llvm/lib/Target/X86/X86FrameLowering.cpp

//===-- X86FrameLowering.cpp - X86 Frame 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 X86 implementation of TargetFrameLowering class.
//
//===----------------------------------------------------------------------===//

#include "X86FrameLowering.h"
#include "X86InstrBuilder.h"
#include "X86InstrInfo.h"
#include "X86MachineFunctionInfo.h"
#include "X86Subtarget.h"
#include "X86TargetMachine.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/Analysis/EHPersonalities.h"
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineModuleInfo.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/WinEHFuncInfo.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/Function.h"
#include "llvm/MC/MCAsmInfo.h"
#include "llvm/MC/MCSymbol.h"
#include "llvm/Target/TargetOptions.h"
#include "llvm/Support/Debug.h"
#include <cstdlib>

using namespace llvm;

X86FrameLowering::X86FrameLowering(const X86Subtarget &STI,
                                   unsigned StackAlignOverride)
    : TargetFrameLowering(StackGrowsDown, StackAlignOverride,
                          STI.is64Bit() ? -8 : -4),
      STI(STI), TII(*STI.getInstrInfo()), TRI(STI.getRegisterInfo()) {
  // Cache a bunch of frame-related predicates for this subtarget.
  SlotSize = TRI->getSlotSize();
  Is64Bit = STI.is64Bit();
  IsLP64 = STI.isTarget64BitLP64();
  // standard x86_64 and NaCl use 64-bit frame/stack pointers, x32 - 32-bit.
  Uses64BitFramePtr = STI.isTarget64BitLP64() || STI.isTargetNaCl64();
  StackPtr = TRI->getStackRegister();
}

bool X86FrameLowering::hasReservedCallFrame(const MachineFunction &MF) const {
  return !MF.getFrameInfo()->hasVarSizedObjects() &&
         !MF.getInfo<X86MachineFunctionInfo>()->getHasPushSequences();
}

/// canSimplifyCallFramePseudos - If there is a reserved call frame, the
/// call frame pseudos can be simplified.  Having a FP, as in the default
/// implementation, is not sufficient here since we can't always use it.
/// Use a more nuanced condition.
bool
X86FrameLowering::canSimplifyCallFramePseudos(const MachineFunction &MF) const {
  return hasReservedCallFrame(MF) ||
         (hasFP(MF) && !TRI->needsStackRealignment(MF)) ||
         TRI->hasBasePointer(MF);
}

// needsFrameIndexResolution - Do we need to perform FI resolution for
// this function. Normally, this is required only when the function
// has any stack objects. However, FI resolution actually has another job,
// not apparent from the title - it resolves callframesetup/destroy 
// that were not simplified earlier.
// So, this is required for x86 functions that have push sequences even
// when there are no stack objects.
bool
X86FrameLowering::needsFrameIndexResolution(const MachineFunction &MF) const {
  return MF.getFrameInfo()->hasStackObjects() ||
         MF.getInfo<X86MachineFunctionInfo>()->getHasPushSequences();
}

/// hasFP - Return true if the specified function should have a dedicated frame
/// pointer register.  This is true if the function has variable sized allocas
/// or if frame pointer elimination is disabled.
bool X86FrameLowering::hasFP(const MachineFunction &MF) const {
  const MachineFrameInfo *MFI = MF.getFrameInfo();
  const MachineModuleInfo &MMI = MF.getMMI();

  return (MF.getTarget().Options.DisableFramePointerElim(MF) ||
          TRI->needsStackRealignment(MF) ||
          MFI->hasVarSizedObjects() ||
          MFI->isFrameAddressTaken() || MFI->hasOpaqueSPAdjustment() ||
          MF.getInfo<X86MachineFunctionInfo>()->getForceFramePointer() ||
          MMI.callsUnwindInit() || MMI.hasEHFunclets() || MMI.callsEHReturn() ||
          MFI->hasStackMap() || MFI->hasPatchPoint() ||
          MFI->hasCopyImplyingStackAdjustment());
}

static unsigned getSUBriOpcode(unsigned IsLP64, int64_t Imm) {
  if (IsLP64) {
    if (isInt<8>(Imm))
      return X86::SUB64ri8;
    return X86::SUB64ri32;
  } else {
    if (isInt<8>(Imm))
      return X86::SUB32ri8;
    return X86::SUB32ri;
  }
}

static unsigned getADDriOpcode(unsigned IsLP64, int64_t Imm) {
  if (IsLP64) {
    if (isInt<8>(Imm))
      return X86::ADD64ri8;
    return X86::ADD64ri32;
  } else {
    if (isInt<8>(Imm))
      return X86::ADD32ri8;
    return X86::ADD32ri;
  }
}

static unsigned getSUBrrOpcode(unsigned isLP64) {
  return isLP64 ? X86::SUB64rr : X86::SUB32rr;
}

static unsigned getADDrrOpcode(unsigned isLP64) {
  return isLP64 ? X86::ADD64rr : X86::ADD32rr;
}

static unsigned getANDriOpcode(bool IsLP64, int64_t Imm) {
  if (IsLP64) {
    if (isInt<8>(Imm))
      return X86::AND64ri8;
    return X86::AND64ri32;
  }
  if (isInt<8>(Imm))
    return X86::AND32ri8;
  return X86::AND32ri;
}

static unsigned getLEArOpcode(unsigned IsLP64) {
  return IsLP64 ? X86::LEA64r : X86::LEA32r;
}

/// findDeadCallerSavedReg - Return a caller-saved register that isn't live
/// when it reaches the "return" instruction. We can then pop a stack object
/// to this register without worry about clobbering it.
static unsigned findDeadCallerSavedReg(MachineBasicBlock &MBB,
                                       MachineBasicBlock::iterator &MBBI,
                                       const X86RegisterInfo *TRI,
                                       bool Is64Bit) {
  const MachineFunction *MF = MBB.getParent();
  const Function *F = MF->getFunction();
  if (!F || MF->getMMI().callsEHReturn())
    return 0;

  const TargetRegisterClass &AvailableRegs = *TRI->getGPRsForTailCall(*MF);

  unsigned Opc = MBBI->getOpcode();
  switch (Opc) {
  default: return 0;
  case X86::RETL:
  case X86::RETQ:
  case X86::RETIL:
  case X86::RETIQ:
  case X86::TCRETURNdi:
  case X86::TCRETURNri:
  case X86::TCRETURNmi:
  case X86::TCRETURNdi64:
  case X86::TCRETURNri64:
  case X86::TCRETURNmi64:
  case X86::EH_RETURN:
  case X86::EH_RETURN64: {
    SmallSet<uint16_t, 8> Uses;
    for (unsigned i = 0, e = MBBI->getNumOperands(); i != e; ++i) {
      MachineOperand &MO = MBBI->getOperand(i);
      if (!MO.isReg() || MO.isDef())
        continue;
      unsigned Reg = MO.getReg();
      if (!Reg)
        continue;
      for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI)
        Uses.insert(*AI);
    }

    for (auto CS : AvailableRegs)
      if (!Uses.count(CS) && CS != X86::RIP)
        return CS;
  }
  }

  return 0;
}

static bool isEAXLiveIn(MachineFunction &MF) {
  for (MachineRegisterInfo::livein_iterator II = MF.getRegInfo().livein_begin(),
       EE = MF.getRegInfo().livein_end(); II != EE; ++II) {
    unsigned Reg = II->first;

    if (Reg == X86::RAX || Reg == X86::EAX || Reg == X86::AX ||
        Reg == X86::AH || Reg == X86::AL)
      return true;
  }

  return false;
}

/// Check if the flags need to be preserved before the terminators.
/// This would be the case, if the eflags is live-in of the region
/// composed by the terminators or live-out of that region, without
/// being defined by a terminator.
static bool
flagsNeedToBePreservedBeforeTheTerminators(const MachineBasicBlock &MBB) {
  for (const MachineInstr &MI : MBB.terminators()) {
    bool BreakNext = false;
    for (const MachineOperand &MO : MI.operands()) {
      if (!MO.isReg())
        continue;
      unsigned Reg = MO.getReg();
      if (Reg != X86::EFLAGS)
        continue;

      // This terminator needs an eflags that is not defined
      // by a previous another terminator:
      // EFLAGS is live-in of the region composed by the terminators.
      if (!MO.isDef())
        return true;
      // This terminator defines the eflags, i.e., we don't need to preserve it.
      // However, we still need to check this specific terminator does not
      // read a live-in value.
      BreakNext = true;
    }
    // We found a definition of the eflags, no need to preserve them.
    if (BreakNext)
      return false;
  }

  // None of the terminators use or define the eflags.
  // Check if they are live-out, that would imply we need to preserve them.
  for (const MachineBasicBlock *Succ : MBB.successors())
    if (Succ->isLiveIn(X86::EFLAGS))
      return true;

  return false;
}

/// emitSPUpdate - Emit a series of instructions to increment / decrement the
/// stack pointer by a constant value.
void X86FrameLowering::emitSPUpdate(MachineBasicBlock &MBB,
                                    MachineBasicBlock::iterator &MBBI,
                                    int64_t NumBytes, bool InEpilogue) const {
  bool isSub = NumBytes < 0;
  uint64_t Offset = isSub ? -NumBytes : NumBytes;

  uint64_t Chunk = (1LL << 31) - 1;
  DebugLoc DL = MBB.findDebugLoc(MBBI);

  while (Offset) {
    if (Offset > Chunk) {
      // Rather than emit a long series of instructions for large offsets,
      // load the offset into a register and do one sub/add
      unsigned Reg = 0;

      if (isSub && !isEAXLiveIn(*MBB.getParent()))
        Reg = (unsigned)(Is64Bit ? X86::RAX : X86::EAX);
      else
        Reg = findDeadCallerSavedReg(MBB, MBBI, TRI, Is64Bit);

      if (Reg) {
        unsigned Opc = Is64Bit ? X86::MOV64ri : X86::MOV32ri;
        BuildMI(MBB, MBBI, DL, TII.get(Opc), Reg)
          .addImm(Offset);
        Opc = isSub
          ? getSUBrrOpcode(Is64Bit)
          : getADDrrOpcode(Is64Bit);
        MachineInstr *MI = BuildMI(MBB, MBBI, DL, TII.get(Opc), StackPtr)
          .addReg(StackPtr)
          .addReg(Reg);
        MI->getOperand(3).setIsDead(); // The EFLAGS implicit def is dead.
        Offset = 0;
        continue;
      }
    }

    uint64_t ThisVal = std::min(Offset, Chunk);
    if (ThisVal == (Is64Bit ? 8 : 4)) {
      // Use push / pop instead.
      unsigned Reg = isSub
        ? (unsigned)(Is64Bit ? X86::RAX : X86::EAX)
        : findDeadCallerSavedReg(MBB, MBBI, TRI, Is64Bit);
      if (Reg) {
        unsigned Opc = isSub
          ? (Is64Bit ? X86::PUSH64r : X86::PUSH32r)
          : (Is64Bit ? X86::POP64r  : X86::POP32r);
        MachineInstr *MI = BuildMI(MBB, MBBI, DL, TII.get(Opc))
          .addReg(Reg, getDefRegState(!isSub) | getUndefRegState(isSub));
        if (isSub)
          MI->setFlag(MachineInstr::FrameSetup);
        else
          MI->setFlag(MachineInstr::FrameDestroy);
        Offset -= ThisVal;
        continue;
      }
    }

    MachineInstrBuilder MI = BuildStackAdjustment(
        MBB, MBBI, DL, isSub ? -ThisVal : ThisVal, InEpilogue);
    if (isSub)
      MI.setMIFlag(MachineInstr::FrameSetup);
    else
      MI.setMIFlag(MachineInstr::FrameDestroy);

    Offset -= ThisVal;
  }
}

MachineInstrBuilder X86FrameLowering::BuildStackAdjustment(
    MachineBasicBlock &MBB, MachineBasicBlock::iterator MBBI, DebugLoc DL,
    int64_t Offset, bool InEpilogue) const {
  assert(Offset != 0 && "zero offset stack adjustment requested");

  // On Atom, using LEA to adjust SP is preferred, but using it in the epilogue
  // is tricky.
  bool UseLEA;
  if (!InEpilogue) {
    // Check if inserting the prologue at the beginning
    // of MBB would require to use LEA operations.
    // We need to use LEA operations if EFLAGS is live in, because
    // it means an instruction will read it before it gets defined.
    UseLEA = STI.useLeaForSP() || MBB.isLiveIn(X86::EFLAGS);
  } else {
    // If we can use LEA for SP but we shouldn't, check that none
    // of the terminators uses the eflags. Otherwise we will insert
    // a ADD that will redefine the eflags and break the condition.
    // Alternatively, we could move the ADD, but this may not be possible
    // and is an optimization anyway.
    UseLEA = canUseLEAForSPInEpilogue(*MBB.getParent());
    if (UseLEA && !STI.useLeaForSP())
      UseLEA = flagsNeedToBePreservedBeforeTheTerminators(MBB);
    // If that assert breaks, that means we do not do the right thing
    // in canUseAsEpilogue.
    assert((UseLEA || !flagsNeedToBePreservedBeforeTheTerminators(MBB)) &&
           "We shouldn't have allowed this insertion point");
  }

  MachineInstrBuilder MI;
  if (UseLEA) {
    MI = addRegOffset(BuildMI(MBB, MBBI, DL,
                              TII.get(getLEArOpcode(Uses64BitFramePtr)),
                              StackPtr),
                      StackPtr, false, Offset);
  } else {
    bool IsSub = Offset < 0;
    uint64_t AbsOffset = IsSub ? -Offset : Offset;
    unsigned Opc = IsSub ? getSUBriOpcode(Uses64BitFramePtr, AbsOffset)
                         : getADDriOpcode(Uses64BitFramePtr, AbsOffset);
    MI = BuildMI(MBB, MBBI, DL, TII.get(Opc), StackPtr)
             .addReg(StackPtr)
             .addImm(AbsOffset);
    MI->getOperand(3).setIsDead(); // The EFLAGS implicit def is dead.
  }
  return MI;
}

int X86FrameLowering::mergeSPUpdates(MachineBasicBlock &MBB,
                                     MachineBasicBlock::iterator &MBBI,
                                     bool doMergeWithPrevious) const {
  if ((doMergeWithPrevious && MBBI == MBB.begin()) ||
      (!doMergeWithPrevious && MBBI == MBB.end()))
    return 0;

  MachineBasicBlock::iterator PI = doMergeWithPrevious ? std::prev(MBBI) : MBBI;
  MachineBasicBlock::iterator NI = doMergeWithPrevious ? nullptr
                                                       : std::next(MBBI);
  unsigned Opc = PI->getOpcode();
  int Offset = 0;

  if ((Opc == X86::ADD64ri32 || Opc == X86::ADD64ri8 ||
       Opc == X86::ADD32ri || Opc == X86::ADD32ri8) &&
      PI->getOperand(0).getReg() == StackPtr){
    Offset += PI->getOperand(2).getImm();
    MBB.erase(PI);
    if (!doMergeWithPrevious) MBBI = NI;
  } else if ((Opc == X86::LEA32r || Opc == X86::LEA64_32r) &&
             PI->getOperand(0).getReg() == StackPtr) {
    // For LEAs we have: def = lea SP, FI, noreg, Offset, noreg.
    Offset += PI->getOperand(4).getImm();
    MBB.erase(PI);
    if (!doMergeWithPrevious) MBBI = NI;
  } else if ((Opc == X86::SUB64ri32 || Opc == X86::SUB64ri8 ||
              Opc == X86::SUB32ri || Opc == X86::SUB32ri8) &&
             PI->getOperand(0).getReg() == StackPtr) {
    Offset -= PI->getOperand(2).getImm();
    MBB.erase(PI);
    if (!doMergeWithPrevious) MBBI = NI;
  }

  return Offset;
}

void X86FrameLowering::BuildCFI(MachineBasicBlock &MBB,
                                MachineBasicBlock::iterator MBBI, DebugLoc DL,
                                MCCFIInstruction CFIInst) const {
  MachineFunction &MF = *MBB.getParent();
  unsigned CFIIndex = MF.getMMI().addFrameInst(CFIInst);
  BuildMI(MBB, MBBI, DL, TII.get(TargetOpcode::CFI_INSTRUCTION))
      .addCFIIndex(CFIIndex);
}

void
X86FrameLowering::emitCalleeSavedFrameMoves(MachineBasicBlock &MBB,
                                            MachineBasicBlock::iterator MBBI,
                                            DebugLoc DL) const {
  MachineFunction &MF = *MBB.getParent();
  MachineFrameInfo *MFI = MF.getFrameInfo();
  MachineModuleInfo &MMI = MF.getMMI();
  const MCRegisterInfo *MRI = MMI.getContext().getRegisterInfo();

  // Add callee saved registers to move list.
  const std::vector<CalleeSavedInfo> &CSI = MFI->getCalleeSavedInfo();
  if (CSI.empty()) return;

  // Calculate offsets.
  for (std::vector<CalleeSavedInfo>::const_iterator
         I = CSI.begin(), E = CSI.end(); I != E; ++I) {
    int64_t Offset = MFI->getObjectOffset(I->getFrameIdx());
    unsigned Reg = I->getReg();

    unsigned DwarfReg = MRI->getDwarfRegNum(Reg, true);
    BuildCFI(MBB, MBBI, DL,
             MCCFIInstruction::createOffset(nullptr, DwarfReg, Offset));
  }
}

MachineInstr *X86FrameLowering::emitStackProbe(MachineFunction &MF,
                                               MachineBasicBlock &MBB,
                                               MachineBasicBlock::iterator MBBI,
                                               DebugLoc DL,
                                               bool InProlog) const {
  const X86Subtarget &STI = MF.getSubtarget<X86Subtarget>();
  if (STI.isTargetWindowsCoreCLR()) {
    if (InProlog) {
      return emitStackProbeInlineStub(MF, MBB, MBBI, DL, true);
    } else {
      return emitStackProbeInline(MF, MBB, MBBI, DL, false);
    }
  } else {
    return emitStackProbeCall(MF, MBB, MBBI, DL, InProlog);
  }
}

void X86FrameLowering::inlineStackProbe(MachineFunction &MF,
                                        MachineBasicBlock &PrologMBB) const {
  const StringRef ChkStkStubSymbol = "__chkstk_stub";
  MachineInstr *ChkStkStub = nullptr;

  for (MachineInstr &MI : PrologMBB) {
    if (MI.isCall() && MI.getOperand(0).isSymbol() &&
        ChkStkStubSymbol == MI.getOperand(0).getSymbolName()) {
      ChkStkStub = &MI;
      break;
    }
  }

  if (ChkStkStub != nullptr) {
    MachineBasicBlock::iterator MBBI = std::next(ChkStkStub->getIterator());
    assert(std::prev(MBBI).operator==(ChkStkStub) &&
      "MBBI expected after __chkstk_stub.");
    DebugLoc DL = PrologMBB.findDebugLoc(MBBI);
    emitStackProbeInline(MF, PrologMBB, MBBI, DL, true);
    ChkStkStub->eraseFromParent();
  }
}

MachineInstr *X86FrameLowering::emitStackProbeInline(
  MachineFunction &MF, MachineBasicBlock &MBB,
  MachineBasicBlock::iterator MBBI, DebugLoc DL, bool InProlog) const {
  const X86Subtarget &STI = MF.getSubtarget<X86Subtarget>();
  assert(STI.is64Bit() && "different expansion needed for 32 bit");
  assert(STI.isTargetWindowsCoreCLR() && "custom expansion expects CoreCLR");
  const TargetInstrInfo &TII = *STI.getInstrInfo();
  const BasicBlock *LLVM_BB = MBB.getBasicBlock();

  // RAX contains the number of bytes of desired stack adjustment.
  // The handling here assumes this value has already been updated so as to
  // maintain stack alignment.
  //
  // We need to exit with RSP modified by this amount and execute suitable
  // page touches to notify the OS that we're growing the stack responsibly.
  // All stack probing must be done without modifying RSP.
  //
  // MBB:
  //    SizeReg = RAX;
  //    ZeroReg = 0
  //    CopyReg = RSP
  //    Flags, TestReg = CopyReg - SizeReg
  //    FinalReg = !Flags.Ovf ? TestReg : ZeroReg
  //    LimitReg = gs magic thread env access
  //    if FinalReg >= LimitReg goto ContinueMBB
  // RoundBB:
  //    RoundReg = page address of FinalReg
  // LoopMBB:
  //    LoopReg = PHI(LimitReg,ProbeReg)
  //    ProbeReg = LoopReg - PageSize
  //    [ProbeReg] = 0
  //    if (ProbeReg > RoundReg) goto LoopMBB
  // ContinueMBB:
  //    RSP = RSP - RAX
  //    [rest of original MBB]

  // Set up the new basic blocks
  MachineBasicBlock *RoundMBB = MF.CreateMachineBasicBlock(LLVM_BB);
  MachineBasicBlock *LoopMBB = MF.CreateMachineBasicBlock(LLVM_BB);
  MachineBasicBlock *ContinueMBB = MF.CreateMachineBasicBlock(LLVM_BB);

  MachineFunction::iterator MBBIter = std::next(MBB.getIterator());
  MF.insert(MBBIter, RoundMBB);
  MF.insert(MBBIter, LoopMBB);
  MF.insert(MBBIter, ContinueMBB);

  // Split MBB and move the tail portion down to ContinueMBB.
  MachineBasicBlock::iterator BeforeMBBI = std::prev(MBBI);
  ContinueMBB->splice(ContinueMBB->begin(), &MBB, MBBI, MBB.end());
  ContinueMBB->transferSuccessorsAndUpdatePHIs(&MBB);

  // Some useful constants
  const int64_t ThreadEnvironmentStackLimit = 0x10;
  const int64_t PageSize = 0x1000;
  const int64_t PageMask = ~(PageSize - 1);

  // Registers we need. For the normal case we use virtual
  // registers. For the prolog expansion we use RAX, RCX and RDX.
  MachineRegisterInfo &MRI = MF.getRegInfo();
  const TargetRegisterClass *RegClass = &X86::GR64RegClass;
  const unsigned SizeReg = InProlog ? (unsigned)X86::RAX
                                    : MRI.createVirtualRegister(RegClass),
                 ZeroReg = InProlog ? (unsigned)X86::RCX
                                    : MRI.createVirtualRegister(RegClass),
                 CopyReg = InProlog ? (unsigned)X86::RDX
                                    : MRI.createVirtualRegister(RegClass),
                 TestReg = InProlog ? (unsigned)X86::RDX
                                    : MRI.createVirtualRegister(RegClass),
                 FinalReg = InProlog ? (unsigned)X86::RDX
                                     : MRI.createVirtualRegister(RegClass),
                 RoundedReg = InProlog ? (unsigned)X86::RDX
                                       : MRI.createVirtualRegister(RegClass),
                 LimitReg = InProlog ? (unsigned)X86::RCX
                                     : MRI.createVirtualRegister(RegClass),
                 JoinReg = InProlog ? (unsigned)X86::RCX
                                    : MRI.createVirtualRegister(RegClass),
                 ProbeReg = InProlog ? (unsigned)X86::RCX
                                     : MRI.createVirtualRegister(RegClass);

  // SP-relative offsets where we can save RCX and RDX.
  int64_t RCXShadowSlot = 0;
  int64_t RDXShadowSlot = 0;

  // If inlining in the prolog, save RCX and RDX.     
  // Future optimization: don't save or restore if not live in.
  if (InProlog) {
    // Compute the offsets. We need to account for things already
    // pushed onto the stack at this point: return address, frame
    // pointer (if used), and callee saves.
    X86MachineFunctionInfo *X86FI = MF.getInfo<X86MachineFunctionInfo>();
    const int64_t CalleeSaveSize = X86FI->getCalleeSavedFrameSize();
    const bool HasFP = hasFP(MF);
    RCXShadowSlot = 8 + CalleeSaveSize + (HasFP ? 8 : 0);
    RDXShadowSlot = RCXShadowSlot + 8;
    // Emit the saves.
    addRegOffset(BuildMI(&MBB, DL, TII.get(X86::MOV64mr)), X86::RSP, false,
                 RCXShadowSlot)
        .addReg(X86::RCX);
    addRegOffset(BuildMI(&MBB, DL, TII.get(X86::MOV64mr)), X86::RSP, false,
                 RDXShadowSlot)
        .addReg(X86::RDX);
  } else {
    // Not in the prolog. Copy RAX to a virtual reg.
    BuildMI(&MBB, DL, TII.get(X86::MOV64rr), SizeReg).addReg(X86::RAX);
  }

  // Add code to MBB to check for overflow and set the new target stack pointer
  // to zero if so.
  BuildMI(&MBB, DL, TII.get(X86::XOR64rr), ZeroReg)
      .addReg(ZeroReg, RegState::Undef)
      .addReg(ZeroReg, RegState::Undef);
  BuildMI(&MBB, DL, TII.get(X86::MOV64rr), CopyReg).addReg(X86::RSP);
  BuildMI(&MBB, DL, TII.get(X86::SUB64rr), TestReg)
      .addReg(CopyReg)
      .addReg(SizeReg);
  BuildMI(&MBB, DL, TII.get(X86::CMOVB64rr), FinalReg)
      .addReg(TestReg)
      .addReg(ZeroReg);

  // FinalReg now holds final stack pointer value, or zero if
  // allocation would overflow. Compare against the current stack
  // limit from the thread environment block. Note this limit is the
  // lowest touched page on the stack, not the point at which the OS
  // will cause an overflow exception, so this is just an optimization
  // to avoid unnecessarily touching pages that are below the current
  // SP but already commited to the stack by the OS.
  BuildMI(&MBB, DL, TII.get(X86::MOV64rm), LimitReg)
      .addReg(0)
      .addImm(1)
      .addReg(0)
      .addImm(ThreadEnvironmentStackLimit)
      .addReg(X86::GS);
  BuildMI(&MBB, DL, TII.get(X86::CMP64rr)).addReg(FinalReg).addReg(LimitReg);
  // Jump if the desired stack pointer is at or above the stack limit.
  BuildMI(&MBB, DL, TII.get(X86::JAE_1)).addMBB(ContinueMBB);

  // Add code to roundMBB to round the final stack pointer to a page boundary.
  BuildMI(RoundMBB, DL, TII.get(X86::AND64ri32), RoundedReg)
      .addReg(FinalReg)
      .addImm(PageMask);
  BuildMI(RoundMBB, DL, TII.get(X86::JMP_1)).addMBB(LoopMBB);

  // LimitReg now holds the current stack limit, RoundedReg page-rounded
  // final RSP value. Add code to loopMBB to decrement LimitReg page-by-page
  // and probe until we reach RoundedReg.
  if (!InProlog) {
    BuildMI(LoopMBB, DL, TII.get(X86::PHI), JoinReg)
        .addReg(LimitReg)
        .addMBB(RoundMBB)
        .addReg(ProbeReg)
        .addMBB(LoopMBB);
  }

  addRegOffset(BuildMI(LoopMBB, DL, TII.get(X86::LEA64r), ProbeReg), JoinReg,
               false, -PageSize);

  // Probe by storing a byte onto the stack.
  BuildMI(LoopMBB, DL, TII.get(X86::MOV8mi))
      .addReg(ProbeReg)
      .addImm(1)
      .addReg(0)
      .addImm(0)
      .addReg(0)
      .addImm(0);
  BuildMI(LoopMBB, DL, TII.get(X86::CMP64rr))
      .addReg(RoundedReg)
      .addReg(ProbeReg);
  BuildMI(LoopMBB, DL, TII.get(X86::JNE_1)).addMBB(LoopMBB);

  MachineBasicBlock::iterator ContinueMBBI = ContinueMBB->getFirstNonPHI();

  // If in prolog, restore RDX and RCX.
  if (InProlog) {
    addRegOffset(BuildMI(*ContinueMBB, ContinueMBBI, DL, TII.get(X86::MOV64rm),
                         X86::RCX),
                 X86::RSP, false, RCXShadowSlot);
    addRegOffset(BuildMI(*ContinueMBB, ContinueMBBI, DL, TII.get(X86::MOV64rm),
                         X86::RDX),
                 X86::RSP, false, RDXShadowSlot);
  }

  // Now that the probing is done, add code to continueMBB to update
  // the stack pointer for real.
  BuildMI(*ContinueMBB, ContinueMBBI, DL, TII.get(X86::SUB64rr), X86::RSP)
      .addReg(X86::RSP)
      .addReg(SizeReg);

  // Add the control flow edges we need.
  MBB.addSuccessor(ContinueMBB);
  MBB.addSuccessor(RoundMBB);
  RoundMBB->addSuccessor(LoopMBB);
  LoopMBB->addSuccessor(ContinueMBB);
  LoopMBB->addSuccessor(LoopMBB);

  // Mark all the instructions added to the prolog as frame setup.
  if (InProlog) {
    for (++BeforeMBBI; BeforeMBBI != MBB.end(); ++BeforeMBBI) {
      BeforeMBBI->setFlag(MachineInstr::FrameSetup);
    }
    for (MachineInstr &MI : *RoundMBB) {
      MI.setFlag(MachineInstr::FrameSetup);
    }
    for (MachineInstr &MI : *LoopMBB) {
      MI.setFlag(MachineInstr::FrameSetup);
    }
    for (MachineBasicBlock::iterator CMBBI = ContinueMBB->begin();
         CMBBI != ContinueMBBI; ++CMBBI) {
      CMBBI->setFlag(MachineInstr::FrameSetup);
    }
  }

  // Possible TODO: physreg liveness for InProlog case.

  return ContinueMBBI;
}

MachineInstr *X86FrameLowering::emitStackProbeCall(
    MachineFunction &MF, MachineBasicBlock &MBB,
    MachineBasicBlock::iterator MBBI, DebugLoc DL, bool InProlog) const {
  bool IsLargeCodeModel = MF.getTarget().getCodeModel() == CodeModel::Large;

  unsigned CallOp;
  if (Is64Bit)
    CallOp = IsLargeCodeModel ? X86::CALL64r : X86::CALL64pcrel32;
  else
    CallOp = X86::CALLpcrel32;

  const char *Symbol;
  if (Is64Bit) {
    if (STI.isTargetCygMing()) {
      Symbol = "___chkstk_ms";
    } else {
      Symbol = "__chkstk";
    }
  } else if (STI.isTargetCygMing())
    Symbol = "_alloca";
  else
    Symbol = "_chkstk";

  MachineInstrBuilder CI;
  MachineBasicBlock::iterator ExpansionMBBI = std::prev(MBBI);

  // All current stack probes take AX and SP as input, clobber flags, and
  // preserve all registers. x86_64 probes leave RSP unmodified.
  if (Is64Bit && MF.getTarget().getCodeModel() == CodeModel::Large) {
    // For the large code model, we have to call through a register. Use R11,
    // as it is scratch in all supported calling conventions.
    BuildMI(MBB, MBBI, DL, TII.get(X86::MOV64ri), X86::R11)
        .addExternalSymbol(Symbol);
    CI = BuildMI(MBB, MBBI, DL, TII.get(CallOp)).addReg(X86::R11);
  } else {
    CI = BuildMI(MBB, MBBI, DL, TII.get(CallOp)).addExternalSymbol(Symbol);
  }

  unsigned AX = Is64Bit ? X86::RAX : X86::EAX;
  unsigned SP = Is64Bit ? X86::RSP : X86::ESP;
  CI.addReg(AX, RegState::Implicit)
      .addReg(SP, RegState::Implicit)
      .addReg(AX, RegState::Define | RegState::Implicit)
      .addReg(SP, RegState::Define | RegState::Implicit)
      .addReg(X86::EFLAGS, RegState::Define | RegState::Implicit);

  if (Is64Bit) {
    // MSVC x64's __chkstk and cygwin/mingw's ___chkstk_ms do not adjust %rsp
    // themselves. It also does not clobber %rax so we can reuse it when
    // adjusting %rsp.
    BuildMI(MBB, MBBI, DL, TII.get(X86::SUB64rr), X86::RSP)
        .addReg(X86::RSP)
        .addReg(X86::RAX);
  }

  if (InProlog) {
    // Apply the frame setup flag to all inserted instrs.
    for (++ExpansionMBBI; ExpansionMBBI != MBBI; ++ExpansionMBBI)
      ExpansionMBBI->setFlag(MachineInstr::FrameSetup);
  }

  return MBBI;
}

MachineInstr *X86FrameLowering::emitStackProbeInlineStub(
    MachineFunction &MF, MachineBasicBlock &MBB,
    MachineBasicBlock::iterator MBBI, DebugLoc DL, bool InProlog) const {

  assert(InProlog && "ChkStkStub called outside prolog!");

  BuildMI(MBB, MBBI, DL, TII.get(X86::CALLpcrel32))
      .addExternalSymbol("__chkstk_stub");

  return MBBI;
}

static unsigned calculateSetFPREG(uint64_t SPAdjust) {
  // Win64 ABI has a less restrictive limitation of 240; 128 works equally well
  // and might require smaller successive adjustments.
  const uint64_t Win64MaxSEHOffset = 128;
  uint64_t SEHFrameOffset = std::min(SPAdjust, Win64MaxSEHOffset);
  // Win64 ABI requires 16-byte alignment for the UWOP_SET_FPREG opcode.
  return SEHFrameOffset & -16;
}

// If we're forcing a stack realignment we can't rely on just the frame
// info, we need to know the ABI stack alignment as well in case we
// have a call out.  Otherwise just make sure we have some alignment - we'll
// go with the minimum SlotSize.
uint64_t X86FrameLowering::calculateMaxStackAlign(const MachineFunction &MF) const {
  const MachineFrameInfo *MFI = MF.getFrameInfo();
  uint64_t MaxAlign = MFI->getMaxAlignment(); // Desired stack alignment.
  unsigned StackAlign = getStackAlignment();
  if (MF.getFunction()->hasFnAttribute("stackrealign")) {
    if (MFI->hasCalls())
      MaxAlign = (StackAlign > MaxAlign) ? StackAlign : MaxAlign;
    else if (MaxAlign < SlotSize)
      MaxAlign = SlotSize;
  }
  return MaxAlign;
}

void X86FrameLowering::BuildStackAlignAND(MachineBasicBlock &MBB,
                                          MachineBasicBlock::iterator MBBI,
                                          DebugLoc DL, unsigned Reg,
                                          uint64_t MaxAlign) const {
  uint64_t Val = -MaxAlign;
  unsigned AndOp = getANDriOpcode(Uses64BitFramePtr, Val);
  MachineInstr *MI = BuildMI(MBB, MBBI, DL, TII.get(AndOp), Reg)
                         .addReg(Reg)
                         .addImm(Val)
                         .setMIFlag(MachineInstr::FrameSetup);

  // The EFLAGS implicit def is dead.
  MI->getOperand(3).setIsDead();
}

/// emitPrologue - Push callee-saved registers onto the stack, which
/// automatically adjust the stack pointer. Adjust the stack pointer to allocate
/// space for local variables. Also emit labels used by the exception handler to
/// generate the exception handling frames.

/*
  Here's a gist of what gets emitted:

  ; Establish frame pointer, if needed
  [if needs FP]
      push  %rbp
      .cfi_def_cfa_offset 16
      .cfi_offset %rbp, -16
      .seh_pushreg %rpb
      mov  %rsp, %rbp
      .cfi_def_cfa_register %rbp

  ; Spill general-purpose registers
  [for all callee-saved GPRs]
      pushq %<reg>
      [if not needs FP]
         .cfi_def_cfa_offset (offset from RETADDR)
      .seh_pushreg %<reg>

  ; If the required stack alignment > default stack alignment
  ; rsp needs to be re-aligned.  This creates a "re-alignment gap"
  ; of unknown size in the stack frame.
  [if stack needs re-alignment]
      and  $MASK, %rsp

  ; Allocate space for locals
  [if target is Windows and allocated space > 4096 bytes]
      ; Windows needs special care for allocations larger
      ; than one page.
      mov $NNN, %rax
      call ___chkstk_ms/___chkstk
      sub  %rax, %rsp
  [else]
      sub  $NNN, %rsp

  [if needs FP]
      .seh_stackalloc (size of XMM spill slots)
      .seh_setframe %rbp, SEHFrameOffset ; = size of all spill slots
  [else]
      .seh_stackalloc NNN

  ; Spill XMMs
  ; Note, that while only Windows 64 ABI specifies XMMs as callee-preserved,
  ; they may get spilled on any platform, if the current function
  ; calls @llvm.eh.unwind.init
  [if needs FP]
      [for all callee-saved XMM registers]
          movaps  %<xmm reg>, -MMM(%rbp)
      [for all callee-saved XMM registers]
          .seh_savexmm %<xmm reg>, (-MMM + SEHFrameOffset)
              ; i.e. the offset relative to (%rbp - SEHFrameOffset)
  [else]
      [for all callee-saved XMM registers]
          movaps  %<xmm reg>, KKK(%rsp)
      [for all callee-saved XMM registers]
          .seh_savexmm %<xmm reg>, KKK

  .seh_endprologue

  [if needs base pointer]
      mov  %rsp, %rbx
      [if needs to restore base pointer]
          mov %rsp, -MMM(%rbp)

  ; Emit CFI info
  [if needs FP]
      [for all callee-saved registers]
          .cfi_offset %<reg>, (offset from %rbp)
  [else]
       .cfi_def_cfa_offset (offset from RETADDR)
      [for all callee-saved registers]
          .cfi_offset %<reg>, (offset from %rsp)

  Notes:
  - .seh directives are emitted only for Windows 64 ABI
  - .cfi directives are emitted for all other ABIs
  - for 32-bit code, substitute %e?? registers for %r??
*/

void X86FrameLowering::emitPrologue(MachineFunction &MF,
                                    MachineBasicBlock &MBB) const {
  assert(&STI == &MF.getSubtarget<X86Subtarget>() &&
         "MF used frame lowering for wrong subtarget");
  MachineBasicBlock::iterator MBBI = MBB.begin();
  MachineFrameInfo *MFI = MF.getFrameInfo();
  const Function *Fn = MF.getFunction();
  MachineModuleInfo &MMI = MF.getMMI();
  X86MachineFunctionInfo *X86FI = MF.getInfo<X86MachineFunctionInfo>();
  uint64_t MaxAlign = calculateMaxStackAlign(MF); // Desired stack alignment.
  uint64_t StackSize = MFI->getStackSize();    // Number of bytes to allocate.
  bool IsFunclet = MBB.isEHFuncletEntry();
  EHPersonality Personality = EHPersonality::Unknown;
  if (Fn->hasPersonalityFn())
    Personality = classifyEHPersonality(Fn->getPersonalityFn());
  bool FnHasClrFunclet =
      MMI.hasEHFunclets() && Personality == EHPersonality::CoreCLR;
  bool IsClrFunclet = IsFunclet && FnHasClrFunclet;
  bool HasFP = hasFP(MF);
  bool IsWin64CC = STI.isCallingConvWin64(Fn->getCallingConv());
  bool IsWin64Prologue = MF.getTarget().getMCAsmInfo()->usesWindowsCFI();
  bool NeedsWinCFI = IsWin64Prologue && Fn->needsUnwindTableEntry();
  bool NeedsDwarfCFI =
      !IsWin64Prologue && (MMI.hasDebugInfo() || Fn->needsUnwindTableEntry());
  unsigned FramePtr = TRI->getFrameRegister(MF);
  const unsigned MachineFramePtr =
      STI.isTarget64BitILP32()
          ? getX86SubSuperRegister(FramePtr, 64) : FramePtr;
  unsigned BasePtr = TRI->getBaseRegister();
  
  // Debug location must be unknown since the first debug location is used
  // to determine the end of the prologue.
  DebugLoc DL;

  // Add RETADDR move area to callee saved frame size.
  int TailCallReturnAddrDelta = X86FI->getTCReturnAddrDelta();
  if (TailCallReturnAddrDelta && IsWin64Prologue)
    report_fatal_error("Can't handle guaranteed tail call under win64 yet");

  if (TailCallReturnAddrDelta < 0)
    X86FI->setCalleeSavedFrameSize(
      X86FI->getCalleeSavedFrameSize() - TailCallReturnAddrDelta);

  bool UseStackProbe = (STI.isOSWindows() && !STI.isTargetMachO());

  // The default stack probe size is 4096 if the function has no stackprobesize
  // attribute.
  unsigned StackProbeSize = 4096;
  if (Fn->hasFnAttribute("stack-probe-size"))
    Fn->getFnAttribute("stack-probe-size")
        .getValueAsString()
        .getAsInteger(0, StackProbeSize);

  // If this is x86-64 and the Red Zone is not disabled, if we are a leaf
  // function, and use up to 128 bytes of stack space, don't have a frame
  // pointer, calls, or dynamic alloca then we do not need to adjust the
  // stack pointer (we fit in the Red Zone). We also check that we don't
  // push and pop from the stack.
  if (Is64Bit && !Fn->hasFnAttribute(Attribute::NoRedZone) &&
      !TRI->needsStackRealignment(MF) &&
      !MFI->hasVarSizedObjects() &&             // No dynamic alloca.
      !MFI->adjustsStack() &&                   // No calls.
      !IsWin64CC &&                             // Win64 has no Red Zone
      !MFI->hasCopyImplyingStackAdjustment() && // Don't push and pop.
      !MF.shouldSplitStack()) {                 // Regular stack
    uint64_t MinSize = X86FI->getCalleeSavedFrameSize();
    if (HasFP) MinSize += SlotSize;
    StackSize = std::max(MinSize, StackSize > 128 ? StackSize - 128 : 0);
    MFI->setStackSize(StackSize);
  }

  // Insert stack pointer adjustment for later moving of return addr.  Only
  // applies to tail call optimized functions where the callee argument stack
  // size is bigger than the callers.
  if (TailCallReturnAddrDelta < 0) {
    BuildStackAdjustment(MBB, MBBI, DL, TailCallReturnAddrDelta,
                         /*InEpilogue=*/false)
        .setMIFlag(MachineInstr::FrameSetup);
  }

  // Mapping for machine moves:
  //
  //   DST: VirtualFP AND
  //        SRC: VirtualFP              => DW_CFA_def_cfa_offset
  //        ELSE                        => DW_CFA_def_cfa
  //
  //   SRC: VirtualFP AND
  //        DST: Register               => DW_CFA_def_cfa_register
  //
  //   ELSE
  //        OFFSET < 0                  => DW_CFA_offset_extended_sf
  //        REG < 64                    => DW_CFA_offset + Reg
  //        ELSE                        => DW_CFA_offset_extended

  uint64_t NumBytes = 0;
  int stackGrowth = -SlotSize;

  // Find the funclet establisher parameter
  unsigned Establisher = X86::NoRegister;
  if (IsClrFunclet)
    Establisher = Uses64BitFramePtr ? X86::RCX : X86::ECX;
  else if (IsFunclet)
    Establisher = Uses64BitFramePtr ? X86::RDX : X86::EDX;

  if (IsWin64Prologue && IsFunclet && !IsClrFunclet) {
    // Immediately spill establisher into the home slot.
    // The runtime cares about this.
    // MOV64mr %rdx, 16(%rsp)
    unsigned MOVmr = Uses64BitFramePtr ? X86::MOV64mr : X86::MOV32mr;
    addRegOffset(BuildMI(MBB, MBBI, DL, TII.get(MOVmr)), StackPtr, true, 16)
        .addReg(Establisher)
        .setMIFlag(MachineInstr::FrameSetup);
    MBB.addLiveIn(Establisher);
  }

  if (HasFP) {
    // Calculate required stack adjustment.
    uint64_t FrameSize = StackSize - SlotSize;
    // If required, include space for extra hidden slot for stashing base pointer.
    if (X86FI->getRestoreBasePointer())
      FrameSize += SlotSize;

    NumBytes = FrameSize - X86FI->getCalleeSavedFrameSize();

    // Callee-saved registers are pushed on stack before the stack is realigned.
    if (TRI->needsStackRealignment(MF) && !IsWin64Prologue)
      NumBytes = alignTo(NumBytes, MaxAlign);

    // Get the offset of the stack slot for the EBP register, which is
    // guaranteed to be the last slot by processFunctionBeforeFrameFinalized.
    // Update the frame offset adjustment.
    if (!IsFunclet)
      MFI->setOffsetAdjustment(-NumBytes);
    else
      assert(MFI->getOffsetAdjustment() == -(int)NumBytes &&
             "should calculate same local variable offset for funclets");

    // Save EBP/RBP into the appropriate stack slot.
    BuildMI(MBB, MBBI, DL, TII.get(Is64Bit ? X86::PUSH64r : X86::PUSH32r))
      .addReg(MachineFramePtr, RegState::Kill)
      .setMIFlag(MachineInstr::FrameSetup);

    if (NeedsDwarfCFI) {
      // Mark the place where EBP/RBP was saved.
      // Define the current CFA rule to use the provided offset.
      assert(StackSize);
      BuildCFI(MBB, MBBI, DL,
               MCCFIInstruction::createDefCfaOffset(nullptr, 2 * stackGrowth));

      // Change the rule for the FramePtr to be an "offset" rule.
      unsigned DwarfFramePtr = TRI->getDwarfRegNum(MachineFramePtr, true);
      BuildCFI(MBB, MBBI, DL, MCCFIInstruction::createOffset(
                                  nullptr, DwarfFramePtr, 2 * stackGrowth));
    }

    if (NeedsWinCFI) {
      BuildMI(MBB, MBBI, DL, TII.get(X86::SEH_PushReg))
          .addImm(FramePtr)
          .setMIFlag(MachineInstr::FrameSetup);
    }

    if (!IsWin64Prologue && !IsFunclet) {
      // Update EBP with the new base value.
      BuildMI(MBB, MBBI, DL,
              TII.get(Uses64BitFramePtr ? X86::MOV64rr : X86::MOV32rr),
              FramePtr)
          .addReg(StackPtr)
          .setMIFlag(MachineInstr::FrameSetup);

      if (NeedsDwarfCFI) {
        // Mark effective beginning of when frame pointer becomes valid.
        // Define the current CFA to use the EBP/RBP register.
        unsigned DwarfFramePtr = TRI->getDwarfRegNum(MachineFramePtr, true);
        BuildCFI(MBB, MBBI, DL, MCCFIInstruction::createDefCfaRegister(
                                    nullptr, DwarfFramePtr));
      }
    }

    // Mark the FramePtr as live-in in every block. Don't do this again for
    // funclet prologues.
    if (!IsFunclet) {
      for (MachineBasicBlock &EveryMBB : MF)
        EveryMBB.addLiveIn(MachineFramePtr);
    }
  } else {
    assert(!IsFunclet && "funclets without FPs not yet implemented");
    NumBytes = StackSize - X86FI->getCalleeSavedFrameSize();
  }

  // For EH funclets, only allocate enough space for outgoing calls. Save the
  // NumBytes value that we would've used for the parent frame.
  unsigned ParentFrameNumBytes = NumBytes;
  if (IsFunclet)
    NumBytes = getWinEHFuncletFrameSize(MF);

  // Skip the callee-saved push instructions.
  bool PushedRegs = false;
  int StackOffset = 2 * stackGrowth;

  while (MBBI != MBB.end() &&
         MBBI->getFlag(MachineInstr::FrameSetup) &&
         (MBBI->getOpcode() == X86::PUSH32r ||
          MBBI->getOpcode() == X86::PUSH64r)) {
    PushedRegs = true;
    unsigned Reg = MBBI->getOperand(0).getReg();
    ++MBBI;

    if (!HasFP && NeedsDwarfCFI) {
      // Mark callee-saved push instruction.
      // Define the current CFA rule to use the provided offset.
      assert(StackSize);
      BuildCFI(MBB, MBBI, DL,
               MCCFIInstruction::createDefCfaOffset(nullptr, StackOffset));
      StackOffset += stackGrowth;
    }

    if (NeedsWinCFI) {
      BuildMI(MBB, MBBI, DL, TII.get(X86::SEH_PushReg)).addImm(Reg).setMIFlag(
          MachineInstr::FrameSetup);
    }
  }

  // Realign stack after we pushed callee-saved registers (so that we'll be
  // able to calculate their offsets from the frame pointer).
  // Don't do this for Win64, it needs to realign the stack after the prologue.
  if (!IsWin64Prologue && !IsFunclet && TRI->needsStackRealignment(MF)) {
    assert(HasFP && "There should be a frame pointer if stack is realigned.");
    BuildStackAlignAND(MBB, MBBI, DL, StackPtr, MaxAlign);
  }

  // If there is an SUB32ri of ESP immediately before this instruction, merge
  // the two. This can be the case when tail call elimination is enabled and
  // the callee has more arguments then the caller.
  NumBytes -= mergeSPUpdates(MBB, MBBI, true);

  // Adjust stack pointer: ESP -= numbytes.

  // Windows and cygwin/mingw require a prologue helper routine when allocating
  // more than 4K bytes on the stack.  Windows uses __chkstk and cygwin/mingw
  // uses __alloca.  __alloca and the 32-bit version of __chkstk will probe the
  // stack and adjust the stack pointer in one go.  The 64-bit version of
  // __chkstk is only responsible for probing the stack.  The 64-bit prologue is
  // responsible for adjusting the stack pointer.  Touching the stack at 4K
  // increments is necessary to ensure that the guard pages used by the OS
  // virtual memory manager are allocated in correct sequence.
  uint64_t AlignedNumBytes = NumBytes;
  if (IsWin64Prologue && !IsFunclet && TRI->needsStackRealignment(MF))
    AlignedNumBytes = alignTo(AlignedNumBytes, MaxAlign);
  if (AlignedNumBytes >= StackProbeSize && UseStackProbe) {
    // Check whether EAX is livein for this function.
    bool isEAXAlive = isEAXLiveIn(MF);

    if (isEAXAlive) {
      // Sanity check that EAX is not livein for this function.
      // It should not be, so throw an assert.
      assert(!Is64Bit && "EAX is livein in x64 case!");

      // Save EAX
      BuildMI(MBB, MBBI, DL, TII.get(X86::PUSH32r))
        .addReg(X86::EAX, RegState::Kill)
        .setMIFlag(MachineInstr::FrameSetup);
    }

    if (Is64Bit) {
      // Handle the 64-bit Windows ABI case where we need to call __chkstk.
      // Function prologue is responsible for adjusting the stack pointer.
      if (isUInt<32>(NumBytes)) {
        BuildMI(MBB, MBBI, DL, TII.get(X86::MOV32ri), X86::EAX)
            .addImm(NumBytes)
            .setMIFlag(MachineInstr::FrameSetup);
      } else if (isInt<32>(NumBytes)) {
        BuildMI(MBB, MBBI, DL, TII.get(X86::MOV64ri32), X86::RAX)
            .addImm(NumBytes)
            .setMIFlag(MachineInstr::FrameSetup);
      } else {
        BuildMI(MBB, MBBI, DL, TII.get(X86::MOV64ri), X86::RAX)
            .addImm(NumBytes)
            .setMIFlag(MachineInstr::FrameSetup);
      }
    } else {
      // Allocate NumBytes-4 bytes on stack in case of isEAXAlive.
      // We'll also use 4 already allocated bytes for EAX.
      BuildMI(MBB, MBBI, DL, TII.get(X86::MOV32ri), X86::EAX)
          .addImm(isEAXAlive ? NumBytes - 4 : NumBytes)
          .setMIFlag(MachineInstr::FrameSetup);
    }

    // Call __chkstk, __chkstk_ms, or __alloca.
    emitStackProbe(MF, MBB, MBBI, DL, true);

    if (isEAXAlive) {
      // Restore EAX
      MachineInstr *MI =
          addRegOffset(BuildMI(MF, DL, TII.get(X86::MOV32rm), X86::EAX),
                       StackPtr, false, NumBytes - 4);
      MI->setFlag(MachineInstr::FrameSetup);
      MBB.insert(MBBI, MI);
    }
  } else if (NumBytes) {
    emitSPUpdate(MBB, MBBI, -(int64_t)NumBytes, /*InEpilogue=*/false);
  }

  if (NeedsWinCFI && NumBytes)
    BuildMI(MBB, MBBI, DL, TII.get(X86::SEH_StackAlloc))
        .addImm(NumBytes)
        .setMIFlag(MachineInstr::FrameSetup);

  int SEHFrameOffset = 0;
  unsigned SPOrEstablisher;
  if (IsFunclet) {
    if (IsClrFunclet) {
      // The establisher parameter passed to a CLR funclet is actually a pointer
      // to the (mostly empty) frame of its nearest enclosing funclet; we have
      // to find the root function establisher frame by loading the PSPSym from
      // the intermediate frame.
      unsigned PSPSlotOffset = getPSPSlotOffsetFromSP(MF);
      MachinePointerInfo NoInfo;
      MBB.addLiveIn(Establisher);
      addRegOffset(BuildMI(MBB, MBBI, DL, TII.get(X86::MOV64rm), Establisher),
                   Establisher, false, PSPSlotOffset)
          .addMemOperand(MF.getMachineMemOperand(
              NoInfo, MachineMemOperand::MOLoad, SlotSize, SlotSize));
      ;
      // Save the root establisher back into the current funclet's (mostly
      // empty) frame, in case a sub-funclet or the GC needs it.
      addRegOffset(BuildMI(MBB, MBBI, DL, TII.get(X86::MOV64mr)), StackPtr,
                   false, PSPSlotOffset)
          .addReg(Establisher)
          .addMemOperand(
              MF.getMachineMemOperand(NoInfo, MachineMemOperand::MOStore |
                                                  MachineMemOperand::MOVolatile,
                                      SlotSize, SlotSize));
    }
    SPOrEstablisher = Establisher;
  } else {
    SPOrEstablisher = StackPtr;
  }

  if (IsWin64Prologue && HasFP) {
    // Set RBP to a small fixed offset from RSP. In the funclet case, we base
    // this calculation on the incoming establisher, which holds the value of
    // RSP from the parent frame at the end of the prologue.
    SEHFrameOffset = calculateSetFPREG(ParentFrameNumBytes);
    if (SEHFrameOffset)
      addRegOffset(BuildMI(MBB, MBBI, DL, TII.get(X86::LEA64r), FramePtr),
                   SPOrEstablisher, false, SEHFrameOffset);
    else
      BuildMI(MBB, MBBI, DL, TII.get(X86::MOV64rr), FramePtr)
          .addReg(SPOrEstablisher);

    // If this is not a funclet, emit the CFI describing our frame pointer.
    if (NeedsWinCFI && !IsFunclet) {
      BuildMI(MBB, MBBI, DL, TII.get(X86::SEH_SetFrame))
          .addImm(FramePtr)
          .addImm(SEHFrameOffset)
          .setMIFlag(MachineInstr::FrameSetup);
      if (isAsynchronousEHPersonality(Personality))
        MF.getWinEHFuncInfo()->SEHSetFrameOffset = SEHFrameOffset;
    }
  } else if (IsFunclet && STI.is32Bit()) {
    // Reset EBP / ESI to something good for funclets.
    MBBI = restoreWin32EHStackPointers(MBB, MBBI, DL);
    // If we're a catch funclet, we can be returned to via catchret. Save ESP
    // into the registration node so that the runtime will restore it for us.
    if (!MBB.isCleanupFuncletEntry()) {
      assert(Personality == EHPersonality::MSVC_CXX);
      unsigned FrameReg;
      int FI = MF.getWinEHFuncInfo()->EHRegNodeFrameIndex;
      int64_t EHRegOffset = getFrameIndexReference(MF, FI, FrameReg);
      // ESP is the first field, so no extra displacement is needed.
      addRegOffset(BuildMI(MBB, MBBI, DL, TII.get(X86::MOV32mr)), FrameReg,
                   false, EHRegOffset)
          .addReg(X86::ESP);
    }
  }

  while (MBBI != MBB.end() && MBBI->getFlag(MachineInstr::FrameSetup)) {
    const MachineInstr *FrameInstr = &*MBBI;
    ++MBBI;

    if (NeedsWinCFI) {
      int FI;
      if (unsigned Reg = TII.isStoreToStackSlot(FrameInstr, FI)) {
        if (X86::FR64RegClass.contains(Reg)) {
          unsigned IgnoredFrameReg;
          int Offset = getFrameIndexReference(MF, FI, IgnoredFrameReg);
          Offset += SEHFrameOffset;

          BuildMI(MBB, MBBI, DL, TII.get(X86::SEH_SaveXMM))
              .addImm(Reg)
              .addImm(Offset)
              .setMIFlag(MachineInstr::FrameSetup);
        }
      }
    }
  }

  if (NeedsWinCFI)
    BuildMI(MBB, MBBI, DL, TII.get(X86::SEH_EndPrologue))
        .setMIFlag(MachineInstr::FrameSetup);

  if (FnHasClrFunclet && !IsFunclet) {
    // Save the so-called Initial-SP (i.e. the value of the stack pointer
    // immediately after the prolog)  into the PSPSlot so that funclets
    // and the GC can recover it.
    unsigned PSPSlotOffset = getPSPSlotOffsetFromSP(MF);
    auto PSPInfo = MachinePointerInfo::getFixedStack(
        MF, MF.getWinEHFuncInfo()->PSPSymFrameIdx);
    addRegOffset(BuildMI(MBB, MBBI, DL, TII.get(X86::MOV64mr)), StackPtr, false,
                 PSPSlotOffset)
        .addReg(StackPtr)
        .addMemOperand(MF.getMachineMemOperand(
            PSPInfo, MachineMemOperand::MOStore | MachineMemOperand::MOVolatile,
            SlotSize, SlotSize));
  }

  // Realign stack after we spilled callee-saved registers (so that we'll be
  // able to calculate their offsets from the frame pointer).
  // Win64 requires aligning the stack after the prologue.
  if (IsWin64Prologue && TRI->needsStackRealignment(MF)) {
    assert(HasFP && "There should be a frame pointer if stack is realigned.");
    BuildStackAlignAND(MBB, MBBI, DL, SPOrEstablisher, MaxAlign);
  }

  // We already dealt with stack realignment and funclets above.
  if (IsFunclet && STI.is32Bit())
    return;

  // If we need a base pointer, set it up here. It's whatever the value
  // of the stack pointer is at this point. Any variable size objects
  // will be allocated after this, so we can still use the base pointer
  // to reference locals.
  if (TRI->hasBasePointer(MF)) {
    // Update the base pointer with the current stack pointer.
    unsigned Opc = Uses64BitFramePtr ? X86::MOV64rr : X86::MOV32rr;
    BuildMI(MBB, MBBI, DL, TII.get(Opc), BasePtr)
      .addReg(SPOrEstablisher)
      .setMIFlag(MachineInstr::FrameSetup);
    if (X86FI->getRestoreBasePointer()) {
      // Stash value of base pointer.  Saving RSP instead of EBP shortens
      // dependence chain. Used by SjLj EH.
      unsigned Opm = Uses64BitFramePtr ? X86::MOV64mr : X86::MOV32mr;
      addRegOffset(BuildMI(MBB, MBBI, DL, TII.get(Opm)),
                   FramePtr, true, X86FI->getRestoreBasePointerOffset())
        .addReg(SPOrEstablisher)
        .setMIFlag(MachineInstr::FrameSetup);
    }

    if (X86FI->getHasSEHFramePtrSave() && !IsFunclet) {
      // Stash the value of the frame pointer relative to the base pointer for
      // Win32 EH. This supports Win32 EH, which does the inverse of the above:
      // it recovers the frame pointer from the base pointer rather than the
      // other way around.
      unsigned Opm = Uses64BitFramePtr ? X86::MOV64mr : X86::MOV32mr;
      unsigned UsedReg;
      int Offset =
          getFrameIndexReference(MF, X86FI->getSEHFramePtrSaveIndex(), UsedReg);
      assert(UsedReg == BasePtr);
      addRegOffset(BuildMI(MBB, MBBI, DL, TII.get(Opm)), UsedReg, true, Offset)
          .addReg(FramePtr)
          .setMIFlag(MachineInstr::FrameSetup);
    }
  }

  if (((!HasFP && NumBytes) || PushedRegs) && NeedsDwarfCFI) {
    // Mark end of stack pointer adjustment.
    if (!HasFP && NumBytes) {
      // Define the current CFA rule to use the provided offset.
      assert(StackSize);
      BuildCFI(MBB, MBBI, DL, MCCFIInstruction::createDefCfaOffset(
                                  nullptr, -StackSize + stackGrowth));
    }

    // Emit DWARF info specifying the offsets of the callee-saved registers.
    if (PushedRegs)
      emitCalleeSavedFrameMoves(MBB, MBBI, DL);
  }
}

bool X86FrameLowering::canUseLEAForSPInEpilogue(
    const MachineFunction &MF) const {
  // We can't use LEA instructions for adjusting the stack pointer if this is a
  // leaf function in the Win64 ABI.  Only ADD instructions may be used to
  // deallocate the stack.
  // This means that we can use LEA for SP in two situations:
  // 1. We *aren't* using the Win64 ABI which means we are free to use LEA.
  // 2. We *have* a frame pointer which means we are permitted to use LEA.
  return !MF.getTarget().getMCAsmInfo()->usesWindowsCFI() || hasFP(MF);
}

static bool isFuncletReturnInstr(MachineInstr *MI) {
  switch (MI->getOpcode()) {
  case X86::CATCHRET:
  case X86::CLEANUPRET:
    return true;
  default:
    return false;
  }
  llvm_unreachable("impossible");
}

// CLR funclets use a special "Previous Stack Pointer Symbol" slot on the
// stack. It holds a pointer to the bottom of the root function frame.  The
// establisher frame pointer passed to a nested funclet may point to the
// (mostly empty) frame of its parent funclet, but it will need to find
// the frame of the root function to access locals.  To facilitate this,
// every funclet copies the pointer to the bottom of the root function
// frame into a PSPSym slot in its own (mostly empty) stack frame. Using the
// same offset for the PSPSym in the root function frame that's used in the
// funclets' frames allows each funclet to dynamically accept any ancestor
// frame as its establisher argument (the runtime doesn't guarantee the
// immediate parent for some reason lost to history), and also allows the GC,
// which uses the PSPSym for some bookkeeping, to find it in any funclet's
// frame with only a single offset reported for the entire method.
unsigned
X86FrameLowering::getPSPSlotOffsetFromSP(const MachineFunction &MF) const {
  const WinEHFuncInfo &Info = *MF.getWinEHFuncInfo();
  // getFrameIndexReferenceFromSP has an out ref parameter for the stack
  // pointer register; pass a dummy that we ignore
  unsigned SPReg;
  int Offset = getFrameIndexReferenceFromSP(MF, Info.PSPSymFrameIdx, SPReg);
  assert(Offset >= 0);
  return static_cast<unsigned>(Offset);
}

unsigned
X86FrameLowering::getWinEHFuncletFrameSize(const MachineFunction &MF) const {
  // This is the size of the pushed CSRs.
  unsigned CSSize =
      MF.getInfo<X86MachineFunctionInfo>()->getCalleeSavedFrameSize();
  // This is the amount of stack a funclet needs to allocate.
  unsigned UsedSize;
  EHPersonality Personality =
      classifyEHPersonality(MF.getFunction()->getPersonalityFn());
  if (Personality == EHPersonality::CoreCLR) {
    // CLR funclets need to hold enough space to include the PSPSym, at the
    // same offset from the stack pointer (immediately after the prolog) as it
    // resides at in the main function.
    UsedSize = getPSPSlotOffsetFromSP(MF) + SlotSize;
  } else {
    // Other funclets just need enough stack for outgoing call arguments.
    UsedSize = MF.getFrameInfo()->getMaxCallFrameSize();
  }
  // RBP is not included in the callee saved register block. After pushing RBP,
  // everything is 16 byte aligned. Everything we allocate before an outgoing
  // call must also be 16 byte aligned.
  unsigned FrameSizeMinusRBP = alignTo(CSSize + UsedSize, getStackAlignment());
  // Subtract out the size of the callee saved registers. This is how much stack
  // each funclet will allocate.
  return FrameSizeMinusRBP - CSSize;
}

void X86FrameLowering::emitEpilogue(MachineFunction &MF,
                                    MachineBasicBlock &MBB) const {
  const MachineFrameInfo *MFI = MF.getFrameInfo();
  X86MachineFunctionInfo *X86FI = MF.getInfo<X86MachineFunctionInfo>();
  MachineBasicBlock::iterator MBBI = MBB.getFirstTerminator();
  DebugLoc DL;
  if (MBBI != MBB.end())
    DL = MBBI->getDebugLoc();
  // standard x86_64 and NaCl use 64-bit frame/stack pointers, x32 - 32-bit.
  const bool Is64BitILP32 = STI.isTarget64BitILP32();
  unsigned FramePtr = TRI->getFrameRegister(MF);
  unsigned MachineFramePtr =
      Is64BitILP32 ? getX86SubSuperRegister(FramePtr, 64) : FramePtr;

  bool IsWin64Prologue = MF.getTarget().getMCAsmInfo()->usesWindowsCFI();
  bool NeedsWinCFI =
      IsWin64Prologue && MF.getFunction()->needsUnwindTableEntry();
  bool IsFunclet = isFuncletReturnInstr(MBBI);
  MachineBasicBlock *TargetMBB = nullptr;

  // Get the number of bytes to allocate from the FrameInfo.
  uint64_t StackSize = MFI->getStackSize();
  uint64_t MaxAlign = calculateMaxStackAlign(MF);
  unsigned CSSize = X86FI->getCalleeSavedFrameSize();
  uint64_t NumBytes = 0;

  if (MBBI->getOpcode() == X86::CATCHRET) {
    // SEH shouldn't use catchret.
    assert(!isAsynchronousEHPersonality(
               classifyEHPersonality(MF.getFunction()->getPersonalityFn())) &&
           "SEH should not use CATCHRET");

    NumBytes = getWinEHFuncletFrameSize(MF);
    assert(hasFP(MF) && "EH funclets without FP not yet implemented");
    TargetMBB = MBBI->getOperand(0).getMBB();

    // Pop EBP.
    BuildMI(MBB, MBBI, DL, TII.get(Is64Bit ? X86::POP64r : X86::POP32r),
            MachineFramePtr)
        .setMIFlag(MachineInstr::FrameDestroy);
  } else if (MBBI->getOpcode() == X86::CLEANUPRET) {
    NumBytes = getWinEHFuncletFrameSize(MF);
    assert(hasFP(MF) && "EH funclets without FP not yet implemented");
    BuildMI(MBB, MBBI, DL, TII.get(Is64Bit ? X86::POP64r : X86::POP32r),
            MachineFramePtr)
        .setMIFlag(MachineInstr::FrameDestroy);
  } else if (hasFP(MF)) {
    // Calculate required stack adjustment.
    uint64_t FrameSize = StackSize - SlotSize;
    NumBytes = FrameSize - CSSize;

    // Callee-saved registers were pushed on stack before the stack was
    // realigned.
    if (TRI->needsStackRealignment(MF) && !IsWin64Prologue)
      NumBytes = alignTo(FrameSize, MaxAlign);

    // Pop EBP.
    BuildMI(MBB, MBBI, DL,
            TII.get(Is64Bit ? X86::POP64r : X86::POP32r), MachineFramePtr)
        .setMIFlag(MachineInstr::FrameDestroy);
  } else {
    NumBytes = StackSize - CSSize;
  }
  uint64_t SEHStackAllocAmt = NumBytes;

  // Skip the callee-saved pop instructions.
  while (MBBI != MBB.begin()) {
    MachineBasicBlock::iterator PI = std::prev(MBBI);
    unsigned Opc = PI->getOpcode();

    if ((Opc != X86::POP32r || !PI->getFlag(MachineInstr::FrameDestroy)) &&
        (Opc != X86::POP64r || !PI->getFlag(MachineInstr::FrameDestroy)) &&
        Opc != X86::DBG_VALUE && !PI->isTerminator())
      break;

    --MBBI;
  }
  MachineBasicBlock::iterator FirstCSPop = MBBI;

  if (TargetMBB) {
    // Fill EAX/RAX with the address of the target block.
    unsigned ReturnReg = STI.is64Bit() ? X86::RAX : X86::EAX;
    if (STI.is64Bit()) {
      // LEA64r TargetMBB(%rip), %rax
      BuildMI(MBB, FirstCSPop, DL, TII.get(X86::LEA64r), ReturnReg)
          .addReg(X86::RIP)
          .addImm(0)
          .addReg(0)
          .addMBB(TargetMBB)
          .addReg(0);
    } else {
      // MOV32ri $TargetMBB, %eax
      BuildMI(MBB, FirstCSPop, DL, TII.get(X86::MOV32ri), ReturnReg)
          .addMBB(TargetMBB);
    }
    // Record that we've taken the address of TargetMBB and no longer just
    // reference it in a terminator.
    TargetMBB->setHasAddressTaken();
  }

  if (MBBI != MBB.end())
    DL = MBBI->getDebugLoc();

  // If there is an ADD32ri or SUB32ri of ESP immediately before this
  // instruction, merge the two instructions.
  if (NumBytes || MFI->hasVarSizedObjects())
    NumBytes += mergeSPUpdates(MBB, MBBI, true);

  // If dynamic alloca is used, then reset esp to point to the last callee-saved
  // slot before popping them off! Same applies for the case, when stack was
  // realigned. Don't do this if this was a funclet epilogue, since the funclets
  // will not do realignment or dynamic stack allocation.
  if ((TRI->needsStackRealignment(MF) || MFI->hasVarSizedObjects()) &&
      !IsFunclet) {
    if (TRI->needsStackRealignment(MF))
      MBBI = FirstCSPop;
    unsigned SEHFrameOffset = calculateSetFPREG(SEHStackAllocAmt);
    uint64_t LEAAmount =
        IsWin64Prologue ? SEHStackAllocAmt - SEHFrameOffset : -CSSize;

    // There are only two legal forms of epilogue:
    // - add SEHAllocationSize, %rsp
    // - lea SEHAllocationSize(%FramePtr), %rsp
    //
    // 'mov %FramePtr, %rsp' will not be recognized as an epilogue sequence.
    // However, we may use this sequence if we have a frame pointer because the
    // effects of the prologue can safely be undone.
    if (LEAAmount != 0) {
      unsigned Opc = getLEArOpcode(Uses64BitFramePtr);
      addRegOffset(BuildMI(MBB, MBBI, DL, TII.get(Opc), StackPtr),
                   FramePtr, false, LEAAmount);
      --MBBI;
    } else {
      unsigned Opc = (Uses64BitFramePtr ? X86::MOV64rr : X86::MOV32rr);
      BuildMI(MBB, MBBI, DL, TII.get(Opc), StackPtr)
        .addReg(FramePtr);
      --MBBI;
    }
  } else if (NumBytes) {
    // Adjust stack pointer back: ESP += numbytes.
    emitSPUpdate(MBB, MBBI, NumBytes, /*InEpilogue=*/true);
    --MBBI;
  }

  // Windows unwinder will not invoke function's exception handler if IP is
  // either in prologue or in epilogue.  This behavior causes a problem when a
  // call immediately precedes an epilogue, because the return address points
  // into the epilogue.  To cope with that, we insert an epilogue marker here,
  // then replace it with a 'nop' if it ends up immediately after a CALL in the
  // final emitted code.
  if (NeedsWinCFI)
    BuildMI(MBB, MBBI, DL, TII.get(X86::SEH_Epilogue));

  // Add the return addr area delta back since we are not tail calling.
  int Offset = -1 * X86FI->getTCReturnAddrDelta();
  assert(Offset >= 0 && "TCDelta should never be positive");
  if (Offset) {
    MBBI = MBB.getFirstTerminator();

    // Check for possible merge with preceding ADD instruction.
    Offset += mergeSPUpdates(MBB, MBBI, true);
    emitSPUpdate(MBB, MBBI, Offset, /*InEpilogue=*/true);
  }
}

// NOTE: this only has a subset of the full frame index logic. In
// particular, the FI < 0 and AfterFPPop logic is handled in
// X86RegisterInfo::eliminateFrameIndex, but not here. Possibly
// (probably?) it should be moved into here.
int X86FrameLowering::getFrameIndexReference(const MachineFunction &MF, int FI,
                                             unsigned &FrameReg) const {
  const MachineFrameInfo *MFI = MF.getFrameInfo();

  // We can't calculate offset from frame pointer if the stack is realigned,
  // so enforce usage of stack/base pointer.  The base pointer is used when we
  // have dynamic allocas in addition to dynamic realignment.
  if (TRI->hasBasePointer(MF))
    FrameReg = TRI->getBaseRegister();
  else if (TRI->needsStackRealignment(MF))
    FrameReg = TRI->getStackRegister();
  else
    FrameReg = TRI->getFrameRegister(MF);

  // Offset will hold the offset from the stack pointer at function entry to the
  // object.
  // We need to factor in additional offsets applied during the prologue to the
  // frame, base, and stack pointer depending on which is used.
  int Offset = MFI->getObjectOffset(FI) - getOffsetOfLocalArea();
  const X86MachineFunctionInfo *X86FI = MF.getInfo<X86MachineFunctionInfo>();
  unsigned CSSize = X86FI->getCalleeSavedFrameSize();
  uint64_t StackSize = MFI->getStackSize();
  bool HasFP = hasFP(MF);
  bool IsWin64Prologue = MF.getTarget().getMCAsmInfo()->usesWindowsCFI();
  int64_t FPDelta = 0;

  if (IsWin64Prologue) {
    assert(!MFI->hasCalls() || (StackSize % 16) == 8);

    // Calculate required stack adjustment.
    uint64_t FrameSize = StackSize - SlotSize;
    // If required, include space for extra hidden slot for stashing base pointer.
    if (X86FI->getRestoreBasePointer())
      FrameSize += SlotSize;
    uint64_t NumBytes = FrameSize - CSSize;

    uint64_t SEHFrameOffset = calculateSetFPREG(NumBytes);
    if (FI && FI == X86FI->getFAIndex())
      return -SEHFrameOffset;

    // FPDelta is the offset from the "traditional" FP location of the old base
    // pointer followed by return address and the location required by the
    // restricted Win64 prologue.
    // Add FPDelta to all offsets below that go through the frame pointer.
    FPDelta = FrameSize - SEHFrameOffset;
    assert((!MFI->hasCalls() || (FPDelta % 16) == 0) &&
           "FPDelta isn't aligned per the Win64 ABI!");
  }


  if (TRI->hasBasePointer(MF)) {
    assert(HasFP && "VLAs and dynamic stack realign, but no FP?!");
    if (FI < 0) {
      // Skip the saved EBP.
      return Offset + SlotSize + FPDelta;
    } else {
      assert((-(Offset + StackSize)) % MFI->getObjectAlignment(FI) == 0);
      return Offset + StackSize;
    }
  } else if (TRI->needsStackRealignment(MF)) {
    if (FI < 0) {
      // Skip the saved EBP.
      return Offset + SlotSize + FPDelta;
    } else {
      assert((-(Offset + StackSize)) % MFI->getObjectAlignment(FI) == 0);
      return Offset + StackSize;
    }
    // FIXME: Support tail calls
  } else {
    if (!HasFP)
      return Offset + StackSize;

    // Skip the saved EBP.
    Offset += SlotSize;

    // Skip the RETADDR move area
    int TailCallReturnAddrDelta = X86FI->getTCReturnAddrDelta();
    if (TailCallReturnAddrDelta < 0)
      Offset -= TailCallReturnAddrDelta;
  }

  return Offset + FPDelta;
}

// Simplified from getFrameIndexReference keeping only StackPointer cases
int X86FrameLowering::getFrameIndexReferenceFromSP(const MachineFunction &MF,
                                                   int FI,
                                                   unsigned &FrameReg) const {
  const MachineFrameInfo *MFI = MF.getFrameInfo();
  // Does not include any dynamic realign.
  const uint64_t StackSize = MFI->getStackSize();
  {
#ifndef NDEBUG
    // LLVM arranges the stack as follows:
    //   ...
    //   ARG2
    //   ARG1
    //   RETADDR
    //   PUSH RBP   <-- RBP points here
    //   PUSH CSRs
    //   ~~~~~~~    <-- possible stack realignment (non-win64)
    //   ...
    //   STACK OBJECTS
    //   ...        <-- RSP after prologue points here
    //   ~~~~~~~    <-- possible stack realignment (win64)
    //
    // if (hasVarSizedObjects()):
    //   ...        <-- "base pointer" (ESI/RBX) points here
    //   DYNAMIC ALLOCAS
    //   ...        <-- RSP points here
    //
    // Case 1: In the simple case of no stack realignment and no dynamic
    // allocas, both "fixed" stack objects (arguments and CSRs) are addressable
    // with fixed offsets from RSP.
    //
    // Case 2: In the case of stack realignment with no dynamic allocas, fixed
    // stack objects are addressed with RBP and regular stack objects with RSP.
    //
    // Case 3: In the case of dynamic allocas and stack realignment, RSP is used
    // to address stack arguments for outgoing calls and nothing else. The "base
    // pointer" points to local variables, and RBP points to fixed objects.
    //
    // In cases 2 and 3, we can only answer for non-fixed stack objects, and the
    // answer we give is relative to the SP after the prologue, and not the
    // SP in the middle of the function.

    assert((!MFI->isFixedObjectIndex(FI) || !TRI->needsStackRealignment(MF) ||
            STI.isTargetWin64()) &&
           "offset from fixed object to SP is not static");

    // We don't handle tail calls, and shouldn't be seeing them either.
    int TailCallReturnAddrDelta =
        MF.getInfo<X86MachineFunctionInfo>()->getTCReturnAddrDelta();
    assert(!(TailCallReturnAddrDelta < 0) && "we don't handle this case!");
#endif
  }

  // Fill in FrameReg output argument.
  FrameReg = TRI->getStackRegister();

  // This is how the math works out:
  //
  //  %rsp grows (i.e. gets lower) left to right. Each box below is
  //  one word (eight bytes).  Obj0 is the stack slot we're trying to
  //  get to.
  //
  //    ----------------------------------
  //    | BP | Obj0 | Obj1 | ... | ObjN |
  //    ----------------------------------
  //    ^    ^      ^                   ^
  //    A    B      C                   E
  //
  // A is the incoming stack pointer.
  // (B - A) is the local area offset (-8 for x86-64) [1]
  // (C - A) is the Offset returned by MFI->getObjectOffset for Obj0 [2]
  //
  // |(E - B)| is the StackSize (absolute value, positive).  For a
  // stack that grown down, this works out to be (B - E). [3]
  //
  // E is also the value of %rsp after stack has been set up, and we
  // want (C - E) -- the value we can add to %rsp to get to Obj0.  Now
  // (C - E) == (C - A) - (B - A) + (B - E)
  //            { Using [1], [2] and [3] above }
  //         == getObjectOffset - LocalAreaOffset + StackSize
  //

  // Get the Offset from the StackPointer
  int Offset = MFI->getObjectOffset(FI) - getOffsetOfLocalArea();

  return Offset + StackSize;
}

bool X86FrameLowering::assignCalleeSavedSpillSlots(
    MachineFunction &MF, const TargetRegisterInfo *TRI,
    std::vector<CalleeSavedInfo> &CSI) const {
  MachineFrameInfo *MFI = MF.getFrameInfo();
  X86MachineFunctionInfo *X86FI = MF.getInfo<X86MachineFunctionInfo>();

  unsigned CalleeSavedFrameSize = 0;
  int SpillSlotOffset = getOffsetOfLocalArea() + X86FI->getTCReturnAddrDelta();

  if (hasFP(MF)) {
    // emitPrologue always spills frame register the first thing.
    SpillSlotOffset -= SlotSize;
    MFI->CreateFixedSpillStackObject(SlotSize, SpillSlotOffset);

    // Since emitPrologue and emitEpilogue will handle spilling and restoring of
    // the frame register, we can delete it from CSI list and not have to worry
    // about avoiding it later.
    unsigned FPReg = TRI->getFrameRegister(MF);
    for (unsigned i = 0; i < CSI.size(); ++i) {
      if (TRI->regsOverlap(CSI[i].getReg(),FPReg)) {
        CSI.erase(CSI.begin() + i);
        break;
      }
    }
  }

  // Assign slots for GPRs. It increases frame size.
  for (unsigned i = CSI.size(); i != 0; --i) {
    unsigned Reg = CSI[i - 1].getReg();

    if (!X86::GR64RegClass.contains(Reg) && !X86::GR32RegClass.contains(Reg))
      continue;

    SpillSlotOffset -= SlotSize;
    CalleeSavedFrameSize += SlotSize;

    int SlotIndex = MFI->CreateFixedSpillStackObject(SlotSize, SpillSlotOffset);
    CSI[i - 1].setFrameIdx(SlotIndex);
  }

  X86FI->setCalleeSavedFrameSize(CalleeSavedFrameSize);

  // Assign slots for XMMs.
  for (unsigned i = CSI.size(); i != 0; --i) {
    unsigned Reg = CSI[i - 1].getReg();
    if (X86::GR64RegClass.contains(Reg) || X86::GR32RegClass.contains(Reg))
      continue;

    const TargetRegisterClass *RC = TRI->getMinimalPhysRegClass(Reg);
    // ensure alignment
    SpillSlotOffset -= std::abs(SpillSlotOffset) % RC->getAlignment();
    // spill into slot
    SpillSlotOffset -= RC->getSize();
    int SlotIndex =
        MFI->CreateFixedSpillStackObject(RC->getSize(), SpillSlotOffset);
    CSI[i - 1].setFrameIdx(SlotIndex);
    MFI->ensureMaxAlignment(RC->getAlignment());
  }

  return true;
}

bool X86FrameLowering::spillCalleeSavedRegisters(
    MachineBasicBlock &MBB, MachineBasicBlock::iterator MI,
    const std::vector<CalleeSavedInfo> &CSI,
    const TargetRegisterInfo *TRI) const {
  DebugLoc DL = MBB.findDebugLoc(MI);

  // Don't save CSRs in 32-bit EH funclets. The caller saves EBX, EBP, ESI, EDI
  // for us, and there are no XMM CSRs on Win32.
  if (MBB.isEHFuncletEntry() && STI.is32Bit() && STI.isOSWindows())
    return true;

  // Push GPRs. It increases frame size.
  unsigned Opc = STI.is64Bit() ? X86::PUSH64r : X86::PUSH32r;
  for (unsigned i = CSI.size(); i != 0; --i) {
    unsigned Reg = CSI[i - 1].getReg();

    if (!X86::GR64RegClass.contains(Reg) && !X86::GR32RegClass.contains(Reg))
      continue;
    // Add the callee-saved register as live-in. It's killed at the spill.
    MBB.addLiveIn(Reg);

    BuildMI(MBB, MI, DL, TII.get(Opc)).addReg(Reg, RegState::Kill)
      .setMIFlag(MachineInstr::FrameSetup);
  }

  // Make XMM regs spilled. X86 does not have ability of push/pop XMM.
  // It can be done by spilling XMMs to stack frame.
  for (unsigned i = CSI.size(); i != 0; --i) {
    unsigned Reg = CSI[i-1].getReg();
    if (X86::GR64RegClass.contains(Reg) || X86::GR32RegClass.contains(Reg))
      continue;
    // Add the callee-saved register as live-in. It's killed at the spill.
    MBB.addLiveIn(Reg);
    const TargetRegisterClass *RC = TRI->getMinimalPhysRegClass(Reg);

    TII.storeRegToStackSlot(MBB, MI, Reg, true, CSI[i - 1].getFrameIdx(), RC,
                            TRI);
    --MI;
    MI->setFlag(MachineInstr::FrameSetup);
    ++MI;
  }

  return true;
}

bool X86FrameLowering::restoreCalleeSavedRegisters(MachineBasicBlock &MBB,
                                               MachineBasicBlock::iterator MI,
                                        const std::vector<CalleeSavedInfo> &CSI,
                                          const TargetRegisterInfo *TRI) const {
  if (CSI.empty())
    return false;

  if (isFuncletReturnInstr(MI) && STI.isOSWindows()) {
    // Don't restore CSRs in 32-bit EH funclets. Matches
    // spillCalleeSavedRegisters.
    if (STI.is32Bit())
      return true;
    // Don't restore CSRs before an SEH catchret. SEH except blocks do not form
    // funclets. emitEpilogue transforms these to normal jumps.
    if (MI->getOpcode() == X86::CATCHRET) {
      const Function *Func = MBB.getParent()->getFunction();
      bool IsSEH = isAsynchronousEHPersonality(
          classifyEHPersonality(Func->getPersonalityFn()));
      if (IsSEH)
        return true;
    }
  }

  DebugLoc DL = MBB.findDebugLoc(MI);

  // Reload XMMs from stack frame.
  for (unsigned i = 0, e = CSI.size(); i != e; ++i) {
    unsigned Reg = CSI[i].getReg();
    if (X86::GR64RegClass.contains(Reg) ||
        X86::GR32RegClass.contains(Reg))
      continue;

    const TargetRegisterClass *RC = TRI->getMinimalPhysRegClass(Reg);
    TII.loadRegFromStackSlot(MBB, MI, Reg, CSI[i].getFrameIdx(), RC, TRI);
  }

  // POP GPRs.
  unsigned Opc = STI.is64Bit() ? X86::POP64r : X86::POP32r;
  for (unsigned i = 0, e = CSI.size(); i != e; ++i) {
    unsigned Reg = CSI[i].getReg();
    if (!X86::GR64RegClass.contains(Reg) &&
        !X86::GR32RegClass.contains(Reg))
      continue;

    BuildMI(MBB, MI, DL, TII.get(Opc), Reg)
        .setMIFlag(MachineInstr::FrameDestroy);
  }
  return true;
}

void X86FrameLowering::determineCalleeSaves(MachineFunction &MF,
                                            BitVector &SavedRegs,
                                            RegScavenger *RS) const {
  TargetFrameLowering::determineCalleeSaves(MF, SavedRegs, RS);

  MachineFrameInfo *MFI = MF.getFrameInfo();

  X86MachineFunctionInfo *X86FI = MF.getInfo<X86MachineFunctionInfo>();
  int64_t TailCallReturnAddrDelta = X86FI->getTCReturnAddrDelta();

  if (TailCallReturnAddrDelta < 0) {
    // create RETURNADDR area
    //   arg
    //   arg
    //   RETADDR
    //   { ...
    //     RETADDR area
    //     ...
    //   }
    //   [EBP]
    MFI->CreateFixedObject(-TailCallReturnAddrDelta,
                           TailCallReturnAddrDelta - SlotSize, true);
  }

  // Spill the BasePtr if it's used.
  if (TRI->hasBasePointer(MF)) {
    SavedRegs.set(TRI->getBaseRegister());

    // Allocate a spill slot for EBP if we have a base pointer and EH funclets.
    if (MF.getMMI().hasEHFunclets()) {
      int FI = MFI->CreateSpillStackObject(SlotSize, SlotSize);
      X86FI->setHasSEHFramePtrSave(true);
      X86FI->setSEHFramePtrSaveIndex(FI);
    }
  }
}

static bool
HasNestArgument(const MachineFunction *MF) {
  const Function *F = MF->getFunction();
  for (Function::const_arg_iterator I = F->arg_begin(), E = F->arg_end();
       I != E; I++) {
    if (I->hasNestAttr())
      return true;
  }
  return false;
}

/// GetScratchRegister - Get a temp register for performing work in the
/// segmented stack and the Erlang/HiPE stack prologue. Depending on platform
/// and the properties of the function either one or two registers will be
/// needed. Set primary to true for the first register, false for the second.
static unsigned
GetScratchRegister(bool Is64Bit, bool IsLP64, const MachineFunction &MF, bool Primary) {
  CallingConv::ID CallingConvention = MF.getFunction()->getCallingConv();

  // Erlang stuff.
  if (CallingConvention == CallingConv::HiPE) {
    if (Is64Bit)
      return Primary ? X86::R14 : X86::R13;
    else
      return Primary ? X86::EBX : X86::EDI;
  }

  if (Is64Bit) {
    if (IsLP64)
      return Primary ? X86::R11 : X86::R12;
    else
      return Primary ? X86::R11D : X86::R12D;
  }

  bool IsNested = HasNestArgument(&MF);

  if (CallingConvention == CallingConv::X86_FastCall ||
      CallingConvention == CallingConv::Fast) {
    if (IsNested)
      report_fatal_error("Segmented stacks does not support fastcall with "
                         "nested function.");
    return Primary ? X86::EAX : X86::ECX;
  }
  if (IsNested)
    return Primary ? X86::EDX : X86::EAX;
  return Primary ? X86::ECX : X86::EAX;
}

// The stack limit in the TCB is set to this many bytes above the actual stack
// limit.
static const uint64_t kSplitStackAvailable = 256;

void X86FrameLowering::adjustForSegmentedStacks(
    MachineFunction &MF, MachineBasicBlock &PrologueMBB) const {
  MachineFrameInfo *MFI = MF.getFrameInfo();
  uint64_t StackSize;
  unsigned TlsReg, TlsOffset;
  DebugLoc DL;

  // To support shrink-wrapping we would need to insert the new blocks
  // at the right place and update the branches to PrologueMBB.
  assert(&(*MF.begin()) == &PrologueMBB && "Shrink-wrapping not supported yet");

  unsigned ScratchReg = GetScratchRegister(Is64Bit, IsLP64, MF, true);
  assert(!MF.getRegInfo().isLiveIn(ScratchReg) &&
         "Scratch register is live-in");

  if (MF.getFunction()->isVarArg())
    report_fatal_error("Segmented stacks do not support vararg functions.");
  if (!STI.isTargetLinux() && !STI.isTargetDarwin() && !STI.isTargetWin32() &&
      !STI.isTargetWin64() && !STI.isTargetFreeBSD() &&
      !STI.isTargetDragonFly())
    report_fatal_error("Segmented stacks not supported on this platform.");

  // Eventually StackSize will be calculated by a link-time pass; which will
  // also decide whether checking code needs to be injected into this particular
  // prologue.
  StackSize = MFI->getStackSize();

  // Do not generate a prologue for functions with a stack of size zero
  if (StackSize == 0)
    return;

  MachineBasicBlock *allocMBB = MF.CreateMachineBasicBlock();
  MachineBasicBlock *checkMBB = MF.CreateMachineBasicBlock();
  X86MachineFunctionInfo *X86FI = MF.getInfo<X86MachineFunctionInfo>();
  bool IsNested = false;

  // We need to know if the function has a nest argument only in 64 bit mode.
  if (Is64Bit)
    IsNested = HasNestArgument(&MF);

  // The MOV R10, RAX needs to be in a different block, since the RET we emit in
  // allocMBB needs to be last (terminating) instruction.

  for (const auto &LI : PrologueMBB.liveins()) {
    allocMBB->addLiveIn(LI);
    checkMBB->addLiveIn(LI);
  }

  if (IsNested)
    allocMBB->addLiveIn(IsLP64 ? X86::R10 : X86::R10D);

  MF.push_front(allocMBB);
  MF.push_front(checkMBB);

  // When the frame size is less than 256 we just compare the stack
  // boundary directly to the value of the stack pointer, per gcc.
  bool CompareStackPointer = StackSize < kSplitStackAvailable;

  // Read the limit off the current stacklet off the stack_guard location.
  if (Is64Bit) {
    if (STI.isTargetLinux()) {
      TlsReg = X86::FS;
      TlsOffset = IsLP64 ? 0x70 : 0x40;
    } else if (STI.isTargetDarwin()) {
      TlsReg = X86::GS;
      TlsOffset = 0x60 + 90*8; // See pthread_machdep.h. Steal TLS slot 90.
    } else if (STI.isTargetWin64()) {
      TlsReg = X86::GS;
      TlsOffset = 0x28; // pvArbitrary, reserved for application use
    } else if (STI.isTargetFreeBSD()) {
      TlsReg = X86::FS;
      TlsOffset = 0x18;
    } else if (STI.isTargetDragonFly()) {
      TlsReg = X86::FS;
      TlsOffset = 0x20; // use tls_tcb.tcb_segstack
    } else {
      report_fatal_error("Segmented stacks not supported on this platform.");
    }

    if (CompareStackPointer)
      ScratchReg = IsLP64 ? X86::RSP : X86::ESP;
    else
      BuildMI(checkMBB, DL, TII.get(IsLP64 ? X86::LEA64r : X86::LEA64_32r), ScratchReg).addReg(X86::RSP)
        .addImm(1).addReg(0).addImm(-StackSize).addReg(0);

    BuildMI(checkMBB, DL, TII.get(IsLP64 ? X86::CMP64rm : X86::CMP32rm)).addReg(ScratchReg)
      .addReg(0).addImm(1).addReg(0).addImm(TlsOffset).addReg(TlsReg);
  } else {
    if (STI.isTargetLinux()) {
      TlsReg = X86::GS;
      TlsOffset = 0x30;
    } else if (STI.isTargetDarwin()) {
      TlsReg = X86::GS;
      TlsOffset = 0x48 + 90*4;
    } else if (STI.isTargetWin32()) {
      TlsReg = X86::FS;
      TlsOffset = 0x14; // pvArbitrary, reserved for application use
    } else if (STI.isTargetDragonFly()) {
      TlsReg = X86::FS;
      TlsOffset = 0x10; // use tls_tcb.tcb_segstack
    } else if (STI.isTargetFreeBSD()) {
      report_fatal_error("Segmented stacks not supported on FreeBSD i386.");
    } else {
      report_fatal_error("Segmented stacks not supported on this platform.");
    }

    if (CompareStackPointer)
      ScratchReg = X86::ESP;
    else
      BuildMI(checkMBB, DL, TII.get(X86::LEA32r), ScratchReg).addReg(X86::ESP)
        .addImm(1).addReg(0).addImm(-StackSize).addReg(0);

    if (STI.isTargetLinux() || STI.isTargetWin32() || STI.isTargetWin64() ||
        STI.isTargetDragonFly()) {
      BuildMI(checkMBB, DL, TII.get(X86::CMP32rm)).addReg(ScratchReg)
        .addReg(0).addImm(0).addReg(0).addImm(TlsOffset).addReg(TlsReg);
    } else if (STI.isTargetDarwin()) {

      // TlsOffset doesn't fit into a mod r/m byte so we need an extra register.
      unsigned ScratchReg2;
      bool SaveScratch2;
      if (CompareStackPointer) {
        // The primary scratch register is available for holding the TLS offset.
        ScratchReg2 = GetScratchRegister(Is64Bit, IsLP64, MF, true);
        SaveScratch2 = false;
      } else {
        // Need to use a second register to hold the TLS offset
        ScratchReg2 = GetScratchRegister(Is64Bit, IsLP64, MF, false);

        // Unfortunately, with fastcc the second scratch register may hold an
        // argument.
        SaveScratch2 = MF.getRegInfo().isLiveIn(ScratchReg2);
      }

      // If Scratch2 is live-in then it needs to be saved.
      assert((!MF.getRegInfo().isLiveIn(ScratchReg2) || SaveScratch2) &&
             "Scratch register is live-in and not saved");

      if (SaveScratch2)
        BuildMI(checkMBB, DL, TII.get(X86::PUSH32r))
          .addReg(ScratchReg2, RegState::Kill);

      BuildMI(checkMBB, DL, TII.get(X86::MOV32ri), ScratchReg2)
        .addImm(TlsOffset);
      BuildMI(checkMBB, DL, TII.get(X86::CMP32rm))
        .addReg(ScratchReg)
        .addReg(ScratchReg2).addImm(1).addReg(0)
        .addImm(0)
        .addReg(TlsReg);

      if (SaveScratch2)
        BuildMI(checkMBB, DL, TII.get(X86::POP32r), ScratchReg2);
    }
  }

  // This jump is taken if SP >= (Stacklet Limit + Stack Space required).
  // It jumps to normal execution of the function body.
  BuildMI(checkMBB, DL, TII.get(X86::JA_1)).addMBB(&PrologueMBB);

  // On 32 bit we first push the arguments size and then the frame size. On 64
  // bit, we pass the stack frame size in r10 and the argument size in r11.
  if (Is64Bit) {
    // Functions with nested arguments use R10, so it needs to be saved across
    // the call to _morestack

    const unsigned RegAX = IsLP64 ? X86::RAX : X86::EAX;
    const unsigned Reg10 = IsLP64 ? X86::R10 : X86::R10D;
    const unsigned Reg11 = IsLP64 ? X86::R11 : X86::R11D;
    const unsigned MOVrr = IsLP64 ? X86::MOV64rr : X86::MOV32rr;
    const unsigned MOVri = IsLP64 ? X86::MOV64ri : X86::MOV32ri;

    if (IsNested)
      BuildMI(allocMBB, DL, TII.get(MOVrr), RegAX).addReg(Reg10);

    BuildMI(allocMBB, DL, TII.get(MOVri), Reg10)
      .addImm(StackSize);
    BuildMI(allocMBB, DL, TII.get(MOVri), Reg11)
      .addImm(X86FI->getArgumentStackSize());
  } else {
    BuildMI(allocMBB, DL, TII.get(X86::PUSHi32))
      .addImm(X86FI->getArgumentStackSize());
    BuildMI(allocMBB, DL, TII.get(X86::PUSHi32))
      .addImm(StackSize);
  }

  // __morestack is in libgcc
  if (Is64Bit && MF.getTarget().getCodeModel() == CodeModel::Large) {
    // Under the large code model, we cannot assume that __morestack lives
    // within 2^31 bytes of the call site, so we cannot use pc-relative
    // addressing. We cannot perform the call via a temporary register,
    // as the rax register may be used to store the static chain, and all
    // other suitable registers may be either callee-save or used for
    // parameter passing. We cannot use the stack at this point either
    // because __morestack manipulates the stack directly.
    //
    // To avoid these issues, perform an indirect call via a read-only memory
    // location containing the address.
    //
    // This solution is not perfect, as it assumes that the .rodata section
    // is laid out within 2^31 bytes of each function body, but this seems
    // to be sufficient for JIT.
    BuildMI(allocMBB, DL, TII.get(X86::CALL64m))
        .addReg(X86::RIP)
        .addImm(0)
        .addReg(0)
        .addExternalSymbol("__morestack_addr")
        .addReg(0);
    MF.getMMI().setUsesMorestackAddr(true);
  } else {
    if (Is64Bit)
      BuildMI(allocMBB, DL, TII.get(X86::CALL64pcrel32))
        .addExternalSymbol("__morestack");
    else
      BuildMI(allocMBB, DL, TII.get(X86::CALLpcrel32))
        .addExternalSymbol("__morestack");
  }

  if (IsNested)
    BuildMI(allocMBB, DL, TII.get(X86::MORESTACK_RET_RESTORE_R10));
  else
    BuildMI(allocMBB, DL, TII.get(X86::MORESTACK_RET));

  allocMBB->addSuccessor(&PrologueMBB);

  checkMBB->addSuccessor(allocMBB);
  checkMBB->addSuccessor(&PrologueMBB);

#ifdef XDEBUG
  MF.verify();
#endif
}

/// Erlang programs may need a special prologue to handle the stack size they
/// might need at runtime. That is because Erlang/OTP does not implement a C
/// stack but uses a custom implementation of hybrid stack/heap architecture.
/// (for more information see Eric Stenman's Ph.D. thesis:
/// http://publications.uu.se/uu/fulltext/nbn_se_uu_diva-2688.pdf)
///
/// CheckStack:
///       temp0 = sp - MaxStack
///       if( temp0 < SP_LIMIT(P) ) goto IncStack else goto OldStart
/// OldStart:
///       ...
/// IncStack:
///       call inc_stack   # doubles the stack space
///       temp0 = sp - MaxStack
///       if( temp0 < SP_LIMIT(P) ) goto IncStack else goto OldStart
void X86FrameLowering::adjustForHiPEPrologue(
    MachineFunction &MF, MachineBasicBlock &PrologueMBB) const {
  MachineFrameInfo *MFI = MF.getFrameInfo();
  DebugLoc DL;

  // To support shrink-wrapping we would need to insert the new blocks
  // at the right place and update the branches to PrologueMBB.
  assert(&(*MF.begin()) == &PrologueMBB && "Shrink-wrapping not supported yet");

  // HiPE-specific values
  const unsigned HipeLeafWords = 24;
  const unsigned CCRegisteredArgs = Is64Bit ? 6 : 5;
  const unsigned Guaranteed = HipeLeafWords * SlotSize;
  unsigned CallerStkArity = MF.getFunction()->arg_size() > CCRegisteredArgs ?
                            MF.getFunction()->arg_size() - CCRegisteredArgs : 0;
  unsigned MaxStack = MFI->getStackSize() + CallerStkArity*SlotSize + SlotSize;

  assert(STI.isTargetLinux() &&
         "HiPE prologue is only supported on Linux operating systems.");

  // Compute the largest caller's frame that is needed to fit the callees'
  // frames. This 'MaxStack' is computed from:
  //
  // a) the fixed frame size, which is the space needed for all spilled temps,
  // b) outgoing on-stack parameter areas, and
  // c) the minimum stack space this function needs to make available for the
  //    functions it calls (a tunable ABI property).
  if (MFI->hasCalls()) {
    unsigned MoreStackForCalls = 0;

    for (MachineFunction::iterator MBBI = MF.begin(), MBBE = MF.end();
         MBBI != MBBE; ++MBBI)
      for (MachineBasicBlock::iterator MI = MBBI->begin(), ME = MBBI->end();
           MI != ME; ++MI) {
        if (!MI->isCall())
          continue;

        // Get callee operand.
        const MachineOperand &MO = MI->getOperand(0);

        // Only take account of global function calls (no closures etc.).
        if (!MO.isGlobal())
          continue;

        const Function *F = dyn_cast<Function>(MO.getGlobal());
        if (!F)
          continue;

        // Do not update 'MaxStack' for primitive and built-in functions
        // (encoded with names either starting with "erlang."/"bif_" or not
        // having a ".", such as a simple <Module>.<Function>.<Arity>, or an
        // "_", such as the BIF "suspend_0") as they are executed on another
        // stack.
        if (F->getName().find("erlang.") != StringRef::npos ||
            F->getName().find("bif_") != StringRef::npos ||
            F->getName().find_first_of("._") == StringRef::npos)
          continue;

        unsigned CalleeStkArity =
          F->arg_size() > CCRegisteredArgs ? F->arg_size()-CCRegisteredArgs : 0;
        if (HipeLeafWords - 1 > CalleeStkArity)
          MoreStackForCalls = std::max(MoreStackForCalls,
                               (HipeLeafWords - 1 - CalleeStkArity) * SlotSize);
      }
    MaxStack += MoreStackForCalls;
  }

  // If the stack frame needed is larger than the guaranteed then runtime checks
  // and calls to "inc_stack_0" BIF should be inserted in the assembly prologue.
  if (MaxStack > Guaranteed) {
    MachineBasicBlock *stackCheckMBB = MF.CreateMachineBasicBlock();
    MachineBasicBlock *incStackMBB = MF.CreateMachineBasicBlock();

    for (const auto &LI : PrologueMBB.liveins()) {
      stackCheckMBB->addLiveIn(LI);
      incStackMBB->addLiveIn(LI);
    }

    MF.push_front(incStackMBB);
    MF.push_front(stackCheckMBB);

    unsigned ScratchReg, SPReg, PReg, SPLimitOffset;
    unsigned LEAop, CMPop, CALLop;
    if (Is64Bit) {
      SPReg = X86::RSP;
      PReg  = X86::RBP;
      LEAop = X86::LEA64r;
      CMPop = X86::CMP64rm;
      CALLop = X86::CALL64pcrel32;
      SPLimitOffset = 0x90;
    } else {
      SPReg = X86::ESP;
      PReg  = X86::EBP;
      LEAop = X86::LEA32r;
      CMPop = X86::CMP32rm;
      CALLop = X86::CALLpcrel32;
      SPLimitOffset = 0x4c;
    }

    ScratchReg = GetScratchRegister(Is64Bit, IsLP64, MF, true);
    assert(!MF.getRegInfo().isLiveIn(ScratchReg) &&
           "HiPE prologue scratch register is live-in");

    // Create new MBB for StackCheck:
    addRegOffset(BuildMI(stackCheckMBB, DL, TII.get(LEAop), ScratchReg),
                 SPReg, false, -MaxStack);
    // SPLimitOffset is in a fixed heap location (pointed by BP).
    addRegOffset(BuildMI(stackCheckMBB, DL, TII.get(CMPop))
                 .addReg(ScratchReg), PReg, false, SPLimitOffset);
    BuildMI(stackCheckMBB, DL, TII.get(X86::JAE_1)).addMBB(&PrologueMBB);

    // Create new MBB for IncStack:
    BuildMI(incStackMBB, DL, TII.get(CALLop)).
      addExternalSymbol("inc_stack_0");
    addRegOffset(BuildMI(incStackMBB, DL, TII.get(LEAop), ScratchReg),
                 SPReg, false, -MaxStack);
    addRegOffset(BuildMI(incStackMBB, DL, TII.get(CMPop))
                 .addReg(ScratchReg), PReg, false, SPLimitOffset);
    BuildMI(incStackMBB, DL, TII.get(X86::JLE_1)).addMBB(incStackMBB);

    stackCheckMBB->addSuccessor(&PrologueMBB, {99, 100});
    stackCheckMBB->addSuccessor(incStackMBB, {1, 100});
    incStackMBB->addSuccessor(&PrologueMBB, {99, 100});
    incStackMBB->addSuccessor(incStackMBB, {1, 100});
  }
#ifdef XDEBUG
  MF.verify();
#endif
}

bool X86FrameLowering::adjustStackWithPops(MachineBasicBlock &MBB,
    MachineBasicBlock::iterator MBBI, DebugLoc DL, int Offset) const {

  if (Offset <= 0)
    return false;

  if (Offset % SlotSize)
    return false;

  int NumPops = Offset / SlotSize;
  // This is only worth it if we have at most 2 pops.
  if (NumPops != 1 && NumPops != 2)
    return false;

  // Handle only the trivial case where the adjustment directly follows
  // a call. This is the most common one, anyway.
  if (MBBI == MBB.begin())
    return false;
  MachineBasicBlock::iterator Prev = std::prev(MBBI);
  if (!Prev->isCall() || !Prev->getOperand(1).isRegMask())
    return false;

  unsigned Regs[2];
  unsigned FoundRegs = 0;

  auto RegMask = Prev->getOperand(1);

  auto &RegClass =
      Is64Bit ? X86::GR64_NOREX_NOSPRegClass : X86::GR32_NOREX_NOSPRegClass;
  // Try to find up to NumPops free registers.
  for (auto Candidate : RegClass) {

    // Poor man's liveness:
    // Since we're immediately after a call, any register that is clobbered
    // by the call and not defined by it can be considered dead.
    if (!RegMask.clobbersPhysReg(Candidate))
      continue;

    bool IsDef = false;
    for (const MachineOperand &MO : Prev->implicit_operands()) {
      if (MO.isReg() && MO.isDef() && MO.getReg() == Candidate) {
        IsDef = true;
        break;
      }
    }

    if (IsDef)
      continue;

    Regs[FoundRegs++] = Candidate;
    if (FoundRegs == (unsigned)NumPops)
      break;
  }

  if (FoundRegs == 0)
    return false;

  // If we found only one free register, but need two, reuse the same one twice.
  while (FoundRegs < (unsigned)NumPops)
    Regs[FoundRegs++] = Regs[0];

  for (int i = 0; i < NumPops; ++i)
    BuildMI(MBB, MBBI, DL, 
            TII.get(STI.is64Bit() ? X86::POP64r : X86::POP32r), Regs[i]);

  return true;
}

void X86FrameLowering::
eliminateCallFramePseudoInstr(MachineFunction &MF, MachineBasicBlock &MBB,
                              MachineBasicBlock::iterator I) const {
  bool reserveCallFrame = hasReservedCallFrame(MF);
  unsigned Opcode = I->getOpcode();
  bool isDestroy = Opcode == TII.getCallFrameDestroyOpcode();
  DebugLoc DL = I->getDebugLoc();
  uint64_t Amount = !reserveCallFrame ? I->getOperand(0).getImm() : 0;
  uint64_t InternalAmt = (isDestroy || Amount) ? I->getOperand(1).getImm() : 0;
  I = MBB.erase(I);

  if (!reserveCallFrame) {
    // If the stack pointer can be changed after prologue, turn the
    // adjcallstackup instruction into a 'sub ESP, <amt>' and the
    // adjcallstackdown instruction into 'add ESP, <amt>'

    // We need to keep the stack aligned properly.  To do this, we round the
    // amount of space needed for the outgoing arguments up to the next
    // alignment boundary.
    unsigned StackAlign = getStackAlignment();
    Amount = alignTo(Amount, StackAlign);

    MachineModuleInfo &MMI = MF.getMMI();
    const Function *Fn = MF.getFunction();
    bool WindowsCFI = MF.getTarget().getMCAsmInfo()->usesWindowsCFI();
    bool DwarfCFI = !WindowsCFI && 
                    (MMI.hasDebugInfo() || Fn->needsUnwindTableEntry());

    // If we have any exception handlers in this function, and we adjust
    // the SP before calls, we may need to indicate this to the unwinder
    // using GNU_ARGS_SIZE. Note that this may be necessary even when
    // Amount == 0, because the preceding function may have set a non-0
    // GNU_ARGS_SIZE.
    // TODO: We don't need to reset this between subsequent functions,
    // if it didn't change.
    bool HasDwarfEHHandlers = !WindowsCFI &&
                              !MF.getMMI().getLandingPads().empty();

    if (HasDwarfEHHandlers && !isDestroy &&
        MF.getInfo<X86MachineFunctionInfo>()->getHasPushSequences())
      BuildCFI(MBB, I, DL,
               MCCFIInstruction::createGnuArgsSize(nullptr, Amount));

    if (Amount == 0)
      return;

    // Factor out the amount that gets handled inside the sequence
    // (Pushes of argument for frame setup, callee pops for frame destroy)
    Amount -= InternalAmt;

    // TODO: This is needed only if we require precise CFA.
    // If this is a callee-pop calling convention, emit a CFA adjust for
    // the amount the callee popped.
    if (isDestroy && InternalAmt && DwarfCFI && !hasFP(MF))
      BuildCFI(MBB, I, DL, 
               MCCFIInstruction::createAdjustCfaOffset(nullptr, -InternalAmt));

    if (Amount) {
      // Add Amount to SP to destroy a frame, and subtract to setup.
      int Offset = isDestroy ? Amount : -Amount;

      if (!(Fn->optForMinSize() && 
            adjustStackWithPops(MBB, I, DL, Offset)))
        BuildStackAdjustment(MBB, I, DL, Offset, /*InEpilogue=*/false);
    }

    if (DwarfCFI && !hasFP(MF)) {
      // If we don't have FP, but need to generate unwind information,
      // we need to set the correct CFA offset after the stack adjustment.
      // How much we adjust the CFA offset depends on whether we're emitting
      // CFI only for EH purposes or for debugging. EH only requires the CFA
      // offset to be correct at each call site, while for debugging we want
      // it to be more precise.
      int CFAOffset = Amount;
      // TODO: When not using precise CFA, we also need to adjust for the
      // InternalAmt here.

      if (CFAOffset) {
        CFAOffset = isDestroy ? -CFAOffset : CFAOffset;
        BuildCFI(MBB, I, DL, 
                 MCCFIInstruction::createAdjustCfaOffset(nullptr, CFAOffset));
      }
    }

    return;
  }

  if (isDestroy && InternalAmt) {
    // If we are performing frame pointer elimination and if the callee pops
    // something off the stack pointer, add it back.  We do this until we have
    // more advanced stack pointer tracking ability.
    // We are not tracking the stack pointer adjustment by the callee, so make
    // sure we restore the stack pointer immediately after the call, there may
    // be spill code inserted between the CALL and ADJCALLSTACKUP instructions.
    MachineBasicBlock::iterator B = MBB.begin();
    while (I != B && !std::prev(I)->isCall())
      --I;
    BuildStackAdjustment(MBB, I, DL, -InternalAmt, /*InEpilogue=*/false);
  }
}

bool X86FrameLowering::canUseAsEpilogue(const MachineBasicBlock &MBB) const {
  assert(MBB.getParent() && "Block is not attached to a function!");

  // Win64 has strict requirements in terms of epilogue and we are
  // not taking a chance at messing with them.
  // I.e., unless this block is already an exit block, we can't use
  // it as an epilogue.
  if (STI.isTargetWin64() && !MBB.succ_empty() && !MBB.isReturnBlock())
    return false;

  if (canUseLEAForSPInEpilogue(*MBB.getParent()))
    return true;

  // If we cannot use LEA to adjust SP, we may need to use ADD, which
  // clobbers the EFLAGS. Check that we do not need to preserve it,
  // otherwise, conservatively assume this is not
  // safe to insert the epilogue here.
  return !flagsNeedToBePreservedBeforeTheTerminators(MBB);
}

bool X86FrameLowering::enableShrinkWrapping(const MachineFunction &MF) const {
  // If we may need to emit frameless compact unwind information, give
  // up as this is currently broken: PR25614.
  return (MF.getFunction()->hasFnAttribute(Attribute::NoUnwind) || hasFP(MF)) &&
         // The lowering of segmented stack and HiPE only support entry blocks
         // as prologue blocks: PR26107.
         // This limitation may be lifted if we fix:
         // - adjustForSegmentedStacks
         // - adjustForHiPEPrologue
         MF.getFunction()->getCallingConv() != CallingConv::HiPE &&
         !MF.shouldSplitStack();
}

MachineBasicBlock::iterator X86FrameLowering::restoreWin32EHStackPointers(
    MachineBasicBlock &MBB, MachineBasicBlock::iterator MBBI,
    DebugLoc DL, bool RestoreSP) const {
  assert(STI.isTargetWindowsMSVC() && "funclets only supported in MSVC env");
  assert(STI.isTargetWin32() && "EBP/ESI restoration only required on win32");
  assert(STI.is32Bit() && !Uses64BitFramePtr &&
         "restoring EBP/ESI on non-32-bit target");

  MachineFunction &MF = *MBB.getParent();
  unsigned FramePtr = TRI->getFrameRegister(MF);
  unsigned BasePtr = TRI->getBaseRegister();
  WinEHFuncInfo &FuncInfo = *MF.getWinEHFuncInfo();
  X86MachineFunctionInfo *X86FI = MF.getInfo<X86MachineFunctionInfo>();
  MachineFrameInfo *MFI = MF.getFrameInfo();

  // FIXME: Don't set FrameSetup flag in catchret case.

  int FI = FuncInfo.EHRegNodeFrameIndex;
  int EHRegSize = MFI->getObjectSize(FI);

  if (RestoreSP) {
    // MOV32rm -EHRegSize(%ebp), %esp
    addRegOffset(BuildMI(MBB, MBBI, DL, TII.get(X86::MOV32rm), X86::ESP),
                 X86::EBP, true, -EHRegSize)
        .setMIFlag(MachineInstr::FrameSetup);
  }

  unsigned UsedReg;
  int EHRegOffset = getFrameIndexReference(MF, FI, UsedReg);
  int EndOffset = -EHRegOffset - EHRegSize;
  FuncInfo.EHRegNodeEndOffset = EndOffset;

  if (UsedReg == FramePtr) {
    // ADD $offset, %ebp
    unsigned ADDri = getADDriOpcode(false, EndOffset);
    BuildMI(MBB, MBBI, DL, TII.get(ADDri), FramePtr)
        .addReg(FramePtr)
        .addImm(EndOffset)
        .setMIFlag(MachineInstr::FrameSetup)
        ->getOperand(3)
        .setIsDead();
    assert(EndOffset >= 0 &&
           "end of registration object above normal EBP position!");
  } else if (UsedReg == BasePtr) {
    // LEA offset(%ebp), %esi
    addRegOffset(BuildMI(MBB, MBBI, DL, TII.get(X86::LEA32r), BasePtr),
                 FramePtr, false, EndOffset)
        .setMIFlag(MachineInstr::FrameSetup);
    // MOV32rm SavedEBPOffset(%esi), %ebp
    assert(X86FI->getHasSEHFramePtrSave());
    int Offset =
        getFrameIndexReference(MF, X86FI->getSEHFramePtrSaveIndex(), UsedReg);
    assert(UsedReg == BasePtr);
    addRegOffset(BuildMI(MBB, MBBI, DL, TII.get(X86::MOV32rm), FramePtr),
                 UsedReg, true, Offset)
        .setMIFlag(MachineInstr::FrameSetup);
  } else {
    llvm_unreachable("32-bit frames with WinEH must use FramePtr or BasePtr");
  }
  return MBBI;
}

namespace {
// Struct used by orderFrameObjects to help sort the stack objects.
struct X86FrameSortingObject {
  bool IsValid = false;         // true if we care about this Object.
  unsigned ObjectIndex = 0;     // Index of Object into MFI list.
  unsigned ObjectSize = 0;      // Size of Object in bytes.
  unsigned ObjectAlignment = 1; // Alignment of Object in bytes.
  unsigned ObjectNumUses = 0;   // Object static number of uses.
};

// The comparison function we use for std::sort to order our local
// stack symbols. The current algorithm is to use an estimated
// "density". This takes into consideration the size and number of
// uses each object has in order to roughly minimize code size.
// So, for example, an object of size 16B that is referenced 5 times
// will get higher priority than 4 4B objects referenced 1 time each.
// It's not perfect and we may be able to squeeze a few more bytes out of
// it (for example : 0(esp) requires fewer bytes, symbols allocated at the
// fringe end can have special consideration, given their size is less
// important, etc.), but the algorithmic complexity grows too much to be
// worth the extra gains we get. This gets us pretty close.
// The final order leaves us with objects with highest priority going
// at the end of our list.
struct X86FrameSortingComparator {
  inline bool operator()(const X86FrameSortingObject &A,
                         const X86FrameSortingObject &B) {
    uint64_t DensityAScaled, DensityBScaled;

    // For consistency in our comparison, all invalid objects are placed
    // at the end. This also allows us to stop walking when we hit the
    // first invalid item after it's all sorted.
    if (!A.IsValid)
      return false;
    if (!B.IsValid)
      return true;

    // The density is calculated by doing :
    //     (double)DensityA = A.ObjectNumUses / A.ObjectSize
    //     (double)DensityB = B.ObjectNumUses / B.ObjectSize
    // Since this approach may cause inconsistencies in
    // the floating point <, >, == comparisons, depending on the floating
    // point model with which the compiler was built, we're going
    // to scale both sides by multiplying with
    // A.ObjectSize * B.ObjectSize. This ends up factoring away
    // the division and, with it, the need for any floating point
    // arithmetic.
    DensityAScaled = static_cast<uint64_t>(A.ObjectNumUses) *
      static_cast<uint64_t>(B.ObjectSize);
    DensityBScaled = static_cast<uint64_t>(B.ObjectNumUses) *
      static_cast<uint64_t>(A.ObjectSize);

    // If the two densities are equal, prioritize highest alignment
    // objects. This allows for similar alignment objects
    // to be packed together (given the same density).
    // There's room for improvement here, also, since we can pack
    // similar alignment (different density) objects next to each
    // other to save padding. This will also require further
    // complexity/iterations, and the overall gain isn't worth it,
    // in general. Something to keep in mind, though.
    if (DensityAScaled == DensityBScaled)
      return A.ObjectAlignment < B.ObjectAlignment;
    
    return DensityAScaled < DensityBScaled;
  }
};
} // namespace

// Order the symbols in the local stack.
// We want to place the local stack objects in some sort of sensible order.
// The heuristic we use is to try and pack them according to static number
// of uses and size of object in order to minimize code size.
void X86FrameLowering::orderFrameObjects(
    const MachineFunction &MF, SmallVectorImpl<int> &ObjectsToAllocate) const {
  const MachineFrameInfo *MFI = MF.getFrameInfo();

  // Don't waste time if there's nothing to do.
  if (ObjectsToAllocate.empty())
    return;

  // Create an array of all MFI objects. We won't need all of these
  // objects, but we're going to create a full array of them to make
  // it easier to index into when we're counting "uses" down below.
  // We want to be able to easily/cheaply access an object by simply
  // indexing into it, instead of having to search for it every time.
  std::vector<X86FrameSortingObject> SortingObjects(MFI->getObjectIndexEnd());

  // Walk the objects we care about and mark them as such in our working
  // struct.
  for (auto &Obj : ObjectsToAllocate) {
    SortingObjects[Obj].IsValid = true;
    SortingObjects[Obj].ObjectIndex = Obj;
    SortingObjects[Obj].ObjectAlignment = MFI->getObjectAlignment(Obj);
    // Set the size.
    int ObjectSize = MFI->getObjectSize(Obj);
    if (ObjectSize == 0)
      // Variable size. Just use 4.
      SortingObjects[Obj].ObjectSize = 4;
    else      
      SortingObjects[Obj].ObjectSize = ObjectSize;
  }

  // Count the number of uses for each object.
  for (auto &MBB : MF) {
    for (auto &MI : MBB) {
      for (const MachineOperand &MO : MI.operands()) {
        // Check to see if it's a local stack symbol.
        if (!MO.isFI())
          continue;
        int Index = MO.getIndex();
        // Check to see if it falls within our range, and is tagged
        // to require ordering.
        if (Index >= 0 && Index < MFI->getObjectIndexEnd() &&
            SortingObjects[Index].IsValid)
          SortingObjects[Index].ObjectNumUses++;
      }
    }
  }

  // Sort the objects using X86FrameSortingAlgorithm (see its comment for
  // info).
  std::stable_sort(SortingObjects.begin(), SortingObjects.end(),
                   X86FrameSortingComparator());

  // Now modify the original list to represent the final order that
  // we want. The order will depend on whether we're going to access them
  // from the stack pointer or the frame pointer. For SP, the list should
  // end up with the END containing objects that we want with smaller offsets.
  // For FP, it should be flipped.
  int i = 0;
  for (auto &Obj : SortingObjects) {
    // All invalid items are sorted at the end, so it's safe to stop.
    if (!Obj.IsValid)
      break;
    ObjectsToAllocate[i++] = Obj.ObjectIndex;
  }

  // Flip it if we're accessing off of the FP.
  if (!TRI->needsStackRealignment(MF) && hasFP(MF))
    std::reverse(ObjectsToAllocate.begin(), ObjectsToAllocate.end());
}


unsigned X86FrameLowering::getWinEHParentFrameOffset(const MachineFunction &MF) const {
  // RDX, the parent frame pointer, is homed into 16(%rsp) in the prologue.
  unsigned Offset = 16;
  // RBP is immediately pushed.
  Offset += SlotSize;
  // All callee-saved registers are then pushed.
  Offset += MF.getInfo<X86MachineFunctionInfo>()->getCalleeSavedFrameSize();
  // Every funclet allocates enough stack space for the largest outgoing call.
  Offset += getWinEHFuncletFrameSize(MF);
  return Offset;
}

void X86FrameLowering::processFunctionBeforeFrameFinalized(
    MachineFunction &MF, RegScavenger *RS) const {
  // If this function isn't doing Win64-style C++ EH, we don't need to do
  // anything.
  const Function *Fn = MF.getFunction();
  if (!STI.is64Bit() || !MF.getMMI().hasEHFunclets() ||
      classifyEHPersonality(Fn->getPersonalityFn()) != EHPersonality::MSVC_CXX)
    return;

  // Win64 C++ EH needs to allocate the UnwindHelp object at some fixed offset
  // relative to RSP after the prologue.  Find the offset of the last fixed
  // object, so that we can allocate a slot immediately following it. If there
  // were no fixed objects, use offset -SlotSize, which is immediately after the
  // return address. Fixed objects have negative frame indices.
  MachineFrameInfo *MFI = MF.getFrameInfo();
  int64_t MinFixedObjOffset = -SlotSize;
  for (int I = MFI->getObjectIndexBegin(); I < 0; ++I)
    MinFixedObjOffset = std::min(MinFixedObjOffset, MFI->getObjectOffset(I));

  int64_t UnwindHelpOffset = MinFixedObjOffset - SlotSize;
  int UnwindHelpFI =
      MFI->CreateFixedObject(SlotSize, UnwindHelpOffset, /*Immutable=*/false);
  MF.getWinEHFuncInfo()->UnwindHelpFrameIdx = UnwindHelpFI;

  // Store -2 into UnwindHelp on function entry. We have to scan forwards past
  // other frame setup instructions.
  MachineBasicBlock &MBB = MF.front();
  auto MBBI = MBB.begin();
  while (MBBI != MBB.end() && MBBI->getFlag(MachineInstr::FrameSetup))
    ++MBBI;

  DebugLoc DL = MBB.findDebugLoc(MBBI);
  addFrameReference(BuildMI(MBB, MBBI, DL, TII.get(X86::MOV64mi32)),
                    UnwindHelpFI)
      .addImm(-2);
}