src/aarch64/simulator-aarch64.cc

// Copyright 2015, VIXL authors
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are met:
//
//   * Redistributions of source code must retain the above copyright notice,
//     this list of conditions and the following disclaimer.
//   * Redistributions in binary form must reproduce the above copyright notice,
//     this list of conditions and the following disclaimer in the documentation
//     and/or other materials provided with the distribution.
//   * Neither the name of ARM Limited nor the names of its contributors may be
//     used to endorse or promote products derived from this software without
//     specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS CONTRIBUTORS "AS IS" AND
// ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
// WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
// DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE
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// DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
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#ifdef VIXL_INCLUDE_SIMULATOR_AARCH64

#include <cstring>
#include <cmath>

#include "aarch64/simulator-aarch64.h"

namespace vixl {
namespace aarch64 {

const Instruction* Simulator::kEndOfSimAddress = NULL;

void SimSystemRegister::SetBits(int msb, int lsb, uint32_t bits) {
  int width = msb - lsb + 1;
  VIXL_ASSERT(IsUintN(width, bits) || IsIntN(width, bits));

  bits <<= lsb;
  uint32_t mask = ((1 << width) - 1) << lsb;
  VIXL_ASSERT((mask & write_ignore_mask_) == 0);

  value_ = (value_ & ~mask) | (bits & mask);
}


SimSystemRegister SimSystemRegister::DefaultValueFor(SystemRegister id) {
  switch (id) {
    case NZCV:
      return SimSystemRegister(0x00000000, NZCVWriteIgnoreMask);
    case FPCR:
      return SimSystemRegister(0x00000000, FPCRWriteIgnoreMask);
    default:
      VIXL_UNREACHABLE();
      return SimSystemRegister();
  }
}


Simulator::Simulator(Decoder* decoder, FILE* stream) {
  // Ensure that shift operations act as the simulator expects.
  VIXL_ASSERT((static_cast<int32_t>(-1) >> 1) == -1);
  VIXL_ASSERT((static_cast<uint32_t>(-1) >> 1) == 0x7fffffff);

  instruction_stats_ = false;

  // Set up the decoder.
  decoder_ = decoder;
  decoder_->AppendVisitor(this);

  stream_ = stream;
  print_disasm_ = new PrintDisassembler(stream_);
  SetColouredTrace(false);
  trace_parameters_ = LOG_NONE;

  ResetState();

  // Allocate and set up the simulator stack.
  stack_ = new byte[stack_size_];
  stack_limit_ = stack_ + stack_protection_size_;
  // Configure the starting stack pointer.
  //  - Find the top of the stack.
  byte* tos = stack_ + stack_size_;
  //  - There's a protection region at both ends of the stack.
  tos -= stack_protection_size_;
  //  - The stack pointer must be 16-byte aligned.
  tos = AlignDown(tos, 16);
  WriteSp(tos);

  instrumentation_ = NULL;

  // Print a warning about exclusive-access instructions, but only the first
  // time they are encountered. This warning can be silenced using
  // SilenceExclusiveAccessWarning().
  print_exclusive_access_warning_ = true;
}


void Simulator::ResetState() {
  // Reset the system registers.
  nzcv_ = SimSystemRegister::DefaultValueFor(NZCV);
  fpcr_ = SimSystemRegister::DefaultValueFor(FPCR);

  // Reset registers to 0.
  pc_ = NULL;
  pc_modified_ = false;
  for (unsigned i = 0; i < kNumberOfRegisters; i++) {
    WriteXRegister(i, 0xbadbeef);
  }
  // Set FP registers to a value that is a NaN in both 32-bit and 64-bit FP.
  uint64_t nan_bits[] = {
      UINT64_C(0x7ff00cab7f8ba9e1), UINT64_C(0x7ff0dead7f8beef1),
  };
  VIXL_ASSERT(IsSignallingNaN(RawbitsToDouble(nan_bits[0] & kDRegMask)));
  VIXL_ASSERT(IsSignallingNaN(RawbitsToFloat(nan_bits[0] & kSRegMask)));

  qreg_t q_bits;
  VIXL_ASSERT(sizeof(q_bits) == sizeof(nan_bits));
  memcpy(&q_bits, nan_bits, sizeof(nan_bits));

  for (unsigned i = 0; i < kNumberOfVRegisters; i++) {
    WriteQRegister(i, q_bits);
  }
  // Returning to address 0 exits the Simulator.
  WriteLr(kEndOfSimAddress);
}


Simulator::~Simulator() {
  delete[] stack_;
  // The decoder may outlive the simulator.
  decoder_->RemoveVisitor(print_disasm_);
  delete print_disasm_;

  decoder_->RemoveVisitor(instrumentation_);
  delete instrumentation_;
}


void Simulator::Run() {
  // Flush any written registers before executing anything, so that
  // manually-set registers are logged _before_ the first instruction.
  LogAllWrittenRegisters();

  while (pc_ != kEndOfSimAddress) {
    ExecuteInstruction();
  }
}


void Simulator::RunFrom(const Instruction* first) {
  WritePc(first);
  Run();
}


const char* Simulator::xreg_names[] = {"x0",  "x1",  "x2",  "x3",  "x4",  "x5",
                                       "x6",  "x7",  "x8",  "x9",  "x10", "x11",
                                       "x12", "x13", "x14", "x15", "x16", "x17",
                                       "x18", "x19", "x20", "x21", "x22", "x23",
                                       "x24", "x25", "x26", "x27", "x28", "x29",
                                       "lr",  "xzr", "sp"};

const char* Simulator::wreg_names[] = {"w0",  "w1",  "w2",  "w3",  "w4",  "w5",
                                       "w6",  "w7",  "w8",  "w9",  "w10", "w11",
                                       "w12", "w13", "w14", "w15", "w16", "w17",
                                       "w18", "w19", "w20", "w21", "w22", "w23",
                                       "w24", "w25", "w26", "w27", "w28", "w29",
                                       "w30", "wzr", "wsp"};

const char* Simulator::sreg_names[] = {"s0",  "s1",  "s2",  "s3",  "s4",  "s5",
                                       "s6",  "s7",  "s8",  "s9",  "s10", "s11",
                                       "s12", "s13", "s14", "s15", "s16", "s17",
                                       "s18", "s19", "s20", "s21", "s22", "s23",
                                       "s24", "s25", "s26", "s27", "s28", "s29",
                                       "s30", "s31"};

const char* Simulator::dreg_names[] = {"d0",  "d1",  "d2",  "d3",  "d4",  "d5",
                                       "d6",  "d7",  "d8",  "d9",  "d10", "d11",
                                       "d12", "d13", "d14", "d15", "d16", "d17",
                                       "d18", "d19", "d20", "d21", "d22", "d23",
                                       "d24", "d25", "d26", "d27", "d28", "d29",
                                       "d30", "d31"};

const char* Simulator::vreg_names[] = {"v0",  "v1",  "v2",  "v3",  "v4",  "v5",
                                       "v6",  "v7",  "v8",  "v9",  "v10", "v11",
                                       "v12", "v13", "v14", "v15", "v16", "v17",
                                       "v18", "v19", "v20", "v21", "v22", "v23",
                                       "v24", "v25", "v26", "v27", "v28", "v29",
                                       "v30", "v31"};


const char* Simulator::WRegNameForCode(unsigned code, Reg31Mode mode) {
  VIXL_ASSERT(code < kNumberOfRegisters);
  // If the code represents the stack pointer, index the name after zr.
  if ((code == kZeroRegCode) && (mode == Reg31IsStackPointer)) {
    code = kZeroRegCode + 1;
  }
  return wreg_names[code];
}


const char* Simulator::XRegNameForCode(unsigned code, Reg31Mode mode) {
  VIXL_ASSERT(code < kNumberOfRegisters);
  // If the code represents the stack pointer, index the name after zr.
  if ((code == kZeroRegCode) && (mode == Reg31IsStackPointer)) {
    code = kZeroRegCode + 1;
  }
  return xreg_names[code];
}


const char* Simulator::SRegNameForCode(unsigned code) {
  VIXL_ASSERT(code < kNumberOfFPRegisters);
  return sreg_names[code];
}


const char* Simulator::DRegNameForCode(unsigned code) {
  VIXL_ASSERT(code < kNumberOfFPRegisters);
  return dreg_names[code];
}


const char* Simulator::VRegNameForCode(unsigned code) {
  VIXL_ASSERT(code < kNumberOfVRegisters);
  return vreg_names[code];
}


#define COLOUR(colour_code) "\033[0;" colour_code "m"
#define COLOUR_BOLD(colour_code) "\033[1;" colour_code "m"
#define NORMAL ""
#define GREY "30"
#define RED "31"
#define GREEN "32"
#define YELLOW "33"
#define BLUE "34"
#define MAGENTA "35"
#define CYAN "36"
#define WHITE "37"
void Simulator::SetColouredTrace(bool value) {
  coloured_trace_ = value;

  clr_normal = value ? COLOUR(NORMAL) : "";
  clr_flag_name = value ? COLOUR_BOLD(WHITE) : "";
  clr_flag_value = value ? COLOUR(NORMAL) : "";
  clr_reg_name = value ? COLOUR_BOLD(CYAN) : "";
  clr_reg_value = value ? COLOUR(CYAN) : "";
  clr_vreg_name = value ? COLOUR_BOLD(MAGENTA) : "";
  clr_vreg_value = value ? COLOUR(MAGENTA) : "";
  clr_memory_address = value ? COLOUR_BOLD(BLUE) : "";
  clr_warning = value ? COLOUR_BOLD(YELLOW) : "";
  clr_warning_message = value ? COLOUR(YELLOW) : "";
  clr_printf = value ? COLOUR(GREEN) : "";
}


void Simulator::SetTraceParameters(int parameters) {
  bool disasm_before = trace_parameters_ & LOG_DISASM;
  trace_parameters_ = parameters;
  bool disasm_after = trace_parameters_ & LOG_DISASM;

  if (disasm_before != disasm_after) {
    if (disasm_after) {
      decoder_->InsertVisitorBefore(print_disasm_, this);
    } else {
      decoder_->RemoveVisitor(print_disasm_);
    }
  }
}


void Simulator::SetInstructionStats(bool value) {
  if (value != instruction_stats_) {
    if (value) {
      if (instrumentation_ == NULL) {
        // Set the sample period to 10, as the VIXL examples and tests are
        // short.
        instrumentation_ = new Instrument("vixl_stats.csv", 10);
      }
      decoder_->AppendVisitor(instrumentation_);
    } else if (instrumentation_ != NULL) {
      decoder_->RemoveVisitor(instrumentation_);
    }
    instruction_stats_ = value;
  }
}

// Helpers ---------------------------------------------------------------------
uint64_t Simulator::AddWithCarry(unsigned reg_size,
                                 bool set_flags,
                                 uint64_t left,
                                 uint64_t right,
                                 int carry_in) {
  VIXL_ASSERT((carry_in == 0) || (carry_in == 1));
  VIXL_ASSERT((reg_size == kXRegSize) || (reg_size == kWRegSize));

  uint64_t max_uint = (reg_size == kWRegSize) ? kWMaxUInt : kXMaxUInt;
  uint64_t reg_mask = (reg_size == kWRegSize) ? kWRegMask : kXRegMask;
  uint64_t sign_mask = (reg_size == kWRegSize) ? kWSignMask : kXSignMask;

  left &= reg_mask;
  right &= reg_mask;
  uint64_t result = (left + right + carry_in) & reg_mask;

  if (set_flags) {
    ReadNzcv().SetN(CalcNFlag(result, reg_size));
    ReadNzcv().SetZ(CalcZFlag(result));

    // Compute the C flag by comparing the result to the max unsigned integer.
    uint64_t max_uint_2op = max_uint - carry_in;
    bool C = (left > max_uint_2op) || ((max_uint_2op - left) < right);
    ReadNzcv().SetC(C ? 1 : 0);

    // Overflow iff the sign bit is the same for the two inputs and different
    // for the result.
    uint64_t left_sign = left & sign_mask;
    uint64_t right_sign = right & sign_mask;
    uint64_t result_sign = result & sign_mask;
    bool V = (left_sign == right_sign) && (left_sign != result_sign);
    ReadNzcv().SetV(V ? 1 : 0);

    LogSystemRegister(NZCV);
  }
  return result;
}


int64_t Simulator::ShiftOperand(unsigned reg_size,
                                int64_t value,
                                Shift shift_type,
                                unsigned amount) const {
  if (amount == 0) {
    return value;
  }
  int64_t mask = reg_size == kXRegSize ? kXRegMask : kWRegMask;
  switch (shift_type) {
    case LSL:
      return (value << amount) & mask;
    case LSR:
      return static_cast<uint64_t>(value) >> amount;
    case ASR: {
      // Shift used to restore the sign.
      unsigned s_shift = kXRegSize - reg_size;
      // Value with its sign restored.
      int64_t s_value = (value << s_shift) >> s_shift;
      return (s_value >> amount) & mask;
    }
    case ROR: {
      if (reg_size == kWRegSize) {
        value &= kWRegMask;
      }
      return (static_cast<uint64_t>(value) >> amount) |
             ((value & ((INT64_C(1) << amount) - 1)) << (reg_size - amount));
    }
    default:
      VIXL_UNIMPLEMENTED();
      return 0;
  }
}


int64_t Simulator::ExtendValue(unsigned reg_size,
                               int64_t value,
                               Extend extend_type,
                               unsigned left_shift) const {
  switch (extend_type) {
    case UXTB:
      value &= kByteMask;
      break;
    case UXTH:
      value &= kHalfWordMask;
      break;
    case UXTW:
      value &= kWordMask;
      break;
    case SXTB:
      value = (value << 56) >> 56;
      break;
    case SXTH:
      value = (value << 48) >> 48;
      break;
    case SXTW:
      value = (value << 32) >> 32;
      break;
    case UXTX:
    case SXTX:
      break;
    default:
      VIXL_UNREACHABLE();
  }
  int64_t mask = (reg_size == kXRegSize) ? kXRegMask : kWRegMask;
  return (value << left_shift) & mask;
}


void Simulator::FPCompare(double val0, double val1, FPTrapFlags trap) {
  AssertSupportedFPCR();

  // TODO: This assumes that the C++ implementation handles comparisons in the
  // way that we expect (as per AssertSupportedFPCR()).
  bool process_exception = false;
  if ((std::isnan(val0) != 0) || (std::isnan(val1) != 0)) {
    ReadNzcv().SetRawValue(FPUnorderedFlag);
    if (IsSignallingNaN(val0) || IsSignallingNaN(val1) ||
        (trap == EnableTrap)) {
      process_exception = true;
    }
  } else if (val0 < val1) {
    ReadNzcv().SetRawValue(FPLessThanFlag);
  } else if (val0 > val1) {
    ReadNzcv().SetRawValue(FPGreaterThanFlag);
  } else if (val0 == val1) {
    ReadNzcv().SetRawValue(FPEqualFlag);
  } else {
    VIXL_UNREACHABLE();
  }
  LogSystemRegister(NZCV);
  if (process_exception) FPProcessException();
}


uint64_t Simulator::ComputeMemOperandAddress(const MemOperand& mem_op) const {
  VIXL_ASSERT(mem_op.IsValid());
  int64_t base = ReadRegister<int64_t>(mem_op.GetBaseRegister());
  if (mem_op.IsImmediateOffset()) {
    return base + mem_op.GetOffset();
  } else {
    VIXL_ASSERT(mem_op.GetRegisterOffset().IsValid());
    int64_t offset = ReadRegister<int64_t>(mem_op.GetRegisterOffset());
    int64_t shift_amount = mem_op.GetShiftAmount();
    if (mem_op.GetShift() != NO_SHIFT) {
      offset = ShiftOperand(kXRegSize, offset, mem_op.GetShift(), shift_amount);
    }
    if (mem_op.GetExtend() != NO_EXTEND) {
      offset = ExtendValue(kXRegSize, offset, mem_op.GetExtend(), shift_amount);
    }
    return static_cast<uint64_t>(base + offset);
  }
}


Simulator::PrintRegisterFormat Simulator::GetPrintRegisterFormatForSize(
    unsigned reg_size, unsigned lane_size) {
  VIXL_ASSERT(reg_size >= lane_size);

  uint32_t format = 0;
  if (reg_size != lane_size) {
    switch (reg_size) {
      default:
        VIXL_UNREACHABLE();
        break;
      case kQRegSizeInBytes:
        format = kPrintRegAsQVector;
        break;
      case kDRegSizeInBytes:
        format = kPrintRegAsDVector;
        break;
    }
  }

  switch (lane_size) {
    default:
      VIXL_UNREACHABLE();
      break;
    case kQRegSizeInBytes:
      format |= kPrintReg1Q;
      break;
    case kDRegSizeInBytes:
      format |= kPrintReg1D;
      break;
    case kSRegSizeInBytes:
      format |= kPrintReg1S;
      break;
    case kHRegSizeInBytes:
      format |= kPrintReg1H;
      break;
    case kBRegSizeInBytes:
      format |= kPrintReg1B;
      break;
  }
  // These sizes would be duplicate case labels.
  VIXL_STATIC_ASSERT(kXRegSizeInBytes == kDRegSizeInBytes);
  VIXL_STATIC_ASSERT(kWRegSizeInBytes == kSRegSizeInBytes);
  VIXL_STATIC_ASSERT(kPrintXReg == kPrintReg1D);
  VIXL_STATIC_ASSERT(kPrintWReg == kPrintReg1S);

  return static_cast<PrintRegisterFormat>(format);
}


Simulator::PrintRegisterFormat Simulator::GetPrintRegisterFormat(
    VectorFormat vform) {
  switch (vform) {
    default:
      VIXL_UNREACHABLE();
      return kPrintReg16B;
    case kFormat16B:
      return kPrintReg16B;
    case kFormat8B:
      return kPrintReg8B;
    case kFormat8H:
      return kPrintReg8H;
    case kFormat4H:
      return kPrintReg4H;
    case kFormat4S:
      return kPrintReg4S;
    case kFormat2S:
      return kPrintReg2S;
    case kFormat2D:
      return kPrintReg2D;
    case kFormat1D:
      return kPrintReg1D;

    case kFormatB:
      return kPrintReg1B;
    case kFormatH:
      return kPrintReg1H;
    case kFormatS:
      return kPrintReg1S;
    case kFormatD:
      return kPrintReg1D;
  }
}


Simulator::PrintRegisterFormat Simulator::GetPrintRegisterFormatFP(
    VectorFormat vform) {
  switch (vform) {
    default:
      VIXL_UNREACHABLE();
      return kPrintReg16B;
    case kFormat4S:
      return kPrintReg4SFP;
    case kFormat2S:
      return kPrintReg2SFP;
    case kFormat2D:
      return kPrintReg2DFP;
    case kFormat1D:
      return kPrintReg1DFP;

    case kFormatS:
      return kPrintReg1SFP;
    case kFormatD:
      return kPrintReg1DFP;
  }
}


void Simulator::PrintWrittenRegisters() {
  for (unsigned i = 0; i < kNumberOfRegisters; i++) {
    if (registers_[i].WrittenSinceLastLog()) PrintRegister(i);
  }
}


void Simulator::PrintWrittenVRegisters() {
  for (unsigned i = 0; i < kNumberOfVRegisters; i++) {
    // At this point there is no type information, so print as a raw 1Q.
    if (vregisters_[i].WrittenSinceLastLog()) PrintVRegister(i, kPrintReg1Q);
  }
}


void Simulator::PrintSystemRegisters() {
  PrintSystemRegister(NZCV);
  PrintSystemRegister(FPCR);
}


void Simulator::PrintRegisters() {
  for (unsigned i = 0; i < kNumberOfRegisters; i++) {
    PrintRegister(i);
  }
}


void Simulator::PrintVRegisters() {
  for (unsigned i = 0; i < kNumberOfVRegisters; i++) {
    // At this point there is no type information, so print as a raw 1Q.
    PrintVRegister(i, kPrintReg1Q);
  }
}


// Print a register's name and raw value.
//
// Only the least-significant `size_in_bytes` bytes of the register are printed,
// but the value is aligned as if the whole register had been printed.
//
// For typical register updates, size_in_bytes should be set to kXRegSizeInBytes
// -- the default -- so that the whole register is printed. Other values of
// size_in_bytes are intended for use when the register hasn't actually been
// updated (such as in PrintWrite).
//
// No newline is printed. This allows the caller to print more details (such as
// a memory access annotation).
void Simulator::PrintRegisterRawHelper(unsigned code,
                                       Reg31Mode r31mode,
                                       int size_in_bytes) {
  // The template for all supported sizes.
  //   "# x{code}: 0xffeeddccbbaa9988"
  //   "# w{code}:         0xbbaa9988"
  //   "# w{code}<15:0>:       0x9988"
  //   "# w{code}<7:0>:          0x88"
  unsigned padding_chars = (kXRegSizeInBytes - size_in_bytes) * 2;

  const char* name = "";
  const char* suffix = "";
  switch (size_in_bytes) {
    case kXRegSizeInBytes:
      name = XRegNameForCode(code, r31mode);
      break;
    case kWRegSizeInBytes:
      name = WRegNameForCode(code, r31mode);
      break;
    case 2:
      name = WRegNameForCode(code, r31mode);
      suffix = "<15:0>";
      padding_chars -= strlen(suffix);
      break;
    case 1:
      name = WRegNameForCode(code, r31mode);
      suffix = "<7:0>";
      padding_chars -= strlen(suffix);
      break;
    default:
      VIXL_UNREACHABLE();
  }
  fprintf(stream_, "# %s%5s%s: ", clr_reg_name, name, suffix);

  // Print leading padding spaces.
  VIXL_ASSERT(padding_chars < (kXRegSizeInBytes * 2));
  for (unsigned i = 0; i < padding_chars; i++) {
    putc(' ', stream_);
  }

  // Print the specified bits in hexadecimal format.
  uint64_t bits = ReadRegister<uint64_t>(code, r31mode);
  bits &= kXRegMask >> ((kXRegSizeInBytes - size_in_bytes) * 8);
  VIXL_STATIC_ASSERT(sizeof(bits) == kXRegSizeInBytes);

  int chars = size_in_bytes * 2;
  fprintf(stream_,
          "%s0x%0*" PRIx64 "%s",
          clr_reg_value,
          chars,
          bits,
          clr_normal);
}


void Simulator::PrintRegister(unsigned code, Reg31Mode r31mode) {
  registers_[code].NotifyRegisterLogged();

  // Don't print writes into xzr.
  if ((code == kZeroRegCode) && (r31mode == Reg31IsZeroRegister)) {
    return;
  }

  // The template for all x and w registers:
  //   "# x{code}: 0x{value}"
  //   "# w{code}: 0x{value}"

  PrintRegisterRawHelper(code, r31mode);
  fprintf(stream_, "\n");
}


// Print a register's name and raw value.
//
// The `bytes` and `lsb` arguments can be used to limit the bytes that are
// printed. These arguments are intended for use in cases where register hasn't
// actually been updated (such as in PrintVWrite).
//
// No newline is printed. This allows the caller to print more details (such as
// a floating-point interpretation or a memory access annotation).
void Simulator::PrintVRegisterRawHelper(unsigned code, int bytes, int lsb) {
  // The template for vector types:
  //   "# v{code}: 0xffeeddccbbaa99887766554433221100".
  // An example with bytes=4 and lsb=8:
  //   "# v{code}:         0xbbaa9988                ".
  fprintf(stream_,
          "# %s%5s: %s",
          clr_vreg_name,
          VRegNameForCode(code),
          clr_vreg_value);

  int msb = lsb + bytes - 1;
  int byte = kQRegSizeInBytes - 1;

  // Print leading padding spaces. (Two spaces per byte.)
  while (byte > msb) {
    fprintf(stream_, "  ");
    byte--;
  }

  // Print the specified part of the value, byte by byte.
  qreg_t rawbits = ReadQRegister(code);
  fprintf(stream_, "0x");
  while (byte >= lsb) {
    fprintf(stream_, "%02x", rawbits.val[byte]);
    byte--;
  }

  // Print trailing padding spaces.
  while (byte >= 0) {
    fprintf(stream_, "  ");
    byte--;
  }
  fprintf(stream_, "%s", clr_normal);
}


// Print each of the specified lanes of a register as a float or double value.
//
// The `lane_count` and `lslane` arguments can be used to limit the lanes that
// are printed. These arguments are intended for use in cases where register
// hasn't actually been updated (such as in PrintVWrite).
//
// No newline is printed. This allows the caller to print more details (such as
// a memory access annotation).
void Simulator::PrintVRegisterFPHelper(unsigned code,
                                       unsigned lane_size_in_bytes,
                                       int lane_count,
                                       int rightmost_lane) {
  VIXL_ASSERT((lane_size_in_bytes == kSRegSizeInBytes) ||
              (lane_size_in_bytes == kDRegSizeInBytes));

  unsigned msb = ((lane_count + rightmost_lane) * lane_size_in_bytes);
  VIXL_ASSERT(msb <= kQRegSizeInBytes);

  // For scalar types ((lane_count == 1) && (rightmost_lane == 0)), a register
  // name is used:
  //   " (s{code}: {value})"
  //   " (d{code}: {value})"
  // For vector types, "..." is used to represent one or more omitted lanes.
  //   " (..., {value}, {value}, ...)"
  if ((lane_count == 1) && (rightmost_lane == 0)) {
    const char* name = (lane_size_in_bytes == kSRegSizeInBytes)
                           ? SRegNameForCode(code)
                           : DRegNameForCode(code);
    fprintf(stream_, " (%s%s: ", clr_vreg_name, name);
  } else {
    if (msb < (kQRegSizeInBytes - 1)) {
      fprintf(stream_, " (..., ");
    } else {
      fprintf(stream_, " (");
    }
  }

  // Print the list of values.
  const char* separator = "";
  int leftmost_lane = rightmost_lane + lane_count - 1;
  for (int lane = leftmost_lane; lane >= rightmost_lane; lane--) {
    double value = (lane_size_in_bytes == kSRegSizeInBytes)
                       ? ReadVRegister(code).GetLane<float>(lane)
                       : ReadVRegister(code).GetLane<double>(lane);
    if (std::isnan(value)) {
      // The output for NaNs is implementation defined. Always print `nan`, so
      // that traces are coherent across different implementations.
      fprintf(stream_, "%s%snan%s", separator, clr_vreg_value, clr_normal);
    } else {
      fprintf(stream_,
              "%s%s%#g%s",
              separator,
              clr_vreg_value,
              value,
              clr_normal);
    }
    separator = ", ";
  }

  if (rightmost_lane > 0) {
    fprintf(stream_, ", ...");
  }
  fprintf(stream_, ")");
}


void Simulator::PrintVRegister(unsigned code, PrintRegisterFormat format) {
  vregisters_[code].NotifyRegisterLogged();

  int lane_size_log2 = format & kPrintRegLaneSizeMask;

  int reg_size_log2;
  if (format & kPrintRegAsQVector) {
    reg_size_log2 = kQRegSizeInBytesLog2;
  } else if (format & kPrintRegAsDVector) {
    reg_size_log2 = kDRegSizeInBytesLog2;
  } else {
    // Scalar types.
    reg_size_log2 = lane_size_log2;
  }

  int lane_count = 1 << (reg_size_log2 - lane_size_log2);
  int lane_size = 1 << lane_size_log2;

  // The template for vector types:
  //   "# v{code}: 0x{rawbits} (..., {value}, ...)".
  // The template for scalar types:
  //   "# v{code}: 0x{rawbits} ({reg}:{value})".
  // The values in parentheses after the bit representations are floating-point
  // interpretations. They are displayed only if the kPrintVRegAsFP bit is set.

  PrintVRegisterRawHelper(code);
  if (format & kPrintRegAsFP) {
    PrintVRegisterFPHelper(code, lane_size, lane_count);
  }

  fprintf(stream_, "\n");
}


void Simulator::PrintSystemRegister(SystemRegister id) {
  switch (id) {
    case NZCV:
      fprintf(stream_,
              "# %sNZCV: %sN:%d Z:%d C:%d V:%d%s\n",
              clr_flag_name,
              clr_flag_value,
              ReadNzcv().GetN(),
              ReadNzcv().GetZ(),
              ReadNzcv().GetC(),
              ReadNzcv().GetV(),
              clr_normal);
      break;
    case FPCR: {
      static const char* rmode[] = {"0b00 (Round to Nearest)",
                                    "0b01 (Round towards Plus Infinity)",
                                    "0b10 (Round towards Minus Infinity)",
                                    "0b11 (Round towards Zero)"};
      VIXL_ASSERT(ReadFpcr().GetRMode() < (sizeof(rmode) / sizeof(rmode[0])));
      fprintf(stream_,
              "# %sFPCR: %sAHP:%d DN:%d FZ:%d RMode:%s%s\n",
              clr_flag_name,
              clr_flag_value,
              ReadFpcr().GetAHP(),
              ReadFpcr().GetDN(),
              ReadFpcr().GetFZ(),
              rmode[ReadFpcr().GetRMode()],
              clr_normal);
      break;
    }
    default:
      VIXL_UNREACHABLE();
  }
}


void Simulator::PrintRead(uintptr_t address,
                          unsigned reg_code,
                          PrintRegisterFormat format) {
  registers_[reg_code].NotifyRegisterLogged();

  USE(format);

  // The template is "# {reg}: 0x{value} <- {address}".
  PrintRegisterRawHelper(reg_code, Reg31IsZeroRegister);
  fprintf(stream_,
          " <- %s0x%016" PRIxPTR "%s\n",
          clr_memory_address,
          address,
          clr_normal);
}


void Simulator::PrintVRead(uintptr_t address,
                           unsigned reg_code,
                           PrintRegisterFormat format,
                           unsigned lane) {
  vregisters_[reg_code].NotifyRegisterLogged();

  // The template is "# v{code}: 0x{rawbits} <- address".
  PrintVRegisterRawHelper(reg_code);
  if (format & kPrintRegAsFP) {
    PrintVRegisterFPHelper(reg_code,
                           GetPrintRegLaneSizeInBytes(format),
                           GetPrintRegLaneCount(format),
                           lane);
  }
  fprintf(stream_,
          " <- %s0x%016" PRIxPTR "%s\n",
          clr_memory_address,
          address,
          clr_normal);
}


void Simulator::PrintWrite(uintptr_t address,
                           unsigned reg_code,
                           PrintRegisterFormat format) {
  VIXL_ASSERT(GetPrintRegLaneCount(format) == 1);

  // The template is "# v{code}: 0x{value} -> {address}". To keep the trace tidy
  // and readable, the value is aligned with the values in the register trace.
  PrintRegisterRawHelper(reg_code,
                         Reg31IsZeroRegister,
                         GetPrintRegSizeInBytes(format));
  fprintf(stream_,
          " -> %s0x%016" PRIxPTR "%s\n",
          clr_memory_address,
          address,
          clr_normal);
}


void Simulator::PrintVWrite(uintptr_t address,
                            unsigned reg_code,
                            PrintRegisterFormat format,
                            unsigned lane) {
  // The templates:
  //   "# v{code}: 0x{rawbits} -> {address}"
  //   "# v{code}: 0x{rawbits} (..., {value}, ...) -> {address}".
  //   "# v{code}: 0x{rawbits} ({reg}:{value}) -> {address}"
  // Because this trace doesn't represent a change to the source register's
  // value, only the relevant part of the value is printed. To keep the trace
  // tidy and readable, the raw value is aligned with the other values in the
  // register trace.
  int lane_count = GetPrintRegLaneCount(format);
  int lane_size = GetPrintRegLaneSizeInBytes(format);
  int reg_size = GetPrintRegSizeInBytes(format);
  PrintVRegisterRawHelper(reg_code, reg_size, lane_size * lane);
  if (format & kPrintRegAsFP) {
    PrintVRegisterFPHelper(reg_code, lane_size, lane_count, lane);
  }
  fprintf(stream_,
          " -> %s0x%016" PRIxPTR "%s\n",
          clr_memory_address,
          address,
          clr_normal);
}


// Visitors---------------------------------------------------------------------

void Simulator::VisitUnimplemented(const Instruction* instr) {
  printf("Unimplemented instruction at %p: 0x%08" PRIx32 "\n",
         reinterpret_cast<const void*>(instr),
         instr->GetInstructionBits());
  VIXL_UNIMPLEMENTED();
}


void Simulator::VisitUnallocated(const Instruction* instr) {
  printf("Unallocated instruction at %p: 0x%08" PRIx32 "\n",
         reinterpret_cast<const void*>(instr),
         instr->GetInstructionBits());
  VIXL_UNIMPLEMENTED();
}


void Simulator::VisitPCRelAddressing(const Instruction* instr) {
  VIXL_ASSERT((instr->Mask(PCRelAddressingMask) == ADR) ||
              (instr->Mask(PCRelAddressingMask) == ADRP));

  WriteRegister(instr->GetRd(), instr->GetImmPCOffsetTarget());
}


void Simulator::VisitUnconditionalBranch(const Instruction* instr) {
  switch (instr->Mask(UnconditionalBranchMask)) {
    case BL:
      WriteLr(instr->GetNextInstruction());
      VIXL_FALLTHROUGH();
    case B:
      WritePc(instr->GetImmPCOffsetTarget());
      break;
    default:
      VIXL_UNREACHABLE();
  }
}


void Simulator::VisitConditionalBranch(const Instruction* instr) {
  VIXL_ASSERT(instr->Mask(ConditionalBranchMask) == B_cond);
  if (ConditionPassed(instr->GetConditionBranch())) {
    WritePc(instr->GetImmPCOffsetTarget());
  }
}


void Simulator::VisitUnconditionalBranchToRegister(const Instruction* instr) {
  const Instruction* target = Instruction::Cast(ReadXRegister(instr->GetRn()));

  switch (instr->Mask(UnconditionalBranchToRegisterMask)) {
    case BLR:
      WriteLr(instr->GetNextInstruction());
      VIXL_FALLTHROUGH();
    case BR:
    case RET:
      WritePc(target);
      break;
    default:
      VIXL_UNREACHABLE();
  }
}


void Simulator::VisitTestBranch(const Instruction* instr) {
  unsigned bit_pos =
      (instr->GetImmTestBranchBit5() << 5) | instr->GetImmTestBranchBit40();
  bool bit_zero = ((ReadXRegister(instr->GetRt()) >> bit_pos) & 1) == 0;
  bool take_branch = false;
  switch (instr->Mask(TestBranchMask)) {
    case TBZ:
      take_branch = bit_zero;
      break;
    case TBNZ:
      take_branch = !bit_zero;
      break;
    default:
      VIXL_UNIMPLEMENTED();
  }
  if (take_branch) {
    WritePc(instr->GetImmPCOffsetTarget());
  }
}


void Simulator::VisitCompareBranch(const Instruction* instr) {
  unsigned rt = instr->GetRt();
  bool take_branch = false;
  switch (instr->Mask(CompareBranchMask)) {
    case CBZ_w:
      take_branch = (ReadWRegister(rt) == 0);
      break;
    case CBZ_x:
      take_branch = (ReadXRegister(rt) == 0);
      break;
    case CBNZ_w:
      take_branch = (ReadWRegister(rt) != 0);
      break;
    case CBNZ_x:
      take_branch = (ReadXRegister(rt) != 0);
      break;
    default:
      VIXL_UNIMPLEMENTED();
  }
  if (take_branch) {
    WritePc(instr->GetImmPCOffsetTarget());
  }
}


void Simulator::AddSubHelper(const Instruction* instr, int64_t op2) {
  unsigned reg_size = instr->GetSixtyFourBits() ? kXRegSize : kWRegSize;
  bool set_flags = instr->GetFlagsUpdate();
  int64_t new_val = 0;
  Instr operation = instr->Mask(AddSubOpMask);

  switch (operation) {
    case ADD:
    case ADDS: {
      new_val = AddWithCarry(reg_size,
                             set_flags,
                             ReadRegister(reg_size,
                                          instr->GetRn(),
                                          instr->GetRnMode()),
                             op2);
      break;
    }
    case SUB:
    case SUBS: {
      new_val = AddWithCarry(reg_size,
                             set_flags,
                             ReadRegister(reg_size,
                                          instr->GetRn(),
                                          instr->GetRnMode()),
                             ~op2,
                             1);
      break;
    }
    default:
      VIXL_UNREACHABLE();
  }

  WriteRegister(reg_size,
                instr->GetRd(),
                new_val,
                LogRegWrites,
                instr->GetRdMode());
}


void Simulator::VisitAddSubShifted(const Instruction* instr) {
  unsigned reg_size = instr->GetSixtyFourBits() ? kXRegSize : kWRegSize;
  int64_t op2 = ShiftOperand(reg_size,
                             ReadRegister(reg_size, instr->GetRm()),
                             static_cast<Shift>(instr->GetShiftDP()),
                             instr->GetImmDPShift());
  AddSubHelper(instr, op2);
}


void Simulator::VisitAddSubImmediate(const Instruction* instr) {
  int64_t op2 = instr->GetImmAddSub()
                << ((instr->GetShiftAddSub() == 1) ? 12 : 0);
  AddSubHelper(instr, op2);
}


void Simulator::VisitAddSubExtended(const Instruction* instr) {
  unsigned reg_size = instr->GetSixtyFourBits() ? kXRegSize : kWRegSize;
  int64_t op2 = ExtendValue(reg_size,
                            ReadRegister(reg_size, instr->GetRm()),
                            static_cast<Extend>(instr->GetExtendMode()),
                            instr->GetImmExtendShift());
  AddSubHelper(instr, op2);
}


void Simulator::VisitAddSubWithCarry(const Instruction* instr) {
  unsigned reg_size = instr->GetSixtyFourBits() ? kXRegSize : kWRegSize;
  int64_t op2 = ReadRegister(reg_size, instr->GetRm());
  int64_t new_val;

  if ((instr->Mask(AddSubOpMask) == SUB) ||
      (instr->Mask(AddSubOpMask) == SUBS)) {
    op2 = ~op2;
  }

  new_val = AddWithCarry(reg_size,
                         instr->GetFlagsUpdate(),
                         ReadRegister(reg_size, instr->GetRn()),
                         op2,
                         ReadC());

  WriteRegister(reg_size, instr->GetRd(), new_val);
}


void Simulator::VisitLogicalShifted(const Instruction* instr) {
  unsigned reg_size = instr->GetSixtyFourBits() ? kXRegSize : kWRegSize;
  Shift shift_type = static_cast<Shift>(instr->GetShiftDP());
  unsigned shift_amount = instr->GetImmDPShift();
  int64_t op2 = ShiftOperand(reg_size,
                             ReadRegister(reg_size, instr->GetRm()),
                             shift_type,
                             shift_amount);
  if (instr->Mask(NOT) == NOT) {
    op2 = ~op2;
  }
  LogicalHelper(instr, op2);
}


void Simulator::VisitLogicalImmediate(const Instruction* instr) {
  LogicalHelper(instr, instr->GetImmLogical());
}


void Simulator::LogicalHelper(const Instruction* instr, int64_t op2) {
  unsigned reg_size = instr->GetSixtyFourBits() ? kXRegSize : kWRegSize;
  int64_t op1 = ReadRegister(reg_size, instr->GetRn());
  int64_t result = 0;
  bool update_flags = false;

  // Switch on the logical operation, stripping out the NOT bit, as it has a
  // different meaning for logical immediate instructions.
  switch (instr->Mask(LogicalOpMask & ~NOT)) {
    case ANDS:
      update_flags = true;
      VIXL_FALLTHROUGH();
    case AND:
      result = op1 & op2;
      break;
    case ORR:
      result = op1 | op2;
      break;
    case EOR:
      result = op1 ^ op2;
      break;
    default:
      VIXL_UNIMPLEMENTED();
  }

  if (update_flags) {
    ReadNzcv().SetN(CalcNFlag(result, reg_size));
    ReadNzcv().SetZ(CalcZFlag(result));
    ReadNzcv().SetC(0);
    ReadNzcv().SetV(0);
    LogSystemRegister(NZCV);
  }

  WriteRegister(reg_size,
                instr->GetRd(),
                result,
                LogRegWrites,
                instr->GetRdMode());
}


void Simulator::VisitConditionalCompareRegister(const Instruction* instr) {
  unsigned reg_size = instr->GetSixtyFourBits() ? kXRegSize : kWRegSize;
  ConditionalCompareHelper(instr, ReadRegister(reg_size, instr->GetRm()));
}


void Simulator::VisitConditionalCompareImmediate(const Instruction* instr) {
  ConditionalCompareHelper(instr, instr->GetImmCondCmp());
}


void Simulator::ConditionalCompareHelper(const Instruction* instr,
                                         int64_t op2) {
  unsigned reg_size = instr->GetSixtyFourBits() ? kXRegSize : kWRegSize;
  int64_t op1 = ReadRegister(reg_size, instr->GetRn());

  if (ConditionPassed(instr->GetCondition())) {
    // If the condition passes, set the status flags to the result of comparing
    // the operands.
    if (instr->Mask(ConditionalCompareMask) == CCMP) {
      AddWithCarry(reg_size, true, op1, ~op2, 1);
    } else {
      VIXL_ASSERT(instr->Mask(ConditionalCompareMask) == CCMN);
      AddWithCarry(reg_size, true, op1, op2, 0);
    }
  } else {
    // If the condition fails, set the status flags to the nzcv immediate.
    ReadNzcv().SetFlags(instr->GetNzcv());
    LogSystemRegister(NZCV);
  }
}


void Simulator::VisitLoadStoreUnsignedOffset(const Instruction* instr) {
  int offset = instr->GetImmLSUnsigned() << instr->GetSizeLS();
  LoadStoreHelper(instr, offset, Offset);
}


void Simulator::VisitLoadStoreUnscaledOffset(const Instruction* instr) {
  LoadStoreHelper(instr, instr->GetImmLS(), Offset);
}


void Simulator::VisitLoadStorePreIndex(const Instruction* instr) {
  LoadStoreHelper(instr, instr->GetImmLS(), PreIndex);
}


void Simulator::VisitLoadStorePostIndex(const Instruction* instr) {
  LoadStoreHelper(instr, instr->GetImmLS(), PostIndex);
}


void Simulator::VisitLoadStoreRegisterOffset(const Instruction* instr) {
  Extend ext = static_cast<Extend>(instr->GetExtendMode());
  VIXL_ASSERT((ext == UXTW) || (ext == UXTX) || (ext == SXTW) || (ext == SXTX));
  unsigned shift_amount = instr->GetImmShiftLS() * instr->GetSizeLS();

  int64_t offset =
      ExtendValue(kXRegSize, ReadXRegister(instr->GetRm()), ext, shift_amount);
  LoadStoreHelper(instr, offset, Offset);
}


void Simulator::LoadStoreHelper(const Instruction* instr,
                                int64_t offset,
                                AddrMode addrmode) {
  unsigned srcdst = instr->GetRt();
  uintptr_t address = AddressModeHelper(instr->GetRn(), offset, addrmode);

  LoadStoreOp op = static_cast<LoadStoreOp>(instr->Mask(LoadStoreMask));
  switch (op) {
    case LDRB_w:
      WriteWRegister(srcdst, Memory::Read<uint8_t>(address), NoRegLog);
      break;
    case LDRH_w:
      WriteWRegister(srcdst, Memory::Read<uint16_t>(address), NoRegLog);
      break;
    case LDR_w:
      WriteWRegister(srcdst, Memory::Read<uint32_t>(address), NoRegLog);
      break;
    case LDR_x:
      WriteXRegister(srcdst, Memory::Read<uint64_t>(address), NoRegLog);
      break;
    case LDRSB_w:
      WriteWRegister(srcdst, Memory::Read<int8_t>(address), NoRegLog);
      break;
    case LDRSH_w:
      WriteWRegister(srcdst, Memory::Read<int16_t>(address), NoRegLog);
      break;
    case LDRSB_x:
      WriteXRegister(srcdst, Memory::Read<int8_t>(address), NoRegLog);
      break;
    case LDRSH_x:
      WriteXRegister(srcdst, Memory::Read<int16_t>(address), NoRegLog);
      break;
    case LDRSW_x:
      WriteXRegister(srcdst, Memory::Read<int32_t>(address), NoRegLog);
      break;
    case LDR_b:
      WriteBRegister(srcdst, Memory::Read<uint8_t>(address), NoRegLog);
      break;
    case LDR_h:
      WriteHRegister(srcdst, Memory::Read<uint16_t>(address), NoRegLog);
      break;
    case LDR_s:
      WriteSRegister(srcdst, Memory::Read<float>(address), NoRegLog);
      break;
    case LDR_d:
      WriteDRegister(srcdst, Memory::Read<double>(address), NoRegLog);
      break;
    case LDR_q:
      WriteQRegister(srcdst, Memory::Read<qreg_t>(address), NoRegLog);
      break;

    case STRB_w:
      Memory::Write<uint8_t>(address, ReadWRegister(srcdst));
      break;
    case STRH_w:
      Memory::Write<uint16_t>(address, ReadWRegister(srcdst));
      break;
    case STR_w:
      Memory::Write<uint32_t>(address, ReadWRegister(srcdst));
      break;
    case STR_x:
      Memory::Write<uint64_t>(address, ReadXRegister(srcdst));
      break;
    case STR_b:
      Memory::Write<uint8_t>(address, ReadBRegister(srcdst));
      break;
    case STR_h:
      Memory::Write<uint16_t>(address, ReadHRegister(srcdst));
      break;
    case STR_s:
      Memory::Write<float>(address, ReadSRegister(srcdst));
      break;
    case STR_d:
      Memory::Write<double>(address, ReadDRegister(srcdst));
      break;
    case STR_q:
      Memory::Write<qreg_t>(address, ReadQRegister(srcdst));
      break;

    // Ignore prfm hint instructions.
    case PRFM:
      break;

    default:
      VIXL_UNIMPLEMENTED();
  }

  unsigned access_size = 1 << instr->GetSizeLS();
  if (instr->IsLoad()) {
    if ((op == LDR_s) || (op == LDR_d)) {
      LogVRead(address, srcdst, GetPrintRegisterFormatForSizeFP(access_size));
    } else if ((op == LDR_b) || (op == LDR_h) || (op == LDR_q)) {
      LogVRead(address, srcdst, GetPrintRegisterFormatForSize(access_size));
    } else {
      LogRead(address, srcdst, GetPrintRegisterFormatForSize(access_size));
    }
  } else if (instr->IsStore()) {
    if ((op == STR_s) || (op == STR_d)) {
      LogVWrite(address, srcdst, GetPrintRegisterFormatForSizeFP(access_size));
    } else if ((op == STR_b) || (op == STR_h) || (op == STR_q)) {
      LogVWrite(address, srcdst, GetPrintRegisterFormatForSize(access_size));
    } else {
      LogWrite(address, srcdst, GetPrintRegisterFormatForSize(access_size));
    }
  } else {
    VIXL_ASSERT(op == PRFM);
  }

  local_monitor_.MaybeClear();
}


void Simulator::VisitLoadStorePairOffset(const Instruction* instr) {
  LoadStorePairHelper(instr, Offset);
}


void Simulator::VisitLoadStorePairPreIndex(const Instruction* instr) {
  LoadStorePairHelper(instr, PreIndex);
}


void Simulator::VisitLoadStorePairPostIndex(const Instruction* instr) {
  LoadStorePairHelper(instr, PostIndex);
}


void Simulator::VisitLoadStorePairNonTemporal(const Instruction* instr) {
  LoadStorePairHelper(instr, Offset);
}


void Simulator::LoadStorePairHelper(const Instruction* instr,
                                    AddrMode addrmode) {
  unsigned rt = instr->GetRt();
  unsigned rt2 = instr->GetRt2();
  int element_size = 1 << instr->GetSizeLSPair();
  int64_t offset = instr->GetImmLSPair() * element_size;
  uintptr_t address = AddressModeHelper(instr->GetRn(), offset, addrmode);
  uintptr_t address2 = address + element_size;

  LoadStorePairOp op =
      static_cast<LoadStorePairOp>(instr->Mask(LoadStorePairMask));

  // 'rt' and 'rt2' can only be aliased for stores.
  VIXL_ASSERT(((op & LoadStorePairLBit) == 0) || (rt != rt2));

  switch (op) {
    // Use NoRegLog to suppress the register trace (LOG_REGS, LOG_FP_REGS). We
    // will print a more detailed log.
    case LDP_w: {
      WriteWRegister(rt, Memory::Read<uint32_t>(address), NoRegLog);
      WriteWRegister(rt2, Memory::Read<uint32_t>(address2), NoRegLog);
      break;
    }
    case LDP_s: {
      WriteSRegister(rt, Memory::Read<float>(address), NoRegLog);
      WriteSRegister(rt2, Memory::Read<float>(address2), NoRegLog);
      break;
    }
    case LDP_x: {
      WriteXRegister(rt, Memory::Read<uint64_t>(address), NoRegLog);
      WriteXRegister(rt2, Memory::Read<uint64_t>(address2), NoRegLog);
      break;
    }
    case LDP_d: {
      WriteDRegister(rt, Memory::Read<double>(address), NoRegLog);
      WriteDRegister(rt2, Memory::Read<double>(address2), NoRegLog);
      break;
    }
    case LDP_q: {
      WriteQRegister(rt, Memory::Read<qreg_t>(address), NoRegLog);
      WriteQRegister(rt2, Memory::Read<qreg_t>(address2), NoRegLog);
      break;
    }
    case LDPSW_x: {
      WriteXRegister(rt, Memory::Read<int32_t>(address), NoRegLog);
      WriteXRegister(rt2, Memory::Read<int32_t>(address2), NoRegLog);
      break;
    }
    case STP_w: {
      Memory::Write<uint32_t>(address, ReadWRegister(rt));
      Memory::Write<uint32_t>(address2, ReadWRegister(rt2));
      break;
    }
    case STP_s: {
      Memory::Write<float>(address, ReadSRegister(rt));
      Memory::Write<float>(address2, ReadSRegister(rt2));
      break;
    }
    case STP_x: {
      Memory::Write<uint64_t>(address, ReadXRegister(rt));
      Memory::Write<uint64_t>(address2, ReadXRegister(rt2));
      break;
    }
    case STP_d: {
      Memory::Write<double>(address, ReadDRegister(rt));
      Memory::Write<double>(address2, ReadDRegister(rt2));
      break;
    }
    case STP_q: {
      Memory::Write<qreg_t>(address, ReadQRegister(rt));
      Memory::Write<qreg_t>(address2, ReadQRegister(rt2));
      break;
    }
    default:
      VIXL_UNREACHABLE();
  }

  // Print a detailed trace (including the memory address) instead of the basic
  // register:value trace generated by set_*reg().
  if (instr->IsLoad()) {
    if ((op == LDP_s) || (op == LDP_d)) {
      LogVRead(address, rt, GetPrintRegisterFormatForSizeFP(element_size));
      LogVRead(address2, rt2, GetPrintRegisterFormatForSizeFP(element_size));
    } else if (op == LDP_q) {
      LogVRead(address, rt, GetPrintRegisterFormatForSize(element_size));
      LogVRead(address2, rt2, GetPrintRegisterFormatForSize(element_size));
    } else {
      LogRead(address, rt, GetPrintRegisterFormatForSize(element_size));
      LogRead(address2, rt2, GetPrintRegisterFormatForSize(element_size));
    }
  } else {
    if ((op == STP_s) || (op == STP_d)) {
      LogVWrite(address, rt, GetPrintRegisterFormatForSizeFP(element_size));
      LogVWrite(address2, rt2, GetPrintRegisterFormatForSizeFP(element_size));
    } else if (op == STP_q) {
      LogVWrite(address, rt, GetPrintRegisterFormatForSize(element_size));
      LogVWrite(address2, rt2, GetPrintRegisterFormatForSize(element_size));
    } else {
      LogWrite(address, rt, GetPrintRegisterFormatForSize(element_size));
      LogWrite(address2, rt2, GetPrintRegisterFormatForSize(element_size));
    }
  }

  local_monitor_.MaybeClear();
}


void Simulator::PrintExclusiveAccessWarning() {
  if (print_exclusive_access_warning_) {
    fprintf(stderr,
            "%sWARNING:%s VIXL simulator support for "
            "load-/store-/clear-exclusive "
            "instructions is limited. Refer to the README for details.%s\n",
            clr_warning,
            clr_warning_message,
            clr_normal);
    print_exclusive_access_warning_ = false;
  }
}


void Simulator::VisitLoadStoreExclusive(const Instruction* instr) {
  PrintExclusiveAccessWarning();

  unsigned rs = instr->GetRs();
  unsigned rt = instr->GetRt();
  unsigned rt2 = instr->GetRt2();
  unsigned rn = instr->GetRn();

  LoadStoreExclusive op =
      static_cast<LoadStoreExclusive>(instr->Mask(LoadStoreExclusiveMask));

  bool is_acquire_release = instr->GetLdStXAcquireRelease();
  bool is_exclusive = !instr->GetLdStXNotExclusive();
  bool is_load = instr->GetLdStXLoad();
  bool is_pair = instr->GetLdStXPair();

  unsigned element_size = 1 << instr->GetLdStXSizeLog2();
  unsigned access_size = is_pair ? element_size * 2 : element_size;
  uint64_t address = ReadRegister<uint64_t>(rn, Reg31IsStackPointer);

  // Verify that the address is available to the host.
  VIXL_ASSERT(address == static_cast<uintptr_t>(address));

  // Check the alignment of `address`.
  if (AlignDown(address, access_size) != address) {
    VIXL_ALIGNMENT_EXCEPTION();
  }

  // The sp must be aligned to 16 bytes when it is accessed.
  if ((rn == 31) && (AlignDown(address, 16) != address)) {
    VIXL_ALIGNMENT_EXCEPTION();
  }

  if (is_load) {
    if (is_exclusive) {
      local_monitor_.MarkExclusive(address, access_size);
    } else {
      // Any non-exclusive load can clear the local monitor as a side effect. We
      // don't need to do this, but it is useful to stress the simulated code.
      local_monitor_.Clear();
    }

    // Use NoRegLog to suppress the register trace (LOG_REGS, LOG_FP_REGS). We
    // will print a more detailed log.
    switch (op) {
      case LDXRB_w:
      case LDAXRB_w:
      case LDARB_w:
        WriteWRegister(rt, Memory::Read<uint8_t>(address), NoRegLog);
        break;
      case LDXRH_w:
      case LDAXRH_w:
      case LDARH_w:
        WriteWRegister(rt, Memory::Read<uint16_t>(address), NoRegLog);
        break;
      case LDXR_w:
      case LDAXR_w:
      case LDAR_w:
        WriteWRegister(rt, Memory::Read<uint32_t>(address), NoRegLog);
        break;
      case LDXR_x:
      case LDAXR_x:
      case LDAR_x:
        WriteXRegister(rt, Memory::Read<uint64_t>(address), NoRegLog);
        break;
      case LDXP_w:
      case LDAXP_w:
        WriteWRegister(rt, Memory::Read<uint32_t>(address), NoRegLog);
        WriteWRegister(rt2,
                       Memory::Read<uint32_t>(address + element_size),
                       NoRegLog);
        break;
      case LDXP_x:
      case LDAXP_x:
        WriteXRegister(rt, Memory::Read<uint64_t>(address), NoRegLog);
        WriteXRegister(rt2,
                       Memory::Read<uint64_t>(address + element_size),
                       NoRegLog);
        break;
      default:
        VIXL_UNREACHABLE();
    }

    if (is_acquire_release) {
      // Approximate load-acquire by issuing a full barrier after the load.
      __sync_synchronize();
    }

    LogRead(address, rt, GetPrintRegisterFormatForSize(element_size));
    if (is_pair) {
      LogRead(address + element_size,
              rt2,
              GetPrintRegisterFormatForSize(element_size));
    }
  } else {
    if (is_acquire_release) {
      // Approximate store-release by issuing a full barrier before the store.
      __sync_synchronize();
    }

    bool do_store = true;
    if (is_exclusive) {
      do_store = local_monitor_.IsExclusive(address, access_size) &&
                 global_monitor_.IsExclusive(address, access_size);
      WriteWRegister(rs, do_store ? 0 : 1);

      //  - All exclusive stores explicitly clear the local monitor.
      local_monitor_.Clear();
    } else {
      //  - Any other store can clear the local monitor as a side effect.
      local_monitor_.MaybeClear();
    }

    if (do_store) {
      switch (op) {
        case STXRB_w:
        case STLXRB_w:
        case STLRB_w:
          Memory::Write<uint8_t>(address, ReadWRegister(rt));
          break;
        case STXRH_w:
        case STLXRH_w:
        case STLRH_w:
          Memory::Write<uint16_t>(address, ReadWRegister(rt));
          break;
        case STXR_w:
        case STLXR_w:
        case STLR_w:
          Memory::Write<uint32_t>(address, ReadWRegister(rt));
          break;
        case STXR_x:
        case STLXR_x:
        case STLR_x:
          Memory::Write<uint64_t>(address, ReadXRegister(rt));
          break;
        case STXP_w:
        case STLXP_w:
          Memory::Write<uint32_t>(address, ReadWRegister(rt));
          Memory::Write<uint32_t>(address + element_size, ReadWRegister(rt2));
          break;
        case STXP_x:
        case STLXP_x:
          Memory::Write<uint64_t>(address, ReadXRegister(rt));
          Memory::Write<uint64_t>(address + element_size, ReadXRegister(rt2));
          break;
        default:
          VIXL_UNREACHABLE();
      }

      LogWrite(address, rt, GetPrintRegisterFormatForSize(element_size));
      if (is_pair) {
        LogWrite(address + element_size,
                 rt2,
                 GetPrintRegisterFormatForSize(element_size));
      }
    }
  }
}


void Simulator::VisitLoadLiteral(const Instruction* instr) {
  unsigned rt = instr->GetRt();
  uint64_t address = instr->GetLiteralAddress<uint64_t>();

  // Verify that the calculated address is available to the host.
  VIXL_ASSERT(address == static_cast<uintptr_t>(address));

  switch (instr->Mask(LoadLiteralMask)) {
    // Use NoRegLog to suppress the register trace (LOG_REGS, LOG_VREGS), then
    // print a more detailed log.
    case LDR_w_lit:
      WriteWRegister(rt, Memory::Read<uint32_t>(address), NoRegLog);
      LogRead(address, rt, kPrintWReg);
      break;
    case LDR_x_lit:
      WriteXRegister(rt, Memory::Read<uint64_t>(address), NoRegLog);
      LogRead(address, rt, kPrintXReg);
      break;
    case LDR_s_lit:
      WriteSRegister(rt, Memory::Read<float>(address), NoRegLog);
      LogVRead(address, rt, kPrintSReg);
      break;
    case LDR_d_lit:
      WriteDRegister(rt, Memory::Read<double>(address), NoRegLog);
      LogVRead(address, rt, kPrintDReg);
      break;
    case LDR_q_lit:
      WriteQRegister(rt, Memory::Read<qreg_t>(address), NoRegLog);
      LogVRead(address, rt, kPrintReg1Q);
      break;
    case LDRSW_x_lit:
      WriteXRegister(rt, Memory::Read<int32_t>(address), NoRegLog);
      LogRead(address, rt, kPrintWReg);
      break;

    // Ignore prfm hint instructions.
    case PRFM_lit:
      break;

    default:
      VIXL_UNREACHABLE();
  }

  local_monitor_.MaybeClear();
}


uintptr_t Simulator::AddressModeHelper(unsigned addr_reg,
                                       int64_t offset,
                                       AddrMode addrmode) {
  uint64_t address = ReadXRegister(addr_reg, Reg31IsStackPointer);

  if ((addr_reg == 31) && ((address % 16) != 0)) {
    // When the base register is SP the stack pointer is required to be
    // quadword aligned prior to the address calculation and write-backs.
    // Misalignment will cause a stack alignment fault.
    VIXL_ALIGNMENT_EXCEPTION();
  }

  if ((addrmode == PreIndex) || (addrmode == PostIndex)) {
    VIXL_ASSERT(offset != 0);
    // Only preindex should log the register update here. For Postindex, the
    // update will be printed automatically by LogWrittenRegisters _after_ the
    // memory access itself is logged.
    RegLogMode log_mode = (addrmode == PreIndex) ? LogRegWrites : NoRegLog;
    WriteXRegister(addr_reg, address + offset, log_mode, Reg31IsStackPointer);
  }

  if ((addrmode == Offset) || (addrmode == PreIndex)) {
    address += offset;
  }

  // Verify that the calculated address is available to the host.
  VIXL_ASSERT(address == static_cast<uintptr_t>(address));

  return static_cast<uintptr_t>(address);
}


void Simulator::VisitMoveWideImmediate(const Instruction* instr) {
  MoveWideImmediateOp mov_op =
      static_cast<MoveWideImmediateOp>(instr->Mask(MoveWideImmediateMask));
  int64_t new_xn_val = 0;

  bool is_64_bits = instr->GetSixtyFourBits() == 1;
  // Shift is limited for W operations.
  VIXL_ASSERT(is_64_bits || (instr->GetShiftMoveWide() < 2));

  // Get the shifted immediate.
  int64_t shift = instr->GetShiftMoveWide() * 16;
  int64_t shifted_imm16 = static_cast<int64_t>(instr->GetImmMoveWide())
                          << shift;

  // Compute the new value.
  switch (mov_op) {
    case MOVN_w:
    case MOVN_x: {
      new_xn_val = ~shifted_imm16;
      if (!is_64_bits) new_xn_val &= kWRegMask;
      break;
    }
    case MOVK_w:
    case MOVK_x: {
      unsigned reg_code = instr->GetRd();
      int64_t prev_xn_val =
          is_64_bits ? ReadXRegister(reg_code) : ReadWRegister(reg_code);
      new_xn_val = (prev_xn_val & ~(INT64_C(0xffff) << shift)) | shifted_imm16;
      break;
    }
    case MOVZ_w:
    case MOVZ_x: {
      new_xn_val = shifted_imm16;
      break;
    }
    default:
      VIXL_UNREACHABLE();
  }

  // Update the destination register.
  WriteXRegister(instr->GetRd(), new_xn_val);
}


void Simulator::VisitConditionalSelect(const Instruction* instr) {
  uint64_t new_val = ReadXRegister(instr->GetRn());

  if (ConditionFailed(static_cast<Condition>(instr->GetCondition()))) {
    new_val = ReadXRegister(instr->GetRm());
    switch (instr->Mask(ConditionalSelectMask)) {
      case CSEL_w:
      case CSEL_x:
        break;
      case CSINC_w:
      case CSINC_x:
        new_val++;
        break;
      case CSINV_w:
      case CSINV_x:
        new_val = ~new_val;
        break;
      case CSNEG_w:
      case CSNEG_x:
        new_val = -new_val;
        break;
      default:
        VIXL_UNIMPLEMENTED();
    }
  }
  unsigned reg_size = instr->GetSixtyFourBits() ? kXRegSize : kWRegSize;
  WriteRegister(reg_size, instr->GetRd(), new_val);
}


void Simulator::VisitDataProcessing1Source(const Instruction* instr) {
  unsigned dst = instr->GetRd();
  unsigned src = instr->GetRn();

  switch (instr->Mask(DataProcessing1SourceMask)) {
    case RBIT_w:
      WriteWRegister(dst, ReverseBits(ReadWRegister(src)));
      break;
    case RBIT_x:
      WriteXRegister(dst, ReverseBits(ReadXRegister(src)));
      break;
    case REV16_w:
      WriteWRegister(dst, ReverseBytes(ReadWRegister(src), 1));
      break;
    case REV16_x:
      WriteXRegister(dst, ReverseBytes(ReadXRegister(src), 1));
      break;
    case REV_w:
      WriteWRegister(dst, ReverseBytes(ReadWRegister(src), 2));
      break;
    case REV32_x:
      WriteXRegister(dst, ReverseBytes(ReadXRegister(src), 2));
      break;
    case REV_x:
      WriteXRegister(dst, ReverseBytes(ReadXRegister(src), 3));
      break;
    case CLZ_w:
      WriteWRegister(dst, CountLeadingZeros(ReadWRegister(src)));
      break;
    case CLZ_x:
      WriteXRegister(dst, CountLeadingZeros(ReadXRegister(src)));
      break;
    case CLS_w:
      WriteWRegister(dst, CountLeadingSignBits(ReadWRegister(src)));
      break;
    case CLS_x:
      WriteXRegister(dst, CountLeadingSignBits(ReadXRegister(src)));
      break;
    default:
      VIXL_UNIMPLEMENTED();
  }
}


uint32_t Simulator::Poly32Mod2(unsigned n, uint64_t data, uint32_t poly) {
  VIXL_ASSERT((n > 32) && (n <= 64));
  for (unsigned i = (n - 1); i >= 32; i--) {
    if (((data >> i) & 1) != 0) {
      uint64_t polysh32 = (uint64_t)poly << (i - 32);
      uint64_t mask = (UINT64_C(1) << i) - 1;
      data = ((data & mask) ^ polysh32);
    }
  }
  return data & 0xffffffff;
}


template <typename T>
uint32_t Simulator::Crc32Checksum(uint32_t acc, T val, uint32_t poly) {
  unsigned size = sizeof(val) * 8;  // Number of bits in type T.
  VIXL_ASSERT((size == 8) || (size == 16) || (size == 32));
  uint64_t tempacc = static_cast<uint64_t>(ReverseBits(acc)) << size;
  uint64_t tempval = static_cast<uint64_t>(ReverseBits(val)) << 32;
  return ReverseBits(Poly32Mod2(32 + size, tempacc ^ tempval, poly));
}


uint32_t Simulator::Crc32Checksum(uint32_t acc, uint64_t val, uint32_t poly) {
  // Poly32Mod2 cannot handle inputs with more than 32 bits, so compute
  // the CRC of each 32-bit word sequentially.
  acc = Crc32Checksum(acc, (uint32_t)(val & 0xffffffff), poly);
  return Crc32Checksum(acc, (uint32_t)(val >> 32), poly);
}


void Simulator::VisitDataProcessing2Source(const Instruction* instr) {
  Shift shift_op = NO_SHIFT;
  int64_t result = 0;
  unsigned reg_size = instr->GetSixtyFourBits() ? kXRegSize : kWRegSize;

  switch (instr->Mask(DataProcessing2SourceMask)) {
    case SDIV_w: {
      int32_t rn = ReadWRegister(instr->GetRn());
      int32_t rm = ReadWRegister(instr->GetRm());
      if ((rn == kWMinInt) && (rm == -1)) {
        result = kWMinInt;
      } else if (rm == 0) {
        // Division by zero can be trapped, but not on A-class processors.
        result = 0;
      } else {
        result = rn / rm;
      }
      break;
    }
    case SDIV_x: {
      int64_t rn = ReadXRegister(instr->GetRn());
      int64_t rm = ReadXRegister(instr->GetRm());
      if ((rn == kXMinInt) && (rm == -1)) {
        result = kXMinInt;
      } else if (rm == 0) {
        // Division by zero can be trapped, but not on A-class processors.
        result = 0;
      } else {
        result = rn / rm;
      }
      break;
    }
    case UDIV_w: {
      uint32_t rn = static_cast<uint32_t>(ReadWRegister(instr->GetRn()));
      uint32_t rm = static_cast<uint32_t>(ReadWRegister(instr->GetRm()));
      if (rm == 0) {
        // Division by zero can be trapped, but not on A-class processors.
        result = 0;
      } else {
        result = rn / rm;
      }
      break;
    }
    case UDIV_x: {
      uint64_t rn = static_cast<uint64_t>(ReadXRegister(instr->GetRn()));
      uint64_t rm = static_cast<uint64_t>(ReadXRegister(instr->GetRm()));
      if (rm == 0) {
        // Division by zero can be trapped, but not on A-class processors.
        result = 0;
      } else {
        result = rn / rm;
      }
      break;
    }
    case LSLV_w:
    case LSLV_x:
      shift_op = LSL;
      break;
    case LSRV_w:
    case LSRV_x:
      shift_op = LSR;
      break;
    case ASRV_w:
    case ASRV_x:
      shift_op = ASR;
      break;
    case RORV_w:
    case RORV_x:
      shift_op = ROR;
      break;
    case CRC32B: {
      uint32_t acc = ReadRegister<uint32_t>(instr->GetRn());
      uint8_t val = ReadRegister<uint8_t>(instr->GetRm());
      result = Crc32Checksum(acc, val, CRC32_POLY);
      break;
    }
    case CRC32H: {
      uint32_t acc = ReadRegister<uint32_t>(instr->GetRn());
      uint16_t val = ReadRegister<uint16_t>(instr->GetRm());
      result = Crc32Checksum(acc, val, CRC32_POLY);
      break;
    }
    case CRC32W: {
      uint32_t acc = ReadRegister<uint32_t>(instr->GetRn());
      uint32_t val = ReadRegister<uint32_t>(instr->GetRm());
      result = Crc32Checksum(acc, val, CRC32_POLY);
      break;
    }
    case CRC32X: {
      uint32_t acc = ReadRegister<uint32_t>(instr->GetRn());
      uint64_t val = ReadRegister<uint64_t>(instr->GetRm());
      result = Crc32Checksum(acc, val, CRC32_POLY);
      reg_size = kWRegSize;
      break;
    }
    case CRC32CB: {
      uint32_t acc = ReadRegister<uint32_t>(instr->GetRn());
      uint8_t val = ReadRegister<uint8_t>(instr->GetRm());
      result = Crc32Checksum(acc, val, CRC32C_POLY);
      break;
    }
    case CRC32CH: {
      uint32_t acc = ReadRegister<uint32_t>(instr->GetRn());
      uint16_t val = ReadRegister<uint16_t>(instr->GetRm());
      result = Crc32Checksum(acc, val, CRC32C_POLY);
      break;
    }
    case CRC32CW: {
      uint32_t acc = ReadRegister<uint32_t>(instr->GetRn());
      uint32_t val = ReadRegister<uint32_t>(instr->GetRm());
      result = Crc32Checksum(acc, val, CRC32C_POLY);
      break;
    }
    case CRC32CX: {
      uint32_t acc = ReadRegister<uint32_t>(instr->GetRn());
      uint64_t val = ReadRegister<uint64_t>(instr->GetRm());
      result = Crc32Checksum(acc, val, CRC32C_POLY);
      reg_size = kWRegSize;
      break;
    }
    default:
      VIXL_UNIMPLEMENTED();
  }

  if (shift_op != NO_SHIFT) {
    // Shift distance encoded in the least-significant five/six bits of the
    // register.
    int mask = (instr->GetSixtyFourBits() == 1) ? 0x3f : 0x1f;
    unsigned shift = ReadWRegister(instr->GetRm()) & mask;
    result = ShiftOperand(reg_size,
                          ReadRegister(reg_size, instr->GetRn()),
                          shift_op,
                          shift);
  }
  WriteRegister(reg_size, instr->GetRd(), result);
}


// The algorithm used is adapted from the one described in section 8.2 of
//   Hacker's Delight, by Henry S. Warren, Jr.
// It assumes that a right shift on a signed integer is an arithmetic shift.
// Type T must be either uint64_t or int64_t.
template <typename T>
static T MultiplyHigh(T u, T v) {
  uint64_t u0, v0, w0;
  T u1, v1, w1, w2, t;

  VIXL_ASSERT(sizeof(u) == sizeof(u0));

  u0 = u & 0xffffffff;
  u1 = u >> 32;
  v0 = v & 0xffffffff;
  v1 = v >> 32;

  w0 = u0 * v0;
  t = u1 * v0 + (w0 >> 32);
  w1 = t & 0xffffffff;
  w2 = t >> 32;
  w1 = u0 * v1 + w1;

  return u1 * v1 + w2 + (w1 >> 32);
}


void Simulator::VisitDataProcessing3Source(const Instruction* instr) {
  unsigned reg_size = instr->GetSixtyFourBits() ? kXRegSize : kWRegSize;

  uint64_t result = 0;
  // Extract and sign- or zero-extend 32-bit arguments for widening operations.
  uint64_t rn_u32 = ReadRegister<uint32_t>(instr->GetRn());
  uint64_t rm_u32 = ReadRegister<uint32_t>(instr->GetRm());
  int64_t rn_s32 = ReadRegister<int32_t>(instr->GetRn());
  int64_t rm_s32 = ReadRegister<int32_t>(instr->GetRm());
  switch (instr->Mask(DataProcessing3SourceMask)) {
    case MADD_w:
    case MADD_x:
      result = ReadXRegister(instr->GetRa()) +
               (ReadXRegister(instr->GetRn()) * ReadXRegister(instr->GetRm()));
      break;
    case MSUB_w:
    case MSUB_x:
      result = ReadXRegister(instr->GetRa()) -
               (ReadXRegister(instr->GetRn()) * ReadXRegister(instr->GetRm()));
      break;
    case SMADDL_x:
      result = ReadXRegister(instr->GetRa()) + (rn_s32 * rm_s32);
      break;
    case SMSUBL_x:
      result = ReadXRegister(instr->GetRa()) - (rn_s32 * rm_s32);
      break;
    case UMADDL_x:
      result = ReadXRegister(instr->GetRa()) + (rn_u32 * rm_u32);
      break;
    case UMSUBL_x:
      result = ReadXRegister(instr->GetRa()) - (rn_u32 * rm_u32);
      break;
    case UMULH_x:
      result = MultiplyHigh(ReadRegister<uint64_t>(instr->GetRn()),
                            ReadRegister<uint64_t>(instr->GetRm()));
      break;
    case SMULH_x:
      result = MultiplyHigh(ReadXRegister(instr->GetRn()),
                            ReadXRegister(instr->GetRm()));
      break;
    default:
      VIXL_UNIMPLEMENTED();
  }
  WriteRegister(reg_size, instr->GetRd(), result);
}


void Simulator::VisitBitfield(const Instruction* instr) {
  unsigned reg_size = instr->GetSixtyFourBits() ? kXRegSize : kWRegSize;
  int64_t reg_mask = instr->GetSixtyFourBits() ? kXRegMask : kWRegMask;
  int64_t R = instr->GetImmR();
  int64_t S = instr->GetImmS();
  int64_t diff = S - R;
  int64_t mask;
  if (diff >= 0) {
    mask = (diff < (reg_size - 1)) ? (INT64_C(1) << (diff + 1)) - 1 : reg_mask;
  } else {
    mask = (INT64_C(1) << (S + 1)) - 1;
    mask = (static_cast<uint64_t>(mask) >> R) | (mask << (reg_size - R));
    diff += reg_size;
  }

  // inzero indicates if the extracted bitfield is inserted into the
  // destination register value or in zero.
  // If extend is true, extend the sign of the extracted bitfield.
  bool inzero = false;
  bool extend = false;
  switch (instr->Mask(BitfieldMask)) {
    case BFM_x:
    case BFM_w:
      break;
    case SBFM_x:
    case SBFM_w:
      inzero = true;
      extend = true;
      break;
    case UBFM_x:
    case UBFM_w:
      inzero = true;
      break;
    default:
      VIXL_UNIMPLEMENTED();
  }

  int64_t dst = inzero ? 0 : ReadRegister(reg_size, instr->GetRd());
  int64_t src = ReadRegister(reg_size, instr->GetRn());
  // Rotate source bitfield into place.
  int64_t result = (static_cast<uint64_t>(src) >> R) | (src << (reg_size - R));
  // Determine the sign extension.
  int64_t topbits = ((INT64_C(1) << (reg_size - diff - 1)) - 1) << (diff + 1);
  int64_t signbits = extend && ((src >> S) & 1) ? topbits : 0;

  // Merge sign extension, dest/zero and bitfield.
  result = signbits | (result & mask) | (dst & ~mask);

  WriteRegister(reg_size, instr->GetRd(), result);
}


void Simulator::VisitExtract(const Instruction* instr) {
  unsigned lsb = instr->GetImmS();
  unsigned reg_size = (instr->GetSixtyFourBits() == 1) ? kXRegSize : kWRegSize;
  uint64_t low_res =
      static_cast<uint64_t>(ReadRegister(reg_size, instr->GetRm())) >> lsb;
  uint64_t high_res = (lsb == 0) ? 0 : ReadRegister(reg_size, instr->GetRn())
                                           << (reg_size - lsb);
  WriteRegister(reg_size, instr->GetRd(), low_res | high_res);
}


void Simulator::VisitFPImmediate(const Instruction* instr) {
  AssertSupportedFPCR();

  unsigned dest = instr->GetRd();
  switch (instr->Mask(FPImmediateMask)) {
    case FMOV_s_imm:
      WriteSRegister(dest, instr->GetImmFP32());
      break;
    case FMOV_d_imm:
      WriteDRegister(dest, instr->GetImmFP64());
      break;
    default:
      VIXL_UNREACHABLE();
  }
}


void Simulator::VisitFPIntegerConvert(const Instruction* instr) {
  AssertSupportedFPCR();

  unsigned dst = instr->GetRd();
  unsigned src = instr->GetRn();

  FPRounding round = ReadRMode();

  switch (instr->Mask(FPIntegerConvertMask)) {
    case FCVTAS_ws:
      WriteWRegister(dst, FPToInt32(ReadSRegister(src), FPTieAway));
      break;
    case FCVTAS_xs:
      WriteXRegister(dst, FPToInt64(ReadSRegister(src), FPTieAway));
      break;
    case FCVTAS_wd:
      WriteWRegister(dst, FPToInt32(ReadDRegister(src), FPTieAway));
      break;
    case FCVTAS_xd:
      WriteXRegister(dst, FPToInt64(ReadDRegister(src), FPTieAway));
      break;
    case FCVTAU_ws:
      WriteWRegister(dst, FPToUInt32(ReadSRegister(src), FPTieAway));
      break;
    case FCVTAU_xs:
      WriteXRegister(dst, FPToUInt64(ReadSRegister(src), FPTieAway));
      break;
    case FCVTAU_wd:
      WriteWRegister(dst, FPToUInt32(ReadDRegister(src), FPTieAway));
      break;
    case FCVTAU_xd:
      WriteXRegister(dst, FPToUInt64(ReadDRegister(src), FPTieAway));
      break;
    case FCVTMS_ws:
      WriteWRegister(dst, FPToInt32(ReadSRegister(src), FPNegativeInfinity));
      break;
    case FCVTMS_xs:
      WriteXRegister(dst, FPToInt64(ReadSRegister(src), FPNegativeInfinity));
      break;
    case FCVTMS_wd:
      WriteWRegister(dst, FPToInt32(ReadDRegister(src), FPNegativeInfinity));
      break;
    case FCVTMS_xd:
      WriteXRegister(dst, FPToInt64(ReadDRegister(src), FPNegativeInfinity));
      break;
    case FCVTMU_ws:
      WriteWRegister(dst, FPToUInt32(ReadSRegister(src), FPNegativeInfinity));
      break;
    case FCVTMU_xs:
      WriteXRegister(dst, FPToUInt64(ReadSRegister(src), FPNegativeInfinity));
      break;
    case FCVTMU_wd:
      WriteWRegister(dst, FPToUInt32(ReadDRegister(src), FPNegativeInfinity));
      break;
    case FCVTMU_xd:
      WriteXRegister(dst, FPToUInt64(ReadDRegister(src), FPNegativeInfinity));
      break;
    case FCVTPS_ws:
      WriteWRegister(dst, FPToInt32(ReadSRegister(src), FPPositiveInfinity));
      break;
    case FCVTPS_xs:
      WriteXRegister(dst, FPToInt64(ReadSRegister(src), FPPositiveInfinity));
      break;
    case FCVTPS_wd:
      WriteWRegister(dst, FPToInt32(ReadDRegister(src), FPPositiveInfinity));
      break;
    case FCVTPS_xd:
      WriteXRegister(dst, FPToInt64(ReadDRegister(src), FPPositiveInfinity));
      break;
    case FCVTPU_ws:
      WriteWRegister(dst, FPToUInt32(ReadSRegister(src), FPPositiveInfinity));
      break;
    case FCVTPU_xs:
      WriteXRegister(dst, FPToUInt64(ReadSRegister(src), FPPositiveInfinity));
      break;
    case FCVTPU_wd:
      WriteWRegister(dst, FPToUInt32(ReadDRegister(src), FPPositiveInfinity));
      break;
    case FCVTPU_xd:
      WriteXRegister(dst, FPToUInt64(ReadDRegister(src), FPPositiveInfinity));
      break;
    case FCVTNS_ws:
      WriteWRegister(dst, FPToInt32(ReadSRegister(src), FPTieEven));
      break;
    case FCVTNS_xs:
      WriteXRegister(dst, FPToInt64(ReadSRegister(src), FPTieEven));
      break;
    case FCVTNS_wd:
      WriteWRegister(dst, FPToInt32(ReadDRegister(src), FPTieEven));
      break;
    case FCVTNS_xd:
      WriteXRegister(dst, FPToInt64(ReadDRegister(src), FPTieEven));
      break;
    case FCVTNU_ws:
      WriteWRegister(dst, FPToUInt32(ReadSRegister(src), FPTieEven));
      break;
    case FCVTNU_xs:
      WriteXRegister(dst, FPToUInt64(ReadSRegister(src), FPTieEven));
      break;
    case FCVTNU_wd:
      WriteWRegister(dst, FPToUInt32(ReadDRegister(src), FPTieEven));
      break;
    case FCVTNU_xd:
      WriteXRegister(dst, FPToUInt64(ReadDRegister(src), FPTieEven));
      break;
    case FCVTZS_ws:
      WriteWRegister(dst, FPToInt32(ReadSRegister(src), FPZero));
      break;
    case FCVTZS_xs:
      WriteXRegister(dst, FPToInt64(ReadSRegister(src), FPZero));
      break;
    case FCVTZS_wd:
      WriteWRegister(dst, FPToInt32(ReadDRegister(src), FPZero));
      break;
    case FCVTZS_xd:
      WriteXRegister(dst, FPToInt64(ReadDRegister(src), FPZero));
      break;
    case FCVTZU_ws:
      WriteWRegister(dst, FPToUInt32(ReadSRegister(src), FPZero));
      break;
    case FCVTZU_xs:
      WriteXRegister(dst, FPToUInt64(ReadSRegister(src), FPZero));
      break;
    case FCVTZU_wd:
      WriteWRegister(dst, FPToUInt32(ReadDRegister(src), FPZero));
      break;
    case FCVTZU_xd:
      WriteXRegister(dst, FPToUInt64(ReadDRegister(src), FPZero));
      break;
    case FMOV_ws:
      WriteWRegister(dst, ReadSRegisterBits(src));
      break;
    case FMOV_xd:
      WriteXRegister(dst, ReadDRegisterBits(src));
      break;
    case FMOV_sw:
      WriteSRegisterBits(dst, ReadWRegister(src));
      break;
    case FMOV_dx:
      WriteDRegisterBits(dst, ReadXRegister(src));
      break;
    case FMOV_d1_x:
      LogicVRegister(ReadVRegister(dst))
          .SetUint(kFormatD, 1, ReadXRegister(src));
      break;
    case FMOV_x_d1:
      WriteXRegister(dst, LogicVRegister(ReadVRegister(src)).Uint(kFormatD, 1));
      break;

    // A 32-bit input can be handled in the same way as a 64-bit input, since
    // the sign- or zero-extension will not affect the conversion.
    case SCVTF_dx:
      WriteDRegister(dst, FixedToDouble(ReadXRegister(src), 0, round));
      break;
    case SCVTF_dw:
      WriteDRegister(dst, FixedToDouble(ReadWRegister(src), 0, round));
      break;
    case UCVTF_dx:
      WriteDRegister(dst, UFixedToDouble(ReadXRegister(src), 0, round));
      break;
    case UCVTF_dw: {
      WriteDRegister(dst,
                     UFixedToDouble(static_cast<uint32_t>(ReadWRegister(src)),
                                    0,
                                    round));
      break;
    }
    case SCVTF_sx:
      WriteSRegister(dst, FixedToFloat(ReadXRegister(src), 0, round));
      break;
    case SCVTF_sw:
      WriteSRegister(dst, FixedToFloat(ReadWRegister(src), 0, round));
      break;
    case UCVTF_sx:
      WriteSRegister(dst, UFixedToFloat(ReadXRegister(src), 0, round));
      break;
    case UCVTF_sw: {
      WriteSRegister(dst,
                     UFixedToFloat(static_cast<uint32_t>(ReadWRegister(src)),
                                   0,
                                   round));
      break;
    }

    default:
      VIXL_UNREACHABLE();
  }
}


void Simulator::VisitFPFixedPointConvert(const Instruction* instr) {
  AssertSupportedFPCR();

  unsigned dst = instr->GetRd();
  unsigned src = instr->GetRn();
  int fbits = 64 - instr->GetFPScale();

  FPRounding round = ReadRMode();

  switch (instr->Mask(FPFixedPointConvertMask)) {
    // A 32-bit input can be handled in the same way as a 64-bit input, since
    // the sign- or zero-extension will not affect the conversion.
    case SCVTF_dx_fixed:
      WriteDRegister(dst, FixedToDouble(ReadXRegister(src), fbits, round));
      break;
    case SCVTF_dw_fixed:
      WriteDRegister(dst, FixedToDouble(ReadWRegister(src), fbits, round));
      break;
    case UCVTF_dx_fixed:
      WriteDRegister(dst, UFixedToDouble(ReadXRegister(src), fbits, round));
      break;
    case UCVTF_dw_fixed: {
      WriteDRegister(dst,
                     UFixedToDouble(static_cast<uint32_t>(ReadWRegister(src)),
                                    fbits,
                                    round));
      break;
    }
    case SCVTF_sx_fixed:
      WriteSRegister(dst, FixedToFloat(ReadXRegister(src), fbits, round));
      break;
    case SCVTF_sw_fixed:
      WriteSRegister(dst, FixedToFloat(ReadWRegister(src), fbits, round));
      break;
    case UCVTF_sx_fixed:
      WriteSRegister(dst, UFixedToFloat(ReadXRegister(src), fbits, round));
      break;
    case UCVTF_sw_fixed: {
      WriteSRegister(dst,
                     UFixedToFloat(static_cast<uint32_t>(ReadWRegister(src)),
                                   fbits,
                                   round));
      break;
    }
    case FCVTZS_xd_fixed:
      WriteXRegister(dst,
                     FPToInt64(ReadDRegister(src) * std::pow(2.0, fbits),
                               FPZero));
      break;
    case FCVTZS_wd_fixed:
      WriteWRegister(dst,
                     FPToInt32(ReadDRegister(src) * std::pow(2.0, fbits),
                               FPZero));
      break;
    case FCVTZU_xd_fixed:
      WriteXRegister(dst,
                     FPToUInt64(ReadDRegister(src) * std::pow(2.0, fbits),
                                FPZero));
      break;
    case FCVTZU_wd_fixed:
      WriteWRegister(dst,
                     FPToUInt32(ReadDRegister(src) * std::pow(2.0, fbits),
                                FPZero));
      break;
    case FCVTZS_xs_fixed:
      WriteXRegister(dst,
                     FPToInt64(ReadSRegister(src) * std::pow(2.0f, fbits),
                               FPZero));
      break;
    case FCVTZS_ws_fixed:
      WriteWRegister(dst,
                     FPToInt32(ReadSRegister(src) * std::pow(2.0f, fbits),
                               FPZero));
      break;
    case FCVTZU_xs_fixed:
      WriteXRegister(dst,
                     FPToUInt64(ReadSRegister(src) * std::pow(2.0f, fbits),
                                FPZero));
      break;
    case FCVTZU_ws_fixed:
      WriteWRegister(dst,
                     FPToUInt32(ReadSRegister(src) * std::pow(2.0f, fbits),
                                FPZero));
      break;
    default:
      VIXL_UNREACHABLE();
  }
}


void Simulator::VisitFPCompare(const Instruction* instr) {
  AssertSupportedFPCR();

  FPTrapFlags trap = DisableTrap;
  switch (instr->Mask(FPCompareMask)) {
    case FCMPE_s:
      trap = EnableTrap;
      VIXL_FALLTHROUGH();
    case FCMP_s:
      FPCompare(ReadSRegister(instr->GetRn()),
                ReadSRegister(instr->GetRm()),
                trap);
      break;
    case FCMPE_d:
      trap = EnableTrap;
      VIXL_FALLTHROUGH();
    case FCMP_d:
      FPCompare(ReadDRegister(instr->GetRn()),
                ReadDRegister(instr->GetRm()),
                trap);
      break;
    case FCMPE_s_zero:
      trap = EnableTrap;
      VIXL_FALLTHROUGH();
    case FCMP_s_zero:
      FPCompare(ReadSRegister(instr->GetRn()), 0.0f, trap);
      break;
    case FCMPE_d_zero:
      trap = EnableTrap;
      VIXL_FALLTHROUGH();
    case FCMP_d_zero:
      FPCompare(ReadDRegister(instr->GetRn()), 0.0, trap);
      break;
    default:
      VIXL_UNIMPLEMENTED();
  }
}


void Simulator::VisitFPConditionalCompare(const Instruction* instr) {
  AssertSupportedFPCR();

  FPTrapFlags trap = DisableTrap;
  switch (instr->Mask(FPConditionalCompareMask)) {
    case FCCMPE_s:
      trap = EnableTrap;
      VIXL_FALLTHROUGH();
    case FCCMP_s:
      if (ConditionPassed(instr->GetCondition())) {
        FPCompare(ReadSRegister(instr->GetRn()),
                  ReadSRegister(instr->GetRm()),
                  trap);
      } else {
        ReadNzcv().SetFlags(instr->GetNzcv());
        LogSystemRegister(NZCV);
      }
      break;
    case FCCMPE_d:
      trap = EnableTrap;
      VIXL_FALLTHROUGH();
    case FCCMP_d:
      if (ConditionPassed(instr->GetCondition())) {
        FPCompare(ReadDRegister(instr->GetRn()),
                  ReadDRegister(instr->GetRm()),
                  trap);
      } else {
        ReadNzcv().SetFlags(instr->GetNzcv());
        LogSystemRegister(NZCV);
      }
      break;
    default:
      VIXL_UNIMPLEMENTED();
  }
}


void Simulator::VisitFPConditionalSelect(const Instruction* instr) {
  AssertSupportedFPCR();

  Instr selected;
  if (ConditionPassed(instr->GetCondition())) {
    selected = instr->GetRn();
  } else {
    selected = instr->GetRm();
  }

  switch (instr->Mask(FPConditionalSelectMask)) {
    case FCSEL_s:
      WriteSRegister(instr->GetRd(), ReadSRegister(selected));
      break;
    case FCSEL_d:
      WriteDRegister(instr->GetRd(), ReadDRegister(selected));
      break;
    default:
      VIXL_UNIMPLEMENTED();
  }
}


void Simulator::VisitFPDataProcessing1Source(const Instruction* instr) {
  AssertSupportedFPCR();

  FPRounding fpcr_rounding = static_cast<FPRounding>(ReadFpcr().GetRMode());
  VectorFormat vform = (instr->Mask(FP64) == FP64) ? kFormatD : kFormatS;
  SimVRegister& rd = ReadVRegister(instr->GetRd());
  SimVRegister& rn = ReadVRegister(instr->GetRn());
  bool inexact_exception = false;

  unsigned fd = instr->GetRd();
  unsigned fn = instr->GetRn();

  switch (instr->Mask(FPDataProcessing1SourceMask)) {
    case FMOV_s:
      WriteSRegister(fd, ReadSRegister(fn));
      return;
    case FMOV_d:
      WriteDRegister(fd, ReadDRegister(fn));
      return;
    case FABS_s:
    case FABS_d:
      fabs_(vform, ReadVRegister(fd), ReadVRegister(fn));
      // Explicitly log the register update whilst we have type information.
      LogVRegister(fd, GetPrintRegisterFormatFP(vform));
      return;
    case FNEG_s:
    case FNEG_d:
      fneg(vform, ReadVRegister(fd), ReadVRegister(fn));
      // Explicitly log the register update whilst we have type information.
      LogVRegister(fd, GetPrintRegisterFormatFP(vform));
      return;
    case FCVT_ds:
      WriteDRegister(fd, FPToDouble(ReadSRegister(fn)));
      return;
    case FCVT_sd:
      WriteSRegister(fd, FPToFloat(ReadDRegister(fn), FPTieEven));
      return;
    case FCVT_hs:
      WriteHRegister(fd, FPToFloat16(ReadSRegister(fn), FPTieEven));
      return;
    case FCVT_sh:
      WriteSRegister(fd, FPToFloat(ReadHRegister(fn)));
      return;
    case FCVT_dh:
      WriteDRegister(fd, FPToDouble(FPToFloat(ReadHRegister(fn))));
      return;
    case FCVT_hd:
      WriteHRegister(fd, FPToFloat16(ReadDRegister(fn), FPTieEven));
      return;
    case FSQRT_s:
    case FSQRT_d:
      fsqrt(vform, rd, rn);
      // Explicitly log the register update whilst we have type information.
      LogVRegister(fd, GetPrintRegisterFormatFP(vform));
      return;
    case FRINTI_s:
    case FRINTI_d:
      break;  // Use FPCR rounding mode.
    case FRINTX_s:
    case FRINTX_d:
      inexact_exception = true;
      break;
    case FRINTA_s:
    case FRINTA_d:
      fpcr_rounding = FPTieAway;
      break;
    case FRINTM_s:
    case FRINTM_d:
      fpcr_rounding = FPNegativeInfinity;
      break;
    case FRINTN_s:
    case FRINTN_d:
      fpcr_rounding = FPTieEven;
      break;
    case FRINTP_s:
    case FRINTP_d:
      fpcr_rounding = FPPositiveInfinity;
      break;
    case FRINTZ_s:
    case FRINTZ_d:
      fpcr_rounding = FPZero;
      break;
    default:
      VIXL_UNIMPLEMENTED();
  }

  // Only FRINT* instructions fall through the switch above.
  frint(vform, rd, rn, fpcr_rounding, inexact_exception);
  // Explicitly log the register update whilst we have type information.
  LogVRegister(fd, GetPrintRegisterFormatFP(vform));
}


void Simulator::VisitFPDataProcessing2Source(const Instruction* instr) {
  AssertSupportedFPCR();

  VectorFormat vform = (instr->Mask(FP64) == FP64) ? kFormatD : kFormatS;
  SimVRegister& rd = ReadVRegister(instr->GetRd());
  SimVRegister& rn = ReadVRegister(instr->GetRn());
  SimVRegister& rm = ReadVRegister(instr->GetRm());

  switch (instr->Mask(FPDataProcessing2SourceMask)) {
    case FADD_s:
    case FADD_d:
      fadd(vform, rd, rn, rm);
      break;
    case FSUB_s:
    case FSUB_d:
      fsub(vform, rd, rn, rm);
      break;
    case FMUL_s:
    case FMUL_d:
      fmul(vform, rd, rn, rm);
      break;
    case FNMUL_s:
    case FNMUL_d:
      fnmul(vform, rd, rn, rm);
      break;
    case FDIV_s:
    case FDIV_d:
      fdiv(vform, rd, rn, rm);
      break;
    case FMAX_s:
    case FMAX_d:
      fmax(vform, rd, rn, rm);
      break;
    case FMIN_s:
    case FMIN_d:
      fmin(vform, rd, rn, rm);
      break;
    case FMAXNM_s:
    case FMAXNM_d:
      fmaxnm(vform, rd, rn, rm);
      break;
    case FMINNM_s:
    case FMINNM_d:
      fminnm(vform, rd, rn, rm);
      break;
    default:
      VIXL_UNREACHABLE();
  }
  // Explicitly log the register update whilst we have type information.
  LogVRegister(instr->GetRd(), GetPrintRegisterFormatFP(vform));
}


void Simulator::VisitFPDataProcessing3Source(const Instruction* instr) {
  AssertSupportedFPCR();

  unsigned fd = instr->GetRd();
  unsigned fn = instr->GetRn();
  unsigned fm = instr->GetRm();
  unsigned fa = instr->GetRa();

  switch (instr->Mask(FPDataProcessing3SourceMask)) {
    // fd = fa +/- (fn * fm)
    case FMADD_s:
      WriteSRegister(fd,
                     FPMulAdd(ReadSRegister(fa),
                              ReadSRegister(fn),
                              ReadSRegister(fm)));
      break;
    case FMSUB_s:
      WriteSRegister(fd,
                     FPMulAdd(ReadSRegister(fa),
                              -ReadSRegister(fn),
                              ReadSRegister(fm)));
      break;
    case FMADD_d:
      WriteDRegister(fd,
                     FPMulAdd(ReadDRegister(fa),
                              ReadDRegister(fn),
                              ReadDRegister(fm)));
      break;
    case FMSUB_d:
      WriteDRegister(fd,
                     FPMulAdd(ReadDRegister(fa),
                              -ReadDRegister(fn),
                              ReadDRegister(fm)));
      break;
    // Negated variants of the above.
    case FNMADD_s:
      WriteSRegister(fd,
                     FPMulAdd(-ReadSRegister(fa),
                              -ReadSRegister(fn),
                              ReadSRegister(fm)));
      break;
    case FNMSUB_s:
      WriteSRegister(fd,
                     FPMulAdd(-ReadSRegister(fa),
                              ReadSRegister(fn),
                              ReadSRegister(fm)));
      break;
    case FNMADD_d:
      WriteDRegister(fd,
                     FPMulAdd(-ReadDRegister(fa),
                              -ReadDRegister(fn),
                              ReadDRegister(fm)));
      break;
    case FNMSUB_d:
      WriteDRegister(fd,
                     FPMulAdd(-ReadDRegister(fa),
                              ReadDRegister(fn),
                              ReadDRegister(fm)));
      break;
    default:
      VIXL_UNIMPLEMENTED();
  }
}


bool Simulator::FPProcessNaNs(const Instruction* instr) {
  unsigned fd = instr->GetRd();
  unsigned fn = instr->GetRn();
  unsigned fm = instr->GetRm();
  bool done = false;

  if (instr->Mask(FP64) == FP64) {
    double result = FPProcessNaNs(ReadDRegister(fn), ReadDRegister(fm));
    if (std::isnan(result)) {
      WriteDRegister(fd, result);
      done = true;
    }
  } else {
    float result = FPProcessNaNs(ReadSRegister(fn), ReadSRegister(fm));
    if (std::isnan(result)) {
      WriteSRegister(fd, result);
      done = true;
    }
  }

  return done;
}


void Simulator::SysOp_W(int op, int64_t val) {
  switch (op) {
    case IVAU:
    case CVAC:
    case CVAU:
    case CIVAC: {
      // Perform a dummy memory access to ensure that we have read access
      // to the specified address.
      volatile uint8_t y = Memory::Read<uint8_t>(val);
      USE(y);
      // TODO: Implement "case ZVA:".
      break;
    }
    default:
      VIXL_UNIMPLEMENTED();
  }
}


void Simulator::VisitSystem(const Instruction* instr) {
  // Some system instructions hijack their Op and Cp fields to represent a
  // range of immediates instead of indicating a different instruction. This
  // makes the decoding tricky.
  if (instr->Mask(SystemExclusiveMonitorFMask) == SystemExclusiveMonitorFixed) {
    VIXL_ASSERT(instr->Mask(SystemExclusiveMonitorMask) == CLREX);
    switch (instr->Mask(SystemExclusiveMonitorMask)) {
      case CLREX: {
        PrintExclusiveAccessWarning();
        ClearLocalMonitor();
        break;
      }
    }
  } else if (instr->Mask(SystemSysRegFMask) == SystemSysRegFixed) {
    switch (instr->Mask(SystemSysRegMask)) {
      case MRS: {
        switch (instr->GetImmSystemRegister()) {
          case NZCV:
            WriteXRegister(instr->GetRt(), ReadNzcv().GetRawValue());
            break;
          case FPCR:
            WriteXRegister(instr->GetRt(), ReadFpcr().GetRawValue());
            break;
          default:
            VIXL_UNIMPLEMENTED();
        }
        break;
      }
      case MSR: {
        switch (instr->GetImmSystemRegister()) {
          case NZCV:
            ReadNzcv().SetRawValue(ReadWRegister(instr->GetRt()));
            LogSystemRegister(NZCV);
            break;
          case FPCR:
            ReadFpcr().SetRawValue(ReadWRegister(instr->GetRt()));
            LogSystemRegister(FPCR);
            break;
          default:
            VIXL_UNIMPLEMENTED();
        }
        break;
      }
    }
  } else if (instr->Mask(SystemHintFMask) == SystemHintFixed) {
    VIXL_ASSERT(instr->Mask(SystemHintMask) == HINT);
    switch (instr->GetImmHint()) {
      case NOP:
        break;
      default:
        VIXL_UNIMPLEMENTED();
    }
  } else if (instr->Mask(MemBarrierFMask) == MemBarrierFixed) {
    __sync_synchronize();
  } else if ((instr->Mask(SystemSysFMask) == SystemSysFixed)) {
    switch (instr->Mask(SystemSysMask)) {
      case SYS:
        SysOp_W(instr->GetSysOp(), ReadXRegister(instr->GetRt()));
        break;
      default:
        VIXL_UNIMPLEMENTED();
    }
  } else {
    VIXL_UNIMPLEMENTED();
  }
}


void Simulator::VisitException(const Instruction* instr) {
  switch (instr->Mask(ExceptionMask)) {
    case HLT:
      switch (instr->GetImmException()) {
        case kUnreachableOpcode:
          DoUnreachable(instr);
          return;
        case kTraceOpcode:
          DoTrace(instr);
          return;
        case kLogOpcode:
          DoLog(instr);
          return;
        case kPrintfOpcode:
          DoPrintf(instr);
          return;
        case kRuntimeCallOpcode:
          DoRuntimeCall(instr);
          return;
        default:
          HostBreakpoint();
          return;
      }
    case BRK:
      HostBreakpoint();
      return;
    default:
      VIXL_UNIMPLEMENTED();
  }
}


void Simulator::VisitCrypto2RegSHA(const Instruction* instr) {
  VisitUnimplemented(instr);
}


void Simulator::VisitCrypto3RegSHA(const Instruction* instr) {
  VisitUnimplemented(instr);
}


void Simulator::VisitCryptoAES(const Instruction* instr) {
  VisitUnimplemented(instr);
}


void Simulator::VisitNEON2RegMisc(const Instruction* instr) {
  NEONFormatDecoder nfd(instr);
  VectorFormat vf = nfd.GetVectorFormat();

  static const NEONFormatMap map_lp =
      {{23, 22, 30}, {NF_4H, NF_8H, NF_2S, NF_4S, NF_1D, NF_2D}};
  VectorFormat vf_lp = nfd.GetVectorFormat(&map_lp);

  static const NEONFormatMap map_fcvtl = {{22}, {NF_4S, NF_2D}};
  VectorFormat vf_fcvtl = nfd.GetVectorFormat(&map_fcvtl);

  static const NEONFormatMap map_fcvtn = {{22, 30},
                                          {NF_4H, NF_8H, NF_2S, NF_4S}};
  VectorFormat vf_fcvtn = nfd.GetVectorFormat(&map_fcvtn);

  SimVRegister& rd = ReadVRegister(instr->GetRd());
  SimVRegister& rn = ReadVRegister(instr->GetRn());

  if (instr->Mask(NEON2RegMiscOpcode) <= NEON_NEG_opcode) {
    // These instructions all use a two bit size field, except NOT and RBIT,
    // which use the field to encode the operation.
    switch (instr->Mask(NEON2RegMiscMask)) {
      case NEON_REV64:
        rev64(vf, rd, rn);
        break;
      case NEON_REV32:
        rev32(vf, rd, rn);
        break;
      case NEON_REV16:
        rev16(vf, rd, rn);
        break;
      case NEON_SUQADD:
        suqadd(vf, rd, rn);
        break;
      case NEON_USQADD:
        usqadd(vf, rd, rn);
        break;
      case NEON_CLS:
        cls(vf, rd, rn);
        break;
      case NEON_CLZ:
        clz(vf, rd, rn);
        break;
      case NEON_CNT:
        cnt(vf, rd, rn);
        break;
      case NEON_SQABS:
        abs(vf, rd, rn).SignedSaturate(vf);
        break;
      case NEON_SQNEG:
        neg(vf, rd, rn).SignedSaturate(vf);
        break;
      case NEON_CMGT_zero:
        cmp(vf, rd, rn, 0, gt);
        break;
      case NEON_CMGE_zero:
        cmp(vf, rd, rn, 0, ge);
        break;
      case NEON_CMEQ_zero:
        cmp(vf, rd, rn, 0, eq);
        break;
      case NEON_CMLE_zero:
        cmp(vf, rd, rn, 0, le);
        break;
      case NEON_CMLT_zero:
        cmp(vf, rd, rn, 0, lt);
        break;
      case NEON_ABS:
        abs(vf, rd, rn);
        break;
      case NEON_NEG:
        neg(vf, rd, rn);
        break;
      case NEON_SADDLP:
        saddlp(vf_lp, rd, rn);
        break;
      case NEON_UADDLP:
        uaddlp(vf_lp, rd, rn);
        break;
      case NEON_SADALP:
        sadalp(vf_lp, rd, rn);
        break;
      case NEON_UADALP:
        uadalp(vf_lp, rd, rn);
        break;
      case NEON_RBIT_NOT:
        vf = nfd.GetVectorFormat(nfd.LogicalFormatMap());
        switch (instr->GetFPType()) {
          case 0:
            not_(vf, rd, rn);
            break;
          case 1:
            rbit(vf, rd, rn);
            break;
          default:
            VIXL_UNIMPLEMENTED();
        }
        break;
    }
  } else {
    VectorFormat fpf = nfd.GetVectorFormat(nfd.FPFormatMap());
    FPRounding fpcr_rounding = static_cast<FPRounding>(ReadFpcr().GetRMode());
    bool inexact_exception = false;

    // These instructions all use a one bit size field, except XTN, SQXTUN,
    // SHLL, SQXTN and UQXTN, which use a two bit size field.
    switch (instr->Mask(NEON2RegMiscFPMask)) {
      case NEON_FABS:
        fabs_(fpf, rd, rn);
        return;
      case NEON_FNEG:
        fneg(fpf, rd, rn);
        return;
      case NEON_FSQRT:
        fsqrt(fpf, rd, rn);
        return;
      case NEON_FCVTL:
        if (instr->Mask(NEON_Q)) {
          fcvtl2(vf_fcvtl, rd, rn);
        } else {
          fcvtl(vf_fcvtl, rd, rn);
        }
        return;
      case NEON_FCVTN:
        if (instr->Mask(NEON_Q)) {
          fcvtn2(vf_fcvtn, rd, rn);
        } else {
          fcvtn(vf_fcvtn, rd, rn);
        }
        return;
      case NEON_FCVTXN:
        if (instr->Mask(NEON_Q)) {
          fcvtxn2(vf_fcvtn, rd, rn);
        } else {
          fcvtxn(vf_fcvtn, rd, rn);
        }
        return;

      // The following instructions break from the switch statement, rather
      // than return.
      case NEON_FRINTI:
        break;  // Use FPCR rounding mode.
      case NEON_FRINTX:
        inexact_exception = true;
        break;
      case NEON_FRINTA:
        fpcr_rounding = FPTieAway;
        break;
      case NEON_FRINTM:
        fpcr_rounding = FPNegativeInfinity;
        break;
      case NEON_FRINTN:
        fpcr_rounding = FPTieEven;
        break;
      case NEON_FRINTP:
        fpcr_rounding = FPPositiveInfinity;
        break;
      case NEON_FRINTZ:
        fpcr_rounding = FPZero;
        break;

      case NEON_FCVTNS:
        fcvts(fpf, rd, rn, FPTieEven);
        return;
      case NEON_FCVTNU:
        fcvtu(fpf, rd, rn, FPTieEven);
        return;
      case NEON_FCVTPS:
        fcvts(fpf, rd, rn, FPPositiveInfinity);
        return;
      case NEON_FCVTPU:
        fcvtu(fpf, rd, rn, FPPositiveInfinity);
        return;
      case NEON_FCVTMS:
        fcvts(fpf, rd, rn, FPNegativeInfinity);
        return;
      case NEON_FCVTMU:
        fcvtu(fpf, rd, rn, FPNegativeInfinity);
        return;
      case NEON_FCVTZS:
        fcvts(fpf, rd, rn, FPZero);
        return;
      case NEON_FCVTZU:
        fcvtu(fpf, rd, rn, FPZero);
        return;
      case NEON_FCVTAS:
        fcvts(fpf, rd, rn, FPTieAway);
        return;
      case NEON_FCVTAU:
        fcvtu(fpf, rd, rn, FPTieAway);
        return;
      case NEON_SCVTF:
        scvtf(fpf, rd, rn, 0, fpcr_rounding);
        return;
      case NEON_UCVTF:
        ucvtf(fpf, rd, rn, 0, fpcr_rounding);
        return;
      case NEON_URSQRTE:
        ursqrte(fpf, rd, rn);
        return;
      case NEON_URECPE:
        urecpe(fpf, rd, rn);
        return;
      case NEON_FRSQRTE:
        frsqrte(fpf, rd, rn);
        return;
      case NEON_FRECPE:
        frecpe(fpf, rd, rn, fpcr_rounding);
        return;
      case NEON_FCMGT_zero:
        fcmp_zero(fpf, rd, rn, gt);
        return;
      case NEON_FCMGE_zero:
        fcmp_zero(fpf, rd, rn, ge);
        return;
      case NEON_FCMEQ_zero:
        fcmp_zero(fpf, rd, rn, eq);
        return;
      case NEON_FCMLE_zero:
        fcmp_zero(fpf, rd, rn, le);
        return;
      case NEON_FCMLT_zero:
        fcmp_zero(fpf, rd, rn, lt);
        return;
      default:
        if ((NEON_XTN_opcode <= instr->Mask(NEON2RegMiscOpcode)) &&
            (instr->Mask(NEON2RegMiscOpcode) <= NEON_UQXTN_opcode)) {
          switch (instr->Mask(NEON2RegMiscMask)) {
            case NEON_XTN:
              xtn(vf, rd, rn);
              return;
            case NEON_SQXTN:
              sqxtn(vf, rd, rn);
              return;
            case NEON_UQXTN:
              uqxtn(vf, rd, rn);
              return;
            case NEON_SQXTUN:
              sqxtun(vf, rd, rn);
              return;
            case NEON_SHLL:
              vf = nfd.GetVectorFormat(nfd.LongIntegerFormatMap());
              if (instr->Mask(NEON_Q)) {
                shll2(vf, rd, rn);
              } else {
                shll(vf, rd, rn);
              }
              return;
            default:
              VIXL_UNIMPLEMENTED();
          }
        } else {
          VIXL_UNIMPLEMENTED();
        }
    }

    // Only FRINT* instructions fall through the switch above.
    frint(fpf, rd, rn, fpcr_rounding, inexact_exception);
  }
}


void Simulator::VisitNEON3Same(const Instruction* instr) {
  NEONFormatDecoder nfd(instr);
  SimVRegister& rd = ReadVRegister(instr->GetRd());
  SimVRegister& rn = ReadVRegister(instr->GetRn());
  SimVRegister& rm = ReadVRegister(instr->GetRm());

  if (instr->Mask(NEON3SameLogicalFMask) == NEON3SameLogicalFixed) {
    VectorFormat vf = nfd.GetVectorFormat(nfd.LogicalFormatMap());
    switch (instr->Mask(NEON3SameLogicalMask)) {
      case NEON_AND:
        and_(vf, rd, rn, rm);
        break;
      case NEON_ORR:
        orr(vf, rd, rn, rm);
        break;
      case NEON_ORN:
        orn(vf, rd, rn, rm);
        break;
      case NEON_EOR:
        eor(vf, rd, rn, rm);
        break;
      case NEON_BIC:
        bic(vf, rd, rn, rm);
        break;
      case NEON_BIF:
        bif(vf, rd, rn, rm);
        break;
      case NEON_BIT:
        bit(vf, rd, rn, rm);
        break;
      case NEON_BSL:
        bsl(vf, rd, rn, rm);
        break;
      default:
        VIXL_UNIMPLEMENTED();
    }
  } else if (instr->Mask(NEON3SameFPFMask) == NEON3SameFPFixed) {
    VectorFormat vf = nfd.GetVectorFormat(nfd.FPFormatMap());
    switch (instr->Mask(NEON3SameFPMask)) {
      case NEON_FADD:
        fadd(vf, rd, rn, rm);
        break;
      case NEON_FSUB:
        fsub(vf, rd, rn, rm);
        break;
      case NEON_FMUL:
        fmul(vf, rd, rn, rm);
        break;
      case NEON_FDIV:
        fdiv(vf, rd, rn, rm);
        break;
      case NEON_FMAX:
        fmax(vf, rd, rn, rm);
        break;
      case NEON_FMIN:
        fmin(vf, rd, rn, rm);
        break;
      case NEON_FMAXNM:
        fmaxnm(vf, rd, rn, rm);
        break;
      case NEON_FMINNM:
        fminnm(vf, rd, rn, rm);
        break;
      case NEON_FMLA:
        fmla(vf, rd, rn, rm);
        break;
      case NEON_FMLS:
        fmls(vf, rd, rn, rm);
        break;
      case NEON_FMULX:
        fmulx(vf, rd, rn, rm);
        break;
      case NEON_FACGE:
        fabscmp(vf, rd, rn, rm, ge);
        break;
      case NEON_FACGT:
        fabscmp(vf, rd, rn, rm, gt);
        break;
      case NEON_FCMEQ:
        fcmp(vf, rd, rn, rm, eq);
        break;
      case NEON_FCMGE:
        fcmp(vf, rd, rn, rm, ge);
        break;
      case NEON_FCMGT:
        fcmp(vf, rd, rn, rm, gt);
        break;
      case NEON_FRECPS:
        frecps(vf, rd, rn, rm);
        break;
      case NEON_FRSQRTS:
        frsqrts(vf, rd, rn, rm);
        break;
      case NEON_FABD:
        fabd(vf, rd, rn, rm);
        break;
      case NEON_FADDP:
        faddp(vf, rd, rn, rm);
        break;
      case NEON_FMAXP:
        fmaxp(vf, rd, rn, rm);
        break;
      case NEON_FMAXNMP:
        fmaxnmp(vf, rd, rn, rm);
        break;
      case NEON_FMINP:
        fminp(vf, rd, rn, rm);
        break;
      case NEON_FMINNMP:
        fminnmp(vf, rd, rn, rm);
        break;
      default:
        VIXL_UNIMPLEMENTED();
    }
  } else {
    VectorFormat vf = nfd.GetVectorFormat();
    switch (instr->Mask(NEON3SameMask)) {
      case NEON_ADD:
        add(vf, rd, rn, rm);
        break;
      case NEON_ADDP:
        addp(vf, rd, rn, rm);
        break;
      case NEON_CMEQ:
        cmp(vf, rd, rn, rm, eq);
        break;
      case NEON_CMGE:
        cmp(vf, rd, rn, rm, ge);
        break;
      case NEON_CMGT:
        cmp(vf, rd, rn, rm, gt);
        break;
      case NEON_CMHI:
        cmp(vf, rd, rn, rm, hi);
        break;
      case NEON_CMHS:
        cmp(vf, rd, rn, rm, hs);
        break;
      case NEON_CMTST:
        cmptst(vf, rd, rn, rm);
        break;
      case NEON_MLS:
        mls(vf, rd, rn, rm);
        break;
      case NEON_MLA:
        mla(vf, rd, rn, rm);
        break;
      case NEON_MUL:
        mul(vf, rd, rn, rm);
        break;
      case NEON_PMUL:
        pmul(vf, rd, rn, rm);
        break;
      case NEON_SMAX:
        smax(vf, rd, rn, rm);
        break;
      case NEON_SMAXP:
        smaxp(vf, rd, rn, rm);
        break;
      case NEON_SMIN:
        smin(vf, rd, rn, rm);
        break;
      case NEON_SMINP:
        sminp(vf, rd, rn, rm);
        break;
      case NEON_SUB:
        sub(vf, rd, rn, rm);
        break;
      case NEON_UMAX:
        umax(vf, rd, rn, rm);
        break;
      case NEON_UMAXP:
        umaxp(vf, rd, rn, rm);
        break;
      case NEON_UMIN:
        umin(vf, rd, rn, rm);
        break;
      case NEON_UMINP:
        uminp(vf, rd, rn, rm);
        break;
      case NEON_SSHL:
        sshl(vf, rd, rn, rm);
        break;
      case NEON_USHL:
        ushl(vf, rd, rn, rm);
        break;
      case NEON_SABD:
        absdiff(vf, rd, rn, rm, true);
        break;
      case NEON_UABD:
        absdiff(vf, rd, rn, rm, false);
        break;
      case NEON_SABA:
        saba(vf, rd, rn, rm);
        break;
      case NEON_UABA:
        uaba(vf, rd, rn, rm);
        break;
      case NEON_UQADD:
        add(vf, rd, rn, rm).UnsignedSaturate(vf);
        break;
      case NEON_SQADD:
        add(vf, rd, rn, rm).SignedSaturate(vf);
        break;
      case NEON_UQSUB:
        sub(vf, rd, rn, rm).UnsignedSaturate(vf);
        break;
      case NEON_SQSUB:
        sub(vf, rd, rn, rm).SignedSaturate(vf);
        break;
      case NEON_SQDMULH:
        sqdmulh(vf, rd, rn, rm);
        break;
      case NEON_SQRDMULH:
        sqrdmulh(vf, rd, rn, rm);
        break;
      case NEON_UQSHL:
        ushl(vf, rd, rn, rm).UnsignedSaturate(vf);
        break;
      case NEON_SQSHL:
        sshl(vf, rd, rn, rm).SignedSaturate(vf);
        break;
      case NEON_URSHL:
        ushl(vf, rd, rn, rm).Round(vf);
        break;
      case NEON_SRSHL:
        sshl(vf, rd, rn, rm).Round(vf);
        break;
      case NEON_UQRSHL:
        ushl(vf, rd, rn, rm).Round(vf).UnsignedSaturate(vf);
        break;
      case NEON_SQRSHL:
        sshl(vf, rd, rn, rm).Round(vf).SignedSaturate(vf);
        break;
      case NEON_UHADD:
        add(vf, rd, rn, rm).Uhalve(vf);
        break;
      case NEON_URHADD:
        add(vf, rd, rn, rm).Uhalve(vf).Round(vf);
        break;
      case NEON_SHADD:
        add(vf, rd, rn, rm).Halve(vf);
        break;
      case NEON_SRHADD:
        add(vf, rd, rn, rm).Halve(vf).Round(vf);
        break;
      case NEON_UHSUB:
        sub(vf, rd, rn, rm).Uhalve(vf);
        break;
      case NEON_SHSUB:
        sub(vf, rd, rn, rm).Halve(vf);
        break;
      default:
        VIXL_UNIMPLEMENTED();
    }
  }
}


void Simulator::VisitNEON3Different(const Instruction* instr) {
  NEONFormatDecoder nfd(instr);
  VectorFormat vf = nfd.GetVectorFormat();
  VectorFormat vf_l = nfd.GetVectorFormat(nfd.LongIntegerFormatMap());

  SimVRegister& rd = ReadVRegister(instr->GetRd());
  SimVRegister& rn = ReadVRegister(instr->GetRn());
  SimVRegister& rm = ReadVRegister(instr->GetRm());

  switch (instr->Mask(NEON3DifferentMask)) {
    case NEON_PMULL:
      pmull(vf_l, rd, rn, rm);
      break;
    case NEON_PMULL2:
      pmull2(vf_l, rd, rn, rm);
      break;
    case NEON_UADDL:
      uaddl(vf_l, rd, rn, rm);
      break;
    case NEON_UADDL2:
      uaddl2(vf_l, rd, rn, rm);
      break;
    case NEON_SADDL:
      saddl(vf_l, rd, rn, rm);
      break;
    case NEON_SADDL2:
      saddl2(vf_l, rd, rn, rm);
      break;
    case NEON_USUBL:
      usubl(vf_l, rd, rn, rm);
      break;
    case NEON_USUBL2:
      usubl2(vf_l, rd, rn, rm);
      break;
    case NEON_SSUBL:
      ssubl(vf_l, rd, rn, rm);
      break;
    case NEON_SSUBL2:
      ssubl2(vf_l, rd, rn, rm);
      break;
    case NEON_SABAL:
      sabal(vf_l, rd, rn, rm);
      break;
    case NEON_SABAL2:
      sabal2(vf_l, rd, rn, rm);
      break;
    case NEON_UABAL:
      uabal(vf_l, rd, rn, rm);
      break;
    case NEON_UABAL2:
      uabal2(vf_l, rd, rn, rm);
      break;
    case NEON_SABDL:
      sabdl(vf_l, rd, rn, rm);
      break;
    case NEON_SABDL2:
      sabdl2(vf_l, rd, rn, rm);
      break;
    case NEON_UABDL:
      uabdl(vf_l, rd, rn, rm);
      break;
    case NEON_UABDL2:
      uabdl2(vf_l, rd, rn, rm);
      break;
    case NEON_SMLAL:
      smlal(vf_l, rd, rn, rm);
      break;
    case NEON_SMLAL2:
      smlal2(vf_l, rd, rn, rm);
      break;
    case NEON_UMLAL:
      umlal(vf_l, rd, rn, rm);
      break;
    case NEON_UMLAL2:
      umlal2(vf_l, rd, rn, rm);
      break;
    case NEON_SMLSL:
      smlsl(vf_l, rd, rn, rm);
      break;
    case NEON_SMLSL2:
      smlsl2(vf_l, rd, rn, rm);
      break;
    case NEON_UMLSL:
      umlsl(vf_l, rd, rn, rm);
      break;
    case NEON_UMLSL2:
      umlsl2(vf_l, rd, rn, rm);
      break;
    case NEON_SMULL:
      smull(vf_l, rd, rn, rm);
      break;
    case NEON_SMULL2:
      smull2(vf_l, rd, rn, rm);
      break;
    case NEON_UMULL:
      umull(vf_l, rd, rn, rm);
      break;
    case NEON_UMULL2:
      umull2(vf_l, rd, rn, rm);
      break;
    case NEON_SQDMLAL:
      sqdmlal(vf_l, rd, rn, rm);
      break;
    case NEON_SQDMLAL2:
      sqdmlal2(vf_l, rd, rn, rm);
      break;
    case NEON_SQDMLSL:
      sqdmlsl(vf_l, rd, rn, rm);
      break;
    case NEON_SQDMLSL2:
      sqdmlsl2(vf_l, rd, rn, rm);
      break;
    case NEON_SQDMULL:
      sqdmull(vf_l, rd, rn, rm);
      break;
    case NEON_SQDMULL2:
      sqdmull2(vf_l, rd, rn, rm);
      break;
    case NEON_UADDW:
      uaddw(vf_l, rd, rn, rm);
      break;
    case NEON_UADDW2:
      uaddw2(vf_l, rd, rn, rm);
      break;
    case NEON_SADDW:
      saddw(vf_l, rd, rn, rm);
      break;
    case NEON_SADDW2:
      saddw2(vf_l, rd, rn, rm);
      break;
    case NEON_USUBW:
      usubw(vf_l, rd, rn, rm);
      break;
    case NEON_USUBW2:
      usubw2(vf_l, rd, rn, rm);
      break;
    case NEON_SSUBW:
      ssubw(vf_l, rd, rn, rm);
      break;
    case NEON_SSUBW2:
      ssubw2(vf_l, rd, rn, rm);
      break;
    case NEON_ADDHN:
      addhn(vf, rd, rn, rm);
      break;
    case NEON_ADDHN2:
      addhn2(vf, rd, rn, rm);
      break;
    case NEON_RADDHN:
      raddhn(vf, rd, rn, rm);
      break;
    case NEON_RADDHN2:
      raddhn2(vf, rd, rn, rm);
      break;
    case NEON_SUBHN:
      subhn(vf, rd, rn, rm);
      break;
    case NEON_SUBHN2:
      subhn2(vf, rd, rn, rm);
      break;
    case NEON_RSUBHN:
      rsubhn(vf, rd, rn, rm);
      break;
    case NEON_RSUBHN2:
      rsubhn2(vf, rd, rn, rm);
      break;
    default:
      VIXL_UNIMPLEMENTED();
  }
}


void Simulator::VisitNEONAcrossLanes(const Instruction* instr) {
  NEONFormatDecoder nfd(instr);

  SimVRegister& rd = ReadVRegister(instr->GetRd());
  SimVRegister& rn = ReadVRegister(instr->GetRn());

  // The input operand's VectorFormat is passed for these instructions.
  if (instr->Mask(NEONAcrossLanesFPFMask) == NEONAcrossLanesFPFixed) {
    VectorFormat vf = nfd.GetVectorFormat(nfd.FPFormatMap());

    switch (instr->Mask(NEONAcrossLanesFPMask)) {
      case NEON_FMAXV:
        fmaxv(vf, rd, rn);
        break;
      case NEON_FMINV:
        fminv(vf, rd, rn);
        break;
      case NEON_FMAXNMV:
        fmaxnmv(vf, rd, rn);
        break;
      case NEON_FMINNMV:
        fminnmv(vf, rd, rn);
        break;
      default:
        VIXL_UNIMPLEMENTED();
    }
  } else {
    VectorFormat vf = nfd.GetVectorFormat();

    switch (instr->Mask(NEONAcrossLanesMask)) {
      case NEON_ADDV:
        addv(vf, rd, rn);
        break;
      case NEON_SMAXV:
        smaxv(vf, rd, rn);
        break;
      case NEON_SMINV:
        sminv(vf, rd, rn);
        break;
      case NEON_UMAXV:
        umaxv(vf, rd, rn);
        break;
      case NEON_UMINV:
        uminv(vf, rd, rn);
        break;
      case NEON_SADDLV:
        saddlv(vf, rd, rn);
        break;
      case NEON_UADDLV:
        uaddlv(vf, rd, rn);
        break;
      default:
        VIXL_UNIMPLEMENTED();
    }
  }
}


void Simulator::VisitNEONByIndexedElement(const Instruction* instr) {
  NEONFormatDecoder nfd(instr);
  VectorFormat vf_r = nfd.GetVectorFormat();
  VectorFormat vf = nfd.GetVectorFormat(nfd.LongIntegerFormatMap());

  SimVRegister& rd = ReadVRegister(instr->GetRd());
  SimVRegister& rn = ReadVRegister(instr->GetRn());

  ByElementOp Op = NULL;

  int rm_reg = instr->GetRm();
  int index = (instr->GetNEONH() << 1) | instr->GetNEONL();
  if (instr->GetNEONSize() == 1) {
    rm_reg &= 0xf;
    index = (index << 1) | instr->GetNEONM();
  }

  switch (instr->Mask(NEONByIndexedElementMask)) {
    case NEON_MUL_byelement:
      Op = &Simulator::mul;
      vf = vf_r;
      break;
    case NEON_MLA_byelement:
      Op = &Simulator::mla;
      vf = vf_r;
      break;
    case NEON_MLS_byelement:
      Op = &Simulator::mls;
      vf = vf_r;
      break;
    case NEON_SQDMULH_byelement:
      Op = &Simulator::sqdmulh;
      vf = vf_r;
      break;
    case NEON_SQRDMULH_byelement:
      Op = &Simulator::sqrdmulh;
      vf = vf_r;
      break;
    case NEON_SMULL_byelement:
      if (instr->Mask(NEON_Q)) {
        Op = &Simulator::smull2;
      } else {
        Op = &Simulator::smull;
      }
      break;
    case NEON_UMULL_byelement:
      if (instr->Mask(NEON_Q)) {
        Op = &Simulator::umull2;
      } else {
        Op = &Simulator::umull;
      }
      break;
    case NEON_SMLAL_byelement:
      if (instr->Mask(NEON_Q)) {
        Op = &Simulator::smlal2;
      } else {
        Op = &Simulator::smlal;
      }
      break;
    case NEON_UMLAL_byelement:
      if (instr->Mask(NEON_Q)) {
        Op = &Simulator::umlal2;
      } else {
        Op = &Simulator::umlal;
      }
      break;
    case NEON_SMLSL_byelement:
      if (instr->Mask(NEON_Q)) {
        Op = &Simulator::smlsl2;
      } else {
        Op = &Simulator::smlsl;
      }
      break;
    case NEON_UMLSL_byelement:
      if (instr->Mask(NEON_Q)) {
        Op = &Simulator::umlsl2;
      } else {
        Op = &Simulator::umlsl;
      }
      break;
    case NEON_SQDMULL_byelement:
      if (instr->Mask(NEON_Q)) {
        Op = &Simulator::sqdmull2;
      } else {
        Op = &Simulator::sqdmull;
      }
      break;
    case NEON_SQDMLAL_byelement:
      if (instr->Mask(NEON_Q)) {
        Op = &Simulator::sqdmlal2;
      } else {
        Op = &Simulator::sqdmlal;
      }
      break;
    case NEON_SQDMLSL_byelement:
      if (instr->Mask(NEON_Q)) {
        Op = &Simulator::sqdmlsl2;
      } else {
        Op = &Simulator::sqdmlsl;
      }
      break;
    default:
      index = instr->GetNEONH();
      if ((instr->GetFPType() & 1) == 0) {
        index = (index << 1) | instr->GetNEONL();
      }

      vf = nfd.GetVectorFormat(nfd.FPFormatMap());

      switch (instr->Mask(NEONByIndexedElementFPMask)) {
        case NEON_FMUL_byelement:
          Op = &Simulator::fmul;
          break;
        case NEON_FMLA_byelement:
          Op = &Simulator::fmla;
          break;
        case NEON_FMLS_byelement:
          Op = &Simulator::fmls;
          break;
        case NEON_FMULX_byelement:
          Op = &Simulator::fmulx;
          break;
        default:
          VIXL_UNIMPLEMENTED();
      }
  }

  (this->*Op)(vf, rd, rn, ReadVRegister(rm_reg), index);
}


void Simulator::VisitNEONCopy(const Instruction* instr) {
  NEONFormatDecoder nfd(instr, NEONFormatDecoder::TriangularFormatMap());
  VectorFormat vf = nfd.GetVectorFormat();

  SimVRegister& rd = ReadVRegister(instr->GetRd());
  SimVRegister& rn = ReadVRegister(instr->GetRn());
  int imm5 = instr->GetImmNEON5();
  int tz = CountTrailingZeros(imm5, 32);
  int reg_index = imm5 >> (tz + 1);

  if (instr->Mask(NEONCopyInsElementMask) == NEON_INS_ELEMENT) {
    int imm4 = instr->GetImmNEON4();
    int rn_index = imm4 >> tz;
    ins_element(vf, rd, reg_index, rn, rn_index);
  } else if (instr->Mask(NEONCopyInsGeneralMask) == NEON_INS_GENERAL) {
    ins_immediate(vf, rd, reg_index, ReadXRegister(instr->GetRn()));
  } else if (instr->Mask(NEONCopyUmovMask) == NEON_UMOV) {
    uint64_t value = LogicVRegister(rn).Uint(vf, reg_index);
    value &= MaxUintFromFormat(vf);
    WriteXRegister(instr->GetRd(), value);
  } else if (instr->Mask(NEONCopyUmovMask) == NEON_SMOV) {
    int64_t value = LogicVRegister(rn).Int(vf, reg_index);
    if (instr->GetNEONQ()) {
      WriteXRegister(instr->GetRd(), value);
    } else {
      WriteWRegister(instr->GetRd(), (int32_t)value);
    }
  } else if (instr->Mask(NEONCopyDupElementMask) == NEON_DUP_ELEMENT) {
    dup_element(vf, rd, rn, reg_index);
  } else if (instr->Mask(NEONCopyDupGeneralMask) == NEON_DUP_GENERAL) {
    dup_immediate(vf, rd, ReadXRegister(instr->GetRn()));
  } else {
    VIXL_UNIMPLEMENTED();
  }
}


void Simulator::VisitNEONExtract(const Instruction* instr) {
  NEONFormatDecoder nfd(instr, NEONFormatDecoder::LogicalFormatMap());
  VectorFormat vf = nfd.GetVectorFormat();
  SimVRegister& rd = ReadVRegister(instr->GetRd());
  SimVRegister& rn = ReadVRegister(instr->GetRn());
  SimVRegister& rm = ReadVRegister(instr->GetRm());
  if (instr->Mask(NEONExtractMask) == NEON_EXT) {
    int index = instr->GetImmNEONExt();
    ext(vf, rd, rn, rm, index);
  } else {
    VIXL_UNIMPLEMENTED();
  }
}


void Simulator::NEONLoadStoreMultiStructHelper(const Instruction* instr,
                                               AddrMode addr_mode) {
  NEONFormatDecoder nfd(instr, NEONFormatDecoder::LoadStoreFormatMap());
  VectorFormat vf = nfd.GetVectorFormat();

  uint64_t addr_base = ReadXRegister(instr->GetRn(), Reg31IsStackPointer);
  int reg_size = RegisterSizeInBytesFromFormat(vf);

  int reg[4];
  uint64_t addr[4];
  for (int i = 0; i < 4; i++) {
    reg[i] = (instr->GetRt() + i) % kNumberOfVRegisters;
    addr[i] = addr_base + (i * reg_size);
  }
  int count = 1;
  bool log_read = true;

  Instr itype = instr->Mask(NEONLoadStoreMultiStructMask);
  if (((itype == NEON_LD1_1v) || (itype == NEON_LD1_2v) ||
       (itype == NEON_LD1_3v) || (itype == NEON_LD1_4v) ||
       (itype == NEON_ST1_1v) || (itype == NEON_ST1_2v) ||
       (itype == NEON_ST1_3v) || (itype == NEON_ST1_4v)) &&
      (instr->ExtractBits(20, 16) != 0)) {
    VIXL_UNREACHABLE();
  }

  // We use the PostIndex mask here, as it works in this case for both Offset
  // and PostIndex addressing.
  switch (instr->Mask(NEONLoadStoreMultiStructPostIndexMask)) {
    case NEON_LD1_4v:
    case NEON_LD1_4v_post:
      ld1(vf, ReadVRegister(reg[3]), addr[3]);
      count++;
      VIXL_FALLTHROUGH();
    case NEON_LD1_3v:
    case NEON_LD1_3v_post:
      ld1(vf, ReadVRegister(reg[2]), addr[2]);
      count++;
      VIXL_FALLTHROUGH();
    case NEON_LD1_2v:
    case NEON_LD1_2v_post:
      ld1(vf, ReadVRegister(reg[1]), addr[1]);
      count++;
      VIXL_FALLTHROUGH();
    case NEON_LD1_1v:
    case NEON_LD1_1v_post:
      ld1(vf, ReadVRegister(reg[0]), addr[0]);
      break;
    case NEON_ST1_4v:
    case NEON_ST1_4v_post:
      st1(vf, ReadVRegister(reg[3]), addr[3]);
      count++;
      VIXL_FALLTHROUGH();
    case NEON_ST1_3v:
    case NEON_ST1_3v_post:
      st1(vf, ReadVRegister(reg[2]), addr[2]);
      count++;
      VIXL_FALLTHROUGH();
    case NEON_ST1_2v:
    case NEON_ST1_2v_post:
      st1(vf, ReadVRegister(reg[1]), addr[1]);
      count++;
      VIXL_FALLTHROUGH();
    case NEON_ST1_1v:
    case NEON_ST1_1v_post:
      st1(vf, ReadVRegister(reg[0]), addr[0]);
      log_read = false;
      break;
    case NEON_LD2_post:
    case NEON_LD2:
      ld2(vf, ReadVRegister(reg[0]), ReadVRegister(reg[1]), addr[0]);
      count = 2;
      break;
    case NEON_ST2:
    case NEON_ST2_post:
      st2(vf, ReadVRegister(reg[0]), ReadVRegister(reg[1]), addr[0]);
      count = 2;
      break;
    case NEON_LD3_post:
    case NEON_LD3:
      ld3(vf,
          ReadVRegister(reg[0]),
          ReadVRegister(reg[1]),
          ReadVRegister(reg[2]),
          addr[0]);
      count = 3;
      break;
    case NEON_ST3:
    case NEON_ST3_post:
      st3(vf,
          ReadVRegister(reg[0]),
          ReadVRegister(reg[1]),
          ReadVRegister(reg[2]),
          addr[0]);
      count = 3;
      break;
    case NEON_ST4:
    case NEON_ST4_post:
      st4(vf,
          ReadVRegister(reg[0]),
          ReadVRegister(reg[1]),
          ReadVRegister(reg[2]),
          ReadVRegister(reg[3]),
          addr[0]);
      count = 4;
      break;
    case NEON_LD4_post:
    case NEON_LD4:
      ld4(vf,
          ReadVRegister(reg[0]),
          ReadVRegister(reg[1]),
          ReadVRegister(reg[2]),
          ReadVRegister(reg[3]),
          addr[0]);
      count = 4;
      break;
    default:
      VIXL_UNIMPLEMENTED();
  }

  // Explicitly log the register update whilst we have type information.
  for (int i = 0; i < count; i++) {
    // For de-interleaving loads, only print the base address.
    int lane_size = LaneSizeInBytesFromFormat(vf);
    PrintRegisterFormat format = GetPrintRegisterFormatTryFP(
        GetPrintRegisterFormatForSize(reg_size, lane_size));
    if (log_read) {
      LogVRead(addr_base, reg[i], format);
    } else {
      LogVWrite(addr_base, reg[i], format);
    }
  }

  if (addr_mode == PostIndex) {
    int rm = instr->GetRm();
    // The immediate post index addressing mode is indicated by rm = 31.
    // The immediate is implied by the number of vector registers used.
    addr_base += (rm == 31) ? RegisterSizeInBytesFromFormat(vf) * count
                            : ReadXRegister(rm);
    WriteXRegister(instr->GetRn(), addr_base);
  } else {
    VIXL_ASSERT(addr_mode == Offset);
  }
}


void Simulator::VisitNEONLoadStoreMultiStruct(const Instruction* instr) {
  NEONLoadStoreMultiStructHelper(instr, Offset);
}


void Simulator::VisitNEONLoadStoreMultiStructPostIndex(
    const Instruction* instr) {
  NEONLoadStoreMultiStructHelper(instr, PostIndex);
}


void Simulator::NEONLoadStoreSingleStructHelper(const Instruction* instr,
                                                AddrMode addr_mode) {
  uint64_t addr = ReadXRegister(instr->GetRn(), Reg31IsStackPointer);
  int rt = instr->GetRt();

  Instr itype = instr->Mask(NEONLoadStoreSingleStructMask);
  if (((itype == NEON_LD1_b) || (itype == NEON_LD1_h) ||
       (itype == NEON_LD1_s) || (itype == NEON_LD1_d)) &&
      (instr->ExtractBits(20, 16) != 0)) {
    VIXL_UNREACHABLE();
  }

  // We use the PostIndex mask here, as it works in this case for both Offset
  // and PostIndex addressing.
  bool do_load = false;

  NEONFormatDecoder nfd(instr, NEONFormatDecoder::LoadStoreFormatMap());
  VectorFormat vf_t = nfd.GetVectorFormat();

  VectorFormat vf = kFormat16B;
  switch (instr->Mask(NEONLoadStoreSingleStructPostIndexMask)) {
    case NEON_LD1_b:
    case NEON_LD1_b_post:
    case NEON_LD2_b:
    case NEON_LD2_b_post:
    case NEON_LD3_b:
    case NEON_LD3_b_post:
    case NEON_LD4_b:
    case NEON_LD4_b_post:
      do_load = true;
      VIXL_FALLTHROUGH();
    case NEON_ST1_b:
    case NEON_ST1_b_post:
    case NEON_ST2_b:
    case NEON_ST2_b_post:
    case NEON_ST3_b:
    case NEON_ST3_b_post:
    case NEON_ST4_b:
    case NEON_ST4_b_post:
      break;

    case NEON_LD1_h:
    case NEON_LD1_h_post:
    case NEON_LD2_h:
    case NEON_LD2_h_post:
    case NEON_LD3_h:
    case NEON_LD3_h_post:
    case NEON_LD4_h:
    case NEON_LD4_h_post:
      do_load = true;
      VIXL_FALLTHROUGH();
    case NEON_ST1_h:
    case NEON_ST1_h_post:
    case NEON_ST2_h:
    case NEON_ST2_h_post:
    case NEON_ST3_h:
    case NEON_ST3_h_post:
    case NEON_ST4_h:
    case NEON_ST4_h_post:
      vf = kFormat8H;
      break;
    case NEON_LD1_s:
    case NEON_LD1_s_post:
    case NEON_LD2_s:
    case NEON_LD2_s_post:
    case NEON_LD3_s:
    case NEON_LD3_s_post:
    case NEON_LD4_s:
    case NEON_LD4_s_post:
      do_load = true;
      VIXL_FALLTHROUGH();
    case NEON_ST1_s:
    case NEON_ST1_s_post:
    case NEON_ST2_s:
    case NEON_ST2_s_post:
    case NEON_ST3_s:
    case NEON_ST3_s_post:
    case NEON_ST4_s:
    case NEON_ST4_s_post: {
      VIXL_STATIC_ASSERT((NEON_LD1_s | (1 << NEONLSSize_offset)) == NEON_LD1_d);
      VIXL_STATIC_ASSERT((NEON_LD1_s_post | (1 << NEONLSSize_offset)) ==
                         NEON_LD1_d_post);
      VIXL_STATIC_ASSERT((NEON_ST1_s | (1 << NEONLSSize_offset)) == NEON_ST1_d);
      VIXL_STATIC_ASSERT((NEON_ST1_s_post | (1 << NEONLSSize_offset)) ==
                         NEON_ST1_d_post);
      vf = ((instr->GetNEONLSSize() & 1) == 0) ? kFormat4S : kFormat2D;
      break;
    }

    case NEON_LD1R:
    case NEON_LD1R_post: {
      vf = vf_t;
      ld1r(vf, ReadVRegister(rt), addr);
      do_load = true;
      break;
    }

    case NEON_LD2R:
    case NEON_LD2R_post: {
      vf = vf_t;
      int rt2 = (rt + 1) % kNumberOfVRegisters;
      ld2r(vf, ReadVRegister(rt), ReadVRegister(rt2), addr);
      do_load = true;
      break;
    }

    case NEON_LD3R:
    case NEON_LD3R_post: {
      vf = vf_t;
      int rt2 = (rt + 1) % kNumberOfVRegisters;
      int rt3 = (rt2 + 1) % kNumberOfVRegisters;
      ld3r(vf, ReadVRegister(rt), ReadVRegister(rt2), ReadVRegister(rt3), addr);
      do_load = true;
      break;
    }

    case NEON_LD4R:
    case NEON_LD4R_post: {
      vf = vf_t;
      int rt2 = (rt + 1) % kNumberOfVRegisters;
      int rt3 = (rt2 + 1) % kNumberOfVRegisters;
      int rt4 = (rt3 + 1) % kNumberOfVRegisters;
      ld4r(vf,
           ReadVRegister(rt),
           ReadVRegister(rt2),
           ReadVRegister(rt3),
           ReadVRegister(rt4),
           addr);
      do_load = true;
      break;
    }
    default:
      VIXL_UNIMPLEMENTED();
  }

  PrintRegisterFormat print_format =
      GetPrintRegisterFormatTryFP(GetPrintRegisterFormat(vf));
  // Make sure that the print_format only includes a single lane.
  print_format =
      static_cast<PrintRegisterFormat>(print_format & ~kPrintRegAsVectorMask);

  int esize = LaneSizeInBytesFromFormat(vf);
  int index_shift = LaneSizeInBytesLog2FromFormat(vf);
  int lane = instr->GetNEONLSIndex(index_shift);
  int scale = 0;
  int rt2 = (rt + 1) % kNumberOfVRegisters;
  int rt3 = (rt2 + 1) % kNumberOfVRegisters;
  int rt4 = (rt3 + 1) % kNumberOfVRegisters;
  switch (instr->Mask(NEONLoadStoreSingleLenMask)) {
    case NEONLoadStoreSingle1:
      scale = 1;
      if (do_load) {
        ld1(vf, ReadVRegister(rt), lane, addr);
        LogVRead(addr, rt, print_format, lane);
      } else {
        st1(vf, ReadVRegister(rt), lane, addr);
        LogVWrite(addr, rt, print_format, lane);
      }
      break;
    case NEONLoadStoreSingle2:
      scale = 2;
      if (do_load) {
        ld2(vf, ReadVRegister(rt), ReadVRegister(rt2), lane, addr);
        LogVRead(addr, rt, print_format, lane);
        LogVRead(addr + esize, rt2, print_format, lane);
      } else {
        st2(vf, ReadVRegister(rt), ReadVRegister(rt2), lane, addr);
        LogVWrite(addr, rt, print_format, lane);
        LogVWrite(addr + esize, rt2, print_format, lane);
      }
      break;
    case NEONLoadStoreSingle3:
      scale = 3;
      if (do_load) {
        ld3(vf,
            ReadVRegister(rt),
            ReadVRegister(rt2),
            ReadVRegister(rt3),
            lane,
            addr);
        LogVRead(addr, rt, print_format, lane);
        LogVRead(addr + esize, rt2, print_format, lane);
        LogVRead(addr + (2 * esize), rt3, print_format, lane);
      } else {
        st3(vf,
            ReadVRegister(rt),
            ReadVRegister(rt2),
            ReadVRegister(rt3),
            lane,
            addr);
        LogVWrite(addr, rt, print_format, lane);
        LogVWrite(addr + esize, rt2, print_format, lane);
        LogVWrite(addr + (2 * esize), rt3, print_format, lane);
      }
      break;
    case NEONLoadStoreSingle4:
      scale = 4;
      if (do_load) {
        ld4(vf,
            ReadVRegister(rt),
            ReadVRegister(rt2),
            ReadVRegister(rt3),
            ReadVRegister(rt4),
            lane,
            addr);
        LogVRead(addr, rt, print_format, lane);
        LogVRead(addr + esize, rt2, print_format, lane);
        LogVRead(addr + (2 * esize), rt3, print_format, lane);
        LogVRead(addr + (3 * esize), rt4, print_format, lane);
      } else {
        st4(vf,
            ReadVRegister(rt),
            ReadVRegister(rt2),
            ReadVRegister(rt3),
            ReadVRegister(rt4),
            lane,
            addr);
        LogVWrite(addr, rt, print_format, lane);
        LogVWrite(addr + esize, rt2, print_format, lane);
        LogVWrite(addr + (2 * esize), rt3, print_format, lane);
        LogVWrite(addr + (3 * esize), rt4, print_format, lane);
      }
      break;
    default:
      VIXL_UNIMPLEMENTED();
  }

  if (addr_mode == PostIndex) {
    int rm = instr->GetRm();
    int lane_size = LaneSizeInBytesFromFormat(vf);
    WriteXRegister(instr->GetRn(),
                   addr +
                       ((rm == 31) ? (scale * lane_size) : ReadXRegister(rm)));
  }
}


void Simulator::VisitNEONLoadStoreSingleStruct(const Instruction* instr) {
  NEONLoadStoreSingleStructHelper(instr, Offset);
}


void Simulator::VisitNEONLoadStoreSingleStructPostIndex(
    const Instruction* instr) {
  NEONLoadStoreSingleStructHelper(instr, PostIndex);
}


void Simulator::VisitNEONModifiedImmediate(const Instruction* instr) {
  SimVRegister& rd = ReadVRegister(instr->GetRd());
  int cmode = instr->GetNEONCmode();
  int cmode_3_1 = (cmode >> 1) & 7;
  int cmode_3 = (cmode >> 3) & 1;
  int cmode_2 = (cmode >> 2) & 1;
  int cmode_1 = (cmode >> 1) & 1;
  int cmode_0 = cmode & 1;
  int q = instr->GetNEONQ();
  int op_bit = instr->GetNEONModImmOp();
  uint64_t imm8 = instr->GetImmNEONabcdefgh();

  // Find the format and immediate value
  uint64_t imm = 0;
  VectorFormat vform = kFormatUndefined;
  switch (cmode_3_1) {
    case 0x0:
    case 0x1:
    case 0x2:
    case 0x3:
      vform = (q == 1) ? kFormat4S : kFormat2S;
      imm = imm8 << (8 * cmode_3_1);
      break;
    case 0x4:
    case 0x5:
      vform = (q == 1) ? kFormat8H : kFormat4H;
      imm = imm8 << (8 * cmode_1);
      break;
    case 0x6:
      vform = (q == 1) ? kFormat4S : kFormat2S;
      if (cmode_0 == 0) {
        imm = imm8 << 8 | 0x000000ff;
      } else {
        imm = imm8 << 16 | 0x0000ffff;
      }
      break;
    case 0x7:
      if (cmode_0 == 0 && op_bit == 0) {
        vform = q ? kFormat16B : kFormat8B;
        imm = imm8;
      } else if (cmode_0 == 0 && op_bit == 1) {
        vform = q ? kFormat2D : kFormat1D;
        imm = 0;
        for (int i = 0; i < 8; ++i) {
          if (imm8 & (1 << i)) {
            imm |= (UINT64_C(0xff) << (8 * i));
          }
        }
      } else {  // cmode_0 == 1, cmode == 0xf.
        if (op_bit == 0) {
          vform = q ? kFormat4S : kFormat2S;
          imm = FloatToRawbits(instr->GetImmNEONFP32());
        } else if (q == 1) {
          vform = kFormat2D;
          imm = DoubleToRawbits(instr->GetImmNEONFP64());
        } else {
          VIXL_ASSERT((q == 0) && (op_bit == 1) && (cmode == 0xf));
          VisitUnallocated(instr);
        }
      }
      break;
    default:
      VIXL_UNREACHABLE();
      break;
  }

  // Find the operation
  NEONModifiedImmediateOp op;
  if (cmode_3 == 0) {
    if (cmode_0 == 0) {
      op = op_bit ? NEONModifiedImmediate_MVNI : NEONModifiedImmediate_MOVI;
    } else {  // cmode<0> == '1'
      op = op_bit ? NEONModifiedImmediate_BIC : NEONModifiedImmediate_ORR;
    }
  } else {  // cmode<3> == '1'
    if (cmode_2 == 0) {
      if (cmode_0 == 0) {
        op = op_bit ? NEONModifiedImmediate_MVNI : NEONModifiedImmediate_MOVI;
      } else {  // cmode<0> == '1'
        op = op_bit ? NEONModifiedImmediate_BIC : NEONModifiedImmediate_ORR;
      }
    } else {  // cmode<2> == '1'
      if (cmode_1 == 0) {
        op = op_bit ? NEONModifiedImmediate_MVNI : NEONModifiedImmediate_MOVI;
      } else {  // cmode<1> == '1'
        if (cmode_0 == 0) {
          op = NEONModifiedImmediate_MOVI;
        } else {  // cmode<0> == '1'
          op = NEONModifiedImmediate_MOVI;
        }
      }
    }
  }

  // Call the logic function
  if (op == NEONModifiedImmediate_ORR) {
    orr(vform, rd, rd, imm);
  } else if (op == NEONModifiedImmediate_BIC) {
    bic(vform, rd, rd, imm);
  } else if (op == NEONModifiedImmediate_MOVI) {
    movi(vform, rd, imm);
  } else if (op == NEONModifiedImmediate_MVNI) {
    mvni(vform, rd, imm);
  } else {
    VisitUnimplemented(instr);
  }
}


void Simulator::VisitNEONScalar2RegMisc(const Instruction* instr) {
  NEONFormatDecoder nfd(instr, NEONFormatDecoder::ScalarFormatMap());
  VectorFormat vf = nfd.GetVectorFormat();

  SimVRegister& rd = ReadVRegister(instr->GetRd());
  SimVRegister& rn = ReadVRegister(instr->GetRn());

  if (instr->Mask(NEON2RegMiscOpcode) <= NEON_NEG_scalar_opcode) {
    // These instructions all use a two bit size field, except NOT and RBIT,
    // which use the field to encode the operation.
    switch (instr->Mask(NEONScalar2RegMiscMask)) {
      case NEON_CMEQ_zero_scalar:
        cmp(vf, rd, rn, 0, eq);
        break;
      case NEON_CMGE_zero_scalar:
        cmp(vf, rd, rn, 0, ge);
        break;
      case NEON_CMGT_zero_scalar:
        cmp(vf, rd, rn, 0, gt);
        break;
      case NEON_CMLT_zero_scalar:
        cmp(vf, rd, rn, 0, lt);
        break;
      case NEON_CMLE_zero_scalar:
        cmp(vf, rd, rn, 0, le);
        break;
      case NEON_ABS_scalar:
        abs(vf, rd, rn);
        break;
      case NEON_SQABS_scalar:
        abs(vf, rd, rn).SignedSaturate(vf);
        break;
      case NEON_NEG_scalar:
        neg(vf, rd, rn);
        break;
      case NEON_SQNEG_scalar:
        neg(vf, rd, rn).SignedSaturate(vf);
        break;
      case NEON_SUQADD_scalar:
        suqadd(vf, rd, rn);
        break;
      case NEON_USQADD_scalar:
        usqadd(vf, rd, rn);
        break;
      default:
        VIXL_UNIMPLEMENTED();
        break;
    }
  } else {
    VectorFormat fpf = nfd.GetVectorFormat(nfd.FPScalarFormatMap());
    FPRounding fpcr_rounding = static_cast<FPRounding>(ReadFpcr().GetRMode());

    // These instructions all use a one bit size field, except SQXTUN, SQXTN
    // and UQXTN, which use a two bit size field.
    switch (instr->Mask(NEONScalar2RegMiscFPMask)) {
      case NEON_FRECPE_scalar:
        frecpe(fpf, rd, rn, fpcr_rounding);
        break;
      case NEON_FRECPX_scalar:
        frecpx(fpf, rd, rn);
        break;
      case NEON_FRSQRTE_scalar:
        frsqrte(fpf, rd, rn);
        break;
      case NEON_FCMGT_zero_scalar:
        fcmp_zero(fpf, rd, rn, gt);
        break;
      case NEON_FCMGE_zero_scalar:
        fcmp_zero(fpf, rd, rn, ge);
        break;
      case NEON_FCMEQ_zero_scalar:
        fcmp_zero(fpf, rd, rn, eq);
        break;
      case NEON_FCMLE_zero_scalar:
        fcmp_zero(fpf, rd, rn, le);
        break;
      case NEON_FCMLT_zero_scalar:
        fcmp_zero(fpf, rd, rn, lt);
        break;
      case NEON_SCVTF_scalar:
        scvtf(fpf, rd, rn, 0, fpcr_rounding);
        break;
      case NEON_UCVTF_scalar:
        ucvtf(fpf, rd, rn, 0, fpcr_rounding);
        break;
      case NEON_FCVTNS_scalar:
        fcvts(fpf, rd, rn, FPTieEven);
        break;
      case NEON_FCVTNU_scalar:
        fcvtu(fpf, rd, rn, FPTieEven);
        break;
      case NEON_FCVTPS_scalar:
        fcvts(fpf, rd, rn, FPPositiveInfinity);
        break;
      case NEON_FCVTPU_scalar:
        fcvtu(fpf, rd, rn, FPPositiveInfinity);
        break;
      case NEON_FCVTMS_scalar:
        fcvts(fpf, rd, rn, FPNegativeInfinity);
        break;
      case NEON_FCVTMU_scalar:
        fcvtu(fpf, rd, rn, FPNegativeInfinity);
        break;
      case NEON_FCVTZS_scalar:
        fcvts(fpf, rd, rn, FPZero);
        break;
      case NEON_FCVTZU_scalar:
        fcvtu(fpf, rd, rn, FPZero);
        break;
      case NEON_FCVTAS_scalar:
        fcvts(fpf, rd, rn, FPTieAway);
        break;
      case NEON_FCVTAU_scalar:
        fcvtu(fpf, rd, rn, FPTieAway);
        break;
      case NEON_FCVTXN_scalar:
        // Unlike all of the other FP instructions above, fcvtxn encodes dest
        // size S as size<0>=1. There's only one case, so we ignore the form.
        VIXL_ASSERT(instr->ExtractBit(22) == 1);
        fcvtxn(kFormatS, rd, rn);
        break;
      default:
        switch (instr->Mask(NEONScalar2RegMiscMask)) {
          case NEON_SQXTN_scalar:
            sqxtn(vf, rd, rn);
            break;
          case NEON_UQXTN_scalar:
            uqxtn(vf, rd, rn);
            break;
          case NEON_SQXTUN_scalar:
            sqxtun(vf, rd, rn);
            break;
          default:
            VIXL_UNIMPLEMENTED();
        }
    }
  }
}


void Simulator::VisitNEONScalar3Diff(const Instruction* instr) {
  NEONFormatDecoder nfd(instr, NEONFormatDecoder::LongScalarFormatMap());
  VectorFormat vf = nfd.GetVectorFormat();

  SimVRegister& rd = ReadVRegister(instr->GetRd());
  SimVRegister& rn = ReadVRegister(instr->GetRn());
  SimVRegister& rm = ReadVRegister(instr->GetRm());
  switch (instr->Mask(NEONScalar3DiffMask)) {
    case NEON_SQDMLAL_scalar:
      sqdmlal(vf, rd, rn, rm);
      break;
    case NEON_SQDMLSL_scalar:
      sqdmlsl(vf, rd, rn, rm);
      break;
    case NEON_SQDMULL_scalar:
      sqdmull(vf, rd, rn, rm);
      break;
    default:
      VIXL_UNIMPLEMENTED();
  }
}


void Simulator::VisitNEONScalar3Same(const Instruction* instr) {
  NEONFormatDecoder nfd(instr, NEONFormatDecoder::ScalarFormatMap());
  VectorFormat vf = nfd.GetVectorFormat();

  SimVRegister& rd = ReadVRegister(instr->GetRd());
  SimVRegister& rn = ReadVRegister(instr->GetRn());
  SimVRegister& rm = ReadVRegister(instr->GetRm());

  if (instr->Mask(NEONScalar3SameFPFMask) == NEONScalar3SameFPFixed) {
    vf = nfd.GetVectorFormat(nfd.FPScalarFormatMap());
    switch (instr->Mask(NEONScalar3SameFPMask)) {
      case NEON_FMULX_scalar:
        fmulx(vf, rd, rn, rm);
        break;
      case NEON_FACGE_scalar:
        fabscmp(vf, rd, rn, rm, ge);
        break;
      case NEON_FACGT_scalar:
        fabscmp(vf, rd, rn, rm, gt);
        break;
      case NEON_FCMEQ_scalar:
        fcmp(vf, rd, rn, rm, eq);
        break;
      case NEON_FCMGE_scalar:
        fcmp(vf, rd, rn, rm, ge);
        break;
      case NEON_FCMGT_scalar:
        fcmp(vf, rd, rn, rm, gt);
        break;
      case NEON_FRECPS_scalar:
        frecps(vf, rd, rn, rm);
        break;
      case NEON_FRSQRTS_scalar:
        frsqrts(vf, rd, rn, rm);
        break;
      case NEON_FABD_scalar:
        fabd(vf, rd, rn, rm);
        break;
      default:
        VIXL_UNIMPLEMENTED();
    }
  } else {
    switch (instr->Mask(NEONScalar3SameMask)) {
      case NEON_ADD_scalar:
        add(vf, rd, rn, rm);
        break;
      case NEON_SUB_scalar:
        sub(vf, rd, rn, rm);
        break;
      case NEON_CMEQ_scalar:
        cmp(vf, rd, rn, rm, eq);
        break;
      case NEON_CMGE_scalar:
        cmp(vf, rd, rn, rm, ge);
        break;
      case NEON_CMGT_scalar:
        cmp(vf, rd, rn, rm, gt);
        break;
      case NEON_CMHI_scalar:
        cmp(vf, rd, rn, rm, hi);
        break;
      case NEON_CMHS_scalar:
        cmp(vf, rd, rn, rm, hs);
        break;
      case NEON_CMTST_scalar:
        cmptst(vf, rd, rn, rm);
        break;
      case NEON_USHL_scalar:
        ushl(vf, rd, rn, rm);
        break;
      case NEON_SSHL_scalar:
        sshl(vf, rd, rn, rm);
        break;
      case NEON_SQDMULH_scalar:
        sqdmulh(vf, rd, rn, rm);
        break;
      case NEON_SQRDMULH_scalar:
        sqrdmulh(vf, rd, rn, rm);
        break;
      case NEON_UQADD_scalar:
        add(vf, rd, rn, rm).UnsignedSaturate(vf);
        break;
      case NEON_SQADD_scalar:
        add(vf, rd, rn, rm).SignedSaturate(vf);
        break;
      case NEON_UQSUB_scalar:
        sub(vf, rd, rn, rm).UnsignedSaturate(vf);
        break;
      case NEON_SQSUB_scalar:
        sub(vf, rd, rn, rm).SignedSaturate(vf);
        break;
      case NEON_UQSHL_scalar:
        ushl(vf, rd, rn, rm).UnsignedSaturate(vf);
        break;
      case NEON_SQSHL_scalar:
        sshl(vf, rd, rn, rm).SignedSaturate(vf);
        break;
      case NEON_URSHL_scalar:
        ushl(vf, rd, rn, rm).Round(vf);
        break;
      case NEON_SRSHL_scalar:
        sshl(vf, rd, rn, rm).Round(vf);
        break;
      case NEON_UQRSHL_scalar:
        ushl(vf, rd, rn, rm).Round(vf).UnsignedSaturate(vf);
        break;
      case NEON_SQRSHL_scalar:
        sshl(vf, rd, rn, rm).Round(vf).SignedSaturate(vf);
        break;
      default:
        VIXL_UNIMPLEMENTED();
    }
  }
}


void Simulator::VisitNEONScalarByIndexedElement(const Instruction* instr) {
  NEONFormatDecoder nfd(instr, NEONFormatDecoder::LongScalarFormatMap());
  VectorFormat vf = nfd.GetVectorFormat();
  VectorFormat vf_r = nfd.GetVectorFormat(nfd.ScalarFormatMap());

  SimVRegister& rd = ReadVRegister(instr->GetRd());
  SimVRegister& rn = ReadVRegister(instr->GetRn());
  ByElementOp Op = NULL;

  int rm_reg = instr->GetRm();
  int index = (instr->GetNEONH() << 1) | instr->GetNEONL();
  if (instr->GetNEONSize() == 1) {
    rm_reg &= 0xf;
    index = (index << 1) | instr->GetNEONM();
  }

  switch (instr->Mask(NEONScalarByIndexedElementMask)) {
    case NEON_SQDMULL_byelement_scalar:
      Op = &Simulator::sqdmull;
      break;
    case NEON_SQDMLAL_byelement_scalar:
      Op = &Simulator::sqdmlal;
      break;
    case NEON_SQDMLSL_byelement_scalar:
      Op = &Simulator::sqdmlsl;
      break;
    case NEON_SQDMULH_byelement_scalar:
      Op = &Simulator::sqdmulh;
      vf = vf_r;
      break;
    case NEON_SQRDMULH_byelement_scalar:
      Op = &Simulator::sqrdmulh;
      vf = vf_r;
      break;
    default:
      vf = nfd.GetVectorFormat(nfd.FPScalarFormatMap());
      index = instr->GetNEONH();
      if ((instr->GetFPType() & 1) == 0) {
        index = (index << 1) | instr->GetNEONL();
      }
      switch (instr->Mask(NEONScalarByIndexedElementFPMask)) {
        case NEON_FMUL_byelement_scalar:
          Op = &Simulator::fmul;
          break;
        case NEON_FMLA_byelement_scalar:
          Op = &Simulator::fmla;
          break;
        case NEON_FMLS_byelement_scalar:
          Op = &Simulator::fmls;
          break;
        case NEON_FMULX_byelement_scalar:
          Op = &Simulator::fmulx;
          break;
        default:
          VIXL_UNIMPLEMENTED();
      }
  }

  (this->*Op)(vf, rd, rn, ReadVRegister(rm_reg), index);
}


void Simulator::VisitNEONScalarCopy(const Instruction* instr) {
  NEONFormatDecoder nfd(instr, NEONFormatDecoder::TriangularScalarFormatMap());
  VectorFormat vf = nfd.GetVectorFormat();

  SimVRegister& rd = ReadVRegister(instr->GetRd());
  SimVRegister& rn = ReadVRegister(instr->GetRn());

  if (instr->Mask(NEONScalarCopyMask) == NEON_DUP_ELEMENT_scalar) {
    int imm5 = instr->GetImmNEON5();
    int tz = CountTrailingZeros(imm5, 32);
    int rn_index = imm5 >> (tz + 1);
    dup_element(vf, rd, rn, rn_index);
  } else {
    VIXL_UNIMPLEMENTED();
  }
}


void Simulator::VisitNEONScalarPairwise(const Instruction* instr) {
  NEONFormatDecoder nfd(instr, NEONFormatDecoder::FPScalarFormatMap());
  VectorFormat vf = nfd.GetVectorFormat();

  SimVRegister& rd = ReadVRegister(instr->GetRd());
  SimVRegister& rn = ReadVRegister(instr->GetRn());
  switch (instr->Mask(NEONScalarPairwiseMask)) {
    case NEON_ADDP_scalar:
      addp(vf, rd, rn);
      break;
    case NEON_FADDP_scalar:
      faddp(vf, rd, rn);
      break;
    case NEON_FMAXP_scalar:
      fmaxp(vf, rd, rn);
      break;
    case NEON_FMAXNMP_scalar:
      fmaxnmp(vf, rd, rn);
      break;
    case NEON_FMINP_scalar:
      fminp(vf, rd, rn);
      break;
    case NEON_FMINNMP_scalar:
      fminnmp(vf, rd, rn);
      break;
    default:
      VIXL_UNIMPLEMENTED();
  }
}


void Simulator::VisitNEONScalarShiftImmediate(const Instruction* instr) {
  SimVRegister& rd = ReadVRegister(instr->GetRd());
  SimVRegister& rn = ReadVRegister(instr->GetRn());
  FPRounding fpcr_rounding = static_cast<FPRounding>(ReadFpcr().GetRMode());

  static const NEONFormatMap map = {{22, 21, 20, 19},
                                    {NF_UNDEF,
                                     NF_B,
                                     NF_H,
                                     NF_H,
                                     NF_S,
                                     NF_S,
                                     NF_S,
                                     NF_S,
                                     NF_D,
                                     NF_D,
                                     NF_D,
                                     NF_D,
                                     NF_D,
                                     NF_D,
                                     NF_D,
                                     NF_D}};
  NEONFormatDecoder nfd(instr, &map);
  VectorFormat vf = nfd.GetVectorFormat();

  int highestSetBit = HighestSetBitPosition(instr->GetImmNEONImmh());
  int immhimmb = instr->GetImmNEONImmhImmb();
  int right_shift = (16 << highestSetBit) - immhimmb;
  int left_shift = immhimmb - (8 << highestSetBit);
  switch (instr->Mask(NEONScalarShiftImmediateMask)) {
    case NEON_SHL_scalar:
      shl(vf, rd, rn, left_shift);
      break;
    case NEON_SLI_scalar:
      sli(vf, rd, rn, left_shift);
      break;
    case NEON_SQSHL_imm_scalar:
      sqshl(vf, rd, rn, left_shift);
      break;
    case NEON_UQSHL_imm_scalar:
      uqshl(vf, rd, rn, left_shift);
      break;
    case NEON_SQSHLU_scalar:
      sqshlu(vf, rd, rn, left_shift);
      break;
    case NEON_SRI_scalar:
      sri(vf, rd, rn, right_shift);
      break;
    case NEON_SSHR_scalar:
      sshr(vf, rd, rn, right_shift);
      break;
    case NEON_USHR_scalar:
      ushr(vf, rd, rn, right_shift);
      break;
    case NEON_SRSHR_scalar:
      sshr(vf, rd, rn, right_shift).Round(vf);
      break;
    case NEON_URSHR_scalar:
      ushr(vf, rd, rn, right_shift).Round(vf);
      break;
    case NEON_SSRA_scalar:
      ssra(vf, rd, rn, right_shift);
      break;
    case NEON_USRA_scalar:
      usra(vf, rd, rn, right_shift);
      break;
    case NEON_SRSRA_scalar:
      srsra(vf, rd, rn, right_shift);
      break;
    case NEON_URSRA_scalar:
      ursra(vf, rd, rn, right_shift);
      break;
    case NEON_UQSHRN_scalar:
      uqshrn(vf, rd, rn, right_shift);
      break;
    case NEON_UQRSHRN_scalar:
      uqrshrn(vf, rd, rn, right_shift);
      break;
    case NEON_SQSHRN_scalar:
      sqshrn(vf, rd, rn, right_shift);
      break;
    case NEON_SQRSHRN_scalar:
      sqrshrn(vf, rd, rn, right_shift);
      break;
    case NEON_SQSHRUN_scalar:
      sqshrun(vf, rd, rn, right_shift);
      break;
    case NEON_SQRSHRUN_scalar:
      sqrshrun(vf, rd, rn, right_shift);
      break;
    case NEON_FCVTZS_imm_scalar:
      fcvts(vf, rd, rn, FPZero, right_shift);
      break;
    case NEON_FCVTZU_imm_scalar:
      fcvtu(vf, rd, rn, FPZero, right_shift);
      break;
    case NEON_SCVTF_imm_scalar:
      scvtf(vf, rd, rn, right_shift, fpcr_rounding);
      break;
    case NEON_UCVTF_imm_scalar:
      ucvtf(vf, rd, rn, right_shift, fpcr_rounding);
      break;
    default:
      VIXL_UNIMPLEMENTED();
  }
}


void Simulator::VisitNEONShiftImmediate(const Instruction* instr) {
  SimVRegister& rd = ReadVRegister(instr->GetRd());
  SimVRegister& rn = ReadVRegister(instr->GetRn());
  FPRounding fpcr_rounding = static_cast<FPRounding>(ReadFpcr().GetRMode());

  // 00010->8B, 00011->16B, 001x0->4H, 001x1->8H,
  // 01xx0->2S, 01xx1->4S, 1xxx1->2D, all others undefined.
  static const NEONFormatMap map = {{22, 21, 20, 19, 30},
                                    {NF_UNDEF,
                                     NF_UNDEF,
                                     NF_8B,
                                     NF_16B,
                                     NF_4H,
                                     NF_8H,
                                     NF_4H,
                                     NF_8H,
                                     NF_2S,
                                     NF_4S,
                                     NF_2S,
                                     NF_4S,
                                     NF_2S,
                                     NF_4S,
                                     NF_2S,
                                     NF_4S,
                                     NF_UNDEF,
                                     NF_2D,
                                     NF_UNDEF,
                                     NF_2D,
                                     NF_UNDEF,
                                     NF_2D,
                                     NF_UNDEF,
                                     NF_2D,
                                     NF_UNDEF,
                                     NF_2D,
                                     NF_UNDEF,
                                     NF_2D,
                                     NF_UNDEF,
                                     NF_2D,
                                     NF_UNDEF,
                                     NF_2D}};
  NEONFormatDecoder nfd(instr, &map);
  VectorFormat vf = nfd.GetVectorFormat();

  // 0001->8H, 001x->4S, 01xx->2D, all others undefined.
  static const NEONFormatMap map_l =
      {{22, 21, 20, 19},
       {NF_UNDEF, NF_8H, NF_4S, NF_4S, NF_2D, NF_2D, NF_2D, NF_2D}};
  VectorFormat vf_l = nfd.GetVectorFormat(&map_l);

  int highestSetBit = HighestSetBitPosition(instr->GetImmNEONImmh());
  int immhimmb = instr->GetImmNEONImmhImmb();
  int right_shift = (16 << highestSetBit) - immhimmb;
  int left_shift = immhimmb - (8 << highestSetBit);

  switch (instr->Mask(NEONShiftImmediateMask)) {
    case NEON_SHL:
      shl(vf, rd, rn, left_shift);
      break;
    case NEON_SLI:
      sli(vf, rd, rn, left_shift);
      break;
    case NEON_SQSHLU:
      sqshlu(vf, rd, rn, left_shift);
      break;
    case NEON_SRI:
      sri(vf, rd, rn, right_shift);
      break;
    case NEON_SSHR:
      sshr(vf, rd, rn, right_shift);
      break;
    case NEON_USHR:
      ushr(vf, rd, rn, right_shift);
      break;
    case NEON_SRSHR:
      sshr(vf, rd, rn, right_shift).Round(vf);
      break;
    case NEON_URSHR:
      ushr(vf, rd, rn, right_shift).Round(vf);
      break;
    case NEON_SSRA:
      ssra(vf, rd, rn, right_shift);
      break;
    case NEON_USRA:
      usra(vf, rd, rn, right_shift);
      break;
    case NEON_SRSRA:
      srsra(vf, rd, rn, right_shift);
      break;
    case NEON_URSRA:
      ursra(vf, rd, rn, right_shift);
      break;
    case NEON_SQSHL_imm:
      sqshl(vf, rd, rn, left_shift);
      break;
    case NEON_UQSHL_imm:
      uqshl(vf, rd, rn, left_shift);
      break;
    case NEON_SCVTF_imm:
      scvtf(vf, rd, rn, right_shift, fpcr_rounding);
      break;
    case NEON_UCVTF_imm:
      ucvtf(vf, rd, rn, right_shift, fpcr_rounding);
      break;
    case NEON_FCVTZS_imm:
      fcvts(vf, rd, rn, FPZero, right_shift);
      break;
    case NEON_FCVTZU_imm:
      fcvtu(vf, rd, rn, FPZero, right_shift);
      break;
    case NEON_SSHLL:
      vf = vf_l;
      if (instr->Mask(NEON_Q)) {
        sshll2(vf, rd, rn, left_shift);
      } else {
        sshll(vf, rd, rn, left_shift);
      }
      break;
    case NEON_USHLL:
      vf = vf_l;
      if (instr->Mask(NEON_Q)) {
        ushll2(vf, rd, rn, left_shift);
      } else {
        ushll(vf, rd, rn, left_shift);
      }
      break;
    case NEON_SHRN:
      if (instr->Mask(NEON_Q)) {
        shrn2(vf, rd, rn, right_shift);
      } else {
        shrn(vf, rd, rn, right_shift);
      }
      break;
    case NEON_RSHRN:
      if (instr->Mask(NEON_Q)) {
        rshrn2(vf, rd, rn, right_shift);
      } else {
        rshrn(vf, rd, rn, right_shift);
      }
      break;
    case NEON_UQSHRN:
      if (instr->Mask(NEON_Q)) {
        uqshrn2(vf, rd, rn, right_shift);
      } else {
        uqshrn(vf, rd, rn, right_shift);
      }
      break;
    case NEON_UQRSHRN:
      if (instr->Mask(NEON_Q)) {
        uqrshrn2(vf, rd, rn, right_shift);
      } else {
        uqrshrn(vf, rd, rn, right_shift);
      }
      break;
    case NEON_SQSHRN:
      if (instr->Mask(NEON_Q)) {
        sqshrn2(vf, rd, rn, right_shift);
      } else {
        sqshrn(vf, rd, rn, right_shift);
      }
      break;
    case NEON_SQRSHRN:
      if (instr->Mask(NEON_Q)) {
        sqrshrn2(vf, rd, rn, right_shift);
      } else {
        sqrshrn(vf, rd, rn, right_shift);
      }
      break;
    case NEON_SQSHRUN:
      if (instr->Mask(NEON_Q)) {
        sqshrun2(vf, rd, rn, right_shift);
      } else {
        sqshrun(vf, rd, rn, right_shift);
      }
      break;
    case NEON_SQRSHRUN:
      if (instr->Mask(NEON_Q)) {
        sqrshrun2(vf, rd, rn, right_shift);
      } else {
        sqrshrun(vf, rd, rn, right_shift);
      }
      break;
    default:
      VIXL_UNIMPLEMENTED();
  }
}


void Simulator::VisitNEONTable(const Instruction* instr) {
  NEONFormatDecoder nfd(instr, NEONFormatDecoder::LogicalFormatMap());
  VectorFormat vf = nfd.GetVectorFormat();

  SimVRegister& rd = ReadVRegister(instr->GetRd());
  SimVRegister& rn = ReadVRegister(instr->GetRn());
  SimVRegister& rn2 = ReadVRegister((instr->GetRn() + 1) % kNumberOfVRegisters);
  SimVRegister& rn3 = ReadVRegister((instr->GetRn() + 2) % kNumberOfVRegisters);
  SimVRegister& rn4 = ReadVRegister((instr->GetRn() + 3) % kNumberOfVRegisters);
  SimVRegister& rm = ReadVRegister(instr->GetRm());

  switch (instr->Mask(NEONTableMask)) {
    case NEON_TBL_1v:
      tbl(vf, rd, rn, rm);
      break;
    case NEON_TBL_2v:
      tbl(vf, rd, rn, rn2, rm);
      break;
    case NEON_TBL_3v:
      tbl(vf, rd, rn, rn2, rn3, rm);
      break;
    case NEON_TBL_4v:
      tbl(vf, rd, rn, rn2, rn3, rn4, rm);
      break;
    case NEON_TBX_1v:
      tbx(vf, rd, rn, rm);
      break;
    case NEON_TBX_2v:
      tbx(vf, rd, rn, rn2, rm);
      break;
    case NEON_TBX_3v:
      tbx(vf, rd, rn, rn2, rn3, rm);
      break;
    case NEON_TBX_4v:
      tbx(vf, rd, rn, rn2, rn3, rn4, rm);
      break;
    default:
      VIXL_UNIMPLEMENTED();
  }
}


void Simulator::VisitNEONPerm(const Instruction* instr) {
  NEONFormatDecoder nfd(instr);
  VectorFormat vf = nfd.GetVectorFormat();

  SimVRegister& rd = ReadVRegister(instr->GetRd());
  SimVRegister& rn = ReadVRegister(instr->GetRn());
  SimVRegister& rm = ReadVRegister(instr->GetRm());

  switch (instr->Mask(NEONPermMask)) {
    case NEON_TRN1:
      trn1(vf, rd, rn, rm);
      break;
    case NEON_TRN2:
      trn2(vf, rd, rn, rm);
      break;
    case NEON_UZP1:
      uzp1(vf, rd, rn, rm);
      break;
    case NEON_UZP2:
      uzp2(vf, rd, rn, rm);
      break;
    case NEON_ZIP1:
      zip1(vf, rd, rn, rm);
      break;
    case NEON_ZIP2:
      zip2(vf, rd, rn, rm);
      break;
    default:
      VIXL_UNIMPLEMENTED();
  }
}


void Simulator::DoUnreachable(const Instruction* instr) {
  VIXL_ASSERT((instr->Mask(ExceptionMask) == HLT) &&
              (instr->GetImmException() == kUnreachableOpcode));

  fprintf(stream_,
          "Hit UNREACHABLE marker at pc=%p.\n",
          reinterpret_cast<const void*>(instr));
  abort();
}


void Simulator::DoTrace(const Instruction* instr) {
  VIXL_ASSERT((instr->Mask(ExceptionMask) == HLT) &&
              (instr->GetImmException() == kTraceOpcode));

  // Read the arguments encoded inline in the instruction stream.
  uint32_t parameters;
  uint32_t command;

  VIXL_STATIC_ASSERT(sizeof(*instr) == 1);
  memcpy(&parameters, instr + kTraceParamsOffset, sizeof(parameters));
  memcpy(&command, instr + kTraceCommandOffset, sizeof(command));

  switch (command) {
    case TRACE_ENABLE:
      SetTraceParameters(GetTraceParameters() | parameters);
      break;
    case TRACE_DISABLE:
      SetTraceParameters(GetTraceParameters() & ~parameters);
      break;
    default:
      VIXL_UNREACHABLE();
  }

  WritePc(instr->GetInstructionAtOffset(kTraceLength));
}


void Simulator::DoLog(const Instruction* instr) {
  VIXL_ASSERT((instr->Mask(ExceptionMask) == HLT) &&
              (instr->GetImmException() == kLogOpcode));

  // Read the arguments encoded inline in the instruction stream.
  uint32_t parameters;

  VIXL_STATIC_ASSERT(sizeof(*instr) == 1);
  memcpy(&parameters, instr + kTraceParamsOffset, sizeof(parameters));

  // We don't support a one-shot LOG_DISASM.
  VIXL_ASSERT((parameters & LOG_DISASM) == 0);
  // Print the requested information.
  if (parameters & LOG_SYSREGS) PrintSystemRegisters();
  if (parameters & LOG_REGS) PrintRegisters();
  if (parameters & LOG_VREGS) PrintVRegisters();

  WritePc(instr->GetInstructionAtOffset(kLogLength));
}


void Simulator::DoPrintf(const Instruction* instr) {
  VIXL_ASSERT((instr->Mask(ExceptionMask) == HLT) &&
              (instr->GetImmException() == kPrintfOpcode));

  // Read the arguments encoded inline in the instruction stream.
  uint32_t arg_count;
  uint32_t arg_pattern_list;
  VIXL_STATIC_ASSERT(sizeof(*instr) == 1);
  memcpy(&arg_count, instr + kPrintfArgCountOffset, sizeof(arg_count));
  memcpy(&arg_pattern_list,
         instr + kPrintfArgPatternListOffset,
         sizeof(arg_pattern_list));

  VIXL_ASSERT(arg_count <= kPrintfMaxArgCount);
  VIXL_ASSERT((arg_pattern_list >> (kPrintfArgPatternBits * arg_count)) == 0);

  // We need to call the host printf function with a set of arguments defined by
  // arg_pattern_list. Because we don't know the types and sizes of the
  // arguments, this is very difficult to do in a robust and portable way. To
  // work around the problem, we pick apart the format string, and print one
  // format placeholder at a time.

  // Allocate space for the format string. We take a copy, so we can modify it.
  // Leave enough space for one extra character per expected argument (plus the
  // '\0' termination).
  const char* format_base = ReadRegister<const char*>(0);
  VIXL_ASSERT(format_base != NULL);
  size_t length = strlen(format_base) + 1;
  char* const format = new char[length + arg_count];

  // A list of chunks, each with exactly one format placeholder.
  const char* chunks[kPrintfMaxArgCount];

  // Copy the format string and search for format placeholders.
  uint32_t placeholder_count = 0;
  char* format_scratch = format;
  for (size_t i = 0; i < length; i++) {
    if (format_base[i] != '%') {
      *format_scratch++ = format_base[i];
    } else {
      if (format_base[i + 1] == '%') {
        // Ignore explicit "%%" sequences.
        *format_scratch++ = format_base[i];
        i++;
        // Chunks after the first are passed as format strings to printf, so we
        // need to escape '%' characters in those chunks.
        if (placeholder_count > 0) *format_scratch++ = format_base[i];
      } else {
        VIXL_CHECK(placeholder_count < arg_count);
        // Insert '\0' before placeholders, and store their locations.
        *format_scratch++ = '\0';
        chunks[placeholder_count++] = format_scratch;
        *format_scratch++ = format_base[i];
      }
    }
  }
  VIXL_CHECK(placeholder_count == arg_count);

  // Finally, call printf with each chunk, passing the appropriate register
  // argument. Normally, printf returns the number of bytes transmitted, so we
  // can emulate a single printf call by adding the result from each chunk. If
  // any call returns a negative (error) value, though, just return that value.

  printf("%s", clr_printf);

  // Because '\0' is inserted before each placeholder, the first string in
  // 'format' contains no format placeholders and should be printed literally.
  int result = printf("%s", format);
  int pcs_r = 1;  // Start at x1. x0 holds the format string.
  int pcs_f = 0;  // Start at d0.
  if (result >= 0) {
    for (uint32_t i = 0; i < placeholder_count; i++) {
      int part_result = -1;

      uint32_t arg_pattern = arg_pattern_list >> (i * kPrintfArgPatternBits);
      arg_pattern &= (1 << kPrintfArgPatternBits) - 1;
      switch (arg_pattern) {
        case kPrintfArgW:
          part_result = printf(chunks[i], ReadWRegister(pcs_r++));
          break;
        case kPrintfArgX:
          part_result = printf(chunks[i], ReadXRegister(pcs_r++));
          break;
        case kPrintfArgD:
          part_result = printf(chunks[i], ReadDRegister(pcs_f++));
          break;
        default:
          VIXL_UNREACHABLE();
      }

      if (part_result < 0) {
        // Handle error values.
        result = part_result;
        break;
      }

      result += part_result;
    }
  }

  printf("%s", clr_normal);

  // Printf returns its result in x0 (just like the C library's printf).
  WriteXRegister(0, result);

  // The printf parameters are inlined in the code, so skip them.
  WritePc(instr->GetInstructionAtOffset(kPrintfLength));

  // Set LR as if we'd just called a native printf function.
  WriteLr(ReadPc());

  delete[] format;
}


#ifdef VIXL_HAS_SIMULATED_RUNTIME_CALL_SUPPORT
void Simulator::DoRuntimeCall(const Instruction* instr) {
  VIXL_STATIC_ASSERT(kRuntimeCallAddressSize == sizeof(uintptr_t));
  // The appropriate `Simulator::SimulateRuntimeCall()` wrapper and the function
  // to call are passed inlined in the assembly.
  uintptr_t call_wrapper_address =
      Memory::Read<uintptr_t>(instr + kRuntimeCallWrapperOffset);
  uintptr_t function_address =
      Memory::Read<uintptr_t>(instr + kRuntimeCallFunctionOffset);
  auto runtime_call_wrapper =
      reinterpret_cast<void (*)(Simulator*, uintptr_t)>(call_wrapper_address);
  runtime_call_wrapper(this, function_address);
  WritePc(instr->GetInstructionAtOffset(kRuntimeCallLength));
}
#else
void Simulator::DoRuntimeCall(const Instruction* instr) {
  USE(instr);
  VIXL_UNREACHABLE();
}
#endif

}  // namespace aarch64
}  // namespace vixl

#endif  // VIXL_INCLUDE_SIMULATOR_AARCH64