cppgc-js: Account for C++ object sizes

Previously, for wrapper/wrappable pairs, only JS object size was
accounted for. With this change, the C++ part is also accounted for.

Change-Id: Ibd945cb28c808d8c01fa41453f94a6de9883b764
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2615258
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#71959}

src/heap/cppgc-js/cpp-snapshot.cc

@@ -34,11 +34,12 @@ using cppgc::internal::HeapObjectHeader;
 // Node representing a C++ object on the heap.
 class EmbedderNode : public v8::EmbedderGraph::Node {
  public:
-  explicit EmbedderNode(const char* name) : name_(name) {}
+  explicit EmbedderNode(const char* name, size_t size)
+      : name_(name), size_(size) {}
   ~EmbedderNode() override = default;
 
   const char* Name() final { return name_; }
-  size_t SizeInBytes() override { return 0; }
+  size_t SizeInBytes() final { return size_; }
 
   void SetWrapperNode(v8::EmbedderGraph::Node* wrapper_node) {
     wrapper_node_ = wrapper_node;
@@ -52,6 +53,7 @@ class EmbedderNode : public v8::EmbedderGraph::Node {
 
  private:
   const char* name_;
+  size_t size_;
   Node* wrapper_node_ = nullptr;
   Detachedness detachedness_ = Detachedness::kUnknown;
 };
@@ -59,11 +61,10 @@ class EmbedderNode : public v8::EmbedderGraph::Node {
 // Node representing an artificial root group, e.g., set of Persistent handles.
 class EmbedderRootNode final : public EmbedderNode {
  public:
-  explicit EmbedderRootNode(const char* name) : EmbedderNode(name) {}
+  explicit EmbedderRootNode(const char* name) : EmbedderNode(name, 0) {}
   ~EmbedderRootNode() final = default;
 
   bool IsRootNode() final { return true; }
-  size_t SizeInBytes() final { return 0; }
 };
 
 // Canonical state representing real and artificial (e.g. root) objects.
@@ -373,7 +374,7 @@ class CppGraphBuilderImpl final {
   EmbedderNode* AddNode(const HeapObjectHeader& header) {
     return static_cast<EmbedderNode*>(
         graph_.AddNode(std::unique_ptr<v8::EmbedderGraph::Node>{
-            new EmbedderNode(header.GetName().value)}));
+            new EmbedderNode(header.GetName().value, header.GetSize())}));
   }
 
   void AddEdge(State& parent, const HeapObjectHeader& header) {

src/profiler/heap-snapshot-generator.cc

@@ -2000,6 +2000,9 @@ void NativeObjectsExplorer::MergeNodeIntoEntry(
   entry->set_name(MergeNames(
       names_, EmbedderGraphNodeName(names_, original_node), entry->name()));
   entry->set_type(EmbedderGraphNodeType(original_node));
+  DCHECK_GE(entry->self_size() + original_node->SizeInBytes(),
+            entry->self_size());
+  entry->add_self_size(original_node->SizeInBytes());
 }
 
 HeapEntry* NativeObjectsExplorer::EntryForEmbedderGraphNode(

src/profiler/heap-snapshot-generator.h

@@ -126,6 +126,7 @@ class HeapEntry {
   void set_name(const char* name) { name_ = name; }
   SnapshotObjectId id() const { return id_; }
   size_t self_size() const { return self_size_; }
+  void add_self_size(size_t size) { self_size_ += size; }
   unsigned trace_node_id() const { return trace_node_id_; }
   int index() const { return index_; }
   V8_INLINE int children_count() const;

test/unittests/heap/unified-heap-snapshot-unittest.cc

@@ -14,7 +14,9 @@
 #include "include/v8-profiler.h"
 #include "src/api/api-inl.h"
 #include "src/heap/cppgc-js/cpp-heap.h"
+#include "src/heap/cppgc/heap-object-header.h"
 #include "src/heap/cppgc/object-allocator.h"
+#include "src/objects/heap-object.h"
 #include "src/objects/objects-inl.h"
 #include "src/profiler/heap-snapshot-generator-inl.h"
 #include "src/profiler/heap-snapshot-generator.h"
@@ -314,6 +316,18 @@ cppgc::Persistent<GCedWithJSRef> SetupWrapperWrappablePair(
   return std::move(gc_w_js_ref);
 }
 
+template <typename Callback>
+void ForEachEntryWithName(const v8::HeapSnapshot* snapshot, const char* needle,
+                          Callback callback) {
+  const HeapSnapshot* heap_snapshot =
+      reinterpret_cast<const HeapSnapshot*>(snapshot);
+  for (const HeapEntry& entry : heap_snapshot->entries()) {
+    if (strcmp(entry.name(), needle) == 0) {
+      callback(entry);
+    }
+  }
+}
+
 }  // namespace
 
 TEST_F(UnifiedHeapSnapshotTest, JSReferenceForcesVisibleObject) {
@@ -335,8 +349,8 @@ TEST_F(UnifiedHeapSnapshotTest, JSReferenceForcesVisibleObject) {
 
 TEST_F(UnifiedHeapSnapshotTest, MergedWrapperNode) {
   // Test ensures that the snapshot sets a wrapper node for C++->JS references
-  // that have a class id set and that object nodes are merged into the C++
-  // node, i.e., the directly reachable JS object is merged into the C++ object.
+  // that have a class id set and that object nodes are merged. In practice, the
+  // C++ node is merged into the existing JS node.
   JsTestingScope testing_scope(v8_isolate());
   cppgc::Persistent<GCedWithJSRef> gc_w_js_ref = SetupWrapperWrappablePair(
       testing_scope, allocation_handle(), "MergedObject");
@@ -356,14 +370,22 @@ TEST_F(UnifiedHeapSnapshotTest, MergedWrapperNode) {
       .ToChecked();
   const v8::HeapSnapshot* snapshot = TakeHeapSnapshot();
   EXPECT_TRUE(IsValidSnapshot(snapshot));
-  EXPECT_TRUE(
-      ContainsRetainingPath(*snapshot,
+  EXPECT_TRUE(ContainsRetainingPath(
+      *snapshot,
       {
           kExpectedCppRootsName,             // NOLINT
           GetExpectedName<GCedWithJSRef>(),  // NOLINT
-                                // MergedObject is merged into GCedWithJSRef.
+          // GCedWithJSRef is merged into MergedObject, replacing its name.
           "NextObject"  // NOLINT
       }));
+  const size_t cpp_size =
+      cppgc::internal::HeapObjectHeader::FromPayload(gc_w_js_ref.Get())
+          .GetSize();
+  const size_t js_size = Utils::OpenHandle(*wrapper_object)->Size();
+  ForEachEntryWithName(snapshot, GetExpectedName<GCedWithJSRef>(),
+                       [cpp_size, js_size](const HeapEntry& entry) {
+                         EXPECT_EQ(cpp_size + js_size, entry.self_size());
+                       });
 }
 
 namespace {
@@ -388,18 +410,6 @@ class DetachednessHandler {
 // static
 size_t DetachednessHandler::callback_count = 0;
 
-template <typename Callback>
-void ForEachEntryWithName(const v8::HeapSnapshot* snapshot, const char* needle,
-                          Callback callback) {
-  const HeapSnapshot* heap_snapshot =
-      reinterpret_cast<const HeapSnapshot*>(snapshot);
-  for (const HeapEntry& entry : heap_snapshot->entries()) {
-    if (strcmp(entry.name(), needle) == 0) {
-      callback(entry);
-    }
-  }
-}
-
 constexpr uint8_t kExpectedDetachedValueForUnknown =
     static_cast<uint8_t>(v8::EmbedderGraph::Node::Detachedness::kUnknown);
 constexpr uint8_t kExpectedDetachedValueForAttached =