v8/include/v8-internal.h
Benedikt Meurer c7a0049e1b [objects] Change String::length field to uint32_t.
This changes the Name::hash_field and Symbol::flags to uint32_t as
well, so that both Symbols and Strings consume one fewer word on 64-bit
architectures now. More importantly the access to String::length is
always a 32-bit field load now, even with 31-bit Smis (i.e. on ARM or
on 64-bit with pointer compression), so the access should be faster.

Bug: v8:7065, v8:8171
Change-Id: I1a38f4470d62fbeba2b3bc5fcf4ecdbada7d6b8a
Tbr: ulan@chromium.org, yangguo@chromium.org, ishell@chromium.org
Cq-Include-Trybots: luci.chromium.try:linux_chromium_rel_ng;luci.v8.try:v8_linux_noi18n_rel_ng
Reviewed-on: https://chromium-review.googlesource.com/1224432
Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55861}
2018-09-13 13:07:08 +00:00

317 lines
12 KiB
C++

// Copyright 2018 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_V8_INTERNAL_H_
#define INCLUDE_V8_INTERNAL_H_
#include <stddef.h>
#include <stdint.h>
#include <type_traits>
#include "v8-version.h" // NOLINT(build/include)
#include "v8config.h" // NOLINT(build/include)
namespace v8 {
class Context;
class Data;
class Isolate;
namespace internal {
class Object;
/**
* Configuration of tagging scheme.
*/
const int kApiPointerSize = sizeof(void*); // NOLINT
const int kApiDoubleSize = sizeof(double); // NOLINT
const int kApiIntSize = sizeof(int); // NOLINT
const int kApiInt64Size = sizeof(int64_t); // NOLINT
// Tag information for HeapObject.
const int kHeapObjectTag = 1;
const int kWeakHeapObjectTag = 3;
const int kHeapObjectTagSize = 2;
const intptr_t kHeapObjectTagMask = (1 << kHeapObjectTagSize) - 1;
// Tag information for Smi.
const int kSmiTag = 0;
const int kSmiTagSize = 1;
const intptr_t kSmiTagMask = (1 << kSmiTagSize) - 1;
template <size_t tagged_ptr_size>
struct SmiTagging;
template <int kSmiShiftSize>
V8_INLINE internal::Object* IntToSmi(int value) {
int smi_shift_bits = kSmiTagSize + kSmiShiftSize;
intptr_t tagged_value =
(static_cast<intptr_t>(value) << smi_shift_bits) | kSmiTag;
return reinterpret_cast<internal::Object*>(tagged_value);
}
// Smi constants for systems where tagged pointer is a 32-bit value.
template <>
struct SmiTagging<4> {
enum { kSmiShiftSize = 0, kSmiValueSize = 31 };
static int SmiShiftSize() { return kSmiShiftSize; }
static int SmiValueSize() { return kSmiValueSize; }
V8_INLINE static int SmiToInt(const internal::Object* value) {
int shift_bits = kSmiTagSize + kSmiShiftSize;
// Throw away top 32 bits and shift down (requires >> to be sign extending).
return static_cast<int>(reinterpret_cast<intptr_t>(value)) >> shift_bits;
}
V8_INLINE static internal::Object* IntToSmi(int value) {
return internal::IntToSmi<kSmiShiftSize>(value);
}
V8_INLINE static constexpr bool IsValidSmi(intptr_t value) {
// To be representable as an tagged small integer, the two
// most-significant bits of 'value' must be either 00 or 11 due to
// sign-extension. To check this we add 01 to the two
// most-significant bits, and check if the most-significant bit is 0
//
// CAUTION: The original code below:
// bool result = ((value + 0x40000000) & 0x80000000) == 0;
// may lead to incorrect results according to the C language spec, and
// in fact doesn't work correctly with gcc4.1.1 in some cases: The
// compiler may produce undefined results in case of signed integer
// overflow. The computation must be done w/ unsigned ints.
return static_cast<uintptr_t>(value) + 0x40000000U < 0x80000000U;
}
};
// Smi constants for systems where tagged pointer is a 64-bit value.
template <>
struct SmiTagging<8> {
enum { kSmiShiftSize = 31, kSmiValueSize = 32 };
static int SmiShiftSize() { return kSmiShiftSize; }
static int SmiValueSize() { return kSmiValueSize; }
V8_INLINE static int SmiToInt(const internal::Object* value) {
int shift_bits = kSmiTagSize + kSmiShiftSize;
// Shift down and throw away top 32 bits.
return static_cast<int>(reinterpret_cast<intptr_t>(value) >> shift_bits);
}
V8_INLINE static internal::Object* IntToSmi(int value) {
return internal::IntToSmi<kSmiShiftSize>(value);
}
V8_INLINE static constexpr bool IsValidSmi(intptr_t value) {
// To be representable as a long smi, the value must be a 32-bit integer.
return (value == static_cast<int32_t>(value));
}
};
#if V8_COMPRESS_POINTERS
static_assert(
kApiPointerSize == kApiInt64Size,
"Pointer compression can be enabled only for 64-bit architectures");
typedef SmiTagging<4> PlatformSmiTagging;
#else
typedef SmiTagging<kApiPointerSize> PlatformSmiTagging;
#endif
const int kSmiShiftSize = PlatformSmiTagging::kSmiShiftSize;
const int kSmiValueSize = PlatformSmiTagging::kSmiValueSize;
const int kSmiMinValue = (static_cast<unsigned int>(-1)) << (kSmiValueSize - 1);
const int kSmiMaxValue = -(kSmiMinValue + 1);
constexpr bool SmiValuesAre31Bits() { return kSmiValueSize == 31; }
constexpr bool SmiValuesAre32Bits() { return kSmiValueSize == 32; }
/**
* This class exports constants and functionality from within v8 that
* is necessary to implement inline functions in the v8 api. Don't
* depend on functions and constants defined here.
*/
class Internals {
public:
// These values match non-compiler-dependent values defined within
// the implementation of v8.
static const int kHeapObjectMapOffset = 0;
static const int kMapInstanceTypeOffset = 1 * kApiPointerSize + kApiIntSize;
static const int kStringResourceOffset =
1 * kApiPointerSize + 2 * kApiIntSize;
static const int kOddballKindOffset = 4 * kApiPointerSize + kApiDoubleSize;
static const int kForeignAddressOffset = kApiPointerSize;
static const int kJSObjectHeaderSize = 3 * kApiPointerSize;
static const int kFixedArrayHeaderSize = 2 * kApiPointerSize;
static const int kContextHeaderSize = 2 * kApiPointerSize;
static const int kContextEmbedderDataIndex = 5;
static const int kFullStringRepresentationMask = 0x0f;
static const int kStringEncodingMask = 0x8;
static const int kExternalTwoByteRepresentationTag = 0x02;
static const int kExternalOneByteRepresentationTag = 0x0a;
static const int kIsolateEmbedderDataOffset = 0 * kApiPointerSize;
static const int kExternalMemoryOffset = 4 * kApiPointerSize;
static const int kExternalMemoryLimitOffset =
kExternalMemoryOffset + kApiInt64Size;
static const int kExternalMemoryAtLastMarkCompactOffset =
kExternalMemoryLimitOffset + kApiInt64Size;
static const int kIsolateRootsOffset = kExternalMemoryLimitOffset +
kApiInt64Size + kApiInt64Size +
kApiPointerSize + kApiPointerSize;
static const int kUndefinedValueRootIndex = 4;
static const int kTheHoleValueRootIndex = 5;
static const int kNullValueRootIndex = 6;
static const int kTrueValueRootIndex = 7;
static const int kFalseValueRootIndex = 8;
static const int kEmptyStringRootIndex = 9;
static const int kNodeClassIdOffset = 1 * kApiPointerSize;
static const int kNodeFlagsOffset = 1 * kApiPointerSize + 3;
static const int kNodeStateMask = 0x7;
static const int kNodeStateIsWeakValue = 2;
static const int kNodeStateIsPendingValue = 3;
static const int kNodeStateIsNearDeathValue = 4;
static const int kNodeIsIndependentShift = 3;
static const int kNodeIsActiveShift = 4;
static const int kFirstNonstringType = 0x80;
static const int kOddballType = 0x83;
static const int kForeignType = 0x87;
static const int kJSSpecialApiObjectType = 0x410;
static const int kJSApiObjectType = 0x420;
static const int kJSObjectType = 0x421;
static const int kUndefinedOddballKind = 5;
static const int kNullOddballKind = 3;
static const uint32_t kNumIsolateDataSlots = 4;
// Soft limit for AdjustAmountofExternalAllocatedMemory. Trigger an
// incremental GC once the external memory reaches this limit.
static constexpr int kExternalAllocationSoftLimit = 64 * 1024 * 1024;
V8_EXPORT static void CheckInitializedImpl(v8::Isolate* isolate);
V8_INLINE static void CheckInitialized(v8::Isolate* isolate) {
#ifdef V8_ENABLE_CHECKS
CheckInitializedImpl(isolate);
#endif
}
V8_INLINE static bool HasHeapObjectTag(const internal::Object* value) {
return ((reinterpret_cast<intptr_t>(value) & kHeapObjectTagMask) ==
kHeapObjectTag);
}
V8_INLINE static int SmiValue(const internal::Object* value) {
return PlatformSmiTagging::SmiToInt(value);
}
V8_INLINE static internal::Object* IntToSmi(int value) {
return PlatformSmiTagging::IntToSmi(value);
}
V8_INLINE static constexpr bool IsValidSmi(intptr_t value) {
return PlatformSmiTagging::IsValidSmi(value);
}
V8_INLINE static int GetInstanceType(const internal::Object* obj) {
typedef internal::Object O;
O* map = ReadField<O*>(obj, kHeapObjectMapOffset);
return ReadField<uint16_t>(map, kMapInstanceTypeOffset);
}
V8_INLINE static int GetOddballKind(const internal::Object* obj) {
typedef internal::Object O;
return SmiValue(ReadField<O*>(obj, kOddballKindOffset));
}
V8_INLINE static bool IsExternalTwoByteString(int instance_type) {
int representation = (instance_type & kFullStringRepresentationMask);
return representation == kExternalTwoByteRepresentationTag;
}
V8_INLINE static uint8_t GetNodeFlag(internal::Object** obj, int shift) {
uint8_t* addr = reinterpret_cast<uint8_t*>(obj) + kNodeFlagsOffset;
return *addr & static_cast<uint8_t>(1U << shift);
}
V8_INLINE static void UpdateNodeFlag(internal::Object** obj, bool value,
int shift) {
uint8_t* addr = reinterpret_cast<uint8_t*>(obj) + kNodeFlagsOffset;
uint8_t mask = static_cast<uint8_t>(1U << shift);
*addr = static_cast<uint8_t>((*addr & ~mask) | (value << shift));
}
V8_INLINE static uint8_t GetNodeState(internal::Object** obj) {
uint8_t* addr = reinterpret_cast<uint8_t*>(obj) + kNodeFlagsOffset;
return *addr & kNodeStateMask;
}
V8_INLINE static void UpdateNodeState(internal::Object** obj, uint8_t value) {
uint8_t* addr = reinterpret_cast<uint8_t*>(obj) + kNodeFlagsOffset;
*addr = static_cast<uint8_t>((*addr & ~kNodeStateMask) | value);
}
V8_INLINE static void SetEmbedderData(v8::Isolate* isolate, uint32_t slot,
void* data) {
uint8_t* addr = reinterpret_cast<uint8_t*>(isolate) +
kIsolateEmbedderDataOffset + slot * kApiPointerSize;
*reinterpret_cast<void**>(addr) = data;
}
V8_INLINE static void* GetEmbedderData(const v8::Isolate* isolate,
uint32_t slot) {
const uint8_t* addr = reinterpret_cast<const uint8_t*>(isolate) +
kIsolateEmbedderDataOffset + slot * kApiPointerSize;
return *reinterpret_cast<void* const*>(addr);
}
V8_INLINE static internal::Object** GetRoot(v8::Isolate* isolate, int index) {
uint8_t* addr = reinterpret_cast<uint8_t*>(isolate) + kIsolateRootsOffset;
return reinterpret_cast<internal::Object**>(addr + index * kApiPointerSize);
}
template <typename T>
V8_INLINE static T ReadField(const internal::Object* ptr, int offset) {
const uint8_t* addr =
reinterpret_cast<const uint8_t*>(ptr) + offset - kHeapObjectTag;
return *reinterpret_cast<const T*>(addr);
}
template <typename T>
V8_INLINE static T ReadEmbedderData(const v8::Context* context, int index) {
typedef internal::Object O;
typedef internal::Internals I;
O* ctx = *reinterpret_cast<O* const*>(context);
int embedder_data_offset =
I::kContextHeaderSize +
(internal::kApiPointerSize * I::kContextEmbedderDataIndex);
O* embedder_data = I::ReadField<O*>(ctx, embedder_data_offset);
int value_offset =
I::kFixedArrayHeaderSize + (internal::kApiPointerSize * index);
return I::ReadField<T>(embedder_data, value_offset);
}
};
// Only perform cast check for types derived from v8::Data since
// other types do not implement the Cast method.
template <bool PerformCheck>
struct CastCheck {
template <class T>
static void Perform(T* data);
};
template <>
template <class T>
void CastCheck<true>::Perform(T* data) {
T::Cast(data);
}
template <>
template <class T>
void CastCheck<false>::Perform(T* data) {}
template <class T>
V8_INLINE void PerformCastCheck(T* data) {
CastCheck<std::is_base_of<Data, T>::value>::Perform(data);
}
} // namespace internal
} // namespace v8
#endif // INCLUDE_V8_INTERNAL_H_