lib/Target/AArch64/AArch64LowerHomogeneousPrologEpilog.cpp - llvm-project/llvm - Git at Google

 //===- AArch64LowerHomogeneousPrologEpilog.cpp ----------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
 // This file contains a pass that lowers homogeneous prolog/epilog instructions.
 //
 //===----------------------------------------------------------------------===//

 #include "AArch64InstrInfo.h"
 #include "AArch64Subtarget.h"
 #include "MCTargetDesc/AArch64InstPrinter.h"
 #include "Utils/AArch64BaseInfo.h"
 #include "llvm/CodeGen/MachineBasicBlock.h"
 #include "llvm/CodeGen/MachineFunction.h"
 #include "llvm/CodeGen/MachineFunctionPass.h"
 #include "llvm/CodeGen/MachineInstr.h"
 #include "llvm/CodeGen/MachineInstrBuilder.h"
 #include "llvm/CodeGen/MachineModuleInfo.h"
 #include "llvm/CodeGen/MachineOperand.h"
 #include "llvm/CodeGen/TargetSubtargetInfo.h"
 #include "llvm/IR/DebugLoc.h"
 #include "llvm/Pass.h"
 #include "llvm/Support/raw_ostream.h"
 #include <sstream>

 using namespace llvm;

 #define AARCH64_LOWER_HOMOGENEOUS_PROLOG_EPILOG_NAME                           \
   "AArch64 homogeneous prolog/epilog lowering pass"

 cl::opt<int> FrameHelperSizeThreshold(
     "frame-helper-size-threshold", cl::init(2), cl::Hidden,
     cl::desc("The minimum number of instructions that are outlined in a frame "
              "helper (default = 2)"));

 namespace {

 class AArch64LowerHomogeneousPE {
 public:
   const AArch64InstrInfo *TII;

   AArch64LowerHomogeneousPE(Module *M, MachineModuleInfo *MMI)
       : M(M), MMI(MMI) {}

   bool run();
   bool runOnMachineFunction(MachineFunction &Fn);

 private:
   Module *M;
   MachineModuleInfo *MMI;

   bool runOnMBB(MachineBasicBlock &MBB);
   bool runOnMI(MachineBasicBlock &MBB, MachineBasicBlock::iterator MBBI,
                MachineBasicBlock::iterator &NextMBBI);

   /// Lower a HOM_Prolog pseudo instruction into a helper call
   /// or a sequence of homogeneous stores.
   /// When a a fp setup follows, it can be optimized.
   bool lowerProlog(MachineBasicBlock &MBB, MachineBasicBlock::iterator MBBI,
                    MachineBasicBlock::iterator &NextMBBI);
   /// Lower a HOM_Epilog pseudo instruction into a helper call
   /// or a sequence of homogeneous loads.
   /// When a return follow, it can be optimized.
   bool lowerEpilog(MachineBasicBlock &MBB, MachineBasicBlock::iterator MBBI,
                    MachineBasicBlock::iterator &NextMBBI);
 };

 class AArch64LowerHomogeneousPrologEpilog : public ModulePass {
 public:
   static char ID;

   AArch64LowerHomogeneousPrologEpilog() : ModulePass(ID) {
     initializeAArch64LowerHomogeneousPrologEpilogPass(
         *PassRegistry::getPassRegistry());
   }
   void getAnalysisUsage(AnalysisUsage &AU) const override {
     AU.addRequired<MachineModuleInfoWrapperPass>();
     AU.addPreserved<MachineModuleInfoWrapperPass>();
     AU.setPreservesAll();
     ModulePass::getAnalysisUsage(AU);
   }
   bool runOnModule(Module &M) override;

   StringRef getPassName() const override {
     return AARCH64_LOWER_HOMOGENEOUS_PROLOG_EPILOG_NAME;
   }
 };

 } // end anonymous namespace

 char AArch64LowerHomogeneousPrologEpilog::ID = 0;

 INITIALIZE_PASS(AArch64LowerHomogeneousPrologEpilog,
                 "aarch64-lower-homogeneous-prolog-epilog",
                 AARCH64_LOWER_HOMOGENEOUS_PROLOG_EPILOG_NAME, false, false)

 bool AArch64LowerHomogeneousPrologEpilog::runOnModule(Module &M) {
   if (skipModule(M))
     return false;

   MachineModuleInfo *MMI =
       &getAnalysis<MachineModuleInfoWrapperPass>().getMMI();
   return AArch64LowerHomogeneousPE(&M, MMI).run();
 }

 bool AArch64LowerHomogeneousPE::run() {
   bool Changed = false;
   for (auto &F : *M) {
     if (F.empty())
       continue;

     MachineFunction *MF = MMI->getMachineFunction(F);
     if (!MF)
       continue;
     Changed |= runOnMachineFunction(*MF);
   }

   return Changed;
 }
 enum FrameHelperType { Prolog, PrologFrame, Epilog, EpilogTail };

 /// Return a frame helper name with the given CSRs and the helper type.
 /// For instance, a prolog helper that saves x19 and x20 is named as
 /// OUTLINED_FUNCTION_PROLOG_x19x20.
 static std::string getFrameHelperName(SmallVectorImpl<unsigned> &Regs,
                                       FrameHelperType Type, unsigned FpOffset) {
   std::ostringstream RegStream;
   switch (Type) {
   case FrameHelperType::Prolog:
     RegStream << "OUTLINED_FUNCTION_PROLOG_";
     break;
   case FrameHelperType::PrologFrame:
     RegStream << "OUTLINED_FUNCTION_PROLOG_FRAME" << FpOffset << "_";
     break;
   case FrameHelperType::Epilog:
     RegStream << "OUTLINED_FUNCTION_EPILOG_";
     break;
   case FrameHelperType::EpilogTail:
     RegStream << "OUTLINED_FUNCTION_EPILOG_TAIL_";
     break;
   }

   for (auto Reg : Regs)
     RegStream << AArch64InstPrinter::getRegisterName(Reg);

   return RegStream.str();
 }

 /// Create a Function for the unique frame helper with the given name.
 /// Return a newly created MachineFunction with an empty MachineBasicBlock.
 static MachineFunction &createFrameHelperMachineFunction(Module *M,
                                                          MachineModuleInfo *MMI,
                                                          StringRef Name) {
   LLVMContext &C = M->getContext();
   Function *F = M->getFunction(Name);
   assert(F == nullptr && "Function has been created before");
   F = Function::Create(FunctionType::get(Type::getVoidTy(C), false),
                        Function::ExternalLinkage, Name, M);
   assert(F && "Function was null!");

   // Use ODR linkage to avoid duplication.
   F->setLinkage(GlobalValue::LinkOnceODRLinkage);
   F->setUnnamedAddr(GlobalValue::UnnamedAddr::Global);

   // Set no-opt/minsize, so we don't insert padding between outlined
   // functions.
   F->addFnAttr(Attribute::OptimizeNone);
   F->addFnAttr(Attribute::NoInline);
   F->addFnAttr(Attribute::MinSize);
   F->addFnAttr(Attribute::Naked);

   MachineFunction &MF = MMI->getOrCreateMachineFunction(*F);
   // Remove unnecessary register liveness and set NoVRegs.
   MF.getProperties().reset(MachineFunctionProperties::Property::TracksLiveness);
   MF.getProperties().reset(MachineFunctionProperties::Property::IsSSA);
   MF.getProperties().set(MachineFunctionProperties::Property::NoVRegs);
   MF.getRegInfo().freezeReservedRegs(MF);

   // Create entry block.
   BasicBlock *EntryBB = BasicBlock::Create(C, "entry", F);
   IRBuilder<> Builder(EntryBB);
   Builder.CreateRetVoid();

   // Insert the new block into the function.
   MachineBasicBlock *MBB = MF.CreateMachineBasicBlock();
   MF.insert(MF.begin(), MBB);

   return MF;
 }

 /// Emit a store-pair instruction for frame-setup.
 static void emitStore(MachineFunction &MF, MachineBasicBlock &MBB,
                       MachineBasicBlock::iterator Pos,
                       const TargetInstrInfo &TII, unsigned Reg1, unsigned Reg2,
                       int Offset, bool IsPreDec) {
   bool IsFloat = AArch64::FPR64RegClass.contains(Reg1);
   assert(!(IsFloat ^ AArch64::FPR64RegClass.contains(Reg2)));
   unsigned Opc;
   if (IsPreDec)
     Opc = IsFloat ? AArch64::STPDpre : AArch64::STPXpre;
   else
     Opc = IsFloat ? AArch64::STPDi : AArch64::STPXi;

   MachineInstrBuilder MIB = BuildMI(MBB, Pos, DebugLoc(), TII.get(Opc));
   if (IsPreDec)
     MIB.addDef(AArch64::SP);
   MIB.addReg(Reg2)
       .addReg(Reg1)
       .addReg(AArch64::SP)
       .addImm(Offset)
       .setMIFlag(MachineInstr::FrameSetup);
 }

 /// Emit a load-pair instruction for frame-destroy.
 static void emitLoad(MachineFunction &MF, MachineBasicBlock &MBB,
                      MachineBasicBlock::iterator Pos,
                      const TargetInstrInfo &TII, unsigned Reg1, unsigned Reg2,
                      int Offset, bool IsPostDec) {
   bool IsFloat = AArch64::FPR64RegClass.contains(Reg1);
   assert(!(IsFloat ^ AArch64::FPR64RegClass.contains(Reg2)));
   unsigned Opc;
   if (IsPostDec)
     Opc = IsFloat ? AArch64::LDPDpost : AArch64::LDPXpost;
   else
     Opc = IsFloat ? AArch64::LDPDi : AArch64::LDPXi;

   MachineInstrBuilder MIB = BuildMI(MBB, Pos, DebugLoc(), TII.get(Opc));
   if (IsPostDec)
     MIB.addDef(AArch64::SP);
   MIB.addReg(Reg2, getDefRegState(true))
       .addReg(Reg1, getDefRegState(true))
       .addReg(AArch64::SP)
       .addImm(Offset)
       .setMIFlag(MachineInstr::FrameDestroy);
 }

 /// Return a unique function if a helper can be formed with the given Regs
 /// and frame type.
 /// 1) _OUTLINED_FUNCTION_PROLOG_x30x29x19x20x21x22:
 ///    stp x22, x21, [sp, #-32]!    ; x29/x30 has been stored at the caller
 ///    stp x20, x19, [sp, #16]
 ///    ret
 ///
 /// 2) _OUTLINED_FUNCTION_PROLOG_FRAME32_x30x29x19x20x21x22:
 ///    stp x22, x21, [sp, #-32]!    ; x29/x30 has been stored at the caller
 ///    stp x20, x19, [sp, #16]
 ///    add fp, sp, #32
 ///    ret
 ///
 /// 3) _OUTLINED_FUNCTION_EPILOG_x30x29x19x20x21x22:
 ///    mov x16, x30
 ///    ldp x29, x30, [sp, #32]
 ///    ldp x20, x19, [sp, #16]
 ///    ldp x22, x21, [sp], #48
 ///    ret x16
 ///
 /// 4) _OUTLINED_FUNCTION_EPILOG_TAIL_x30x29x19x20x21x22:
 ///    ldp x29, x30, [sp, #32]
 ///    ldp x20, x19, [sp, #16]
 ///    ldp x22, x21, [sp], #48
 ///    ret
 /// @param M module
 /// @param MMI machine module info
 /// @param Regs callee save regs that the helper will handle
 /// @param Type frame helper type
 /// @return a helper function
 static Function *getOrCreateFrameHelper(Module *M, MachineModuleInfo *MMI,
                                         SmallVectorImpl<unsigned> &Regs,
                                         FrameHelperType Type,
                                         unsigned FpOffset = 0) {
   assert(Regs.size() >= 2);
   auto Name = getFrameHelperName(Regs, Type, FpOffset);
   auto *F = M->getFunction(Name);
   if (F)
     return F;

   auto &MF = createFrameHelperMachineFunction(M, MMI, Name);
   MachineBasicBlock &MBB = *MF.begin();
   const TargetSubtargetInfo &STI = MF.getSubtarget();
   const TargetInstrInfo &TII = *STI.getInstrInfo();

   int Size = (int)Regs.size();
   switch (Type) {
   case FrameHelperType::Prolog:
   case FrameHelperType::PrologFrame: {
     // Compute the remaining SP adjust beyond FP/LR.
     auto LRIdx = std::distance(
         Regs.begin(), std::find(Regs.begin(), Regs.end(), AArch64::LR));

     // If the register stored to the lowest address is not LR, we must subtract
     // more from SP here.
     if (LRIdx != Size - 2) {
       assert(Regs[Size - 2] != AArch64::LR);
       emitStore(MF, MBB, MBB.end(), TII, Regs[Size - 2], Regs[Size - 1],
                 LRIdx - Size + 2, true);
     }

     // Store CSRs in the reverse order.
     for (int I = Size - 3; I >= 0; I -= 2) {
       // FP/LR has been stored at call-site.
       if (Regs[I - 1] == AArch64::LR)
         continue;
       emitStore(MF, MBB, MBB.end(), TII, Regs[I - 1], Regs[I], Size - I - 1,
                 false);
     }
     if (Type == FrameHelperType::PrologFrame)
       BuildMI(MBB, MBB.end(), DebugLoc(), TII.get(AArch64::ADDXri))
           .addDef(AArch64::FP)
           .addUse(AArch64::SP)
           .addImm(FpOffset)
           .addImm(0)
           .setMIFlag(MachineInstr::FrameSetup);

     BuildMI(MBB, MBB.end(), DebugLoc(), TII.get(AArch64::RET))
         .addReg(AArch64::LR);
     break;
   }
   case FrameHelperType::Epilog:
   case FrameHelperType::EpilogTail:
     if (Type == FrameHelperType::Epilog)
       // Stash LR to X16
       BuildMI(MBB, MBB.end(), DebugLoc(), TII.get(AArch64::ORRXrs))
           .addDef(AArch64::X16)
           .addReg(AArch64::XZR)
           .addUse(AArch64::LR)
           .addImm(0);

     for (int I = 0; I < Size - 2; I += 2)
       emitLoad(MF, MBB, MBB.end(), TII, Regs[I], Regs[I + 1], Size - I - 2,
                false);
     // Restore the last CSR with post-increment of SP.
     emitLoad(MF, MBB, MBB.end(), TII, Regs[Size - 2], Regs[Size - 1], Size,
              true);

     BuildMI(MBB, MBB.end(), DebugLoc(), TII.get(AArch64::RET))
         .addReg(Type == FrameHelperType::Epilog ? AArch64::X16 : AArch64::LR);
     break;
   }

   return M->getFunction(Name);
 }

 /// This function checks if a frame helper should be used for
 /// HOM_Prolog/HOM_Epilog pseudo instruction expansion.
 /// @param MBB machine basic block
 /// @param NextMBBI  next instruction following HOM_Prolog/HOM_Epilog
 /// @param Regs callee save registers that are saved or restored.
 /// @param Type frame helper type
 /// @return True if a use of helper is qualified.
 static bool shouldUseFrameHelper(MachineBasicBlock &MBB,
                                  MachineBasicBlock::iterator &NextMBBI,
                                  SmallVectorImpl<unsigned> &Regs,
                                  FrameHelperType Type) {
   const auto *TRI = MBB.getParent()->getSubtarget().getRegisterInfo();
   auto RegCount = Regs.size();
   assert(RegCount > 0 && (RegCount % 2 == 0));
   // # of instructions that will be outlined.
   int InstCount = RegCount / 2;

   // Do not use a helper call when not saving LR.
   if (std::find(Regs.begin(), Regs.end(), AArch64::LR) == Regs.end())
     return false;

   switch (Type) {
   case FrameHelperType::Prolog:
     // Prolog helper cannot save FP/LR.
     InstCount--;
     break;
   case FrameHelperType::PrologFrame: {
     // Effecitvely no change in InstCount since FpAdjusment is included.
     break;
   }
   case FrameHelperType::Epilog:
     // Bail-out if X16 is live across the epilog helper because it is used in
     // the helper to handle X30.
     for (auto NextMI = NextMBBI; NextMI != MBB.end(); NextMI++) {
       if (NextMI->readsRegister(AArch64::W16, TRI))
         return false;
     }
     // Epilog may not be in the last block. Check the liveness in successors.
     for (const MachineBasicBlock *SuccMBB : MBB.successors()) {
       if (SuccMBB->isLiveIn(AArch64::W16) || SuccMBB->isLiveIn(AArch64::X16))
         return false;
     }
     // No change in InstCount for the regular epilog case.
     break;
   case FrameHelperType::EpilogTail: {
     // EpilogTail helper includes the caller's return.
     if (NextMBBI == MBB.end())
       return false;
     if (NextMBBI->getOpcode() != AArch64::RET_ReallyLR)
       return false;
     InstCount++;
     break;
   }
   }

   return InstCount >= FrameHelperSizeThreshold;
 }

 /// Lower a HOM_Epilog pseudo instruction into a helper call while
 /// creating the helper on demand. Or emit a sequence of loads in place when not
 /// using a helper call.
 ///
 /// 1. With a helper including ret
 ///    HOM_Epilog x30, x29, x19, x20, x21, x22              ; MBBI
 ///    ret                                                  ; NextMBBI
 ///    =>
 ///    b _OUTLINED_FUNCTION_EPILOG_TAIL_x30x29x19x20x21x22
 ///    ...                                                  ; NextMBBI
 ///
 /// 2. With a helper
 ///    HOM_Epilog x30, x29, x19, x20, x21, x22
 ///    =>
 ///    bl _OUTLINED_FUNCTION_EPILOG_x30x29x19x20x21x22
 ///
 /// 3. Without a helper
 ///    HOM_Epilog x30, x29, x19, x20, x21, x22
 ///    =>
 ///    ldp x29, x30, [sp, #32]
 ///    ldp x20, x19, [sp, #16]
 ///    ldp x22, x21, [sp], #48
 bool AArch64LowerHomogeneousPE::lowerEpilog(
     MachineBasicBlock &MBB, MachineBasicBlock::iterator MBBI,
     MachineBasicBlock::iterator &NextMBBI) {
   auto &MF = *MBB.getParent();
   MachineInstr &MI = *MBBI;

   DebugLoc DL = MI.getDebugLoc();
   SmallVector<unsigned, 8> Regs;
   for (auto &MO : MI.operands())
     if (MO.isReg())
       Regs.push_back(MO.getReg());
   int Size = (int)Regs.size();
   if (Size == 0)
     return false;
   // Registers are in pair.
   assert(Size % 2 == 0);
   assert(MI.getOpcode() == AArch64::HOM_Epilog);

   auto Return = NextMBBI;
   if (shouldUseFrameHelper(MBB, NextMBBI, Regs, FrameHelperType::EpilogTail)) {
     // When MBB ends with a return, emit a tail-call to the epilog helper
     auto *EpilogTailHelper =
         getOrCreateFrameHelper(M, MMI, Regs, FrameHelperType::EpilogTail);
     BuildMI(MBB, MBBI, DL, TII->get(AArch64::TCRETURNdi))
         .addGlobalAddress(EpilogTailHelper)
         .addImm(0)
         .setMIFlag(MachineInstr::FrameDestroy)
         .copyImplicitOps(MI)
         .copyImplicitOps(*Return);
     NextMBBI = std::next(Return);
     Return->removeFromParent();
   } else if (shouldUseFrameHelper(MBB, NextMBBI, Regs,
                                   FrameHelperType::Epilog)) {
     // The default epilog helper case.
     auto *EpilogHelper =
         getOrCreateFrameHelper(M, MMI, Regs, FrameHelperType::Epilog);
     BuildMI(MBB, MBBI, DL, TII->get(AArch64::BL))
         .addGlobalAddress(EpilogHelper)
         .setMIFlag(MachineInstr::FrameDestroy)
         .copyImplicitOps(MI);
   } else {
     // Fall back to no-helper.
     for (int I = 0; I < Size - 2; I += 2)
       emitLoad(MF, MBB, MBBI, *TII, Regs[I], Regs[I + 1], Size - I - 2, false);
     // Restore the last CSR with post-increment of SP.
     emitLoad(MF, MBB, MBBI, *TII, Regs[Size - 2], Regs[Size - 1], Size, true);
   }

   MBBI->removeFromParent();
   return true;
 }

 /// Lower a HOM_Prolog pseudo instruction into a helper call while
 /// creating the helper on demand. Or emit a sequence of stores in place when
 /// not using a helper call.
 ///
 /// 1. With a helper including frame-setup
 ///    HOM_Prolog x30, x29, x19, x20, x21, x22, 32
 ///    =>
 ///    stp x29, x30, [sp, #-16]!
 ///    bl _OUTLINED_FUNCTION_PROLOG_FRAME32_x30x29x19x20x21x22
 ///
 /// 2. With a helper
 ///    HOM_Prolog x30, x29, x19, x20, x21, x22
 ///    =>
 ///    stp x29, x30, [sp, #-16]!
 ///    bl _OUTLINED_FUNCTION_PROLOG_x30x29x19x20x21x22
 ///
 /// 3. Without a helper
 ///    HOM_Prolog x30, x29, x19, x20, x21, x22
 ///    =>
 ///    stp	x22, x21, [sp, #-48]!
 ///    stp	x20, x19, [sp, #16]
 ///    stp	x29, x30, [sp, #32]
 bool AArch64LowerHomogeneousPE::lowerProlog(
     MachineBasicBlock &MBB, MachineBasicBlock::iterator MBBI,
     MachineBasicBlock::iterator &NextMBBI) {
   auto &MF = *MBB.getParent();
   MachineInstr &MI = *MBBI;

   DebugLoc DL = MI.getDebugLoc();
   SmallVector<unsigned, 8> Regs;
   int LRIdx = 0;
   Optional<int> FpOffset;
   for (auto &MO : MI.operands()) {
     if (MO.isReg()) {
       if (MO.getReg() == AArch64::LR)
         LRIdx = Regs.size();
       Regs.push_back(MO.getReg());
     } else if (MO.isImm()) {
       FpOffset = MO.getImm();
     }
   }
   int Size = (int)Regs.size();
   if (Size == 0)
     return false;
   // Allow compact unwind case only for oww.
   assert(Size % 2 == 0);
   assert(MI.getOpcode() == AArch64::HOM_Prolog);

   if (FpOffset &&
       shouldUseFrameHelper(MBB, NextMBBI, Regs, FrameHelperType::PrologFrame)) {
     // FP/LR is stored at the top of stack before the prolog helper call.
     emitStore(MF, MBB, MBBI, *TII, AArch64::LR, AArch64::FP, -LRIdx - 2, true);
     auto *PrologFrameHelper = getOrCreateFrameHelper(
         M, MMI, Regs, FrameHelperType::PrologFrame, *FpOffset);
     BuildMI(MBB, MBBI, DL, TII->get(AArch64::BL))
         .addGlobalAddress(PrologFrameHelper)
         .setMIFlag(MachineInstr::FrameSetup)
         .copyImplicitOps(MI)
         .addReg(AArch64::FP, RegState::Implicit | RegState::Define)
         .addReg(AArch64::SP, RegState::Implicit);
   } else if (!FpOffset && shouldUseFrameHelper(MBB, NextMBBI, Regs,
                                                FrameHelperType::Prolog)) {
     // FP/LR is stored at the top of stack before the prolog helper call.
     emitStore(MF, MBB, MBBI, *TII, AArch64::LR, AArch64::FP, -LRIdx - 2, true);
     auto *PrologHelper =
         getOrCreateFrameHelper(M, MMI, Regs, FrameHelperType::Prolog);
     BuildMI(MBB, MBBI, DL, TII->get(AArch64::BL))
         .addGlobalAddress(PrologHelper)
         .setMIFlag(MachineInstr::FrameSetup)
         .copyImplicitOps(MI);
   } else {
     // Fall back to no-helper.
     emitStore(MF, MBB, MBBI, *TII, Regs[Size - 2], Regs[Size - 1], -Size, true);
     for (int I = Size - 3; I >= 0; I -= 2)
       emitStore(MF, MBB, MBBI, *TII, Regs[I - 1], Regs[I], Size - I - 1, false);
     if (FpOffset) {
       BuildMI(MBB, MBBI, DL, TII->get(AArch64::ADDXri))
           .addDef(AArch64::FP)
           .addUse(AArch64::SP)
           .addImm(*FpOffset)
           .addImm(0)
           .setMIFlag(MachineInstr::FrameSetup);
     }
   }

   MBBI->removeFromParent();
   return true;
 }

 /// Process each machine instruction
 /// @param MBB machine basic block
 /// @param MBBI current instruction iterator
 /// @param NextMBBI next instruction iterator which can be updated
 /// @return True when IR is changed.
 bool AArch64LowerHomogeneousPE::runOnMI(MachineBasicBlock &MBB,
                                         MachineBasicBlock::iterator MBBI,
                                         MachineBasicBlock::iterator &NextMBBI) {
   MachineInstr &MI = *MBBI;
   unsigned Opcode = MI.getOpcode();
   switch (Opcode) {
   default:
     break;
   case AArch64::HOM_Prolog:
     return lowerProlog(MBB, MBBI, NextMBBI);
   case AArch64::HOM_Epilog:
     return lowerEpilog(MBB, MBBI, NextMBBI);
   }
   return false;
 }

 bool AArch64LowerHomogeneousPE::runOnMBB(MachineBasicBlock &MBB) {
   bool Modified = false;

   MachineBasicBlock::iterator MBBI = MBB.begin(), E = MBB.end();
   while (MBBI != E) {
     MachineBasicBlock::iterator NMBBI = std::next(MBBI);
     Modified |= runOnMI(MBB, MBBI, NMBBI);
     MBBI = NMBBI;
   }

   return Modified;
 }

 bool AArch64LowerHomogeneousPE::runOnMachineFunction(MachineFunction &MF) {
   TII = static_cast<const AArch64InstrInfo *>(MF.getSubtarget().getInstrInfo());

   bool Modified = false;
   for (auto &MBB : MF)
     Modified |= runOnMBB(MBB);
   return Modified;
 }

 ModulePass *llvm::createAArch64LowerHomogeneousPrologEpilogPass() {
   return new AArch64LowerHomogeneousPrologEpilog();
 }
	//===- AArch64LowerHomogeneousPrologEpilog.cpp ----------------------------===//
	//
	// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
	// See https://llvm.org/LICENSE.txt for license information.
	// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
	//
	//===----------------------------------------------------------------------===//
	//
	// This file contains a pass that lowers homogeneous prolog/epilog instructions.
	//
	//===----------------------------------------------------------------------===//

	#include "AArch64InstrInfo.h"
	#include "AArch64Subtarget.h"
	#include "MCTargetDesc/AArch64InstPrinter.h"
	#include "Utils/AArch64BaseInfo.h"
	#include "llvm/CodeGen/MachineBasicBlock.h"
	#include "llvm/CodeGen/MachineFunction.h"
	#include "llvm/CodeGen/MachineFunctionPass.h"
	#include "llvm/CodeGen/MachineInstr.h"
	#include "llvm/CodeGen/MachineInstrBuilder.h"
	#include "llvm/CodeGen/MachineModuleInfo.h"
	#include "llvm/CodeGen/MachineOperand.h"
	#include "llvm/CodeGen/TargetSubtargetInfo.h"
	#include "llvm/IR/DebugLoc.h"
	#include "llvm/Pass.h"
	#include "llvm/Support/raw_ostream.h"
	#include <sstream>

	using namespace llvm;

	#define AARCH64_LOWER_HOMOGENEOUS_PROLOG_EPILOG_NAME \
	"AArch64 homogeneous prolog/epilog lowering pass"

	cl::opt<int> FrameHelperSizeThreshold(
	"frame-helper-size-threshold", cl::init(2), cl::Hidden,
	cl::desc("The minimum number of instructions that are outlined in a frame "
	"helper (default = 2)"));

	namespace {

	class AArch64LowerHomogeneousPE {
	public:
	const AArch64InstrInfo *TII;

	AArch64LowerHomogeneousPE(Module M, MachineModuleInfo MMI)
	: M(M), MMI(MMI) {}

	bool run();
	bool runOnMachineFunction(MachineFunction &Fn);

	private:
	Module *M;
	MachineModuleInfo *MMI;

	bool runOnMBB(MachineBasicBlock &MBB);
	bool runOnMI(MachineBasicBlock &MBB, MachineBasicBlock::iterator MBBI,
	MachineBasicBlock::iterator &NextMBBI);

	/// Lower a HOM_Prolog pseudo instruction into a helper call
	/// or a sequence of homogeneous stores.
	/// When a a fp setup follows, it can be optimized.
	bool lowerProlog(MachineBasicBlock &MBB, MachineBasicBlock::iterator MBBI,
	MachineBasicBlock::iterator &NextMBBI);
	/// Lower a HOM_Epilog pseudo instruction into a helper call
	/// or a sequence of homogeneous loads.
	/// When a return follow, it can be optimized.
	bool lowerEpilog(MachineBasicBlock &MBB, MachineBasicBlock::iterator MBBI,
	MachineBasicBlock::iterator &NextMBBI);
	};

	class AArch64LowerHomogeneousPrologEpilog : public ModulePass {
	public:
	static char ID;

	AArch64LowerHomogeneousPrologEpilog() : ModulePass(ID) {
	initializeAArch64LowerHomogeneousPrologEpilogPass(
	*PassRegistry::getPassRegistry());
	}
	void getAnalysisUsage(AnalysisUsage &AU) const override {
	AU.addRequired<MachineModuleInfoWrapperPass>();
	AU.addPreserved<MachineModuleInfoWrapperPass>();
	AU.setPreservesAll();
	ModulePass::getAnalysisUsage(AU);
	}
	bool runOnModule(Module &M) override;

	StringRef getPassName() const override {
	return AARCH64_LOWER_HOMOGENEOUS_PROLOG_EPILOG_NAME;
	}
	};

	} // end anonymous namespace

	char AArch64LowerHomogeneousPrologEpilog::ID = 0;

	INITIALIZE_PASS(AArch64LowerHomogeneousPrologEpilog,
	"aarch64-lower-homogeneous-prolog-epilog",
	AARCH64_LOWER_HOMOGENEOUS_PROLOG_EPILOG_NAME, false, false)

	bool AArch64LowerHomogeneousPrologEpilog::runOnModule(Module &M) {
	if (skipModule(M))
	return false;

	MachineModuleInfo *MMI =
	&getAnalysis<MachineModuleInfoWrapperPass>().getMMI();
	return AArch64LowerHomogeneousPE(&M, MMI).run();
	}

	bool AArch64LowerHomogeneousPE::run() {
	bool Changed = false;
	for (auto &F : *M) {
	if (F.empty())
	continue;

	MachineFunction *MF = MMI->getMachineFunction(F);
	if (!MF)
	continue;
	Changed \|= runOnMachineFunction(*MF);
	}

	return Changed;
	}
	enum FrameHelperType { Prolog, PrologFrame, Epilog, EpilogTail };

	/// Return a frame helper name with the given CSRs and the helper type.
	/// For instance, a prolog helper that saves x19 and x20 is named as
	/// OUTLINED_FUNCTION_PROLOG_x19x20.
	static std::string getFrameHelperName(SmallVectorImpl<unsigned> &Regs,
	FrameHelperType Type, unsigned FpOffset) {
	std::ostringstream RegStream;
	switch (Type) {
	case FrameHelperType::Prolog:
	RegStream << "OUTLINED_FUNCTION_PROLOG_";
	break;
	case FrameHelperType::PrologFrame:
	RegStream << "OUTLINED_FUNCTION_PROLOG_FRAME" << FpOffset << "_";
	break;
	case FrameHelperType::Epilog:
	RegStream << "OUTLINED_FUNCTION_EPILOG_";
	break;
	case FrameHelperType::EpilogTail:
	RegStream << "OUTLINED_FUNCTION_EPILOG_TAIL_";
	break;
	}

	for (auto Reg : Regs)
	RegStream << AArch64InstPrinter::getRegisterName(Reg);

	return RegStream.str();
	}

	/// Create a Function for the unique frame helper with the given name.
	/// Return a newly created MachineFunction with an empty MachineBasicBlock.
	static MachineFunction &createFrameHelperMachineFunction(Module *M,
	MachineModuleInfo *MMI,
	StringRef Name) {
	LLVMContext &C = M->getContext();
	Function *F = M->getFunction(Name);
	assert(F == nullptr && "Function has been created before");
	F = Function::Create(FunctionType::get(Type::getVoidTy(C), false),
	Function::ExternalLinkage, Name, M);
	assert(F && "Function was null!");

	// Use ODR linkage to avoid duplication.
	F->setLinkage(GlobalValue::LinkOnceODRLinkage);
	F->setUnnamedAddr(GlobalValue::UnnamedAddr::Global);

	// Set no-opt/minsize, so we don't insert padding between outlined
	// functions.
	F->addFnAttr(Attribute::OptimizeNone);
	F->addFnAttr(Attribute::NoInline);
	F->addFnAttr(Attribute::MinSize);
	F->addFnAttr(Attribute::Naked);

	MachineFunction &MF = MMI->getOrCreateMachineFunction(*F);
	// Remove unnecessary register liveness and set NoVRegs.
	MF.getProperties().reset(MachineFunctionProperties::Property::TracksLiveness);
	MF.getProperties().reset(MachineFunctionProperties::Property::IsSSA);
	MF.getProperties().set(MachineFunctionProperties::Property::NoVRegs);
	MF.getRegInfo().freezeReservedRegs(MF);

	// Create entry block.
	BasicBlock *EntryBB = BasicBlock::Create(C, "entry", F);
	IRBuilder<> Builder(EntryBB);
	Builder.CreateRetVoid();

	// Insert the new block into the function.
	MachineBasicBlock *MBB = MF.CreateMachineBasicBlock();
	MF.insert(MF.begin(), MBB);

	return MF;
	}

	/// Emit a store-pair instruction for frame-setup.
	static void emitStore(MachineFunction &MF, MachineBasicBlock &MBB,
	MachineBasicBlock::iterator Pos,
	const TargetInstrInfo &TII, unsigned Reg1, unsigned Reg2,
	int Offset, bool IsPreDec) {
	bool IsFloat = AArch64::FPR64RegClass.contains(Reg1);
	assert(!(IsFloat ^ AArch64::FPR64RegClass.contains(Reg2)));
	unsigned Opc;
	if (IsPreDec)
	Opc = IsFloat ? AArch64::STPDpre : AArch64::STPXpre;
	else
	Opc = IsFloat ? AArch64::STPDi : AArch64::STPXi;

	MachineInstrBuilder MIB = BuildMI(MBB, Pos, DebugLoc(), TII.get(Opc));
	if (IsPreDec)
	MIB.addDef(AArch64::SP);
	MIB.addReg(Reg2)
	.addReg(Reg1)
	.addReg(AArch64::SP)
	.addImm(Offset)
	.setMIFlag(MachineInstr::FrameSetup);
	}

	/// Emit a load-pair instruction for frame-destroy.
	static void emitLoad(MachineFunction &MF, MachineBasicBlock &MBB,
	MachineBasicBlock::iterator Pos,
	const TargetInstrInfo &TII, unsigned Reg1, unsigned Reg2,
	int Offset, bool IsPostDec) {
	bool IsFloat = AArch64::FPR64RegClass.contains(Reg1);
	assert(!(IsFloat ^ AArch64::FPR64RegClass.contains(Reg2)));
	unsigned Opc;
	if (IsPostDec)
	Opc = IsFloat ? AArch64::LDPDpost : AArch64::LDPXpost;
	else
	Opc = IsFloat ? AArch64::LDPDi : AArch64::LDPXi;

	MachineInstrBuilder MIB = BuildMI(MBB, Pos, DebugLoc(), TII.get(Opc));
	if (IsPostDec)
	MIB.addDef(AArch64::SP);
	MIB.addReg(Reg2, getDefRegState(true))
	.addReg(Reg1, getDefRegState(true))
	.addReg(AArch64::SP)
	.addImm(Offset)
	.setMIFlag(MachineInstr::FrameDestroy);
	}

	/// Return a unique function if a helper can be formed with the given Regs
	/// and frame type.
	/// 1) _OUTLINED_FUNCTION_PROLOG_x30x29x19x20x21x22:
	/// stp x22, x21, [sp, #-32]! ; x29/x30 has been stored at the caller
	/// stp x20, x19, [sp, #16]
	/// ret
	///
	/// 2) _OUTLINED_FUNCTION_PROLOG_FRAME32_x30x29x19x20x21x22:
	/// stp x22, x21, [sp, #-32]! ; x29/x30 has been stored at the caller
	/// stp x20, x19, [sp, #16]
	/// add fp, sp, #32
	/// ret
	///
	/// 3) _OUTLINED_FUNCTION_EPILOG_x30x29x19x20x21x22:
	/// mov x16, x30
	/// ldp x29, x30, [sp, #32]
	/// ldp x20, x19, [sp, #16]
	/// ldp x22, x21, [sp], #48
	/// ret x16
	///
	/// 4) _OUTLINED_FUNCTION_EPILOG_TAIL_x30x29x19x20x21x22:
	/// ldp x29, x30, [sp, #32]
	/// ldp x20, x19, [sp, #16]
	/// ldp x22, x21, [sp], #48
	/// ret
	/// @param M module
	/// @param MMI machine module info
	/// @param Regs callee save regs that the helper will handle
	/// @param Type frame helper type
	/// @return a helper function
	static Function getOrCreateFrameHelper(Module M, MachineModuleInfo *MMI,
	SmallVectorImpl<unsigned> &Regs,
	FrameHelperType Type,
	unsigned FpOffset = 0) {
	assert(Regs.size() >= 2);
	auto Name = getFrameHelperName(Regs, Type, FpOffset);
	auto *F = M->getFunction(Name);
	if (F)
	return F;

	auto &MF = createFrameHelperMachineFunction(M, MMI, Name);
	MachineBasicBlock &MBB = *MF.begin();
	const TargetSubtargetInfo &STI = MF.getSubtarget();
	const TargetInstrInfo &TII = *STI.getInstrInfo();

	int Size = (int)Regs.size();
	switch (Type) {
	case FrameHelperType::Prolog:
	case FrameHelperType::PrologFrame: {
	// Compute the remaining SP adjust beyond FP/LR.
	auto LRIdx = std::distance(
	Regs.begin(), std::find(Regs.begin(), Regs.end(), AArch64::LR));

	// If the register stored to the lowest address is not LR, we must subtract
	// more from SP here.
	if (LRIdx != Size - 2) {
	assert(Regs[Size - 2] != AArch64::LR);
	emitStore(MF, MBB, MBB.end(), TII, Regs[Size - 2], Regs[Size - 1],
	LRIdx - Size + 2, true);
	}

	// Store CSRs in the reverse order.
	for (int I = Size - 3; I >= 0; I -= 2) {
	// FP/LR has been stored at call-site.
	if (Regs[I - 1] == AArch64::LR)
	continue;
	emitStore(MF, MBB, MBB.end(), TII, Regs[I - 1], Regs[I], Size - I - 1,
	false);
	}
	if (Type == FrameHelperType::PrologFrame)
	BuildMI(MBB, MBB.end(), DebugLoc(), TII.get(AArch64::ADDXri))
	.addDef(AArch64::FP)
	.addUse(AArch64::SP)
	.addImm(FpOffset)
	.addImm(0)
	.setMIFlag(MachineInstr::FrameSetup);

	BuildMI(MBB, MBB.end(), DebugLoc(), TII.get(AArch64::RET))
	.addReg(AArch64::LR);
	break;
	}
	case FrameHelperType::Epilog:
	case FrameHelperType::EpilogTail:
	if (Type == FrameHelperType::Epilog)
	// Stash LR to X16
	BuildMI(MBB, MBB.end(), DebugLoc(), TII.get(AArch64::ORRXrs))
	.addDef(AArch64::X16)
	.addReg(AArch64::XZR)
	.addUse(AArch64::LR)
	.addImm(0);

	for (int I = 0; I < Size - 2; I += 2)
	emitLoad(MF, MBB, MBB.end(), TII, Regs[I], Regs[I + 1], Size - I - 2,
	false);
	// Restore the last CSR with post-increment of SP.
	emitLoad(MF, MBB, MBB.end(), TII, Regs[Size - 2], Regs[Size - 1], Size,
	true);

	BuildMI(MBB, MBB.end(), DebugLoc(), TII.get(AArch64::RET))
	.addReg(Type == FrameHelperType::Epilog ? AArch64::X16 : AArch64::LR);
	break;
	}

	return M->getFunction(Name);
	}

	/// This function checks if a frame helper should be used for
	/// HOM_Prolog/HOM_Epilog pseudo instruction expansion.
	/// @param MBB machine basic block
	/// @param NextMBBI next instruction following HOM_Prolog/HOM_Epilog
	/// @param Regs callee save registers that are saved or restored.
	/// @param Type frame helper type
	/// @return True if a use of helper is qualified.
	static bool shouldUseFrameHelper(MachineBasicBlock &MBB,
	MachineBasicBlock::iterator &NextMBBI,
	SmallVectorImpl<unsigned> &Regs,
	FrameHelperType Type) {
	const auto *TRI = MBB.getParent()->getSubtarget().getRegisterInfo();
	auto RegCount = Regs.size();
	assert(RegCount > 0 && (RegCount % 2 == 0));
	// # of instructions that will be outlined.
	int InstCount = RegCount / 2;

	// Do not use a helper call when not saving LR.
	if (std::find(Regs.begin(), Regs.end(), AArch64::LR) == Regs.end())
	return false;

	switch (Type) {
	case FrameHelperType::Prolog:
	// Prolog helper cannot save FP/LR.
	InstCount--;
	break;
	case FrameHelperType::PrologFrame: {
	// Effecitvely no change in InstCount since FpAdjusment is included.
	break;
	}
	case FrameHelperType::Epilog:
	// Bail-out if X16 is live across the epilog helper because it is used in
	// the helper to handle X30.
	for (auto NextMI = NextMBBI; NextMI != MBB.end(); NextMI++) {
	if (NextMI->readsRegister(AArch64::W16, TRI))
	return false;
	}
	// Epilog may not be in the last block. Check the liveness in successors.
	for (const MachineBasicBlock *SuccMBB : MBB.successors()) {
	if (SuccMBB->isLiveIn(AArch64::W16) \|\| SuccMBB->isLiveIn(AArch64::X16))
	return false;
	}
	// No change in InstCount for the regular epilog case.
	break;
	case FrameHelperType::EpilogTail: {
	// EpilogTail helper includes the caller's return.
	if (NextMBBI == MBB.end())
	return false;
	if (NextMBBI->getOpcode() != AArch64::RET_ReallyLR)
	return false;
	InstCount++;
	break;
	}
	}

	return InstCount >= FrameHelperSizeThreshold;
	}

	/// Lower a HOM_Epilog pseudo instruction into a helper call while
	/// creating the helper on demand. Or emit a sequence of loads in place when not
	/// using a helper call.
	///
	/// 1. With a helper including ret
	/// HOM_Epilog x30, x29, x19, x20, x21, x22 ; MBBI
	/// ret ; NextMBBI
	/// =>
	/// b _OUTLINED_FUNCTION_EPILOG_TAIL_x30x29x19x20x21x22
	/// ... ; NextMBBI
	///
	/// 2. With a helper
	/// HOM_Epilog x30, x29, x19, x20, x21, x22
	/// =>
	/// bl _OUTLINED_FUNCTION_EPILOG_x30x29x19x20x21x22
	///
	/// 3. Without a helper
	/// HOM_Epilog x30, x29, x19, x20, x21, x22
	/// =>
	/// ldp x29, x30, [sp, #32]
	/// ldp x20, x19, [sp, #16]
	/// ldp x22, x21, [sp], #48
	bool AArch64LowerHomogeneousPE::lowerEpilog(
	MachineBasicBlock &MBB, MachineBasicBlock::iterator MBBI,
	MachineBasicBlock::iterator &NextMBBI) {
	auto &MF = *MBB.getParent();
	MachineInstr &MI = *MBBI;

	DebugLoc DL = MI.getDebugLoc();
	SmallVector<unsigned, 8> Regs;
	for (auto &MO : MI.operands())
	if (MO.isReg())
	Regs.push_back(MO.getReg());
	int Size = (int)Regs.size();
	if (Size == 0)
	return false;
	// Registers are in pair.
	assert(Size % 2 == 0);
	assert(MI.getOpcode() == AArch64::HOM_Epilog);

	auto Return = NextMBBI;
	if (shouldUseFrameHelper(MBB, NextMBBI, Regs, FrameHelperType::EpilogTail)) {
	// When MBB ends with a return, emit a tail-call to the epilog helper
	auto *EpilogTailHelper =
	getOrCreateFrameHelper(M, MMI, Regs, FrameHelperType::EpilogTail);
	BuildMI(MBB, MBBI, DL, TII->get(AArch64::TCRETURNdi))
	.addGlobalAddress(EpilogTailHelper)
	.addImm(0)
	.setMIFlag(MachineInstr::FrameDestroy)
	.copyImplicitOps(MI)
	.copyImplicitOps(*Return);
	NextMBBI = std::next(Return);
	Return->removeFromParent();
	} else if (shouldUseFrameHelper(MBB, NextMBBI, Regs,
	FrameHelperType::Epilog)) {
	// The default epilog helper case.
	auto *EpilogHelper =
	getOrCreateFrameHelper(M, MMI, Regs, FrameHelperType::Epilog);
	BuildMI(MBB, MBBI, DL, TII->get(AArch64::BL))
	.addGlobalAddress(EpilogHelper)
	.setMIFlag(MachineInstr::FrameDestroy)
	.copyImplicitOps(MI);
	} else {
	// Fall back to no-helper.
	for (int I = 0; I < Size - 2; I += 2)
	emitLoad(MF, MBB, MBBI, *TII, Regs[I], Regs[I + 1], Size - I - 2, false);
	// Restore the last CSR with post-increment of SP.
	emitLoad(MF, MBB, MBBI, *TII, Regs[Size - 2], Regs[Size - 1], Size, true);
	}

	MBBI->removeFromParent();
	return true;
	}

	/// Lower a HOM_Prolog pseudo instruction into a helper call while
	/// creating the helper on demand. Or emit a sequence of stores in place when
	/// not using a helper call.
	///
	/// 1. With a helper including frame-setup
	/// HOM_Prolog x30, x29, x19, x20, x21, x22, 32
	/// =>
	/// stp x29, x30, [sp, #-16]!
	/// bl _OUTLINED_FUNCTION_PROLOG_FRAME32_x30x29x19x20x21x22
	///
	/// 2. With a helper
	/// HOM_Prolog x30, x29, x19, x20, x21, x22
	/// =>
	/// stp x29, x30, [sp, #-16]!
	/// bl _OUTLINED_FUNCTION_PROLOG_x30x29x19x20x21x22
	///
	/// 3. Without a helper
	/// HOM_Prolog x30, x29, x19, x20, x21, x22
	/// =>
	/// stp x22, x21, [sp, #-48]!
	/// stp x20, x19, [sp, #16]
	/// stp x29, x30, [sp, #32]
	bool AArch64LowerHomogeneousPE::lowerProlog(
	MachineBasicBlock &MBB, MachineBasicBlock::iterator MBBI,
	MachineBasicBlock::iterator &NextMBBI) {
	auto &MF = *MBB.getParent();
	MachineInstr &MI = *MBBI;

	DebugLoc DL = MI.getDebugLoc();
	SmallVector<unsigned, 8> Regs;
	int LRIdx = 0;
	Optional<int> FpOffset;
	for (auto &MO : MI.operands()) {
	if (MO.isReg()) {
	if (MO.getReg() == AArch64::LR)
	LRIdx = Regs.size();
	Regs.push_back(MO.getReg());
	} else if (MO.isImm()) {
	FpOffset = MO.getImm();
	}
	}
	int Size = (int)Regs.size();
	if (Size == 0)
	return false;
	// Allow compact unwind case only for oww.
	assert(Size % 2 == 0);
	assert(MI.getOpcode() == AArch64::HOM_Prolog);

	if (FpOffset &&
	shouldUseFrameHelper(MBB, NextMBBI, Regs, FrameHelperType::PrologFrame)) {
	// FP/LR is stored at the top of stack before the prolog helper call.
	emitStore(MF, MBB, MBBI, *TII, AArch64::LR, AArch64::FP, -LRIdx - 2, true);
	auto *PrologFrameHelper = getOrCreateFrameHelper(
	M, MMI, Regs, FrameHelperType::PrologFrame, *FpOffset);
	BuildMI(MBB, MBBI, DL, TII->get(AArch64::BL))
	.addGlobalAddress(PrologFrameHelper)
	.setMIFlag(MachineInstr::FrameSetup)
	.copyImplicitOps(MI)
	.addReg(AArch64::FP, RegState::Implicit \| RegState::Define)
	.addReg(AArch64::SP, RegState::Implicit);
	} else if (!FpOffset && shouldUseFrameHelper(MBB, NextMBBI, Regs,
	FrameHelperType::Prolog)) {
	// FP/LR is stored at the top of stack before the prolog helper call.
	emitStore(MF, MBB, MBBI, *TII, AArch64::LR, AArch64::FP, -LRIdx - 2, true);
	auto *PrologHelper =
	getOrCreateFrameHelper(M, MMI, Regs, FrameHelperType::Prolog);
	BuildMI(MBB, MBBI, DL, TII->get(AArch64::BL))
	.addGlobalAddress(PrologHelper)
	.setMIFlag(MachineInstr::FrameSetup)
	.copyImplicitOps(MI);
	} else {
	// Fall back to no-helper.
	emitStore(MF, MBB, MBBI, *TII, Regs[Size - 2], Regs[Size - 1], -Size, true);
	for (int I = Size - 3; I >= 0; I -= 2)
	emitStore(MF, MBB, MBBI, *TII, Regs[I - 1], Regs[I], Size - I - 1, false);
	if (FpOffset) {
	BuildMI(MBB, MBBI, DL, TII->get(AArch64::ADDXri))
	.addDef(AArch64::FP)
	.addUse(AArch64::SP)
	.addImm(*FpOffset)
	.addImm(0)
	.setMIFlag(MachineInstr::FrameSetup);
	}
	}

	MBBI->removeFromParent();
	return true;
	}

	/// Process each machine instruction
	/// @param MBB machine basic block
	/// @param MBBI current instruction iterator
	/// @param NextMBBI next instruction iterator which can be updated
	/// @return True when IR is changed.
	bool AArch64LowerHomogeneousPE::runOnMI(MachineBasicBlock &MBB,
	MachineBasicBlock::iterator MBBI,
	MachineBasicBlock::iterator &NextMBBI) {
	MachineInstr &MI = *MBBI;
	unsigned Opcode = MI.getOpcode();
	switch (Opcode) {
	default:
	break;
	case AArch64::HOM_Prolog:
	return lowerProlog(MBB, MBBI, NextMBBI);
	case AArch64::HOM_Epilog:
	return lowerEpilog(MBB, MBBI, NextMBBI);
	}
	return false;
	}

	bool AArch64LowerHomogeneousPE::runOnMBB(MachineBasicBlock &MBB) {
	bool Modified = false;

	MachineBasicBlock::iterator MBBI = MBB.begin(), E = MBB.end();
	while (MBBI != E) {
	MachineBasicBlock::iterator NMBBI = std::next(MBBI);
	Modified \|= runOnMI(MBB, MBBI, NMBBI);
	MBBI = NMBBI;
	}

	return Modified;
	}

	bool AArch64LowerHomogeneousPE::runOnMachineFunction(MachineFunction &MF) {
	TII = static_cast<const AArch64InstrInfo *>(MF.getSubtarget().getInstrInfo());

	bool Modified = false;
	for (auto &MBB : MF)
	Modified \|= runOnMBB(MBB);
	return Modified;
	}

	ModulePass *llvm::createAArch64LowerHomogeneousPrologEpilogPass() {
	return new AArch64LowerHomogeneousPrologEpilog();
	}