cppgc: Revise WeakContainerTest.*

For some reason the compiler was optimizing away the reference to the
object in WeakContainerTest.ConservativeGCTracesWeakContainer and thus
not finding it conservatively.
This CL revises the tests such that the compiler is no longer able to
optimize references away.

Bug: v8:12824
Change-Id: Ie598a1cf1124c2983a6c61fd4e990734d36f5832
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3610627Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Omer Katz <omerkatz@chromium.org>
Reviewed-by: Anton Bikineev <bikineev@chromium.org>
Cr-Commit-Position: refs/heads/main@{#80257}

test/unittests/heap/cppgc/weak-container-unittest.cc

@@ -56,24 +56,17 @@ class TraceableGCed : public GarbageCollected<TraceableGCed> {
     reinterpret_cast<std::atomic<size_t>*>(&n_trace_calls)
         ->fetch_add(1, std::memory_order_relaxed);
   }
-  static size_t n_trace_calls;
+  mutable size_t n_trace_calls = 0;
 };
-size_t TraceableGCed::n_trace_calls = 0u;
 
 class NonTraceableGCed : public GarbageCollected<NonTraceableGCed> {
  public:
   void Trace(cppgc::Visitor*) const { n_trace_calls++; }
-  static size_t n_trace_calls;
+  mutable size_t n_trace_calls = 0;
 };
-size_t NonTraceableGCed::n_trace_calls = 0u;
 
 void EmptyWeakCallback(const LivenessBroker&, const void*) {}
 
-template <typename T>
-V8_NOINLINE T access(volatile const T& t) {
-  return t;
-}
-
 }  // namespace
 
 }  // namespace internal
@@ -99,61 +92,56 @@ namespace internal {
 TEST_F(WeakContainerTest, TraceableGCedTraced) {
   TraceableGCed* obj =
       MakeGarbageCollected<TraceableGCed>(GetAllocationHandle());
-  TraceableGCed::n_trace_calls = 0u;
+  obj->n_trace_calls = 0u;
   StartMarking();
   GetMarkerRef()->Visitor().TraceWeakContainer(obj, EmptyWeakCallback, nullptr);
   FinishMarking(Config::StackState::kNoHeapPointers);
-  EXPECT_NE(0u, TraceableGCed::n_trace_calls);
+  EXPECT_NE(0u, obj->n_trace_calls);
   EXPECT_EQ(SizeOf<TraceableGCed>(), GetMarkedBytes());
-  access(obj);
 }
 
 TEST_F(WeakContainerTest, NonTraceableGCedNotTraced) {
   NonTraceableGCed* obj =
       MakeGarbageCollected<NonTraceableGCed>(GetAllocationHandle());
-  NonTraceableGCed::n_trace_calls = 0u;
+  obj->n_trace_calls = 0u;
   StartMarking();
   GetMarkerRef()->Visitor().TraceWeakContainer(obj, EmptyWeakCallback, nullptr);
   FinishMarking(Config::StackState::kNoHeapPointers);
-  EXPECT_EQ(0u, NonTraceableGCed::n_trace_calls);
+  EXPECT_EQ(0u, obj->n_trace_calls);
   EXPECT_EQ(SizeOf<NonTraceableGCed>(), GetMarkedBytes());
-  access(obj);
 }
 
 TEST_F(WeakContainerTest, NonTraceableGCedNotTracedConservatively) {
   NonTraceableGCed* obj =
       MakeGarbageCollected<NonTraceableGCed>(GetAllocationHandle());
-  NonTraceableGCed::n_trace_calls = 0u;
+  obj->n_trace_calls = 0u;
   StartMarking();
   GetMarkerRef()->Visitor().TraceWeakContainer(obj, EmptyWeakCallback, nullptr);
   FinishMarking(Config::StackState::kMayContainHeapPointers);
-  EXPECT_NE(0u, NonTraceableGCed::n_trace_calls);
+  EXPECT_NE(0u, obj->n_trace_calls);
   EXPECT_EQ(SizeOf<NonTraceableGCed>(), GetMarkedBytes());
-  access(obj);
 }
 
 TEST_F(WeakContainerTest, PreciseGCTracesWeakContainerWhenTraced) {
   TraceableGCed* obj =
       MakeGarbageCollected<TraceableGCed>(GetAllocationHandle());
-  TraceableGCed::n_trace_calls = 0u;
+  obj->n_trace_calls = 0u;
   StartMarking();
   GetMarkerRef()->Visitor().TraceWeakContainer(obj, EmptyWeakCallback, nullptr);
   FinishMarking(Config::StackState::kNoHeapPointers);
-  EXPECT_EQ(1u, TraceableGCed::n_trace_calls);
+  EXPECT_EQ(1u, obj->n_trace_calls);
   EXPECT_EQ(SizeOf<TraceableGCed>(), GetMarkedBytes());
-  access(obj);
 }
 
 TEST_F(WeakContainerTest, ConservativeGCTracesWeakContainer) {
   TraceableGCed* obj =
       MakeGarbageCollected<TraceableGCed>(GetAllocationHandle());
-  TraceableGCed::n_trace_calls = 0u;
+  obj->n_trace_calls = 0u;
   StartMarking();
   GetMarkerRef()->Visitor().TraceWeakContainer(obj, EmptyWeakCallback, nullptr);
   FinishMarking(Config::StackState::kMayContainHeapPointers);
-  EXPECT_EQ(2u, TraceableGCed::n_trace_calls);
+  EXPECT_EQ(2u, obj->n_trace_calls);
   EXPECT_EQ(SizeOf<TraceableGCed>(), GetMarkedBytes());
-  access(obj);
 }
 
 TEST_F(WeakContainerTest, ConservativeGCTracesWeakContainerOnce) {
@@ -163,13 +151,12 @@ TEST_F(WeakContainerTest, ConservativeGCTracesWeakContainerOnce) {
   USE(copy_obj);
   NonTraceableGCed* another_copy_obj = obj;
   USE(another_copy_obj);
-  NonTraceableGCed::n_trace_calls = 0u;
+  obj->n_trace_calls = 0u;
   StartMarking();
   GetMarkerRef()->Visitor().TraceWeakContainer(obj, EmptyWeakCallback, nullptr);
   FinishMarking(Config::StackState::kMayContainHeapPointers);
-  EXPECT_EQ(1u, NonTraceableGCed::n_trace_calls);
+  EXPECT_EQ(1u, obj->n_trace_calls);
   EXPECT_EQ(SizeOf<NonTraceableGCed>(), GetMarkedBytes());
-  access(obj);
 }
 
 namespace {