third_party/llvm-10.0/llvm/lib/Target/AVR/AVRFrameLowering.cpp - SwiftShader - Git at Google

 //===-- AVRFrameLowering.cpp - AVR Frame Information ----------------------===//
 //
 // 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 the AVR implementation of TargetFrameLowering class.
 //
 //===----------------------------------------------------------------------===//

 #include "AVRFrameLowering.h"

 #include "AVR.h"
 #include "AVRInstrInfo.h"
 #include "AVRMachineFunctionInfo.h"
 #include "AVRTargetMachine.h"
 #include "MCTargetDesc/AVRMCTargetDesc.h"

 #include "llvm/CodeGen/MachineFrameInfo.h"
 #include "llvm/CodeGen/MachineFunction.h"
 #include "llvm/CodeGen/MachineFunctionPass.h"
 #include "llvm/CodeGen/MachineInstrBuilder.h"
 #include "llvm/CodeGen/MachineRegisterInfo.h"
 #include "llvm/IR/Function.h"

 #include <vector>

 namespace llvm {

 AVRFrameLowering::AVRFrameLowering()
     : TargetFrameLowering(TargetFrameLowering::StackGrowsDown, Align::None(),
                           -2) {}

 bool AVRFrameLowering::canSimplifyCallFramePseudos(
     const MachineFunction &MF) const {
   // Always simplify call frame pseudo instructions, even when
   // hasReservedCallFrame is false.
   return true;
 }

 bool AVRFrameLowering::hasReservedCallFrame(const MachineFunction &MF) const {
   // Reserve call frame memory in function prologue under the following
   // conditions:
   // - Y pointer is reserved to be the frame pointer.
   // - The function does not contain variable sized objects.

   const MachineFrameInfo &MFI = MF.getFrameInfo();
   return hasFP(MF) && !MFI.hasVarSizedObjects();
 }

 void AVRFrameLowering::emitPrologue(MachineFunction &MF,
                                     MachineBasicBlock &MBB) const {
   MachineBasicBlock::iterator MBBI = MBB.begin();
   CallingConv::ID CallConv = MF.getFunction().getCallingConv();
   DebugLoc DL = (MBBI != MBB.end()) ? MBBI->getDebugLoc() : DebugLoc();
   const AVRSubtarget &STI = MF.getSubtarget<AVRSubtarget>();
   const AVRInstrInfo &TII = *STI.getInstrInfo();
   bool HasFP = hasFP(MF);

   // Interrupt handlers re-enable interrupts in function entry.
   if (CallConv == CallingConv::AVR_INTR) {
     BuildMI(MBB, MBBI, DL, TII.get(AVR::BSETs))
         .addImm(0x07)
         .setMIFlag(MachineInstr::FrameSetup);
   }

   // Save the frame pointer if we have one.
   if (HasFP) {
     BuildMI(MBB, MBBI, DL, TII.get(AVR::PUSHWRr))
         .addReg(AVR::R29R28, RegState::Kill)
         .setMIFlag(MachineInstr::FrameSetup);
   }

   // Emit special prologue code to save R1, R0 and SREG in interrupt/signal
   // handlers before saving any other registers.
   if (CallConv == CallingConv::AVR_INTR ||
       CallConv == CallingConv::AVR_SIGNAL) {
     BuildMI(MBB, MBBI, DL, TII.get(AVR::PUSHWRr))
         .addReg(AVR::R1R0, RegState::Kill)
         .setMIFlag(MachineInstr::FrameSetup);

     BuildMI(MBB, MBBI, DL, TII.get(AVR::INRdA), AVR::R0)
         .addImm(0x3f)
         .setMIFlag(MachineInstr::FrameSetup);
     BuildMI(MBB, MBBI, DL, TII.get(AVR::PUSHRr))
         .addReg(AVR::R0, RegState::Kill)
         .setMIFlag(MachineInstr::FrameSetup);
     BuildMI(MBB, MBBI, DL, TII.get(AVR::EORRdRr))
         .addReg(AVR::R0, RegState::Define)
         .addReg(AVR::R0, RegState::Kill)
         .addReg(AVR::R0, RegState::Kill)
         .setMIFlag(MachineInstr::FrameSetup);
   }

   // Early exit if the frame pointer is not needed in this function.
   if (!HasFP) {
     return;
   }

   const MachineFrameInfo &MFI = MF.getFrameInfo();
   const AVRMachineFunctionInfo *AFI = MF.getInfo<AVRMachineFunctionInfo>();
   unsigned FrameSize = MFI.getStackSize() - AFI->getCalleeSavedFrameSize();

   // Skip the callee-saved push instructions.
   while (
       (MBBI != MBB.end()) && MBBI->getFlag(MachineInstr::FrameSetup) &&
       (MBBI->getOpcode() == AVR::PUSHRr || MBBI->getOpcode() == AVR::PUSHWRr)) {
     ++MBBI;
   }

   // Update Y with the new base value.
   BuildMI(MBB, MBBI, DL, TII.get(AVR::SPREAD), AVR::R29R28)
       .addReg(AVR::SP)
       .setMIFlag(MachineInstr::FrameSetup);

   // Mark the FramePtr as live-in in every block except the entry.
   for (MachineFunction::iterator I = std::next(MF.begin()), E = MF.end();
        I != E; ++I) {
     I->addLiveIn(AVR::R29R28);
   }

   if (!FrameSize) {
     return;
   }

   // Reserve the necessary frame memory by doing FP -= <size>.
   unsigned Opcode = (isUInt<6>(FrameSize)) ? AVR::SBIWRdK : AVR::SUBIWRdK;

   MachineInstr *MI = BuildMI(MBB, MBBI, DL, TII.get(Opcode), AVR::R29R28)
                          .addReg(AVR::R29R28, RegState::Kill)
                          .addImm(FrameSize)
                          .setMIFlag(MachineInstr::FrameSetup);
   // The SREG implicit def is dead.
   MI->getOperand(3).setIsDead();

   // Write back R29R28 to SP and temporarily disable interrupts.
   BuildMI(MBB, MBBI, DL, TII.get(AVR::SPWRITE), AVR::SP)
       .addReg(AVR::R29R28)
       .setMIFlag(MachineInstr::FrameSetup);
 }

 void AVRFrameLowering::emitEpilogue(MachineFunction &MF,
                                     MachineBasicBlock &MBB) const {
   CallingConv::ID CallConv = MF.getFunction().getCallingConv();
   bool isHandler = (CallConv == CallingConv::AVR_INTR ||
                     CallConv == CallingConv::AVR_SIGNAL);

   // Early exit if the frame pointer is not needed in this function except for
   // signal/interrupt handlers where special code generation is required.
   if (!hasFP(MF) && !isHandler) {
     return;
   }

   MachineBasicBlock::iterator MBBI = MBB.getLastNonDebugInstr();
   assert(MBBI->getDesc().isReturn() &&
          "Can only insert epilog into returning blocks");

   DebugLoc DL = MBBI->getDebugLoc();
   const MachineFrameInfo &MFI = MF.getFrameInfo();
   const AVRMachineFunctionInfo *AFI = MF.getInfo<AVRMachineFunctionInfo>();
   unsigned FrameSize = MFI.getStackSize() - AFI->getCalleeSavedFrameSize();
   const AVRSubtarget &STI = MF.getSubtarget<AVRSubtarget>();
   const AVRInstrInfo &TII = *STI.getInstrInfo();

   // Emit special epilogue code to restore R1, R0 and SREG in interrupt/signal
   // handlers at the very end of the function, just before reti.
   if (isHandler) {
     BuildMI(MBB, MBBI, DL, TII.get(AVR::POPRd), AVR::R0);
     BuildMI(MBB, MBBI, DL, TII.get(AVR::OUTARr))
         .addImm(0x3f)
         .addReg(AVR::R0, RegState::Kill);
     BuildMI(MBB, MBBI, DL, TII.get(AVR::POPWRd), AVR::R1R0);
   }

   if (hasFP(MF))
     BuildMI(MBB, MBBI, DL, TII.get(AVR::POPWRd), AVR::R29R28);

   // Early exit if there is no need to restore the frame pointer.
   if (!FrameSize) {
     return;
   }

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

     if (Opc != AVR::POPRd && Opc != AVR::POPWRd && !PI->isTerminator()) {
       break;
     }

     --MBBI;
   }

   unsigned Opcode;

   // Select the optimal opcode depending on how big it is.
   if (isUInt<6>(FrameSize)) {
     Opcode = AVR::ADIWRdK;
   } else {
     Opcode = AVR::SUBIWRdK;
     FrameSize = -FrameSize;
   }

   // Restore the frame pointer by doing FP += <size>.
   MachineInstr *MI = BuildMI(MBB, MBBI, DL, TII.get(Opcode), AVR::R29R28)
                          .addReg(AVR::R29R28, RegState::Kill)
                          .addImm(FrameSize);
   // The SREG implicit def is dead.
   MI->getOperand(3).setIsDead();

   // Write back R29R28 to SP and temporarily disable interrupts.
   BuildMI(MBB, MBBI, DL, TII.get(AVR::SPWRITE), AVR::SP)
       .addReg(AVR::R29R28, RegState::Kill);
 }

 // Return true if the specified function should have a dedicated frame
 // pointer register. This is true if the function meets any of the following
 // conditions:
 //  - a register has been spilled
 //  - has allocas
 //  - input arguments are passed using the stack
 //
 // Notice that strictly this is not a frame pointer because it contains SP after
 // frame allocation instead of having the original SP in function entry.
 bool AVRFrameLowering::hasFP(const MachineFunction &MF) const {
   const AVRMachineFunctionInfo *FuncInfo = MF.getInfo<AVRMachineFunctionInfo>();

   return (FuncInfo->getHasSpills() || FuncInfo->getHasAllocas() ||
           FuncInfo->getHasStackArgs());
 }

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

   unsigned CalleeFrameSize = 0;
   DebugLoc DL = MBB.findDebugLoc(MI);
   MachineFunction &MF = *MBB.getParent();
   const AVRSubtarget &STI = MF.getSubtarget<AVRSubtarget>();
   const TargetInstrInfo &TII = *STI.getInstrInfo();
   AVRMachineFunctionInfo *AVRFI = MF.getInfo<AVRMachineFunctionInfo>();

   for (unsigned i = CSI.size(); i != 0; --i) {
     unsigned Reg = CSI[i - 1].getReg();
     bool IsNotLiveIn = !MBB.isLiveIn(Reg);

     assert(TRI->getRegSizeInBits(*TRI->getMinimalPhysRegClass(Reg)) == 8 &&
            "Invalid register size");

     // Add the callee-saved register as live-in only if it is not already a
     // live-in register, this usually happens with arguments that are passed
     // through callee-saved registers.
     if (IsNotLiveIn) {
       MBB.addLiveIn(Reg);
     }

     // Do not kill the register when it is an input argument.
     BuildMI(MBB, MI, DL, TII.get(AVR::PUSHRr))
         .addReg(Reg, getKillRegState(IsNotLiveIn))
         .setMIFlag(MachineInstr::FrameSetup);
     ++CalleeFrameSize;
   }

   AVRFI->setCalleeSavedFrameSize(CalleeFrameSize);

   return true;
 }

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

   DebugLoc DL = MBB.findDebugLoc(MI);
   const MachineFunction &MF = *MBB.getParent();
   const AVRSubtarget &STI = MF.getSubtarget<AVRSubtarget>();
   const TargetInstrInfo &TII = *STI.getInstrInfo();

   for (const CalleeSavedInfo &CCSI : CSI) {
     unsigned Reg = CCSI.getReg();

     assert(TRI->getRegSizeInBits(*TRI->getMinimalPhysRegClass(Reg)) == 8 &&
            "Invalid register size");

     BuildMI(MBB, MI, DL, TII.get(AVR::POPRd), Reg);
   }

   return true;
 }

 /// Replace pseudo store instructions that pass arguments through the stack with
 /// real instructions. If insertPushes is true then all instructions are
 /// replaced with push instructions, otherwise regular std instructions are
 /// inserted.
 static void fixStackStores(MachineBasicBlock &MBB,
                            MachineBasicBlock::iterator MI,
                            const TargetInstrInfo &TII, bool insertPushes) {
   const AVRSubtarget &STI = MBB.getParent()->getSubtarget<AVRSubtarget>();
   const TargetRegisterInfo &TRI = *STI.getRegisterInfo();

   // Iterate through the BB until we hit a call instruction or we reach the end.
   for (auto I = MI, E = MBB.end(); I != E && !I->isCall();) {
     MachineBasicBlock::iterator NextMI = std::next(I);
     MachineInstr &MI = *I;
     unsigned Opcode = I->getOpcode();

     // Only care of pseudo store instructions where SP is the base pointer.
     if (Opcode != AVR::STDSPQRr && Opcode != AVR::STDWSPQRr) {
       I = NextMI;
       continue;
     }

     assert(MI.getOperand(0).getReg() == AVR::SP &&
            "Invalid register, should be SP!");
     if (insertPushes) {
       // Replace this instruction with a push.
       Register SrcReg = MI.getOperand(2).getReg();
       bool SrcIsKill = MI.getOperand(2).isKill();

       // We can't use PUSHWRr here because when expanded the order of the new
       // instructions are reversed from what we need. Perform the expansion now.
       if (Opcode == AVR::STDWSPQRr) {
         BuildMI(MBB, I, MI.getDebugLoc(), TII.get(AVR::PUSHRr))
             .addReg(TRI.getSubReg(SrcReg, AVR::sub_hi),
                     getKillRegState(SrcIsKill));
         BuildMI(MBB, I, MI.getDebugLoc(), TII.get(AVR::PUSHRr))
             .addReg(TRI.getSubReg(SrcReg, AVR::sub_lo),
                     getKillRegState(SrcIsKill));
       } else {
         BuildMI(MBB, I, MI.getDebugLoc(), TII.get(AVR::PUSHRr))
             .addReg(SrcReg, getKillRegState(SrcIsKill));
       }

       MI.eraseFromParent();
       I = NextMI;
       continue;
     }

     // Replace this instruction with a regular store. Use Y as the base
     // pointer since it is guaranteed to contain a copy of SP.
     unsigned STOpc =
         (Opcode == AVR::STDWSPQRr) ? AVR::STDWPtrQRr : AVR::STDPtrQRr;

     MI.setDesc(TII.get(STOpc));
     MI.getOperand(0).setReg(AVR::R29R28);

     I = NextMI;
   }
 }

 MachineBasicBlock::iterator AVRFrameLowering::eliminateCallFramePseudoInstr(
     MachineFunction &MF, MachineBasicBlock &MBB,
     MachineBasicBlock::iterator MI) const {
   const AVRSubtarget &STI = MF.getSubtarget<AVRSubtarget>();
   const AVRInstrInfo &TII = *STI.getInstrInfo();

   // There is nothing to insert when the call frame memory is allocated during
   // function entry. Delete the call frame pseudo and replace all pseudo stores
   // with real store instructions.
   if (hasReservedCallFrame(MF)) {
     fixStackStores(MBB, MI, TII, false);
     return MBB.erase(MI);
   }

   DebugLoc DL = MI->getDebugLoc();
   unsigned int Opcode = MI->getOpcode();
   int Amount = TII.getFrameSize(*MI);

   // Adjcallstackup does not need to allocate stack space for the call, instead
   // we insert push instructions that will allocate the necessary stack.
   // For adjcallstackdown we convert it into an 'adiw reg, <amt>' handling
   // the read and write of SP in I/O space.
   if (Amount != 0) {
     assert(getStackAlignment() == 1 && "Unsupported stack alignment");

     if (Opcode == TII.getCallFrameSetupOpcode()) {
       fixStackStores(MBB, MI, TII, true);
     } else {
       assert(Opcode == TII.getCallFrameDestroyOpcode());

       // Select the best opcode to adjust SP based on the offset size.
       unsigned addOpcode;
       if (isUInt<6>(Amount)) {
         addOpcode = AVR::ADIWRdK;
       } else {
         addOpcode = AVR::SUBIWRdK;
         Amount = -Amount;
       }

       // Build the instruction sequence.
       BuildMI(MBB, MI, DL, TII.get(AVR::SPREAD), AVR::R31R30).addReg(AVR::SP);

       MachineInstr *New = BuildMI(MBB, MI, DL, TII.get(addOpcode), AVR::R31R30)
                               .addReg(AVR::R31R30, RegState::Kill)
                               .addImm(Amount);
       New->getOperand(3).setIsDead();

       BuildMI(MBB, MI, DL, TII.get(AVR::SPWRITE), AVR::SP)
           .addReg(AVR::R31R30, RegState::Kill);
     }
   }

   return MBB.erase(MI);
 }

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

   // If we have a frame pointer, the Y register needs to be saved as well.
   // We don't do that here however - the prologue and epilogue generation
   // code will handle it specially.
 }
 /// The frame analyzer pass.
 ///
 /// Scans the function for allocas and used arguments
 /// that are passed through the stack.
 struct AVRFrameAnalyzer : public MachineFunctionPass {
   static char ID;
   AVRFrameAnalyzer() : MachineFunctionPass(ID) {}

   bool runOnMachineFunction(MachineFunction &MF) {
     const MachineFrameInfo &MFI = MF.getFrameInfo();
     AVRMachineFunctionInfo *FuncInfo = MF.getInfo<AVRMachineFunctionInfo>();

     // If there are no fixed frame indexes during this stage it means there
     // are allocas present in the function.
     if (MFI.getNumObjects() != MFI.getNumFixedObjects()) {
       // Check for the type of allocas present in the function. We only care
       // about fixed size allocas so do not give false positives if only
       // variable sized allocas are present.
       for (unsigned i = 0, e = MFI.getObjectIndexEnd(); i != e; ++i) {
         // Variable sized objects have size 0.
         if (MFI.getObjectSize(i)) {
           FuncInfo->setHasAllocas(true);
           break;
         }
       }
     }

     // If there are fixed frame indexes present, scan the function to see if
     // they are really being used.
     if (MFI.getNumFixedObjects() == 0) {
       return false;
     }

     // Ok fixed frame indexes present, now scan the function to see if they
     // are really being used, otherwise we can ignore them.
     for (const MachineBasicBlock &BB : MF) {
       for (const MachineInstr &MI : BB) {
         int Opcode = MI.getOpcode();

         if ((Opcode != AVR::LDDRdPtrQ) && (Opcode != AVR::LDDWRdPtrQ) &&
             (Opcode != AVR::STDPtrQRr) && (Opcode != AVR::STDWPtrQRr)) {
           continue;
         }

         for (const MachineOperand &MO : MI.operands()) {
           if (!MO.isFI()) {
             continue;
           }

           if (MFI.isFixedObjectIndex(MO.getIndex())) {
             FuncInfo->setHasStackArgs(true);
             return false;
           }
         }
       }
     }

     return false;
   }

   StringRef getPassName() const { return "AVR Frame Analyzer"; }
 };

 char AVRFrameAnalyzer::ID = 0;

 /// Creates instance of the frame analyzer pass.
 FunctionPass *createAVRFrameAnalyzerPass() { return new AVRFrameAnalyzer(); }

 /// Create the Dynalloca Stack Pointer Save/Restore pass.
 /// Insert a copy of SP before allocating the dynamic stack memory and restore
 /// it in function exit to restore the original SP state. This avoids the need
 /// of reserving a register pair for a frame pointer.
 struct AVRDynAllocaSR : public MachineFunctionPass {
   static char ID;
   AVRDynAllocaSR() : MachineFunctionPass(ID) {}

   bool runOnMachineFunction(MachineFunction &MF) {
     // Early exit when there are no variable sized objects in the function.
     if (!MF.getFrameInfo().hasVarSizedObjects()) {
       return false;
     }

     const AVRSubtarget &STI = MF.getSubtarget<AVRSubtarget>();
     const TargetInstrInfo &TII = *STI.getInstrInfo();
     MachineBasicBlock &EntryMBB = MF.front();
     MachineBasicBlock::iterator MBBI = EntryMBB.begin();
     DebugLoc DL = EntryMBB.findDebugLoc(MBBI);

     unsigned SPCopy =
         MF.getRegInfo().createVirtualRegister(&AVR::DREGSRegClass);

     // Create a copy of SP in function entry before any dynallocas are
     // inserted.
     BuildMI(EntryMBB, MBBI, DL, TII.get(AVR::COPY), SPCopy).addReg(AVR::SP);

     // Restore SP in all exit basic blocks.
     for (MachineBasicBlock &MBB : MF) {
       // If last instruction is a return instruction, add a restore copy.
       if (!MBB.empty() && MBB.back().isReturn()) {
         MBBI = MBB.getLastNonDebugInstr();
         DL = MBBI->getDebugLoc();
         BuildMI(MBB, MBBI, DL, TII.get(AVR::COPY), AVR::SP)
             .addReg(SPCopy, RegState::Kill);
       }
     }

     return true;
   }

   StringRef getPassName() const {
     return "AVR dynalloca stack pointer save/restore";
   }
 };

 char AVRDynAllocaSR::ID = 0;

 /// createAVRDynAllocaSRPass - returns an instance of the dynalloca stack
 /// pointer save/restore pass.
 FunctionPass *createAVRDynAllocaSRPass() { return new AVRDynAllocaSR(); }

 } // end of namespace llvm
	//===-- AVRFrameLowering.cpp - AVR Frame Information ----------------------===//
	//
	// 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 the AVR implementation of TargetFrameLowering class.
	//
	//===----------------------------------------------------------------------===//

	#include "AVRFrameLowering.h"

	#include "AVR.h"
	#include "AVRInstrInfo.h"
	#include "AVRMachineFunctionInfo.h"
	#include "AVRTargetMachine.h"
	#include "MCTargetDesc/AVRMCTargetDesc.h"

	#include "llvm/CodeGen/MachineFrameInfo.h"
	#include "llvm/CodeGen/MachineFunction.h"
	#include "llvm/CodeGen/MachineFunctionPass.h"
	#include "llvm/CodeGen/MachineInstrBuilder.h"
	#include "llvm/CodeGen/MachineRegisterInfo.h"
	#include "llvm/IR/Function.h"

	#include <vector>

	namespace llvm {

	AVRFrameLowering::AVRFrameLowering()
	: TargetFrameLowering(TargetFrameLowering::StackGrowsDown, Align::None(),
	-2) {}

	bool AVRFrameLowering::canSimplifyCallFramePseudos(
	const MachineFunction &MF) const {
	// Always simplify call frame pseudo instructions, even when
	// hasReservedCallFrame is false.
	return true;
	}

	bool AVRFrameLowering::hasReservedCallFrame(const MachineFunction &MF) const {
	// Reserve call frame memory in function prologue under the following
	// conditions:
	// - Y pointer is reserved to be the frame pointer.
	// - The function does not contain variable sized objects.

	const MachineFrameInfo &MFI = MF.getFrameInfo();
	return hasFP(MF) && !MFI.hasVarSizedObjects();
	}

	void AVRFrameLowering::emitPrologue(MachineFunction &MF,
	MachineBasicBlock &MBB) const {
	MachineBasicBlock::iterator MBBI = MBB.begin();
	CallingConv::ID CallConv = MF.getFunction().getCallingConv();
	DebugLoc DL = (MBBI != MBB.end()) ? MBBI->getDebugLoc() : DebugLoc();
	const AVRSubtarget &STI = MF.getSubtarget<AVRSubtarget>();
	const AVRInstrInfo &TII = *STI.getInstrInfo();
	bool HasFP = hasFP(MF);

	// Interrupt handlers re-enable interrupts in function entry.
	if (CallConv == CallingConv::AVR_INTR) {
	BuildMI(MBB, MBBI, DL, TII.get(AVR::BSETs))
	.addImm(0x07)
	.setMIFlag(MachineInstr::FrameSetup);
	}

	// Save the frame pointer if we have one.
	if (HasFP) {
	BuildMI(MBB, MBBI, DL, TII.get(AVR::PUSHWRr))
	.addReg(AVR::R29R28, RegState::Kill)
	.setMIFlag(MachineInstr::FrameSetup);
	}

	// Emit special prologue code to save R1, R0 and SREG in interrupt/signal
	// handlers before saving any other registers.
	if (CallConv == CallingConv::AVR_INTR \|\|
	CallConv == CallingConv::AVR_SIGNAL) {
	BuildMI(MBB, MBBI, DL, TII.get(AVR::PUSHWRr))
	.addReg(AVR::R1R0, RegState::Kill)
	.setMIFlag(MachineInstr::FrameSetup);

	BuildMI(MBB, MBBI, DL, TII.get(AVR::INRdA), AVR::R0)
	.addImm(0x3f)
	.setMIFlag(MachineInstr::FrameSetup);
	BuildMI(MBB, MBBI, DL, TII.get(AVR::PUSHRr))
	.addReg(AVR::R0, RegState::Kill)
	.setMIFlag(MachineInstr::FrameSetup);
	BuildMI(MBB, MBBI, DL, TII.get(AVR::EORRdRr))
	.addReg(AVR::R0, RegState::Define)
	.addReg(AVR::R0, RegState::Kill)
	.addReg(AVR::R0, RegState::Kill)
	.setMIFlag(MachineInstr::FrameSetup);
	}

	// Early exit if the frame pointer is not needed in this function.
	if (!HasFP) {
	return;
	}

	const MachineFrameInfo &MFI = MF.getFrameInfo();
	const AVRMachineFunctionInfo *AFI = MF.getInfo<AVRMachineFunctionInfo>();
	unsigned FrameSize = MFI.getStackSize() - AFI->getCalleeSavedFrameSize();

	// Skip the callee-saved push instructions.
	while (
	(MBBI != MBB.end()) && MBBI->getFlag(MachineInstr::FrameSetup) &&
	(MBBI->getOpcode() == AVR::PUSHRr \|\| MBBI->getOpcode() == AVR::PUSHWRr)) {
	++MBBI;
	}

	// Update Y with the new base value.
	BuildMI(MBB, MBBI, DL, TII.get(AVR::SPREAD), AVR::R29R28)
	.addReg(AVR::SP)
	.setMIFlag(MachineInstr::FrameSetup);

	// Mark the FramePtr as live-in in every block except the entry.
	for (MachineFunction::iterator I = std::next(MF.begin()), E = MF.end();
	I != E; ++I) {
	I->addLiveIn(AVR::R29R28);
	}

	if (!FrameSize) {
	return;
	}

	// Reserve the necessary frame memory by doing FP -= <size>.
	unsigned Opcode = (isUInt<6>(FrameSize)) ? AVR::SBIWRdK : AVR::SUBIWRdK;

	MachineInstr *MI = BuildMI(MBB, MBBI, DL, TII.get(Opcode), AVR::R29R28)
	.addReg(AVR::R29R28, RegState::Kill)
	.addImm(FrameSize)
	.setMIFlag(MachineInstr::FrameSetup);
	// The SREG implicit def is dead.
	MI->getOperand(3).setIsDead();

	// Write back R29R28 to SP and temporarily disable interrupts.
	BuildMI(MBB, MBBI, DL, TII.get(AVR::SPWRITE), AVR::SP)
	.addReg(AVR::R29R28)
	.setMIFlag(MachineInstr::FrameSetup);
	}

	void AVRFrameLowering::emitEpilogue(MachineFunction &MF,
	MachineBasicBlock &MBB) const {
	CallingConv::ID CallConv = MF.getFunction().getCallingConv();
	bool isHandler = (CallConv == CallingConv::AVR_INTR \|\|
	CallConv == CallingConv::AVR_SIGNAL);

	// Early exit if the frame pointer is not needed in this function except for
	// signal/interrupt handlers where special code generation is required.
	if (!hasFP(MF) && !isHandler) {
	return;
	}

	MachineBasicBlock::iterator MBBI = MBB.getLastNonDebugInstr();
	assert(MBBI->getDesc().isReturn() &&
	"Can only insert epilog into returning blocks");

	DebugLoc DL = MBBI->getDebugLoc();
	const MachineFrameInfo &MFI = MF.getFrameInfo();
	const AVRMachineFunctionInfo *AFI = MF.getInfo<AVRMachineFunctionInfo>();
	unsigned FrameSize = MFI.getStackSize() - AFI->getCalleeSavedFrameSize();
	const AVRSubtarget &STI = MF.getSubtarget<AVRSubtarget>();
	const AVRInstrInfo &TII = *STI.getInstrInfo();

	// Emit special epilogue code to restore R1, R0 and SREG in interrupt/signal
	// handlers at the very end of the function, just before reti.
	if (isHandler) {
	BuildMI(MBB, MBBI, DL, TII.get(AVR::POPRd), AVR::R0);
	BuildMI(MBB, MBBI, DL, TII.get(AVR::OUTARr))
	.addImm(0x3f)
	.addReg(AVR::R0, RegState::Kill);
	BuildMI(MBB, MBBI, DL, TII.get(AVR::POPWRd), AVR::R1R0);
	}

	if (hasFP(MF))
	BuildMI(MBB, MBBI, DL, TII.get(AVR::POPWRd), AVR::R29R28);

	// Early exit if there is no need to restore the frame pointer.
	if (!FrameSize) {
	return;
	}

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

	if (Opc != AVR::POPRd && Opc != AVR::POPWRd && !PI->isTerminator()) {
	break;
	}

	--MBBI;
	}

	unsigned Opcode;

	// Select the optimal opcode depending on how big it is.
	if (isUInt<6>(FrameSize)) {
	Opcode = AVR::ADIWRdK;
	} else {
	Opcode = AVR::SUBIWRdK;
	FrameSize = -FrameSize;
	}

	// Restore the frame pointer by doing FP += <size>.
	MachineInstr *MI = BuildMI(MBB, MBBI, DL, TII.get(Opcode), AVR::R29R28)
	.addReg(AVR::R29R28, RegState::Kill)
	.addImm(FrameSize);
	// The SREG implicit def is dead.
	MI->getOperand(3).setIsDead();

	// Write back R29R28 to SP and temporarily disable interrupts.
	BuildMI(MBB, MBBI, DL, TII.get(AVR::SPWRITE), AVR::SP)
	.addReg(AVR::R29R28, RegState::Kill);
	}

	// Return true if the specified function should have a dedicated frame
	// pointer register. This is true if the function meets any of the following
	// conditions:
	// - a register has been spilled
	// - has allocas
	// - input arguments are passed using the stack
	//
	// Notice that strictly this is not a frame pointer because it contains SP after
	// frame allocation instead of having the original SP in function entry.
	bool AVRFrameLowering::hasFP(const MachineFunction &MF) const {
	const AVRMachineFunctionInfo *FuncInfo = MF.getInfo<AVRMachineFunctionInfo>();

	return (FuncInfo->getHasSpills() \|\| FuncInfo->getHasAllocas() \|\|
	FuncInfo->getHasStackArgs());
	}

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

	unsigned CalleeFrameSize = 0;
	DebugLoc DL = MBB.findDebugLoc(MI);
	MachineFunction &MF = *MBB.getParent();
	const AVRSubtarget &STI = MF.getSubtarget<AVRSubtarget>();
	const TargetInstrInfo &TII = *STI.getInstrInfo();
	AVRMachineFunctionInfo *AVRFI = MF.getInfo<AVRMachineFunctionInfo>();

	for (unsigned i = CSI.size(); i != 0; --i) {
	unsigned Reg = CSI[i - 1].getReg();
	bool IsNotLiveIn = !MBB.isLiveIn(Reg);

	assert(TRI->getRegSizeInBits(*TRI->getMinimalPhysRegClass(Reg)) == 8 &&
	"Invalid register size");

	// Add the callee-saved register as live-in only if it is not already a
	// live-in register, this usually happens with arguments that are passed
	// through callee-saved registers.
	if (IsNotLiveIn) {
	MBB.addLiveIn(Reg);
	}

	// Do not kill the register when it is an input argument.
	BuildMI(MBB, MI, DL, TII.get(AVR::PUSHRr))
	.addReg(Reg, getKillRegState(IsNotLiveIn))
	.setMIFlag(MachineInstr::FrameSetup);
	++CalleeFrameSize;
	}

	AVRFI->setCalleeSavedFrameSize(CalleeFrameSize);

	return true;
	}

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

	DebugLoc DL = MBB.findDebugLoc(MI);
	const MachineFunction &MF = *MBB.getParent();
	const AVRSubtarget &STI = MF.getSubtarget<AVRSubtarget>();
	const TargetInstrInfo &TII = *STI.getInstrInfo();

	for (const CalleeSavedInfo &CCSI : CSI) {
	unsigned Reg = CCSI.getReg();

	assert(TRI->getRegSizeInBits(*TRI->getMinimalPhysRegClass(Reg)) == 8 &&
	"Invalid register size");

	BuildMI(MBB, MI, DL, TII.get(AVR::POPRd), Reg);
	}

	return true;
	}

	/// Replace pseudo store instructions that pass arguments through the stack with
	/// real instructions. If insertPushes is true then all instructions are
	/// replaced with push instructions, otherwise regular std instructions are
	/// inserted.
	static void fixStackStores(MachineBasicBlock &MBB,
	MachineBasicBlock::iterator MI,
	const TargetInstrInfo &TII, bool insertPushes) {
	const AVRSubtarget &STI = MBB.getParent()->getSubtarget<AVRSubtarget>();
	const TargetRegisterInfo &TRI = *STI.getRegisterInfo();

	// Iterate through the BB until we hit a call instruction or we reach the end.
	for (auto I = MI, E = MBB.end(); I != E && !I->isCall();) {
	MachineBasicBlock::iterator NextMI = std::next(I);
	MachineInstr &MI = *I;
	unsigned Opcode = I->getOpcode();

	// Only care of pseudo store instructions where SP is the base pointer.
	if (Opcode != AVR::STDSPQRr && Opcode != AVR::STDWSPQRr) {
	I = NextMI;
	continue;
	}

	assert(MI.getOperand(0).getReg() == AVR::SP &&
	"Invalid register, should be SP!");
	if (insertPushes) {
	// Replace this instruction with a push.
	Register SrcReg = MI.getOperand(2).getReg();
	bool SrcIsKill = MI.getOperand(2).isKill();

	// We can't use PUSHWRr here because when expanded the order of the new
	// instructions are reversed from what we need. Perform the expansion now.
	if (Opcode == AVR::STDWSPQRr) {
	BuildMI(MBB, I, MI.getDebugLoc(), TII.get(AVR::PUSHRr))
	.addReg(TRI.getSubReg(SrcReg, AVR::sub_hi),
	getKillRegState(SrcIsKill));
	BuildMI(MBB, I, MI.getDebugLoc(), TII.get(AVR::PUSHRr))
	.addReg(TRI.getSubReg(SrcReg, AVR::sub_lo),
	getKillRegState(SrcIsKill));
	} else {
	BuildMI(MBB, I, MI.getDebugLoc(), TII.get(AVR::PUSHRr))
	.addReg(SrcReg, getKillRegState(SrcIsKill));
	}

	MI.eraseFromParent();
	I = NextMI;
	continue;
	}

	// Replace this instruction with a regular store. Use Y as the base
	// pointer since it is guaranteed to contain a copy of SP.
	unsigned STOpc =
	(Opcode == AVR::STDWSPQRr) ? AVR::STDWPtrQRr : AVR::STDPtrQRr;

	MI.setDesc(TII.get(STOpc));
	MI.getOperand(0).setReg(AVR::R29R28);

	I = NextMI;
	}
	}

	MachineBasicBlock::iterator AVRFrameLowering::eliminateCallFramePseudoInstr(
	MachineFunction &MF, MachineBasicBlock &MBB,
	MachineBasicBlock::iterator MI) const {
	const AVRSubtarget &STI = MF.getSubtarget<AVRSubtarget>();
	const AVRInstrInfo &TII = *STI.getInstrInfo();

	// There is nothing to insert when the call frame memory is allocated during
	// function entry. Delete the call frame pseudo and replace all pseudo stores
	// with real store instructions.
	if (hasReservedCallFrame(MF)) {
	fixStackStores(MBB, MI, TII, false);
	return MBB.erase(MI);
	}

	DebugLoc DL = MI->getDebugLoc();
	unsigned int Opcode = MI->getOpcode();
	int Amount = TII.getFrameSize(*MI);

	// Adjcallstackup does not need to allocate stack space for the call, instead
	// we insert push instructions that will allocate the necessary stack.
	// For adjcallstackdown we convert it into an 'adiw reg, <amt>' handling
	// the read and write of SP in I/O space.
	if (Amount != 0) {
	assert(getStackAlignment() == 1 && "Unsupported stack alignment");

	if (Opcode == TII.getCallFrameSetupOpcode()) {
	fixStackStores(MBB, MI, TII, true);
	} else {
	assert(Opcode == TII.getCallFrameDestroyOpcode());

	// Select the best opcode to adjust SP based on the offset size.
	unsigned addOpcode;
	if (isUInt<6>(Amount)) {
	addOpcode = AVR::ADIWRdK;
	} else {
	addOpcode = AVR::SUBIWRdK;
	Amount = -Amount;
	}

	// Build the instruction sequence.
	BuildMI(MBB, MI, DL, TII.get(AVR::SPREAD), AVR::R31R30).addReg(AVR::SP);

	MachineInstr *New = BuildMI(MBB, MI, DL, TII.get(addOpcode), AVR::R31R30)
	.addReg(AVR::R31R30, RegState::Kill)
	.addImm(Amount);
	New->getOperand(3).setIsDead();

	BuildMI(MBB, MI, DL, TII.get(AVR::SPWRITE), AVR::SP)
	.addReg(AVR::R31R30, RegState::Kill);
	}
	}

	return MBB.erase(MI);
	}

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

	// If we have a frame pointer, the Y register needs to be saved as well.
	// We don't do that here however - the prologue and epilogue generation
	// code will handle it specially.
	}
	/// The frame analyzer pass.
	///
	/// Scans the function for allocas and used arguments
	/// that are passed through the stack.
	struct AVRFrameAnalyzer : public MachineFunctionPass {
	static char ID;
	AVRFrameAnalyzer() : MachineFunctionPass(ID) {}

	bool runOnMachineFunction(MachineFunction &MF) {
	const MachineFrameInfo &MFI = MF.getFrameInfo();
	AVRMachineFunctionInfo *FuncInfo = MF.getInfo<AVRMachineFunctionInfo>();

	// If there are no fixed frame indexes during this stage it means there
	// are allocas present in the function.
	if (MFI.getNumObjects() != MFI.getNumFixedObjects()) {
	// Check for the type of allocas present in the function. We only care
	// about fixed size allocas so do not give false positives if only
	// variable sized allocas are present.
	for (unsigned i = 0, e = MFI.getObjectIndexEnd(); i != e; ++i) {
	// Variable sized objects have size 0.
	if (MFI.getObjectSize(i)) {
	FuncInfo->setHasAllocas(true);
	break;
	}
	}
	}

	// If there are fixed frame indexes present, scan the function to see if
	// they are really being used.
	if (MFI.getNumFixedObjects() == 0) {
	return false;
	}

	// Ok fixed frame indexes present, now scan the function to see if they
	// are really being used, otherwise we can ignore them.
	for (const MachineBasicBlock &BB : MF) {
	for (const MachineInstr &MI : BB) {
	int Opcode = MI.getOpcode();

	if ((Opcode != AVR::LDDRdPtrQ) && (Opcode != AVR::LDDWRdPtrQ) &&
	(Opcode != AVR::STDPtrQRr) && (Opcode != AVR::STDWPtrQRr)) {
	continue;
	}

	for (const MachineOperand &MO : MI.operands()) {
	if (!MO.isFI()) {
	continue;
	}

	if (MFI.isFixedObjectIndex(MO.getIndex())) {
	FuncInfo->setHasStackArgs(true);
	return false;
	}
	}
	}
	}

	return false;
	}

	StringRef getPassName() const { return "AVR Frame Analyzer"; }
	};

	char AVRFrameAnalyzer::ID = 0;

	/// Creates instance of the frame analyzer pass.
	FunctionPass *createAVRFrameAnalyzerPass() { return new AVRFrameAnalyzer(); }

	/// Create the Dynalloca Stack Pointer Save/Restore pass.
	/// Insert a copy of SP before allocating the dynamic stack memory and restore
	/// it in function exit to restore the original SP state. This avoids the need
	/// of reserving a register pair for a frame pointer.
	struct AVRDynAllocaSR : public MachineFunctionPass {
	static char ID;
	AVRDynAllocaSR() : MachineFunctionPass(ID) {}

	bool runOnMachineFunction(MachineFunction &MF) {
	// Early exit when there are no variable sized objects in the function.
	if (!MF.getFrameInfo().hasVarSizedObjects()) {
	return false;
	}

	const AVRSubtarget &STI = MF.getSubtarget<AVRSubtarget>();
	const TargetInstrInfo &TII = *STI.getInstrInfo();
	MachineBasicBlock &EntryMBB = MF.front();
	MachineBasicBlock::iterator MBBI = EntryMBB.begin();
	DebugLoc DL = EntryMBB.findDebugLoc(MBBI);

	unsigned SPCopy =
	MF.getRegInfo().createVirtualRegister(&AVR::DREGSRegClass);

	// Create a copy of SP in function entry before any dynallocas are
	// inserted.
	BuildMI(EntryMBB, MBBI, DL, TII.get(AVR::COPY), SPCopy).addReg(AVR::SP);

	// Restore SP in all exit basic blocks.
	for (MachineBasicBlock &MBB : MF) {
	// If last instruction is a return instruction, add a restore copy.
	if (!MBB.empty() && MBB.back().isReturn()) {
	MBBI = MBB.getLastNonDebugInstr();
	DL = MBBI->getDebugLoc();
	BuildMI(MBB, MBBI, DL, TII.get(AVR::COPY), AVR::SP)
	.addReg(SPCopy, RegState::Kill);
	}
	}

	return true;
	}

	StringRef getPassName() const {
	return "AVR dynalloca stack pointer save/restore";
	}
	};

	char AVRDynAllocaSR::ID = 0;

	/// createAVRDynAllocaSRPass - returns an instance of the dynalloca stack
	/// pointer save/restore pass.
	FunctionPass *createAVRDynAllocaSRPass() { return new AVRDynAllocaSR(); }

	} // end of namespace llvm