lib/Target/X86/X86FrameInfo.cpp

//=======- X86FrameInfo.cpp - X86 Frame Information ------------*- C++ -*-====//
//
//                     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 TargetFrameInfo class.
//
//===----------------------------------------------------------------------===//

#include "X86FrameInfo.h"
#include "X86InstrBuilder.h"
#include "X86InstrInfo.h"
#include "X86MachineFunctionInfo.h"
#include "llvm/Function.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/Target/TargetData.h"
#include "llvm/Target/TargetOptions.h"
#include "llvm/Support/CommandLine.h"

using namespace llvm;

// FIXME: completely move here.
extern cl::opt<bool> ForceStackAlign;

bool X86FrameInfo::hasReservedCallFrame(const MachineFunction &MF) const {
  return !MF.getFrameInfo()->hasVarSizedObjects();
}

/// 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 X86FrameInfo::hasFP(const MachineFunction &MF) const {
  const MachineFrameInfo *MFI = MF.getFrameInfo();
  const MachineModuleInfo &MMI = MF.getMMI();
  const TargetRegisterInfo *RI = MF.getTarget().getRegisterInfo();

  return (DisableFramePointerElim(MF) ||
          RI->needsStackRealignment(MF) ||
          MFI->hasVarSizedObjects() ||
          MFI->isFrameAddressTaken() ||
          MF.getInfo<X86MachineFunctionInfo>()->getForceFramePointer() ||
          MMI.callsUnwindInit());
}

static unsigned getSUBriOpcode(unsigned is64Bit, int64_t Imm) {
  if (is64Bit) {
    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 is64Bit, int64_t Imm) {
  if (is64Bit) {
    if (isInt<8>(Imm))
      return X86::ADD64ri8;
    return X86::ADD64ri32;
  } else {
    if (isInt<8>(Imm))
      return X86::ADD32ri8;
    return X86::ADD32ri;
  }
}

/// emitSPUpdate - Emit a series of instructions to increment / decrement the
/// stack pointer by a constant value.
static
void emitSPUpdate(MachineBasicBlock &MBB, MachineBasicBlock::iterator &MBBI,
                  unsigned StackPtr, int64_t NumBytes, bool Is64Bit,
                  const TargetInstrInfo &TII) {
  bool isSub = NumBytes < 0;
  uint64_t Offset = isSub ? -NumBytes : NumBytes;
  unsigned Opc = isSub ?
    getSUBriOpcode(Is64Bit, Offset) :
    getADDriOpcode(Is64Bit, Offset);
  uint64_t Chunk = (1LL << 31) - 1;
  DebugLoc DL = MBB.findDebugLoc(MBBI);

  while (Offset) {
    uint64_t ThisVal = (Offset > Chunk) ? Chunk : Offset;
    MachineInstr *MI =
      BuildMI(MBB, MBBI, DL, TII.get(Opc), StackPtr)
        .addReg(StackPtr)
        .addImm(ThisVal);
    MI->getOperand(3).setIsDead(); // The EFLAGS implicit def is dead.
    Offset -= ThisVal;
  }
}

/// mergeSPUpdatesUp - Merge two stack-manipulating instructions upper iterator.
static
void mergeSPUpdatesUp(MachineBasicBlock &MBB, MachineBasicBlock::iterator &MBBI,
                      unsigned StackPtr, uint64_t *NumBytes = NULL) {
  if (MBBI == MBB.begin()) return;

  MachineBasicBlock::iterator PI = prior(MBBI);
  unsigned Opc = PI->getOpcode();
  if ((Opc == X86::ADD64ri32 || Opc == X86::ADD64ri8 ||
       Opc == X86::ADD32ri || Opc == X86::ADD32ri8) &&
      PI->getOperand(0).getReg() == StackPtr) {
    if (NumBytes)
      *NumBytes += PI->getOperand(2).getImm();
    MBB.erase(PI);
  } else if ((Opc == X86::SUB64ri32 || Opc == X86::SUB64ri8 ||
              Opc == X86::SUB32ri || Opc == X86::SUB32ri8) &&
             PI->getOperand(0).getReg() == StackPtr) {
    if (NumBytes)
      *NumBytes -= PI->getOperand(2).getImm();
    MBB.erase(PI);
  }
}

/// mergeSPUpdatesDown - Merge two stack-manipulating instructions lower iterator.
static
void mergeSPUpdatesDown(MachineBasicBlock &MBB,
                        MachineBasicBlock::iterator &MBBI,
                        unsigned StackPtr, uint64_t *NumBytes = NULL) {
  // FIXME: THIS ISN'T RUN!!!
  return;

  if (MBBI == MBB.end()) return;

  MachineBasicBlock::iterator NI = llvm::next(MBBI);
  if (NI == MBB.end()) return;

  unsigned Opc = NI->getOpcode();
  if ((Opc == X86::ADD64ri32 || Opc == X86::ADD64ri8 ||
       Opc == X86::ADD32ri || Opc == X86::ADD32ri8) &&
      NI->getOperand(0).getReg() == StackPtr) {
    if (NumBytes)
      *NumBytes -= NI->getOperand(2).getImm();
    MBB.erase(NI);
    MBBI = NI;
  } else if ((Opc == X86::SUB64ri32 || Opc == X86::SUB64ri8 ||
              Opc == X86::SUB32ri || Opc == X86::SUB32ri8) &&
             NI->getOperand(0).getReg() == StackPtr) {
    if (NumBytes)
      *NumBytes += NI->getOperand(2).getImm();
    MBB.erase(NI);
    MBBI = NI;
  }
}

/// mergeSPUpdates - Checks the instruction before/after the passed
/// instruction. If it is an ADD/SUB instruction it is deleted argument and the
/// stack adjustment is returned as a positive value for ADD and a negative for
/// SUB.
static int mergeSPUpdates(MachineBasicBlock &MBB,
                           MachineBasicBlock::iterator &MBBI,
                           unsigned StackPtr,
                           bool doMergeWithPrevious) {
  if ((doMergeWithPrevious && MBBI == MBB.begin()) ||
      (!doMergeWithPrevious && MBBI == MBB.end()))
    return 0;

  MachineBasicBlock::iterator PI = doMergeWithPrevious ? prior(MBBI) : MBBI;
  MachineBasicBlock::iterator NI = doMergeWithPrevious ? 0 : llvm::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::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;
}

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

  return false;
}

void X86FrameInfo::emitCalleeSavedFrameMoves(MachineFunction &MF,
                                             MCSymbol *Label,
                                             unsigned FramePtr) const {
  MachineFrameInfo *MFI = MF.getFrameInfo();
  MachineModuleInfo &MMI = MF.getMMI();

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

  std::vector<MachineMove> &Moves = MMI.getFrameMoves();
  const TargetData *TD = MF.getTarget().getTargetData();
  bool HasFP = hasFP(MF);

  // Calculate amount of bytes used for return address storing.
  int stackGrowth =
    (MF.getTarget().getFrameInfo()->getStackGrowthDirection() ==
     TargetFrameInfo::StackGrowsUp ?
     TD->getPointerSize() : -TD->getPointerSize());

  // FIXME: This is dirty hack. The code itself is pretty mess right now.
  // It should be rewritten from scratch and generalized sometimes.

  // Determine maximum offset (minumum due to stack growth).
  int64_t MaxOffset = 0;
  for (std::vector<CalleeSavedInfo>::const_iterator
         I = CSI.begin(), E = CSI.end(); I != E; ++I)
    MaxOffset = std::min(MaxOffset,
                         MFI->getObjectOffset(I->getFrameIdx()));

  // Calculate offsets.
  int64_t saveAreaOffset = (HasFP ? 3 : 2) * stackGrowth;
  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();
    Offset = MaxOffset - Offset + saveAreaOffset;

    // Don't output a new machine move if we're re-saving the frame
    // pointer. This happens when the PrologEpilogInserter has inserted an extra
    // "PUSH" of the frame pointer -- the "emitPrologue" method automatically
    // generates one when frame pointers are used. If we generate a "machine
    // move" for this extra "PUSH", the linker will lose track of the fact that
    // the frame pointer should have the value of the first "PUSH" when it's
    // trying to unwind.
    // 
    // FIXME: This looks inelegant. It's possibly correct, but it's covering up
    //        another bug. I.e., one where we generate a prolog like this:
    //
    //          pushl  %ebp
    //          movl   %esp, %ebp
    //          pushl  %ebp
    //          pushl  %esi
    //           ...
    //
    //        The immediate re-push of EBP is unnecessary. At the least, it's an
    //        optimization bug. EBP can be used as a scratch register in certain
    //        cases, but probably not when we have a frame pointer.
    if (HasFP && FramePtr == Reg)
      continue;

    MachineLocation CSDst(MachineLocation::VirtualFP, Offset);
    MachineLocation CSSrc(Reg);
    Moves.push_back(MachineMove(Label, CSDst, CSSrc));
  }
}

/// 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.
void X86FrameInfo::emitPrologue(MachineFunction &MF) const {
  MachineBasicBlock &MBB = MF.front(); // Prologue goes in entry BB.
  MachineBasicBlock::iterator MBBI = MBB.begin();
  MachineFrameInfo *MFI = MF.getFrameInfo();
  const Function *Fn = MF.getFunction();
  const X86Subtarget *Subtarget = &MF.getTarget().getSubtarget<X86Subtarget>();
  const X86RegisterInfo *RegInfo =
    static_cast<const X86RegisterInfo*>(MF.getTarget().getRegisterInfo());
  const X86InstrInfo &TII =
    *static_cast<const X86InstrInfo*>(MF.getTarget().getInstrInfo());
  MachineModuleInfo &MMI = MF.getMMI();
  X86MachineFunctionInfo *X86FI = MF.getInfo<X86MachineFunctionInfo>();
  bool needsFrameMoves = MMI.hasDebugInfo() ||
                          !Fn->doesNotThrow() || UnwindTablesMandatory;
  uint64_t MaxAlign  = MFI->getMaxAlignment(); // Desired stack alignment.
  uint64_t StackSize = MFI->getStackSize();    // Number of bytes to allocate.
  bool HasFP = hasFP(MF);
  bool Is64Bit = STI.is64Bit();
  bool IsWin64 = STI.isTargetWin64();
  unsigned StackAlign = getStackAlignment();
  unsigned SlotSize = RegInfo->getSlotSize();
  unsigned FramePtr = RegInfo->getFrameRegister(MF);
  unsigned StackPtr = RegInfo->getStackRegister();

  DebugLoc DL;

  // 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.
  if (ForceStackAlign) {
    if (MFI->hasCalls())
      MaxAlign = (StackAlign > MaxAlign) ? StackAlign : MaxAlign;
    else if (MaxAlign < SlotSize)
      MaxAlign = SlotSize;
  }

  // Add RETADDR move area to callee saved frame size.
  int TailCallReturnAddrDelta = X86FI->getTCReturnAddrDelta();
  if (TailCallReturnAddrDelta < 0)
    X86FI->setCalleeSavedFrameSize(
      X86FI->getCalleeSavedFrameSize() - TailCallReturnAddrDelta);

  // 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).
  if (Is64Bit && !Fn->hasFnAttr(Attribute::NoRedZone) &&
      !RegInfo->needsStackRealignment(MF) &&
      !MFI->hasVarSizedObjects() &&                // No dynamic alloca.
      !MFI->adjustsStack() &&                      // No calls.
      !IsWin64) {                                  // Win64 has no Red Zone
    uint64_t MinSize = X86FI->getCalleeSavedFrameSize();
    if (HasFP) MinSize += SlotSize;
    StackSize = std::max(MinSize, StackSize > 128 ? StackSize - 128 : 0);
    MFI->setStackSize(StackSize);
  } else if (IsWin64) {
    // We need to always allocate 32 bytes as register spill area.
    // FIXME: We might reuse these 32 bytes for leaf functions.
    StackSize += 32;
    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) {
    MachineInstr *MI =
      BuildMI(MBB, MBBI, DL,
              TII.get(getSUBriOpcode(Is64Bit, -TailCallReturnAddrDelta)),
              StackPtr)
        .addReg(StackPtr)
        .addImm(-TailCallReturnAddrDelta);
    MI->getOperand(3).setIsDead(); // The EFLAGS implicit def is dead.
  }

  // 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

  std::vector<MachineMove> &Moves = MMI.getFrameMoves();
  const TargetData *TD = MF.getTarget().getTargetData();
  uint64_t NumBytes = 0;
  int stackGrowth = -TD->getPointerSize();

  if (HasFP) {
    // Calculate required stack adjustment.
    uint64_t FrameSize = StackSize - SlotSize;
    if (RegInfo->needsStackRealignment(MF))
      FrameSize = (FrameSize + MaxAlign - 1) / MaxAlign * MaxAlign;

    NumBytes = FrameSize - X86FI->getCalleeSavedFrameSize();

    // 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.
    MFI->setOffsetAdjustment(-NumBytes);

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

    if (needsFrameMoves) {
      // Mark the place where EBP/RBP was saved.
      MCSymbol *FrameLabel = MMI.getContext().CreateTempSymbol();
      BuildMI(MBB, MBBI, DL, TII.get(X86::PROLOG_LABEL)).addSym(FrameLabel);

      // Define the current CFA rule to use the provided offset.
      if (StackSize) {
        MachineLocation SPDst(MachineLocation::VirtualFP);
        MachineLocation SPSrc(MachineLocation::VirtualFP, 2 * stackGrowth);
        Moves.push_back(MachineMove(FrameLabel, SPDst, SPSrc));
      } else {
        // FIXME: Verify & implement for FP
        MachineLocation SPDst(StackPtr);
        MachineLocation SPSrc(StackPtr, stackGrowth);
        Moves.push_back(MachineMove(FrameLabel, SPDst, SPSrc));
      }

      // Change the rule for the FramePtr to be an "offset" rule.
      MachineLocation FPDst(MachineLocation::VirtualFP, 2 * stackGrowth);
      MachineLocation FPSrc(FramePtr);
      Moves.push_back(MachineMove(FrameLabel, FPDst, FPSrc));
    }

    // Update EBP with the new base value...
    BuildMI(MBB, MBBI, DL,
            TII.get(Is64Bit ? X86::MOV64rr : X86::MOV32rr), FramePtr)
        .addReg(StackPtr);

    if (needsFrameMoves) {
      // Mark effective beginning of when frame pointer becomes valid.
      MCSymbol *FrameLabel = MMI.getContext().CreateTempSymbol();
      BuildMI(MBB, MBBI, DL, TII.get(X86::PROLOG_LABEL)).addSym(FrameLabel);

      // Define the current CFA to use the EBP/RBP register.
      MachineLocation FPDst(FramePtr);
      MachineLocation FPSrc(MachineLocation::VirtualFP);
      Moves.push_back(MachineMove(FrameLabel, FPDst, FPSrc));
    }

    // Mark the FramePtr as live-in in every block except the entry.
    for (MachineFunction::iterator I = llvm::next(MF.begin()), E = MF.end();
         I != E; ++I)
      I->addLiveIn(FramePtr);

    // Realign stack
    if (RegInfo->needsStackRealignment(MF)) {
      MachineInstr *MI =
        BuildMI(MBB, MBBI, DL,
                TII.get(Is64Bit ? X86::AND64ri32 : X86::AND32ri),
                StackPtr).addReg(StackPtr).addImm(-MaxAlign);

      // The EFLAGS implicit def is dead.
      MI->getOperand(3).setIsDead();
    }
  } else {
    NumBytes = StackSize - X86FI->getCalleeSavedFrameSize();
  }

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

  while (MBBI != MBB.end() &&
         (MBBI->getOpcode() == X86::PUSH32r ||
          MBBI->getOpcode() == X86::PUSH64r)) {
    PushedRegs = true;
    ++MBBI;

    if (!HasFP && needsFrameMoves) {
      // Mark callee-saved push instruction.
      MCSymbol *Label = MMI.getContext().CreateTempSymbol();
      BuildMI(MBB, MBBI, DL, TII.get(X86::PROLOG_LABEL)).addSym(Label);

      // Define the current CFA rule to use the provided offset.
      unsigned Ptr = StackSize ?
        MachineLocation::VirtualFP : StackPtr;
      MachineLocation SPDst(Ptr);
      MachineLocation SPSrc(Ptr, StackOffset);
      Moves.push_back(MachineMove(Label, SPDst, SPSrc));
      StackOffset += stackGrowth;
    }
  }

  DL = MBB.findDebugLoc(MBBI);

  // 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, StackPtr, true);

  // If there is an ADD32ri or SUB32ri of ESP immediately after this
  // instruction, merge the two instructions.
  mergeSPUpdatesDown(MBB, MBBI, StackPtr, &NumBytes);

  // 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.
  if (NumBytes >= 4096 &&
     (Subtarget->isTargetCygMing() || Subtarget->isTargetWin32())) {
    // Check whether EAX is livein for this function.
    bool isEAXAlive = isEAXLiveIn(MF);

    const char *StackProbeSymbol =
      Subtarget->isTargetWindows() ? "_chkstk" : "_alloca";
    unsigned CallOp = Is64Bit ? X86::CALL64pcrel32 : X86::CALLpcrel32;
    if (!isEAXAlive) {
      BuildMI(MBB, MBBI, DL, TII.get(X86::MOV32ri), X86::EAX)
        .addImm(NumBytes);
      BuildMI(MBB, MBBI, DL, TII.get(CallOp))
        .addExternalSymbol(StackProbeSymbol)
        .addReg(StackPtr,    RegState::Define | RegState::Implicit)
        .addReg(X86::EFLAGS, RegState::Define | RegState::Implicit);
    } else {
      // Save EAX
      BuildMI(MBB, MBBI, DL, TII.get(X86::PUSH32r))
        .addReg(X86::EAX, RegState::Kill);

      // Allocate NumBytes-4 bytes on stack. We'll also use 4 already
      // allocated bytes for EAX.
      BuildMI(MBB, MBBI, DL, TII.get(X86::MOV32ri), X86::EAX)
        .addImm(NumBytes - 4);
      BuildMI(MBB, MBBI, DL, TII.get(CallOp))
        .addExternalSymbol(StackProbeSymbol)
        .addReg(StackPtr,    RegState::Define | RegState::Implicit)
        .addReg(X86::EFLAGS, RegState::Define | RegState::Implicit);

      // Restore EAX
      MachineInstr *MI = addRegOffset(BuildMI(MF, DL, TII.get(X86::MOV32rm),
                                              X86::EAX),
                                      StackPtr, false, NumBytes - 4);
      MBB.insert(MBBI, MI);
    }
  } else if (NumBytes >= 4096 && Subtarget->isTargetWin64()) {
    // Sanity check that EAX is not livein for this function.  It should
    // should not be, so throw an assert.
    assert(!isEAXLiveIn(MF) && "EAX is livein in the Win64 case!");

    // Handle the 64-bit Windows ABI case where we need to call __chkstk.
    // Function prologue is responsible for adjusting the stack pointer.
    BuildMI(MBB, MBBI, DL, TII.get(X86::MOV32ri), X86::EAX)
      .addImm(NumBytes);
    BuildMI(MBB, MBBI, DL, TII.get(X86::WINCALL64pcrel32))
      .addExternalSymbol("__chkstk")
      .addReg(StackPtr, RegState::Define | RegState::Implicit);
    emitSPUpdate(MBB, MBBI, StackPtr, -(int64_t)NumBytes, Is64Bit, TII);
  } else if (NumBytes)
    emitSPUpdate(MBB, MBBI, StackPtr, -(int64_t)NumBytes, Is64Bit, TII);

  if ((NumBytes || PushedRegs) && needsFrameMoves) {
    // Mark end of stack pointer adjustment.
    MCSymbol *Label = MMI.getContext().CreateTempSymbol();
    BuildMI(MBB, MBBI, DL, TII.get(X86::PROLOG_LABEL)).addSym(Label);

    if (!HasFP && NumBytes) {
      // Define the current CFA rule to use the provided offset.
      if (StackSize) {
        MachineLocation SPDst(MachineLocation::VirtualFP);
        MachineLocation SPSrc(MachineLocation::VirtualFP,
                              -StackSize + stackGrowth);
        Moves.push_back(MachineMove(Label, SPDst, SPSrc));
      } else {
        // FIXME: Verify & implement for FP
        MachineLocation SPDst(StackPtr);
        MachineLocation SPSrc(StackPtr, stackGrowth);
        Moves.push_back(MachineMove(Label, SPDst, SPSrc));
      }
    }

    // Emit DWARF info specifying the offsets of the callee-saved registers.
    if (PushedRegs)
      emitCalleeSavedFrameMoves(MF, Label, HasFP ? FramePtr : StackPtr);
  }
}

void X86FrameInfo::emitEpilogue(MachineFunction &MF,
                                MachineBasicBlock &MBB) const {
  const MachineFrameInfo *MFI = MF.getFrameInfo();
  X86MachineFunctionInfo *X86FI = MF.getInfo<X86MachineFunctionInfo>();
  const X86RegisterInfo *RegInfo =
    static_cast<const X86RegisterInfo*>(MF.getTarget().getRegisterInfo());
  const X86InstrInfo &TII =
    *static_cast<const X86InstrInfo*>(MF.getTarget().getInstrInfo());
  MachineBasicBlock::iterator MBBI = prior(MBB.end());
  unsigned RetOpcode = MBBI->getOpcode();
  DebugLoc DL = MBBI->getDebugLoc();
  bool Is64Bit = STI.is64Bit();
  unsigned StackAlign = getStackAlignment();
  unsigned SlotSize = RegInfo->getSlotSize();
  unsigned FramePtr = RegInfo->getFrameRegister(MF);
  unsigned StackPtr = RegInfo->getStackRegister();

  switch (RetOpcode) {
  default:
    llvm_unreachable("Can only insert epilog into returning blocks");
  case X86::RET:
  case X86::RETI:
  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:
    break;  // These are ok
  }

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

  // 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.
  if (ForceStackAlign) {
    if (MFI->hasCalls())
      MaxAlign = (StackAlign > MaxAlign) ? StackAlign : MaxAlign;
    else
      MaxAlign = MaxAlign ? MaxAlign : 4;
  }

  if (hasFP(MF)) {
    // Calculate required stack adjustment.
    uint64_t FrameSize = StackSize - SlotSize;
    if (RegInfo->needsStackRealignment(MF))
      FrameSize = (FrameSize + MaxAlign - 1)/MaxAlign*MaxAlign;

    NumBytes = FrameSize - CSSize;

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

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

    if (Opc != X86::POP32r && Opc != X86::POP64r &&
        !PI->getDesc().isTerminator())
      break;

    --MBBI;
  }

  DL = MBBI->getDebugLoc();

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

  // 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.
  if (RegInfo->needsStackRealignment(MF)) {
    // We cannot use LEA here, because stack pointer was realigned. We need to
    // deallocate local frame back.
    if (CSSize) {
      emitSPUpdate(MBB, MBBI, StackPtr, NumBytes, Is64Bit, TII);
      MBBI = prior(LastCSPop);
    }

    BuildMI(MBB, MBBI, DL,
            TII.get(Is64Bit ? X86::MOV64rr : X86::MOV32rr),
            StackPtr).addReg(FramePtr);
  } else if (MFI->hasVarSizedObjects()) {
    if (CSSize) {
      unsigned Opc = Is64Bit ? X86::LEA64r : X86::LEA32r;
      MachineInstr *MI =
        addRegOffset(BuildMI(MF, DL, TII.get(Opc), StackPtr),
                     FramePtr, false, -CSSize);
      MBB.insert(MBBI, MI);
    } else {
      BuildMI(MBB, MBBI, DL,
              TII.get(Is64Bit ? X86::MOV64rr : X86::MOV32rr), StackPtr)
        .addReg(FramePtr);
    }
  } else if (NumBytes) {
    // Adjust stack pointer back: ESP += numbytes.
    emitSPUpdate(MBB, MBBI, StackPtr, NumBytes, Is64Bit, TII);
  }

  // We're returning from function via eh_return.
  if (RetOpcode == X86::EH_RETURN || RetOpcode == X86::EH_RETURN64) {
    MBBI = prior(MBB.end());
    MachineOperand &DestAddr  = MBBI->getOperand(0);
    assert(DestAddr.isReg() && "Offset should be in register!");
    BuildMI(MBB, MBBI, DL,
            TII.get(Is64Bit ? X86::MOV64rr : X86::MOV32rr),
            StackPtr).addReg(DestAddr.getReg());
  } else if (RetOpcode == X86::TCRETURNri || RetOpcode == X86::TCRETURNdi ||
             RetOpcode == X86::TCRETURNmi ||
             RetOpcode == X86::TCRETURNri64 || RetOpcode == X86::TCRETURNdi64 ||
             RetOpcode == X86::TCRETURNmi64) {
    bool isMem = RetOpcode == X86::TCRETURNmi || RetOpcode == X86::TCRETURNmi64;
    // Tail call return: adjust the stack pointer and jump to callee.
    MBBI = prior(MBB.end());
    MachineOperand &JumpTarget = MBBI->getOperand(0);
    MachineOperand &StackAdjust = MBBI->getOperand(isMem ? 5 : 1);
    assert(StackAdjust.isImm() && "Expecting immediate value.");

    // Adjust stack pointer.
    int StackAdj = StackAdjust.getImm();
    int MaxTCDelta = X86FI->getTCReturnAddrDelta();
    int Offset = 0;
    assert(MaxTCDelta <= 0 && "MaxTCDelta should never be positive");

    // Incoporate the retaddr area.
    Offset = StackAdj-MaxTCDelta;
    assert(Offset >= 0 && "Offset should never be negative");

    if (Offset) {
      // Check for possible merge with preceeding ADD instruction.
      Offset += mergeSPUpdates(MBB, MBBI, StackPtr, true);
      emitSPUpdate(MBB, MBBI, StackPtr, Offset, Is64Bit, TII);
    }

    // Jump to label or value in register.
    if (RetOpcode == X86::TCRETURNdi || RetOpcode == X86::TCRETURNdi64) {
      BuildMI(MBB, MBBI, DL, TII.get((RetOpcode == X86::TCRETURNdi)
                                     ? X86::TAILJMPd : X86::TAILJMPd64)).
        addGlobalAddress(JumpTarget.getGlobal(), JumpTarget.getOffset(),
                         JumpTarget.getTargetFlags());
    } else if (RetOpcode == X86::TCRETURNmi || RetOpcode == X86::TCRETURNmi64) {
      MachineInstrBuilder MIB =
        BuildMI(MBB, MBBI, DL, TII.get((RetOpcode == X86::TCRETURNmi)
                                       ? X86::TAILJMPm : X86::TAILJMPm64));
      for (unsigned i = 0; i != 5; ++i)
        MIB.addOperand(MBBI->getOperand(i));
    } else if (RetOpcode == X86::TCRETURNri64) {
      BuildMI(MBB, MBBI, DL, TII.get(X86::TAILJMPr64)).
        addReg(JumpTarget.getReg(), RegState::Kill);
    } else {
      BuildMI(MBB, MBBI, DL, TII.get(X86::TAILJMPr)).
        addReg(JumpTarget.getReg(), RegState::Kill);
    }

    MachineInstr *NewMI = prior(MBBI);
    for (unsigned i = 2, e = MBBI->getNumOperands(); i != e; ++i)
      NewMI->addOperand(MBBI->getOperand(i));

    // Delete the pseudo instruction TCRETURN.
    MBB.erase(MBBI);
  } else if ((RetOpcode == X86::RET || RetOpcode == X86::RETI) &&
             (X86FI->getTCReturnAddrDelta() < 0)) {
    // Add the return addr area delta back since we are not tail calling.
    int delta = -1*X86FI->getTCReturnAddrDelta();
    MBBI = prior(MBB.end());

    // Check for possible merge with preceeding ADD instruction.
    delta += mergeSPUpdates(MBB, MBBI, StackPtr, true);
    emitSPUpdate(MBB, MBBI, StackPtr, delta, Is64Bit, TII);
  }
}