[d8] Add a stress mode to test web snapshot / json deserializing

Bug: v8:11525
Change-Id: I74190f2136e91107deea2c31f750a2d1a43dc18a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3528502Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Commit-Queue: Marja Hölttä <marja@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79531}

src/d8/d8.cc

@@ -1441,9 +1441,12 @@ bool Shell::ExecuteWebSnapshot(Isolate* isolate, const char* file_name) {
   if (length == 0) {
     isolate->ThrowError("Could not read the web snapshot file");
   } else {
+    for (int r = 0; r < DeserializationRunCount(); ++r) {
+      bool skip_exports = r > 0;
       i::WebSnapshotDeserializer deserializer(isolate, snapshot_data.get(),
                                               static_cast<size_t>(length));
-    success = deserializer.Deserialize();
+      success = deserializer.Deserialize({}, skip_exports);
+    }
   }
   if (!success) {
     CHECK(try_catch.HasCaught());
@@ -1471,9 +1474,11 @@ bool Shell::LoadJSON(Isolate* isolate, const char* file_name) {
   std::stringstream stream(data.get());
   std::string line;
   while (std::getline(stream, line, '\n')) {
+    for (int r = 0; r < DeserializationRunCount(); ++r) {
       Local<String> source =
           String::NewFromUtf8(isolate, line.c_str()).ToLocalChecked();
       MaybeLocal<Value> maybe_value = JSON::Parse(realm, source);
+
       Local<Value> value;
       if (!maybe_value.ToLocal(&value)) {
         DCHECK(try_catch.HasCaught());
@@ -1481,6 +1486,7 @@ bool Shell::LoadJSON(Isolate* isolate, const char* file_name) {
         return false;
       }
     }
+  }
   return true;
 }
 
@@ -4517,6 +4523,9 @@ bool Shell::SetOptions(int argc, char* argv[]) {
       options.cpu_profiler = true;
       options.cpu_profiler_print = true;
       argv[i] = nullptr;
+    } else if (strcmp(argv[i], "--stress-deserialize") == 0) {
+      options.stress_deserialize = true;
+      argv[i] = nullptr;
     } else if (strncmp(argv[i], "--web-snapshot-config=", 22) == 0) {
       options.web_snapshot_config = argv[i] + 22;
       argv[i] = nullptr;

src/d8/d8.h

@@ -464,6 +464,8 @@ class ShellOptions {
       "web-snapshot-output", nullptr};
   DisallowReassignment<bool> d8_web_snapshot_api = {
       "experimental-d8-web-snapshot-api", false};
+  // Applies to web snapshot and JSON deserialization.
+  DisallowReassignment<bool> stress_deserialize = {"stress-deserialize", false};
   DisallowReassignment<bool> compile_only = {"compile-only", false};
   DisallowReassignment<int> repeat_compile = {"repeat-compile", 1};
 #if V8_ENABLE_WEBASSEMBLY
@@ -691,6 +693,10 @@ class Shell : public i::AllStatic {
   static Local<FunctionTemplate> CreateSnapshotTemplate(Isolate* isolate);
 
  private:
+  static inline int DeserializationRunCount() {
+    return options.stress_deserialize ? 1000 : 1;
+  }
+
   static Global<Context> evaluation_context_;
   static base::OnceType quit_once_;
   static Global<Function> stringify_function_;

src/web-snapshot/web-snapshot.cc

@@ -1345,7 +1345,7 @@ void WebSnapshotDeserializer::Throw(const char* message) {
 }
 
 bool WebSnapshotDeserializer::Deserialize(
-    MaybeHandle<FixedArray> external_references) {
+    MaybeHandle<FixedArray> external_references, bool skip_exports) {
   RCS_SCOPE(isolate_, RuntimeCallCounterId::kWebSnapshotDeserialize);
   if (external_references.ToHandle(&external_references_handle_)) {
     external_references_ = *external_references_handle_;
@@ -1364,7 +1364,7 @@ bool WebSnapshotDeserializer::Deserialize(
   if (FLAG_trace_web_snapshot) {
     timer.Start();
   }
-  if (!DeserializeSnapshot()) {
+  if (!DeserializeSnapshot(skip_exports)) {
     return false;
   }
   if (!DeserializeScript()) {
@@ -1379,7 +1379,7 @@ bool WebSnapshotDeserializer::Deserialize(
   return true;
 }
 
-bool WebSnapshotDeserializer::DeserializeSnapshot() {
+bool WebSnapshotDeserializer::DeserializeSnapshot(bool skip_exports) {
   deferred_references_ = ArrayList::New(isolate_, 30);
 
   const void* magic_bytes;
@@ -1397,7 +1397,7 @@ bool WebSnapshotDeserializer::DeserializeSnapshot() {
   DeserializeObjects();
   DeserializeClasses();
   ProcessDeferredReferences();
-  DeserializeExports();
+  DeserializeExports(skip_exports);
   DCHECK_EQ(0, deferred_references_->Length());
 
   return !has_error();
@@ -2041,13 +2041,29 @@ void WebSnapshotDeserializer::DeserializeArrays() {
   }
 }
 
-void WebSnapshotDeserializer::DeserializeExports() {
+void WebSnapshotDeserializer::DeserializeExports(bool skip_exports) {
   RCS_SCOPE(isolate_, RuntimeCallCounterId::kWebSnapshotDeserialize_Exports);
   uint32_t count;
   if (!deserializer_.ReadUint32(&count) || count > kMaxItemCount) {
     Throw("Malformed export table");
     return;
   }
+
+  if (skip_exports) {
+    // In the skip_exports mode, we read the exports but don't do anything about
+    // them. This is useful for stress testing; otherwise the GlobalDictionary
+    // handling below dominates.
+    for (uint32_t i = 0; i < count; ++i) {
+      Handle<String> export_name(ReadString(true), isolate_);
+      // No deferred references should occur at this point, since all objects
+      // have been deserialized.
+      Object export_value = ReadValue();
+      USE(export_name);
+      USE(export_value);
+    }
+    return;
+  }
+
   // Pre-reserve the space for the properties we're going to add to the global
   // object.
   Handle<JSGlobalObject> global = isolate_->global_object();

src/web-snapshot/web-snapshot.h

@@ -278,7 +278,8 @@ class V8_EXPORT WebSnapshotDeserializer
                           size_t buffer_size);
   WebSnapshotDeserializer(Isolate* isolate, Handle<Script> snapshot_as_script);
   ~WebSnapshotDeserializer();
-  bool Deserialize(MaybeHandle<FixedArray> external_references = {});
+  bool Deserialize(MaybeHandle<FixedArray> external_references = {},
+                   bool skip_exports = false);
 
   // For inspecting the state after deserializing a snapshot.
   uint32_t string_count() const { return string_count_; }
@@ -304,7 +305,7 @@ class V8_EXPORT WebSnapshotDeserializer
                           base::Vector<const uint8_t> buffer);
   base::Vector<const uint8_t> ExtractScriptBuffer(
       Isolate* isolate, Handle<Script> snapshot_as_script);
-  bool DeserializeSnapshot();
+  bool DeserializeSnapshot(bool skip_exports);
   bool DeserializeScript();
 
   WebSnapshotDeserializer(const WebSnapshotDeserializer&) = delete;
@@ -323,7 +324,7 @@ class V8_EXPORT WebSnapshotDeserializer
   void DeserializeClasses();
   void DeserializeArrays();
   void DeserializeObjects();
-  void DeserializeExports();
+  void DeserializeExports(bool skip_exports);
 
   Object ReadValue(
       Handle<HeapObject> object_for_deferred_reference = Handle<HeapObject>(),