//===-- SystemZFrameLowering.cpp - Frame lowering for SystemZ -------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#include "SystemZFrameLowering.h"
#include "SystemZCallingConv.h"
#include "SystemZInstrInfo.h"
#include "SystemZMachineFunctionInfo.h"
#include "SystemZRegisterInfo.h"
#include "SystemZSubtarget.h"
#include "llvm/CodeGen/LivePhysRegs.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineModuleInfo.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/RegisterScavenging.h"
#include "llvm/CodeGen/TargetLoweringObjectFileImpl.h"
#include "llvm/IR/CallingConv.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/Module.h"
#include "llvm/Target/TargetMachine.h"

using namespace llvm;

namespace {
// The ABI-defined register save slots, relative to the CFA (i.e.
// incoming stack pointer + SystemZMC::ELFCallFrameSize).
static const TargetFrameLowering::SpillSlot ELFSpillOffsetTable[] = {
  { SystemZ::R2D,  0x10 },
  { SystemZ::R3D,  0x18 },
  { SystemZ::R4D,  0x20 },
  { SystemZ::R5D,  0x28 },
  { SystemZ::R6D,  0x30 },
  { SystemZ::R7D,  0x38 },
  { SystemZ::R8D,  0x40 },
  { SystemZ::R9D,  0x48 },
  { SystemZ::R10D, 0x50 },
  { SystemZ::R11D, 0x58 },
  { SystemZ::R12D, 0x60 },
  { SystemZ::R13D, 0x68 },
  { SystemZ::R14D, 0x70 },
  { SystemZ::R15D, 0x78 },
  { SystemZ::F0D,  0x80 },
  { SystemZ::F2D,  0x88 },
  { SystemZ::F4D,  0x90 },
  { SystemZ::F6D,  0x98 }
};

static const TargetFrameLowering::SpillSlot XPLINKSpillOffsetTable[] = {
    {SystemZ::R4D, 0x00},  {SystemZ::R5D, 0x08},  {SystemZ::R6D, 0x10},
    {SystemZ::R7D, 0x18},  {SystemZ::R8D, 0x20},  {SystemZ::R9D, 0x28},
    {SystemZ::R10D, 0x30}, {SystemZ::R11D, 0x38}, {SystemZ::R12D, 0x40},
    {SystemZ::R13D, 0x48}, {SystemZ::R14D, 0x50}, {SystemZ::R15D, 0x58}};
} // end anonymous namespace

SystemZFrameLowering::SystemZFrameLowering(StackDirection D, Align StackAl,
                                           int LAO, Align TransAl,
                                           bool StackReal, unsigned PointerSize)
    : TargetFrameLowering(D, StackAl, LAO, TransAl, StackReal),
      PointerSize(PointerSize) {}

std::unique_ptr<SystemZFrameLowering>
SystemZFrameLowering::create(const SystemZSubtarget &STI) {
  unsigned PtrSz =
      STI.getTargetLowering()->getTargetMachine().getPointerSize(0);
  if (STI.isTargetXPLINK64())
    return std::make_unique<SystemZXPLINKFrameLowering>(PtrSz);
  return std::make_unique<SystemZELFFrameLowering>(PtrSz);
}

namespace {
struct SZFrameSortingObj {
  bool IsValid = false;     // True if we care about this Object.
  uint32_t ObjectIndex = 0; // Index of Object into MFI list.
  uint64_t ObjectSize = 0;  // Size of Object in bytes.
  uint32_t D12Count = 0;    // 12-bit displacement only.
  uint32_t DPairCount = 0;  // 12 or 20 bit displacement.
};
typedef std::vector<SZFrameSortingObj> SZFrameObjVec;
} // namespace

// TODO: Move to base class.
void SystemZELFFrameLowering::orderFrameObjects(
    const MachineFunction &MF, SmallVectorImpl<int> &ObjectsToAllocate) const {
  const MachineFrameInfo &MFI = MF.getFrameInfo();
  auto *TII = MF.getSubtarget<SystemZSubtarget>().getInstrInfo();

  // Make a vector of sorting objects to track all MFI objects and mark those
  // to be sorted as valid.
  if (ObjectsToAllocate.size() <= 1)
    return;
  SZFrameObjVec SortingObjects(MFI.getObjectIndexEnd());
  for (auto &Obj : ObjectsToAllocate) {
    SortingObjects[Obj].IsValid = true;
    SortingObjects[Obj].ObjectIndex = Obj;
    SortingObjects[Obj].ObjectSize = MFI.getObjectSize(Obj);
  }

  // Examine uses for each object and record short (12-bit) and "pair"
  // displacement types.
  for (auto &MBB : MF)
    for (auto &MI : MBB) {
      if (MI.isDebugInstr())
        continue;
      for (unsigned I = 0, E = MI.getNumOperands(); I != E; ++I) {
        const MachineOperand &MO = MI.getOperand(I);
        if (!MO.isFI())
          continue;
        int Index = MO.getIndex();
        if (Index >= 0 && Index < MFI.getObjectIndexEnd() &&
            SortingObjects[Index].IsValid) {
          if (TII->hasDisplacementPairInsn(MI.getOpcode()))
            SortingObjects[Index].DPairCount++;
          else if (!(MI.getDesc().TSFlags & SystemZII::Has20BitOffset))
            SortingObjects[Index].D12Count++;
        }
      }
    }

  // Sort all objects for short/paired displacements, which should be
  // sufficient as it seems like all frame objects typically are within the
  // long displacement range.  Sorting works by computing the "density" as
  // Count / ObjectSize. The comparisons of two such fractions are refactored
  // by multiplying both sides with A.ObjectSize * B.ObjectSize, in order to
  // eliminate the (fp) divisions.  A higher density object needs to go after
  // in the list in order for it to end up lower on the stack.
  auto CmpD12 = [](const SZFrameSortingObj &A, const SZFrameSortingObj &B) {
    // Put all invalid and variable sized objects at the end.
    if (!A.IsValid || !B.IsValid)
      return A.IsValid;
    if (!A.ObjectSize || !B.ObjectSize)
      return A.ObjectSize > 0;
    uint64_t ADensityCmp = A.D12Count * B.ObjectSize;
    uint64_t BDensityCmp = B.D12Count * A.ObjectSize;
    if (ADensityCmp != BDensityCmp)
      return ADensityCmp < BDensityCmp;
    return A.DPairCount * B.ObjectSize < B.DPairCount * A.ObjectSize;
  };
  llvm::stable_sort(SortingObjects, CmpD12);

  // Now modify the original list to represent the final order that
  // we want.
  unsigned Idx = 0;
  for (auto &Obj : SortingObjects) {
    // All invalid items are sorted at the end, so it's safe to stop.
    if (!Obj.IsValid)
      break;
    ObjectsToAllocate[Idx++] = Obj.ObjectIndex;
  }
}

bool SystemZFrameLowering::hasReservedCallFrame(
    const MachineFunction &MF) const {
  // The ELF ABI requires us to allocate 160 bytes of stack space for the
  // callee, with any outgoing stack arguments being placed above that. It
  // seems better to make that area a permanent feature of the frame even if
  // we're using a frame pointer. Similarly, 64-bit XPLINK requires 96 bytes
  // of stack space for the register save area.
  return true;
}

bool SystemZELFFrameLowering::assignCalleeSavedSpillSlots(
    MachineFunction &MF, const TargetRegisterInfo *TRI,
    std::vector<CalleeSavedInfo> &CSI) const {
  SystemZMachineFunctionInfo *ZFI = MF.getInfo<SystemZMachineFunctionInfo>();
  MachineFrameInfo &MFFrame = MF.getFrameInfo();
  bool IsVarArg = MF.getFunction().isVarArg();
  if (CSI.empty())
    return true; // Early exit if no callee saved registers are modified!

  unsigned LowGPR = 0;
  unsigned HighGPR = SystemZ::R15D;
  int StartSPOffset = SystemZMC::ELFCallFrameSize;
  for (auto &CS : CSI) {
    MCRegister Reg = CS.getReg();
    int Offset = getRegSpillOffset(MF, Reg);
    if (Offset) {
      if (SystemZ::GR64BitRegClass.contains(Reg) && StartSPOffset > Offset) {
        LowGPR = Reg;
        StartSPOffset = Offset;
      }
      Offset -= SystemZMC::ELFCallFrameSize;
      int FrameIdx =
          MFFrame.CreateFixedSpillStackObject(getPointerSize(), Offset);
      CS.setFrameIdx(FrameIdx);
    } else
      CS.setFrameIdx(INT32_MAX);
  }

  // Save the range of call-saved registers, for use by the
  // prologue/epilogue inserters.
  ZFI->setRestoreGPRRegs(LowGPR, HighGPR, StartSPOffset);
  if (IsVarArg) {
    // Also save the GPR varargs, if any.  R6D is call-saved, so would
    // already be included, but we also need to handle the call-clobbered
    // argument registers.
    Register FirstGPR = ZFI->getVarArgsFirstGPR();
    if (FirstGPR < SystemZ::ELFNumArgGPRs) {
      unsigned Reg = SystemZ::ELFArgGPRs[FirstGPR];
      int Offset = getRegSpillOffset(MF, Reg);
      if (StartSPOffset > Offset) {
        LowGPR = Reg; StartSPOffset = Offset;
      }
    }
  }
  ZFI->setSpillGPRRegs(LowGPR, HighGPR, StartSPOffset);

  // Create fixed stack objects for the remaining registers.
  int CurrOffset = -SystemZMC::ELFCallFrameSize;
  if (usePackedStack(MF))
    CurrOffset += StartSPOffset;

  for (auto &CS : CSI) {
    if (CS.getFrameIdx() != INT32_MAX)
      continue;
    MCRegister Reg = CS.getReg();
    const TargetRegisterClass *RC = TRI->getMinimalPhysRegClass(Reg);
    unsigned Size = TRI->getSpillSize(*RC);
    CurrOffset -= Size;
    assert(CurrOffset % 8 == 0 &&
           "8-byte alignment required for for all register save slots");
    int FrameIdx = MFFrame.CreateFixedSpillStackObject(Size, CurrOffset);
    CS.setFrameIdx(FrameIdx);
  }

  return true;
}

void SystemZELFFrameLowering::determineCalleeSaves(MachineFunction &MF,
                                                   BitVector &SavedRegs,
                                                   RegScavenger *RS) const {
  TargetFrameLowering::determineCalleeSaves(MF, SavedRegs, RS);

  MachineFrameInfo &MFFrame = MF.getFrameInfo();
  const TargetRegisterInfo *TRI = MF.getSubtarget().getRegisterInfo();
  bool HasFP = hasFP(MF);
  SystemZMachineFunctionInfo *MFI = MF.getInfo<SystemZMachineFunctionInfo>();
  bool IsVarArg = MF.getFunction().isVarArg();

  // va_start stores incoming FPR varargs in the normal way, but delegates
  // the saving of incoming GPR varargs to spillCalleeSavedRegisters().
  // Record these pending uses, which typically include the call-saved
  // argument register R6D.
  if (IsVarArg)
    for (unsigned I = MFI->getVarArgsFirstGPR(); I < SystemZ::ELFNumArgGPRs; ++I)
      SavedRegs.set(SystemZ::ELFArgGPRs[I]);

  // If there are any landing pads, entering them will modify r6/r7.
  if (!MF.getLandingPads().empty()) {
    SavedRegs.set(SystemZ::R6D);
    SavedRegs.set(SystemZ::R7D);
  }

  // If the function requires a frame pointer, record that the hard
  // frame pointer will be clobbered.
  if (HasFP)
    SavedRegs.set(SystemZ::R11D);

  // If the function calls other functions, record that the return
  // address register will be clobbered.
  if (MFFrame.hasCalls())
    SavedRegs.set(SystemZ::R14D);

  // If we are saving GPRs other than the stack pointer, we might as well
  // save and restore the stack pointer at the same time, via STMG and LMG.
  // This allows the deallocation to be done by the LMG, rather than needing
  // a separate %r15 addition.
  const MCPhysReg *CSRegs = TRI->getCalleeSavedRegs(&MF);
  for (unsigned I = 0; CSRegs[I]; ++I) {
    unsigned Reg = CSRegs[I];
    if (SystemZ::GR64BitRegClass.contains(Reg) && SavedRegs.test(Reg)) {
      SavedRegs.set(SystemZ::R15D);
      break;
    }
  }
}

SystemZELFFrameLowering::SystemZELFFrameLowering(unsigned PointerSize)
    : SystemZFrameLowering(TargetFrameLowering::StackGrowsDown, Align(8), 0,
                           Align(8), /* StackRealignable */ false, PointerSize),
      RegSpillOffsets(0) {

  // Due to the SystemZ ABI, the DWARF CFA (Canonical Frame Address) is not
  // equal to the incoming stack pointer, but to incoming stack pointer plus
  // 160.  Instead of using a Local Area Offset, the Register save area will
  // be occupied by fixed frame objects, and all offsets are actually
  // relative to CFA.

  // Create a mapping from register number to save slot offset.
  // These offsets are relative to the start of the register save area.
  RegSpillOffsets.grow(SystemZ::NUM_TARGET_REGS);
  for (const auto &Entry : ELFSpillOffsetTable)
    RegSpillOffsets[Entry.Reg] = Entry.Offset;
}

// Add GPR64 to the save instruction being built by MIB, which is in basic
// block MBB.  IsImplicit says whether this is an explicit operand to the
// instruction, or an implicit one that comes between the explicit start
// and end registers.
static void addSavedGPR(MachineBasicBlock &MBB, MachineInstrBuilder &MIB,
                        unsigned GPR64, bool IsImplicit) {
  const TargetRegisterInfo *RI =
      MBB.getParent()->getSubtarget().getRegisterInfo();
  Register GPR32 = RI->getSubReg(GPR64, SystemZ::subreg_l32);
  bool IsLive = MBB.isLiveIn(GPR64) || MBB.isLiveIn(GPR32);
  if (!IsLive || !IsImplicit) {
    MIB.addReg(GPR64, getImplRegState(IsImplicit) | getKillRegState(!IsLive));
    if (!IsLive)
      MBB.addLiveIn(GPR64);
  }
}

bool SystemZELFFrameLowering::spillCalleeSavedRegisters(
    MachineBasicBlock &MBB, MachineBasicBlock::iterator MBBI,
    ArrayRef<CalleeSavedInfo> CSI, const TargetRegisterInfo *TRI) const {
  if (CSI.empty())
    return false;

  MachineFunction &MF = *MBB.getParent();
  const TargetInstrInfo *TII = MF.getSubtarget().getInstrInfo();
  SystemZMachineFunctionInfo *ZFI = MF.getInfo<SystemZMachineFunctionInfo>();
  bool IsVarArg = MF.getFunction().isVarArg();
  DebugLoc DL;

  // Save GPRs
  SystemZ::GPRRegs SpillGPRs = ZFI->getSpillGPRRegs();
  if (SpillGPRs.LowGPR) {
    assert(SpillGPRs.LowGPR != SpillGPRs.HighGPR &&
           "Should be saving %r15 and something else");

    // Build an STMG instruction.
    MachineInstrBuilder MIB = BuildMI(MBB, MBBI, DL, TII->get(SystemZ::STMG));

    // Add the explicit register operands.
    addSavedGPR(MBB, MIB, SpillGPRs.LowGPR, false);
    addSavedGPR(MBB, MIB, SpillGPRs.HighGPR, false);

    // Add the address.
    MIB.addReg(SystemZ::R15D).addImm(SpillGPRs.GPROffset);

    // Make sure all call-saved GPRs are included as operands and are
    // marked as live on entry.
    for (const CalleeSavedInfo &I : CSI) {
      MCRegister Reg = I.getReg();
      if (SystemZ::GR64BitRegClass.contains(Reg))
        addSavedGPR(MBB, MIB, Reg, true);
    }

    // ...likewise GPR varargs.
    if (IsVarArg)
      for (unsigned I = ZFI->getVarArgsFirstGPR(); I < SystemZ::ELFNumArgGPRs; ++I)
        addSavedGPR(MBB, MIB, SystemZ::ELFArgGPRs[I], true);
  }

  // Save FPRs/VRs in the normal TargetInstrInfo way.
  for (const CalleeSavedInfo &I : CSI) {
    MCRegister Reg = I.getReg();
    if (SystemZ::FP64BitRegClass.contains(Reg)) {
      MBB.addLiveIn(Reg);
      TII->storeRegToStackSlot(MBB, MBBI, Reg, true, I.getFrameIdx(),
                               &SystemZ::FP64BitRegClass, TRI, Register());
    }
    if (SystemZ::VR128BitRegClass.contains(Reg)) {
      MBB.addLiveIn(Reg);
      TII->storeRegToStackSlot(MBB, MBBI, Reg, true, I.getFrameIdx(),
                               &SystemZ::VR128BitRegClass, TRI, Register());
    }
  }

  return true;
}

bool SystemZELFFrameLowering::restoreCalleeSavedRegisters(
    MachineBasicBlock &MBB, MachineBasicBlock::iterator MBBI,
    MutableArrayRef<CalleeSavedInfo> CSI, const TargetRegisterInfo *TRI) const {
  if (CSI.empty())
    return false;

  MachineFunction &MF = *MBB.getParent();
  const TargetInstrInfo *TII = MF.getSubtarget().getInstrInfo();
  SystemZMachineFunctionInfo *ZFI = MF.getInfo<SystemZMachineFunctionInfo>();
  bool HasFP = hasFP(MF);
  DebugLoc DL = MBBI != MBB.end() ? MBBI->getDebugLoc() : DebugLoc();

  // Restore FPRs/VRs in the normal TargetInstrInfo way.
  for (const CalleeSavedInfo &I : CSI) {
    MCRegister Reg = I.getReg();
    if (SystemZ::FP64BitRegClass.contains(Reg))
      TII->loadRegFromStackSlot(MBB, MBBI, Reg, I.getFrameIdx(),
                                &SystemZ::FP64BitRegClass, TRI, Register());
    if (SystemZ::VR128BitRegClass.contains(Reg))
      TII->loadRegFromStackSlot(MBB, MBBI, Reg, I.getFrameIdx(),
                                &SystemZ::VR128BitRegClass, TRI, Register());
  }

  // Restore call-saved GPRs (but not call-clobbered varargs, which at
  // this point might hold return values).
  SystemZ::GPRRegs RestoreGPRs = ZFI->getRestoreGPRRegs();
  if (RestoreGPRs.LowGPR) {
    // If we saved any of %r2-%r5 as varargs, we should also be saving
    // and restoring %r6.  If we're saving %r6 or above, we should be
    // restoring it too.
    assert(RestoreGPRs.LowGPR != RestoreGPRs.HighGPR &&
           "Should be loading %r15 and something else");

    // Build an LMG instruction.
    MachineInstrBuilder MIB = BuildMI(MBB, MBBI, DL, TII->get(SystemZ::LMG));

    // Add the explicit register operands.
    MIB.addReg(RestoreGPRs.LowGPR, RegState::Define);
    MIB.addReg(RestoreGPRs.HighGPR, RegState::Define);

    // Add the address.
    MIB.addReg(HasFP ? SystemZ::R11D : SystemZ::R15D);
    MIB.addImm(RestoreGPRs.GPROffset);

    // Do a second scan adding regs as being defined by instruction
    for (const CalleeSavedInfo &I : CSI) {
      MCRegister Reg = I.getReg();
      if (Reg != RestoreGPRs.LowGPR && Reg != RestoreGPRs.HighGPR &&
          SystemZ::GR64BitRegClass.contains(Reg))
        MIB.addReg(Reg, RegState::ImplicitDefine);
    }
  }

  return true;
}

void SystemZELFFrameLowering::processFunctionBeforeFrameFinalized(
    MachineFunction &MF, RegScavenger *RS) const {
  MachineFrameInfo &MFFrame = MF.getFrameInfo();
  SystemZMachineFunctionInfo *ZFI = MF.getInfo<SystemZMachineFunctionInfo>();
  MachineRegisterInfo *MRI = &MF.getRegInfo();
  bool BackChain = MF.getSubtarget<SystemZSubtarget>().hasBackChain();

  if (!usePackedStack(MF) || BackChain)
    // Create the incoming register save area.
    getOrCreateFramePointerSaveIndex(MF);

  // Get the size of our stack frame to be allocated ...
  uint64_t StackSize = (MFFrame.estimateStackSize(MF) +
                        SystemZMC::ELFCallFrameSize);
  // ... and the maximum offset we may need to reach into the
  // caller's frame to access the save area or stack arguments.
  int64_t MaxArgOffset = 0;
  for (int I = MFFrame.getObjectIndexBegin(); I != 0; ++I)
    if (MFFrame.getObjectOffset(I) >= 0) {
      int64_t ArgOffset = MFFrame.getObjectOffset(I) +
                          MFFrame.getObjectSize(I);
      MaxArgOffset = std::max(MaxArgOffset, ArgOffset);
    }

  uint64_t MaxReach = StackSize + MaxArgOffset;
  if (!isUInt<12>(MaxReach)) {
    // We may need register scavenging slots if some parts of the frame
    // are outside the reach of an unsigned 12-bit displacement.
    // Create 2 for the case where both addresses in an MVC are
    // out of range.
    RS->addScavengingFrameIndex(
        MFFrame.CreateSpillStackObject(getPointerSize(), Align(8)));
    RS->addScavengingFrameIndex(
        MFFrame.CreateSpillStackObject(getPointerSize(), Align(8)));
  }

  // If R6 is used as an argument register it is still callee saved. If it in
  // this case is not clobbered (and restored) it should never be marked as
  // killed.
  if (MF.front().isLiveIn(SystemZ::R6D) &&
      ZFI->getRestoreGPRRegs().LowGPR != SystemZ::R6D)
    for (auto &MO : MRI->use_nodbg_operands(SystemZ::R6D))
      MO.setIsKill(false);
}

// Emit instructions before MBBI (in MBB) to add NumBytes to Reg.
static void emitIncrement(MachineBasicBlock &MBB,
                          MachineBasicBlock::iterator &MBBI, const DebugLoc &DL,
                          Register Reg, int64_t NumBytes,
                          const TargetInstrInfo *TII) {
  while (NumBytes) {
    unsigned Opcode;
    int64_t ThisVal = NumBytes;
    if (isInt<16>(NumBytes))
      Opcode = SystemZ::AGHI;
    else {
      Opcode = SystemZ::AGFI;
      // Make sure we maintain 8-byte stack alignment.
      int64_t MinVal = -uint64_t(1) << 31;
      int64_t MaxVal = (int64_t(1) << 31) - 8;
      if (ThisVal < MinVal)
        ThisVal = MinVal;
      else if (ThisVal > MaxVal)
        ThisVal = MaxVal;
    }
    MachineInstr *MI = BuildMI(MBB, MBBI, DL, TII->get(Opcode), Reg)
      .addReg(Reg).addImm(ThisVal);
    // The CC implicit def is dead.
    MI->getOperand(3).setIsDead();
    NumBytes -= ThisVal;
  }
}

// Add CFI for the new CFA offset.
static void buildCFAOffs(MachineBasicBlock &MBB,
                         MachineBasicBlock::iterator MBBI,
                         const DebugLoc &DL, int Offset,
                         const SystemZInstrInfo *ZII) {
  unsigned CFIIndex = MBB.getParent()->addFrameInst(
    MCCFIInstruction::cfiDefCfaOffset(nullptr, -Offset));
  BuildMI(MBB, MBBI, DL, ZII->get(TargetOpcode::CFI_INSTRUCTION))
    .addCFIIndex(CFIIndex);
}

// Add CFI for the new frame location.
static void buildDefCFAReg(MachineBasicBlock &MBB,
                           MachineBasicBlock::iterator MBBI,
                           const DebugLoc &DL, unsigned Reg,
                           const SystemZInstrInfo *ZII) {
  MachineFunction &MF = *MBB.getParent();
  const MCRegisterInfo *MRI = MF.getContext().getRegisterInfo();
  unsigned RegNum = MRI->getDwarfRegNum(Reg, true);
  unsigned CFIIndex = MF.addFrameInst(
                        MCCFIInstruction::createDefCfaRegister(nullptr, RegNum));
  BuildMI(MBB, MBBI, DL, ZII->get(TargetOpcode::CFI_INSTRUCTION))
    .addCFIIndex(CFIIndex);
}

void SystemZELFFrameLowering::emitPrologue(MachineFunction &MF,
                                           MachineBasicBlock &MBB) const {
  assert(&MF.front() == &MBB && "Shrink-wrapping not yet supported");
  const SystemZSubtarget &STI = MF.getSubtarget<SystemZSubtarget>();
  const SystemZTargetLowering &TLI = *STI.getTargetLowering();
  MachineFrameInfo &MFFrame = MF.getFrameInfo();
  auto *ZII = STI.getInstrInfo();
  SystemZMachineFunctionInfo *ZFI = MF.getInfo<SystemZMachineFunctionInfo>();
  MachineBasicBlock::iterator MBBI = MBB.begin();
  const MCRegisterInfo *MRI = MF.getContext().getRegisterInfo();
  const std::vector<CalleeSavedInfo> &CSI = MFFrame.getCalleeSavedInfo();
  bool HasFP = hasFP(MF);

  // In GHC calling convention C stack space, including the ABI-defined
  // 160-byte base area, is (de)allocated by GHC itself.  This stack space may
  // be used by LLVM as spill slots for the tail recursive GHC functions.  Thus
  // do not allocate stack space here, too.
  if (MF.getFunction().getCallingConv() == CallingConv::GHC) {
    if (MFFrame.getStackSize() > 2048 * sizeof(long)) {
      report_fatal_error(
          "Pre allocated stack space for GHC function is too small");
    }
    if (HasFP) {
      report_fatal_error(
          "In GHC calling convention a frame pointer is not supported");
    }
    MFFrame.setStackSize(MFFrame.getStackSize() + SystemZMC::ELFCallFrameSize);
    return;
  }

  // Debug location must be unknown since the first debug location is used
  // to determine the end of the prologue.
  DebugLoc DL;
  // Add mcount instrumentation if necessary.
  if (MF.getFunction()
          .getFnAttribute("systemz-instrument-function-entry")
          .getValueAsString() == "mcount") {

    // Store return address 8 bytes above stack pointer.
    BuildMI(MBB, MBBI, DL, ZII->get(SystemZ::STG))
        .addReg(SystemZ::R14D)
        .addReg(SystemZ::R15D)
        .addImm(8)
        .addReg(0);

    // Call mcount (Regmask from CC AnyReg since mcount preserves all normal
    // argument registers).
    const uint32_t *Mask = MF.getSubtarget<SystemZSubtarget>()
                               .getSpecialRegisters()
                               ->getCallPreservedMask(MF, CallingConv::AnyReg);
    BuildMI(MBB, MBBI, DL, ZII->get(SystemZ::CallBRASL))
        .addExternalSymbol("mcount")
        .addRegMask(Mask);

    // Reload return address from 8 bytes above stack pointer.
    BuildMI(MBB, MBBI, DL, ZII->get(SystemZ::LG))
        .addReg(SystemZ::R14D, RegState::Define)
        .addReg(SystemZ::R15D)
        .addImm(8)
        .addReg(0);
  }

  // The current offset of the stack pointer from the CFA.
  int64_t SPOffsetFromCFA = -SystemZMC::ELFCFAOffsetFromInitialSP;

  if (ZFI->getSpillGPRRegs().LowGPR) {
    // Skip over the GPR saves.
    if (MBBI != MBB.end() && MBBI->getOpcode() == SystemZ::STMG)
      ++MBBI;
    else
      llvm_unreachable("Couldn't skip over GPR saves");

    // Add CFI for the GPR saves.
    for (auto &Save : CSI) {
      MCRegister Reg = Save.getReg();
      if (SystemZ::GR64BitRegClass.contains(Reg)) {
        int FI = Save.getFrameIdx();
        int64_t Offset = MFFrame.getObjectOffset(FI);
        unsigned CFIIndex = MF.addFrameInst(MCCFIInstruction::createOffset(
            nullptr, MRI->getDwarfRegNum(Reg, true), Offset));
        BuildMI(MBB, MBBI, DL, ZII->get(TargetOpcode::CFI_INSTRUCTION))
            .addCFIIndex(CFIIndex);
      }
    }
  }

  uint64_t StackSize = MFFrame.getStackSize();
  // We need to allocate the ABI-defined 160-byte base area whenever
  // we allocate stack space for our own use and whenever we call another
  // function.
  bool HasStackObject = false;
  for (unsigned i = 0, e = MFFrame.getObjectIndexEnd(); i != e; ++i)
    if (!MFFrame.isDeadObjectIndex(i)) {
      HasStackObject = true;
      break;
    }
  if (HasStackObject || MFFrame.hasCalls())
    StackSize += SystemZMC::ELFCallFrameSize;
  // Don't allocate the incoming reg save area.
  StackSize = StackSize > SystemZMC::ELFCallFrameSize
                  ? StackSize - SystemZMC::ELFCallFrameSize
                  : 0;
  MFFrame.setStackSize(StackSize);

  if (StackSize) {
    // Allocate StackSize bytes.
    int64_t Delta = -int64_t(StackSize);
    const unsigned ProbeSize = TLI.getStackProbeSize(MF);
    bool FreeProbe = (ZFI->getSpillGPRRegs().GPROffset &&
           (ZFI->getSpillGPRRegs().GPROffset + StackSize) < ProbeSize);
    if (!FreeProbe &&
        MF.getSubtarget().getTargetLowering()->hasInlineStackProbe(MF)) {
      // Stack probing may involve looping, but splitting the prologue block
      // is not possible at this point since it would invalidate the
      // SaveBlocks / RestoreBlocks sets of PEI in the single block function
      // case. Build a pseudo to be handled later by inlineStackProbe().
      BuildMI(MBB, MBBI, DL, ZII->get(SystemZ::PROBED_STACKALLOC))
        .addImm(StackSize);
    }
    else {
      bool StoreBackchain = MF.getSubtarget<SystemZSubtarget>().hasBackChain();
      // If we need backchain, save current stack pointer.  R1 is free at
      // this point.
      if (StoreBackchain)
        BuildMI(MBB, MBBI, DL, ZII->get(SystemZ::LGR))
          .addReg(SystemZ::R1D, RegState::Define).addReg(SystemZ::R15D);
      emitIncrement(MBB, MBBI, DL, SystemZ::R15D, Delta, ZII);
      buildCFAOffs(MBB, MBBI, DL, SPOffsetFromCFA + Delta, ZII);
      if (StoreBackchain)
        BuildMI(MBB, MBBI, DL, ZII->get(SystemZ::STG))
          .addReg(SystemZ::R1D, RegState::Kill).addReg(SystemZ::R15D)
          .addImm(getBackchainOffset(MF)).addReg(0);
    }
    SPOffsetFromCFA += Delta;
  }

  if (HasFP) {
    // Copy the base of the frame to R11.
    BuildMI(MBB, MBBI, DL, ZII->get(SystemZ::LGR), SystemZ::R11D)
      .addReg(SystemZ::R15D);

    // Add CFI for the new frame location.
    buildDefCFAReg(MBB, MBBI, DL, SystemZ::R11D, ZII);

    // Mark the FramePtr as live at the beginning of every block except
    // the entry block.  (We'll have marked R11 as live on entry when
    // saving the GPRs.)
    for (MachineBasicBlock &MBBJ : llvm::drop_begin(MF))
      MBBJ.addLiveIn(SystemZ::R11D);
  }

  // Skip over the FPR/VR saves.
  SmallVector<unsigned, 8> CFIIndexes;
  for (auto &Save : CSI) {
    MCRegister Reg = Save.getReg();
    if (SystemZ::FP64BitRegClass.contains(Reg)) {
      if (MBBI != MBB.end() &&
          (MBBI->getOpcode() == SystemZ::STD ||
           MBBI->getOpcode() == SystemZ::STDY))
        ++MBBI;
      else
        llvm_unreachable("Couldn't skip over FPR save");
    } else if (SystemZ::VR128BitRegClass.contains(Reg)) {
      if (MBBI != MBB.end() &&
          MBBI->getOpcode() == SystemZ::VST)
        ++MBBI;
      else
        llvm_unreachable("Couldn't skip over VR save");
    } else
      continue;

    // Add CFI for the this save.
    unsigned DwarfReg = MRI->getDwarfRegNum(Reg, true);
    Register IgnoredFrameReg;
    int64_t Offset =
        getFrameIndexReference(MF, Save.getFrameIdx(), IgnoredFrameReg)
            .getFixed();

    unsigned CFIIndex = MF.addFrameInst(MCCFIInstruction::createOffset(
          nullptr, DwarfReg, SPOffsetFromCFA + Offset));
    CFIIndexes.push_back(CFIIndex);
  }
  // Complete the CFI for the FPR/VR saves, modelling them as taking effect
  // after the last save.
  for (auto CFIIndex : CFIIndexes) {
    BuildMI(MBB, MBBI, DL, ZII->get(TargetOpcode::CFI_INSTRUCTION))
        .addCFIIndex(CFIIndex);
  }
}

void SystemZELFFrameLowering::emitEpilogue(MachineFunction &MF,
                                           MachineBasicBlock &MBB) const {
  MachineBasicBlock::iterator MBBI = MBB.getLastNonDebugInstr();
  auto *ZII =
      static_cast<const SystemZInstrInfo *>(MF.getSubtarget().getInstrInfo());
  SystemZMachineFunctionInfo *ZFI = MF.getInfo<SystemZMachineFunctionInfo>();
  MachineFrameInfo &MFFrame = MF.getFrameInfo();

  // See SystemZELFFrameLowering::emitPrologue
  if (MF.getFunction().getCallingConv() == CallingConv::GHC)
    return;

  // Skip the return instruction.
  assert(MBBI->isReturn() && "Can only insert epilogue into returning blocks");

  uint64_t StackSize = MFFrame.getStackSize();
  if (ZFI->getRestoreGPRRegs().LowGPR) {
    --MBBI;
    unsigned Opcode = MBBI->getOpcode();
    if (Opcode != SystemZ::LMG)
      llvm_unreachable("Expected to see callee-save register restore code");

    unsigned AddrOpNo = 2;
    DebugLoc DL = MBBI->getDebugLoc();
    uint64_t Offset = StackSize + MBBI->getOperand(AddrOpNo + 1).getImm();
    unsigned NewOpcode = ZII->getOpcodeForOffset(Opcode, Offset);

    // If the offset is too large, use the largest stack-aligned offset
    // and add the rest to the base register (the stack or frame pointer).
    if (!NewOpcode) {
      uint64_t NumBytes = Offset - 0x7fff8;
      emitIncrement(MBB, MBBI, DL, MBBI->getOperand(AddrOpNo).getReg(),
                    NumBytes, ZII);
      Offset -= NumBytes;
      NewOpcode = ZII->getOpcodeForOffset(Opcode, Offset);
      assert(NewOpcode && "No restore instruction available");
    }

    MBBI->setDesc(ZII->get(NewOpcode));
    MBBI->getOperand(AddrOpNo + 1).ChangeToImmediate(Offset);
  } else if (StackSize) {
    DebugLoc DL = MBBI->getDebugLoc();
    emitIncrement(MBB, MBBI, DL, SystemZ::R15D, StackSize, ZII);
  }
}

void SystemZELFFrameLowering::inlineStackProbe(
    MachineFunction &MF, MachineBasicBlock &PrologMBB) const {
  auto *ZII =
    static_cast<const SystemZInstrInfo *>(MF.getSubtarget().getInstrInfo());
  const SystemZSubtarget &STI = MF.getSubtarget<SystemZSubtarget>();
  const SystemZTargetLowering &TLI = *STI.getTargetLowering();

  MachineInstr *StackAllocMI = nullptr;
  for (MachineInstr &MI : PrologMBB)
    if (MI.getOpcode() == SystemZ::PROBED_STACKALLOC) {
      StackAllocMI = &MI;
      break;
    }
  if (StackAllocMI == nullptr)
    return;
  uint64_t StackSize = StackAllocMI->getOperand(0).getImm();
  const unsigned ProbeSize = TLI.getStackProbeSize(MF);
  uint64_t NumFullBlocks = StackSize / ProbeSize;
  uint64_t Residual = StackSize % ProbeSize;
  int64_t SPOffsetFromCFA = -SystemZMC::ELFCFAOffsetFromInitialSP;
  MachineBasicBlock *MBB = &PrologMBB;
  MachineBasicBlock::iterator MBBI = StackAllocMI;
  const DebugLoc DL = StackAllocMI->getDebugLoc();

  // Allocate a block of Size bytes on the stack and probe it.
  auto allocateAndProbe = [&](MachineBasicBlock &InsMBB,
                              MachineBasicBlock::iterator InsPt, unsigned Size,
                              bool EmitCFI) -> void {
    emitIncrement(InsMBB, InsPt, DL, SystemZ::R15D, -int64_t(Size), ZII);
    if (EmitCFI) {
      SPOffsetFromCFA -= Size;
      buildCFAOffs(InsMBB, InsPt, DL, SPOffsetFromCFA, ZII);
    }
    // Probe by means of a volatile compare.
    MachineMemOperand *MMO = MF.getMachineMemOperand(MachinePointerInfo(),
      MachineMemOperand::MOVolatile | MachineMemOperand::MOLoad, 8, Align(1));
    BuildMI(InsMBB, InsPt, DL, ZII->get(SystemZ::CG))
      .addReg(SystemZ::R0D, RegState::Undef)
      .addReg(SystemZ::R15D).addImm(Size - 8).addReg(0)
      .addMemOperand(MMO);
  };

  bool StoreBackchain = MF.getSubtarget<SystemZSubtarget>().hasBackChain();
  if (StoreBackchain)
    BuildMI(*MBB, MBBI, DL, ZII->get(SystemZ::LGR))
      .addReg(SystemZ::R1D, RegState::Define).addReg(SystemZ::R15D);

  MachineBasicBlock *DoneMBB = nullptr;
  MachineBasicBlock *LoopMBB = nullptr;
  if (NumFullBlocks < 3) {
    // Emit unrolled probe statements.
    for (unsigned int i = 0; i < NumFullBlocks; i++)
      allocateAndProbe(*MBB, MBBI, ProbeSize, true/*EmitCFI*/);
  } else {
    // Emit a loop probing the pages.
    uint64_t LoopAlloc = ProbeSize * NumFullBlocks;
    SPOffsetFromCFA -= LoopAlloc;

    // Use R0D to hold the exit value.
    BuildMI(*MBB, MBBI, DL, ZII->get(SystemZ::LGR), SystemZ::R0D)
      .addReg(SystemZ::R15D);
    buildDefCFAReg(*MBB, MBBI, DL, SystemZ::R0D, ZII);
    emitIncrement(*MBB, MBBI, DL, SystemZ::R0D, -int64_t(LoopAlloc), ZII);
    buildCFAOffs(*MBB, MBBI, DL, -int64_t(SystemZMC::ELFCallFrameSize + LoopAlloc),
                 ZII);

    DoneMBB = SystemZ::splitBlockBefore(MBBI, MBB);
    LoopMBB = SystemZ::emitBlockAfter(MBB);
    MBB->addSuccessor(LoopMBB);
    LoopMBB->addSuccessor(LoopMBB);
    LoopMBB->addSuccessor(DoneMBB);

    MBB = LoopMBB;
    allocateAndProbe(*MBB, MBB->end(), ProbeSize, false/*EmitCFI*/);
    BuildMI(*MBB, MBB->end(), DL, ZII->get(SystemZ::CLGR))
      .addReg(SystemZ::R15D).addReg(SystemZ::R0D);
    BuildMI(*MBB, MBB->end(), DL, ZII->get(SystemZ::BRC))
      .addImm(SystemZ::CCMASK_ICMP).addImm(SystemZ::CCMASK_CMP_GT).addMBB(MBB);

    MBB = DoneMBB;
    MBBI = DoneMBB->begin();
    buildDefCFAReg(*MBB, MBBI, DL, SystemZ::R15D, ZII);
  }

  if (Residual)
    allocateAndProbe(*MBB, MBBI, Residual, true/*EmitCFI*/);

  if (StoreBackchain)
    BuildMI(*MBB, MBBI, DL, ZII->get(SystemZ::STG))
      .addReg(SystemZ::R1D, RegState::Kill).addReg(SystemZ::R15D)
      .addImm(getBackchainOffset(MF)).addReg(0);

  StackAllocMI->eraseFromParent();
  if (DoneMBB != nullptr) {
    // Compute the live-in lists for the new blocks.
    fullyRecomputeLiveIns({DoneMBB, LoopMBB});
  }
}

bool SystemZELFFrameLowering::hasFPImpl(const MachineFunction &MF) const {
  return (MF.getTarget().Options.DisableFramePointerElim(MF) ||
          MF.getFrameInfo().hasVarSizedObjects());
}

StackOffset SystemZELFFrameLowering::getFrameIndexReference(
    const MachineFunction &MF, int FI, Register &FrameReg) const {
  // Our incoming SP is actually SystemZMC::ELFCallFrameSize below the CFA, so
  // add that difference here.
  StackOffset Offset =
      TargetFrameLowering::getFrameIndexReference(MF, FI, FrameReg);
  return Offset + StackOffset::getFixed(SystemZMC::ELFCallFrameSize);
}

unsigned SystemZELFFrameLowering::getRegSpillOffset(MachineFunction &MF,
                                                    Register Reg) const {
  bool IsVarArg = MF.getFunction().isVarArg();
  const SystemZSubtarget &Subtarget = MF.getSubtarget<SystemZSubtarget>();
  bool BackChain = Subtarget.hasBackChain();
  bool SoftFloat = Subtarget.hasSoftFloat();
  unsigned Offset = RegSpillOffsets[Reg];
  if (usePackedStack(MF) && !(IsVarArg && !SoftFloat)) {
    if (SystemZ::GR64BitRegClass.contains(Reg))
      // Put all GPRs at the top of the Register save area with packed
      // stack. Make room for the backchain if needed.
      Offset += BackChain ? 24 : 32;
    else
      Offset = 0;
  }
  return Offset;
}

int SystemZELFFrameLowering::getOrCreateFramePointerSaveIndex(
    MachineFunction &MF) const {
  SystemZMachineFunctionInfo *ZFI = MF.getInfo<SystemZMachineFunctionInfo>();
  int FI = ZFI->getFramePointerSaveIndex();
  if (!FI) {
    MachineFrameInfo &MFFrame = MF.getFrameInfo();
    int Offset = getBackchainOffset(MF) - SystemZMC::ELFCallFrameSize;
    FI = MFFrame.CreateFixedObject(getPointerSize(), Offset, false);
    ZFI->setFramePointerSaveIndex(FI);
  }
  return FI;
}

bool SystemZELFFrameLowering::usePackedStack(MachineFunction &MF) const {
  bool HasPackedStackAttr = MF.getFunction().hasFnAttribute("packed-stack");
  const SystemZSubtarget &Subtarget = MF.getSubtarget<SystemZSubtarget>();
  bool BackChain = Subtarget.hasBackChain();
  bool SoftFloat = Subtarget.hasSoftFloat();
  if (HasPackedStackAttr && BackChain && !SoftFloat)
    report_fatal_error("packed-stack + backchain + hard-float is unsupported.");
  bool CallConv = MF.getFunction().getCallingConv() != CallingConv::GHC;
  return HasPackedStackAttr && CallConv;
}

SystemZXPLINKFrameLowering::SystemZXPLINKFrameLowering(unsigned PointerSize)
    : SystemZFrameLowering(TargetFrameLowering::StackGrowsDown, Align(32), 0,
                           Align(32), /* StackRealignable */ false,
                           PointerSize),
      RegSpillOffsets(-1) {

  // Create a mapping from register number to save slot offset.
  // These offsets are relative to the start of the local are area.
  RegSpillOffsets.grow(SystemZ::NUM_TARGET_REGS);
  for (const auto &Entry : XPLINKSpillOffsetTable)
    RegSpillOffsets[Entry.Reg] = Entry.Offset;
}

int SystemZXPLINKFrameLowering::getOrCreateFramePointerSaveIndex(
    MachineFunction &MF) const {
  SystemZMachineFunctionInfo *ZFI = MF.getInfo<SystemZMachineFunctionInfo>();
  int FI = ZFI->getFramePointerSaveIndex();
  if (!FI) {
    MachineFrameInfo &MFFrame = MF.getFrameInfo();
    FI = MFFrame.CreateFixedObject(getPointerSize(), 0, false);
    MFFrame.setStackID(FI, TargetStackID::NoAlloc);
    ZFI->setFramePointerSaveIndex(FI);
  }
  return FI;
}

// Checks if the function is a potential candidate for being a XPLeaf routine.
static bool isXPLeafCandidate(const MachineFunction &MF) {
  const MachineFrameInfo &MFFrame = MF.getFrameInfo();
  const MachineRegisterInfo &MRI = MF.getRegInfo();
  const SystemZSubtarget &Subtarget = MF.getSubtarget<SystemZSubtarget>();
  auto *Regs =
      static_cast<SystemZXPLINK64Registers *>(Subtarget.getSpecialRegisters());

  // If function calls other functions including alloca, then it is not a XPLeaf
  // routine.
  if (MFFrame.hasCalls())
    return false;

  // If the function has var Sized Objects, then it is not a XPLeaf routine.
  if (MFFrame.hasVarSizedObjects())
    return false;

  // If the function adjusts the stack, then it is not a XPLeaf routine.
  if (MFFrame.adjustsStack())
    return false;

  // If function modifies the stack pointer register, then it is not a XPLeaf
  // routine.
  if (MRI.isPhysRegModified(Regs->getStackPointerRegister()))
    return false;

  // If function modifies the ADA register, then it is not a XPLeaf routine.
  if (MRI.isPhysRegModified(Regs->getAddressOfCalleeRegister()))
    return false;

  // If function modifies the return address register, then it is not a XPLeaf
  // routine.
  if (MRI.isPhysRegModified(Regs->getReturnFunctionAddressRegister()))
    return false;

  // If the backchain pointer should be stored, then it is not a XPLeaf routine.
  if (MF.getSubtarget<SystemZSubtarget>().hasBackChain())
    return false;

  // If function acquires its own stack frame, then it is not a XPLeaf routine.
  // At the time this function is called, only slots for local variables are
  // allocated, so this is a very rough estimate.
  if (MFFrame.estimateStackSize(MF) > 0)
    return false;

  return true;
}

bool SystemZXPLINKFrameLowering::assignCalleeSavedSpillSlots(
    MachineFunction &MF, const TargetRegisterInfo *TRI,
    std::vector<CalleeSavedInfo> &CSI) const {
  MachineFrameInfo &MFFrame = MF.getFrameInfo();
  SystemZMachineFunctionInfo *MFI = MF.getInfo<SystemZMachineFunctionInfo>();
  const SystemZSubtarget &Subtarget = MF.getSubtarget<SystemZSubtarget>();
  auto &Regs = Subtarget.getSpecialRegisters<SystemZXPLINK64Registers>();
  auto &GRRegClass = SystemZ::GR64BitRegClass;

  // At this point, the result of isXPLeafCandidate() is not accurate because
  // the size of the save area has not yet been determined. If
  // isXPLeafCandidate() indicates a potential leaf function, and there are no
  // callee-save registers, then it is indeed a leaf function, and we can early
  // exit.
  // TODO: It is possible for leaf functions to use callee-saved registers.
  // It can use the 0-2k range between R4 and the caller's stack frame without
  // acquiring its own stack frame.
  bool IsLeaf = CSI.empty() && isXPLeafCandidate(MF);
  if (IsLeaf)
    return true;

  // For non-leaf functions:
  // - the address of callee (entry point) register R6 must be saved
  CSI.push_back(CalleeSavedInfo(Regs.getAddressOfCalleeRegister()));
  CSI.back().setRestored(false);

  // The return address register R7 must be saved and restored.
  CSI.push_back(CalleeSavedInfo(Regs.getReturnFunctionAddressRegister()));

  // If the function needs a frame pointer, or if the backchain pointer should
  // be stored, then save the stack pointer register R4.
  if (hasFP(MF) || Subtarget.hasBackChain())
    CSI.push_back(CalleeSavedInfo(Regs.getStackPointerRegister()));

  // If this function has an associated personality function then the
  // environment register R5 must be saved in the DSA.
  if (!MF.getLandingPads().empty())
    CSI.push_back(CalleeSavedInfo(Regs.getADARegister()));

  // Scan the call-saved GPRs and find the bounds of the register spill area.
  Register LowRestoreGPR = 0;
  int LowRestoreOffset = INT32_MAX;
  Register LowSpillGPR = 0;
  int LowSpillOffset = INT32_MAX;
  Register HighGPR = 0;
  int HighOffset = -1;

  // Query index of the saved frame pointer.
  int FPSI = MFI->getFramePointerSaveIndex();

  for (auto &CS : CSI) {
    MCRegister Reg = CS.getReg();
    int Offset = RegSpillOffsets[Reg];
    if (Offset >= 0) {
      if (GRRegClass.contains(Reg)) {
        if (LowSpillOffset > Offset) {
          LowSpillOffset = Offset;
          LowSpillGPR = Reg;
        }
        if (CS.isRestored() && LowRestoreOffset > Offset) {
          LowRestoreOffset = Offset;
          LowRestoreGPR = Reg;
        }

        if (Offset > HighOffset) {
          HighOffset = Offset;
          HighGPR = Reg;
        }
        // Non-volatile GPRs are saved in the dedicated register save area at
        // the bottom of the stack and are not truly part of the "normal" stack
        // frame. Mark the frame index as NoAlloc to indicate it as such.
        unsigned RegSize = getPointerSize();
        int FrameIdx =
            (FPSI && Offset == 0)
                ? FPSI
                : MFFrame.CreateFixedSpillStackObject(RegSize, Offset);
        CS.setFrameIdx(FrameIdx);
        MFFrame.setStackID(FrameIdx, TargetStackID::NoAlloc);
      }
    } else {
      MCRegister Reg = CS.getReg();
      const TargetRegisterClass *RC = TRI->getMinimalPhysRegClass(Reg);
      Align Alignment = TRI->getSpillAlign(*RC);
      unsigned Size = TRI->getSpillSize(*RC);
      Alignment = std::min(Alignment, getStackAlign());
      int FrameIdx = MFFrame.CreateStackObject(Size, Alignment, true);
      CS.setFrameIdx(FrameIdx);
    }
  }

  // Save the range of call-saved registers, for use by the
  // prologue/epilogue inserters.
  if (LowRestoreGPR)
    MFI->setRestoreGPRRegs(LowRestoreGPR, HighGPR, LowRestoreOffset);

  // Save the range of call-saved registers, for use by the epilogue inserter.
  assert(LowSpillGPR && "Expected registers to spill");
  MFI->setSpillGPRRegs(LowSpillGPR, HighGPR, LowSpillOffset);

  return true;
}

void SystemZXPLINKFrameLowering::determineCalleeSaves(MachineFunction &MF,
                                                      BitVector &SavedRegs,
                                                      RegScavenger *RS) const {
  TargetFrameLowering::determineCalleeSaves(MF, SavedRegs, RS);

  bool HasFP = hasFP(MF);
  const SystemZSubtarget &Subtarget = MF.getSubtarget<SystemZSubtarget>();
  auto &Regs = Subtarget.getSpecialRegisters<SystemZXPLINK64Registers>();

  // If the function requires a frame pointer, record that the hard
  // frame pointer will be clobbered.
  if (HasFP)
    SavedRegs.set(Regs.getFramePointerRegister());
}

bool SystemZXPLINKFrameLowering::spillCalleeSavedRegisters(
    MachineBasicBlock &MBB, MachineBasicBlock::iterator MBBI,
    ArrayRef<CalleeSavedInfo> CSI, const TargetRegisterInfo *TRI) const {
  if (CSI.empty())
    return true;

  MachineFunction &MF = *MBB.getParent();
  SystemZMachineFunctionInfo *ZFI = MF.getInfo<SystemZMachineFunctionInfo>();
  const SystemZSubtarget &Subtarget = MF.getSubtarget<SystemZSubtarget>();
  const TargetInstrInfo *TII = Subtarget.getInstrInfo();
  auto &Regs = Subtarget.getSpecialRegisters<SystemZXPLINK64Registers>();
  SystemZ::GPRRegs SpillGPRs = ZFI->getSpillGPRRegs();
  DebugLoc DL;

  // Save GPRs
  if (SpillGPRs.LowGPR) {
    assert(SpillGPRs.LowGPR != SpillGPRs.HighGPR &&
           "Should be saving multiple registers");

    // Build an STM/STMG instruction.
    MachineInstrBuilder MIB = BuildMI(MBB, MBBI, DL, TII->get(SystemZ::STMG));

    // Add the explicit register operands.
    addSavedGPR(MBB, MIB, SpillGPRs.LowGPR, false);
    addSavedGPR(MBB, MIB, SpillGPRs.HighGPR, false);

    // Add the address r4
    MIB.addReg(Regs.getStackPointerRegister());

    // Add the partial offset
    // We cannot add the actual offset as, at the stack is not finalized
    MIB.addImm(SpillGPRs.GPROffset);

    // Make sure all call-saved GPRs are included as operands and are
    // marked as live on entry.
    auto &GRRegClass = SystemZ::GR64BitRegClass;
    for (const CalleeSavedInfo &I : CSI) {
      MCRegister Reg = I.getReg();
      if (GRRegClass.contains(Reg))
        addSavedGPR(MBB, MIB, Reg, true);
    }
  }

  // Spill FPRs to the stack in the normal TargetInstrInfo way
  for (const CalleeSavedInfo &I : CSI) {
    MCRegister Reg = I.getReg();
    if (SystemZ::FP64BitRegClass.contains(Reg)) {
      MBB.addLiveIn(Reg);
      TII->storeRegToStackSlot(MBB, MBBI, Reg, true, I.getFrameIdx(),
                               &SystemZ::FP64BitRegClass, TRI, Register());
    }
    if (SystemZ::VR128BitRegClass.contains(Reg)) {
      MBB.addLiveIn(Reg);
      TII->storeRegToStackSlot(MBB, MBBI, Reg, true, I.getFrameIdx(),
                               &SystemZ::VR128BitRegClass, TRI, Register());
    }
  }

  return true;
}

bool SystemZXPLINKFrameLowering::restoreCalleeSavedRegisters(
    MachineBasicBlock &MBB, MachineBasicBlock::iterator MBBI,
    MutableArrayRef<CalleeSavedInfo> CSI, const TargetRegisterInfo *TRI) const {

  if (CSI.empty())
    return false;

  MachineFunction &MF = *MBB.getParent();
  SystemZMachineFunctionInfo *ZFI = MF.getInfo<SystemZMachineFunctionInfo>();
  const SystemZSubtarget &Subtarget = MF.getSubtarget<SystemZSubtarget>();
  const TargetInstrInfo *TII = Subtarget.getInstrInfo();
  auto &Regs = Subtarget.getSpecialRegisters<SystemZXPLINK64Registers>();

  DebugLoc DL = MBBI != MBB.end() ? MBBI->getDebugLoc() : DebugLoc();

  // Restore FPRs in the normal TargetInstrInfo way.
  for (const CalleeSavedInfo &I : CSI) {
    MCRegister Reg = I.getReg();
    if (SystemZ::FP64BitRegClass.contains(Reg))
      TII->loadRegFromStackSlot(MBB, MBBI, Reg, I.getFrameIdx(),
                                &SystemZ::FP64BitRegClass, TRI, Register());
    if (SystemZ::VR128BitRegClass.contains(Reg))
      TII->loadRegFromStackSlot(MBB, MBBI, Reg, I.getFrameIdx(),
                                &SystemZ::VR128BitRegClass, TRI, Register());
  }

  // Restore call-saved GPRs (but not call-clobbered varargs, which at
  // this point might hold return values).
  SystemZ::GPRRegs RestoreGPRs = ZFI->getRestoreGPRRegs();
  if (RestoreGPRs.LowGPR) {
    assert(isInt<20>(Regs.getStackPointerBias() + RestoreGPRs.GPROffset));
    if (RestoreGPRs.LowGPR == RestoreGPRs.HighGPR)
      // Build an LG/L instruction.
      BuildMI(MBB, MBBI, DL, TII->get(SystemZ::LG), RestoreGPRs.LowGPR)
          .addReg(Regs.getStackPointerRegister())
          .addImm(Regs.getStackPointerBias() + RestoreGPRs.GPROffset)
          .addReg(0);
    else {
      // Build an LMG/LM instruction.
      MachineInstrBuilder MIB = BuildMI(MBB, MBBI, DL, TII->get(SystemZ::LMG));

      // Add the explicit register operands.
      MIB.addReg(RestoreGPRs.LowGPR, RegState::Define);
      MIB.addReg(RestoreGPRs.HighGPR, RegState::Define);

      // Add the address.
      MIB.addReg(Regs.getStackPointerRegister());
      MIB.addImm(Regs.getStackPointerBias() + RestoreGPRs.GPROffset);

      // Do a second scan adding regs as being defined by instruction
      for (const CalleeSavedInfo &I : CSI) {
        MCRegister Reg = I.getReg();
        if (Reg > RestoreGPRs.LowGPR && Reg < RestoreGPRs.HighGPR)
          MIB.addReg(Reg, RegState::ImplicitDefine);
      }
    }
  }

  return true;
}

void SystemZXPLINKFrameLowering::emitPrologue(MachineFunction &MF,
                                              MachineBasicBlock &MBB) const {
  assert(&MF.front() == &MBB && "Shrink-wrapping not yet supported");
  const SystemZSubtarget &Subtarget = MF.getSubtarget<SystemZSubtarget>();
  SystemZMachineFunctionInfo *ZFI = MF.getInfo<SystemZMachineFunctionInfo>();
  MachineBasicBlock::iterator MBBI = MBB.begin();
  auto *ZII = Subtarget.getInstrInfo();
  auto &Regs = Subtarget.getSpecialRegisters<SystemZXPLINK64Registers>();
  MachineFrameInfo &MFFrame = MF.getFrameInfo();
  MachineInstr *StoreInstr = nullptr;

  determineFrameLayout(MF);

  bool HasFP = hasFP(MF);
  // Debug location must be unknown since the first debug location is used
  // to determine the end of the prologue.
  DebugLoc DL;
  uint64_t Offset = 0;

  const uint64_t StackSize = MFFrame.getStackSize();

  if (ZFI->getSpillGPRRegs().LowGPR) {
    // Skip over the GPR saves.
    if ((MBBI != MBB.end()) && ((MBBI->getOpcode() == SystemZ::STMG))) {
      const int Operand = 3;
      // Now we can set the offset for the operation, since now the Stack
      // has been finalized.
      Offset = Regs.getStackPointerBias() + MBBI->getOperand(Operand).getImm();
      // Maximum displacement for STMG instruction.
      if (isInt<20>(Offset - StackSize))
        Offset -= StackSize;
      else
        StoreInstr = &*MBBI;
      MBBI->getOperand(Operand).setImm(Offset);
      ++MBBI;
    } else
      llvm_unreachable("Couldn't skip over GPR saves");
  }

  if (StackSize) {
    MachineBasicBlock::iterator InsertPt = StoreInstr ? StoreInstr : MBBI;
    // Allocate StackSize bytes.
    int64_t Delta = -int64_t(StackSize);

    // In case the STM(G) instruction also stores SP (R4), but the displacement
    // is too large, the SP register is manipulated first before storing,
    // resulting in the wrong value stored and retrieved later. In this case, we
    // need to temporarily save the value of SP, and store it later to memory.
    if (StoreInstr && HasFP) {
      // Insert LR r0,r4 before STMG instruction.
      BuildMI(MBB, InsertPt, DL, ZII->get(SystemZ::LGR))
          .addReg(SystemZ::R0D, RegState::Define)
          .addReg(SystemZ::R4D);
      // Insert ST r0,xxx(,r4) after STMG instruction.
      BuildMI(MBB, MBBI, DL, ZII->get(SystemZ::STG))
          .addReg(SystemZ::R0D, RegState::Kill)
          .addReg(SystemZ::R4D)
          .addImm(Offset)
          .addReg(0);
    }

    emitIncrement(MBB, InsertPt, DL, Regs.getStackPointerRegister(), Delta,
                  ZII);

    // If the requested stack size is larger than the guard page, then we need
    // to check if we need to call the stack extender. This requires adding a
    // conditional branch, but splitting the prologue block is not possible at
    // this point since it would invalidate the SaveBlocks / RestoreBlocks sets
    // of PEI in the single block function case. Build a pseudo to be handled
    // later by inlineStackProbe().
    const uint64_t GuardPageSize = 1024 * 1024;
    if (StackSize > GuardPageSize) {
      assert(StoreInstr && "Wrong insertion point");
      BuildMI(MBB, InsertPt, DL, ZII->get(SystemZ::XPLINK_STACKALLOC));
    }
  }

  if (HasFP) {
    // Copy the base of the frame to Frame Pointer Register.
    BuildMI(MBB, MBBI, DL, ZII->get(SystemZ::LGR),
            Regs.getFramePointerRegister())
        .addReg(Regs.getStackPointerRegister());

    // Mark the FramePtr as live at the beginning of every block except
    // the entry block.  (We'll have marked R8 as live on entry when
    // saving the GPRs.)
    for (MachineBasicBlock &B : llvm::drop_begin(MF))
      B.addLiveIn(Regs.getFramePointerRegister());
  }

  // Save GPRs used for varargs, if any.
  const TargetInstrInfo *TII = Subtarget.getInstrInfo();
  bool IsVarArg = MF.getFunction().isVarArg();

  if (IsVarArg) {
    // FixedRegs is the number of used registers, accounting for shadow
    // registers.
    unsigned FixedRegs = ZFI->getVarArgsFirstGPR() + ZFI->getVarArgsFirstFPR();
    auto &GPRs = SystemZ::XPLINK64ArgGPRs;
    for (unsigned I = FixedRegs; I < SystemZ::XPLINK64NumArgGPRs; I++) {
      uint64_t StartOffset = MFFrame.getOffsetAdjustment() +
                             MFFrame.getStackSize() + Regs.getCallFrameSize() +
                             getOffsetOfLocalArea() + I * getPointerSize();
      unsigned Reg = GPRs[I];
      BuildMI(MBB, MBBI, DL, TII->get(SystemZ::STG))
          .addReg(Reg)
          .addReg(Regs.getStackPointerRegister())
          .addImm(StartOffset)
          .addReg(0);
      if (!MBB.isLiveIn(Reg))
        MBB.addLiveIn(Reg);
    }
  }
}

void SystemZXPLINKFrameLowering::emitEpilogue(MachineFunction &MF,
                                              MachineBasicBlock &MBB) const {
  const SystemZSubtarget &Subtarget = MF.getSubtarget<SystemZSubtarget>();
  MachineBasicBlock::iterator MBBI = MBB.getLastNonDebugInstr();
  SystemZMachineFunctionInfo *ZFI = MF.getInfo<SystemZMachineFunctionInfo>();
  MachineFrameInfo &MFFrame = MF.getFrameInfo();
  auto *ZII = Subtarget.getInstrInfo();
  auto &Regs = Subtarget.getSpecialRegisters<SystemZXPLINK64Registers>();

  // Skip the return instruction.
  assert(MBBI->isReturn() && "Can only insert epilogue into returning blocks");

  uint64_t StackSize = MFFrame.getStackSize();
  if (StackSize) {
    unsigned SPReg = Regs.getStackPointerRegister();
    if (ZFI->getRestoreGPRRegs().LowGPR != SPReg) {
      DebugLoc DL = MBBI->getDebugLoc();
      emitIncrement(MBB, MBBI, DL, SPReg, StackSize, ZII);
    }
  }
}

// Emit a compare of the stack pointer against the stack floor, and a call to
// the LE stack extender if needed.
void SystemZXPLINKFrameLowering::inlineStackProbe(
    MachineFunction &MF, MachineBasicBlock &PrologMBB) const {
  auto *ZII =
      static_cast<const SystemZInstrInfo *>(MF.getSubtarget().getInstrInfo());

  MachineInstr *StackAllocMI = nullptr;
  for (MachineInstr &MI : PrologMBB)
    if (MI.getOpcode() == SystemZ::XPLINK_STACKALLOC) {
      StackAllocMI = &MI;
      break;
    }
  if (StackAllocMI == nullptr)
    return;

  bool NeedSaveSP = hasFP(MF);
  bool NeedSaveArg = PrologMBB.isLiveIn(SystemZ::R3D);
  const int64_t SaveSlotR3 = 2192;

  MachineBasicBlock &MBB = PrologMBB;
  const DebugLoc DL = StackAllocMI->getDebugLoc();

  // The 2nd half of block MBB after split.
  MachineBasicBlock *NextMBB;

  // Add new basic block for the call to the stack overflow function.
  MachineBasicBlock *StackExtMBB =
      MF.CreateMachineBasicBlock(MBB.getBasicBlock());
  MF.push_back(StackExtMBB);

  // LG r3,72(,r3)
  BuildMI(StackExtMBB, DL, ZII->get(SystemZ::LG), SystemZ::R3D)
      .addReg(SystemZ::R3D)
      .addImm(72)
      .addReg(0);
  // BASR r3,r3
  BuildMI(StackExtMBB, DL, ZII->get(SystemZ::CallBASR_STACKEXT))
      .addReg(SystemZ::R3D);
  if (NeedSaveArg) {
    if (!NeedSaveSP) {
      // LGR r0,r3
      BuildMI(MBB, StackAllocMI, DL, ZII->get(SystemZ::LGR))
          .addReg(SystemZ::R0D, RegState::Define)
          .addReg(SystemZ::R3D);
    } else {
      // In this case, the incoming value of r4 is saved in r0 so the
      // latter register is unavailable. Store r3 in its corresponding
      // slot in the parameter list instead. Do this at the start of
      // the prolog before r4 is manipulated by anything else.
      // STG r3, 2192(r4)
      BuildMI(MBB, MBB.begin(), DL, ZII->get(SystemZ::STG))
          .addReg(SystemZ::R3D)
          .addReg(SystemZ::R4D)
          .addImm(SaveSlotR3)
          .addReg(0);
    }
  }
  // LLGT r3,1208
  BuildMI(MBB, StackAllocMI, DL, ZII->get(SystemZ::LLGT), SystemZ::R3D)
      .addReg(0)
      .addImm(1208)
      .addReg(0);
  // CG r4,64(,r3)
  BuildMI(MBB, StackAllocMI, DL, ZII->get(SystemZ::CG))
      .addReg(SystemZ::R4D)
      .addReg(SystemZ::R3D)
      .addImm(64)
      .addReg(0);
  // JLL b'0100',F'37'
  BuildMI(MBB, StackAllocMI, DL, ZII->get(SystemZ::BRC))
      .addImm(SystemZ::CCMASK_ICMP)
      .addImm(SystemZ::CCMASK_CMP_LT)
      .addMBB(StackExtMBB);

  NextMBB = SystemZ::splitBlockBefore(StackAllocMI, &MBB);
  MBB.addSuccessor(NextMBB);
  MBB.addSuccessor(StackExtMBB);
  if (NeedSaveArg) {
    if (!NeedSaveSP) {
      // LGR r3, r0
      BuildMI(*NextMBB, StackAllocMI, DL, ZII->get(SystemZ::LGR))
          .addReg(SystemZ::R3D, RegState::Define)
          .addReg(SystemZ::R0D, RegState::Kill);
    } else {
      // In this case, the incoming value of r4 is saved in r0 so the
      // latter register is unavailable. We stored r3 in its corresponding
      // slot in the parameter list instead and we now restore it from there.
      // LGR r3, r0
      BuildMI(*NextMBB, StackAllocMI, DL, ZII->get(SystemZ::LGR))
          .addReg(SystemZ::R3D, RegState::Define)
          .addReg(SystemZ::R0D);
      // LG r3, 2192(r3)
      BuildMI(*NextMBB, StackAllocMI, DL, ZII->get(SystemZ::LG))
          .addReg(SystemZ::R3D, RegState::Define)
          .addReg(SystemZ::R3D)
          .addImm(SaveSlotR3)
          .addReg(0);
    }
  }

  // Add jump back from stack extension BB.
  BuildMI(StackExtMBB, DL, ZII->get(SystemZ::J)).addMBB(NextMBB);
  StackExtMBB->addSuccessor(NextMBB);

  StackAllocMI->eraseFromParent();

  // Compute the live-in lists for the new blocks.
  fullyRecomputeLiveIns({StackExtMBB, NextMBB});
}

bool SystemZXPLINKFrameLowering::hasFPImpl(const MachineFunction &MF) const {
  return (MF.getFrameInfo().hasVarSizedObjects());
}

void SystemZXPLINKFrameLowering::processFunctionBeforeFrameFinalized(
    MachineFunction &MF, RegScavenger *RS) const {
  MachineFrameInfo &MFFrame = MF.getFrameInfo();
  const SystemZSubtarget &Subtarget = MF.getSubtarget<SystemZSubtarget>();
  auto &Regs = Subtarget.getSpecialRegisters<SystemZXPLINK64Registers>();

  // Setup stack frame offset
  MFFrame.setOffsetAdjustment(Regs.getStackPointerBias());

  // Nothing to do for leaf functions.
  uint64_t StackSize = MFFrame.estimateStackSize(MF);
  if (StackSize == 0 && MFFrame.getCalleeSavedInfo().empty())
    return;

  // Although the XPLINK specifications for AMODE64 state that minimum size
  // of the param area is minimum 32 bytes and no rounding is otherwise
  // specified, we round this area in 64 bytes increments to be compatible
  // with existing compilers.
  MFFrame.setMaxCallFrameSize(
      std::max(64U, (unsigned)alignTo(MFFrame.getMaxCallFrameSize(), 64)));

  // Add frame values with positive object offsets. Since the displacement from
  // the SP/FP is calculated by ObjectOffset + StackSize + Bias, object offsets
  // with positive values are in the caller's stack frame. We need to include
  // that since it is accessed by displacement to SP/FP.
  int64_t LargestArgOffset = 0;
  for (int I = MFFrame.getObjectIndexBegin(); I != 0; ++I) {
    if (MFFrame.getObjectOffset(I) >= 0) {
      int64_t ObjOffset = MFFrame.getObjectOffset(I) + MFFrame.getObjectSize(I);
      LargestArgOffset = std::max(ObjOffset, LargestArgOffset);
    }
  }

  uint64_t MaxReach = (StackSize + Regs.getCallFrameSize() +
                       Regs.getStackPointerBias() + LargestArgOffset);

  if (!isUInt<12>(MaxReach)) {
    // We may need register scavenging slots if some parts of the frame
    // are outside the reach of an unsigned 12-bit displacement.
    RS->addScavengingFrameIndex(MFFrame.CreateSpillStackObject(8, Align(8)));
    RS->addScavengingFrameIndex(MFFrame.CreateSpillStackObject(8, Align(8)));
  }
}

// Determines the size of the frame, and creates the deferred spill objects.
void SystemZXPLINKFrameLowering::determineFrameLayout(
    MachineFunction &MF) const {
  MachineFrameInfo &MFFrame = MF.getFrameInfo();
  const SystemZSubtarget &Subtarget = MF.getSubtarget<SystemZSubtarget>();
  auto *Regs =
      static_cast<SystemZXPLINK64Registers *>(Subtarget.getSpecialRegisters());

  uint64_t StackSize = MFFrame.getStackSize();
  if (StackSize == 0)
    return;

  // Add the size of the register save area and the reserved area to the size.
  StackSize += Regs->getCallFrameSize();
  MFFrame.setStackSize(StackSize);

  // We now know the stack size. Update the stack objects for the register save
  // area now. This has no impact on the stack frame layout, as this is already
  // computed. However, it makes sure that all callee saved registers have a
  // valid offset assigned.
  for (int FrameIdx = MFFrame.getObjectIndexBegin(); FrameIdx != 0;
       ++FrameIdx) {
    if (MFFrame.getStackID(FrameIdx) == TargetStackID::NoAlloc) {
      int64_t SPOffset = MFFrame.getObjectOffset(FrameIdx);
      SPOffset -= StackSize;
      MFFrame.setObjectOffset(FrameIdx, SPOffset);
    }
  }
}