[snapshot] Remove builtins area from startup snapshot

This removes the builtins area from the startup snapshot. It's now
completely contained in the separate builtins blob area.

Bug: v8:6624
Change-Id: Id3c43a177c7e1ed418eec59cf620fa461eb6df81
Reviewed-on: https://chromium-review.googlesource.com/715759
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48636}

src/snapshot/deserializer.cc

@@ -54,6 +54,9 @@ Deserializer<AllocatorT>::~Deserializer() {
 template <class AllocatorT>
 void Deserializer<AllocatorT>::VisitRootPointers(Root root, Object** start,
                                                  Object** end) {
+  // Builtins are deserialized in a separate pass by the BuiltinDeserializer.
+  if (root == Root::kBuiltins) return;
+
   // The space must be new space.  Any other space would cause ReadChunk to try
   // to update the remembered using nullptr as the address.
   ReadData(start, end, NEW_SPACE, nullptr);
@@ -64,7 +67,6 @@ void Deserializer<AllocatorT>::Synchronize(
     VisitorSynchronization::SyncTag tag) {
   static const byte expected = kSynchronize;
   CHECK_EQ(expected, source_.Get());
-  deserializing_builtins_ = (tag == VisitorSynchronization::kHandleScope);
 }
 
 template <class AllocatorT>
@@ -217,8 +219,7 @@ HeapObject* Deserializer<AllocatorT>::PostProcessNewObject(HeapObject* obj,
 template <class AllocatorT>
 int Deserializer<AllocatorT>::MaybeReplaceWithDeserializeLazy(int builtin_id) {
   DCHECK(Builtins::IsBuiltinId(builtin_id));
-  return (IsLazyDeserializationEnabled() && Builtins::IsLazy(builtin_id) &&
-          !deserializing_builtins_)
+  return IsLazyDeserializationEnabled() && Builtins::IsLazy(builtin_id)
              ? Builtins::kDeserializeLazy
              : builtin_id;
 }

src/snapshot/deserializer.h

@@ -151,10 +151,6 @@ class Deserializer : public SerializerDeserializer {
   AllocatorT allocator_;
   const bool deserializing_user_code_;
 
-  // TODO(jgruber): This workaround will no longer be necessary once builtin
-  // reference patching has been removed (through advance allocation).
-  bool deserializing_builtins_ = false;
-
   // TODO(6593): generalize rehashing, and remove this flag.
   bool can_rehash_;
 

src/snapshot/serializer.cc

@@ -91,6 +91,9 @@ bool Serializer<AllocatorT>::MustBeDeferred(HeapObject* object) {
 template <class AllocatorT>
 void Serializer<AllocatorT>::VisitRootPointers(Root root, Object** start,
                                                Object** end) {
+  // Builtins are serialized in a separate pass by the BuiltinSerializer.
+  if (root == Root::kBuiltins) return;
+
   for (Object** current = start; current < end; current++) {
     if ((*current)->IsSmi()) {
       PutSmi(Smi::cast(*current));

src/snapshot/startup-serializer.cc

@@ -17,7 +17,6 @@ StartupSerializer::StartupSerializer(
     : Serializer(isolate),
       clear_function_code_(function_code_handling ==
                            v8::SnapshotCreator::FunctionCodeHandling::kClear),
-      serializing_builtins_(false),
       can_be_rehashed_(true) {
   InitializeCodeAddressMap();
 }
@@ -36,9 +35,7 @@ void StartupSerializer::SerializeObject(HeapObject* obj, HowToCode how_to_code,
   }
 
   BuiltinReferenceSerializationMode mode =
-      (clear_function_code() && !serializing_builtins_)
-          ? kCanonicalizeCompileLazy
-          : kDefault;
+      clear_function_code() ? kCanonicalizeCompileLazy : kDefault;
   if (SerializeBuiltinReference(obj, how_to_code, where_to_point, skip, mode)) {
     return;
   }
@@ -107,9 +104,6 @@ int StartupSerializer::PartialSnapshotCacheIndex(HeapObject* heap_object) {
 }
 
 void StartupSerializer::Synchronize(VisitorSynchronization::SyncTag tag) {
-  // We expect the builtins tag after builtins have been serialized.
-  DCHECK(!serializing_builtins_ || tag == VisitorSynchronization::kBuiltins);
-  serializing_builtins_ = (tag == VisitorSynchronization::kHandleScope);
   sink_.Put(kSynchronize, "Synchronize");
 }
 

src/snapshot/startup-serializer.h

@@ -78,7 +78,6 @@ class StartupSerializer : public Serializer<> {
   void CheckRehashability(HeapObject* hashtable);
 
   const 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_;