassemble(nullptr, os);
+      }
+    }
+  }
+#endif
+}
+
+void StartupDeserializer::Rehash() {
+  DCHECK(FLAG_rehash_snapshot && can_rehash());
+  isolate()->heap()->InitializeHashSeed();
+  isolate()->heap()->string_table()->Rehash();
+  isolate()->heap()->weak_object_to_code_table()->Rehash();
+  SortMapDescriptors();
+}
+
+}  // namespace internal
 }  // namespace v8

src/snapshot/startup-deserializer.h

@@ -12,15 +12,20 @@ namespace v8 {
 namespace internal {
 
 // Initializes an isolate with context-independent data from a given snapshot.
-class StartupDeserializer : public Deserializer {
+class StartupDeserializer final : public Deserializer {
  public:
-  explicit StartupDeserializer(SnapshotData* data)
+  explicit StartupDeserializer(const SnapshotData* data)
       : Deserializer(data, false) {}
 
   // Deserialize the snapshot into an empty heap.
-  void Deserialize(Isolate* isolate) {
-    return Deserializer::Deserialize(isolate);
-  }
+  void Deserialize(Isolate* isolate);
+
+ private:
+  void FlushICacheForNewIsolate();
+  void PrintDisassembledCodeObjects();
+
+  // Rehash after deserializing an isolate.
+  void Rehash();
 };
 
 }  // namespace internal