path: root/js/src/jit/arm64/vixl/Simulator-vixl.cpp

// 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
// FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
// DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
// SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
// CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
// OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

#include "jstypes.h"

#ifdef JS_SIMULATOR_ARM64

#include "jit/arm64/vixl/Simulator-vixl.h"

#include <cmath>
#include <string.h>

#include "jit/AtomicOperations.h"

namespace vixl {

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();
  }
}


void Simulator::Run() {
  pc_modified_ = false;
  while (pc_ != kEndOfSimAddress) {
    ExecuteInstruction();
    LogAllWrittenRegisters();
  }
}


void Simulator::RunFrom(const Instruction* first) {
  set_pc(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::set_coloured_trace(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)         : "";
}
#undef COLOUR
#undef COLOUR_BOLD
#undef NORMAL
#undef GREY
#undef RED
#undef GREEN
#undef YELLOW
#undef BLUE
#undef MAGENTA
#undef CYAN
#undef WHITE


void Simulator::set_trace_parameters(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::set_instruction_stats(bool value) {
  if (instrumentation_ == nullptr) {
    return;
  }

  if (value != instruction_stats_) {
    if (value) {
      decoder_->AppendVisitor(instrumentation_);
    } else {
      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) {
    nzcv().SetN(CalcNFlag(result, reg_size));
    nzcv().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);
    nzcv().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);
    nzcv().SetV(V ? 1 : 0);

    LogSystemRegister(NZCV);
  }
  return result;
}


int64_t Simulator::ShiftOperand(unsigned reg_size,
                                int64_t value,
                                Shift shift_type,
                                unsigned amount) {
  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) {
  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)) {
    nzcv().SetRawValue(FPUnorderedFlag);
    if (IsSignallingNaN(val0) || IsSignallingNaN(val1) ||
        (trap == EnableTrap)) {
      process_exception = true;
    }
  } else if (val0 < val1) {
    nzcv().SetRawValue(FPLessThanFlag);
  } else if (val0 > val1) {
    nzcv().SetRawValue(FPGreaterThanFlag);
  } else if (val0 == val1) {
    nzcv().SetRawValue(FPEqualFlag);
  } else {
    VIXL_UNREACHABLE();
  }
  LogSystemRegister(NZCV);
  if (process_exception) FPProcessException();
}


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;
  }
}


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 = reg<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 = qreg(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) ? vreg(code).Get<float>(lane)
                                                 : vreg(code).Get<double>(lane);
    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,
              nzcv().N(), nzcv().Z(), nzcv().C(), nzcv().V(),
              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(fpcr().RMode() < (sizeof(rmode) / sizeof(rmode[0])));
      fprintf(stream_,
              "# %sFPCR: %sAHP:%d DN:%d FZ:%d RMode:%s%s\n",
              clr_flag_name, clr_flag_value,
              fpcr().AHP(), fpcr().DN(), fpcr().FZ(), rmode[fpcr().RMode()],
              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->InstructionBits());
  VIXL_UNIMPLEMENTED();
}


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


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

  set_reg(instr->Rd(), instr->ImmPCOffsetTarget());
}


void Simulator::VisitUnconditionalBranch(const Instruction* instr) {
  switch (instr->Mask(UnconditionalBranchMask)) {
    case BL:
      set_lr(instr->NextInstruction());
      VIXL_FALLTHROUGH();
    case B:
      set_pc(instr->ImmPCOffsetTarget());
      break;
    default: VIXL_UNREACHABLE();
  }
}


void Simulator::VisitConditionalBranch(const Instruction* instr) {
  VIXL_ASSERT(instr->Mask(ConditionalBranchMask) == B_cond);
  if (ConditionPassed(instr->ConditionBranch())) {
    set_pc(instr->ImmPCOffsetTarget());
  }
}


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

  switch (instr->Mask(UnconditionalBranchToRegisterMask)) {
    case BLR:
      set_lr(instr->NextInstruction());
      VIXL_FALLTHROUGH();
    case BR:
    case RET: set_pc(target); break;
    default: VIXL_UNREACHABLE();
  }
}


void Simulator::VisitTestBranch(const Instruction* instr) {
  unsigned bit_pos = (instr->ImmTestBranchBit5() << 5) |
                     instr->ImmTestBranchBit40();
  bool bit_zero = ((xreg(instr->Rt()) >> 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) {
    set_pc(instr->ImmPCOffsetTarget());
  }
}


void Simulator::VisitCompareBranch(const Instruction* instr) {
  unsigned rt = instr->Rt();
  bool take_branch = false;
  switch (instr->Mask(CompareBranchMask)) {
    case CBZ_w: take_branch = (wreg(rt) == 0); break;
    case CBZ_x: take_branch = (xreg(rt) == 0); break;
    case CBNZ_w: take_branch = (wreg(rt) != 0); break;
    case CBNZ_x: take_branch = (xreg(rt) != 0); break;
    default: VIXL_UNIMPLEMENTED();
  }
  if (take_branch) {
    set_pc(instr->ImmPCOffsetTarget());
  }
}


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

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

  set_reg(reg_size, instr->Rd(), new_val, LogRegWrites, instr->RdMode());
}


void Simulator::VisitAddSubShifted(const Instruction* instr) {
  unsigned reg_size = instr->SixtyFourBits() ? kXRegSize : kWRegSize;
  int64_t op2 = ShiftOperand(reg_size,
                             reg(reg_size, instr->Rm()),
                             static_cast<Shift>(instr->ShiftDP()),
                             instr->ImmDPShift());
  AddSubHelper(instr, op2);
}


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


void Simulator::VisitAddSubExtended(const Instruction* instr) {
  unsigned reg_size = instr->SixtyFourBits() ? kXRegSize : kWRegSize;
  int64_t op2 = ExtendValue(reg_size,
                            reg(reg_size, instr->Rm()),
                            static_cast<Extend>(instr->ExtendMode()),
                            instr->ImmExtendShift());
  AddSubHelper(instr, op2);
}


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

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

  new_val = AddWithCarry(reg_size,
                         instr->FlagsUpdate(),
                         reg(reg_size, instr->Rn()),
                         op2,
                         C());

  set_reg(reg_size, instr->Rd(), new_val);
}


void Simulator::VisitLogicalShifted(const Instruction* instr) {
  unsigned reg_size = instr->SixtyFourBits() ? kXRegSize : kWRegSize;
  Shift shift_type = static_cast<Shift>(instr->ShiftDP());
  unsigned shift_amount = instr->ImmDPShift();
  int64_t op2 = ShiftOperand(reg_size, reg(reg_size, instr->Rm()), shift_type,
                             shift_amount);
  if (instr->Mask(NOT) == NOT) {
    op2 = ~op2;
  }
  LogicalHelper(instr, op2);
}


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


void Simulator::LogicalHelper(const Instruction* instr, int64_t op2) {
  unsigned reg_size = instr->SixtyFourBits() ? kXRegSize : kWRegSize;
  int64_t op1 = reg(reg_size, instr->Rn());
  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) {
    nzcv().SetN(CalcNFlag(result, reg_size));
    nzcv().SetZ(CalcZFlag(result));
    nzcv().SetC(0);
    nzcv().SetV(0);
    LogSystemRegister(NZCV);
  }

  set_reg(reg_size, instr->Rd(), result, LogRegWrites, instr->RdMode());
}


void Simulator::VisitConditionalCompareRegister(const Instruction* instr) {
  unsigned reg_size = instr->SixtyFourBits() ? kXRegSize : kWRegSize;
  ConditionalCompareHelper(instr, reg(reg_size, instr->Rm()));
}


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


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

  if (ConditionPassed(instr->Condition())) {
    // 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.
    nzcv().SetFlags(instr->Nzcv());
    LogSystemRegister(NZCV);
  }
}


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


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


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


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


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

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

template<typename T>
static T Faulted() {
    return ~0;
}

template<>
Simulator::qreg_t Faulted() {
    static_assert(kQRegSizeInBytes == 16, "Known constraint");
    static Simulator::qreg_t dummy = { {
	255, 255, 255, 255, 255, 255, 255, 255,
	255, 255, 255, 255, 255, 255, 255, 255
    } };
    return dummy;
}

template<typename T> T
Simulator::Read(uintptr_t address)
{
    address = Memory::AddressUntag(address);
    if (handle_wasm_seg_fault(address, sizeof(T)))
	return Faulted<T>();
    return Memory::Read<T>(address);
}

template <typename T> void
Simulator::Write(uintptr_t address, T value)
{
    address = Memory::AddressUntag(address);
    if (handle_wasm_seg_fault(address, sizeof(T)))
	return;
    Memory::Write<T>(address, value);
}

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

  LoadStoreOp op = static_cast<LoadStoreOp>(instr->Mask(LoadStoreMask));
  switch (op) {
    case LDRB_w:
      set_wreg(srcdst, Read<uint8_t>(address), NoRegLog); break;
    case LDRH_w:
      set_wreg(srcdst, Read<uint16_t>(address), NoRegLog); break;
    case LDR_w:
      set_wreg(srcdst, Read<uint32_t>(address), NoRegLog); break;
    case LDR_x:
      set_xreg(srcdst, Read<uint64_t>(address), NoRegLog); break;
    case LDRSB_w:
      set_wreg(srcdst, Read<int8_t>(address), NoRegLog); break;
    case LDRSH_w:
      set_wreg(srcdst, Read<int16_t>(address), NoRegLog); break;
    case LDRSB_x:
      set_xreg(srcdst, Read<int8_t>(address), NoRegLog); break;
    case LDRSH_x:
      set_xreg(srcdst, Read<int16_t>(address), NoRegLog); break;
    case LDRSW_x:
      set_xreg(srcdst, Read<int32_t>(address), NoRegLog); break;
    case LDR_b:
      set_breg(srcdst, Read<uint8_t>(address), NoRegLog); break;
    case LDR_h:
      set_hreg(srcdst, Read<uint16_t>(address), NoRegLog); break;
    case LDR_s:
      set_sreg(srcdst, Read<float>(address), NoRegLog); break;
    case LDR_d:
      set_dreg(srcdst, Read<double>(address), NoRegLog); break;
    case LDR_q:
      set_qreg(srcdst, Read<qreg_t>(address), NoRegLog); break;

    case STRB_w:  Write<uint8_t>(address, wreg(srcdst)); break;
    case STRH_w:  Write<uint16_t>(address, wreg(srcdst)); break;
    case STR_w:   Write<uint32_t>(address, wreg(srcdst)); break;
    case STR_x:   Write<uint64_t>(address, xreg(srcdst)); break;
    case STR_b:   Write<uint8_t>(address, breg(srcdst)); break;
    case STR_h:   Write<uint16_t>(address, hreg(srcdst)); break;
    case STR_s:   Write<float>(address, sreg(srcdst)); break;
    case STR_d:   Write<double>(address, dreg(srcdst)); break;
    case STR_q:   Write<qreg_t>(address, qreg(srcdst)); break;

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

    default: VIXL_UNIMPLEMENTED();
  }

  unsigned access_size = 1 << instr->SizeLS();
  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 ((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));
    }
  }

  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->Rt();
  unsigned rt2 = instr->Rt2();
  int element_size = 1 << instr->SizeLSPair();
  int64_t offset = instr->ImmLSPair() * element_size;
  uintptr_t address = AddressModeHelper(instr->Rn(), 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: {
      set_wreg(rt, Read<uint32_t>(address), NoRegLog);
      set_wreg(rt2, Read<uint32_t>(address2), NoRegLog);
      break;
    }
    case LDP_s: {
      set_sreg(rt, Read<float>(address), NoRegLog);
      set_sreg(rt2, Read<float>(address2), NoRegLog);
      break;
    }
    case LDP_x: {
      set_xreg(rt, Read<uint64_t>(address), NoRegLog);
      set_xreg(rt2, Read<uint64_t>(address2), NoRegLog);
      break;
    }
    case LDP_d: {
      set_dreg(rt, Read<double>(address), NoRegLog);
      set_dreg(rt2, Read<double>(address2), NoRegLog);
      break;
    }
    case LDP_q: {
      set_qreg(rt, Read<qreg_t>(address), NoRegLog);
      set_qreg(rt2, Read<qreg_t>(address2), NoRegLog);
      break;
    }
    case LDPSW_x: {
      set_xreg(rt, Read<int32_t>(address), NoRegLog);
      set_xreg(rt2, Read<int32_t>(address2), NoRegLog);
      break;
    }
    case STP_w: {
      Write<uint32_t>(address, wreg(rt));
      Write<uint32_t>(address2, wreg(rt2));
      break;
    }
    case STP_s: {
      Write<float>(address, sreg(rt));
      Write<float>(address2, sreg(rt2));
      break;
    }
    case STP_x: {
      Write<uint64_t>(address, xreg(rt));
      Write<uint64_t>(address2, xreg(rt2));
      break;
    }
    case STP_d: {
      Write<double>(address, dreg(rt));
      Write<double>(address2, dreg(rt2));
      break;
    }
    case STP_q: {
      Write<qreg_t>(address, qreg(rt));
      Write<qreg_t>(address2, qreg(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;
  }
}

template <typename T>
void Simulator::CompareAndSwapHelper(const Instruction* instr) {
  unsigned rs = instr->Rs();
  unsigned rt = instr->Rt();
  unsigned rn = instr->Rn();

  unsigned element_size = sizeof(T);
  uint64_t address = reg<uint64_t>(rn, Reg31IsStackPointer);

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

  address = Memory::AddressUntag(address);
  if (handle_wasm_seg_fault(address, element_size))
    return;

  bool is_acquire = instr->Bit(22) == 1;
  bool is_release = instr->Bit(15) == 1;

  T comparevalue = reg<T>(rs);
  T newvalue = reg<T>(rt);

  // The architecture permits that the data read clears any exclusive monitors
  // associated with that location, even if the compare subsequently fails.
  local_monitor_.Clear();

  T data = Memory::Read<T>(address);
  if (is_acquire) {
    // Approximate load-acquire by issuing a full barrier after the load.
    __sync_synchronize();
  }

  if (data == comparevalue) {
    if (is_release) {
      // Approximate store-release by issuing a full barrier before the store.
      __sync_synchronize();
    }
    Memory::Write<T>(address, newvalue);
    LogWrite(address, rt, GetPrintRegisterFormatForSize(element_size));
  }
  set_reg<T>(rs, data);
  LogRead(address, rs, GetPrintRegisterFormatForSize(element_size));
}

template <typename T>
void Simulator::CompareAndSwapPairHelper(const Instruction* instr) {
  VIXL_ASSERT((sizeof(T) == 4) || (sizeof(T) == 8));
  unsigned rs = instr->Rs();
  unsigned rt = instr->Rt();
  unsigned rn = instr->Rn();

  VIXL_ASSERT((rs % 2 == 0) && (rs % 2 == 0));

  unsigned element_size = sizeof(T);
  uint64_t address = reg<uint64_t>(rn, Reg31IsStackPointer);

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

  address = Memory::AddressUntag(address);
  if (handle_wasm_seg_fault(address, element_size))
    return;

  uint64_t address2 = address + element_size;

  bool is_acquire = instr->Bit(22) == 1;
  bool is_release = instr->Bit(15) == 1;

  T comparevalue_high = reg<T>(rs + 1);
  T comparevalue_low = reg<T>(rs);
  T newvalue_high = reg<T>(rt + 1);
  T newvalue_low = reg<T>(rt);

  // The architecture permits that the data read clears any exclusive monitors
  // associated with that location, even if the compare subsequently fails.
  local_monitor_.Clear();

  T data_high = Memory::Read<T>(address);
  T data_low = Memory::Read<T>(address2);

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

  bool same =
      (data_high == comparevalue_high) && (data_low == comparevalue_low);
  if (same) {
    if (is_release) {
      // Approximate store-release by issuing a full barrier before the store.
      __sync_synchronize();
    }

    Memory::Write<T>(address, newvalue_high);
    Memory::Write<T>(address2, newvalue_low);
  }

  set_reg<T>(rs + 1, data_high);
  set_reg<T>(rs, data_low);

  LogRead(address, rs + 1, GetPrintRegisterFormatForSize(element_size));
  LogRead(address2, rs, GetPrintRegisterFormatForSize(element_size));

  if (same) {
    LogWrite(address, rt + 1, GetPrintRegisterFormatForSize(element_size));
    LogWrite(address2, rt, GetPrintRegisterFormatForSize(element_size));
  }
}

void Simulator::VisitLoadStoreExclusive(const Instruction* instr) {
  LoadStoreExclusive op =
      static_cast<LoadStoreExclusive>(instr->Mask(LoadStoreExclusiveMask));

  switch (op) {
    case CAS_w:
    case CASA_w:
    case CASL_w:
    case CASAL_w:
      CompareAndSwapHelper<uint32_t>(instr);
      break;
    case CAS_x:
    case CASA_x:
    case CASL_x:
    case CASAL_x:
      CompareAndSwapHelper<uint64_t>(instr);
      break;
    case CASB:
    case CASAB:
    case CASLB:
    case CASALB:
      CompareAndSwapHelper<uint8_t>(instr);
      break;
    case CASH:
    case CASAH:
    case CASLH:
    case CASALH:
      CompareAndSwapHelper<uint16_t>(instr);
      break;
    case CASP_w:
    case CASPA_w:
    case CASPL_w:
    case CASPAL_w:
      CompareAndSwapPairHelper<uint32_t>(instr);
      break;
    case CASP_x:
    case CASPA_x:
    case CASPL_x:
    case CASPAL_x:
      CompareAndSwapPairHelper<uint64_t>(instr);
      break;
    default:
      PrintExclusiveAccessWarning();

      unsigned rs = instr->Rs();
      unsigned rt = instr->Rt();
      unsigned rt2 = instr->Rt2();
      unsigned rn = instr->Rn();

      bool is_exclusive = !instr->LdStXNotExclusive();
      bool is_acquire_release = !is_exclusive || instr->LdStXAcquireRelease();
      bool is_load = instr->LdStXLoad();
      bool is_pair = instr->LdStXPair();

      unsigned element_size = 1 << instr->LdStXSizeLog2();
      unsigned access_size = is_pair ? element_size * 2 : element_size;
      uint64_t address = reg<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:
            set_wreg(rt, Read<uint8_t>(address), NoRegLog);
            break;
          case LDXRH_w:
          case LDAXRH_w:
          case LDARH_w:
            set_wreg(rt, Read<uint16_t>(address), NoRegLog);
            break;
          case LDXR_w:
          case LDAXR_w:
          case LDAR_w:
            set_wreg(rt, Read<uint32_t>(address), NoRegLog);
            break;
          case LDXR_x:
          case LDAXR_x:
          case LDAR_x:
            set_xreg(rt, Read<uint64_t>(address), NoRegLog);
            break;
          case LDXP_w:
          case LDAXP_w:
            set_wreg(rt, Read<uint32_t>(address), NoRegLog);
            set_wreg(rt2, Read<uint32_t>(address + element_size), NoRegLog);
            break;
          case LDXP_x:
          case LDAXP_x:
            set_xreg(rt, Read<uint64_t>(address), NoRegLog);
            set_xreg(rt2, 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.
          js::jit::AtomicOperations::fenceSeqCst();
        }

        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.
          js::jit::AtomicOperations::fenceSeqCst();
        }

        bool do_store = true;
        if (is_exclusive) {
          do_store = local_monitor_.IsExclusive(address, access_size) &&
                     global_monitor_.IsExclusive(address, access_size);
          set_wreg(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:
              Write<uint8_t>(address, wreg(rt));
              break;
            case STXRH_w:
            case STLXRH_w:
            case STLRH_w:
              Write<uint16_t>(address, wreg(rt));
              break;
            case STXR_w:
            case STLXR_w:
            case STLR_w:
              Write<uint32_t>(address, wreg(rt));
              break;
            case STXR_x:
            case STLXR_x:
            case STLR_x:
              Write<uint64_t>(address, xreg(rt));
              break;
            case STXP_w:
            case STLXP_w:
              Write<uint32_t>(address, wreg(rt));
              Write<uint32_t>(address + element_size, wreg(rt2));
              break;
            case STXP_x:
            case STLXP_x:
              Write<uint64_t>(address, xreg(rt));
              Write<uint64_t>(address + element_size, xreg(rt2));
              break;
            default:
              VIXL_UNREACHABLE();
          }

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

template <typename T>
void Simulator::AtomicMemorySimpleHelper(const Instruction* instr) {
  unsigned rs = instr->Rs();
  unsigned rt = instr->Rt();
  unsigned rn = instr->Rn();

  bool is_acquire = (instr->Bit(23) == 1) && (rt != kZeroRegCode);
  bool is_release = instr->Bit(22) == 1;

  unsigned element_size = sizeof(T);
  uint64_t address = reg<uint64_t>(rn, Reg31IsStackPointer);

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

  address = Memory::AddressUntag(address);
  if (handle_wasm_seg_fault(address, sizeof(T)))
    return;

  T value = reg<T>(rs);

  T data = Memory::Read<T>(address);

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

  T result = 0;
  switch (instr->Mask(AtomicMemorySimpleOpMask)) {
    case LDADDOp:
      result = data + value;
      break;
    case LDCLROp:
      VIXL_ASSERT(!std::numeric_limits<T>::is_signed);
      result = data & ~value;
      break;
    case LDEOROp:
      VIXL_ASSERT(!std::numeric_limits<T>::is_signed);
      result = data ^ value;
      break;
    case LDSETOp:
      VIXL_ASSERT(!std::numeric_limits<T>::is_signed);
      result = data | value;
      break;

    // Signed/Unsigned difference is done via the templated type T.
    case LDSMAXOp:
    case LDUMAXOp:
      result = (data > value) ? data : value;
      break;
    case LDSMINOp:
    case LDUMINOp:
      result = (data > value) ? value : data;
      break;
  }

  if (is_release) {
    // Approximate store-release by issuing a full barrier before the store.
    __sync_synchronize();
  }

  Memory::Write<T>(address, result);
  set_reg<T>(rt, data, NoRegLog);

  LogRead(address, rt, GetPrintRegisterFormatForSize(element_size));
  LogWrite(address, rs, GetPrintRegisterFormatForSize(element_size));
}

template <typename T>
void Simulator::AtomicMemorySwapHelper(const Instruction* instr) {
  unsigned rs = instr->Rs();
  unsigned rt = instr->Rt();
  unsigned rn = instr->Rn();

  bool is_acquire = (instr->Bit(23) == 1) && (rt != kZeroRegCode);
  bool is_release = instr->Bit(22) == 1;

  unsigned element_size = sizeof(T);
  uint64_t address = reg<uint64_t>(rn, Reg31IsStackPointer);

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

  address = Memory::AddressUntag(address);
  if (handle_wasm_seg_fault(address, sizeof(T)))
    return;

  T data = Memory::Read<T>(address);
  if (is_acquire) {
    // Approximate load-acquire by issuing a full barrier after the load.
    __sync_synchronize();
  }

  if (is_release) {
    // Approximate store-release by issuing a full barrier before the store.
    __sync_synchronize();
  }
  Memory::Write<T>(address, reg<T>(rs));

  set_reg<T>(rt, data);

  LogRead(address, rt, GetPrintRegisterFormat(element_size));
  LogWrite(address, rs, GetPrintRegisterFormat(element_size));
}

template <typename T>
void Simulator::LoadAcquireRCpcHelper(const Instruction* instr) {
  unsigned rt = instr->Rt();
  unsigned rn = instr->Rn();

  unsigned element_size = sizeof(T);
  uint64_t address = reg<uint64_t>(rn, Reg31IsStackPointer);

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

  address = Memory::AddressUntag(address);
  if (handle_wasm_seg_fault(address, sizeof(T)))
    return;

  set_reg<T>(rt, Memory::Read<T>(address));

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

  LogRead(address, rt, GetPrintRegisterFormat(element_size));
}

#define ATOMIC_MEMORY_SIMPLE_UINT_LIST(V) \
  V(LDADD)                                \
  V(LDCLR)                                \
  V(LDEOR)                                \
  V(LDSET)                                \
  V(LDUMAX)                               \
  V(LDUMIN)

#define ATOMIC_MEMORY_SIMPLE_INT_LIST(V) \
  V(LDSMAX)                              \
  V(LDSMIN)

void Simulator::VisitAtomicMemory(const Instruction* instr) {
  switch (instr->Mask(AtomicMemoryMask)) {
// clang-format off
#define SIM_FUNC_B(A) \
    case A##B:        \
    case A##AB:       \
    case A##LB:       \
    case A##ALB:
#define SIM_FUNC_H(A) \
    case A##H:        \
    case A##AH:       \
    case A##LH:       \
    case A##ALH:
#define SIM_FUNC_w(A) \
    case A##_w:       \
    case A##A_w:      \
    case A##L_w:      \
    case A##AL_w:
#define SIM_FUNC_x(A) \
    case A##_x:       \
    case A##A_x:      \
    case A##L_x:      \
    case A##AL_x:

    ATOMIC_MEMORY_SIMPLE_UINT_LIST(SIM_FUNC_B)
      AtomicMemorySimpleHelper<uint8_t>(instr);
      break;
    ATOMIC_MEMORY_SIMPLE_INT_LIST(SIM_FUNC_B)
      AtomicMemorySimpleHelper<int8_t>(instr);
      break;
    ATOMIC_MEMORY_SIMPLE_UINT_LIST(SIM_FUNC_H)
      AtomicMemorySimpleHelper<uint16_t>(instr);
      break;
    ATOMIC_MEMORY_SIMPLE_INT_LIST(SIM_FUNC_H)
      AtomicMemorySimpleHelper<int16_t>(instr);
      break;
    ATOMIC_MEMORY_SIMPLE_UINT_LIST(SIM_FUNC_w)
      AtomicMemorySimpleHelper<uint32_t>(instr);
      break;
    ATOMIC_MEMORY_SIMPLE_INT_LIST(SIM_FUNC_w)
      AtomicMemorySimpleHelper<int32_t>(instr);
      break;
    ATOMIC_MEMORY_SIMPLE_UINT_LIST(SIM_FUNC_x)
      AtomicMemorySimpleHelper<uint64_t>(instr);
      break;
    ATOMIC_MEMORY_SIMPLE_INT_LIST(SIM_FUNC_x)
      AtomicMemorySimpleHelper<int64_t>(instr);
      break;
      // clang-format on

    case SWPB:
    case SWPAB:
    case SWPLB:
    case SWPALB:
      AtomicMemorySwapHelper<uint8_t>(instr);
      break;
    case SWPH:
    case SWPAH:
    case SWPLH:
    case SWPALH:
      AtomicMemorySwapHelper<uint16_t>(instr);
      break;
    case SWP_w:
    case SWPA_w:
    case SWPL_w:
    case SWPAL_w:
      AtomicMemorySwapHelper<uint32_t>(instr);
      break;
    case SWP_x:
    case SWPA_x:
    case SWPL_x:
    case SWPAL_x:
      AtomicMemorySwapHelper<uint64_t>(instr);
      break;
    case LDAPRB:
      LoadAcquireRCpcHelper<uint8_t>(instr);
      break;
    case LDAPRH:
      LoadAcquireRCpcHelper<uint16_t>(instr);
      break;
    case LDAPR_w:
      LoadAcquireRCpcHelper<uint32_t>(instr);
      break;
    case LDAPR_x:
      LoadAcquireRCpcHelper<uint64_t>(instr);
      break;
  }
}

void Simulator::VisitLoadLiteral(const Instruction* instr) {
  unsigned rt = instr->Rt();
  uint64_t address = instr->LiteralAddress<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:
      set_wreg(rt, Read<uint32_t>(address), NoRegLog);
      LogRead(address, rt, kPrintWReg);
      break;
    case LDR_x_lit:
      set_xreg(rt, Read<uint64_t>(address), NoRegLog);
      LogRead(address, rt, kPrintXReg);
      break;
    case LDR_s_lit:
      set_sreg(rt, Read<float>(address), NoRegLog);
      LogVRead(address, rt, kPrintSReg);
      break;
    case LDR_d_lit:
      set_dreg(rt, Read<double>(address), NoRegLog);
      LogVRead(address, rt, kPrintDReg);
      break;
    case LDR_q_lit:
      set_qreg(rt, Read<qreg_t>(address), NoRegLog);
      LogVRead(address, rt, kPrintReg1Q);
      break;
    case LDRSW_x_lit:
      set_xreg(rt, 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 = xreg(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;
    set_xreg(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->SixtyFourBits() == 1;
  // Shift is limited for W operations.
  VIXL_ASSERT(is_64_bits || (instr->ShiftMoveWide() < 2));

  // Get the shifted immediate.
  int64_t shift = instr->ShiftMoveWide() * 16;
  int64_t shifted_imm16 = static_cast<int64_t>(instr->ImmMoveWide()) << 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->Rd();
        int64_t prev_xn_val = is_64_bits ? xreg(reg_code)
                                         : wreg(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.
  set_xreg(instr->Rd(), new_xn_val);
}


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

  if (ConditionFailed(static_cast<Condition>(instr->Condition()))) {
    new_val = xreg(instr->Rm());
    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->SixtyFourBits() ? kXRegSize : kWRegSize;
  set_reg(reg_size, instr->Rd(), new_val);
}


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

  switch (instr->Mask(DataProcessing1SourceMask)) {
    case RBIT_w: set_wreg(dst, ReverseBits(wreg(src))); break;
    case RBIT_x: set_xreg(dst, ReverseBits(xreg(src))); break;
    case REV16_w: set_wreg(dst, ReverseBytes(wreg(src), 1)); break;
    case REV16_x: set_xreg(dst, ReverseBytes(xreg(src), 1)); break;
    case REV_w: set_wreg(dst, ReverseBytes(wreg(src), 2)); break;
    case REV32_x: set_xreg(dst, ReverseBytes(xreg(src), 2)); break;
    case REV_x: set_xreg(dst, ReverseBytes(xreg(src), 3)); break;
    case CLZ_w: set_wreg(dst, CountLeadingZeros(wreg(src))); break;
    case CLZ_x: set_xreg(dst, CountLeadingZeros(xreg(src))); break;
    case CLS_w: {
      set_wreg(dst, CountLeadingSignBits(wreg(src)));
      break;
    }
    case CLS_x: {
      set_xreg(dst, CountLeadingSignBits(xreg(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->SixtyFourBits() ? kXRegSize : kWRegSize;

  switch (instr->Mask(DataProcessing2SourceMask)) {
    case SDIV_w: {
      int32_t rn = wreg(instr->Rn());
      int32_t rm = wreg(instr->Rm());
      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 = xreg(instr->Rn());
      int64_t rm = xreg(instr->Rm());
      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>(wreg(instr->Rn()));
      uint32_t rm = static_cast<uint32_t>(wreg(instr->Rm()));
      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>(xreg(instr->Rn()));
      uint64_t rm = static_cast<uint64_t>(xreg(instr->Rm()));
      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 = reg<uint32_t>(instr->Rn());
      uint8_t  val = reg<uint8_t>(instr->Rm());
      result = Crc32Checksum(acc, val, CRC32_POLY);
      break;
    }
    case CRC32H: {
      uint32_t acc = reg<uint32_t>(instr->Rn());
      uint16_t val = reg<uint16_t>(instr->Rm());
      result = Crc32Checksum(acc, val, CRC32_POLY);
      break;
    }
    case CRC32W: {
      uint32_t acc = reg<uint32_t>(instr->Rn());
      uint32_t val = reg<uint32_t>(instr->Rm());
      result = Crc32Checksum(acc, val, CRC32_POLY);
      break;
    }
    case CRC32X: {
      uint32_t acc = reg<uint32_t>(instr->Rn());
      uint64_t val = reg<uint64_t>(instr->Rm());
      result = Crc32Checksum(acc, val, CRC32_POLY);
      reg_size = kWRegSize;
      break;
    }
    case CRC32CB: {
      uint32_t acc = reg<uint32_t>(instr->Rn());
      uint8_t  val = reg<uint8_t>(instr->Rm());
      result = Crc32Checksum(acc, val, CRC32C_POLY);
      break;
    }
    case CRC32CH: {
      uint32_t acc = reg<uint32_t>(instr->Rn());
      uint16_t val = reg<uint16_t>(instr->Rm());
      result = Crc32Checksum(acc, val, CRC32C_POLY);
      break;
    }
    case CRC32CW: {
      uint32_t acc = reg<uint32_t>(instr->Rn());
      uint32_t val = reg<uint32_t>(instr->Rm());
      result = Crc32Checksum(acc, val, CRC32C_POLY);
      break;
    }
    case CRC32CX: {
      uint32_t acc = reg<uint32_t>(instr->Rn());
      uint64_t val = reg<uint64_t>(instr->Rm());
      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->SixtyFourBits() == 1) ? 0x3f : 0x1f;
    unsigned shift = wreg(instr->Rm()) & mask;
    result = ShiftOperand(reg_size, reg(reg_size, instr->Rn()), shift_op,
                          shift);
  }
  set_reg(reg_size, instr->Rd(), 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->SixtyFourBits() ? kXRegSize : kWRegSize;

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


void Simulator::VisitBitfield(const Instruction* instr) {
  unsigned reg_size = instr->SixtyFourBits() ? kXRegSize : kWRegSize;
  int64_t reg_mask = instr->SixtyFourBits() ? kXRegMask : kWRegMask;
  int64_t R = instr->ImmR();
  int64_t S = instr->ImmS();
  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 : reg(reg_size, instr->Rd());
  int64_t src = reg(reg_size, instr->Rn());
  // 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);

  set_reg(reg_size, instr->Rd(), result);
}


void Simulator::VisitExtract(const Instruction* instr) {
  unsigned lsb = instr->ImmS();
  unsigned reg_size = (instr->SixtyFourBits() == 1) ? kXRegSize
                                                    : kWRegSize;
  uint64_t low_res = static_cast<uint64_t>(reg(reg_size, instr->Rm())) >> lsb;
  uint64_t high_res =
      (lsb == 0) ? 0 : reg(reg_size, instr->Rn()) << (reg_size - lsb);
  set_reg(reg_size, instr->Rd(), low_res | high_res);
}


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

  unsigned dest = instr->Rd();
  switch (instr->Mask(FPImmediateMask)) {
    case FMOV_s_imm: set_sreg(dest, instr->ImmFP32()); break;
    case FMOV_d_imm: set_dreg(dest, instr->ImmFP64()); break;
    default: VIXL_UNREACHABLE();
  }
}


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

  unsigned dst = instr->Rd();
  unsigned src = instr->Rn();

  FPRounding round = RMode();

  switch (instr->Mask(FPIntegerConvertMask)) {
    case FCVTAS_ws: set_wreg(dst, FPToInt32(sreg(src), FPTieAway)); break;
    case FCVTAS_xs: set_xreg(dst, FPToInt64(sreg(src), FPTieAway)); break;
    case FCVTAS_wd: set_wreg(dst, FPToInt32(dreg(src), FPTieAway)); break;
    case FCVTAS_xd: set_xreg(dst, FPToInt64(dreg(src), FPTieAway)); break;
    case FCVTAU_ws: set_wreg(dst, FPToUInt32(sreg(src), FPTieAway)); break;
    case FCVTAU_xs: set_xreg(dst, FPToUInt64(sreg(src), FPTieAway)); break;
    case FCVTAU_wd: set_wreg(dst, FPToUInt32(dreg(src), FPTieAway)); break;
    case FCVTAU_xd: set_xreg(dst, FPToUInt64(dreg(src), FPTieAway)); break;
    case FCVTMS_ws:
      set_wreg(dst, FPToInt32(sreg(src), FPNegativeInfinity));
      break;
    case FCVTMS_xs:
      set_xreg(dst, FPToInt64(sreg(src), FPNegativeInfinity));
      break;
    case FCVTMS_wd:
      set_wreg(dst, FPToInt32(dreg(src), FPNegativeInfinity));
      break;
    case FCVTMS_xd:
      set_xreg(dst, FPToInt64(dreg(src), FPNegativeInfinity));
      break;
    case FCVTMU_ws:
      set_wreg(dst, FPToUInt32(sreg(src), FPNegativeInfinity));
      break;
    case FCVTMU_xs:
      set_xreg(dst, FPToUInt64(sreg(src), FPNegativeInfinity));
      break;
    case FCVTMU_wd:
      set_wreg(dst, FPToUInt32(dreg(src), FPNegativeInfinity));
      break;
    case FCVTMU_xd:
      set_xreg(dst, FPToUInt64(dreg(src), FPNegativeInfinity));
      break;
    case FCVTPS_ws:
      set_wreg(dst, FPToInt32(sreg(src), FPPositiveInfinity));
      break;
    case FCVTPS_xs:
      set_xreg(dst, FPToInt64(sreg(src), FPPositiveInfinity));
      break;
    case FCVTPS_wd:
      set_wreg(dst, FPToInt32(dreg(src), FPPositiveInfinity));
      break;
    case FCVTPS_xd:
      set_xreg(dst, FPToInt64(dreg(src), FPPositiveInfinity));
      break;
    case FCVTPU_ws:
      set_wreg(dst, FPToUInt32(sreg(src), FPPositiveInfinity));
      break;
    case FCVTPU_xs:
      set_xreg(dst, FPToUInt64(sreg(src), FPPositiveInfinity));
      break;
    case FCVTPU_wd:
      set_wreg(dst, FPToUInt32(dreg(src), FPPositiveInfinity));
      break;
    case FCVTPU_xd:
      set_xreg(dst, FPToUInt64(dreg(src), FPPositiveInfinity));
      break;
    case FCVTNS_ws: set_wreg(dst, FPToInt32(sreg(src), FPTieEven)); break;
    case FCVTNS_xs: set_xreg(dst, FPToInt64(sreg(src), FPTieEven)); break;
    case FCVTNS_wd: set_wreg(dst, FPToInt32(dreg(src), FPTieEven)); break;
    case FCVTNS_xd: set_xreg(dst, FPToInt64(dreg(src), FPTieEven)); break;
    case FCVTNU_ws: set_wreg(dst, FPToUInt32(sreg(src), FPTieEven)); break;
    case FCVTNU_xs: set_xreg(dst, FPToUInt64(sreg(src), FPTieEven)); break;
    case FCVTNU_wd: set_wreg(dst, FPToUInt32(dreg(src), FPTieEven)); break;
    case FCVTNU_xd: set_xreg(dst, FPToUInt64(dreg(src), FPTieEven)); break;
    case FCVTZS_ws: set_wreg(dst, FPToInt32(sreg(src), FPZero)); break;
    case FCVTZS_xs: set_xreg(dst, FPToInt64(sreg(src), FPZero)); break;
    case FCVTZS_wd: set_wreg(dst, FPToInt32(dreg(src), FPZero)); break;
    case FCVTZS_xd: set_xreg(dst, FPToInt64(dreg(src), FPZero)); break;
    case FCVTZU_ws: set_wreg(dst, FPToUInt32(sreg(src), FPZero)); break;
    case FCVTZU_xs: set_xreg(dst, FPToUInt64(sreg(src), FPZero)); break;
    case FCVTZU_wd: set_wreg(dst, FPToUInt32(dreg(src), FPZero)); break;
    case FCVTZU_xd: set_xreg(dst, FPToUInt64(dreg(src), FPZero)); break;
    case FJCVTZS: set_wreg(dst, FPToFixedJS(dreg(src))); break;
    case FMOV_ws: set_wreg(dst, sreg_bits(src)); break;
    case FMOV_xd: set_xreg(dst, dreg_bits(src)); break;
    case FMOV_sw: set_sreg_bits(dst, wreg(src)); break;
    case FMOV_dx: set_dreg_bits(dst, xreg(src)); break;
    case FMOV_d1_x:
      LogicVRegister(vreg(dst)).SetUint(kFormatD, 1, xreg(src));
      break;
    case FMOV_x_d1:
      set_xreg(dst, LogicVRegister(vreg(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: set_dreg(dst, FixedToDouble(xreg(src), 0, round)); break;
    case SCVTF_dw: set_dreg(dst, FixedToDouble(wreg(src), 0, round)); break;
    case UCVTF_dx: set_dreg(dst, UFixedToDouble(xreg(src), 0, round)); break;
    case UCVTF_dw: {
      set_dreg(dst, UFixedToDouble(static_cast<uint32_t>(wreg(src)), 0, round));
      break;
    }
    case SCVTF_sx: set_sreg(dst, FixedToFloat(xreg(src), 0, round)); break;
    case SCVTF_sw: set_sreg(dst, FixedToFloat(wreg(src), 0, round)); break;
    case UCVTF_sx: set_sreg(dst, UFixedToFloat(xreg(src), 0, round)); break;
    case UCVTF_sw: {
      set_sreg(dst, UFixedToFloat(static_cast<uint32_t>(wreg(src)), 0, round));
      break;
    }

    default: VIXL_UNREACHABLE();
  }
}


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

  unsigned dst = instr->Rd();
  unsigned src = instr->Rn();
  int fbits = 64 - instr->FPScale();

  FPRounding round = RMode();

  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:
      set_dreg(dst, FixedToDouble(xreg(src), fbits, round));
      break;
    case SCVTF_dw_fixed:
      set_dreg(dst, FixedToDouble(wreg(src), fbits, round));
      break;
    case UCVTF_dx_fixed:
      set_dreg(dst, UFixedToDouble(xreg(src), fbits, round));
      break;
    case UCVTF_dw_fixed: {
      set_dreg(dst,
               UFixedToDouble(static_cast<uint32_t>(wreg(src)), fbits, round));
      break;
    }
    case SCVTF_sx_fixed:
      set_sreg(dst, FixedToFloat(xreg(src), fbits, round));
      break;
    case SCVTF_sw_fixed:
      set_sreg(dst, FixedToFloat(wreg(src), fbits, round));
      break;
    case UCVTF_sx_fixed:
      set_sreg(dst, UFixedToFloat(xreg(src), fbits, round));
      break;
    case UCVTF_sw_fixed: {
      set_sreg(dst,
               UFixedToFloat(static_cast<uint32_t>(wreg(src)), fbits, round));
      break;
    }
    case FCVTZS_xd_fixed:
      set_xreg(dst, FPToInt64(dreg(src) * std::pow(2.0, fbits), FPZero));
      break;
    case FCVTZS_wd_fixed:
      set_wreg(dst, FPToInt32(dreg(src) * std::pow(2.0, fbits), FPZero));
      break;
    case FCVTZU_xd_fixed:
      set_xreg(dst, FPToUInt64(dreg(src) * std::pow(2.0, fbits), FPZero));
      break;
    case FCVTZU_wd_fixed:
      set_wreg(dst, FPToUInt32(dreg(src) * std::pow(2.0, fbits), FPZero));
      break;
    case FCVTZS_xs_fixed:
      set_xreg(dst, FPToInt64(sreg(src) * std::pow(2.0f, fbits), FPZero));
      break;
    case FCVTZS_ws_fixed:
      set_wreg(dst, FPToInt32(sreg(src) * std::pow(2.0f, fbits), FPZero));
      break;
    case FCVTZU_xs_fixed:
      set_xreg(dst, FPToUInt64(sreg(src) * std::pow(2.0f, fbits), FPZero));
      break;
    case FCVTZU_ws_fixed:
      set_wreg(dst, FPToUInt32(sreg(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(sreg(instr->Rn()), sreg(instr->Rm()), trap); break;
    case FCMPE_d: trap = EnableTrap; VIXL_FALLTHROUGH();
    case FCMP_d: FPCompare(dreg(instr->Rn()), dreg(instr->Rm()), trap); break;
    case FCMPE_s_zero: trap = EnableTrap; VIXL_FALLTHROUGH();
    case FCMP_s_zero: FPCompare(sreg(instr->Rn()), 0.0f, trap); break;
    case FCMPE_d_zero: trap = EnableTrap; VIXL_FALLTHROUGH();
    case FCMP_d_zero: FPCompare(dreg(instr->Rn()), 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->Condition())) {
        FPCompare(sreg(instr->Rn()), sreg(instr->Rm()), trap);
      } else {
        nzcv().SetFlags(instr->Nzcv());
        LogSystemRegister(NZCV);
      }
      break;
    case FCCMPE_d: trap = EnableTrap;
      VIXL_FALLTHROUGH();
    case FCCMP_d:
      if (ConditionPassed(instr->Condition())) {
        FPCompare(dreg(instr->Rn()), dreg(instr->Rm()), trap);
      } else {
        nzcv().SetFlags(instr->Nzcv());
        LogSystemRegister(NZCV);
      }
      break;
    default: VIXL_UNIMPLEMENTED();
  }
}


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

  Instr selected;
  if (ConditionPassed(instr->Condition())) {
    selected = instr->Rn();
  } else {
    selected = instr->Rm();
  }

  switch (instr->Mask(FPConditionalSelectMask)) {
    case FCSEL_s: set_sreg(instr->Rd(), sreg(selected)); break;
    case FCSEL_d: set_dreg(instr->Rd(), dreg(selected)); break;
    default: VIXL_UNIMPLEMENTED();
  }
}


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

  FPRounding fpcr_rounding = static_cast<FPRounding>(fpcr().RMode());
  VectorFormat vform = (instr->Mask(FP64) == FP64) ? kFormatD : kFormatS;
  SimVRegister& rd = vreg(instr->Rd());
  SimVRegister& rn = vreg(instr->Rn());
  bool inexact_exception = false;

  unsigned fd = instr->Rd();
  unsigned fn = instr->Rn();

  switch (instr->Mask(FPDataProcessing1SourceMask)) {
    case FMOV_s: set_sreg(fd, sreg(fn)); return;
    case FMOV_d: set_dreg(fd, dreg(fn)); return;
    case FABS_s: fabs_(kFormatS, vreg(fd), vreg(fn)); return;
    case FABS_d: fabs_(kFormatD, vreg(fd), vreg(fn)); return;
    case FNEG_s: fneg(kFormatS, vreg(fd), vreg(fn)); return;
    case FNEG_d: fneg(kFormatD, vreg(fd), vreg(fn)); return;
    case FCVT_ds:
      set_dreg(fd, FPToDouble(sreg(fn), ReadDN()));
      return;
    case FCVT_sd:
      set_sreg(fd, FPToFloat(dreg(fn), FPTieEven, ReadDN()));
      return;
    case FCVT_hs:
      set_hreg(fd, Float16ToRawbits(FPToFloat16(sreg(fn), FPTieEven, ReadDN())));
      return;
    case FCVT_sh:
      set_sreg(fd, FPToFloat(RawbitsToFloat16(hreg(fn)), ReadDN()));
      return;
    case FCVT_dh:
      set_dreg(fd, FPToDouble(hreg(fn), ReadDN()));
      return;
    case FCVT_hd:
      set_hreg(fd, Float16ToRawbits(FPToFloat16(dreg(fn), FPTieEven, ReadDN())));
      return;
    case FSQRT_s:
    case FSQRT_d: fsqrt(vform, rd, rn); 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);
}


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

  VectorFormat vform = (instr->Mask(FP64) == FP64) ? kFormatD : kFormatS;
  SimVRegister& rd = vreg(instr->Rd());
  SimVRegister& rn = vreg(instr->Rn());
  SimVRegister& rm = vreg(instr->Rm());

  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();
  }
}


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

  unsigned fd = instr->Rd();
  unsigned fn = instr->Rn();
  unsigned fm = instr->Rm();
  unsigned fa = instr->Ra();

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


bool Simulator::FPProcessNaNs(const Instruction* instr) {
  unsigned fd = instr->Rd();
  unsigned fn = instr->Rn();
  unsigned fm = instr->Rm();
  bool done = false;

  if (instr->Mask(FP64) == FP64) {
    double result = FPProcessNaNs(dreg(fn), dreg(fm));
    if (std::isnan(result)) {
      set_dreg(fd, result);
      done = true;
    }
  } else {
    float result = FPProcessNaNs(sreg(fn), sreg(fm));
    if (std::isnan(result)) {
      set_sreg(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 = 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->ImmSystemRegister()) {
          case NZCV: set_xreg(instr->Rt(), nzcv().RawValue()); break;
          case FPCR: set_xreg(instr->Rt(), fpcr().RawValue()); break;
          default: VIXL_UNIMPLEMENTED();
        }
        break;
      }
      case MSR: {
        switch (instr->ImmSystemRegister()) {
          case NZCV:
            nzcv().SetRawValue(wreg(instr->Rt()));
            LogSystemRegister(NZCV);
            break;
          case FPCR:
            fpcr().SetRawValue(wreg(instr->Rt()));
            LogSystemRegister(FPCR);
            break;
          default: VIXL_UNIMPLEMENTED();
        }
        break;
      }
    }
  } else if (instr->Mask(SystemHintFMask) == SystemHintFixed) {
    VIXL_ASSERT(instr->Mask(SystemHintMask) == HINT);
    switch (instr->ImmHint()) {
      case NOP: break;
      case CSDB: break;
      default: VIXL_UNIMPLEMENTED();
    }
  } else if (instr->Mask(MemBarrierFMask) == MemBarrierFixed) {
    js::jit::AtomicOperations::fenceSeqCst();
  } else if ((instr->Mask(SystemSysFMask) == SystemSysFixed)) {
    switch (instr->Mask(SystemSysMask)) {
      case SYS: SysOp_W(instr->SysOp(), xreg(instr->Rt())); break;
      default: VIXL_UNIMPLEMENTED();
    }
  } else {
    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 = vreg(instr->Rd());
  SimVRegister& rn = vreg(instr->Rn());

  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->FPType()) {
          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>(fpcr().RMode());
    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 = vreg(instr->Rd());
  SimVRegister& rn = vreg(instr->Rn());
  SimVRegister& rm = vreg(instr->Rm());

  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 = vreg(instr->Rd());
  SimVRegister& rn = vreg(instr->Rn());
  SimVRegister& rm = vreg(instr->Rm());

  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 = vreg(instr->Rd());
  SimVRegister& rn = vreg(instr->Rn());

  // 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 = vreg(instr->Rd());
  SimVRegister& rn = vreg(instr->Rn());

  ByElementOp Op = NULL;

  int rm_reg = instr->Rm();
  int index = (instr->NEONH() << 1) | instr->NEONL();
  if (instr->NEONSize() == 1) {
    rm_reg &= 0xf;
    index = (index << 1) | instr->NEONM();
  }

  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->NEONH();
      if ((instr->FPType() & 1) == 0) {
        index = (index << 1) | instr->NEONL();
      }

      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, vreg(rm_reg), index);
}


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

  SimVRegister& rd = vreg(instr->Rd());
  SimVRegister& rn = vreg(instr->Rn());
  int imm5 = instr->ImmNEON5();
  int tz = CountTrailingZeros(imm5, 32);
  int reg_index = imm5 >> (tz + 1);

  if (instr->Mask(NEONCopyInsElementMask) == NEON_INS_ELEMENT) {
    int imm4 = instr->ImmNEON4();
    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, xreg(instr->Rn()));
  } else if (instr->Mask(NEONCopyUmovMask) == NEON_UMOV) {
    uint64_t value = LogicVRegister(rn).Uint(vf, reg_index);
    value &= MaxUintFromFormat(vf);
    set_xreg(instr->Rd(), value);
  } else if (instr->Mask(NEONCopyUmovMask) == NEON_SMOV) {
    int64_t value = LogicVRegister(rn).Int(vf, reg_index);
    if (instr->NEONQ()) {
      set_xreg(instr->Rd(), value);
    } else {
      set_wreg(instr->Rd(), (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, xreg(instr->Rn()));
  } else {
    VIXL_UNIMPLEMENTED();
  }
}


void Simulator::VisitNEONExtract(const Instruction* instr) {
  NEONFormatDecoder nfd(instr, NEONFormatDecoder::LogicalFormatMap());
  VectorFormat vf = nfd.GetVectorFormat();
  SimVRegister& rd = vreg(instr->Rd());
  SimVRegister& rn = vreg(instr->Rn());
  SimVRegister& rm = vreg(instr->Rm());
  if (instr->Mask(NEONExtractMask) == NEON_EXT) {
    int index = instr->ImmNEONExt();
    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 = xreg(instr->Rn(), Reg31IsStackPointer);
  int reg_size = RegisterSizeInBytesFromFormat(vf);

  int reg[4];
  uint64_t addr[4];
  for (int i = 0; i < 4; i++) {
    reg[i] = (instr->Rt() + 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->Bits(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, vreg(reg[3]), addr[3]); count++;
      VIXL_FALLTHROUGH();
    case NEON_LD1_3v:
    case NEON_LD1_3v_post: ld1(vf, vreg(reg[2]), addr[2]); count++;
      VIXL_FALLTHROUGH();
    case NEON_LD1_2v:
    case NEON_LD1_2v_post: ld1(vf, vreg(reg[1]), addr[1]); count++;
      VIXL_FALLTHROUGH();
    case NEON_LD1_1v:
    case NEON_LD1_1v_post:
      ld1(vf, vreg(reg[0]), addr[0]);
      log_read = true;
      break;
    case NEON_ST1_4v:
    case NEON_ST1_4v_post: st1(vf, vreg(reg[3]), addr[3]); count++;
      VIXL_FALLTHROUGH();
    case NEON_ST1_3v:
    case NEON_ST1_3v_post: st1(vf, vreg(reg[2]), addr[2]); count++;
      VIXL_FALLTHROUGH();
    case NEON_ST1_2v:
    case NEON_ST1_2v_post: st1(vf, vreg(reg[1]), addr[1]); count++;
      VIXL_FALLTHROUGH();
    case NEON_ST1_1v:
    case NEON_ST1_1v_post:
      st1(vf, vreg(reg[0]), addr[0]);
      log_read = false;
      break;
    case NEON_LD2_post:
    case NEON_LD2:
      ld2(vf, vreg(reg[0]), vreg(reg[1]), addr[0]);
      count = 2;
      break;
    case NEON_ST2:
    case NEON_ST2_post:
      st2(vf, vreg(reg[0]), vreg(reg[1]), addr[0]);
      count = 2;
      break;
    case NEON_LD3_post:
    case NEON_LD3:
      ld3(vf, vreg(reg[0]), vreg(reg[1]), vreg(reg[2]), addr[0]);
      count = 3;
      break;
    case NEON_ST3:
    case NEON_ST3_post:
      st3(vf, vreg(reg[0]), vreg(reg[1]), vreg(reg[2]), addr[0]);
      count = 3;
      break;
    case NEON_ST4:
    case NEON_ST4_post:
      st4(vf, vreg(reg[0]), vreg(reg[1]), vreg(reg[2]), vreg(reg[3]),
          addr[0]);
      count = 4;
      break;
    case NEON_LD4_post:
    case NEON_LD4:
      ld4(vf, vreg(reg[0]), vreg(reg[1]), vreg(reg[2]), vreg(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->Rm();
    // 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
                            : xreg(rm);
    set_xreg(instr->Rn(), 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 = xreg(instr->Rn(), Reg31IsStackPointer);
  int rt = instr->Rt();

  Instr itype = instr->Mask(NEONLoadStoreSingleStructMask);
  if (((itype == NEON_LD1_b) || (itype == NEON_LD1_h) ||
       (itype == NEON_LD1_s) || (itype == NEON_LD1_d)) &&
      (instr->Bits(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;

  bool replicating = 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->NEONLSSize() & 1) == 0) ? kFormat4S : kFormat2D;
      break;
    }

    case NEON_LD1R:
    case NEON_LD1R_post:
    case NEON_LD2R:
    case NEON_LD2R_post:
    case NEON_LD3R:
    case NEON_LD3R_post:
    case NEON_LD4R:
    case NEON_LD4R_post: {
      vf = vf_t;
      do_load = true;
      replicating = 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->NEONLSIndex(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) {
        if (replicating) {
          ld1r(vf, vreg(rt), addr);
        } else  {
          ld1(vf, vreg(rt), lane, addr);
        }
        LogVRead(addr, rt, print_format, lane);
      } else {
        st1(vf, vreg(rt), lane, addr);
        LogVWrite(addr, rt, print_format, lane);
      }
      break;
    case NEONLoadStoreSingle2:
      scale = 2;
      if (do_load) {
        if (replicating) {
          ld2r(vf, vreg(rt), vreg(rt2), addr);
        } else {
          ld2(vf, vreg(rt), vreg(rt2), lane, addr);
        }
        LogVRead(addr, rt, print_format, lane);
        LogVRead(addr + esize, rt2, print_format, lane);
      } else {
        st2(vf, vreg(rt), vreg(rt2), lane, addr);
        LogVWrite(addr, rt, print_format, lane);
        LogVWrite(addr + esize, rt2, print_format, lane);
      }
      break;
    case NEONLoadStoreSingle3:
      scale = 3;
      if (do_load) {
        if (replicating) {
          ld3r(vf, vreg(rt), vreg(rt2), vreg(rt3), addr);
        } else {
          ld3(vf, vreg(rt), vreg(rt2), vreg(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, vreg(rt), vreg(rt2), vreg(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) {
        if (replicating) {
          ld4r(vf, vreg(rt), vreg(rt2), vreg(rt3), vreg(rt4), addr);
        } else {
          ld4(vf, vreg(rt), vreg(rt2), vreg(rt3), vreg(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, vreg(rt), vreg(rt2), vreg(rt3), vreg(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->Rm();
    int lane_size = LaneSizeInBytesFromFormat(vf);
    set_xreg(instr->Rn(), addr + ((rm == 31) ? (scale * lane_size) : xreg(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 = vreg(instr->Rd());
  int cmode = instr->NEONCmode();
  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->NEONQ();
  int op_bit = instr->NEONModImmOp();
  uint64_t imm8  = instr->ImmNEONabcdefgh();

  // 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 & (1ULL << i)) {
            imm |= (UINT64_C(0xff) << (8 * i));
          }
        }
      } else {  // cmode_0 == 1, cmode == 0xf.
        if (op_bit == 0) {
          vform = q ? kFormat4S : kFormat2S;
          imm = FloatToRawbits(instr->ImmNEONFP32());
        } else if (q == 1) {
          vform = kFormat2D;
          imm = DoubleToRawbits(instr->ImmNEONFP64());
        } 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 = vreg(instr->Rd());
  SimVRegister& rn = vreg(instr->Rn());

  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>(fpcr().RMode());

    // 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->Bit(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 = vreg(instr->Rd());
  SimVRegister& rn = vreg(instr->Rn());
  SimVRegister& rm = vreg(instr->Rm());
  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 = vreg(instr->Rd());
  SimVRegister& rn = vreg(instr->Rn());
  SimVRegister& rm = vreg(instr->Rm());

  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 = vreg(instr->Rd());
  SimVRegister& rn = vreg(instr->Rn());
  ByElementOp Op = NULL;

  int rm_reg = instr->Rm();
  int index = (instr->NEONH() << 1) | instr->NEONL();
  if (instr->NEONSize() == 1) {
    rm_reg &= 0xf;
    index = (index << 1) | instr->NEONM();
  }

  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->NEONH();
      if ((instr->FPType() & 1) == 0) {
        index = (index << 1) | instr->NEONL();
      }
      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, vreg(rm_reg), index);
}


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

  SimVRegister& rd = vreg(instr->Rd());
  SimVRegister& rn = vreg(instr->Rn());

  if (instr->Mask(NEONScalarCopyMask) == NEON_DUP_ELEMENT_scalar) {
    int imm5 = instr->ImmNEON5();
    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 = vreg(instr->Rd());
  SimVRegister& rn = vreg(instr->Rn());
  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 = vreg(instr->Rd());
  SimVRegister& rn = vreg(instr->Rn());
  FPRounding fpcr_rounding = static_cast<FPRounding>(fpcr().RMode());

  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->ImmNEONImmh());
  int immhimmb = instr->ImmNEONImmhImmb();
  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 = vreg(instr->Rd());
  SimVRegister& rn = vreg(instr->Rn());
  FPRounding fpcr_rounding = static_cast<FPRounding>(fpcr().RMode());

  // 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->ImmNEONImmh());
  int immhimmb = instr->ImmNEONImmhImmb();
  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 = vreg(instr->Rd());
  SimVRegister& rn = vreg(instr->Rn());
  SimVRegister& rn2 = vreg((instr->Rn() + 1) % kNumberOfVRegisters);
  SimVRegister& rn3 = vreg((instr->Rn() + 2) % kNumberOfVRegisters);
  SimVRegister& rn4 = vreg((instr->Rn() + 3) % kNumberOfVRegisters);
  SimVRegister& rm = vreg(instr->Rm());

  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 = vreg(instr->Rd());
  SimVRegister& rn = vreg(instr->Rn());
  SimVRegister& rm = vreg(instr->Rm());

  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->InstructionBits() == UNDEFINED_INST_PATTERN);

  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->ImmException() == 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:
      set_trace_parameters(trace_parameters() | parameters);
      break;
    case TRACE_DISABLE:
      set_trace_parameters(trace_parameters() & ~parameters);
      break;
    default:
      VIXL_UNREACHABLE();
  }

  set_pc(instr->InstructionAtOffset(kTraceLength));
}


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

  set_pc(instr->InstructionAtOffset(kLogLength));
}


void Simulator::DoPrintf(const Instruction* instr) {
  VIXL_ASSERT((instr->Mask(ExceptionMask) == HLT) &&
              (instr->ImmException() == 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 = reg<const char *>(0);
  VIXL_ASSERT(format_base != NULL);
  size_t length = strlen(format_base) + 1;
  char * const format = (char *)js_calloc(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], wreg(pcs_r++)); break;
        case kPrintfArgX: part_result = printf(chunks[i], xreg(pcs_r++)); break;
        case kPrintfArgD: part_result = printf(chunks[i], dreg(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).
  set_xreg(0, result);

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

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

  js_free(format);
}

}  // namespace vixl

#endif  // JS_SIMULATOR_ARM64