profiler: Provide raw heap snapshots

Omit user roots when raw heap snapshots are used, i.e., when
the gn flag v8_enable_raw_heap_snapshots is enabled. For regular
Chrome production builds this is not the case.

Blink CL: https://crrev.com/c/1529096

Bug: chromium:936797
Change-Id: I5ae0ec1ecfab9a76352d8ce927d1c40e707262cc
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1528994
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Alexei Filippov <alph@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60351}

BUILD.gn

@@ -345,6 +345,9 @@ config("features") {
   }
   defines +=
       [ "V8_TYPED_ARRAY_MAX_SIZE_IN_HEAP=${v8_typed_array_max_size_in_heap}" ]
+  if (v8_enable_raw_heap_snapshots) {
+    defines += [ "V8_ENABLE_RAW_HEAP_SNAPSHOTS" ]
+  }
   if (v8_enable_future) {
     defines += [ "V8_ENABLE_FUTURE" ]
   }

gni/v8.gni

@@ -31,8 +31,12 @@ declare_args() {
   # Support for backtrace_symbols on linux.
   v8_enable_backtrace = ""
 
-  # Enables full heap snapshots containing internals. Used for debugging memory
+  # Enables raw heap snapshots containing internals. Used for debugging memory
   # on platform and embedder level.
+  v8_enable_raw_heap_snapshots = false
+
+  # See v8_enable_raw_heap_snapshots.
+  # TODO(mlippautz): Remove after adjusting Blink embedder code.
   v8_enable_full_heap_snapshots = false
 
   # Enable the snapshot feature, for fast context creation.

src/flag-definitions.h

@@ -292,6 +292,12 @@ HARMONY_SHIPPING(FLAG_SHIPPING_FEATURES)
 DEFINE_BOOL(icu_timezone_data, true, "get information about timezones from ICU")
 #endif
 
+#ifdef V8_ENABLE_RAW_HEAP_SNAPSHOTS
+#define V8_ENABLE_RAW_HEAP_SNAPSHOTS_BOOL true
+#else
+#define V8_ENABLE_RAW_HEAP_SNAPSHOTS_BOOL false
+#endif  // V8_ENABLE_RAW_HEAP_SNAPSHOTS
+
 #ifdef V8_LITE_MODE
 #define V8_LITE_BOOL true
 #else
@@ -1536,6 +1542,9 @@ DEFINE_BOOL(unbox_double_fields, V8_DOUBLE_FIELDS_UNBOXING,
             "enable in-object double fields unboxing (64-bit only)")
 DEFINE_IMPLICATION(unbox_double_fields, track_double_fields)
 
+DEFINE_BOOL(raw_heap_snapshots, V8_ENABLE_RAW_HEAP_SNAPSHOTS_BOOL,
+            "enable raw heap snapshots contain garbage collection internals")
+
 DEFINE_BOOL(lite_mode, V8_LITE_BOOL,
             "enables trade-off of performance for memory savings "
             "(Lite mode only)")

src/profiler/heap-snapshot-generator.cc

@@ -1681,6 +1681,10 @@ void V8HeapExplorer::SetGcSubrootReference(Root root, const char* description,
         edge_type, description, child_entry, names_);
   }
 
+  // For full heap snapshots we do not emit user roots but rather rely on
+  // regular GC roots to retain objects.
+  if (FLAG_raw_heap_snapshots) return;
+
   // Add a shortcut to JS global object reference at snapshot root.
   // That allows the user to easily find global objects. They are
   // also used as starting points in distance calculations.
@@ -1837,7 +1841,7 @@ const char* EmbedderGraphNodeName(StringsStorage* names,
 }
 
 HeapEntry::Type EmbedderGraphNodeType(EmbedderGraphImpl::Node* node) {
-  return HeapEntry::kNative;
+  return node->IsRootNode() ? HeapEntry::kSynthetic : HeapEntry::kNative;
 }
 
 // Merges the names of an embedder node and its wrapper node.

test/cctest/test-heap-profiler.cc

@@ -1672,11 +1672,11 @@ TEST(HeapSnapshotRetainedObjectInfo) {
   CHECK(ValidateSnapshot(snapshot));
 
   const v8::HeapGraphNode* native_group_aaa =
-      GetNode(snapshot->GetRoot(), v8::HeapGraphNode::kNative, "aaa-group");
-  CHECK(native_group_aaa);
+      GetNode(snapshot->GetRoot(), v8::HeapGraphNode::kSynthetic, "aaa-group");
+  CHECK_NOT_NULL(native_group_aaa);
   const v8::HeapGraphNode* native_group_ccc =
-      GetNode(snapshot->GetRoot(), v8::HeapGraphNode::kNative, "ccc-group");
-  CHECK(native_group_ccc);
+      GetNode(snapshot->GetRoot(), v8::HeapGraphNode::kSynthetic, "ccc-group");
+  CHECK_NOT_NULL(native_group_ccc);
 
   const v8::HeapGraphNode* n_AAA =
       GetNode(native_group_aaa, v8::HeapGraphNode::kString, "AAA");