[heap] Adjust cppgc heap statistics

- Avoid adding an Invalid type that can never be reached during
  traversal;
- Expose class names as object names;

Bug: chromium:1321620
Change-Id: Ie3d9f78d97703535ecf67d56235d564ab6a9a7e8
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3763866
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Omer Katz <omerkatz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81758}

src/heap/cppgc/heap-base.cc

@@ -298,5 +298,16 @@ HeapStatistics HeapBase::CollectStatistics(
   return HeapStatisticsCollector().CollectDetailedStatistics(this);
 }
 
+ClassNameAsHeapObjectNameScope::ClassNameAsHeapObjectNameScope(HeapBase& heap)
+    : heap_(heap),
+      saved_heap_object_name_value_(heap_.name_of_unnamed_object()) {
+  heap_.set_name_of_unnamed_object(
+      HeapObjectNameForUnnamedObject::kUseClassNameIfSupported);
+}
+
+ClassNameAsHeapObjectNameScope::~ClassNameAsHeapObjectNameScope() {
+  heap_.set_name_of_unnamed_object(saved_heap_object_name_value_);
+}
+
 }  // namespace internal
 }  // namespace cppgc

src/heap/cppgc/heap-base.h

@@ -310,6 +310,16 @@ class V8_EXPORT_PRIVATE HeapBase : public cppgc::HeapHandle {
   friend class cppgc::testing::OverrideEmbedderStackStateScope;
 };
 
+class V8_NODISCARD V8_EXPORT_PRIVATE ClassNameAsHeapObjectNameScope final {
+ public:
+  explicit ClassNameAsHeapObjectNameScope(HeapBase& heap);
+  ~ClassNameAsHeapObjectNameScope();
+
+ private:
+  HeapBase& heap_;
+  const HeapObjectNameForUnnamedObject saved_heap_object_name_value_;
+};
+
 }  // namespace internal
 }  // namespace cppgc
 

src/heap/cppgc/heap-statistics-collector.cc

@@ -97,11 +97,7 @@ HeapStatistics HeapStatisticsCollector::CollectDetailedStatistics(
   stats.detail_level = HeapStatistics::DetailLevel::kDetailed;
   current_stats_ = &stats;
 
-  if (NameProvider::SupportsCppClassNamesAsObjectNames()) {
-    // Add a dummy type so that a type index of zero has a valid mapping but
-    // shows an invalid type.
-    type_name_to_index_map_.insert({"Invalid type", 0});
-  }
+  ClassNameAsHeapObjectNameScope class_names_scope(*heap);
 
   Traverse(heap->raw_heap());
   FinalizeSpace(current_stats_, &current_space_stats_, &current_page_stats_);

src/heap/heap.cc

@@ -7580,16 +7580,11 @@ EmbedderStackStateScope::~EmbedderStackStateScope() {
 
 CppClassNamesAsHeapObjectNameScope::CppClassNamesAsHeapObjectNameScope(
     v8::CppHeap* heap)
-    : cpp_heap_(CppHeap::From(heap)),
-      saved_heap_object_name_value_(cpp_heap_->name_of_unnamed_object()) {
-  cpp_heap_->set_name_of_unnamed_object(
-      cppgc::internal::HeapObjectNameForUnnamedObject::
-          kUseClassNameIfSupported);
-}
+    : scope_(std::make_unique<cppgc::internal::ClassNameAsHeapObjectNameScope>(
+          *CppHeap::From(heap))) {}
 
-CppClassNamesAsHeapObjectNameScope::~CppClassNamesAsHeapObjectNameScope() {
-  cpp_heap_->set_name_of_unnamed_object(saved_heap_object_name_value_);
-}
+CppClassNamesAsHeapObjectNameScope::~CppClassNamesAsHeapObjectNameScope() =
+    default;
 
 }  // namespace internal
 }  // namespace v8

src/heap/heap.h

@@ -46,6 +46,7 @@ namespace cppgc {
 namespace internal {
 
 enum class HeapObjectNameForUnnamedObject : uint8_t;
+class ClassNameAsHeapObjectNameScope;
 
 }  // namespace internal
 }  // namespace cppgc
@@ -2909,9 +2910,7 @@ class V8_NODISCARD CppClassNamesAsHeapObjectNameScope final {
   ~CppClassNamesAsHeapObjectNameScope();
 
  private:
-  CppHeap* const cpp_heap_;
-  const cppgc::internal::HeapObjectNameForUnnamedObject
-      saved_heap_object_name_value_;
+  std::unique_ptr<cppgc::internal::ClassNameAsHeapObjectNameScope> scope_;
 };
 
 }  // namespace internal

test/unittests/heap/cppgc/name-trait-unittest.cc

@@ -120,8 +120,7 @@ TEST(NameTraitTest, ParsingPrettyFunction) {
 class HeapObjectHeaderNameTest : public testing::TestWithHeap {};
 
 TEST_F(HeapObjectHeaderNameTest, LookupNameThroughGCInfo) {
-  Heap::From(GetHeap())->set_name_of_unnamed_object(
-      HeapObjectNameForUnnamedObject::kUseClassNameIfSupported);
+  ClassNameAsHeapObjectNameScope class_names_scope(*Heap::From(GetHeap()));
   auto* no_name = MakeGarbageCollected<NoName>(GetAllocationHandle());
   auto no_name_tuple = HeapObjectHeader::FromObject(no_name).GetName();
   if (NameProvider::SupportsCppClassNamesAsObjectNames()) {