cppgc-js: Make use of simple unmarker when young gen is enabled

Young generation collection requires that full GCs unmark before
starting marking.

Bug: v8:12324
Change-Id: Id6cc218057252cbf0664326126f34b07ac8ea247
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3229570
Auto-Submit: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Anton Bikineev <bikineev@chromium.org>
Reviewed-by: Anton Bikineev <bikineev@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77445}

BUILD.gn

@@ -357,7 +357,7 @@ declare_args() {
       v8_current_cpu == "x86" || v8_current_cpu == "x64" ||
       v8_current_cpu == "arm" || v8_current_cpu == "arm64" ||
       v8_current_cpu == "mips64el" || v8_current_cpu == "mipsel" ||
-      v8_current_cpu == "loong64"  || v8_current_cpu == "riscv64"
+      v8_current_cpu == "loong64" || v8_current_cpu == "riscv64"
 }
 
 # Derived defaults.
@@ -5504,6 +5504,7 @@ v8_source_set("cppgc_base") {
     "src/heap/cppgc/sweeper.cc",
     "src/heap/cppgc/sweeper.h",
     "src/heap/cppgc/task-handle.h",
+    "src/heap/cppgc/unmarker.h",
 
     # TODO(v8:11952): Remove the testing header here once depending on both,
     # //v8:v8 and //v8:v8_for_testing does not result in ODR violations.

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

@@ -37,6 +37,7 @@
 #include "src/heap/cppgc/raw-heap.h"
 #include "src/heap/cppgc/stats-collector.h"
 #include "src/heap/cppgc/sweeper.h"
+#include "src/heap/cppgc/unmarker.h"
 #include "src/heap/embedder-tracing.h"
 #include "src/heap/gc-tracer.h"
 #include "src/heap/marking-worklist.h"
@@ -417,6 +418,10 @@ bool ShouldReduceMemory(CppHeap::TraceFlags flags) {
 void CppHeap::TracePrologue(TraceFlags flags) {
   CHECK(!sweeper_.IsSweepingInProgress());
 
+#if defined(CPPGC_YOUNG_GENERATION)
+  cppgc::internal::SequentialUnmarker unmarker(raw_heap());
+#endif  // defined(CPPGC_YOUNG_GENERATION)
+
   current_flags_ = flags;
   const UnifiedHeapMarker::MarkingConfig marking_config{
       UnifiedHeapMarker::MarkingConfig::CollectionType::kMajor,

src/heap/cppgc/heap.cc

@@ -15,6 +15,7 @@
 #include "src/heap/cppgc/prefinalizer-handler.h"
 #include "src/heap/cppgc/stats-collector.h"
 #include "src/heap/cppgc/sweeper.h"
+#include "src/heap/cppgc/unmarker.h"
 
 namespace cppgc {
 
@@ -61,19 +62,6 @@ namespace internal {
 
 namespace {
 
-class Unmarker final : private HeapVisitor<Unmarker> {
-  friend class HeapVisitor<Unmarker>;
-
- public:
-  explicit Unmarker(RawHeap& heap) { Traverse(heap); }
-
- private:
-  bool VisitHeapObjectHeader(HeapObjectHeader& header) {
-    if (header.IsMarked()) header.Unmark();
-    return true;
-  }
-};
-
 void CheckConfig(Heap::Config config, Heap::MarkingType marking_support,
                  Heap::SweepingType sweeping_support) {
   CHECK_WITH_MSG(
@@ -160,7 +148,7 @@ void Heap::StartGarbageCollection(Config config) {
 
 #if defined(CPPGC_YOUNG_GENERATION)
   if (config.collection_type == Config::CollectionType::kMajor)
-    Unmarker unmarker(raw_heap());
+    SequentialUnmarker unmarker(raw_heap());
 #endif
 
   const Marker::MarkingConfig marking_config{

src/heap/cppgc/unmarker.h

@@ -0,0 +1,30 @@
+// Copyright 2021 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef V8_HEAP_CPPGC_UNMARKER_H_
+#define V8_HEAP_CPPGC_UNMARKER_H_
+
+#include "src/heap/cppgc/heap-object-header.h"
+#include "src/heap/cppgc/heap-visitor.h"
+
+namespace cppgc {
+namespace internal {
+
+class SequentialUnmarker final : private HeapVisitor<SequentialUnmarker> {
+  friend class HeapVisitor<SequentialUnmarker>;
+
+ public:
+  explicit SequentialUnmarker(RawHeap& heap) { Traverse(heap); }
+
+ private:
+  bool VisitHeapObjectHeader(HeapObjectHeader& header) {
+    if (header.IsMarked()) header.Unmark();
+    return true;
+  }
+};
+
+}  // namespace internal
+}  // namespace cppgc
+
+#endif  // V8_HEAP_CPPGC_UNMARKER_H_