Update Files

v8/include/cppgc/internal/api-constants.h

@@ -0,0 +1,65 @@
+// Copyright 2020 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 INCLUDE_CPPGC_INTERNAL_API_CONSTANTS_H_
+#define INCLUDE_CPPGC_INTERNAL_API_CONSTANTS_H_
+
+#include <cstddef>
+#include <cstdint>
+
+#include "v8config.h"  // NOLINT(build/include_directory)
+
+namespace cppgc {
+namespace internal {
+
+// Embedders should not rely on this code!
+
+// Internal constants to avoid exposing internal types on the API surface.
+namespace api_constants {
+
+constexpr size_t kKB = 1024;
+constexpr size_t kMB = kKB * 1024;
+constexpr size_t kGB = kMB * 1024;
+
+// Offset of the uint16_t bitfield from the payload contaning the
+// in-construction bit. This is subtracted from the payload pointer to get
+// to the right bitfield.
+static constexpr size_t kFullyConstructedBitFieldOffsetFromPayload =
+    2 * sizeof(uint16_t);
+// Mask for in-construction bit.
+static constexpr uint16_t kFullyConstructedBitMask = uint16_t{1};
+
+static constexpr size_t kPageSize = size_t{1} << 17;
+
+#if defined(V8_TARGET_ARCH_ARM64) && defined(V8_OS_MACOS)
+constexpr size_t kGuardPageSize = 0;
+#else
+constexpr size_t kGuardPageSize = 4096;
+#endif
+
+static constexpr size_t kLargeObjectSizeThreshold = kPageSize / 2;
+
+#if defined(CPPGC_CAGED_HEAP)
+#if defined(CPPGC_2GB_CAGE)
+constexpr size_t kCagedHeapReservationSize = static_cast<size_t>(2) * kGB;
+#else   // !defined(CPPGC_2GB_CAGE)
+constexpr size_t kCagedHeapReservationSize = static_cast<size_t>(4) * kGB;
+#endif  // !defined(CPPGC_2GB_CAGE)
+constexpr size_t kCagedHeapReservationAlignment = kCagedHeapReservationSize;
+#endif  // defined(CPPGC_CAGED_HEAP)
+
+static constexpr size_t kDefaultAlignment = sizeof(void*);
+
+// Maximum support alignment for a type as in `alignof(T)`.
+static constexpr size_t kMaxSupportedAlignment = 2 * kDefaultAlignment;
+
+// Granularity of heap allocations.
+constexpr size_t kAllocationGranularity = sizeof(void*);
+
+}  // namespace api_constants
+
+}  // namespace internal
+}  // namespace cppgc
+
+#endif  // INCLUDE_CPPGC_INTERNAL_API_CONSTANTS_H_

v8/include/cppgc/internal/atomic-entry-flag.h

@@ -0,0 +1,48 @@
+// Copyright 2020 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 INCLUDE_CPPGC_INTERNAL_ATOMIC_ENTRY_FLAG_H_
+#define INCLUDE_CPPGC_INTERNAL_ATOMIC_ENTRY_FLAG_H_
+
+#include <atomic>
+
+namespace cppgc {
+namespace internal {
+
+// A flag which provides a fast check whether a scope may be entered on the
+// current thread, without needing to access thread-local storage or mutex.  Can
+// have false positives (i.e., spuriously report that it might be entered), so
+// it is expected that this will be used in tandem with a precise check that the
+// scope is in fact entered on that thread.
+//
+// Example:
+//   g_frobnicating_flag.MightBeEntered() &&
+//   ThreadLocalFrobnicator().IsFrobnicating()
+//
+// Relaxed atomic operations are sufficient, since:
+// - all accesses remain atomic
+// - each thread must observe its own operations in order
+// - no thread ever exits the flag more times than it enters (if used correctly)
+// And so if a thread observes zero, it must be because it has observed an equal
+// number of exits as entries.
+class AtomicEntryFlag final {
+ public:
+  void Enter() { entries_.fetch_add(1, std::memory_order_relaxed); }
+  void Exit() { entries_.fetch_sub(1, std::memory_order_relaxed); }
+
+  // Returns false only if the current thread is not between a call to Enter
+  // and a call to Exit. Returns true if this thread or another thread may
+  // currently be in the scope guarded by this flag.
+  bool MightBeEntered() const {
+    return entries_.load(std::memory_order_relaxed) != 0;
+  }
+
+ private:
+  std::atomic_int entries_{0};
+};
+
+}  // namespace internal
+}  // namespace cppgc
+
+#endif  // INCLUDE_CPPGC_INTERNAL_ATOMIC_ENTRY_FLAG_H_

v8/include/cppgc/internal/base-page-handle.h

@@ -0,0 +1,45 @@
+// Copyright 2022 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 INCLUDE_CPPGC_INTERNAL_BASE_PAGE_HANDLE_H_
+#define INCLUDE_CPPGC_INTERNAL_BASE_PAGE_HANDLE_H_
+
+#include "cppgc/heap-handle.h"
+#include "cppgc/internal/api-constants.h"
+#include "cppgc/internal/logging.h"
+#include "v8config.h"  // NOLINT(build/include_directory)
+
+namespace cppgc {
+namespace internal {
+
+// The class is needed in the header to allow for fast access to HeapHandle in
+// the write barrier.
+class BasePageHandle {
+ public:
+  static V8_INLINE BasePageHandle* FromPayload(void* payload) {
+    return reinterpret_cast<BasePageHandle*>(
+        (reinterpret_cast<uintptr_t>(payload) &
+         ~(api_constants::kPageSize - 1)) +
+        api_constants::kGuardPageSize);
+  }
+  static V8_INLINE const BasePageHandle* FromPayload(const void* payload) {
+    return FromPayload(const_cast<void*>(payload));
+  }
+
+  HeapHandle& heap_handle() { return heap_handle_; }
+  const HeapHandle& heap_handle() const { return heap_handle_; }
+
+ protected:
+  explicit BasePageHandle(HeapHandle& heap_handle) : heap_handle_(heap_handle) {
+    CPPGC_DCHECK(reinterpret_cast<uintptr_t>(this) % api_constants::kPageSize ==
+                 api_constants::kGuardPageSize);
+  }
+
+  HeapHandle& heap_handle_;
+};
+
+}  // namespace internal
+}  // namespace cppgc
+
+#endif  // INCLUDE_CPPGC_INTERNAL_BASE_PAGE_HANDLE_H_

v8/include/cppgc/internal/caged-heap-local-data.h

@@ -0,0 +1,111 @@
+// Copyright 2020 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 INCLUDE_CPPGC_INTERNAL_CAGED_HEAP_LOCAL_DATA_H_
+#define INCLUDE_CPPGC_INTERNAL_CAGED_HEAP_LOCAL_DATA_H_
+
+#include <array>
+#include <cstddef>
+#include <cstdint>
+
+#include "cppgc/internal/api-constants.h"
+#include "cppgc/internal/caged-heap.h"
+#include "cppgc/internal/logging.h"
+#include "cppgc/platform.h"
+#include "v8config.h"  // NOLINT(build/include_directory)
+
+#if __cpp_lib_bitopts
+#include <bit>
+#endif  // __cpp_lib_bitopts
+
+#if defined(CPPGC_CAGED_HEAP)
+
+namespace cppgc {
+namespace internal {
+
+class HeapBase;
+class HeapBaseHandle;
+
+#if defined(CPPGC_YOUNG_GENERATION)
+
+// AgeTable is the bytemap needed for the fast generation check in the write
+// barrier. AgeTable contains entries that correspond to 4096 bytes memory
+// regions (cards). Each entry in the table represents generation of the objects
+// that reside on the corresponding card (young, old or mixed).
+class V8_EXPORT AgeTable final {
+  static constexpr size_t kRequiredSize = 1 * api_constants::kMB;
+  static constexpr size_t kAllocationGranularity =
+      api_constants::kAllocationGranularity;
+
+ public:
+  // Represents age of the objects living on a single card.
+  enum class Age : uint8_t { kOld, kYoung, kMixed };
+  // When setting age for a range, consider or ignore ages of the adjacent
+  // cards.
+  enum class AdjacentCardsPolicy : uint8_t { kConsider, kIgnore };
+
+  static constexpr size_t kCardSizeInBytes =
+      api_constants::kCagedHeapReservationSize / kRequiredSize;
+
+  void SetAge(uintptr_t cage_offset, Age age) {
+    table_[card(cage_offset)] = age;
+  }
+
+  V8_INLINE Age GetAge(uintptr_t cage_offset) const {
+    return table_[card(cage_offset)];
+  }
+
+  void SetAgeForRange(uintptr_t cage_offset_begin, uintptr_t cage_offset_end,
+                      Age age, AdjacentCardsPolicy adjacent_cards_policy);
+
+  Age GetAgeForRange(uintptr_t cage_offset_begin,
+                     uintptr_t cage_offset_end) const;
+
+  void ResetForTesting();
+
+ private:
+  V8_INLINE size_t card(uintptr_t offset) const {
+    constexpr size_t kGranularityBits =
+#if __cpp_lib_bitopts
+        std::countr_zero(static_cast<uint32_t>(kCardSizeInBytes));
+#elif V8_HAS_BUILTIN_CTZ
+        __builtin_ctz(static_cast<uint32_t>(kCardSizeInBytes));
+#else   //! V8_HAS_BUILTIN_CTZ
+        // Hardcode and check with assert.
+#if defined(CPPGC_2GB_CAGE)
+        11;
+#else   // !defined(CPPGC_2GB_CAGE)
+        12;
+#endif  // !defined(CPPGC_2GB_CAGE)
+#endif  // !V8_HAS_BUILTIN_CTZ
+    static_assert((1 << kGranularityBits) == kCardSizeInBytes);
+    const size_t entry = offset >> kGranularityBits;
+    CPPGC_DCHECK(table_.size() > entry);
+    return entry;
+  }
+
+  std::array<Age, kRequiredSize> table_;
+};
+
+static_assert(sizeof(AgeTable) == 1 * api_constants::kMB,
+              "Size of AgeTable is 1MB");
+
+#endif  // CPPGC_YOUNG_GENERATION
+
+struct CagedHeapLocalData final {
+  V8_INLINE static CagedHeapLocalData& Get() {
+    return *reinterpret_cast<CagedHeapLocalData*>(CagedHeapBase::GetBase());
+  }
+
+#if defined(CPPGC_YOUNG_GENERATION)
+  AgeTable age_table;
+#endif
+};
+
+}  // namespace internal
+}  // namespace cppgc
+
+#endif  // defined(CPPGC_CAGED_HEAP)
+
+#endif  // INCLUDE_CPPGC_INTERNAL_CAGED_HEAP_LOCAL_DATA_H_

v8/include/cppgc/internal/caged-heap.h

@@ -0,0 +1,61 @@
+// Copyright 2022 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 INCLUDE_CPPGC_INTERNAL_CAGED_HEAP_H_
+#define INCLUDE_CPPGC_INTERNAL_CAGED_HEAP_H_
+
+#include <climits>
+#include <cstddef>
+
+#include "cppgc/internal/api-constants.h"
+#include "cppgc/internal/base-page-handle.h"
+#include "v8config.h"  // NOLINT(build/include_directory)
+
+#if defined(CPPGC_CAGED_HEAP)
+
+namespace cppgc {
+namespace internal {
+
+class V8_EXPORT CagedHeapBase {
+ public:
+  V8_INLINE static uintptr_t OffsetFromAddress(const void* address) {
+    return reinterpret_cast<uintptr_t>(address) &
+           (api_constants::kCagedHeapReservationAlignment - 1);
+  }
+
+  V8_INLINE static bool IsWithinCage(const void* address) {
+    CPPGC_DCHECK(g_heap_base_);
+    return (reinterpret_cast<uintptr_t>(address) &
+            ~(api_constants::kCagedHeapReservationAlignment - 1)) ==
+           g_heap_base_;
+  }
+
+  V8_INLINE static bool AreWithinCage(const void* addr1, const void* addr2) {
+#if defined(CPPGC_2GB_CAGE)
+    static constexpr size_t kHalfWordShift = sizeof(uint32_t) * CHAR_BIT - 1;
+#else   //! defined(CPPGC_2GB_CAGE)
+    static constexpr size_t kHalfWordShift = sizeof(uint32_t) * CHAR_BIT;
+#endif  //! defined(CPPGC_2GB_CAGE)
+    static_assert((static_cast<size_t>(1) << kHalfWordShift) ==
+                  api_constants::kCagedHeapReservationSize);
+    CPPGC_DCHECK(g_heap_base_);
+    return !(((reinterpret_cast<uintptr_t>(addr1) ^ g_heap_base_) |
+              (reinterpret_cast<uintptr_t>(addr2) ^ g_heap_base_)) >>
+             kHalfWordShift);
+  }
+
+  V8_INLINE static uintptr_t GetBase() { return g_heap_base_; }
+
+ private:
+  friend class CagedHeap;
+
+  static uintptr_t g_heap_base_;
+};
+
+}  // namespace internal
+}  // namespace cppgc
+
+#endif  // defined(CPPGC_CAGED_HEAP)
+
+#endif  // INCLUDE_CPPGC_INTERNAL_CAGED_HEAP_H_

v8/include/cppgc/internal/compiler-specific.h

@@ -0,0 +1,38 @@
+// Copyright 2020 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 INCLUDE_CPPGC_INTERNAL_COMPILER_SPECIFIC_H_
+#define INCLUDE_CPPGC_INTERNAL_COMPILER_SPECIFIC_H_
+
+namespace cppgc {
+
+#if defined(__has_attribute)
+#define CPPGC_HAS_ATTRIBUTE(FEATURE) __has_attribute(FEATURE)
+#else
+#define CPPGC_HAS_ATTRIBUTE(FEATURE) 0
+#endif
+
+#if defined(__has_cpp_attribute)
+#define CPPGC_HAS_CPP_ATTRIBUTE(FEATURE) __has_cpp_attribute(FEATURE)
+#else
+#define CPPGC_HAS_CPP_ATTRIBUTE(FEATURE) 0
+#endif
+
+// [[no_unique_address]] comes in C++20 but supported in clang with -std >=
+// c++11.
+#if CPPGC_HAS_CPP_ATTRIBUTE(no_unique_address)
+#define CPPGC_NO_UNIQUE_ADDRESS [[no_unique_address]]
+#else
+#define CPPGC_NO_UNIQUE_ADDRESS
+#endif
+
+#if CPPGC_HAS_ATTRIBUTE(unused)
+#define CPPGC_UNUSED __attribute__((unused))
+#else
+#define CPPGC_UNUSED
+#endif
+
+}  // namespace cppgc
+
+#endif  // INCLUDE_CPPGC_INTERNAL_COMPILER_SPECIFIC_H_

v8/include/cppgc/internal/finalizer-trait.h

@@ -0,0 +1,93 @@
+// Copyright 2020 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 INCLUDE_CPPGC_INTERNAL_FINALIZER_TRAIT_H_
+#define INCLUDE_CPPGC_INTERNAL_FINALIZER_TRAIT_H_
+
+#include <type_traits>
+
+#include "cppgc/type-traits.h"
+
+namespace cppgc {
+namespace internal {
+
+using FinalizationCallback = void (*)(void*);
+
+template <typename T, typename = void>
+struct HasFinalizeGarbageCollectedObject : std::false_type {};
+
+template <typename T>
+struct HasFinalizeGarbageCollectedObject<
+    T,
+    std::void_t<decltype(std::declval<T>().FinalizeGarbageCollectedObject())>>
+    : std::true_type {};
+
+// The FinalizerTraitImpl specifies how to finalize objects.
+template <typename T, bool isFinalized>
+struct FinalizerTraitImpl;
+
+template <typename T>
+struct FinalizerTraitImpl<T, true> {
+ private:
+  // Dispatch to custom FinalizeGarbageCollectedObject().
+  struct Custom {
+    static void Call(void* obj) {
+      static_cast<T*>(obj)->FinalizeGarbageCollectedObject();
+    }
+  };
+
+  // Dispatch to regular destructor.
+  struct Destructor {
+    static void Call(void* obj) { static_cast<T*>(obj)->~T(); }
+  };
+
+  using FinalizeImpl =
+      std::conditional_t<HasFinalizeGarbageCollectedObject<T>::value, Custom,
+                         Destructor>;
+
+ public:
+  static void Finalize(void* obj) {
+    static_assert(sizeof(T), "T must be fully defined");
+    FinalizeImpl::Call(obj);
+  }
+};
+
+template <typename T>
+struct FinalizerTraitImpl<T, false> {
+  static void Finalize(void* obj) {
+    static_assert(sizeof(T), "T must be fully defined");
+  }
+};
+
+// The FinalizerTrait is used to determine if a type requires finalization and
+// what finalization means.
+template <typename T>
+struct FinalizerTrait {
+ private:
+  // Object has a finalizer if it has
+  // - a custom FinalizeGarbageCollectedObject method, or
+  // - a destructor.
+  static constexpr bool kNonTrivialFinalizer =
+      internal::HasFinalizeGarbageCollectedObject<T>::value ||
+      !std::is_trivially_destructible<typename std::remove_cv<T>::type>::value;
+
+  static void Finalize(void* obj) {
+    internal::FinalizerTraitImpl<T, kNonTrivialFinalizer>::Finalize(obj);
+  }
+
+ public:
+  static constexpr bool HasFinalizer() { return kNonTrivialFinalizer; }
+
+  // The callback used to finalize an object of type T.
+  static constexpr FinalizationCallback kCallback =
+      kNonTrivialFinalizer ? Finalize : nullptr;
+};
+
+template <typename T>
+constexpr FinalizationCallback FinalizerTrait<T>::kCallback;
+
+}  // namespace internal
+}  // namespace cppgc
+
+#endif  // INCLUDE_CPPGC_INTERNAL_FINALIZER_TRAIT_H_

v8/include/cppgc/internal/gc-info.h

@@ -0,0 +1,155 @@
+// Copyright 2020 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 INCLUDE_CPPGC_INTERNAL_GC_INFO_H_
+#define INCLUDE_CPPGC_INTERNAL_GC_INFO_H_
+
+#include <atomic>
+#include <cstdint>
+#include <type_traits>
+
+#include "cppgc/internal/finalizer-trait.h"
+#include "cppgc/internal/name-trait.h"
+#include "cppgc/trace-trait.h"
+#include "v8config.h"  // NOLINT(build/include_directory)
+
+namespace cppgc {
+namespace internal {
+
+using GCInfoIndex = uint16_t;
+
+struct V8_EXPORT EnsureGCInfoIndexTrait final {
+  // Acquires a new GC info object and returns the index. In addition, also
+  // updates `registered_index` atomically.
+  template <typename T>
+  V8_INLINE static GCInfoIndex EnsureIndex(
+      std::atomic<GCInfoIndex>& registered_index) {
+    return EnsureGCInfoIndexTraitDispatch<T>{}(registered_index);
+  }
+
+ private:
+  template <typename T, bool = std::is_polymorphic<T>::value,
+            bool = FinalizerTrait<T>::HasFinalizer(),
+            bool = NameTrait<T>::HasNonHiddenName()>
+  struct EnsureGCInfoIndexTraitDispatch;
+
+  static GCInfoIndex EnsureGCInfoIndexPolymorphic(std::atomic<GCInfoIndex>&,
+                                                  TraceCallback,
+                                                  FinalizationCallback,
+                                                  NameCallback);
+  static GCInfoIndex EnsureGCInfoIndexPolymorphic(std::atomic<GCInfoIndex>&,
+                                                  TraceCallback,
+                                                  FinalizationCallback);
+  static GCInfoIndex EnsureGCInfoIndexPolymorphic(std::atomic<GCInfoIndex>&,
+                                                  TraceCallback, NameCallback);
+  static GCInfoIndex EnsureGCInfoIndexPolymorphic(std::atomic<GCInfoIndex>&,
+                                                  TraceCallback);
+  static GCInfoIndex EnsureGCInfoIndexNonPolymorphic(std::atomic<GCInfoIndex>&,
+                                                     TraceCallback,
+                                                     FinalizationCallback,
+                                                     NameCallback);
+  static GCInfoIndex EnsureGCInfoIndexNonPolymorphic(std::atomic<GCInfoIndex>&,
+                                                     TraceCallback,
+                                                     FinalizationCallback);
+  static GCInfoIndex EnsureGCInfoIndexNonPolymorphic(std::atomic<GCInfoIndex>&,
+                                                     TraceCallback,
+                                                     NameCallback);
+  static GCInfoIndex EnsureGCInfoIndexNonPolymorphic(std::atomic<GCInfoIndex>&,
+                                                     TraceCallback);
+};
+
+#define DISPATCH(is_polymorphic, has_finalizer, has_non_hidden_name, function) \
+  template <typename T>                                                        \
+  struct EnsureGCInfoIndexTrait::EnsureGCInfoIndexTraitDispatch<               \
+      T, is_polymorphic, has_finalizer, has_non_hidden_name> {                 \
+    V8_INLINE GCInfoIndex                                                      \
+    operator()(std::atomic<GCInfoIndex>& registered_index) {                   \
+      return function;                                                         \
+    }                                                                          \
+  };
+
+// --------------------------------------------------------------------- //
+// DISPATCH(is_polymorphic, has_finalizer, has_non_hidden_name, function)
+// --------------------------------------------------------------------- //
+DISPATCH(true, true, true,                                               //
+         EnsureGCInfoIndexPolymorphic(registered_index,                  //
+                                      TraceTrait<T>::Trace,              //
+                                      FinalizerTrait<T>::kCallback,      //
+                                      NameTrait<T>::GetName))            //
+DISPATCH(true, true, false,                                              //
+         EnsureGCInfoIndexPolymorphic(registered_index,                  //
+                                      TraceTrait<T>::Trace,              //
+                                      FinalizerTrait<T>::kCallback))     //
+DISPATCH(true, false, true,                                              //
+         EnsureGCInfoIndexPolymorphic(registered_index,                  //
+                                      TraceTrait<T>::Trace,              //
+                                      NameTrait<T>::GetName))            //
+DISPATCH(true, false, false,                                             //
+         EnsureGCInfoIndexPolymorphic(registered_index,                  //
+                                      TraceTrait<T>::Trace))             //
+DISPATCH(false, true, true,                                              //
+         EnsureGCInfoIndexNonPolymorphic(registered_index,               //
+                                         TraceTrait<T>::Trace,           //
+                                         FinalizerTrait<T>::kCallback,   //
+                                         NameTrait<T>::GetName))         //
+DISPATCH(false, true, false,                                             //
+         EnsureGCInfoIndexNonPolymorphic(registered_index,               //
+                                         TraceTrait<T>::Trace,           //
+                                         FinalizerTrait<T>::kCallback))  //
+DISPATCH(false, false, true,                                             //
+         EnsureGCInfoIndexNonPolymorphic(registered_index,               //
+                                         TraceTrait<T>::Trace,           //
+                                         NameTrait<T>::GetName))         //
+DISPATCH(false, false, false,                                            //
+         EnsureGCInfoIndexNonPolymorphic(registered_index,               //
+                                         TraceTrait<T>::Trace))          //
+
+#undef DISPATCH
+
+// Fold types based on finalizer behavior. Note that finalizer characteristics
+// align with trace behavior, i.e., destructors are virtual when trace methods
+// are and vice versa.
+template <typename T, typename ParentMostGarbageCollectedType>
+struct GCInfoFolding {
+  static constexpr bool kHasVirtualDestructorAtBase =
+      std::has_virtual_destructor<ParentMostGarbageCollectedType>::value;
+  static constexpr bool kBothTypesAreTriviallyDestructible =
+      std::is_trivially_destructible<ParentMostGarbageCollectedType>::value &&
+      std::is_trivially_destructible<T>::value;
+  static constexpr bool kHasCustomFinalizerDispatchAtBase =
+      internal::HasFinalizeGarbageCollectedObject<
+          ParentMostGarbageCollectedType>::value;
+#ifdef CPPGC_SUPPORTS_OBJECT_NAMES
+  static constexpr bool kWantsDetailedObjectNames = true;
+#else   // !CPPGC_SUPPORTS_OBJECT_NAMES
+  static constexpr bool kWantsDetailedObjectNames = false;
+#endif  // !CPPGC_SUPPORTS_OBJECT_NAMES
+
+  // Folding would regresses name resolution when deriving names from C++
+  // class names as it would just folds a name to the base class name.
+  using ResultType = std::conditional_t<(kHasVirtualDestructorAtBase ||
+                                         kBothTypesAreTriviallyDestructible ||
+                                         kHasCustomFinalizerDispatchAtBase) &&
+                                            !kWantsDetailedObjectNames,
+                                        ParentMostGarbageCollectedType, T>;
+};
+
+// Trait determines how the garbage collector treats objects wrt. to traversing,
+// finalization, and naming.
+template <typename T>
+struct GCInfoTrait final {
+  V8_INLINE static GCInfoIndex Index() {
+    static_assert(sizeof(T), "T must be fully defined");
+    static std::atomic<GCInfoIndex>
+        registered_index;  // Uses zero initialization.
+    const GCInfoIndex index = registered_index.load(std::memory_order_acquire);
+    return index ? index
+                 : EnsureGCInfoIndexTrait::EnsureIndex<T>(registered_index);
+  }
+};
+
+}  // namespace internal
+}  // namespace cppgc
+
+#endif  // INCLUDE_CPPGC_INTERNAL_GC_INFO_H_

v8/include/cppgc/internal/logging.h

@@ -0,0 +1,50 @@
+// Copyright 2020 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 INCLUDE_CPPGC_INTERNAL_LOGGING_H_
+#define INCLUDE_CPPGC_INTERNAL_LOGGING_H_
+
+#include "cppgc/source-location.h"
+#include "v8config.h"  // NOLINT(build/include_directory)
+
+namespace cppgc {
+namespace internal {
+
+void V8_EXPORT DCheckImpl(const char*,
+                          const SourceLocation& = SourceLocation::Current());
+[[noreturn]] void V8_EXPORT
+FatalImpl(const char*, const SourceLocation& = SourceLocation::Current());
+
+// Used to ignore -Wunused-variable.
+template <typename>
+struct EatParams {};
+
+#if defined(DEBUG)
+#define CPPGC_DCHECK_MSG(condition, message)  \
+  do {                                        \
+    if (V8_UNLIKELY(!(condition))) {          \
+      ::cppgc::internal::DCheckImpl(message); \
+    }                                         \
+  } while (false)
+#else  // !defined(DEBUG)
+#define CPPGC_DCHECK_MSG(condition, message)                \
+  (static_cast<void>(::cppgc::internal::EatParams<decltype( \
+                         static_cast<void>(condition), message)>{}))
+#endif  // !defined(DEBUG)
+
+#define CPPGC_DCHECK(condition) CPPGC_DCHECK_MSG(condition, #condition)
+
+#define CPPGC_CHECK_MSG(condition, message)  \
+  do {                                       \
+    if (V8_UNLIKELY(!(condition))) {         \
+      ::cppgc::internal::FatalImpl(message); \
+    }                                        \
+  } while (false)
+
+#define CPPGC_CHECK(condition) CPPGC_CHECK_MSG(condition, #condition)
+
+}  // namespace internal
+}  // namespace cppgc
+
+#endif  // INCLUDE_CPPGC_INTERNAL_LOGGING_H_

v8/include/cppgc/internal/member-storage.h

@@ -0,0 +1,236 @@
+// Copyright 2022 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 INCLUDE_CPPGC_INTERNAL_MEMBER_STORAGE_H_
+#define INCLUDE_CPPGC_INTERNAL_MEMBER_STORAGE_H_
+
+#include <atomic>
+#include <cstddef>
+#include <type_traits>
+
+#include "cppgc/internal/api-constants.h"
+#include "cppgc/internal/logging.h"
+#include "cppgc/sentinel-pointer.h"
+#include "v8config.h"  // NOLINT(build/include_directory)
+
+namespace cppgc {
+namespace internal {
+
+#if defined(CPPGC_POINTER_COMPRESSION)
+
+#if defined(__clang__)
+// Attribute const allows the compiler to assume that CageBaseGlobal::g_base_
+// doesn't change (e.g. across calls) and thereby avoid redundant loads.
+#define CPPGC_CONST __attribute__((const))
+#define CPPGC_REQUIRE_CONSTANT_INIT \
+  __attribute__((require_constant_initialization))
+#else  // defined(__clang__)
+#define CPPGC_CONST
+#define CPPGC_REQUIRE_CONSTANT_INIT
+#endif  // defined(__clang__)
+
+class CageBaseGlobal final {
+ public:
+  V8_INLINE CPPGC_CONST static uintptr_t Get() {
+    CPPGC_DCHECK(IsBaseConsistent());
+    return g_base_;
+  }
+
+  V8_INLINE CPPGC_CONST static bool IsSet() {
+    CPPGC_DCHECK(IsBaseConsistent());
+    return (g_base_ & ~kLowerHalfWordMask) != 0;
+  }
+
+ private:
+  // We keep the lower halfword as ones to speed up decompression.
+  static constexpr uintptr_t kLowerHalfWordMask =
+      (api_constants::kCagedHeapReservationAlignment - 1);
+
+  static V8_EXPORT uintptr_t g_base_ CPPGC_REQUIRE_CONSTANT_INIT;
+
+  CageBaseGlobal() = delete;
+
+  V8_INLINE static bool IsBaseConsistent() {
+    return kLowerHalfWordMask == (g_base_ & kLowerHalfWordMask);
+  }
+
+  friend class CageBaseGlobalUpdater;
+};
+
+#undef CPPGC_REQUIRE_CONSTANT_INIT
+#undef CPPGC_CONST
+
+class V8_TRIVIAL_ABI CompressedPointer final {
+ public:
+  using IntegralType = uint32_t;
+
+  V8_INLINE CompressedPointer() : value_(0u) {}
+  V8_INLINE explicit CompressedPointer(const void* ptr)
+      : value_(Compress(ptr)) {}
+  V8_INLINE explicit CompressedPointer(std::nullptr_t) : value_(0u) {}
+  V8_INLINE explicit CompressedPointer(SentinelPointer)
+      : value_(kCompressedSentinel) {}
+
+  V8_INLINE const void* Load() const { return Decompress(value_); }
+  V8_INLINE const void* LoadAtomic() const {
+    return Decompress(
+        reinterpret_cast<const std::atomic<IntegralType>&>(value_).load(
+            std::memory_order_relaxed));
+  }
+
+  V8_INLINE void Store(const void* ptr) { value_ = Compress(ptr); }
+  V8_INLINE void StoreAtomic(const void* value) {
+    reinterpret_cast<std::atomic<IntegralType>&>(value_).store(
+        Compress(value), std::memory_order_relaxed);
+  }
+
+  V8_INLINE void Clear() { value_ = 0u; }
+  V8_INLINE bool IsCleared() const { return !value_; }
+
+  V8_INLINE bool IsSentinel() const { return value_ == kCompressedSentinel; }
+
+  V8_INLINE uint32_t GetAsInteger() const { return value_; }
+
+  V8_INLINE friend bool operator==(CompressedPointer a, CompressedPointer b) {
+    return a.value_ == b.value_;
+  }
+  V8_INLINE friend bool operator!=(CompressedPointer a, CompressedPointer b) {
+    return a.value_ != b.value_;
+  }
+  V8_INLINE friend bool operator<(CompressedPointer a, CompressedPointer b) {
+    return a.value_ < b.value_;
+  }
+  V8_INLINE friend bool operator<=(CompressedPointer a, CompressedPointer b) {
+    return a.value_ <= b.value_;
+  }
+  V8_INLINE friend bool operator>(CompressedPointer a, CompressedPointer b) {
+    return a.value_ > b.value_;
+  }
+  V8_INLINE friend bool operator>=(CompressedPointer a, CompressedPointer b) {
+    return a.value_ >= b.value_;
+  }
+
+  static V8_INLINE IntegralType Compress(const void* ptr) {
+    static_assert(
+        SentinelPointer::kSentinelValue == 0b10,
+        "The compression scheme relies on the sentinel encoded as 0b10");
+    static constexpr size_t kGigaCageMask =
+        ~(api_constants::kCagedHeapReservationAlignment - 1);
+
+    CPPGC_DCHECK(CageBaseGlobal::IsSet());
+    const uintptr_t base = CageBaseGlobal::Get();
+    CPPGC_DCHECK(!ptr || ptr == kSentinelPointer ||
+                 (base & kGigaCageMask) ==
+                     (reinterpret_cast<uintptr_t>(ptr) & kGigaCageMask));
+
+#if defined(CPPGC_2GB_CAGE)
+    // Truncate the pointer.
+    auto compressed =
+        static_cast<IntegralType>(reinterpret_cast<uintptr_t>(ptr));
+#else   // !defined(CPPGC_2GB_CAGE)
+    const auto uptr = reinterpret_cast<uintptr_t>(ptr);
+    // Shift the pointer by one and truncate.
+    auto compressed = static_cast<IntegralType>(uptr >> 1);
+#endif  // !defined(CPPGC_2GB_CAGE)
+    // Normal compressed pointers must have the MSB set.
+    CPPGC_DCHECK((!compressed || compressed == kCompressedSentinel) ||
+                 (compressed & (1 << 31)));
+    return compressed;
+  }
+
+  static V8_INLINE void* Decompress(IntegralType ptr) {
+    CPPGC_DCHECK(CageBaseGlobal::IsSet());
+    const uintptr_t base = CageBaseGlobal::Get();
+    // Treat compressed pointer as signed and cast it to uint64_t, which will
+    // sign-extend it.
+#if defined(CPPGC_2GB_CAGE)
+    const uint64_t mask = static_cast<uint64_t>(static_cast<int32_t>(ptr));
+#else   // !defined(CPPGC_2GB_CAGE)
+    // Then, shift the result by one. It's important to shift the unsigned
+    // value, as otherwise it would result in undefined behavior.
+    const uint64_t mask = static_cast<uint64_t>(static_cast<int32_t>(ptr)) << 1;
+#endif  // !defined(CPPGC_2GB_CAGE)
+    return reinterpret_cast<void*>(mask & base);
+  }
+
+ private:
+#if defined(CPPGC_2GB_CAGE)
+  static constexpr IntegralType kCompressedSentinel =
+      SentinelPointer::kSentinelValue;
+#else   // !defined(CPPGC_2GB_CAGE)
+  static constexpr IntegralType kCompressedSentinel =
+      SentinelPointer::kSentinelValue >> 1;
+#endif  // !defined(CPPGC_2GB_CAGE)
+  // All constructors initialize `value_`. Do not add a default value here as it
+  // results in a non-atomic write on some builds, even when the atomic version
+  // of the constructor is used.
+  IntegralType value_;
+};
+
+#endif  // defined(CPPGC_POINTER_COMPRESSION)
+
+class V8_TRIVIAL_ABI RawPointer final {
+ public:
+  using IntegralType = uintptr_t;
+
+  V8_INLINE RawPointer() : ptr_(nullptr) {}
+  V8_INLINE explicit RawPointer(const void* ptr) : ptr_(ptr) {}
+
+  V8_INLINE const void* Load() const { return ptr_; }
+  V8_INLINE const void* LoadAtomic() const {
+    return reinterpret_cast<const std::atomic<const void*>&>(ptr_).load(
+        std::memory_order_relaxed);
+  }
+
+  V8_INLINE void Store(const void* ptr) { ptr_ = ptr; }
+  V8_INLINE void StoreAtomic(const void* ptr) {
+    reinterpret_cast<std::atomic<const void*>&>(ptr_).store(
+        ptr, std::memory_order_relaxed);
+  }
+
+  V8_INLINE void Clear() { ptr_ = nullptr; }
+  V8_INLINE bool IsCleared() const { return !ptr_; }
+
+  V8_INLINE bool IsSentinel() const { return ptr_ == kSentinelPointer; }
+
+  V8_INLINE uintptr_t GetAsInteger() const {
+    return reinterpret_cast<uintptr_t>(ptr_);
+  }
+
+  V8_INLINE friend bool operator==(RawPointer a, RawPointer b) {
+    return a.ptr_ == b.ptr_;
+  }
+  V8_INLINE friend bool operator!=(RawPointer a, RawPointer b) {
+    return a.ptr_ != b.ptr_;
+  }
+  V8_INLINE friend bool operator<(RawPointer a, RawPointer b) {
+    return a.ptr_ < b.ptr_;
+  }
+  V8_INLINE friend bool operator<=(RawPointer a, RawPointer b) {
+    return a.ptr_ <= b.ptr_;
+  }
+  V8_INLINE friend bool operator>(RawPointer a, RawPointer b) {
+    return a.ptr_ > b.ptr_;
+  }
+  V8_INLINE friend bool operator>=(RawPointer a, RawPointer b) {
+    return a.ptr_ >= b.ptr_;
+  }
+
+ private:
+  // All constructors initialize `ptr_`. Do not add a default value here as it
+  // results in a non-atomic write on some builds, even when the atomic version
+  // of the constructor is used.
+  const void* ptr_;
+};
+
+#if defined(CPPGC_POINTER_COMPRESSION)
+using MemberStorage = CompressedPointer;
+#else   // !defined(CPPGC_POINTER_COMPRESSION)
+using MemberStorage = RawPointer;
+#endif  // !defined(CPPGC_POINTER_COMPRESSION)
+
+}  // namespace internal
+}  // namespace cppgc
+
+#endif  // INCLUDE_CPPGC_INTERNAL_MEMBER_STORAGE_H_

v8/include/cppgc/internal/name-trait.h

@@ -0,0 +1,137 @@
+// Copyright 2020 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 INCLUDE_CPPGC_INTERNAL_NAME_TRAIT_H_
+#define INCLUDE_CPPGC_INTERNAL_NAME_TRAIT_H_
+
+#include <cstddef>
+#include <cstdint>
+#include <type_traits>
+
+#include "cppgc/name-provider.h"
+#include "v8config.h"  // NOLINT(build/include_directory)
+
+namespace cppgc {
+namespace internal {
+
+#if CPPGC_SUPPORTS_OBJECT_NAMES && defined(__clang__)
+#define CPPGC_SUPPORTS_COMPILE_TIME_TYPENAME 1
+
+// Provides constexpr c-string storage for a name of fixed |Size| characters.
+// Automatically appends terminating 0 byte.
+template <size_t Size>
+struct NameBuffer {
+  char name[Size + 1]{};
+
+  static constexpr NameBuffer FromCString(const char* str) {
+    NameBuffer result;
+    for (size_t i = 0; i < Size; ++i) result.name[i] = str[i];
+    result.name[Size] = 0;
+    return result;
+  }
+};
+
+template <typename T>
+const char* GetTypename() {
+  static constexpr char kSelfPrefix[] =
+      "const char *cppgc::internal::GetTypename() [T =";
+  static_assert(__builtin_strncmp(__PRETTY_FUNCTION__, kSelfPrefix,
+                                  sizeof(kSelfPrefix) - 1) == 0,
+                "The prefix must match");
+  static constexpr const char* kTypenameStart =
+      __PRETTY_FUNCTION__ + sizeof(kSelfPrefix);
+  static constexpr size_t kTypenameSize =
+      __builtin_strlen(__PRETTY_FUNCTION__) - sizeof(kSelfPrefix) - 1;
+  // NameBuffer is an indirection that is needed to make sure that only a
+  // substring of __PRETTY_FUNCTION__ gets materialized in the binary.
+  static constexpr auto buffer =
+      NameBuffer<kTypenameSize>::FromCString(kTypenameStart);
+  return buffer.name;
+}
+
+#else
+#define CPPGC_SUPPORTS_COMPILE_TIME_TYPENAME 0
+#endif
+
+struct HeapObjectName {
+  const char* value;
+  bool name_was_hidden;
+};
+
+enum class HeapObjectNameForUnnamedObject : uint8_t {
+  kUseClassNameIfSupported,
+  kUseHiddenName,
+};
+
+class V8_EXPORT NameTraitBase {
+ protected:
+  static HeapObjectName GetNameFromTypeSignature(const char*);
+};
+
+// Trait that specifies how the garbage collector retrieves the name for a
+// given object.
+template <typename T>
+class NameTrait final : public NameTraitBase {
+ public:
+  static constexpr bool HasNonHiddenName() {
+#if CPPGC_SUPPORTS_COMPILE_TIME_TYPENAME
+    return true;
+#elif CPPGC_SUPPORTS_OBJECT_NAMES
+    return true;
+#else   // !CPPGC_SUPPORTS_OBJECT_NAMES
+    return std::is_base_of<NameProvider, T>::value;
+#endif  // !CPPGC_SUPPORTS_OBJECT_NAMES
+  }
+
+  static HeapObjectName GetName(
+      const void* obj, HeapObjectNameForUnnamedObject name_retrieval_mode) {
+    return GetNameFor(static_cast<const T*>(obj), name_retrieval_mode);
+  }
+
+ private:
+  static HeapObjectName GetNameFor(const NameProvider* name_provider,
+                                   HeapObjectNameForUnnamedObject) {
+    // Objects inheriting from `NameProvider` are not considered unnamed as
+    // users already provided a name for them.
+    return {name_provider->GetHumanReadableName(), false};
+  }
+
+  static HeapObjectName GetNameFor(
+      const void*, HeapObjectNameForUnnamedObject name_retrieval_mode) {
+    if (name_retrieval_mode == HeapObjectNameForUnnamedObject::kUseHiddenName)
+      return {NameProvider::kHiddenName, true};
+
+#if CPPGC_SUPPORTS_COMPILE_TIME_TYPENAME
+    return {GetTypename<T>(), false};
+#elif CPPGC_SUPPORTS_OBJECT_NAMES
+
+#if defined(V8_CC_GNU)
+#define PRETTY_FUNCTION_VALUE __PRETTY_FUNCTION__
+#elif defined(V8_CC_MSVC)
+#define PRETTY_FUNCTION_VALUE __FUNCSIG__
+#else
+#define PRETTY_FUNCTION_VALUE nullptr
+#endif
+
+    static const HeapObjectName leaky_name =
+        GetNameFromTypeSignature(PRETTY_FUNCTION_VALUE);
+    return leaky_name;
+
+#undef PRETTY_FUNCTION_VALUE
+
+#else   // !CPPGC_SUPPORTS_OBJECT_NAMES
+    return {NameProvider::kHiddenName, true};
+#endif  // !CPPGC_SUPPORTS_OBJECT_NAMES
+  }
+};
+
+using NameCallback = HeapObjectName (*)(const void*,
+                                        HeapObjectNameForUnnamedObject);
+
+}  // namespace internal
+}  // namespace cppgc
+
+#undef CPPGC_SUPPORTS_COMPILE_TIME_TYPENAME
+
+#endif  // INCLUDE_CPPGC_INTERNAL_NAME_TRAIT_H_

v8/include/cppgc/internal/persistent-node.h

@@ -0,0 +1,214 @@
+// Copyright 2020 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 INCLUDE_CPPGC_INTERNAL_PERSISTENT_NODE_H_
+#define INCLUDE_CPPGC_INTERNAL_PERSISTENT_NODE_H_
+
+#include <array>
+#include <memory>
+#include <vector>
+
+#include "cppgc/internal/logging.h"
+#include "cppgc/trace-trait.h"
+#include "v8config.h"  // NOLINT(build/include_directory)
+
+namespace cppgc {
+namespace internal {
+
+class CrossThreadPersistentRegion;
+class FatalOutOfMemoryHandler;
+class RootVisitor;
+
+// PersistentNode represents a variant of two states:
+// 1) traceable node with a back pointer to the Persistent object;
+// 2) freelist entry.
+class PersistentNode final {
+ public:
+  PersistentNode() = default;
+
+  PersistentNode(const PersistentNode&) = delete;
+  PersistentNode& operator=(const PersistentNode&) = delete;
+
+  void InitializeAsUsedNode(void* owner, TraceRootCallback trace) {
+    CPPGC_DCHECK(trace);
+    owner_ = owner;
+    trace_ = trace;
+  }
+
+  void InitializeAsFreeNode(PersistentNode* next) {
+    next_ = next;
+    trace_ = nullptr;
+  }
+
+  void UpdateOwner(void* owner) {
+    CPPGC_DCHECK(IsUsed());
+    owner_ = owner;
+  }
+
+  PersistentNode* FreeListNext() const {
+    CPPGC_DCHECK(!IsUsed());
+    return next_;
+  }
+
+  void Trace(RootVisitor& root_visitor) const {
+    CPPGC_DCHECK(IsUsed());
+    trace_(root_visitor, owner_);
+  }
+
+  bool IsUsed() const { return trace_; }
+
+  void* owner() const {
+    CPPGC_DCHECK(IsUsed());
+    return owner_;
+  }
+
+ private:
+  // PersistentNode acts as a designated union:
+  // If trace_ != nullptr, owner_ points to the corresponding Persistent handle.
+  // Otherwise, next_ points to the next freed PersistentNode.
+  union {
+    void* owner_ = nullptr;
+    PersistentNode* next_;
+  };
+  TraceRootCallback trace_ = nullptr;
+};
+
+class V8_EXPORT PersistentRegionBase {
+  using PersistentNodeSlots = std::array<PersistentNode, 256u>;
+
+ public:
+  // Clears Persistent fields to avoid stale pointers after heap teardown.
+  ~PersistentRegionBase();
+
+  PersistentRegionBase(const PersistentRegionBase&) = delete;
+  PersistentRegionBase& operator=(const PersistentRegionBase&) = delete;
+
+  void Iterate(RootVisitor&);
+
+  size_t NodesInUse() const;
+
+  void ClearAllUsedNodes();
+
+ protected:
+  explicit PersistentRegionBase(const FatalOutOfMemoryHandler& oom_handler);
+
+  PersistentNode* TryAllocateNodeFromFreeList(void* owner,
+                                              TraceRootCallback trace) {
+    PersistentNode* node = nullptr;
+    if (V8_LIKELY(free_list_head_)) {
+      node = free_list_head_;
+      free_list_head_ = free_list_head_->FreeListNext();
+      CPPGC_DCHECK(!node->IsUsed());
+      node->InitializeAsUsedNode(owner, trace);
+      nodes_in_use_++;
+    }
+    return node;
+  }
+
+  void FreeNode(PersistentNode* node) {
+    CPPGC_DCHECK(node);
+    CPPGC_DCHECK(node->IsUsed());
+    node->InitializeAsFreeNode(free_list_head_);
+    free_list_head_ = node;
+    CPPGC_DCHECK(nodes_in_use_ > 0);
+    nodes_in_use_--;
+  }
+
+  PersistentNode* RefillFreeListAndAllocateNode(void* owner,
+                                                TraceRootCallback trace);
+
+ private:
+  template <typename PersistentBaseClass>
+  void ClearAllUsedNodes();
+
+  void RefillFreeList();
+
+  std::vector<std::unique_ptr<PersistentNodeSlots>> nodes_;
+  PersistentNode* free_list_head_ = nullptr;
+  size_t nodes_in_use_ = 0;
+  const FatalOutOfMemoryHandler& oom_handler_;
+
+  friend class CrossThreadPersistentRegion;
+};
+
+// Variant of PersistentRegionBase that checks whether the allocation and
+// freeing happens only on the thread that created the region.
+class V8_EXPORT PersistentRegion final : public PersistentRegionBase {
+ public:
+  explicit PersistentRegion(const FatalOutOfMemoryHandler&);
+  // Clears Persistent fields to avoid stale pointers after heap teardown.
+  ~PersistentRegion() = default;
+
+  PersistentRegion(const PersistentRegion&) = delete;
+  PersistentRegion& operator=(const PersistentRegion&) = delete;
+
+  V8_INLINE PersistentNode* AllocateNode(void* owner, TraceRootCallback trace) {
+    CPPGC_DCHECK(IsCreationThread());
+    auto* node = TryAllocateNodeFromFreeList(owner, trace);
+    if (V8_LIKELY(node)) return node;
+
+    // Slow path allocation allows for checking thread correspondence.
+    CPPGC_CHECK(IsCreationThread());
+    return RefillFreeListAndAllocateNode(owner, trace);
+  }
+
+  V8_INLINE void FreeNode(PersistentNode* node) {
+    CPPGC_DCHECK(IsCreationThread());
+    PersistentRegionBase::FreeNode(node);
+  }
+
+ private:
+  bool IsCreationThread();
+
+  int creation_thread_id_;
+};
+
+// CrossThreadPersistent uses PersistentRegionBase but protects it using this
+// lock when needed.
+class V8_EXPORT PersistentRegionLock final {
+ public:
+  PersistentRegionLock();
+  ~PersistentRegionLock();
+
+  static void AssertLocked();
+};
+
+// Variant of PersistentRegionBase that checks whether the PersistentRegionLock
+// is locked.
+class V8_EXPORT CrossThreadPersistentRegion final
+    : protected PersistentRegionBase {
+ public:
+  explicit CrossThreadPersistentRegion(const FatalOutOfMemoryHandler&);
+  // Clears Persistent fields to avoid stale pointers after heap teardown.
+  ~CrossThreadPersistentRegion();
+
+  CrossThreadPersistentRegion(const CrossThreadPersistentRegion&) = delete;
+  CrossThreadPersistentRegion& operator=(const CrossThreadPersistentRegion&) =
+      delete;
+
+  V8_INLINE PersistentNode* AllocateNode(void* owner, TraceRootCallback trace) {
+    PersistentRegionLock::AssertLocked();
+    auto* node = TryAllocateNodeFromFreeList(owner, trace);
+    if (V8_LIKELY(node)) return node;
+
+    return RefillFreeListAndAllocateNode(owner, trace);
+  }
+
+  V8_INLINE void FreeNode(PersistentNode* node) {
+    PersistentRegionLock::AssertLocked();
+    PersistentRegionBase::FreeNode(node);
+  }
+
+  void Iterate(RootVisitor&);
+
+  size_t NodesInUse() const;
+
+  void ClearAllUsedNodes();
+};
+
+}  // namespace internal
+
+}  // namespace cppgc
+
+#endif  // INCLUDE_CPPGC_INTERNAL_PERSISTENT_NODE_H_

v8/include/cppgc/internal/pointer-policies.h

@@ -0,0 +1,207 @@
+// Copyright 2020 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 INCLUDE_CPPGC_INTERNAL_POINTER_POLICIES_H_
+#define INCLUDE_CPPGC_INTERNAL_POINTER_POLICIES_H_
+
+#include <cstdint>
+#include <type_traits>
+
+#include "cppgc/internal/member-storage.h"
+#include "cppgc/internal/write-barrier.h"
+#include "cppgc/sentinel-pointer.h"
+#include "cppgc/source-location.h"
+#include "cppgc/type-traits.h"
+#include "v8config.h"  // NOLINT(build/include_directory)
+
+namespace cppgc {
+namespace internal {
+
+class HeapBase;
+class PersistentRegion;
+class CrossThreadPersistentRegion;
+
+// Tags to distinguish between strong and weak member types.
+class StrongMemberTag;
+class WeakMemberTag;
+class UntracedMemberTag;
+
+struct DijkstraWriteBarrierPolicy {
+  V8_INLINE static void InitializingBarrier(const void*, const void*) {
+    // Since in initializing writes the source object is always white, having no
+    // barrier doesn't break the tri-color invariant.
+  }
+
+  V8_INLINE static void AssigningBarrier(const void* slot, const void* value) {
+    WriteBarrier::Params params;
+    const WriteBarrier::Type type =
+        WriteBarrier::GetWriteBarrierType(slot, value, params);
+    WriteBarrier(type, params, slot, value);
+  }
+
+  V8_INLINE static void AssigningBarrier(const void* slot,
+                                         MemberStorage storage) {
+    WriteBarrier::Params params;
+    const WriteBarrier::Type type =
+        WriteBarrier::GetWriteBarrierType(slot, storage, params);
+    WriteBarrier(type, params, slot, storage.Load());
+  }
+
+ private:
+  V8_INLINE static void WriteBarrier(WriteBarrier::Type type,
+                                     const WriteBarrier::Params& params,
+                                     const void* slot, const void* value) {
+    switch (type) {
+      case WriteBarrier::Type::kGenerational:
+        WriteBarrier::GenerationalBarrier<
+            WriteBarrier::GenerationalBarrierType::kPreciseSlot>(params, slot);
+        break;
+      case WriteBarrier::Type::kMarking:
+        WriteBarrier::DijkstraMarkingBarrier(params, value);
+        break;
+      case WriteBarrier::Type::kNone:
+        break;
+    }
+  }
+};
+
+struct NoWriteBarrierPolicy {
+  V8_INLINE static void InitializingBarrier(const void*, const void*) {}
+  V8_INLINE static void AssigningBarrier(const void*, const void*) {}
+  V8_INLINE static void AssigningBarrier(const void*, MemberStorage) {}
+};
+
+class V8_EXPORT SameThreadEnabledCheckingPolicyBase {
+ protected:
+  void CheckPointerImpl(const void* ptr, bool points_to_payload,
+                        bool check_off_heap_assignments);
+
+  const HeapBase* heap_ = nullptr;
+};
+
+template <bool kCheckOffHeapAssignments>
+class V8_EXPORT SameThreadEnabledCheckingPolicy
+    : private SameThreadEnabledCheckingPolicyBase {
+ protected:
+  template <typename T>
+  void CheckPointer(const T* ptr) {
+    if (!ptr || (kSentinelPointer == ptr)) return;
+
+    CheckPointersImplTrampoline<T>::Call(this, ptr);
+  }
+
+ private:
+  template <typename T, bool = IsCompleteV<T>>
+  struct CheckPointersImplTrampoline {
+    static void Call(SameThreadEnabledCheckingPolicy* policy, const T* ptr) {
+      policy->CheckPointerImpl(ptr, false, kCheckOffHeapAssignments);
+    }
+  };
+
+  template <typename T>
+  struct CheckPointersImplTrampoline<T, true> {
+    static void Call(SameThreadEnabledCheckingPolicy* policy, const T* ptr) {
+      policy->CheckPointerImpl(ptr, IsGarbageCollectedTypeV<T>,
+                               kCheckOffHeapAssignments);
+    }
+  };
+};
+
+class DisabledCheckingPolicy {
+ protected:
+  V8_INLINE void CheckPointer(const void*) {}
+};
+
+#ifdef DEBUG
+// Off heap members are not connected to object graph and thus cannot ressurect
+// dead objects.
+using DefaultMemberCheckingPolicy =
+    SameThreadEnabledCheckingPolicy<false /* kCheckOffHeapAssignments*/>;
+using DefaultPersistentCheckingPolicy =
+    SameThreadEnabledCheckingPolicy<true /* kCheckOffHeapAssignments*/>;
+#else   // !DEBUG
+using DefaultMemberCheckingPolicy = DisabledCheckingPolicy;
+using DefaultPersistentCheckingPolicy = DisabledCheckingPolicy;
+#endif  // !DEBUG
+// For CT(W)P neither marking information (for value), nor objectstart bitmap
+// (for slot) are guaranteed to be present because there's no synchronization
+// between heaps after marking.
+using DefaultCrossThreadPersistentCheckingPolicy = DisabledCheckingPolicy;
+
+class KeepLocationPolicy {
+ public:
+  constexpr const SourceLocation& Location() const { return location_; }
+
+ protected:
+  constexpr KeepLocationPolicy() = default;
+  constexpr explicit KeepLocationPolicy(const SourceLocation& location)
+      : location_(location) {}
+
+  // KeepLocationPolicy must not copy underlying source locations.
+  KeepLocationPolicy(const KeepLocationPolicy&) = delete;
+  KeepLocationPolicy& operator=(const KeepLocationPolicy&) = delete;
+
+  // Location of the original moved from object should be preserved.
+  KeepLocationPolicy(KeepLocationPolicy&&) = default;
+  KeepLocationPolicy& operator=(KeepLocationPolicy&&) = default;
+
+ private:
+  SourceLocation location_;
+};
+
+class IgnoreLocationPolicy {
+ public:
+  constexpr SourceLocation Location() const { return {}; }
+
+ protected:
+  constexpr IgnoreLocationPolicy() = default;
+  constexpr explicit IgnoreLocationPolicy(const SourceLocation&) {}
+};
+
+#if CPPGC_SUPPORTS_OBJECT_NAMES
+using DefaultLocationPolicy = KeepLocationPolicy;
+#else
+using DefaultLocationPolicy = IgnoreLocationPolicy;
+#endif
+
+struct StrongPersistentPolicy {
+  using IsStrongPersistent = std::true_type;
+  static V8_EXPORT PersistentRegion& GetPersistentRegion(const void* object);
+};
+
+struct WeakPersistentPolicy {
+  using IsStrongPersistent = std::false_type;
+  static V8_EXPORT PersistentRegion& GetPersistentRegion(const void* object);
+};
+
+struct StrongCrossThreadPersistentPolicy {
+  using IsStrongPersistent = std::true_type;
+  static V8_EXPORT CrossThreadPersistentRegion& GetPersistentRegion(
+      const void* object);
+};
+
+struct WeakCrossThreadPersistentPolicy {
+  using IsStrongPersistent = std::false_type;
+  static V8_EXPORT CrossThreadPersistentRegion& GetPersistentRegion(
+      const void* object);
+};
+
+// Forward declarations setting up the default policies.
+template <typename T, typename WeaknessPolicy,
+          typename LocationPolicy = DefaultLocationPolicy,
+          typename CheckingPolicy = DefaultCrossThreadPersistentCheckingPolicy>
+class BasicCrossThreadPersistent;
+template <typename T, typename WeaknessPolicy,
+          typename LocationPolicy = DefaultLocationPolicy,
+          typename CheckingPolicy = DefaultPersistentCheckingPolicy>
+class BasicPersistent;
+template <typename T, typename WeaknessTag, typename WriteBarrierPolicy,
+          typename CheckingPolicy = DefaultMemberCheckingPolicy>
+class BasicMember;
+
+}  // namespace internal
+
+}  // namespace cppgc
+
+#endif  // INCLUDE_CPPGC_INTERNAL_POINTER_POLICIES_H_

v8/include/cppgc/internal/write-barrier.h

@@ -0,0 +1,477 @@
+// Copyright 2020 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 INCLUDE_CPPGC_INTERNAL_WRITE_BARRIER_H_
+#define INCLUDE_CPPGC_INTERNAL_WRITE_BARRIER_H_
+
+#include <cstddef>
+#include <cstdint>
+
+#include "cppgc/heap-handle.h"
+#include "cppgc/heap-state.h"
+#include "cppgc/internal/api-constants.h"
+#include "cppgc/internal/atomic-entry-flag.h"
+#include "cppgc/internal/base-page-handle.h"
+#include "cppgc/internal/member-storage.h"
+#include "cppgc/platform.h"
+#include "cppgc/sentinel-pointer.h"
+#include "cppgc/trace-trait.h"
+#include "v8config.h"  // NOLINT(build/include_directory)
+
+#if defined(CPPGC_CAGED_HEAP)
+#include "cppgc/internal/caged-heap-local-data.h"
+#include "cppgc/internal/caged-heap.h"
+#endif
+
+namespace cppgc {
+
+class HeapHandle;
+
+namespace internal {
+
+#if defined(CPPGC_CAGED_HEAP)
+class WriteBarrierTypeForCagedHeapPolicy;
+#else   // !CPPGC_CAGED_HEAP
+class WriteBarrierTypeForNonCagedHeapPolicy;
+#endif  // !CPPGC_CAGED_HEAP
+
+class V8_EXPORT WriteBarrier final {
+ public:
+  enum class Type : uint8_t {
+    kNone,
+    kMarking,
+    kGenerational,
+  };
+
+  enum class GenerationalBarrierType : uint8_t {
+    kPreciseSlot,
+    kPreciseUncompressedSlot,
+    kImpreciseSlot,
+  };
+
+  struct Params {
+    HeapHandle* heap = nullptr;
+#if V8_ENABLE_CHECKS
+    Type type = Type::kNone;
+#endif  // !V8_ENABLE_CHECKS
+#if defined(CPPGC_CAGED_HEAP)
+    uintptr_t slot_offset = 0;
+    uintptr_t value_offset = 0;
+#endif  // CPPGC_CAGED_HEAP
+  };
+
+  enum class ValueMode {
+    kValuePresent,
+    kNoValuePresent,
+  };
+
+  // Returns the required write barrier for a given `slot` and `value`.
+  static V8_INLINE Type GetWriteBarrierType(const void* slot, const void* value,
+                                            Params& params);
+  // Returns the required write barrier for a given `slot` and `value`.
+  static V8_INLINE Type GetWriteBarrierType(const void* slot, MemberStorage,
+                                            Params& params);
+  // Returns the required write barrier for a given `slot`.
+  template <typename HeapHandleCallback>
+  static V8_INLINE Type GetWriteBarrierType(const void* slot, Params& params,
+                                            HeapHandleCallback callback);
+  // Returns the required write barrier for a given  `value`.
+  static V8_INLINE Type GetWriteBarrierType(const void* value, Params& params);
+
+  static V8_INLINE void DijkstraMarkingBarrier(const Params& params,
+                                               const void* object);
+  static V8_INLINE void DijkstraMarkingBarrierRange(
+      const Params& params, const void* first_element, size_t element_size,
+      size_t number_of_elements, TraceCallback trace_callback);
+  static V8_INLINE void SteeleMarkingBarrier(const Params& params,
+                                             const void* object);
+#if defined(CPPGC_YOUNG_GENERATION)
+  template <GenerationalBarrierType>
+  static V8_INLINE void GenerationalBarrier(const Params& params,
+                                            const void* slot);
+#else  // !CPPGC_YOUNG_GENERATION
+  template <GenerationalBarrierType>
+  static V8_INLINE void GenerationalBarrier(const Params& params,
+                                            const void* slot){}
+#endif  // CPPGC_YOUNG_GENERATION
+
+#if V8_ENABLE_CHECKS
+  static void CheckParams(Type expected_type, const Params& params);
+#else   // !V8_ENABLE_CHECKS
+  static void CheckParams(Type expected_type, const Params& params) {}
+#endif  // !V8_ENABLE_CHECKS
+
+  // The FlagUpdater class allows cppgc internal to update
+  // |write_barrier_enabled_|.
+  class FlagUpdater;
+  static bool IsEnabled() { return write_barrier_enabled_.MightBeEntered(); }
+
+ private:
+  WriteBarrier() = delete;
+
+#if defined(CPPGC_CAGED_HEAP)
+  using WriteBarrierTypePolicy = WriteBarrierTypeForCagedHeapPolicy;
+#else   // !CPPGC_CAGED_HEAP
+  using WriteBarrierTypePolicy = WriteBarrierTypeForNonCagedHeapPolicy;
+#endif  // !CPPGC_CAGED_HEAP
+
+  static void DijkstraMarkingBarrierSlow(const void* value);
+  static void DijkstraMarkingBarrierSlowWithSentinelCheck(const void* value);
+  static void DijkstraMarkingBarrierRangeSlow(HeapHandle& heap_handle,
+                                              const void* first_element,
+                                              size_t element_size,
+                                              size_t number_of_elements,
+                                              TraceCallback trace_callback);
+  static void SteeleMarkingBarrierSlow(const void* value);
+  static void SteeleMarkingBarrierSlowWithSentinelCheck(const void* value);
+
+#if defined(CPPGC_YOUNG_GENERATION)
+  static CagedHeapLocalData& GetLocalData(HeapHandle&);
+  static void GenerationalBarrierSlow(const CagedHeapLocalData& local_data,
+                                      const AgeTable& age_table,
+                                      const void* slot, uintptr_t value_offset,
+                                      HeapHandle* heap_handle);
+  static void GenerationalBarrierForUncompressedSlotSlow(
+      const CagedHeapLocalData& local_data, const AgeTable& age_table,
+      const void* slot, uintptr_t value_offset, HeapHandle* heap_handle);
+  static void GenerationalBarrierForSourceObjectSlow(
+      const CagedHeapLocalData& local_data, const void* object,
+      HeapHandle* heap_handle);
+#endif  // CPPGC_YOUNG_GENERATION
+
+  static AtomicEntryFlag write_barrier_enabled_;
+};
+
+template <WriteBarrier::Type type>
+V8_INLINE WriteBarrier::Type SetAndReturnType(WriteBarrier::Params& params) {
+  if constexpr (type == WriteBarrier::Type::kNone)
+    return WriteBarrier::Type::kNone;
+#if V8_ENABLE_CHECKS
+  params.type = type;
+#endif  // !V8_ENABLE_CHECKS
+  return type;
+}
+
+#if defined(CPPGC_CAGED_HEAP)
+class V8_EXPORT WriteBarrierTypeForCagedHeapPolicy final {
+ public:
+  template <WriteBarrier::ValueMode value_mode, typename HeapHandleCallback>
+  static V8_INLINE WriteBarrier::Type Get(const void* slot, const void* value,
+                                          WriteBarrier::Params& params,
+                                          HeapHandleCallback callback) {
+    return ValueModeDispatch<value_mode>::Get(slot, value, params, callback);
+  }
+
+  template <WriteBarrier::ValueMode value_mode, typename HeapHandleCallback>
+  static V8_INLINE WriteBarrier::Type Get(const void* slot, MemberStorage value,
+                                          WriteBarrier::Params& params,
+                                          HeapHandleCallback callback) {
+    return ValueModeDispatch<value_mode>::Get(slot, value, params, callback);
+  }
+
+  template <WriteBarrier::ValueMode value_mode, typename HeapHandleCallback>
+  static V8_INLINE WriteBarrier::Type Get(const void* value,
+                                          WriteBarrier::Params& params,
+                                          HeapHandleCallback callback) {
+    return GetNoSlot(value, params, callback);
+  }
+
+ private:
+  WriteBarrierTypeForCagedHeapPolicy() = delete;
+
+  template <typename HeapHandleCallback>
+  static V8_INLINE WriteBarrier::Type GetNoSlot(const void* value,
+                                                WriteBarrier::Params& params,
+                                                HeapHandleCallback) {
+    const bool within_cage = CagedHeapBase::IsWithinCage(value);
+    if (!within_cage) return WriteBarrier::Type::kNone;
+
+    // We know that |value| points either within the normal page or to the
+    // beginning of large-page, so extract the page header by bitmasking.
+    BasePageHandle* page =
+        BasePageHandle::FromPayload(const_cast<void*>(value));
+
+    HeapHandle& heap_handle = page->heap_handle();
+    if (V8_UNLIKELY(heap_handle.is_incremental_marking_in_progress())) {
+      return SetAndReturnType<WriteBarrier::Type::kMarking>(params);
+    }
+
+    return SetAndReturnType<WriteBarrier::Type::kNone>(params);
+  }
+
+  template <WriteBarrier::ValueMode value_mode>
+  struct ValueModeDispatch;
+};
+
+template <>
+struct WriteBarrierTypeForCagedHeapPolicy::ValueModeDispatch<
+    WriteBarrier::ValueMode::kValuePresent> {
+  template <typename HeapHandleCallback>
+  static V8_INLINE WriteBarrier::Type Get(const void* slot,
+                                          MemberStorage storage,
+                                          WriteBarrier::Params& params,
+                                          HeapHandleCallback) {
+    if (V8_LIKELY(!WriteBarrier::IsEnabled()))
+      return SetAndReturnType<WriteBarrier::Type::kNone>(params);
+
+    return BarrierEnabledGet(slot, storage.Load(), params);
+  }
+
+  template <typename HeapHandleCallback>
+  static V8_INLINE WriteBarrier::Type Get(const void* slot, const void* value,
+                                          WriteBarrier::Params& params,
+                                          HeapHandleCallback) {
+    if (V8_LIKELY(!WriteBarrier::IsEnabled()))
+      return SetAndReturnType<WriteBarrier::Type::kNone>(params);
+
+    return BarrierEnabledGet(slot, value, params);
+  }
+
+ private:
+  static V8_INLINE WriteBarrier::Type BarrierEnabledGet(
+      const void* slot, const void* value, WriteBarrier::Params& params) {
+    const bool within_cage = CagedHeapBase::AreWithinCage(slot, value);
+    if (!within_cage) return WriteBarrier::Type::kNone;
+
+    // We know that |value| points either within the normal page or to the
+    // beginning of large-page, so extract the page header by bitmasking.
+    BasePageHandle* page =
+        BasePageHandle::FromPayload(const_cast<void*>(value));
+
+    HeapHandle& heap_handle = page->heap_handle();
+    if (V8_LIKELY(!heap_handle.is_incremental_marking_in_progress())) {
+#if defined(CPPGC_YOUNG_GENERATION)
+      if (!heap_handle.is_young_generation_enabled())
+        return WriteBarrier::Type::kNone;
+      params.heap = &heap_handle;
+      params.slot_offset = CagedHeapBase::OffsetFromAddress(slot);
+      params.value_offset = CagedHeapBase::OffsetFromAddress(value);
+      return SetAndReturnType<WriteBarrier::Type::kGenerational>(params);
+#else   // !CPPGC_YOUNG_GENERATION
+      return SetAndReturnType<WriteBarrier::Type::kNone>(params);
+#endif  // !CPPGC_YOUNG_GENERATION
+    }
+
+    // Use marking barrier.
+    params.heap = &heap_handle;
+    return SetAndReturnType<WriteBarrier::Type::kMarking>(params);
+  }
+};
+
+template <>
+struct WriteBarrierTypeForCagedHeapPolicy::ValueModeDispatch<
+    WriteBarrier::ValueMode::kNoValuePresent> {
+  template <typename HeapHandleCallback>
+  static V8_INLINE WriteBarrier::Type Get(const void* slot, const void*,
+                                          WriteBarrier::Params& params,
+                                          HeapHandleCallback callback) {
+    if (V8_LIKELY(!WriteBarrier::IsEnabled()))
+      return SetAndReturnType<WriteBarrier::Type::kNone>(params);
+
+    HeapHandle& handle = callback();
+#if defined(CPPGC_YOUNG_GENERATION)
+    if (V8_LIKELY(!handle.is_incremental_marking_in_progress())) {
+      if (!handle.is_young_generation_enabled()) {
+        return WriteBarrier::Type::kNone;
+      }
+      params.heap = &handle;
+      // Check if slot is on stack.
+      if (V8_UNLIKELY(!CagedHeapBase::IsWithinCage(slot))) {
+        return SetAndReturnType<WriteBarrier::Type::kNone>(params);
+      }
+      params.slot_offset = CagedHeapBase::OffsetFromAddress(slot);
+      return SetAndReturnType<WriteBarrier::Type::kGenerational>(params);
+    }
+#else   // !defined(CPPGC_YOUNG_GENERATION)
+    if (V8_UNLIKELY(!handle.is_incremental_marking_in_progress())) {
+      return SetAndReturnType<WriteBarrier::Type::kNone>(params);
+    }
+#endif  // !defined(CPPGC_YOUNG_GENERATION)
+    params.heap = &handle;
+    return SetAndReturnType<WriteBarrier::Type::kMarking>(params);
+  }
+};
+
+#endif  // CPPGC_CAGED_HEAP
+
+class V8_EXPORT WriteBarrierTypeForNonCagedHeapPolicy final {
+ public:
+  template <WriteBarrier::ValueMode value_mode, typename HeapHandleCallback>
+  static V8_INLINE WriteBarrier::Type Get(const void* slot, const void* value,
+                                          WriteBarrier::Params& params,
+                                          HeapHandleCallback callback) {
+    return ValueModeDispatch<value_mode>::Get(slot, value, params, callback);
+  }
+
+  template <WriteBarrier::ValueMode value_mode, typename HeapHandleCallback>
+  static V8_INLINE WriteBarrier::Type Get(const void* slot, MemberStorage value,
+                                          WriteBarrier::Params& params,
+                                          HeapHandleCallback callback) {
+    // `MemberStorage` will always be `RawPointer` for non-caged heap builds.
+    // Just convert to `void*` in this case.
+    return ValueModeDispatch<value_mode>::Get(slot, value.Load(), params,
+                                              callback);
+  }
+
+  template <WriteBarrier::ValueMode value_mode, typename HeapHandleCallback>
+  static V8_INLINE WriteBarrier::Type Get(const void* value,
+                                          WriteBarrier::Params& params,
+                                          HeapHandleCallback callback) {
+    // The slot will never be used in `Get()` below.
+    return Get<WriteBarrier::ValueMode::kValuePresent>(nullptr, value, params,
+                                                       callback);
+  }
+
+ private:
+  template <WriteBarrier::ValueMode value_mode>
+  struct ValueModeDispatch;
+
+  WriteBarrierTypeForNonCagedHeapPolicy() = delete;
+};
+
+template <>
+struct WriteBarrierTypeForNonCagedHeapPolicy::ValueModeDispatch<
+    WriteBarrier::ValueMode::kValuePresent> {
+  template <typename HeapHandleCallback>
+  static V8_INLINE WriteBarrier::Type Get(const void*, const void* object,
+                                          WriteBarrier::Params& params,
+                                          HeapHandleCallback callback) {
+    // The following check covers nullptr as well as sentinel pointer.
+    if (object <= static_cast<void*>(kSentinelPointer)) {
+      return SetAndReturnType<WriteBarrier::Type::kNone>(params);
+    }
+    if (V8_LIKELY(!WriteBarrier::IsEnabled())) {
+      return SetAndReturnType<WriteBarrier::Type::kNone>(params);
+    }
+    // We know that |object| is within the normal page or in the beginning of a
+    // large page, so extract the page header by bitmasking.
+    BasePageHandle* page =
+        BasePageHandle::FromPayload(const_cast<void*>(object));
+
+    HeapHandle& heap_handle = page->heap_handle();
+    if (V8_LIKELY(heap_handle.is_incremental_marking_in_progress())) {
+      return SetAndReturnType<WriteBarrier::Type::kMarking>(params);
+    }
+    return SetAndReturnType<WriteBarrier::Type::kNone>(params);
+  }
+};
+
+template <>
+struct WriteBarrierTypeForNonCagedHeapPolicy::ValueModeDispatch<
+    WriteBarrier::ValueMode::kNoValuePresent> {
+  template <typename HeapHandleCallback>
+  static V8_INLINE WriteBarrier::Type Get(const void*, const void*,
+                                          WriteBarrier::Params& params,
+                                          HeapHandleCallback callback) {
+    if (V8_UNLIKELY(WriteBarrier::IsEnabled())) {
+      HeapHandle& handle = callback();
+      if (V8_LIKELY(handle.is_incremental_marking_in_progress())) {
+        params.heap = &handle;
+        return SetAndReturnType<WriteBarrier::Type::kMarking>(params);
+      }
+    }
+    return WriteBarrier::Type::kNone;
+  }
+};
+
+// static
+WriteBarrier::Type WriteBarrier::GetWriteBarrierType(
+    const void* slot, const void* value, WriteBarrier::Params& params) {
+  return WriteBarrierTypePolicy::Get<ValueMode::kValuePresent>(slot, value,
+                                                               params, []() {});
+}
+
+// static
+WriteBarrier::Type WriteBarrier::GetWriteBarrierType(
+    const void* slot, MemberStorage value, WriteBarrier::Params& params) {
+  return WriteBarrierTypePolicy::Get<ValueMode::kValuePresent>(slot, value,
+                                                               params, []() {});
+}
+
+// static
+template <typename HeapHandleCallback>
+WriteBarrier::Type WriteBarrier::GetWriteBarrierType(
+    const void* slot, WriteBarrier::Params& params,
+    HeapHandleCallback callback) {
+  return WriteBarrierTypePolicy::Get<ValueMode::kNoValuePresent>(
+      slot, nullptr, params, callback);
+}
+
+// static
+WriteBarrier::Type WriteBarrier::GetWriteBarrierType(
+    const void* value, WriteBarrier::Params& params) {
+  return WriteBarrierTypePolicy::Get<ValueMode::kValuePresent>(value, params,
+                                                               []() {});
+}
+
+// static
+void WriteBarrier::DijkstraMarkingBarrier(const Params& params,
+                                          const void* object) {
+  CheckParams(Type::kMarking, params);
+#if defined(CPPGC_CAGED_HEAP)
+  // Caged heap already filters out sentinels.
+  DijkstraMarkingBarrierSlow(object);
+#else   // !CPPGC_CAGED_HEAP
+  DijkstraMarkingBarrierSlowWithSentinelCheck(object);
+#endif  // !CPPGC_CAGED_HEAP
+}
+
+// static
+void WriteBarrier::DijkstraMarkingBarrierRange(const Params& params,
+                                               const void* first_element,
+                                               size_t element_size,
+                                               size_t number_of_elements,
+                                               TraceCallback trace_callback) {
+  CheckParams(Type::kMarking, params);
+  DijkstraMarkingBarrierRangeSlow(*params.heap, first_element, element_size,
+                                  number_of_elements, trace_callback);
+}
+
+// static
+void WriteBarrier::SteeleMarkingBarrier(const Params& params,
+                                        const void* object) {
+  CheckParams(Type::kMarking, params);
+#if defined(CPPGC_CAGED_HEAP)
+  // Caged heap already filters out sentinels.
+  SteeleMarkingBarrierSlow(object);
+#else   // !CPPGC_CAGED_HEAP
+  SteeleMarkingBarrierSlowWithSentinelCheck(object);
+#endif  // !CPPGC_CAGED_HEAP
+}
+
+#if defined(CPPGC_YOUNG_GENERATION)
+
+// static
+template <WriteBarrier::GenerationalBarrierType type>
+void WriteBarrier::GenerationalBarrier(const Params& params, const void* slot) {
+  CheckParams(Type::kGenerational, params);
+
+  const CagedHeapLocalData& local_data = CagedHeapLocalData::Get();
+  const AgeTable& age_table = local_data.age_table;
+
+  // Bail out if the slot (precise or imprecise) is in young generation.
+  if (V8_LIKELY(age_table.GetAge(params.slot_offset) == AgeTable::Age::kYoung))
+    return;
+
+  // Dispatch between different types of barriers.
+  // TODO(chromium:1029379): Consider reload local_data in the slow path to
+  // reduce register pressure.
+  if constexpr (type == GenerationalBarrierType::kPreciseSlot) {
+    GenerationalBarrierSlow(local_data, age_table, slot, params.value_offset,
+                            params.heap);
+  } else if constexpr (type ==
+                       GenerationalBarrierType::kPreciseUncompressedSlot) {
+    GenerationalBarrierForUncompressedSlotSlow(
+        local_data, age_table, slot, params.value_offset, params.heap);
+  } else {
+    GenerationalBarrierForSourceObjectSlow(local_data, slot, params.heap);
+  }
+}
+
+#endif  // !CPPGC_YOUNG_GENERATION
+
+}  // namespace internal
+}  // namespace cppgc
+
+#endif  // INCLUDE_CPPGC_INTERNAL_WRITE_BARRIER_H_