heap: Annote strong roots with a label

This aids debugging as it gives the root set a name.

Bug: chromium:1164553, chromium:1186901
Change-Id: I2c2aed369823b059629b35bb170b4966b47156d0
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2933661
Auto-Submit: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#74960}

src/heap/heap.cc

@@ -4713,7 +4713,7 @@ void Heap::IterateRoots(RootVisitor* v, base::EnumSet<SkipRoot> options) {
     // deoptimization entries).
     for (StrongRootsEntry* current = strong_roots_head_; current;
          current = current->next) {
-      v->VisitRootPointers(Root::kStrongRoots, nullptr, current->start,
+      v->VisitRootPointers(Root::kStrongRoots, current->label, current->start,
                            current->end);
     }
     v->Synchronize(VisitorSynchronization::kStrongRoots);
@@ -6419,11 +6419,12 @@ size_t Heap::OldArrayBufferBytes() {
   return array_buffer_sweeper()->OldBytes();
 }
 
-StrongRootsEntry* Heap::RegisterStrongRoots(FullObjectSlot start,
+StrongRootsEntry* Heap::RegisterStrongRoots(const char* label,
+                                            FullObjectSlot start,
                                             FullObjectSlot end) {
   base::MutexGuard guard(&strong_roots_mutex_);
 
-  StrongRootsEntry* entry = new StrongRootsEntry();
+  StrongRootsEntry* entry = new StrongRootsEntry(label);
   entry->start = start;
   entry->end = end;
   entry->prev = nullptr;
@@ -7084,8 +7085,8 @@ Address* StrongRootBlockAllocator::allocate(size_t n) {
                                             sizeof(StrongRootsEntry*));
 
   memset(ret, kNullAddress, n * sizeof(Address));
-  *header =
-      heap_->RegisterStrongRoots(FullObjectSlot(ret), FullObjectSlot(ret + n));
+  *header = heap_->RegisterStrongRoots(
+      "StrongRootBlockAllocator", FullObjectSlot(ret), FullObjectSlot(ret + n));
 
   return ret;
 }

src/heap/heap.h

@@ -186,12 +186,13 @@ enum class SkipRoot {
   kWeak
 };
 
-class StrongRootsEntry {
-  StrongRootsEntry() = default;
+class StrongRootsEntry final {
+  explicit StrongRootsEntry(const char* label) : label(label) {}
 
+  // Label that identifies the roots in tooling.
+  const char* label;
   FullObjectSlot start;
   FullObjectSlot end;
-
   StrongRootsEntry* prev;
   StrongRootsEntry* next;
 
@@ -931,7 +932,7 @@ class Heap {
   V8_INLINE void SetMessageListeners(TemplateList value);
   V8_INLINE void SetPendingOptimizeForTestBytecode(Object bytecode);
 
-  StrongRootsEntry* RegisterStrongRoots(FullObjectSlot start,
+  StrongRootsEntry* RegisterStrongRoots(const char* label, FullObjectSlot start,
                                         FullObjectSlot end);
   void UnregisterStrongRoots(StrongRootsEntry* entry);
   void UpdateStrongRoots(StrongRootsEntry* entry, FullObjectSlot start,

src/snapshot/serializer.cc

@@ -1190,9 +1190,9 @@ void Serializer::ObjectSerializer::SerializeCode(Map map, int size) {
 }
 
 Serializer::HotObjectsList::HotObjectsList(Heap* heap) : heap_(heap) {
-  strong_roots_entry_ =
-      heap->RegisterStrongRoots(FullObjectSlot(&circular_queue_[0]),
-                                FullObjectSlot(&circular_queue_[kSize]));
+  strong_roots_entry_ = heap->RegisterStrongRoots(
+      "Serializer::HotObjectsList", FullObjectSlot(&circular_queue_[0]),
+      FullObjectSlot(&circular_queue_[kSize]));
 }
 Serializer::HotObjectsList::~HotObjectsList() {
   heap_->UnregisterStrongRoots(strong_roots_entry_);

src/utils/identity-map.cc

@@ -205,8 +205,9 @@ IdentityMapBase::RawEntry IdentityMapBase::InsertEntry(Address key) {
     values_ = NewPointerArray(capacity_);
     memset(values_, 0, sizeof(uintptr_t) * capacity_);
 
-    strong_roots_entry_ = heap_->RegisterStrongRoots(
-        FullObjectSlot(keys_), FullObjectSlot(keys_ + capacity_));
+    strong_roots_entry_ =
+        heap_->RegisterStrongRoots("IdentityMapBase", FullObjectSlot(keys_),
+                                   FullObjectSlot(keys_ + capacity_));
   } else {
     // Rehash if there was a GC, then insert.
     if (gc_counter_ != heap_->gc_count()) Rehash();