lib/Target/Mips/MipsInstrInfo.cpp

//===-- MipsInstrInfo.cpp - Mips Instruction Information ------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file contains the Mips implementation of the TargetInstrInfo class.
//
//===----------------------------------------------------------------------===//

#include "MipsAnalyzeImmediate.h"
#include "MipsInstrInfo.h"
#include "MipsTargetMachine.h"
#include "MipsMachineFunction.h"
#include "InstPrinter/MipsInstPrinter.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/TargetRegistry.h"
#include "llvm/ADT/STLExtras.h"

#define GET_INSTRINFO_CTOR
#include "MipsGenInstrInfo.inc"

using namespace llvm;

MipsInstrInfo::MipsInstrInfo(MipsTargetMachine &tm)
  : MipsGenInstrInfo(Mips::ADJCALLSTACKDOWN, Mips::ADJCALLSTACKUP),
    TM(tm), IsN64(TM.getSubtarget<MipsSubtarget>().isABI_N64()),
    InMips16Mode(TM.getSubtarget<MipsSubtarget>().inMips16Mode()),
    RI(*TM.getSubtargetImpl(), *this),
    UncondBrOpc(TM.getRelocationModel() == Reloc::PIC_ ? Mips::B : Mips::J) {}

const MipsRegisterInfo &MipsInstrInfo::getRegisterInfo() const {
  return RI;
}

static bool isZeroImm(const MachineOperand &op) {
  return op.isImm() && op.getImm() == 0;
}

/// isLoadFromStackSlot - If the specified machine instruction is a direct
/// load from a stack slot, return the virtual or physical register number of
/// the destination along with the FrameIndex of the loaded stack slot.  If
/// not, return 0.  This predicate must return 0 if the instruction has
/// any side effects other than loading from the stack slot.
unsigned MipsInstrInfo::
isLoadFromStackSlot(const MachineInstr *MI, int &FrameIndex) const
{
  unsigned Opc = MI->getOpcode();

  if ((Opc == Mips::LW)    || (Opc == Mips::LW_P8)  || (Opc == Mips::LD) ||
      (Opc == Mips::LD_P8) || (Opc == Mips::LWC1)   || (Opc == Mips::LWC1_P8) ||
      (Opc == Mips::LDC1)  || (Opc == Mips::LDC164) ||
      (Opc == Mips::LDC164_P8)) {
    if ((MI->getOperand(1).isFI()) && // is a stack slot
        (MI->getOperand(2).isImm()) &&  // the imm is zero
        (isZeroImm(MI->getOperand(2)))) {
      FrameIndex = MI->getOperand(1).getIndex();
      return MI->getOperand(0).getReg();
    }
  }

  return 0;
}

/// isStoreToStackSlot - If the specified machine instruction is a direct
/// store to a stack slot, return the virtual or physical register number of
/// the source reg along with the FrameIndex of the loaded stack slot.  If
/// not, return 0.  This predicate must return 0 if the instruction has
/// any side effects other than storing to the stack slot.
unsigned MipsInstrInfo::
isStoreToStackSlot(const MachineInstr *MI, int &FrameIndex) const
{
  unsigned Opc = MI->getOpcode();

  if ((Opc == Mips::SW)    || (Opc == Mips::SW_P8)  || (Opc == Mips::SD) ||
      (Opc == Mips::SD_P8) || (Opc == Mips::SWC1)   || (Opc == Mips::SWC1_P8) ||
      (Opc == Mips::SDC1)  || (Opc == Mips::SDC164) ||
      (Opc == Mips::SDC164_P8)) {
    if ((MI->getOperand(1).isFI()) && // is a stack slot
        (MI->getOperand(2).isImm()) &&  // the imm is zero
        (isZeroImm(MI->getOperand(2)))) {
      FrameIndex = MI->getOperand(1).getIndex();
      return MI->getOperand(0).getReg();
    }
  }
  return 0;
}

/// insertNoop - If data hazard condition is found insert the target nop
/// instruction.
void MipsInstrInfo::
insertNoop(MachineBasicBlock &MBB, MachineBasicBlock::iterator MI) const
{
  DebugLoc DL;
  BuildMI(MBB, MI, DL, get(Mips::NOP));
}

void MipsInstrInfo::
copyPhysReg(MachineBasicBlock &MBB,
            MachineBasicBlock::iterator I, DebugLoc DL,
            unsigned DestReg, unsigned SrcReg,
            bool KillSrc) const {
  unsigned Opc = 0, ZeroReg = 0;

  if (Mips::CPURegsRegClass.contains(DestReg)) { // Copy to CPU Reg.
    if (Mips::CPURegsRegClass.contains(SrcReg)) {
      if (InMips16Mode)
        Opc=Mips::Mov32R16;
      else {
        Opc = Mips::ADDu, ZeroReg = Mips::ZERO;
      }
    }
    else if (Mips::CCRRegClass.contains(SrcReg))
      Opc = Mips::CFC1;
    else if (Mips::FGR32RegClass.contains(SrcReg))
      Opc = Mips::MFC1;
    else if (SrcReg == Mips::HI)
      Opc = Mips::MFHI, SrcReg = 0;
    else if (SrcReg == Mips::LO)
      Opc = Mips::MFLO, SrcReg = 0;
  }
  else if (Mips::CPURegsRegClass.contains(SrcReg)) { // Copy from CPU Reg.
    if (Mips::CCRRegClass.contains(DestReg))
      Opc = Mips::CTC1;
    else if (Mips::FGR32RegClass.contains(DestReg))
      Opc = Mips::MTC1;
    else if (DestReg == Mips::HI)
      Opc = Mips::MTHI, DestReg = 0;
    else if (DestReg == Mips::LO)
      Opc = Mips::MTLO, DestReg = 0;
  }
  else if (Mips::FGR32RegClass.contains(DestReg, SrcReg))
    Opc = Mips::FMOV_S;
  else if (Mips::AFGR64RegClass.contains(DestReg, SrcReg))
    Opc = Mips::FMOV_D32;
  else if (Mips::FGR64RegClass.contains(DestReg, SrcReg))
    Opc = Mips::FMOV_D64;
  else if (Mips::CCRRegClass.contains(DestReg, SrcReg))
    Opc = Mips::MOVCCRToCCR;
  else if (Mips::CPU64RegsRegClass.contains(DestReg)) { // Copy to CPU64 Reg.
    if (Mips::CPU64RegsRegClass.contains(SrcReg))
      Opc = Mips::DADDu, ZeroReg = Mips::ZERO_64;
    else if (SrcReg == Mips::HI64)
      Opc = Mips::MFHI64, SrcReg = 0;
    else if (SrcReg == Mips::LO64)
      Opc = Mips::MFLO64, SrcReg = 0;
    else if (Mips::FGR64RegClass.contains(SrcReg))
      Opc = Mips::DMFC1;
  }
  else if (Mips::CPU64RegsRegClass.contains(SrcReg)) { // Copy from CPU64 Reg.
    if (DestReg == Mips::HI64)
      Opc = Mips::MTHI64, DestReg = 0;
    else if (DestReg == Mips::LO64)
      Opc = Mips::MTLO64, DestReg = 0;
    else if (Mips::FGR64RegClass.contains(DestReg))
      Opc = Mips::DMTC1;
  }

  assert(Opc && "Cannot copy registers");

  MachineInstrBuilder MIB = BuildMI(MBB, I, DL, get(Opc));

  if (DestReg)
    MIB.addReg(DestReg, RegState::Define);

  if (ZeroReg)
    MIB.addReg(ZeroReg);

  if (SrcReg)
    MIB.addReg(SrcReg, getKillRegState(KillSrc));
}

static MachineMemOperand* GetMemOperand(MachineBasicBlock &MBB, int FI,
                                        unsigned Flag) {
  MachineFunction &MF = *MBB.getParent();
  MachineFrameInfo &MFI = *MF.getFrameInfo();
  unsigned Align = MFI.getObjectAlignment(FI);

  return MF.getMachineMemOperand(MachinePointerInfo::getFixedStack(FI), Flag,
                                 MFI.getObjectSize(FI), Align);
}

void MipsInstrInfo::
storeRegToStackSlot(MachineBasicBlock &MBB, MachineBasicBlock::iterator I,
                    unsigned SrcReg, bool isKill, int FI,
                    const TargetRegisterClass *RC,
                    const TargetRegisterInfo *TRI) const {
  DebugLoc DL;
  if (I != MBB.end()) DL = I->getDebugLoc();
  MachineMemOperand *MMO = GetMemOperand(MBB, FI, MachineMemOperand::MOStore);

  unsigned Opc = 0;

  if (Mips::CPURegsRegClass.hasSubClassEq(RC))
    Opc = IsN64 ? Mips::SW_P8 : Mips::SW;
  else if (Mips::CPU64RegsRegClass.hasSubClassEq(RC))
    Opc = IsN64 ? Mips::SD_P8 : Mips::SD;
  else if (Mips::FGR32RegClass.hasSubClassEq(RC))
    Opc = IsN64 ? Mips::SWC1_P8 : Mips::SWC1;
  else if (Mips::AFGR64RegClass.hasSubClassEq(RC))
    Opc = Mips::SDC1;
  else if (Mips::FGR64RegClass.hasSubClassEq(RC))
    Opc = IsN64 ? Mips::SDC164_P8 : Mips::SDC164;

  assert(Opc && "Register class not handled!");
  BuildMI(MBB, I, DL, get(Opc)).addReg(SrcReg, getKillRegState(isKill))
    .addFrameIndex(FI).addImm(0).addMemOperand(MMO);
}

void MipsInstrInfo::
loadRegFromStackSlot(MachineBasicBlock &MBB, MachineBasicBlock::iterator I,
                     unsigned DestReg, int FI,
                     const TargetRegisterClass *RC,
                     const TargetRegisterInfo *TRI) const
{
  DebugLoc DL;
  if (I != MBB.end()) DL = I->getDebugLoc();
  MachineMemOperand *MMO = GetMemOperand(MBB, FI, MachineMemOperand::MOLoad);
  unsigned Opc = 0;

  if (Mips::CPURegsRegClass.hasSubClassEq(RC))
    Opc = IsN64 ? Mips::LW_P8 : Mips::LW;
  else if (Mips::CPU64RegsRegClass.hasSubClassEq(RC))
    Opc = IsN64 ? Mips::LD_P8 : Mips::LD;
  else if (Mips::FGR32RegClass.hasSubClassEq(RC))
    Opc = IsN64 ? Mips::LWC1_P8 : Mips::LWC1;
  else if (Mips::AFGR64RegClass.hasSubClassEq(RC))
    Opc = Mips::LDC1;
  else if (Mips::FGR64RegClass.hasSubClassEq(RC))
    Opc = IsN64 ? Mips::LDC164_P8 : Mips::LDC164;

  assert(Opc && "Register class not handled!");
  BuildMI(MBB, I, DL, get(Opc), DestReg).addFrameIndex(FI).addImm(0)
    .addMemOperand(MMO);
}

void MipsInstrInfo::ExpandRetRA(MachineBasicBlock &MBB,
                                MachineBasicBlock::iterator I,
                                unsigned Opc) const {
  BuildMI(MBB, I, I->getDebugLoc(), TM.getInstrInfo()->get(Opc))
    .addReg(Mips::RA);
}

void MipsInstrInfo::ExpandRetRA16(MachineBasicBlock &MBB,
                                MachineBasicBlock::iterator I,
                                unsigned Opc) const {
  BuildMI(MBB, I, I->getDebugLoc(), TM.getInstrInfo()->get(Opc));
}

void MipsInstrInfo::ExpandExtractElementF64(MachineBasicBlock &MBB,
                                          MachineBasicBlock::iterator I) const {
  const TargetInstrInfo *TII = TM.getInstrInfo();
  unsigned DstReg = I->getOperand(0).getReg();
  unsigned SrcReg = I->getOperand(1).getReg();
  unsigned N = I->getOperand(2).getImm();
  const MCInstrDesc& Mfc1Tdd = TII->get(Mips::MFC1);
  DebugLoc dl = I->getDebugLoc();

  assert(N < 2 && "Invalid immediate");
  unsigned SubIdx = N ? Mips::sub_fpodd : Mips::sub_fpeven;
  unsigned SubReg = TM.getRegisterInfo()->getSubReg(SrcReg, SubIdx);

  BuildMI(MBB, I, dl, Mfc1Tdd, DstReg).addReg(SubReg);
}

void MipsInstrInfo::ExpandBuildPairF64(MachineBasicBlock &MBB,
                                       MachineBasicBlock::iterator I) const {
  const TargetInstrInfo *TII = TM.getInstrInfo();
  unsigned DstReg = I->getOperand(0).getReg();
  unsigned LoReg = I->getOperand(1).getReg(), HiReg = I->getOperand(2).getReg();
  const MCInstrDesc& Mtc1Tdd = TII->get(Mips::MTC1);
  DebugLoc dl = I->getDebugLoc();
  const TargetRegisterInfo *TRI = TM.getRegisterInfo();

  // mtc1 Lo, $fp
  // mtc1 Hi, $fp + 1
  BuildMI(MBB, I, dl, Mtc1Tdd, TRI->getSubReg(DstReg, Mips::sub_fpeven))
    .addReg(LoReg);
  BuildMI(MBB, I, dl, Mtc1Tdd, TRI->getSubReg(DstReg, Mips::sub_fpodd))
    .addReg(HiReg);
}

bool MipsInstrInfo::expandPostRAPseudo(MachineBasicBlock::iterator MI) const {
  MachineBasicBlock &MBB = *MI->getParent();

  switch(MI->getDesc().getOpcode()) {
  default:
    return false;
  case Mips::RetRA:
    ExpandRetRA(MBB, MI, Mips::RET);
    break;
  case Mips::RetRA16:
    ExpandRetRA16(MBB, MI, Mips::JrRa16);
    break;
  case Mips::BuildPairF64:
    ExpandBuildPairF64(MBB, MI);
    break;
  case Mips::ExtractElementF64:
    ExpandExtractElementF64(MBB, MI);
    break;
  }

  MBB.erase(MI);
  return true;
}

MachineInstr*
MipsInstrInfo::emitFrameIndexDebugValue(MachineFunction &MF, int FrameIx,
                                        uint64_t Offset, const MDNode *MDPtr,
                                        DebugLoc DL) const {
  MachineInstrBuilder MIB = BuildMI(MF, DL, get(Mips::DBG_VALUE))
    .addFrameIndex(FrameIx).addImm(0).addImm(Offset).addMetadata(MDPtr);
  return &*MIB;
}

//===----------------------------------------------------------------------===//
// Branch Analysis
//===----------------------------------------------------------------------===//

static unsigned GetAnalyzableBrOpc(unsigned Opc) {
  return (Opc == Mips::BEQ    || Opc == Mips::BNE    || Opc == Mips::BGTZ   ||
          Opc == Mips::BGEZ   || Opc == Mips::BLTZ   || Opc == Mips::BLEZ   ||
          Opc == Mips::BEQ64  || Opc == Mips::BNE64  || Opc == Mips::BGTZ64 ||
          Opc == Mips::BGEZ64 || Opc == Mips::BLTZ64 || Opc == Mips::BLEZ64 ||
          Opc == Mips::BC1T   || Opc == Mips::BC1F   || Opc == Mips::B      ||
          Opc == Mips::J) ?
         Opc : 0;
}

/// GetOppositeBranchOpc - Return the inverse of the specified
/// opcode, e.g. turning BEQ to BNE.
unsigned Mips::GetOppositeBranchOpc(unsigned Opc)
{
  switch (Opc) {
  default:           llvm_unreachable("Illegal opcode!");
  case Mips::BEQ:    return Mips::BNE;
  case Mips::BNE:    return Mips::BEQ;
  case Mips::BGTZ:   return Mips::BLEZ;
  case Mips::BGEZ:   return Mips::BLTZ;
  case Mips::BLTZ:   return Mips::BGEZ;
  case Mips::BLEZ:   return Mips::BGTZ;
  case Mips::BEQ64:  return Mips::BNE64;
  case Mips::BNE64:  return Mips::BEQ64;
  case Mips::BGTZ64: return Mips::BLEZ64;
  case Mips::BGEZ64: return Mips::BLTZ64;
  case Mips::BLTZ64: return Mips::BGEZ64;
  case Mips::BLEZ64: return Mips::BGTZ64;
  case Mips::BC1T:   return Mips::BC1F;
  case Mips::BC1F:   return Mips::BC1T;
  }
}

static void AnalyzeCondBr(const MachineInstr *Inst, unsigned Opc,
                          MachineBasicBlock *&BB,
                          SmallVectorImpl<MachineOperand> &Cond) {
  assert(GetAnalyzableBrOpc(Opc) && "Not an analyzable branch");
  int NumOp = Inst->getNumExplicitOperands();

  // for both int and fp branches, the last explicit operand is the
  // MBB.
  BB = Inst->getOperand(NumOp-1).getMBB();
  Cond.push_back(MachineOperand::CreateImm(Opc));

  for (int i=0; i<NumOp-1; i++)
    Cond.push_back(Inst->getOperand(i));
}

bool MipsInstrInfo::AnalyzeBranch(MachineBasicBlock &MBB,
                                  MachineBasicBlock *&TBB,
                                  MachineBasicBlock *&FBB,
                                  SmallVectorImpl<MachineOperand> &Cond,
                                  bool AllowModify) const
{
  MachineBasicBlock::reverse_iterator I = MBB.rbegin(), REnd = MBB.rend();

  // Skip all the debug instructions.
  while (I != REnd && I->isDebugValue())
    ++I;

  if (I == REnd || !isUnpredicatedTerminator(&*I)) {
    // If this block ends with no branches (it just falls through to its succ)
    // just return false, leaving TBB/FBB null.
    TBB = FBB = NULL;
    return false;
  }

  MachineInstr *LastInst = &*I;
  unsigned LastOpc = LastInst->getOpcode();

  // Not an analyzable branch (must be an indirect jump).
  if (!GetAnalyzableBrOpc(LastOpc))
    return true;

  // Get the second to last instruction in the block.
  unsigned SecondLastOpc = 0;
  MachineInstr *SecondLastInst = NULL;

  if (++I != REnd) {
    SecondLastInst = &*I;
    SecondLastOpc = GetAnalyzableBrOpc(SecondLastInst->getOpcode());

    // Not an analyzable branch (must be an indirect jump).
    if (isUnpredicatedTerminator(SecondLastInst) && !SecondLastOpc)
      return true;
  }

  // If there is only one terminator instruction, process it.
  if (!SecondLastOpc) {
    // Unconditional branch
    if (LastOpc == UncondBrOpc) {
      TBB = LastInst->getOperand(0).getMBB();
      return false;
    }

    // Conditional branch
    AnalyzeCondBr(LastInst, LastOpc, TBB, Cond);
    return false;
  }

  // If we reached here, there are two branches.
  // If there are three terminators, we don't know what sort of block this is.
  if (++I != REnd && isUnpredicatedTerminator(&*I))
    return true;

  // If second to last instruction is an unconditional branch,
  // analyze it and remove the last instruction.
  if (SecondLastOpc == UncondBrOpc) {
    // Return if the last instruction cannot be removed.
    if (!AllowModify)
      return true;

    TBB = SecondLastInst->getOperand(0).getMBB();
    LastInst->eraseFromParent();
    return false;
  }

  // Conditional branch followed by an unconditional branch.
  // The last one must be unconditional.
  if (LastOpc != UncondBrOpc)
    return true;

  AnalyzeCondBr(SecondLastInst, SecondLastOpc, TBB, Cond);
  FBB = LastInst->getOperand(0).getMBB();

  return false;
}

void MipsInstrInfo::BuildCondBr(MachineBasicBlock &MBB,
                                MachineBasicBlock *TBB, DebugLoc DL,
                                const SmallVectorImpl<MachineOperand>& Cond)
  const {
  unsigned Opc = Cond[0].getImm();
  const MCInstrDesc &MCID = get(Opc);
  MachineInstrBuilder MIB = BuildMI(&MBB, DL, MCID);

  for (unsigned i = 1; i < Cond.size(); ++i)
    MIB.addReg(Cond[i].getReg());

  MIB.addMBB(TBB);
}

unsigned MipsInstrInfo::
InsertBranch(MachineBasicBlock &MBB, MachineBasicBlock *TBB,
             MachineBasicBlock *FBB,
             const SmallVectorImpl<MachineOperand> &Cond,
             DebugLoc DL) const {
  // Shouldn't be a fall through.
  assert(TBB && "InsertBranch must not be told to insert a fallthrough");

  // # of condition operands:
  //  Unconditional branches: 0
  //  Floating point branches: 1 (opc)
  //  Int BranchZero: 2 (opc, reg)
  //  Int Branch: 3 (opc, reg0, reg1)
  assert((Cond.size() <= 3) &&
         "# of Mips branch conditions must be <= 3!");

  // Two-way Conditional branch.
  if (FBB) {
    BuildCondBr(MBB, TBB, DL, Cond);
    BuildMI(&MBB, DL, get(UncondBrOpc)).addMBB(FBB);
    return 2;
  }

  // One way branch.
  // Unconditional branch.
  if (Cond.empty())
    BuildMI(&MBB, DL, get(UncondBrOpc)).addMBB(TBB);
  else // Conditional branch.
    BuildCondBr(MBB, TBB, DL, Cond);
  return 1;
}

unsigned MipsInstrInfo::
RemoveBranch(MachineBasicBlock &MBB) const
{
  MachineBasicBlock::reverse_iterator I = MBB.rbegin(), REnd = MBB.rend();
  MachineBasicBlock::reverse_iterator FirstBr;
  unsigned removed;

  // Skip all the debug instructions.
  while (I != REnd && I->isDebugValue())
    ++I;

  FirstBr = I;

  // Up to 2 branches are removed.
  // Note that indirect branches are not removed.
  for(removed = 0; I != REnd && removed < 2; ++I, ++removed)
    if (!GetAnalyzableBrOpc(I->getOpcode()))
      break;

  MBB.erase(I.base(), FirstBr.base());

  return removed;
}

/// ReverseBranchCondition - Return the inverse opcode of the
/// specified Branch instruction.
bool MipsInstrInfo::
ReverseBranchCondition(SmallVectorImpl<MachineOperand> &Cond) const
{
  assert( (Cond.size() && Cond.size() <= 3) &&
          "Invalid Mips branch condition!");
  Cond[0].setImm(Mips::GetOppositeBranchOpc(Cond[0].getImm()));
  return false;
}

/// Return the number of bytes of code the specified instruction may be.
unsigned MipsInstrInfo::GetInstSizeInBytes(const MachineInstr *MI) const {
  switch (MI->getOpcode()) {
  default:
    return MI->getDesc().getSize();
  case  TargetOpcode::INLINEASM: {       // Inline Asm: Variable size.
    const MachineFunction *MF = MI->getParent()->getParent();
    const char *AsmStr = MI->getOperand(0).getSymbolName();
    return getInlineAsmLength(AsmStr, *MF->getTarget().getMCAsmInfo());
  }
  }
}

unsigned
llvm::Mips::loadImmediate(int64_t Imm, bool IsN64, const TargetInstrInfo &TII,
                          MachineBasicBlock& MBB,
                          MachineBasicBlock::iterator II, DebugLoc DL,
                          bool LastInstrIsADDiu,
                          MipsAnalyzeImmediate::Inst *LastInst) {
  MipsAnalyzeImmediate AnalyzeImm;
  unsigned Size = IsN64 ? 64 : 32;
  unsigned LUi = IsN64 ? Mips::LUi64 : Mips::LUi;
  unsigned ZEROReg = IsN64 ? Mips::ZERO_64 : Mips::ZERO;
  unsigned ATReg = IsN64 ? Mips::AT_64 : Mips::AT;

  const MipsAnalyzeImmediate::InstSeq &Seq =
    AnalyzeImm.Analyze(Imm, Size, LastInstrIsADDiu);
  MipsAnalyzeImmediate::InstSeq::const_iterator Inst = Seq.begin();

  if (LastInst && (Seq.size() == 1)) {
    *LastInst = *Inst;
    return 0;
  }

  // The first instruction can be a LUi, which is different from other
  // instructions (ADDiu, ORI and SLL) in that it does not have a register
  // operand.
  if (Inst->Opc == LUi)
    BuildMI(MBB, II, DL, TII.get(LUi), ATReg)
      .addImm(SignExtend64<16>(Inst->ImmOpnd));
  else
    BuildMI(MBB, II, DL, TII.get(Inst->Opc), ATReg).addReg(ZEROReg)
      .addImm(SignExtend64<16>(Inst->ImmOpnd));

  // Build the remaining instructions in Seq. Skip the last instruction if
  // LastInst is not 0.
  for (++Inst; Inst != Seq.end() - !!LastInst; ++Inst)
    BuildMI(MBB, II, DL, TII.get(Inst->Opc), ATReg).addReg(ATReg)
      .addImm(SignExtend64<16>(Inst->ImmOpnd));

  if (LastInst)
    *LastInst = *Inst;

  return Seq.size() - !!LastInst;
}