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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::kCagedHeapDefaultReservationSize / kRequiredSize;
static constexpr size_t CalculateAgeTableSizeForHeapSize(size_t heap_size) {
return heap_size / kCardSizeInBytes;
}
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.
12;
#endif // !V8_HAS_BUILTIN_CTZ
static_assert((1 << kGranularityBits) == kCardSizeInBytes);
const size_t entry = offset >> kGranularityBits;
CPPGC_DCHECK(CagedHeapBase::GetAgeTableSize() > entry);
return entry;
}
#if defined(V8_CC_GNU)
// gcc disallows flexible arrays in otherwise empty classes.
Age table_[0];
#else // !defined(V8_CC_GNU)
Age table_[];
#endif // !defined(V8_CC_GNU)
};
#endif // CPPGC_YOUNG_GENERATION
struct CagedHeapLocalData final {
V8_INLINE static CagedHeapLocalData& Get() {
return *reinterpret_cast<CagedHeapLocalData*>(CagedHeapBase::GetBase());
}
static constexpr size_t CalculateLocalDataSizeForHeapSize(size_t heap_size) {
return AgeTable::CalculateAgeTableSizeForHeapSize(heap_size);
}
#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_
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