heap: Sweeper: Only emit trace scope when running

Avoids emitting scopes when not even running. This can be a problem for
metrics computation which may recursively invoke
EnsureSweepingCompleted() when starting marking even though the sweeper
is guaranteed to be not running at this point.

Bug: chromium:1211795
Change-Id: I8d7692f4e8c640f38d3c52df5c111fff4f06df9e
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3109674
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Auto-Submit: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Omer Katz <omerkatz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#76411}

src/heap/array-buffer-sweeper.cc

@@ -71,6 +71,7 @@ size_t ArrayBufferList::BytesSlow() {
 void ArrayBufferSweeper::EnsureFinished() {
   if (!sweeping_in_progress_) return;
 
+  TRACE_GC(heap_->tracer(), GCTracer::Scope::MC_COMPLETE_SWEEP_ARRAY_BUFFERS);
   TryAbortResult abort_result =
       heap_->isolate()->cancelable_task_manager()->TryAbort(job_->id_);
 

src/heap/heap.cc

@@ -1929,14 +1929,7 @@ void Heap::StartIncrementalMarking(int gc_flags,
 }
 
 void Heap::CompleteSweepingFull() {
-  TRACE_GC_EPOCH(tracer(), GCTracer::Scope::MC_COMPLETE_SWEEPING,
-                 ThreadKind::kMain);
-
-  {
-    TRACE_GC(tracer(), GCTracer::Scope::MC_COMPLETE_SWEEP_ARRAY_BUFFERS);
-    array_buffer_sweeper()->EnsureFinished();
-  }
-
+  array_buffer_sweeper()->EnsureFinished();
   mark_compact_collector()->EnsureSweepingCompleted();
   DCHECK(!mark_compact_collector()->sweeping_in_progress());
 }

src/heap/mark-compact.cc

@@ -646,6 +646,9 @@ void MarkCompactCollector::VerifyMarkbitsAreClean() {
 void MarkCompactCollector::EnsureSweepingCompleted() {
   if (!sweeper()->sweeping_in_progress()) return;
 
+  TRACE_GC_EPOCH(heap()->tracer(), GCTracer::Scope::MC_COMPLETE_SWEEPING,
+                 ThreadKind::kMain);
+
   sweeper()->EnsureCompleted();
   heap()->old_space()->RefillFreeList();
   heap()->code_space()->RefillFreeList();