[serializer][web snapshot] Speed up ValueDeserializer

- Unroll loop in ReadVarInt to skip checks for uncommon branches and
  improve by ~15%
- Use cage_base more aggressively
- Use more dehandlified code if possible
- Allow allocating strings directly in old-space to avoid filling up the
  new space when deserialising web-snapshots

Cleanup:
- ThrowDataCloneError now returns Nothing<bool>() for more consistency

Bug: v8:11525
Change-Id: I69ac635e2bcab83e92fba5ab34603146fa21f043
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3437049Reviewed-by: Marja Hölttä <marja@chromium.org>
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/main@{#78999}

src/objects/value-serializer.h

@@ -153,9 +153,11 @@ class ValueSerializer {
    * Asks the delegate to handle an error that occurred during data cloning, by
    * throwing an exception appropriate for the host.
    */
-  void ThrowDataCloneError(MessageTemplate template_index);
-  V8_NOINLINE void ThrowDataCloneError(MessageTemplate template_index,
-                                       Handle<Object> arg0);
+  V8_NOINLINE Maybe<bool> ThrowDataCloneError(MessageTemplate template_index)
+      V8_WARN_UNUSED_RESULT;
+  V8_NOINLINE Maybe<bool> ThrowDataCloneError(MessageTemplate template_index,
+                                              Handle<Object> arg0)
+      V8_WARN_UNUSED_RESULT;
 
   Maybe<bool> ThrowIfOutOfMemory();
 
@@ -243,11 +245,13 @@ class ValueDeserializer {
   void ConsumeTag(SerializationTag peeked_tag);
   Maybe<SerializationTag> ReadTag() V8_WARN_UNUSED_RESULT;
   template <typename T>
-  Maybe<T> ReadVarint() V8_WARN_UNUSED_RESULT;
+  V8_INLINE Maybe<T> ReadVarint() V8_WARN_UNUSED_RESULT;
+  template <typename T>
+  V8_NOINLINE Maybe<T> ReadVarintLoop() V8_WARN_UNUSED_RESULT;
   template <typename T>
   Maybe<T> ReadZigZag() V8_WARN_UNUSED_RESULT;
   Maybe<double> ReadDouble() V8_WARN_UNUSED_RESULT;
-  Maybe<base::Vector<const uint8_t>> ReadRawBytes(int size)
+  Maybe<base::Vector<const uint8_t>> ReadRawBytes(size_t size)
       V8_WARN_UNUSED_RESULT;
 
   // Reads a string if it matches the one provided.
@@ -266,9 +270,12 @@ class ValueDeserializer {
   // Reading V8 objects of specific kinds.
   // The tag is assumed to have already been read.
   MaybeHandle<BigInt> ReadBigInt() V8_WARN_UNUSED_RESULT;
-  MaybeHandle<String> ReadUtf8String() V8_WARN_UNUSED_RESULT;
-  MaybeHandle<String> ReadOneByteString() V8_WARN_UNUSED_RESULT;
-  MaybeHandle<String> ReadTwoByteString() V8_WARN_UNUSED_RESULT;
+  MaybeHandle<String> ReadUtf8String(
+      AllocationType allocation = AllocationType::kYoung) V8_WARN_UNUSED_RESULT;
+  MaybeHandle<String> ReadOneByteString(
+      AllocationType allocation = AllocationType::kYoung) V8_WARN_UNUSED_RESULT;
+  MaybeHandle<String> ReadTwoByteString(
+      AllocationType allocation = AllocationType::kYoung) V8_WARN_UNUSED_RESULT;
   MaybeHandle<JSObject> ReadJSObject() V8_WARN_UNUSED_RESULT;
   MaybeHandle<JSArray> ReadSparseJSArray() V8_WARN_UNUSED_RESULT;
   MaybeHandle<JSArray> ReadDenseJSArray() V8_WARN_UNUSED_RESULT;

src/web-snapshot/web-snapshot.cc

@@ -1239,7 +1239,8 @@ void WebSnapshotDeserializer::DeserializeStrings() {
   strings_handle_ = isolate_->factory()->NewFixedArray(string_count_);
   strings_ = *strings_handle_;
   for (uint32_t i = 0; i < string_count_; ++i) {
-    MaybeHandle<String> maybe_string = deserializer_.ReadUtf8String();
+    MaybeHandle<String> maybe_string =
+        deserializer_.ReadUtf8String(AllocationType::kOld);
     Handle<String> string;
     if (!maybe_string.ToHandle(&string)) {
       Throw("Malformed string");
@@ -1257,7 +1258,7 @@ String WebSnapshotDeserializer::ReadString(bool internalize) {
     return ReadOnlyRoots(isolate_).empty_string();
   }
   String string = String::cast(strings_.get(string_id));
-  if (internalize && !string.IsInternalizedString()) {
+  if (internalize && !string.IsInternalizedString(isolate_)) {
     string = *isolate_->factory()->InternalizeString(handle(string, isolate_));
     strings_.set(string_id, string);
   }