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

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+// 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_