text: //===- PrologEpilogInserter.cpp - Insert Prolog/Epilog code in function ---===//
  //
  // 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 pass is responsible for finalizing the functions frame layout, saving
  // callee saved registers, and for emitting prolog & epilog code for the
  // function.
  //
  // This pass must be run after register allocation.  After this pass is
  // executed, it is illegal to construct MO_FrameIndex operands.
  //
  //===----------------------------------------------------------------------===//
  
  #include "llvm/ADT/ArrayRef.h"
  #include "llvm/ADT/BitVector.h"
  #include "llvm/ADT/DepthFirstIterator.h"
  #include "llvm/ADT/STLExtras.h"
  #include "llvm/ADT/SetVector.h"
  #include "llvm/ADT/SmallPtrSet.h"
  #include "llvm/ADT/SmallSet.h"
  #include "llvm/ADT/SmallVector.h"
  #include "llvm/ADT/Statistic.h"
  #include "llvm/Analysis/OptimizationRemarkEmitter.h"
  #include "llvm/CodeGen/MachineBasicBlock.h"
  #include "llvm/CodeGen/MachineDominators.h"
  #include "llvm/CodeGen/MachineFrameInfo.h"
  #include "llvm/CodeGen/MachineFunction.h"
  #include "llvm/CodeGen/MachineFunctionPass.h"
  #include "llvm/CodeGen/MachineInstr.h"
  #include "llvm/CodeGen/MachineInstrBuilder.h"
  #include "llvm/CodeGen/MachineLoopInfo.h"
  #include "llvm/CodeGen/MachineModuleInfo.h"
  #include "llvm/CodeGen/MachineOperand.h"
  #include "llvm/CodeGen/MachineOptimizationRemarkEmitter.h"
  #include "llvm/CodeGen/MachineRegisterInfo.h"
  #include "llvm/CodeGen/RegisterScavenging.h"
  #include "llvm/CodeGen/TargetFrameLowering.h"
  #include "llvm/CodeGen/TargetInstrInfo.h"
  #include "llvm/CodeGen/TargetOpcodes.h"
  #include "llvm/CodeGen/TargetRegisterInfo.h"
  #include "llvm/CodeGen/TargetSubtargetInfo.h"
  #include "llvm/CodeGen/WinEHFuncInfo.h"
  #include "llvm/IR/Attributes.h"
  #include "llvm/IR/CallingConv.h"
  #include "llvm/IR/DebugInfoMetadata.h"
  #include "llvm/IR/DiagnosticInfo.h"
  #include "llvm/IR/Function.h"
  #include "llvm/IR/InlineAsm.h"
  #include "llvm/IR/LLVMContext.h"
  #include "llvm/MC/MCRegisterInfo.h"
  #include "llvm/Pass.h"
  #include "llvm/Support/CodeGen.h"
  #include "llvm/Support/CommandLine.h"
  #include "llvm/Support/Debug.h"
  #include "llvm/Support/ErrorHandling.h"
  #include "llvm/Support/MathExtras.h"
  #include "llvm/Support/raw_ostream.h"
  #include "llvm/Target/TargetMachine.h"
  #include "llvm/Target/TargetOptions.h"
  #include <algorithm>
  #include <cassert>
  #include <cstdint>
  #include <functional>
  #include <limits>
  #include <utility>
  #include <vector>
  
  using namespace llvm;
  
  #define DEBUG_TYPE "prologepilog"
  
  using MBBVector = SmallVector<MachineBasicBlock *, 4>;
  
  STATISTIC(NumLeafFuncWithSpills, "Number of leaf functions with CSRs");
  STATISTIC(NumFuncSeen, "Number of functions seen in PEI");
  
  
  namespace {
  
  class PEI : public MachineFunctionPass {
  public:
    static char ID;
  
    PEI() : MachineFunctionPass(ID) {
      initializePEIPass(*PassRegistry::getPassRegistry());
    }
  
    void getAnalysisUsage(AnalysisUsage &AU) const override;
  
    /// runOnMachineFunction - Insert prolog/epilog code and replace abstract
    /// frame indexes with appropriate references.
    bool runOnMachineFunction(MachineFunction &MF) override;
  
  private:
    RegScavenger *RS;
  
    // MinCSFrameIndex, MaxCSFrameIndex - Keeps the range of callee saved
    // stack frame indexes.
    unsigned MinCSFrameIndex = std::numeric_limits<unsigned>::max();
    unsigned MaxCSFrameIndex = 0;
  
    // Save and Restore blocks of the current function. Typically there is a
    // single save block, unless Windows EH funclets are involved.
    MBBVector SaveBlocks;
    MBBVector RestoreBlocks;
  
    // Flag to control whether to use the register scavenger to resolve
    // frame index materialization registers. Set according to
    // TRI->requiresFrameIndexScavenging() for the current function.
    bool FrameIndexVirtualScavenging;
  
    // Flag to control whether the scavenger should be passed even though
    // FrameIndexVirtualScavenging is used.
    bool FrameIndexEliminationScavenging;
  
    // Emit remarks.
    MachineOptimizationRemarkEmitter *ORE = nullptr;
  
    void calculateCallFrameInfo(MachineFunction &MF);
    void calculateSaveRestoreBlocks(MachineFunction &MF);
    void spillCalleeSavedRegs(MachineFunction &MF);
  
    void calculateFrameObjectOffsets(MachineFunction &MF);
    void replaceFrameIndices(MachineFunction &MF);
    void replaceFrameIndices(MachineBasicBlock *BB, MachineFunction &MF,
                             int &SPAdj);
    void insertPrologEpilogCode(MachineFunction &MF);
  };
  
  } // end anonymous namespace
  
  char PEI::ID = 0;
  
  char &llvm::PrologEpilogCodeInserterID = PEI::ID;
  
  static cl::opt<unsigned>
  WarnStackSize("warn-stack-size", cl::Hidden, cl::init((unsigned)-1),
                cl::desc("Warn for stack size bigger than the given"
                         " number"));
  
  INITIALIZE_PASS_BEGIN(PEI, DEBUG_TYPE, "Prologue/Epilogue Insertion", false,
                        false)
  INITIALIZE_PASS_DEPENDENCY(MachineLoopInfo)
  INITIALIZE_PASS_DEPENDENCY(MachineDominatorTree)
  INITIALIZE_PASS_DEPENDENCY(MachineOptimizationRemarkEmitterPass)
  INITIALIZE_PASS_END(PEI, DEBUG_TYPE,
                      "Prologue/Epilogue Insertion & Frame Finalization", false,
                      false)
  
  MachineFunctionPass *llvm::createPrologEpilogInserterPass() {
    return new PEI();
  }
  
  STATISTIC(NumBytesStackSpace,
            "Number of bytes used for stack in all functions");
  
  void PEI::getAnalysisUsage(AnalysisUsage &AU) const {
    AU.setPreservesCFG();
    AU.addPreserved<MachineLoopInfo>();
    AU.addPreserved<MachineDominatorTree>();
    AU.addRequired<MachineOptimizationRemarkEmitterPass>();
    MachineFunctionPass::getAnalysisUsage(AU);
  }
  
  /// StackObjSet - A set of stack object indexes
  using StackObjSet = SmallSetVector<int, 8>;
  
  using SavedDbgValuesMap =
      SmallDenseMap<MachineBasicBlock *, SmallVector<MachineInstr *, 4>, 4>;
  
  /// Stash DBG_VALUEs that describe parameters and which are placed at the start
  /// of the block. Later on, after the prologue code has been emitted, the
  /// stashed DBG_VALUEs will be reinserted at the start of the block.
  static void stashEntryDbgValues(MachineBasicBlock &MBB,
                                  SavedDbgValuesMap &EntryDbgValues) {
    SmallVector<const MachineInstr *, 4> FrameIndexValues;
  
    for (auto &MI : MBB) {
      if (!MI.isDebugInstr())
        break;
      if (!MI.isDebugValue() || !MI.getDebugVariable()->isParameter())
        continue;
      if (MI.getOperand(0).isFI()) {
        // We can only emit valid locations for frame indices after the frame
        // setup, so do not stash away them.
        FrameIndexValues.push_back(&MI);
        continue;
      }
      const DILocalVariable *Var = MI.getDebugVariable();
      const DIExpression *Expr = MI.getDebugExpression();
      auto Overlaps = [Var, Expr](const MachineInstr *DV) {
        return Var == DV->getDebugVariable() &&
               Expr->fragmentsOverlap(DV->getDebugExpression());
      };
      // See if the debug value overlaps with any preceding debug value that will
      // not be stashed. If that is the case, then we can't stash this value, as
      // we would then reorder the values at reinsertion.
      if (llvm::none_of(FrameIndexValues, Overlaps))
        EntryDbgValues[&MBB].push_back(&MI);
    }
  
    // Remove stashed debug values from the block.
    if (EntryDbgValues.count(&MBB))
      for (auto *MI : EntryDbgValues[&MBB])
        MI->removeFromParent();
  }
  
  /// runOnMachineFunction - Insert prolog/epilog code and replace abstract
  /// frame indexes with appropriate references.
  bool PEI::runOnMachineFunction(MachineFunction &MF) {
    NumFuncSeen++;
    const Function &F = MF.getFunction();
    const TargetRegisterInfo *TRI = MF.getSubtarget().getRegisterInfo();
    const TargetFrameLowering *TFI = MF.getSubtarget().getFrameLowering();
  
    RS = TRI->requiresRegisterScavenging(MF) ? new RegScavenger() : nullptr;
    FrameIndexVirtualScavenging = TRI->requiresFrameIndexScavenging(MF);
    ORE = &getAnalysis<MachineOptimizationRemarkEmitterPass>().getORE();
  
    // Calculate the MaxCallFrameSize and AdjustsStack variables for the
    // function's frame information. Also eliminates call frame pseudo
    // instructions.
    calculateCallFrameInfo(MF);
  
    // Determine placement of CSR spill/restore code and prolog/epilog code:
    // place all spills in the entry block, all restores in return blocks.
    calculateSaveRestoreBlocks(MF);
  
    // Stash away DBG_VALUEs that should not be moved by insertion of prolog code.
    SavedDbgValuesMap EntryDbgValues;
    for (MachineBasicBlock *SaveBlock : SaveBlocks)
      stashEntryDbgValues(*SaveBlock, EntryDbgValues);
  
    // Handle CSR spilling and restoring, for targets that need it.
    if (MF.getTarget().usesPhysRegsForPEI())
      spillCalleeSavedRegs(MF);
  
    // Allow the target machine to make final modifications to the function
    // before the frame layout is finalized.
    TFI->processFunctionBeforeFrameFinalized(MF, RS);
  
    // Calculate actual frame offsets for all abstract stack objects...
    calculateFrameObjectOffsets(MF);
  
    // Add prolog and epilog code to the function.  This function is required
    // to align the stack frame as necessary for any stack variables or
    // called functions.  Because of this, calculateCalleeSavedRegisters()
    // must be called before this function in order to set the AdjustsStack
    // and MaxCallFrameSize variables.
    if (!F.hasFnAttribute(Attribute::Naked))
      insertPrologEpilogCode(MF);
  
    // Reinsert stashed debug values at the start of the entry blocks.
    for (auto &I : EntryDbgValues)
      I.first->insert(I.first->begin(), I.second.begin(), I.second.end());
  
    // Replace all MO_FrameIndex operands with physical register references
    // and actual offsets.
    //
    replaceFrameIndices(MF);
  
    // If register scavenging is needed, as we've enabled doing it as a
    // post-pass, scavenge the virtual registers that frame index elimination
    // inserted.
    if (TRI->requiresRegisterScavenging(MF) && FrameIndexVirtualScavenging)
      scavengeFrameVirtualRegs(MF, *RS);
  
    // Warn on stack size when we exceeds the given limit.
    MachineFrameInfo &MFI = MF.getFrameInfo();
    uint64_t StackSize = MFI.getStackSize();
    if (WarnStackSize.getNumOccurrences() > 0 && WarnStackSize < StackSize) {
      DiagnosticInfoStackSize DiagStackSize(F, StackSize);
      F.getContext().diagnose(DiagStackSize);
    }
    ORE->emit([&]() {
      return MachineOptimizationRemarkAnalysis(DEBUG_TYPE, "StackSize",
                                               MF.getFunction().getSubprogram(),
                                               &MF.front())
             << ore::NV("NumStackBytes", StackSize) << " stack bytes in function";
    });
  
    delete RS;
    SaveBlocks.clear();
    RestoreBlocks.clear();
    MFI.setSavePoint(nullptr);
    MFI.setRestorePoint(nullptr);
    return true;
  }
  
  /// Calculate the MaxCallFrameSize and AdjustsStack
  /// variables for the function's frame information and eliminate call frame
  /// pseudo instructions.
  void PEI::calculateCallFrameInfo(MachineFunction &MF) {
    const TargetInstrInfo &TII = *MF.getSubtarget().getInstrInfo();
    const TargetFrameLowering *TFI = MF.getSubtarget().getFrameLowering();
    MachineFrameInfo &MFI = MF.getFrameInfo();
  
    unsigned MaxCallFrameSize = 0;
    bool AdjustsStack = MFI.adjustsStack();
  
    // Get the function call frame set-up and tear-down instruction opcode
    unsigned FrameSetupOpcode = TII.getCallFrameSetupOpcode();
    unsigned FrameDestroyOpcode = TII.getCallFrameDestroyOpcode();
  
    // Early exit for targets which have no call frame setup/destroy pseudo
    // instructions.
    if (FrameSetupOpcode == ~0u && FrameDestroyOpcode == ~0u)
      return;
  
    std::vector<MachineBasicBlock::iterator> FrameSDOps;
    for (MachineFunction::iterator BB = MF.begin(), E = MF.end(); BB != E; ++BB)
      for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); ++I)
        if (TII.isFrameInstr(*I)) {
          unsigned Size = TII.getFrameSize(*I);
          if (Size > MaxCallFrameSize) MaxCallFrameSize = Size;
          AdjustsStack = true;
          FrameSDOps.push_back(I);
        } else if (I->isInlineAsm()) {
          // Some inline asm's need a stack frame, as indicated by operand 1.
          unsigned ExtraInfo = I->getOperand(InlineAsm::MIOp_ExtraInfo).getImm();
          if (ExtraInfo & InlineAsm::Extra_IsAlignStack)
            AdjustsStack = true;
        }
  
    assert(!MFI.isMaxCallFrameSizeComputed() ||
           (MFI.getMaxCallFrameSize() == MaxCallFrameSize &&
            MFI.adjustsStack() == AdjustsStack));
    MFI.setAdjustsStack(AdjustsStack);
    MFI.setMaxCallFrameSize(MaxCallFrameSize);
  
    for (std::vector<MachineBasicBlock::iterator>::iterator
           i = FrameSDOps.begin(), e = FrameSDOps.end(); i != e; ++i) {
      MachineBasicBlock::iterator I = *i;
  
      // If call frames are not being included as part of the stack frame, and
      // the target doesn't indicate otherwise, remove the call frame pseudos
      // here. The sub/add sp instruction pairs are still inserted, but we don't
      // need to track the SP adjustment for frame index elimination.
      if (TFI->canSimplifyCallFramePseudos(MF))
        TFI->eliminateCallFramePseudoInstr(MF, *I->getParent(), I);
    }
  }
  
  /// Compute the sets of entry and return blocks for saving and restoring
  /// callee-saved registers, and placing prolog and epilog code.
  void PEI::calculateSaveRestoreBlocks(MachineFunction &MF) {
    const MachineFrameInfo &MFI = MF.getFrameInfo();
  
    // Even when we do not change any CSR, we still want to insert the
    // prologue and epilogue of the function.
    // So set the save points for those.
  
    // Use the points found by shrink-wrapping, if any.
    if (MFI.getSavePoint()) {
      SaveBlocks.push_back(MFI.getSavePoint());
      assert(MFI.getRestorePoint() && "Both restore and save must be set");
      MachineBasicBlock *RestoreBlock = MFI.getRestorePoint();
      // If RestoreBlock does not have any successor and is not a return block
      // then the end point is unreachable and we do not need to insert any
      // epilogue.
      if (!RestoreBlock->succ_empty() || RestoreBlock->isReturnBlock())
        RestoreBlocks.push_back(RestoreBlock);
      return;
    }
  
    // Save refs to entry and return blocks.
    SaveBlocks.push_back(&MF.front());
    for (MachineBasicBlock &MBB : MF) {
      if (MBB.isEHFuncletEntry())
        SaveBlocks.push_back(&MBB);
      if (MBB.isReturnBlock())
        RestoreBlocks.push_back(&MBB);
    }
  }
  
  static void assignCalleeSavedSpillSlots(MachineFunction &F,
                                          const BitVector &SavedRegs,
                                          unsigned &MinCSFrameIndex,
                                          unsigned &MaxCSFrameIndex) {
    if (SavedRegs.empty())
      return;
  
    const TargetRegisterInfo *RegInfo = F.getSubtarget().getRegisterInfo();
    const MCPhysReg *CSRegs = F.getRegInfo().getCalleeSavedRegs();
  
    std::vector<CalleeSavedInfo> CSI;
    for (unsigned i = 0; CSRegs[i]; ++i) {
      unsigned Reg = CSRegs[i];
      if (SavedRegs.test(Reg))
        CSI.push_back(CalleeSavedInfo(Reg));
    }
  
    const TargetFrameLowering *TFI = F.getSubtarget().getFrameLowering();
    MachineFrameInfo &MFI = F.getFrameInfo();
    if (!TFI->assignCalleeSavedSpillSlots(F, RegInfo, CSI)) {
      // If target doesn't implement this, use generic code.
  
      if (CSI.empty())
        return; // Early exit if no callee saved registers are modified!
  
      unsigned NumFixedSpillSlots;
      const TargetFrameLowering::SpillSlot *FixedSpillSlots =
          TFI->getCalleeSavedSpillSlots(NumFixedSpillSlots);
  
      // Now that we know which registers need to be saved and restored, allocate
      // stack slots for them.
      for (auto &CS : CSI) {
        // If the target has spilled this register to another register, we don't
        // need to allocate a stack slot.
        if (CS.isSpilledToReg())
          continue;
  
        unsigned Reg = CS.getReg();
        const TargetRegisterClass *RC = RegInfo->getMinimalPhysRegClass(Reg);
  
        int FrameIdx;
        if (RegInfo->hasReservedSpillSlot(F, Reg, FrameIdx)) {
          CS.setFrameIdx(FrameIdx);
          continue;
        }
  
        // Check to see if this physreg must be spilled to a particular stack slot
        // on this target.
        const TargetFrameLowering::SpillSlot *FixedSlot = FixedSpillSlots;
        while (FixedSlot != FixedSpillSlots + NumFixedSpillSlots &&
               FixedSlot->Reg != Reg)
          ++FixedSlot;
  
        unsigned Size = RegInfo->getSpillSize(*RC);
        if (FixedSlot == FixedSpillSlots + NumFixedSpillSlots) {
          // Nope, just spill it anywhere convenient.
          unsigned Align = RegInfo->getSpillAlignment(*RC);
          unsigned StackAlign = TFI->getStackAlignment();
  
          // We may not be able to satisfy the desired alignment specification of
          // the TargetRegisterClass if the stack alignment is smaller. Use the
          // min.
          Align = std::min(Align, StackAlign);
          FrameIdx = MFI.CreateStackObject(Size, Align, true);
          if ((unsigned)FrameIdx < MinCSFrameIndex) MinCSFrameIndex = FrameIdx;
          if ((unsigned)FrameIdx > MaxCSFrameIndex) MaxCSFrameIndex = FrameIdx;
        } else {
          // Spill it to the stack where we must.
          FrameIdx = MFI.CreateFixedSpillStackObject(Size, FixedSlot->Offset);
        }
  
        CS.setFrameIdx(FrameIdx);
      }
    }
  
    MFI.setCalleeSavedInfo(CSI);
  }
  
  /// Helper function to update the liveness information for the callee-saved
  /// registers.
  static void updateLiveness(MachineFunction &MF) {
    MachineFrameInfo &MFI = MF.getFrameInfo();
    // Visited will contain all the basic blocks that are in the region
    // where the callee saved registers are alive:
    // - Anything that is not Save or Restore -> LiveThrough.
    // - Save -> LiveIn.
    // - Restore -> LiveOut.
    // The live-out is not attached to the block, so no need to keep
    // Restore in this set.
    SmallPtrSet<MachineBasicBlock *, 8> Visited;
    SmallVector<MachineBasicBlock *, 8> WorkList;
    MachineBasicBlock *Entry = &MF.front();
    MachineBasicBlock *Save = MFI.getSavePoint();
  
    if (!Save)
      Save = Entry;
  
    if (Entry != Save) {
      WorkList.push_back(Entry);
      Visited.insert(Entry);
    }
    Visited.insert(Save);
  
    MachineBasicBlock *Restore = MFI.getRestorePoint();
    if (Restore)
      // By construction Restore cannot be visited, otherwise it
      // means there exists a path to Restore that does not go
      // through Save.
      WorkList.push_back(Restore);
  
    while (!WorkList.empty()) {
      const MachineBasicBlock *CurBB = WorkList.pop_back_val();
      // By construction, the region that is after the save point is
      // dominated by the Save and post-dominated by the Restore.
      if (CurBB == Save && Save != Restore)
        continue;
      // Enqueue all the successors not already visited.
      // Those are by construction either before Save or after Restore.
      for (MachineBasicBlock *SuccBB : CurBB->successors())
        if (Visited.insert(SuccBB).second)
          WorkList.push_back(SuccBB);
    }
  
    const std::vector<CalleeSavedInfo> &CSI = MFI.getCalleeSavedInfo();
  
    MachineRegisterInfo &MRI = MF.getRegInfo();
    for (unsigned i = 0, e = CSI.size(); i != e; ++i) {
      for (MachineBasicBlock *MBB : Visited) {
        MCPhysReg Reg = CSI[i].getReg();
        // Add the callee-saved register as live-in.
        // It's killed at the spill.
        if (!MRI.isReserved(Reg) && !MBB->isLiveIn(Reg))
          MBB->addLiveIn(Reg);
      }
      // If callee-saved register is spilled to another register rather than
      // spilling to stack, the destination register has to be marked as live for
      // each MBB between the prologue and epilogue so that it is not clobbered
      // before it is reloaded in the epilogue. The Visited set contains all
      // blocks outside of the region delimited by prologue/epilogue.
      if (CSI[i].isSpilledToReg()) {
        for (MachineBasicBlock &MBB : MF) {
          if (Visited.count(&MBB))
            continue;
          MCPhysReg DstReg = CSI[i].getDstReg();
          if (!MBB.isLiveIn(DstReg))
            MBB.addLiveIn(DstReg);
        }
      }
    }
  
  }
  
  /// Insert restore code for the callee-saved registers used in the function.
  static void insertCSRSaves(MachineBasicBlock &SaveBlock,
                             ArrayRef<CalleeSavedInfo> CSI) {
    MachineFunction &MF = *SaveBlock.getParent();
    const TargetInstrInfo &TII = *MF.getSubtarget().getInstrInfo();
    const TargetFrameLowering *TFI = MF.getSubtarget().getFrameLowering();
    const TargetRegisterInfo *TRI = MF.getSubtarget().getRegisterInfo();
  
    MachineBasicBlock::iterator I = SaveBlock.begin();
    if (!TFI->spillCalleeSavedRegisters(SaveBlock, I, CSI, TRI)) {
      for (const CalleeSavedInfo &CS : CSI) {
        // Insert the spill to the stack frame.
        unsigned Reg = CS.getReg();
  
        if (CS.isSpilledToReg()) {
          BuildMI(SaveBlock, I, DebugLoc(),
                  TII.get(TargetOpcode::COPY), CS.getDstReg())
            .addReg(Reg, getKillRegState(true));
        } else {
          const TargetRegisterClass *RC = TRI->getMinimalPhysRegClass(Reg);
          TII.storeRegToStackSlot(SaveBlock, I, Reg, true, CS.getFrameIdx(), RC,
                                  TRI);
        }
      }
    }
  }
  
  /// Insert restore code for the callee-saved registers used in the function.
  static void insertCSRRestores(MachineBasicBlock &RestoreBlock,
                                std::vector<CalleeSavedInfo> &CSI) {
    MachineFunction &MF = *RestoreBlock.getParent();
    const TargetInstrInfo &TII = *MF.getSubtarget().getInstrInfo();
    const TargetFrameLowering *TFI = MF.getSubtarget().getFrameLowering();
    const TargetRegisterInfo *TRI = MF.getSubtarget().getRegisterInfo();
  
    // Restore all registers immediately before the return and any
    // terminators that precede it.
    MachineBasicBlock::iterator I = RestoreBlock.getFirstTerminator();
  
    if (!TFI->restoreCalleeSavedRegisters(RestoreBlock, I, CSI, TRI)) {
      for (const CalleeSavedInfo &CI : reverse(CSI)) {
        unsigned Reg = CI.getReg();
        if (CI.isSpilledToReg()) {
          BuildMI(RestoreBlock, I, DebugLoc(), TII.get(TargetOpcode::COPY), Reg)
            .addReg(CI.getDstReg(), getKillRegState(true));
        } else {
          const TargetRegisterClass *RC = TRI->getMinimalPhysRegClass(Reg);
          TII.loadRegFromStackSlot(RestoreBlock, I, Reg, CI.getFrameIdx(), RC, TRI);
          assert(I != RestoreBlock.begin() &&
                 "loadRegFromStackSlot didn't insert any code!");
          // Insert in reverse order.  loadRegFromStackSlot can insert
          // multiple instructions.
        }
      }
    }
  }
  
  void PEI::spillCalleeSavedRegs(MachineFunction &MF) {
    // We can't list this requirement in getRequiredProperties because some
    // targets (WebAssembly) use virtual registers past this point, and the pass
    // pipeline is set up without giving the passes a chance to look at the
    // TargetMachine.
    // FIXME: Find a way to express this in getRequiredProperties.
    assert(MF.getProperties().hasProperty(
        MachineFunctionProperties::Property::NoVRegs));
  
    const Function &F = MF.getFunction();
    const TargetFrameLowering *TFI = MF.getSubtarget().getFrameLowering();
    MachineFrameInfo &MFI = MF.getFrameInfo();
    MinCSFrameIndex = std::numeric_limits<unsigned>::max();
    MaxCSFrameIndex = 0;
  
    // Determine which of the registers in the callee save list should be saved.
    BitVector SavedRegs;
    TFI->determineCalleeSaves(MF, SavedRegs, RS);
  
    // Assign stack slots for any callee-saved registers that must be spilled.
    assignCalleeSavedSpillSlots(MF, SavedRegs, MinCSFrameIndex, MaxCSFrameIndex);
  
    // Add the code to save and restore the callee saved registers.
    if (!F.hasFnAttribute(Attribute::Naked)) {
      MFI.setCalleeSavedInfoValid(true);
  
      std::vector<CalleeSavedInfo> &CSI = MFI.getCalleeSavedInfo();
      if (!CSI.empty()) {
        if (!MFI.hasCalls())
          NumLeafFuncWithSpills++;
  
        for (MachineBasicBlock *SaveBlock : SaveBlocks) {
          insertCSRSaves(*SaveBlock, CSI);
          // Update the live-in information of all the blocks up to the save
          // point.
          updateLiveness(MF);
        }
        for (MachineBasicBlock *RestoreBlock : RestoreBlocks)
          insertCSRRestores(*RestoreBlock, CSI);
      }
    }
  }
  
  /// AdjustStackOffset - Helper function used to adjust the stack frame offset.
  static inline void
  AdjustStackOffset(MachineFrameInfo &MFI, int FrameIdx,
                    bool StackGrowsDown, int64_t &Offset,
                    unsigned &MaxAlign, unsigned Skew) {
    // If the stack grows down, add the object size to find the lowest address.
    if (StackGrowsDown)
      Offset += MFI.getObjectSize(FrameIdx);
  
    unsigned Align = MFI.getObjectAlignment(FrameIdx);
  
    // If the alignment of this object is greater than that of the stack, then
    // increase the stack alignment to match.
    MaxAlign = std::max(MaxAlign, Align);
  
    // Adjust to alignment boundary.
    Offset = alignTo(Offset, Align, Skew);
  
    if (StackGrowsDown) {
      LLVM_DEBUG(dbgs() << "alloc FI(" << FrameIdx << ") at SP[" << -Offset
                        << "]\n");
      MFI.setObjectOffset(FrameIdx, -Offset); // Set the computed offset
    } else {
      LLVM_DEBUG(dbgs() << "alloc FI(" << FrameIdx << ") at SP[" << Offset
                        << "]\n");
      MFI.setObjectOffset(FrameIdx, Offset);
      Offset += MFI.getObjectSize(FrameIdx);
    }
  }
  
  /// Compute which bytes of fixed and callee-save stack area are unused and keep
  /// track of them in StackBytesFree.
  static inline void
  computeFreeStackSlots(MachineFrameInfo &MFI, bool StackGrowsDown,
                        unsigned MinCSFrameIndex, unsigned MaxCSFrameIndex,
                        int64_t FixedCSEnd, BitVector &StackBytesFree) {
    // Avoid undefined int64_t -> int conversion below in extreme case.
    if (FixedCSEnd > std::numeric_limits<int>::max())
      return;
  
    StackBytesFree.resize(FixedCSEnd, true);
  
    SmallVector<int, 16> AllocatedFrameSlots;
    // Add fixed objects.
    for (int i = MFI.getObjectIndexBegin(); i != 0; ++i)
      // StackSlot scavenging is only implemented for the default stack.
      if (MFI.getStackID(i) == TargetStackID::Default)
        AllocatedFrameSlots.push_back(i);
    // Add callee-save objects.
    for (int i = MinCSFrameIndex; i <= (int)MaxCSFrameIndex; ++i)
      if (MFI.getStackID(i) == TargetStackID::Default)
        AllocatedFrameSlots.push_back(i);
  
    for (int i : AllocatedFrameSlots) {
      // These are converted from int64_t, but they should always fit in int
      // because of the FixedCSEnd check above.
      int ObjOffset = MFI.getObjectOffset(i);
      int ObjSize = MFI.getObjectSize(i);
      int ObjStart, ObjEnd;
      if (StackGrowsDown) {
        // ObjOffset is negative when StackGrowsDown is true.
        ObjStart = -ObjOffset - ObjSize;
        ObjEnd = -ObjOffset;
      } else {
        ObjStart = ObjOffset;
        ObjEnd = ObjOffset + ObjSize;
      }
      // Ignore fixed holes that are in the previous stack frame.
      if (ObjEnd > 0)
        StackBytesFree.reset(ObjStart, ObjEnd);
    }
  }
  
  /// Assign frame object to an unused portion of the stack in the fixed stack
  /// object range.  Return true if the allocation was successful.
  static inline bool scavengeStackSlot(MachineFrameInfo &MFI, int FrameIdx,
                                       bool StackGrowsDown, unsigned MaxAlign,
                                       BitVector &StackBytesFree) {
    if (MFI.isVariableSizedObjectIndex(FrameIdx))
      return false;
  
    if (StackBytesFree.none()) {
      // clear it to speed up later scavengeStackSlot calls to
      // StackBytesFree.none()
      StackBytesFree.clear();
      return false;
    }
  
    unsigned ObjAlign = MFI.getObjectAlignment(FrameIdx);
    if (ObjAlign > MaxAlign)
      return false;
  
    int64_t ObjSize = MFI.getObjectSize(FrameIdx);
    int FreeStart;
    for (FreeStart = StackBytesFree.find_first(); FreeStart != -1;
         FreeStart = StackBytesFree.find_next(FreeStart)) {
  
      // Check that free space has suitable alignment.
      unsigned ObjStart = StackGrowsDown ? FreeStart + ObjSize : FreeStart;
      if (alignTo(ObjStart, ObjAlign) != ObjStart)
        continue;
  
      if (FreeStart + ObjSize > StackBytesFree.size())
        return false;
  
      bool AllBytesFree = true;
      for (unsigned Byte = 0; Byte < ObjSize; ++Byte)
        if (!StackBytesFree.test(FreeStart + Byte)) {
          AllBytesFree = false;
          break;
        }
      if (AllBytesFree)
        break;
    }
  
    if (FreeStart == -1)
      return false;
  
    if (StackGrowsDown) {
      int ObjStart = -(FreeStart + ObjSize);
      LLVM_DEBUG(dbgs() << "alloc FI(" << FrameIdx << ") scavenged at SP["
                        << ObjStart << "]\n");
      MFI.setObjectOffset(FrameIdx, ObjStart);
    } else {
      LLVM_DEBUG(dbgs() << "alloc FI(" << FrameIdx << ") scavenged at SP["
                        << FreeStart << "]\n");
      MFI.setObjectOffset(FrameIdx, FreeStart);
    }
  
    StackBytesFree.reset(FreeStart, FreeStart + ObjSize);
    return true;
  }
  
  /// AssignProtectedObjSet - Helper function to assign large stack objects (i.e.,
  /// those required to be close to the Stack Protector) to stack offsets.
  static void
  AssignProtectedObjSet(const StackObjSet &UnassignedObjs,
                        SmallSet<int, 16> &ProtectedObjs,
                        MachineFrameInfo &MFI, bool StackGrowsDown,
                        int64_t &Offset, unsigned &MaxAlign, unsigned Skew) {
  
    for (StackObjSet::const_iterator I = UnassignedObjs.begin(),
          E = UnassignedObjs.end(); I != E; ++I) {
      int i = *I;
      AdjustStackOffset(MFI, i, StackGrowsDown, Offset, MaxAlign, Skew);
      ProtectedObjs.insert(i);
    }
  }
  
  /// calculateFrameObjectOffsets - Calculate actual frame offsets for all of the
  /// abstract stack objects.
  void PEI::calculateFrameObjectOffsets(MachineFunction &MF) {
    const TargetFrameLowering &TFI = *MF.getSubtarget().getFrameLowering();
  
    bool StackGrowsDown =
      TFI.getStackGrowthDirection() == TargetFrameLowering::StackGrowsDown;
  
    // Loop over all of the stack objects, assigning sequential addresses...
    MachineFrameInfo &MFI = MF.getFrameInfo();
  
    // Start at the beginning of the local area.
    // The Offset is the distance from the stack top in the direction
    // of stack growth -- so it's always nonnegative.
    int LocalAreaOffset = TFI.getOffsetOfLocalArea();
    if (StackGrowsDown)
      LocalAreaOffset = -LocalAreaOffset;
    assert(LocalAreaOffset >= 0
           && "Local area offset should be in direction of stack growth");
    int64_t Offset = LocalAreaOffset;
  
    // Skew to be applied to alignment.
    unsigned Skew = TFI.getStackAlignmentSkew(MF);
  
  #ifdef EXPENSIVE_CHECKS
    for (unsigned i = 0, e = MFI.getObjectIndexEnd(); i != e; ++i)
      if (!MFI.isDeadObjectIndex(i) &&
          MFI.getStackID(i) == TargetStackID::Default)
        assert(MFI.getObjectAlignment(i) <= MFI.getMaxAlignment() &&
               "MaxAlignment is invalid");
  #endif
  
    // If there are fixed sized objects that are preallocated in the local area,
    // non-fixed objects can't be allocated right at the start of local area.
    // Adjust 'Offset' to point to the end of last fixed sized preallocated
    // object.
    for (int i = MFI.getObjectIndexBegin(); i != 0; ++i) {
      if (MFI.getStackID(i) !=
          TargetStackID::Default) // Only allocate objects on the default stack.
        continue;
  
      int64_t FixedOff;
      if (StackGrowsDown) {
        // The maximum distance from the stack pointer is at lower address of
        // the object -- which is given by offset. For down growing stack
        // the offset is negative, so we negate the offset to get the distance.
        FixedOff = -MFI.getObjectOffset(i);
      } else {
        // The maximum distance from the start pointer is at the upper
        // address of the object.
        FixedOff = MFI.getObjectOffset(i) + MFI.getObjectSize(i);
      }
      if (FixedOff > Offset) Offset = FixedOff;
    }
  
    // First assign frame offsets to stack objects that are used to spill
    // callee saved registers.
    if (StackGrowsDown) {
      for (unsigned i = MinCSFrameIndex; i <= MaxCSFrameIndex; ++i) {
        if (MFI.getStackID(i) !=
            TargetStackID::Default) // Only allocate objects on the default stack.
          continue;
  
        // If the stack grows down, we need to add the size to find the lowest
        // address of the object.
        Offset += MFI.getObjectSize(i);
  
        unsigned Align = MFI.getObjectAlignment(i);
        // Adjust to alignment boundary
        Offset = alignTo(Offset, Align, Skew);
  
        LLVM_DEBUG(dbgs() << "alloc FI(" << i << ") at SP[" << -Offset << "]\n");
        MFI.setObjectOffset(i, -Offset);        // Set the computed offset
      }
    } else if (MaxCSFrameIndex >= MinCSFrameIndex) {
      // Be careful about underflow in comparisons agains MinCSFrameIndex.
      for (unsigned i = MaxCSFrameIndex; i != MinCSFrameIndex - 1; --i) {
        if (MFI.getStackID(i) !=
            TargetStackID::Default) // Only allocate objects on the default stack.
          continue;
  
        if (MFI.isDeadObjectIndex(i))
          continue;
  
        unsigned Align = MFI.getObjectAlignment(i);
        // Adjust to alignment boundary
        Offset = alignTo(Offset, Align, Skew);
  
        LLVM_DEBUG(dbgs() << "alloc FI(" << i << ") at SP[" << Offset << "]\n");
        MFI.setObjectOffset(i, Offset);
        Offset += MFI.getObjectSize(i);
      }
    }
  
    // FixedCSEnd is the stack offset to the end of the fixed and callee-save
    // stack area.
    int64_t FixedCSEnd = Offset;
    unsigned MaxAlign = MFI.getMaxAlignment();
  
    // Make sure the special register scavenging spill slot is closest to the
    // incoming stack pointer if a frame pointer is required and is closer
    // to the incoming rather than the final stack pointer.
    const TargetRegisterInfo *RegInfo = MF.getSubtarget().getRegisterInfo();
    bool EarlyScavengingSlots = (TFI.hasFP(MF) &&
                                 TFI.isFPCloseToIncomingSP() &&
                                 RegInfo->useFPForScavengingIndex(MF) &&
                                 !RegInfo->needsStackRealignment(MF));
    if (RS && EarlyScavengingSlots) {
      SmallVector<int, 2> SFIs;
      RS->getScavengingFrameIndices(SFIs);
      for (SmallVectorImpl<int>::iterator I = SFIs.begin(),
             IE = SFIs.end(); I != IE; ++I)
        AdjustStackOffset(MFI, *I, StackGrowsDown, Offset, MaxAlign, Skew);
    }
  
    // FIXME: Once this is working, then enable flag will change to a target
    // check for whether the frame is large enough to want to use virtual
    // frame index registers. Functions which don't want/need this optimization
    // will continue to use the existing code path.
    if (MFI.getUseLocalStackAllocationBlock()) {
      unsigned Align = MFI.getLocalFrameMaxAlign();
  
      // Adjust to alignment boundary.
      Offset = alignTo(Offset, Align, Skew);
  
      LLVM_DEBUG(dbgs() << "Local frame base offset: " << Offset << "\n");
  
      // Resolve offsets for objects in the local block.
      for (unsigned i = 0, e = MFI.getLocalFrameObjectCount(); i != e; ++i) {
        std::pair<int, int64_t> Entry = MFI.getLocalFrameObjectMap(i);
        int64_t FIOffset = (StackGrowsDown ? -Offset : Offset) + Entry.second;
        LLVM_DEBUG(dbgs() << "alloc FI(" << Entry.first << ") at SP[" << FIOffset
                          << "]\n");
        MFI.setObjectOffset(Entry.first, FIOffset);
      }
      // Allocate the local block
      Offset += MFI.getLocalFrameSize();
  
      MaxAlign = std::max(Align, MaxAlign);
    }
  
    // Retrieve the Exception Handler registration node.
    int EHRegNodeFrameIndex = std::numeric_limits<int>::max();
    if (const WinEHFuncInfo *FuncInfo = MF.getWinEHFuncInfo())
      EHRegNodeFrameIndex = FuncInfo->EHRegNodeFrameIndex;
  
    // Make sure that the stack protector comes before the local variables on the
    // stack.
    SmallSet<int, 16> ProtectedObjs;
    if (MFI.hasStackProtectorIndex()) {
      int StackProtectorFI = MFI.getStackProtectorIndex();
      StackObjSet LargeArrayObjs;
      StackObjSet SmallArrayObjs;
      StackObjSet AddrOfObjs;
  
      // If we need a stack protector, we need to make sure that
      // LocalStackSlotPass didn't already allocate a slot for it.
      // If we are told to use the LocalStackAllocationBlock, the stack protector
      // is expected to be already pre-allocated.
      if (!MFI.getUseLocalStackAllocationBlock())
        AdjustStackOffset(MFI, StackProtectorFI, StackGrowsDown, Offset, MaxAlign,
                          Skew);
      else if (!MFI.isObjectPreAllocated(MFI.getStackProtectorIndex()))
        llvm_unreachable(
            "Stack protector not pre-allocated by LocalStackSlotPass.");
  
      // Assign large stack objects first.
      for (unsigned i = 0, e = MFI.getObjectIndexEnd(); i != e; ++i) {
        if (MFI.isObjectPreAllocated(i) && MFI.getUseLocalStackAllocationBlock())
          continue;
        if (i >= MinCSFrameIndex && i <= MaxCSFrameIndex)
          continue;
        if (RS && RS->isScavengingFrameIndex((int)i))
          continue;
        if (MFI.isDeadObjectIndex(i))
          continue;
        if (StackProtectorFI == (int)i || EHRegNodeFrameIndex == (int)i)
          continue;
        if (MFI.getStackID(i) !=
            TargetStackID::Default) // Only allocate objects on the default stack.
          continue;
  
        switch (MFI.getObjectSSPLayout(i)) {
        case MachineFrameInfo::SSPLK_None:
          continue;
        case MachineFrameInfo::SSPLK_SmallArray:
          SmallArrayObjs.insert(i);
          continue;
        case MachineFrameInfo::SSPLK_AddrOf:
          AddrOfObjs.insert(i);
          continue;
        case MachineFrameInfo::SSPLK_LargeArray:
          LargeArrayObjs.insert(i);
          continue;
        }
        llvm_unreachable("Unexpected SSPLayoutKind.");
      }
  
      // We expect **all** the protected stack objects to be pre-allocated by
      // LocalStackSlotPass. If it turns out that PEI still has to allocate some
      // of them, we may end up messing up the expected order of the objects.
      if (MFI.getUseLocalStackAllocationBlock() &&
          !(LargeArrayObjs.empty() && SmallArrayObjs.empty() &&
            AddrOfObjs.empty()))
        llvm_unreachable("Found protected stack objects not pre-allocated by "
                         "LocalStackSlotPass.");
  
      AssignProtectedObjSet(LargeArrayObjs, ProtectedObjs, MFI, StackGrowsDown,
                            Offset, MaxAlign, Skew);
      AssignProtectedObjSet(SmallArrayObjs, ProtectedObjs, MFI, StackGrowsDown,
                            Offset, MaxAlign, Skew);
      AssignProtectedObjSet(AddrOfObjs, ProtectedObjs, MFI, StackGrowsDown,
                            Offset, MaxAlign, Skew);
    }
  
    SmallVector<int, 8> ObjectsToAllocate;
  
    // Then prepare to assign frame offsets to stack objects that are not used to
    // spill callee saved registers.
    for (unsigned i = 0, e = MFI.getObjectIndexEnd(); i != e; ++i) {
      if (MFI.isObjectPreAllocated(i) && MFI.getUseLocalStackAllocationBlock())
        continue;
      if (i >= MinCSFrameIndex && i <= MaxCSFrameIndex)
        continue;
      if (RS && RS->isScavengingFrameIndex((int)i))
        continue;
      if (MFI.isDeadObjectIndex(i))
        continue;
      if (MFI.getStackProtectorIndex() == (int)i || EHRegNodeFrameIndex == (int)i)
        continue;
      if (ProtectedObjs.count(i))
        continue;
      if (MFI.getStackID(i) !=
          TargetStackID::Default) // Only allocate objects on the default stack.
        continue;
  
      // Add the objects that we need to allocate to our working set.
      ObjectsToAllocate.push_back(i);
    }
  
    // Allocate the EH registration node first if one is present.
    if (EHRegNodeFrameIndex != std::numeric_limits<int>::max())
      AdjustStackOffset(MFI, EHRegNodeFrameIndex, StackGrowsDown, Offset,
                        MaxAlign, Skew);
  
    // Give the targets a chance to order the objects the way they like it.
    if (MF.getTarget().getOptLevel() != CodeGenOpt::None &&
        MF.getTarget().Options.StackSymbolOrdering)
      TFI.orderFrameObjects(MF, ObjectsToAllocate);
  
    // Keep track of which bytes in the fixed and callee-save range are used so we
    // can use the holes when allocating later stack objects.  Only do this if
    // stack protector isn't being used and the target requests it and we're
    // optimizing.
    BitVector StackBytesFree;
    if (!ObjectsToAllocate.empty() &&
        MF.getTarget().getOptLevel() != CodeGenOpt::None &&
        MFI.getStackProtectorIndex() < 0 && TFI.enableStackSlotScavenging(MF))
      computeFreeStackSlots(MFI, StackGrowsDown, MinCSFrameIndex, MaxCSFrameIndex,
                            FixedCSEnd, StackBytesFree);
  
    // Now walk the objects and actually assign base offsets to them.
    for (auto &Object : ObjectsToAllocate)
      if (!scavengeStackSlot(MFI, Object, StackGrowsDown, MaxAlign,
                             StackBytesFree))
        AdjustStackOffset(MFI, Object, StackGrowsDown, Offset, MaxAlign, Skew);
  
    // Make sure the special register scavenging spill slot is closest to the
    // stack pointer.
    if (RS && !EarlyScavengingSlots) {
      SmallVector<int, 2> SFIs;
      RS->getScavengingFrameIndices(SFIs);
      for (SmallVectorImpl<int>::iterator I = SFIs.begin(),
             IE = SFIs.end(); I != IE; ++I)
        AdjustStackOffset(MFI, *I, StackGrowsDown, Offset, MaxAlign, Skew);
    }
  
    if (!TFI.targetHandlesStackFrameRounding()) {
      // If we have reserved argument space for call sites in the function
      // immediately on entry to the current function, count it as part of the
      // overall stack size.
      if (MFI.adjustsStack() && TFI.hasReservedCallFrame(MF))
        Offset += MFI.getMaxCallFrameSize();
  
      // Round up the size to a multiple of the alignment.  If the function has
      // any calls or alloca's, align to the target's StackAlignment value to
      // ensure that the callee's frame or the alloca data is suitably aligned;
      // otherwise, for leaf functions, align to the TransientStackAlignment
      // value.
      unsigned StackAlign;
      if (MFI.adjustsStack() || MFI.hasVarSizedObjects() ||
          (RegInfo->needsStackRealignment(MF) && MFI.getObjectIndexEnd() != 0))
        StackAlign = TFI.getStackAlignment();
      else
        StackAlign = TFI.getTransientStackAlignment();
  
      // If the frame pointer is eliminated, all frame offsets will be relative to
      // SP not FP. Align to MaxAlign so this works.
      StackAlign = std::max(StackAlign, MaxAlign);
      Offset = alignTo(Offset, StackAlign, Skew);
    }
  
    // Update frame info to pretend that this is part of the stack...
    int64_t StackSize = Offset - LocalAreaOffset;
    MFI.setStackSize(StackSize);
    NumBytesStackSpace += StackSize;
  }
  
  /// insertPrologEpilogCode - Scan the function for modified callee saved
  /// registers, insert spill code for these callee saved registers, then add
  /// prolog and epilog code to the function.
  void PEI::insertPrologEpilogCode(MachineFunction &MF) {
    const TargetFrameLowering &TFI = *MF.getSubtarget().getFrameLowering();
  
    // Add prologue to the function...
    for (MachineBasicBlock *SaveBlock : SaveBlocks)
      TFI.emitPrologue(MF, *SaveBlock);
  
    // Add epilogue to restore the callee-save registers in each exiting block.
    for (MachineBasicBlock *RestoreBlock : RestoreBlocks)
      TFI.emitEpilogue(MF, *RestoreBlock);
  
    for (MachineBasicBlock *SaveBlock : SaveBlocks)
      TFI.inlineStackProbe(MF, *SaveBlock);
  
    // Emit additional code that is required to support segmented stacks, if
    // we've been asked for it.  This, when linked with a runtime with support
    // for segmented stacks (libgcc is one), will result in allocating stack
    // space in small chunks instead of one large contiguous block.
    if (MF.shouldSplitStack()) {
      for (MachineBasicBlock *SaveBlock : SaveBlocks)
        TFI.adjustForSegmentedStacks(MF, *SaveBlock);
      // Record that there are split-stack functions, so we will emit a
      // special section to tell the linker.
      MF.getMMI().setHasSplitStack(true);
    } else
      MF.getMMI().setHasNosplitStack(true);
  
    // Emit additional code that is required to explicitly handle the stack in
    // HiPE native code (if needed) when loaded in the Erlang/OTP runtime. The
    // approach is rather similar to that of Segmented Stacks, but it uses a
    // different conditional check and another BIF for allocating more stack
    // space.
    if (MF.getFunction().getCallingConv() == CallingConv::HiPE)
      for (MachineBasicBlock *SaveBlock : SaveBlocks)
        TFI.adjustForHiPEPrologue(MF, *SaveBlock);
  }
  
  /// replaceFrameIndices - Replace all MO_FrameIndex operands with physical
  /// register references and actual offsets.
  void PEI::replaceFrameIndices(MachineFunction &MF) {
    const auto &ST = MF.getSubtarget();
    const TargetFrameLowering &TFI = *ST.getFrameLowering();
    if (!TFI.needsFrameIndexResolution(MF))
      return;
  
    const TargetRegisterInfo *TRI = ST.getRegisterInfo();
  
    // Allow the target to determine this after knowing the frame size.
    FrameIndexEliminationScavenging = (RS && !FrameIndexVirtualScavenging) ||
      TRI->requiresFrameIndexReplacementScavenging(MF);
  
    // Store SPAdj at exit of a basic block.
    SmallVector<int, 8> SPState;
    SPState.resize(MF.getNumBlockIDs());
    df_iterator_default_set<MachineBasicBlock*> Reachable;
  
    // Iterate over the reachable blocks in DFS order.
    for (auto DFI = df_ext_begin(&MF, Reachable), DFE = df_ext_end(&MF, Reachable);
         DFI != DFE; ++DFI) {
      int SPAdj = 0;
      // Check the exit state of the DFS stack predecessor.
      if (DFI.getPathLength() >= 2) {
        MachineBasicBlock *StackPred = DFI.getPath(DFI.getPathLength() - 2);
        assert(Reachable.count(StackPred) &&
               "DFS stack predecessor is already visited.\n");
        SPAdj = SPState[StackPred->getNumber()];
      }
      MachineBasicBlock *BB = *DFI;
      replaceFrameIndices(BB, MF, SPAdj);
      SPState[BB->getNumber()] = SPAdj;
    }
  
    // Handle the unreachable blocks.
    for (auto &BB : MF) {
      if (Reachable.count(&BB))
        // Already handled in DFS traversal.
        continue;
      int SPAdj = 0;
      replaceFrameIndices(&BB, MF, SPAdj);
    }
  }
  
  void PEI::replaceFrameIndices(MachineBasicBlock *BB, MachineFunction &MF,
                                int &SPAdj) {
    assert(MF.getSubtarget().getRegisterInfo() &&
           "getRegisterInfo() must be implemented!");
    const TargetInstrInfo &TII = *MF.getSubtarget().getInstrInfo();
    const TargetRegisterInfo &TRI = *MF.getSubtarget().getRegisterInfo();
    const TargetFrameLowering *TFI = MF.getSubtarget().getFrameLowering();
  
    if (RS && FrameIndexEliminationScavenging)
      RS->enterBasicBlock(*BB);
  
    bool InsideCallSequence = false;
  
    for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); ) {
      if (TII.isFrameInstr(*I)) {
        InsideCallSequence = TII.isFrameSetup(*I);
        SPAdj += TII.getSPAdjust(*I);
        I = TFI->eliminateCallFramePseudoInstr(MF, *BB, I);
        continue;
      }
  
      MachineInstr &MI = *I;
      bool DoIncr = true;
      bool DidFinishLoop = true;
      for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
        if (!MI.getOperand(i).isFI())
          continue;
  
        // Frame indices in debug values are encoded in a target independent
        // way with simply the frame index and offset rather than any
        // target-specific addressing mode.
        if (MI.isDebugValue()) {
          assert(i == 0 && "Frame indices can only appear as the first "
                           "operand of a DBG_VALUE machine instruction");
          unsigned Reg;
          unsigned FrameIdx = MI.getOperand(0).getIndex();
          unsigned Size = MF.getFrameInfo().getObjectSize(FrameIdx);
  
          int64_t Offset =
              TFI->getFrameIndexReference(MF, FrameIdx, Reg);
          MI.getOperand(0).ChangeToRegister(Reg, false /*isDef*/);
          MI.getOperand(0).setIsDebug();
  
          const DIExpression *DIExpr = MI.getDebugExpression();
  
          // If we have a direct DBG_VALUE, and its location expression isn't
          // currently complex, then adding an offset will morph it into a
          // complex location that is interpreted as being a memory address.
          // This changes a pointer-valued variable to dereference that pointer,
          // which is incorrect. Fix by adding DW_OP_stack_value.
          unsigned PrependFlags = DIExpression::ApplyOffset;
          if (!MI.isIndirectDebugValue() && !DIExpr->isComplex())
            PrependFlags |= DIExpression::StackValue;
  
          // If we have DBG_VALUE that is indirect and has a Implicit location
          // expression need to insert a deref before prepending a Memory
          // location expression. Also after doing this we change the DBG_VALUE
          // to be direct.
          if (MI.isIndirectDebugValue() && DIExpr->isImplicit()) {
            SmallVector<uint64_t, 2> Ops = {dwarf::DW_OP_deref_size, Size};
            bool WithStackValue = true;
            DIExpr = DIExpression::prependOpcodes(DIExpr, Ops, WithStackValue);
            // Make the DBG_VALUE direct.
            MI.getOperand(1).ChangeToRegister(0, false);
          }
          DIExpr = DIExpression::prepend(DIExpr, PrependFlags, Offset);
          MI.getOperand(3).setMetadata(DIExpr);
          continue;
        }
  
        // TODO: This code should be commoned with the code for
        // PATCHPOINT. There's no good reason for the difference in
        // implementation other than historical accident.  The only
        // remaining difference is the unconditional use of the stack
        // pointer as the base register.
        if (MI.getOpcode() == TargetOpcode::STATEPOINT) {
          assert((!MI.isDebugValue() || i == 0) &&
                 "Frame indicies can only appear as the first operand of a "
                 "DBG_VALUE machine instruction");
          unsigned Reg;
          MachineOperand &Offset = MI.getOperand(i + 1);
          int refOffset = TFI->getFrameIndexReferencePreferSP(
              MF, MI.getOperand(i).getIndex(), Reg, /*IgnoreSPUpdates*/ false);
          Offset.setImm(Offset.getImm() + refOffset + SPAdj);
          MI.getOperand(i).ChangeToRegister(Reg, false /*isDef*/);
          continue;
        }
  
        // Some instructions (e.g. inline asm instructions) can have
        // multiple frame indices and/or cause eliminateFrameIndex
        // to insert more than one instruction. We need the register
        // scavenger to go through all of these instructions so that
        // it can update its register information. We keep the
        // iterator at the point before insertion so that we can
        // revisit them in full.
        bool AtBeginning = (I == BB->begin());
        if (!AtBeginning) --I;
  
        // If this instruction has a FrameIndex operand, we need to
        // use that target machine register info object to eliminate
        // it.
        TRI.eliminateFrameIndex(MI, SPAdj, i,
                                FrameIndexEliminationScavenging ?  RS : nullptr);
  
        // Reset the iterator if we were at the beginning of the BB.
        if (AtBeginning) {
          I = BB->begin();
          DoIncr = false;
        }
  
        DidFinishLoop = false;
        break;
      }
  
      // If we are looking at a call sequence, we need to keep track of
      // the SP adjustment made by each instruction in the sequence.
      // This includes both the frame setup/destroy pseudos (handled above),
      // as well as other instructions that have side effects w.r.t the SP.
      // Note that this must come after eliminateFrameIndex, because
      // if I itself referred to a frame index, we shouldn't count its own
      // adjustment.
      if (DidFinishLoop && InsideCallSequence)
        SPAdj += TII.getSPAdjust(MI);
  
      if (DoIncr && I != BB->end()) ++I;
  
      // Update register states.
      if (RS && FrameIndexEliminationScavenging && DidFinishLoop)
        RS->forward(MI);
    }
  }
  