src/safepoint-table.cc

// 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/safepoint-table.h"

#include "src/deoptimizer.h"
#include "src/disasm.h"
#include "src/frames-inl.h"
#include "src/macro-assembler.h"
#include "src/ostreams.h"

namespace v8 {
namespace internal {


bool SafepointEntry::HasRegisters() const {
  DCHECK(is_valid());
  DCHECK(IsAligned(kNumSafepointRegisters, kBitsPerByte));
  const int num_reg_bytes = kNumSafepointRegisters >> kBitsPerByteLog2;
  for (int i = 0; i < num_reg_bytes; i++) {
    if (bits_[i] != SafepointTable::kNoRegisters) return true;
  }
  return false;
}


bool SafepointEntry::HasRegisterAt(int reg_index) const {
  DCHECK(is_valid());
  DCHECK(reg_index >= 0 && reg_index < kNumSafepointRegisters);
  int byte_index = reg_index >> kBitsPerByteLog2;
  int bit_index = reg_index & (kBitsPerByte - 1);
  return (bits_[byte_index] & (1 << bit_index)) != 0;
}


SafepointTable::SafepointTable(Code* code) {
  DCHECK(code->is_crankshafted());
  code_ = code;
  Address header = code->instruction_start() + code->safepoint_table_offset();
  length_ = Memory::uint32_at(header + kLengthOffset);
  entry_size_ = Memory::uint32_at(header + kEntrySizeOffset);
  pc_and_deoptimization_indexes_ = header + kHeaderSize;
  entries_ = pc_and_deoptimization_indexes_ +
             (length_ * kPcAndDeoptimizationIndexSize);
  DCHECK(entry_size_ > 0);
  STATIC_ASSERT(SafepointEntry::DeoptimizationIndexField::kMax ==
                Safepoint::kNoDeoptimizationIndex);
}


SafepointEntry SafepointTable::FindEntry(Address pc) const {
  unsigned pc_offset = static_cast<unsigned>(pc - code_->instruction_start());
  for (unsigned i = 0; i < length(); i++) {
    // TODO(kasperl): Replace the linear search with binary search.
    if (GetPcOffset(i) == pc_offset) return GetEntry(i);
  }
  return SafepointEntry();
}


void SafepointTable::PrintEntry(unsigned index,
                                std::ostream& os) const {  // NOLINT
  disasm::NameConverter converter;
  SafepointEntry entry = GetEntry(index);
  uint8_t* bits = entry.bits();

  // Print the stack slot bits.
  if (entry_size_ > 0) {
    DCHECK(IsAligned(kNumSafepointRegisters, kBitsPerByte));
    const int first = kNumSafepointRegisters >> kBitsPerByteLog2;
    int last = entry_size_ - 1;
    for (int i = first; i < last; i++) PrintBits(os, bits[i], kBitsPerByte);
    int last_bits = code_->stack_slots() - ((last - first) * kBitsPerByte);
    PrintBits(os, bits[last], last_bits);

    // Print the registers (if any).
    if (!entry.HasRegisters()) return;
    for (int j = 0; j < kNumSafepointRegisters; j++) {
      if (entry.HasRegisterAt(j)) {
        os << " | " << converter.NameOfCPURegister(j);
      }
    }
  }
}


void SafepointTable::PrintBits(std::ostream& os,  // NOLINT
                               uint8_t byte, int digits) {
  DCHECK(digits >= 0 && digits <= kBitsPerByte);
  for (int i = 0; i < digits; i++) {
    os << (((byte & (1 << i)) == 0) ? "0" : "1");
  }
}


void Safepoint::DefinePointerRegister(Register reg, Zone* zone) {
  registers_->Add(reg.code(), zone);
}


Safepoint SafepointTableBuilder::DefineSafepoint(
    Assembler* assembler,
    Safepoint::Kind kind,
    int arguments,
    Safepoint::DeoptMode deopt_mode) {
  DCHECK(arguments >= 0);
  DeoptimizationInfo info;
  info.pc = assembler->pc_offset();
  info.arguments = arguments;
  info.has_doubles = (kind & Safepoint::kWithDoubles);
  deoptimization_info_.Add(info, zone_);
  deopt_index_list_.Add(Safepoint::kNoDeoptimizationIndex, zone_);
  if (deopt_mode == Safepoint::kNoLazyDeopt) {
    last_lazy_safepoint_ = deopt_index_list_.length();
  }
  indexes_.Add(new(zone_) ZoneList<int>(8, zone_), zone_);
  registers_.Add((kind & Safepoint::kWithRegisters)
      ? new(zone_) ZoneList<int>(4, zone_)
      : NULL,
      zone_);
  return Safepoint(indexes_.last(), registers_.last());
}


void SafepointTableBuilder::RecordLazyDeoptimizationIndex(int index) {
  while (last_lazy_safepoint_ < deopt_index_list_.length()) {
    deopt_index_list_[last_lazy_safepoint_++] = index;
  }
}

unsigned SafepointTableBuilder::GetCodeOffset() const {
  DCHECK(emitted_);
  return offset_;
}


void SafepointTableBuilder::Emit(Assembler* assembler, int bits_per_entry) {
  // Make sure the safepoint table is properly aligned. Pad with nops.
  assembler->Align(kIntSize);
  assembler->RecordComment(";;; Safepoint table.");
  offset_ = assembler->pc_offset();

  // Take the register bits into account.
  bits_per_entry += kNumSafepointRegisters;

  // Compute the number of bytes per safepoint entry.
  int bytes_per_entry =
      RoundUp(bits_per_entry, kBitsPerByte) >> kBitsPerByteLog2;

  // Emit the table header.
  int length = deoptimization_info_.length();
  assembler->dd(length);
  assembler->dd(bytes_per_entry);

  // Emit sorted table of pc offsets together with deoptimization indexes.
  for (int i = 0; i < length; i++) {
    assembler->dd(deoptimization_info_[i].pc);
    assembler->dd(EncodeExceptPC(deoptimization_info_[i],
                                 deopt_index_list_[i]));
  }

  // Emit table of bitmaps.
  ZoneList<uint8_t> bits(bytes_per_entry, zone_);
  for (int i = 0; i < length; i++) {
    ZoneList<int>* indexes = indexes_[i];
    ZoneList<int>* registers = registers_[i];
    bits.Clear();
    bits.AddBlock(0, bytes_per_entry, zone_);

    // Run through the registers (if any).
    DCHECK(IsAligned(kNumSafepointRegisters, kBitsPerByte));
    if (registers == NULL) {
      const int num_reg_bytes = kNumSafepointRegisters >> kBitsPerByteLog2;
      for (int j = 0; j < num_reg_bytes; j++) {
        bits[j] = SafepointTable::kNoRegisters;
      }
    } else {
      for (int j = 0; j < registers->length(); j++) {
        int index = registers->at(j);
        DCHECK(index >= 0 && index < kNumSafepointRegisters);
        int byte_index = index >> kBitsPerByteLog2;
        int bit_index = index & (kBitsPerByte - 1);
        bits[byte_index] |= (1 << bit_index);
      }
    }

    // Run through the indexes and build a bitmap.
    for (int j = 0; j < indexes->length(); j++) {
      int index = bits_per_entry - 1 - indexes->at(j);
      int byte_index = index >> kBitsPerByteLog2;
      int bit_index = index & (kBitsPerByte - 1);
      bits[byte_index] |= (1U << bit_index);
    }

    // Emit the bitmap for the current entry.
    for (int k = 0; k < bytes_per_entry; k++) {
      assembler->db(bits[k]);
    }
  }
  emitted_ = true;
}


uint32_t SafepointTableBuilder::EncodeExceptPC(const DeoptimizationInfo& info,
                                               unsigned index) {
  uint32_t encoding = SafepointEntry::DeoptimizationIndexField::encode(index);
  encoding |= SafepointEntry::ArgumentsField::encode(info.arguments);
  encoding |= SafepointEntry::SaveDoublesField::encode(info.has_doubles);
  return encoding;
}


}  // namespace internal
}  // namespace v8