src/safepoint-table.cc

// Copyright 2011 the V8 project authors. All rights reserved.
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#include "safepoint-table.h"

#include "deoptimizer.h"
#include "disasm.h"
#include "macro-assembler.h"

namespace v8 {
namespace internal {


bool SafepointEntry::HasRegisters() const {
  ASSERT(is_valid());
  ASSERT(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 {
  ASSERT(is_valid());
  ASSERT(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) {
  ASSERT(code->kind() == Code::OPTIMIZED_FUNCTION);
  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);
  ASSERT(entry_size_ > 0);
  ASSERT_EQ(SafepointEntry::DeoptimizationIndexField::max(),
            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) const {
  disasm::NameConverter converter;
  SafepointEntry entry = GetEntry(index);
  uint8_t* bits = entry.bits();

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

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


void SafepointTable::PrintBits(uint8_t byte, int digits) {
  ASSERT(digits >= 0 && digits <= kBitsPerByte);
  for (int i = 0; i < digits; i++) {
    PrintF("%c", ((byte & (1 << i)) == 0) ? '0' : '1');
  }
}


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


Safepoint SafepointTableBuilder::DefineSafepoint(
    Assembler* assembler, Safepoint::Kind kind, int arguments,
    int deoptimization_index) {
  ASSERT(deoptimization_index != -1);
  ASSERT(arguments >= 0);
  DeoptimizationInfo pc_and_deoptimization_index;
  pc_and_deoptimization_index.pc = assembler->pc_offset();
  pc_and_deoptimization_index.deoptimization_index = deoptimization_index;
  pc_and_deoptimization_index.pc_after_gap = assembler->pc_offset();
  pc_and_deoptimization_index.arguments = arguments;
  pc_and_deoptimization_index.has_doubles = (kind & Safepoint::kWithDoubles);
  deoptimization_info_.Add(pc_and_deoptimization_index);
  indexes_.Add(new ZoneList<int>(8));
  registers_.Add((kind & Safepoint::kWithRegisters)
      ? new ZoneList<int>(4)
      : NULL);
  return Safepoint(indexes_.last(), registers_.last());
}


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


void SafepointTableBuilder::Emit(Assembler* assembler, int bits_per_entry) {
  // For lazy deoptimization we need space to patch a call after every call.
  // Ensure there is always space for such patching, even if the code ends
  // in a call.
  int target_offset = assembler->pc_offset() + Deoptimizer::patch_size();
  while (assembler->pc_offset() < target_offset) {
    assembler->nop();
  }

  // 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 and
  // pc after gap information.
  for (int i = 0; i < length; i++) {
    assembler->dd(deoptimization_info_[i].pc);
    assembler->dd(EncodeExceptPC(deoptimization_info_[i]));
  }

  // Emit table of bitmaps.
  ZoneList<uint8_t> bits(bytes_per_entry);
  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);

    // Run through the registers (if any).
    ASSERT(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);
        ASSERT(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 = info.deoptimization_index;
  unsigned gap_size = info.pc_after_gap - info.pc;
  uint32_t encoding = SafepointEntry::DeoptimizationIndexField::encode(index);
  encoding |= SafepointEntry::GapCodeSizeField::encode(gap_size);
  encoding |= SafepointEntry::ArgumentsField::encode(info.arguments);
  encoding |= SafepointEntry::SaveDoublesField::encode(info.has_doubles);
  return encoding;
}


int SafepointTableBuilder::CountShortDeoptimizationIntervals(unsigned limit) {
  int result = 0;
  if (!deoptimization_info_.is_empty()) {
    unsigned previous_gap_end = deoptimization_info_[0].pc_after_gap;
    for (int i = 1, n = deoptimization_info_.length(); i < n; i++) {
      DeoptimizationInfo info = deoptimization_info_[i];
      if (static_cast<int>(info.deoptimization_index) !=
          Safepoint::kNoDeoptimizationIndex) {
        if (previous_gap_end + limit > info.pc) {
          result++;
        }
        previous_gap_end = info.pc_after_gap;
      }
    }
  }
  return result;
}



} }  // namespace v8::internal