Revert "Implement and use VectorSegment to avoid repeated allocation of ZoneVector properties."

This reverts commit d3104923.

Reason for revert: Breaks win debug, causes lots of timeouts.
https://build.chromium.org/p/client.v8/builders/V8%20Win64%20-%20debug/builds/20387

Original change's description:
> Implement and use VectorSegment to avoid repeated allocation of ZoneVector properties.
> 
> The parser holds a single vector whose backing storage is reused in calls
> to ParseJsonObject, so that once we reach the peak number of unstored
> properties no more allocations are required.
> 
> This improves performance of parsing inputs like those in Speedometer VanillaJS
> by about 2% in my local measurement, and would presumably do better on more
> pathological inputs.
> 
> This should also have the side effect of reducing peak memory usage at this time
> slightly, since we do fewer zone allocations which cannot be freed until the
> parse finishes.
> 
> Bug: chromium:771227
> Change-Id: I8aa1514b37a74f82539f95f94292c8fa1582d66a
> Reviewed-on: https://chromium-review.googlesource.com/789511
> Reviewed-by: Camillo Bruni <cbruni@chromium.org>
> Reviewed-by: Marja Hölttä <marja@chromium.org>
> Commit-Queue: Jeremy Roman <jbroman@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#49693}

TBR=jbroman@chromium.org,marja@chromium.org,cbruni@chromium.org

Change-Id: I5b198aeffed6f1543f6110709dc74b311d4ba144
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: chromium:771227
Reviewed-on: https://chromium-review.googlesource.com/796151Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49705}

src/json-parser.cc

@@ -20,38 +20,6 @@
 namespace v8 {
 namespace internal {
 
-namespace {
-
-// A vector-like data structure that uses a larger vector for allocation, and
-// provides limited utility access. The original vector must not be used for the
-// duration, and it may even be reallocated. This allows vector storage to be
-// reused for the properties of sibling objects.
-template <typename Container>
-class VectorSegment {
- public:
-  using value_type = typename Container::value_type;
-
-  explicit VectorSegment(Container* container)
-      : container_(*container), begin_(container->size()) {}
-  ~VectorSegment() { container_.resize(begin_); }
-
-  Vector<const value_type> GetVector() const {
-    return Vector<const value_type>(&container_[begin_],
-                                    container_.size() - begin_);
-  }
-
-  template <typename T>
-  void push_back(T&& value) {
-    container_.push_back(std::forward<T>(value));
-  }
-
- private:
-  Container& container_;
-  const typename Container::size_type begin_;
-};
-
-}  // namespace
-
 MaybeHandle<Object> JsonParseInternalizer::Internalize(Isolate* isolate,
                                                        Handle<Object> object,
                                                        Handle<Object> reviver) {
@@ -143,8 +111,7 @@ JsonParser<seq_one_byte>::JsonParser(Isolate* isolate, Handle<String> source)
       zone_(isolate_->allocator(), ZONE_NAME),
       object_constructor_(isolate_->native_context()->object_function(),
                           isolate_),
-      position_(-1),
-      properties_(&zone_) {
+      position_(-1) {
   source_ = String::Flatten(source_);
   pretenure_ = (source_length_ >= kPretenureTreshold) ? TENURED : NOT_TENURED;
 
@@ -366,7 +333,7 @@ Handle<Object> JsonParser<seq_one_byte>::ParseJsonObject() {
       factory()->NewJSObject(object_constructor(), pretenure_);
   Handle<Map> map(json_object->map());
   int descriptor = 0;
-  VectorSegment<ZoneVector<Handle<Object>>> properties(&properties_);
+  ZoneVector<Handle<Object>> properties(zone());
   DCHECK_EQ(c0_, '{');
 
   bool transitioning = true;
@@ -457,7 +424,7 @@ Handle<Object> JsonParser<seq_one_byte>::ParseJsonObject() {
       DCHECK(!transitioning);
 
       // Commit the intermediate state to the object and stop transitioning.
-      CommitStateToJsonObject(json_object, map, properties.GetVector());
+      CommitStateToJsonObject(json_object, map, &properties);
 
       JSObject::DefinePropertyOrElementIgnoreAttributes(json_object, key, value)
           .Check();
@@ -465,7 +432,7 @@ Handle<Object> JsonParser<seq_one_byte>::ParseJsonObject() {
 
     // If we transitioned until the very end, transition the map now.
     if (transitioning) {
-      CommitStateToJsonObject(json_object, map, properties.GetVector());
+      CommitStateToJsonObject(json_object, map, &properties);
     } else {
       while (MatchSkipWhiteSpace(',')) {
         HandleScope local_scope(isolate());
@@ -513,14 +480,15 @@ Handle<Object> JsonParser<seq_one_byte>::ParseJsonObject() {
 template <bool seq_one_byte>
 void JsonParser<seq_one_byte>::CommitStateToJsonObject(
     Handle<JSObject> json_object, Handle<Map> map,
-    Vector<const Handle<Object>> properties) {
+    ZoneVector<Handle<Object>>* properties) {
   JSObject::AllocateStorageForMap(json_object, map);
   DCHECK(!json_object->map()->is_dictionary_map());
 
   DisallowHeapAllocation no_gc;
   DescriptorArray* descriptors = json_object->map()->instance_descriptors();
-  for (int i = 0; i < properties.length(); i++) {
-    Handle<Object> value = properties[i];
+  int length = static_cast<int>(properties->size());
+  for (int i = 0; i < length; i++) {
+    Handle<Object> value = (*properties)[i];
     // Initializing store.
     json_object->WriteToField(i, descriptors->GetDetails(i), *value);
   }

src/json-parser.h

@@ -144,7 +144,7 @@ class JsonParser BASE_EMBEDDED {
   Zone* zone() { return &zone_; }
 
   void CommitStateToJsonObject(Handle<JSObject> json_object, Handle<Map> map,
-                               Vector<const Handle<Object>> properties);
+                               ZoneVector<Handle<Object>>* properties);
 
   Handle<String> source_;
   int source_length_;
@@ -157,9 +157,6 @@ class JsonParser BASE_EMBEDDED {
   Handle<JSFunction> object_constructor_;
   uc32 c0_;
   int position_;
-
-  // Property handles are stored here inside ParseJsonObject.
-  ZoneVector<Handle<Object>> properties_;
 };
 
 }  // namespace internal