src/safepoint-table.h

// Copyright 2011 the V8 project authors. All rights reserved.
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// modification, are permitted provided that the following conditions are
// met:
//
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#ifndef V8_SAFEPOINT_TABLE_H_
#define V8_SAFEPOINT_TABLE_H_

#include "allocation.h"
#include "heap.h"
#include "v8memory.h"
#include "zone.h"

namespace v8 {
namespace internal {

struct Register;

class SafepointEntry BASE_EMBEDDED {
 public:
  SafepointEntry() : info_(0), bits_(NULL) {}

  SafepointEntry(unsigned info, uint8_t* bits) : info_(info), bits_(bits) {
    ASSERT(is_valid());
  }

  bool is_valid() const { return bits_ != NULL; }

  bool Equals(const SafepointEntry& other) const {
    return info_ == other.info_ && bits_ == other.bits_;
  }

  void Reset() {
    info_ = 0;
    bits_ = NULL;
  }

  int deoptimization_index() const {
    ASSERT(is_valid());
    return DeoptimizationIndexField::decode(info_);
  }

  int gap_code_size() const {
    ASSERT(is_valid());
    return GapCodeSizeField::decode(info_);
  }

  int argument_count() const {
    ASSERT(is_valid());
    return ArgumentsField::decode(info_);
  }

  bool has_doubles() const {
    ASSERT(is_valid());
    return SaveDoublesField::decode(info_);
  }

  uint8_t* bits() {
    ASSERT(is_valid());
    return bits_;
  }

  bool HasRegisters() const;
  bool HasRegisterAt(int reg_index) const;

  // Reserve 13 bits for the gap code size. On ARM a constant pool can be
  // emitted when generating the gap code. The size of the const pool is less
  // than what can be represented in 12 bits, so 13 bits gives room for having
  // instructions before potentially emitting a constant pool.
  static const int kGapCodeSizeBits = 13;
  static const int kArgumentsFieldBits = 3;
  static const int kSaveDoublesFieldBits = 1;
  static const int kDeoptIndexBits =
      32 - kGapCodeSizeBits - kArgumentsFieldBits - kSaveDoublesFieldBits;
  class GapCodeSizeField: public BitField<unsigned, 0, kGapCodeSizeBits> {};
  class DeoptimizationIndexField: public BitField<int,
                                                  kGapCodeSizeBits,
                                                  kDeoptIndexBits> {};  // NOLINT
  class ArgumentsField: public BitField<unsigned,
                                        kGapCodeSizeBits + kDeoptIndexBits,
                                        kArgumentsFieldBits> {};  // NOLINT
  class SaveDoublesField: public BitField<bool,
                                          kGapCodeSizeBits + kDeoptIndexBits +
                                          kArgumentsFieldBits,
                                          kSaveDoublesFieldBits> { }; // NOLINT

 private:
  unsigned info_;
  uint8_t* bits_;
};


class SafepointTable BASE_EMBEDDED {
 public:
  explicit SafepointTable(Code* code);

  int size() const {
    return kHeaderSize +
           (length_ * (kPcAndDeoptimizationIndexSize + entry_size_)); }
  unsigned length() const { return length_; }
  unsigned entry_size() const { return entry_size_; }

  unsigned GetPcOffset(unsigned index) const {
    ASSERT(index < length_);
    return Memory::uint32_at(GetPcOffsetLocation(index));
  }

  SafepointEntry GetEntry(unsigned index) const {
    ASSERT(index < length_);
    unsigned info = Memory::uint32_at(GetInfoLocation(index));
    uint8_t* bits = &Memory::uint8_at(entries_ + (index * entry_size_));
    return SafepointEntry(info, bits);
  }

  // Returns the entry for the given pc.
  SafepointEntry FindEntry(Address pc) const;

  void PrintEntry(unsigned index) const;

 private:
  static const uint8_t kNoRegisters = 0xFF;

  static const int kLengthOffset = 0;
  static const int kEntrySizeOffset = kLengthOffset + kIntSize;
  static const int kHeaderSize = kEntrySizeOffset + kIntSize;

  static const int kPcSize = kIntSize;
  static const int kDeoptimizationIndexSize = kIntSize;
  static const int kPcAndDeoptimizationIndexSize =
      kPcSize + kDeoptimizationIndexSize;

  Address GetPcOffsetLocation(unsigned index) const {
    return pc_and_deoptimization_indexes_ +
           (index * kPcAndDeoptimizationIndexSize);
  }

  Address GetInfoLocation(unsigned index) const {
    return GetPcOffsetLocation(index) + kPcSize;
  }

  static void PrintBits(uint8_t byte, int digits);

  AssertNoAllocation no_allocation_;
  Code* code_;
  unsigned length_;
  unsigned entry_size_;

  Address pc_and_deoptimization_indexes_;
  Address entries_;

  friend class SafepointTableBuilder;
  friend class SafepointEntry;

  DISALLOW_COPY_AND_ASSIGN(SafepointTable);
};


class Safepoint BASE_EMBEDDED {
 public:
  typedef enum {
    kSimple = 0,
    kWithRegisters = 1 << 0,
    kWithDoubles = 1 << 1,
    kWithRegistersAndDoubles = kWithRegisters | kWithDoubles
  } Kind;

  static const int kNoDeoptimizationIndex =
      (1 << (SafepointEntry::kDeoptIndexBits)) - 1;

  void DefinePointerSlot(int index) { indexes_->Add(index); }
  void DefinePointerRegister(Register reg);

 private:
  Safepoint(ZoneList<int>* indexes, ZoneList<int>* registers) :
      indexes_(indexes), registers_(registers) { }
  ZoneList<int>* indexes_;
  ZoneList<int>* registers_;

  friend class SafepointTableBuilder;
};


class SafepointTableBuilder BASE_EMBEDDED {
 public:
  SafepointTableBuilder()
      : deoptimization_info_(32),
        indexes_(32),
        registers_(32),
        emitted_(false) { }

  // 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::Kind kind,
                            int arguments,
                            int deoptimization_index);

  // Update the last safepoint with the size of the code generated until the
  // end of the gap following it.
  void SetPcAfterGap(int pc) {
    ASSERT(!deoptimization_info_.is_empty());
    int index = deoptimization_info_.length() - 1;
    deoptimization_info_[index].pc_after_gap = pc;
  }

  // Get the end pc offset of the last safepoint, including the code generated
  // until the end of the gap following it.
  unsigned GetPcAfterGap() {
    int index = deoptimization_info_.length();
    if (index == 0) return 0;
    return deoptimization_info_[index - 1].pc_after_gap;
  }

  // Emit the safepoint table after the body. The number of bits per
  // entry must be enough to hold all the pointer indexes.
  void Emit(Assembler* assembler, int bits_per_entry);

  // Count the number of deoptimization points where the next
  // following deoptimization point comes less than limit bytes
  // after the end of this point's gap.
  int CountShortDeoptimizationIntervals(unsigned limit);

 private:
  struct DeoptimizationInfo {
    unsigned pc;
    unsigned deoptimization_index;
    unsigned pc_after_gap;
    unsigned arguments;
    bool has_doubles;
  };

  uint32_t EncodeExceptPC(const DeoptimizationInfo& info);

  ZoneList<DeoptimizationInfo> deoptimization_info_;
  ZoneList<ZoneList<int>*> indexes_;
  ZoneList<ZoneList<int>*> registers_;

  unsigned offset_;
  bool emitted_;

  DISALLOW_COPY_AND_ASSIGN(SafepointTableBuilder);
};

} }  // namespace v8::internal

#endif  // V8_SAFEPOINT_TABLE_H_