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// Copyright 2011 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.
#include "src/base/memory.h"
#include "src/common/assert-scope.h"
#include "src/utils/allocation.h"
#include "src/utils/utils.h"
#include "src/zone/zone-chunk-list.h"
#include "src/zone/zone.h"
namespace v8 {
namespace internal {
class SafepointEntry {
SafepointEntry() : deopt_index_(0), bits_(nullptr), trampoline_pc_(-1) {}
SafepointEntry(unsigned deopt_index, uint8_t* bits, int trampoline_pc)
: deopt_index_(deopt_index), bits_(bits), trampoline_pc_(trampoline_pc) {
bool is_valid() const { return bits_ != nullptr; }
bool Equals(const SafepointEntry& other) const {
return deopt_index_ == other.deopt_index_ && bits_ == other.bits_;
void Reset() {
deopt_index_ = 0;
bits_ = nullptr;
int trampoline_pc() { return trampoline_pc_; }
static const unsigned kNoDeoptIndex = kMaxUInt32;
int deoptimization_index() const {
DCHECK(is_valid() && has_deoptimization_index());
return deopt_index_;
bool has_deoptimization_index() const {
return deopt_index_ != kNoDeoptIndex;
uint8_t* bits() {
return bits_;
unsigned deopt_index_;
uint8_t* bits_;
// It needs to be an integer as it is -1 for eager deoptimizations.
int trampoline_pc_;
class SafepointTable {
explicit SafepointTable(Code code);
explicit SafepointTable(Address instruction_start,
size_t safepoint_table_offset, uint32_t stack_slots,
bool has_deopt = false);
int size() const {
return kHeaderSize + (length_ * (kFixedEntrySize + entry_size_));
unsigned length() const { return length_; }
unsigned entry_size() const { return entry_size_; }
unsigned GetPcOffset(unsigned index) const {
DCHECK(index < length_);
return base::Memory<uint32_t>(GetPcOffsetLocation(index));
int GetTrampolinePcOffset(unsigned index) const {
DCHECK(index < length_);
return base::Memory<int>(GetTrampolineLocation(index));
unsigned find_return_pc(unsigned pc_offset);
SafepointEntry GetEntry(unsigned index) const {
DCHECK(index < length_);
unsigned deopt_index =
uint8_t* bits = &base::Memory<uint8_t>(entries_ + (index * entry_size_));
int trampoline_pc =
has_deopt_ ? base::Memory<int>(GetTrampolineLocation(index)) : -1;
return SafepointEntry(deopt_index, bits, trampoline_pc);
// Returns the entry for the given pc.
SafepointEntry FindEntry(Address pc) const;
void PrintEntry(unsigned index, std::ostream& os) const; // NOLINT
static const uint8_t kNoRegisters = 0xFF;
// Layout information
static const int kLengthOffset = 0;
static const int kEntrySizeOffset = kLengthOffset + kIntSize;
static const int kHeaderSize = kEntrySizeOffset + kIntSize;
static const int kPcOffset = 0;
static const int kEncodedInfoOffset = kPcOffset + kIntSize;
static const int kTrampolinePcOffset = kEncodedInfoOffset + kIntSize;
static const int kFixedEntrySize = kTrampolinePcOffset + kIntSize;
Address GetPcOffsetLocation(unsigned index) const {
return pc_and_deoptimization_indexes_ + (index * kFixedEntrySize);
Address GetEncodedInfoLocation(unsigned index) const {
return GetPcOffsetLocation(index) + kEncodedInfoOffset;
Address GetTrampolineLocation(unsigned index) const {
return GetPcOffsetLocation(index) + kTrampolinePcOffset;
static void PrintBits(std::ostream& os, // NOLINT
uint8_t byte, int digits);
Address instruction_start_;
uint32_t stack_slots_;
unsigned length_;
unsigned entry_size_;
Address pc_and_deoptimization_indexes_;
Address entries_;
bool has_deopt_;
friend class SafepointTableBuilder;
friend class SafepointEntry;
class Safepoint {
enum DeoptMode { kNoLazyDeopt, kLazyDeopt };
static const int kNoDeoptimizationIndex = SafepointEntry::kNoDeoptIndex;
void DefinePointerSlot(int index) { indexes_->push_back(index); }
explicit Safepoint(ZoneChunkList<int>* indexes) : indexes_(indexes) {}
ZoneChunkList<int>* const indexes_;
friend class SafepointTableBuilder;
class SafepointTableBuilder {
explicit SafepointTableBuilder(Zone* zone)
: deoptimization_info_(zone),
zone_(zone) {}
// Get the offset of the emitted safepoint table in the code.
unsigned GetCodeOffset() const;
// Define a new safepoint for the current position in the body.
Safepoint DefineSafepoint(Assembler* assembler, Safepoint::DeoptMode mode);
// Record deoptimization index for lazy deoptimization for the last
// outstanding safepoints.
void RecordLazyDeoptimizationIndex(int index);
void BumpLastLazySafepointIndex() {
last_lazy_safepoint_ = deoptimization_info_.size();
// Emit the safepoint table after the body. The number of bits per
// entry must be enough to hold all the pointer indexes.
V8_EXPORT_PRIVATE void Emit(Assembler* assembler, int bits_per_entry);
// Find the Deoptimization Info with pc offset {pc} and update its
// trampoline field. Calling this function ensures that the safepoint
// table contains the trampoline PC {trampoline} that replaced the
// return PC {pc} on the stack.
int UpdateDeoptimizationInfo(int pc, int trampoline, int start);
struct DeoptimizationInfo {
unsigned pc;
unsigned deopt_index;
int trampoline;
ZoneChunkList<int>* indexes;
DeoptimizationInfo(Zone* zone, unsigned pc)
: pc(pc),
indexes(new (zone) ZoneChunkList<int>(
zone, ZoneChunkList<int>::StartMode::kSmall)) {}
// Compares all fields of a {DeoptimizationInfo} except {pc} and {trampoline}.
bool IsIdenticalExceptForPc(const DeoptimizationInfo&,
const DeoptimizationInfo&) const;
// If all entries are identical, replace them by 1 entry with pc = kMaxUInt32.
void RemoveDuplicates();
ZoneChunkList<DeoptimizationInfo> deoptimization_info_;
unsigned offset_;
bool emitted_;
size_t last_lazy_safepoint_;
Zone* zone_;
} // namespace internal
} // namespace v8