lib/Target/ARM/ARMMCCodeEmitter.cpp

//===-- ARM/ARMMCCodeEmitter.cpp - Convert ARM code to machine code -------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the ARMMCCodeEmitter class.
//
//===----------------------------------------------------------------------===//

#define DEBUG_TYPE "mccodeemitter"
#include "ARM.h"
#include "ARMAddressingModes.h"
#include "ARMFixupKinds.h"
#include "ARMInstrInfo.h"
#include "llvm/MC/MCCodeEmitter.h"
#include "llvm/MC/MCExpr.h"
#include "llvm/MC/MCInst.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Support/raw_ostream.h"
using namespace llvm;

STATISTIC(MCNumEmitted, "Number of MC instructions emitted.");
STATISTIC(MCNumCPRelocations, "Number of constant pool relocations created.");

namespace {
class ARMMCCodeEmitter : public MCCodeEmitter {
  ARMMCCodeEmitter(const ARMMCCodeEmitter &); // DO NOT IMPLEMENT
  void operator=(const ARMMCCodeEmitter &); // DO NOT IMPLEMENT
  const TargetMachine &TM;
  const TargetInstrInfo &TII;
  MCContext &Ctx;

public:
  ARMMCCodeEmitter(TargetMachine &tm, MCContext &ctx)
    : TM(tm), TII(*TM.getInstrInfo()), Ctx(ctx) {
  }

  ~ARMMCCodeEmitter() {}

  unsigned getNumFixupKinds() const { return ARM::NumTargetFixupKinds; }

  const MCFixupKindInfo &getFixupKindInfo(MCFixupKind Kind) const {
    const static MCFixupKindInfo Infos[] = {
      // name                     offset  bits  flags
      { "fixup_arm_pcrel_12",     2,      12,   MCFixupKindInfo::FKF_IsPCRel },
      { "fixup_arm_vfp_pcrel_12", 3,      8,    MCFixupKindInfo::FKF_IsPCRel },
      { "fixup_arm_branch",       1,      24,   MCFixupKindInfo::FKF_IsPCRel },
    };

    if (Kind < FirstTargetFixupKind)
      return MCCodeEmitter::getFixupKindInfo(Kind);

    assert(unsigned(Kind - FirstTargetFixupKind) < getNumFixupKinds() &&
           "Invalid kind!");
    return Infos[Kind - FirstTargetFixupKind];
  }
  unsigned getMachineSoImmOpValue(unsigned SoImm) const;

  // getBinaryCodeForInstr - TableGen'erated function for getting the
  // binary encoding for an instruction.
  unsigned getBinaryCodeForInstr(const MCInst &MI,
                                 SmallVectorImpl<MCFixup> &Fixups) const;

  /// getMachineOpValue - Return binary encoding of operand. If the machine
  /// operand requires relocation, record the relocation and return zero.
  unsigned getMachineOpValue(const MCInst &MI,const MCOperand &MO,
                             SmallVectorImpl<MCFixup> &Fixups) const;

  /// getMovtImmOpValue - Return the encoding for the movw/movt pair
  uint32_t getMovtImmOpValue(const MCInst &MI, unsigned OpIdx,
                             SmallVectorImpl<MCFixup> &Fixups) const;

  bool EncodeAddrModeOpValues(const MCInst &MI, unsigned OpIdx,
                              unsigned &Reg, unsigned &Imm,
                              SmallVectorImpl<MCFixup> &Fixups) const;

  /// getBranchTargetOpValue - Return encoding info for 24-bit immediate
  /// branch target.
  uint32_t getBranchTargetOpValue(const MCInst &MI, unsigned OpIdx,
                                  SmallVectorImpl<MCFixup> &Fixups) const;

  /// getAddrModeImm12OpValue - Return encoding info for 'reg +/- imm12'
  /// operand.
  uint32_t getAddrModeImm12OpValue(const MCInst &MI, unsigned OpIdx,
                                   SmallVectorImpl<MCFixup> &Fixups) const;

  /// getLdStSORegOpValue - Return encoding info for 'reg +/- reg shop imm'
  /// operand as needed by load/store instructions.
  uint32_t getLdStSORegOpValue(const MCInst &MI, unsigned OpIdx,
                               SmallVectorImpl<MCFixup> &Fixups) const;

  /// getLdStmModeOpValue - Return encoding for load/store multiple mode.
  uint32_t getLdStmModeOpValue(const MCInst &MI, unsigned OpIdx,
                               SmallVectorImpl<MCFixup> &Fixups) const {
    ARM_AM::AMSubMode Mode = (ARM_AM::AMSubMode)MI.getOperand(OpIdx).getImm();
    switch (Mode) {
    default: assert(0 && "Unknown addressing sub-mode!");
    case ARM_AM::da: return 0;
    case ARM_AM::ia: return 1;
    case ARM_AM::db: return 2;
    case ARM_AM::ib: return 3;
    }
  }
  /// getShiftOp - Return the shift opcode (bit[6:5]) of the immediate value.
  ///
  unsigned getShiftOp(ARM_AM::ShiftOpc ShOpc) const {
    switch (ShOpc) {
    default: llvm_unreachable("Unknown shift opc!");
    case ARM_AM::no_shift:
    case ARM_AM::lsl: return 0;
    case ARM_AM::lsr: return 1;
    case ARM_AM::asr: return 2;
    case ARM_AM::ror:
    case ARM_AM::rrx: return 3;
    }
    return 0;
  }

  /// getAddrMode2OpValue - Return encoding for addrmode2 operands.
  uint32_t getAddrMode2OpValue(const MCInst &MI, unsigned OpIdx,
                               SmallVectorImpl<MCFixup> &Fixups) const;

  /// getAddrMode2OffsetOpValue - Return encoding for am2offset operands.
  uint32_t getAddrMode2OffsetOpValue(const MCInst &MI, unsigned OpIdx,
                                     SmallVectorImpl<MCFixup> &Fixups) const;

  /// getAddrMode3OffsetOpValue - Return encoding for am3offset operands.
  uint32_t getAddrMode3OffsetOpValue(const MCInst &MI, unsigned OpIdx,
                                     SmallVectorImpl<MCFixup> &Fixups) const;

  /// getAddrMode3OpValue - Return encoding for addrmode3 operands.
  uint32_t getAddrMode3OpValue(const MCInst &MI, unsigned OpIdx,
                               SmallVectorImpl<MCFixup> &Fixups) const;

  /// getAddrMode5OpValue - Return encoding info for 'reg +/- imm8' operand.
  uint32_t getAddrMode5OpValue(const MCInst &MI, unsigned OpIdx,
                               SmallVectorImpl<MCFixup> &Fixups) const;

  /// getCCOutOpValue - Return encoding of the 's' bit.
  unsigned getCCOutOpValue(const MCInst &MI, unsigned Op,
                           SmallVectorImpl<MCFixup> &Fixups) const {
    // The operand is either reg0 or CPSR. The 's' bit is encoded as '0' or
    // '1' respectively.
    return MI.getOperand(Op).getReg() == ARM::CPSR;
  }

  /// getSOImmOpValue - Return an encoded 12-bit shifted-immediate value.
  unsigned getSOImmOpValue(const MCInst &MI, unsigned Op,
                           SmallVectorImpl<MCFixup> &Fixups) const {
    unsigned SoImm = MI.getOperand(Op).getImm();
    int SoImmVal = ARM_AM::getSOImmVal(SoImm);
    assert(SoImmVal != -1 && "Not a valid so_imm value!");

    // Encode rotate_imm.
    unsigned Binary = (ARM_AM::getSOImmValRot((unsigned)SoImmVal) >> 1)
      << ARMII::SoRotImmShift;

    // Encode immed_8.
    Binary |= ARM_AM::getSOImmValImm((unsigned)SoImmVal);
    return Binary;
  }
  
  /// getT2SOImmOpValue - Return an encoded 12-bit shifted-immediate value.
  unsigned getT2SOImmOpValue(const MCInst &MI, unsigned Op,
                           SmallVectorImpl<MCFixup> &Fixups) const {
    unsigned SoImm = MI.getOperand(Op).getImm();
    unsigned Encoded =  ARM_AM::getT2SOImmVal(SoImm);
    assert(Encoded != ~0U && "Not a Thumb2 so_imm value?");
    return Encoded;
  }

  /// getSORegOpValue - Return an encoded so_reg shifted register value.
  unsigned getSORegOpValue(const MCInst &MI, unsigned Op,
                           SmallVectorImpl<MCFixup> &Fixups) const;
  unsigned getT2SORegOpValue(const MCInst &MI, unsigned Op,
                             SmallVectorImpl<MCFixup> &Fixups) const;

  unsigned getRotImmOpValue(const MCInst &MI, unsigned Op,
                            SmallVectorImpl<MCFixup> &Fixups) const {
    switch (MI.getOperand(Op).getImm()) {
    default: assert (0 && "Not a valid rot_imm value!");
    case 0:  return 0;
    case 8:  return 1;
    case 16: return 2;
    case 24: return 3;
    }
  }

  unsigned getImmMinusOneOpValue(const MCInst &MI, unsigned Op,
                                 SmallVectorImpl<MCFixup> &Fixups) const {
    return MI.getOperand(Op).getImm() - 1;
  }

  unsigned getNEONVcvtImm32OpValue(const MCInst &MI, unsigned Op,
                                   SmallVectorImpl<MCFixup> &Fixups) const {
    return 64 - MI.getOperand(Op).getImm();
  }

  unsigned getBitfieldInvertedMaskOpValue(const MCInst &MI, unsigned Op,
                                      SmallVectorImpl<MCFixup> &Fixups) const;

  unsigned getRegisterListOpValue(const MCInst &MI, unsigned Op,
                                  SmallVectorImpl<MCFixup> &Fixups) const;
  unsigned getAddrMode6AddressOpValue(const MCInst &MI, unsigned Op,
                                      SmallVectorImpl<MCFixup> &Fixups) const;
  unsigned getAddrMode6OffsetOpValue(const MCInst &MI, unsigned Op,
                                     SmallVectorImpl<MCFixup> &Fixups) const;

  unsigned NEONThumb2DataIPostEncoder(const MCInst &MI,
                                      unsigned EncodedValue) const;
  unsigned NEONThumb2LoadStorePostEncoder(const MCInst &MI,
                                      unsigned EncodedValue) const;
  unsigned NEONThumb2DupPostEncoder(const MCInst &MI,
                                      unsigned EncodedValue) const;

  void EmitByte(unsigned char C, raw_ostream &OS) const {
    OS << (char)C;
  }

  void EmitConstant(uint64_t Val, unsigned Size, raw_ostream &OS) const {
    // Output the constant in little endian byte order.
    for (unsigned i = 0; i != Size; ++i) {
      EmitByte(Val & 255, OS);
      Val >>= 8;
    }
  }

  void EncodeInstruction(const MCInst &MI, raw_ostream &OS,
                         SmallVectorImpl<MCFixup> &Fixups) const;
};

} // end anonymous namespace

MCCodeEmitter *llvm::createARMMCCodeEmitter(const Target &, TargetMachine &TM,
                                            MCContext &Ctx) {
  return new ARMMCCodeEmitter(TM, Ctx);
}

/// NEONThumb2DataIPostEncoder - Post-process encoded NEON data-processing 
/// instructions, and rewrite them to their Thumb2 form if we are currently in 
/// Thumb2 mode.
unsigned ARMMCCodeEmitter::NEONThumb2DataIPostEncoder(const MCInst &MI,
                                                 unsigned EncodedValue) const {
  const ARMSubtarget &Subtarget = TM.getSubtarget<ARMSubtarget>();
  if (Subtarget.isThumb2()) {
    // NEON Thumb2 data-processsing encodings are very simple: bit 24 is moved 
    // to bit 12 of the high half-word (i.e. bit 28), and bits 27-24 are
    // set to 1111.
    unsigned Bit24 = EncodedValue & 0x01000000;
    unsigned Bit28 = Bit24 << 4;
    EncodedValue &= 0xEFFFFFFF;
    EncodedValue |= Bit28;
    EncodedValue |= 0x0F000000;
  }
  
  return EncodedValue;
}

/// NEONThumb2LoadStorePostEncoder - Post-process encoded NEON load/store
/// instructions, and rewrite them to their Thumb2 form if we are currently in 
/// Thumb2 mode.
unsigned ARMMCCodeEmitter::NEONThumb2LoadStorePostEncoder(const MCInst &MI,
                                                 unsigned EncodedValue) const {
  const ARMSubtarget &Subtarget = TM.getSubtarget<ARMSubtarget>();
  if (Subtarget.isThumb2()) {
    EncodedValue &= 0xF0FFFFFF;
    EncodedValue |= 0x09000000;
  }
  
  return EncodedValue;
}

/// NEONThumb2DupPostEncoder - Post-process encoded NEON vdup
/// instructions, and rewrite them to their Thumb2 form if we are currently in 
/// Thumb2 mode.
unsigned ARMMCCodeEmitter::NEONThumb2DupPostEncoder(const MCInst &MI,
                                                 unsigned EncodedValue) const {
  const ARMSubtarget &Subtarget = TM.getSubtarget<ARMSubtarget>();
  if (Subtarget.isThumb2()) {
    EncodedValue &= 0x00FFFFFF;
    EncodedValue |= 0xEE000000;
  }
  
  return EncodedValue;
}



/// getMachineOpValue - Return binary encoding of operand. If the machine
/// operand requires relocation, record the relocation and return zero.
unsigned ARMMCCodeEmitter::
getMachineOpValue(const MCInst &MI, const MCOperand &MO,
                  SmallVectorImpl<MCFixup> &Fixups) const {
  if (MO.isReg()) {
    unsigned Reg = MO.getReg();
    unsigned RegNo = getARMRegisterNumbering(Reg);

    // Q registers are encodes as 2x their register number.
    switch (Reg) {
    default:
      return RegNo;
    case ARM::Q0:  case ARM::Q1:  case ARM::Q2:  case ARM::Q3:
    case ARM::Q4:  case ARM::Q5:  case ARM::Q6:  case ARM::Q7:
    case ARM::Q8:  case ARM::Q9:  case ARM::Q10: case ARM::Q11:
    case ARM::Q12: case ARM::Q13: case ARM::Q14: case ARM::Q15:
      return 2 * RegNo;
    }
  } else if (MO.isImm()) {
    return static_cast<unsigned>(MO.getImm());
  } else if (MO.isFPImm()) {
    return static_cast<unsigned>(APFloat(MO.getFPImm())
                     .bitcastToAPInt().getHiBits(32).getLimitedValue());
  }

  llvm_unreachable("Unable to encode MCOperand!");
  return 0;
}

/// getAddrModeImmOpValue - Return encoding info for 'reg +/- imm' operand.
bool ARMMCCodeEmitter::
EncodeAddrModeOpValues(const MCInst &MI, unsigned OpIdx, unsigned &Reg,
                       unsigned &Imm, SmallVectorImpl<MCFixup> &Fixups) const {
  const MCOperand &MO  = MI.getOperand(OpIdx);
  const MCOperand &MO1 = MI.getOperand(OpIdx + 1);

  Reg = getARMRegisterNumbering(MO.getReg());

  int32_t SImm = MO1.getImm();
  bool isAdd = true;

  // Special value for #-0
  if (SImm == INT32_MIN)
    SImm = 0;

  // Immediate is always encoded as positive. The 'U' bit controls add vs sub.
  if (SImm < 0) {
    SImm = -SImm;
    isAdd = false;
  }

  Imm = SImm;
  return isAdd;
}

/// getBranchTargetOpValue - Return encoding info for 24-bit immediate
/// branch target.
uint32_t ARMMCCodeEmitter::
getBranchTargetOpValue(const MCInst &MI, unsigned OpIdx,
                        SmallVectorImpl<MCFixup> &Fixups) const {
  const MCOperand &MO = MI.getOperand(OpIdx);

  // If the destination is an immediate, we have nothing to do.
  if (MO.isImm()) return MO.getImm();
  assert (MO.isExpr() && "Unexpected branch target type!");
  const MCExpr *Expr = MO.getExpr();
  MCFixupKind Kind = MCFixupKind(ARM::fixup_arm_branch);
  Fixups.push_back(MCFixup::Create(0, Expr, Kind));

  // All of the information is in the fixup.
  return 0;
}

/// getAddrModeImm12OpValue - Return encoding info for 'reg +/- imm12' operand.
uint32_t ARMMCCodeEmitter::
getAddrModeImm12OpValue(const MCInst &MI, unsigned OpIdx,
                        SmallVectorImpl<MCFixup> &Fixups) const {
  // {17-13} = reg
  // {12}    = (U)nsigned (add == '1', sub == '0')
  // {11-0}  = imm12
  unsigned Reg, Imm12;
  bool isAdd = true;
  // If The first operand isn't a register, we have a label reference.
  const MCOperand &MO = MI.getOperand(OpIdx);
  if (!MO.isReg()) {
    Reg = getARMRegisterNumbering(ARM::PC);   // Rn is PC.
    Imm12 = 0;

    assert(MO.isExpr() && "Unexpected machine operand type!");
    const MCExpr *Expr = MO.getExpr();
    MCFixupKind Kind = MCFixupKind(ARM::fixup_arm_pcrel_12);
    Fixups.push_back(MCFixup::Create(0, Expr, Kind));

    ++MCNumCPRelocations;
  } else
    isAdd = EncodeAddrModeOpValues(MI, OpIdx, Reg, Imm12, Fixups);

  uint32_t Binary = Imm12 & 0xfff;
  // Immediate is always encoded as positive. The 'U' bit controls add vs sub.
  if (isAdd)
    Binary |= (1 << 12);
  Binary |= (Reg << 13);
  return Binary;
}

uint32_t ARMMCCodeEmitter::
getMovtImmOpValue(const MCInst &MI, unsigned OpIdx,
                  SmallVectorImpl<MCFixup> &Fixups) const {
  // {20-16} = imm{15-12}
  // {11-0}  = imm{11-0}
  const MCOperand &MO = MI.getOperand(OpIdx); 
  if (MO.isImm()) {
    return static_cast<unsigned>(MO.getImm());
  } else if (const MCSymbolRefExpr *Expr = 
             dyn_cast<MCSymbolRefExpr>(MO.getExpr())) {
    MCFixupKind Kind;
    switch (Expr->getKind()) {
    default: assert(0 && "Unsupported ARMFixup");
    case MCSymbolRefExpr::VK_ARM_HI16:
      Kind = MCFixupKind(ARM::fixup_arm_movt_hi16);
      break;
    case MCSymbolRefExpr::VK_ARM_LO16:
      Kind = MCFixupKind(ARM::fixup_arm_movw_lo16);
      break;
    }
    Fixups.push_back(MCFixup::Create(0, Expr, Kind));
    return 0;
  };
  llvm_unreachable("Unsupported MCExpr type in MCOperand!");
  return 0;
}

uint32_t ARMMCCodeEmitter::
getLdStSORegOpValue(const MCInst &MI, unsigned OpIdx,
                    SmallVectorImpl<MCFixup> &Fixups) const {
  const MCOperand &MO = MI.getOperand(OpIdx);
  const MCOperand &MO1 = MI.getOperand(OpIdx+1);
  const MCOperand &MO2 = MI.getOperand(OpIdx+2);
  unsigned Rn = getARMRegisterNumbering(MO.getReg());
  unsigned Rm = getARMRegisterNumbering(MO1.getReg());
  unsigned ShImm = ARM_AM::getAM2Offset(MO2.getImm());
  bool isAdd = ARM_AM::getAM2Op(MO2.getImm()) == ARM_AM::add;
  ARM_AM::ShiftOpc ShOp = ARM_AM::getAM2ShiftOpc(MO2.getImm());
  unsigned SBits = getShiftOp(ShOp);

  // {16-13} = Rn
  // {12}    = isAdd
  // {11-0}  = shifter
  //  {3-0}  = Rm
  //  {4}    = 0
  //  {6-5}  = type
  //  {11-7} = imm
  uint32_t Binary = Rm;
  Binary |= Rn << 13;
  Binary |= SBits << 5;
  Binary |= ShImm << 7;
  if (isAdd)
    Binary |= 1 << 12;
  return Binary;
}

uint32_t ARMMCCodeEmitter::
getAddrMode2OpValue(const MCInst &MI, unsigned OpIdx,
                    SmallVectorImpl<MCFixup> &Fixups) const {
  // {17-14}  Rn
  // {13}     1 == imm12, 0 == Rm
  // {12}     isAdd
  // {11-0}   imm12/Rm
  const MCOperand &MO = MI.getOperand(OpIdx);
  unsigned Rn = getARMRegisterNumbering(MO.getReg());
  uint32_t Binary = getAddrMode2OffsetOpValue(MI, OpIdx + 1, Fixups);
  Binary |= Rn << 14;
  return Binary;
}

uint32_t ARMMCCodeEmitter::
getAddrMode2OffsetOpValue(const MCInst &MI, unsigned OpIdx,
                          SmallVectorImpl<MCFixup> &Fixups) const {
  // {13}     1 == imm12, 0 == Rm
  // {12}     isAdd
  // {11-0}   imm12/Rm
  const MCOperand &MO = MI.getOperand(OpIdx);
  const MCOperand &MO1 = MI.getOperand(OpIdx+1);
  unsigned Imm = MO1.getImm();
  bool isAdd = ARM_AM::getAM2Op(Imm) == ARM_AM::add;
  bool isReg = MO.getReg() != 0;
  uint32_t Binary = ARM_AM::getAM2Offset(Imm);
  // if reg +/- reg, Rm will be non-zero. Otherwise, we have reg +/- imm12
  if (isReg) {
    ARM_AM::ShiftOpc ShOp = ARM_AM::getAM2ShiftOpc(Imm);
    Binary <<= 7;                    // Shift amount is bits [11:7]
    Binary |= getShiftOp(ShOp) << 5; // Shift type is bits [6:5]
    Binary |= getARMRegisterNumbering(MO.getReg()); // Rm is bits [3:0]
  }
  return Binary | (isAdd << 12) | (isReg << 13);
}

uint32_t ARMMCCodeEmitter::
getAddrMode3OffsetOpValue(const MCInst &MI, unsigned OpIdx,
                          SmallVectorImpl<MCFixup> &Fixups) const {
  // {9}      1 == imm8, 0 == Rm
  // {8}      isAdd
  // {7-4}    imm7_4/zero
  // {3-0}    imm3_0/Rm
  const MCOperand &MO = MI.getOperand(OpIdx);
  const MCOperand &MO1 = MI.getOperand(OpIdx+1);
  unsigned Imm = MO1.getImm();
  bool isAdd = ARM_AM::getAM3Op(Imm) == ARM_AM::add;
  bool isImm = MO.getReg() == 0;
  uint32_t Imm8 = ARM_AM::getAM3Offset(Imm);
  // if reg +/- reg, Rm will be non-zero. Otherwise, we have reg +/- imm8
  if (!isImm)
    Imm8 = getARMRegisterNumbering(MO.getReg());
  return Imm8 | (isAdd << 8) | (isImm << 9);
}

uint32_t ARMMCCodeEmitter::
getAddrMode3OpValue(const MCInst &MI, unsigned OpIdx,
                    SmallVectorImpl<MCFixup> &Fixups) const {
  // {13}     1 == imm8, 0 == Rm
  // {12-9}   Rn
  // {8}      isAdd
  // {7-4}    imm7_4/zero
  // {3-0}    imm3_0/Rm
  const MCOperand &MO = MI.getOperand(OpIdx);
  const MCOperand &MO1 = MI.getOperand(OpIdx+1);
  const MCOperand &MO2 = MI.getOperand(OpIdx+2);
  unsigned Rn = getARMRegisterNumbering(MO.getReg());
  unsigned Imm = MO2.getImm();
  bool isAdd = ARM_AM::getAM3Op(Imm) == ARM_AM::add;
  bool isImm = MO1.getReg() == 0;
  uint32_t Imm8 = ARM_AM::getAM3Offset(Imm);
  // if reg +/- reg, Rm will be non-zero. Otherwise, we have reg +/- imm8
  if (!isImm)
    Imm8 = getARMRegisterNumbering(MO1.getReg());
  return (Rn << 9) | Imm8 | (isAdd << 8) | (isImm << 13);
}

/// getAddrMode5OpValue - Return encoding info for 'reg +/- imm12' operand.
uint32_t ARMMCCodeEmitter::
getAddrMode5OpValue(const MCInst &MI, unsigned OpIdx,
                    SmallVectorImpl<MCFixup> &Fixups) const {
  // {12-9} = reg
  // {8}    = (U)nsigned (add == '1', sub == '0')
  // {7-0}  = imm8
  unsigned Reg, Imm8;
  // If The first operand isn't a register, we have a label reference.
  const MCOperand &MO = MI.getOperand(OpIdx);
  if (!MO.isReg()) {
    Reg = getARMRegisterNumbering(ARM::PC);   // Rn is PC.
    Imm8 = 0;

    assert(MO.isExpr() && "Unexpected machine operand type!");
    const MCExpr *Expr = MO.getExpr();
    MCFixupKind Kind = MCFixupKind(ARM::fixup_arm_vfp_pcrel_12);
    Fixups.push_back(MCFixup::Create(0, Expr, Kind));

    ++MCNumCPRelocations;
  } else
    EncodeAddrModeOpValues(MI, OpIdx, Reg, Imm8, Fixups);

  uint32_t Binary = ARM_AM::getAM5Offset(Imm8);
  // Immediate is always encoded as positive. The 'U' bit controls add vs sub.
  if (ARM_AM::getAM5Op(Imm8) == ARM_AM::add)
    Binary |= (1 << 8);
  Binary |= (Reg << 9);
  return Binary;
}

unsigned ARMMCCodeEmitter::
getSORegOpValue(const MCInst &MI, unsigned OpIdx,
                SmallVectorImpl<MCFixup> &Fixups) const {
  // Sub-operands are [reg, reg, imm]. The first register is Rm, the reg to be
  // shifted. The second is either Rs, the amount to shift by, or reg0 in which
  // case the imm contains the amount to shift by.
  //
  // {3-0} = Rm.
  // {4}   = 1 if reg shift, 0 if imm shift
  // {6-5} = type
  //    If reg shift:
  //      {11-8} = Rs
  //      {7}    = 0
  //    else (imm shift)
  //      {11-7} = imm

  const MCOperand &MO  = MI.getOperand(OpIdx);
  const MCOperand &MO1 = MI.getOperand(OpIdx + 1);
  const MCOperand &MO2 = MI.getOperand(OpIdx + 2);
  ARM_AM::ShiftOpc SOpc = ARM_AM::getSORegShOp(MO2.getImm());

  // Encode Rm.
  unsigned Binary = getARMRegisterNumbering(MO.getReg());

  // Encode the shift opcode.
  unsigned SBits = 0;
  unsigned Rs = MO1.getReg();
  if (Rs) {
    // Set shift operand (bit[7:4]).
    // LSL - 0001
    // LSR - 0011
    // ASR - 0101
    // ROR - 0111
    // RRX - 0110 and bit[11:8] clear.
    switch (SOpc) {
    default: llvm_unreachable("Unknown shift opc!");
    case ARM_AM::lsl: SBits = 0x1; break;
    case ARM_AM::lsr: SBits = 0x3; break;
    case ARM_AM::asr: SBits = 0x5; break;
    case ARM_AM::ror: SBits = 0x7; break;
    case ARM_AM::rrx: SBits = 0x6; break;
    }
  } else {
    // Set shift operand (bit[6:4]).
    // LSL - 000
    // LSR - 010
    // ASR - 100
    // ROR - 110
    switch (SOpc) {
    default: llvm_unreachable("Unknown shift opc!");
    case ARM_AM::lsl: SBits = 0x0; break;
    case ARM_AM::lsr: SBits = 0x2; break;
    case ARM_AM::asr: SBits = 0x4; break;
    case ARM_AM::ror: SBits = 0x6; break;
    }
  }

  Binary |= SBits << 4;
  if (SOpc == ARM_AM::rrx)
    return Binary;

  // Encode the shift operation Rs or shift_imm (except rrx).
  if (Rs) {
    // Encode Rs bit[11:8].
    assert(ARM_AM::getSORegOffset(MO2.getImm()) == 0);
    return Binary | (getARMRegisterNumbering(Rs) << ARMII::RegRsShift);
  }

  // Encode shift_imm bit[11:7].
  return Binary | ARM_AM::getSORegOffset(MO2.getImm()) << 7;
}

unsigned ARMMCCodeEmitter::
getT2SORegOpValue(const MCInst &MI, unsigned OpIdx,
                SmallVectorImpl<MCFixup> &Fixups) const {
  // Sub-operands are [reg, imm]. The first register is Rm, the reg to be
  // shifted. The second is the amount to shift by.
  //
  // {3-0} = Rm.
  // {4}   = 0
  // {6-5} = type
  // {11-7} = imm

  const MCOperand &MO  = MI.getOperand(OpIdx);
  const MCOperand &MO1 = MI.getOperand(OpIdx + 1);
  ARM_AM::ShiftOpc SOpc = ARM_AM::getSORegShOp(MO1.getImm());

  // Encode Rm.
  unsigned Binary = getARMRegisterNumbering(MO.getReg());

  // Encode the shift opcode.
  unsigned SBits = 0;
  // Set shift operand (bit[6:4]).
  // LSL - 000
  // LSR - 010
  // ASR - 100
  // ROR - 110
  switch (SOpc) {
  default: llvm_unreachable("Unknown shift opc!");
  case ARM_AM::lsl: SBits = 0x0; break;
  case ARM_AM::lsr: SBits = 0x2; break;
  case ARM_AM::asr: SBits = 0x4; break;
  case ARM_AM::ror: SBits = 0x6; break;
  }

  Binary |= SBits << 4;
  if (SOpc == ARM_AM::rrx)
    return Binary;

  // Encode shift_imm bit[11:7].
  return Binary | ARM_AM::getSORegOffset(MO1.getImm()) << 7;
}

unsigned ARMMCCodeEmitter::
getBitfieldInvertedMaskOpValue(const MCInst &MI, unsigned Op,
                               SmallVectorImpl<MCFixup> &Fixups) const {
  // 10 bits. lower 5 bits are are the lsb of the mask, high five bits are the
  // msb of the mask.
  const MCOperand &MO = MI.getOperand(Op);
  uint32_t v = ~MO.getImm();
  uint32_t lsb = CountTrailingZeros_32(v);
  uint32_t msb = (32 - CountLeadingZeros_32 (v)) - 1;
  assert (v != 0 && lsb < 32 && msb < 32 && "Illegal bitfield mask!");
  return lsb | (msb << 5);
}

unsigned ARMMCCodeEmitter::
getRegisterListOpValue(const MCInst &MI, unsigned Op,
                       SmallVectorImpl<MCFixup> &Fixups) const {
  // VLDM/VSTM:
  //   {12-8} = Vd
  //   {7-0}  = Number of registers
  //
  // LDM/STM:
  //   {15-0}  = Bitfield of GPRs.
  unsigned Reg = MI.getOperand(Op).getReg();
  bool SPRRegs = ARM::SPRRegClass.contains(Reg);
  bool DPRRegs = ARM::DPRRegClass.contains(Reg);

  unsigned Binary = 0;

  if (SPRRegs || DPRRegs) {
    // VLDM/VSTM
    unsigned RegNo = getARMRegisterNumbering(Reg);
    unsigned NumRegs = (MI.getNumOperands() - Op) & 0xff;
    Binary |= (RegNo & 0x1f) << 8;
    if (SPRRegs)
      Binary |= NumRegs;
    else
      Binary |= NumRegs * 2;
  } else {
    for (unsigned I = Op, E = MI.getNumOperands(); I < E; ++I) {
      unsigned RegNo = getARMRegisterNumbering(MI.getOperand(I).getReg());
      Binary |= 1 << RegNo;
    }
  }

  return Binary;
}

unsigned ARMMCCodeEmitter::
getAddrMode6AddressOpValue(const MCInst &MI, unsigned Op,
                           SmallVectorImpl<MCFixup> &Fixups) const {
  const MCOperand &Reg = MI.getOperand(Op);
  const MCOperand &Imm = MI.getOperand(Op + 1);

  unsigned RegNo = getARMRegisterNumbering(Reg.getReg());
  unsigned Align = 0;

  switch (Imm.getImm()) {
  default: break;
  case 2:
  case 4:
  case 8:  Align = 0x01; break;
  case 16: Align = 0x02; break;
  case 32: Align = 0x03; break;
  }

  return RegNo | (Align << 4);
}

unsigned ARMMCCodeEmitter::
getAddrMode6OffsetOpValue(const MCInst &MI, unsigned Op,
                          SmallVectorImpl<MCFixup> &Fixups) const {
  const MCOperand &MO = MI.getOperand(Op);
  if (MO.getReg() == 0) return 0x0D;
  return MO.getReg();
}

void ARMMCCodeEmitter::
EncodeInstruction(const MCInst &MI, raw_ostream &OS,
                  SmallVectorImpl<MCFixup> &Fixups) const {
  // Pseudo instructions don't get encoded.
  const TargetInstrDesc &Desc = TII.get(MI.getOpcode());
  uint64_t TSFlags = Desc.TSFlags;
  if ((TSFlags & ARMII::FormMask) == ARMII::Pseudo)
    return;
  int Size;
  // Basic size info comes from the TSFlags field.
  switch ((TSFlags & ARMII::SizeMask) >> ARMII::SizeShift) {
  default: llvm_unreachable("Unexpected instruction size!");
  case ARMII::Size2Bytes: Size = 2; break;
  case ARMII::Size4Bytes: Size = 4; break;
  }
  EmitConstant(getBinaryCodeForInstr(MI, Fixups), Size, OS);
  ++MCNumEmitted;  // Keep track of the # of mi's emitted.
}

#include "ARMGenMCCodeEmitter.inc"