llvm/lib/Target/X86/X86SelectionDAGInfo.cpp - llvm-project - Git at Google

 //===-- X86SelectionDAGInfo.cpp - X86 SelectionDAG Info -------------------===//
 //
 // 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 implements the X86SelectionDAGInfo class.
 //
 //===----------------------------------------------------------------------===//

 #include "X86SelectionDAGInfo.h"
 #include "X86ISelLowering.h"
 #include "X86InstrInfo.h"
 #include "X86RegisterInfo.h"
 #include "X86Subtarget.h"
 #include "llvm/CodeGen/MachineFrameInfo.h"
 #include "llvm/CodeGen/SelectionDAG.h"
 #include "llvm/CodeGen/TargetLowering.h"
 #include "llvm/IR/DerivedTypes.h"

 using namespace llvm;

 #define DEBUG_TYPE "x86-selectiondag-info"

 static cl::opt<bool>
     UseFSRMForMemcpy("x86-use-fsrm-for-memcpy", cl::Hidden, cl::init(false),
                      cl::desc("Use fast short rep mov in memcpy lowering"));

 bool X86SelectionDAGInfo::isBaseRegConflictPossible(
     SelectionDAG &DAG, ArrayRef<MCPhysReg> ClobberSet) const {
   // We cannot use TRI->hasBasePointer() until *after* we select all basic
   // blocks.  Legalization may introduce new stack temporaries with large
   // alignment requirements.  Fall back to generic code if there are any
   // dynamic stack adjustments (hopefully rare) and the base pointer would
   // conflict if we had to use it.
   MachineFrameInfo &MFI = DAG.getMachineFunction().getFrameInfo();
   if (!MFI.hasVarSizedObjects() && !MFI.hasOpaqueSPAdjustment())
     return false;

   const X86RegisterInfo *TRI = static_cast<const X86RegisterInfo *>(
       DAG.getSubtarget().getRegisterInfo());
   return llvm::is_contained(ClobberSet, TRI->getBaseRegister());
 }

 SDValue X86SelectionDAGInfo::EmitTargetCodeForMemset(
     SelectionDAG &DAG, const SDLoc &dl, SDValue Chain, SDValue Dst, SDValue Val,
     SDValue Size, Align Alignment, bool isVolatile,
     MachinePointerInfo DstPtrInfo) const {
   ConstantSDNode *ConstantSize = dyn_cast<ConstantSDNode>(Size);
   const X86Subtarget &Subtarget =
       DAG.getMachineFunction().getSubtarget<X86Subtarget>();

 #ifndef NDEBUG
   // If the base register might conflict with our physical registers, bail out.
   const MCPhysReg ClobberSet[] = {X86::RCX, X86::RAX, X86::RDI,
                                   X86::ECX, X86::EAX, X86::EDI};
   assert(!isBaseRegConflictPossible(DAG, ClobberSet));
 #endif

   // If to a segment-relative address space, use the default lowering.
   if (DstPtrInfo.getAddrSpace() >= 256)
     return SDValue();

   // If not DWORD aligned or size is more than the threshold, call the library.
   // The libc version is likely to be faster for these cases. It can use the
   // address value and run time information about the CPU.
   if (Alignment < Align(4) || !ConstantSize ||
       ConstantSize->getZExtValue() > Subtarget.getMaxInlineSizeThreshold()) {
     // Check to see if there is a specialized entry-point for memory zeroing.
     ConstantSDNode *ValC = dyn_cast<ConstantSDNode>(Val);

     if (const char *bzeroName =
             (ValC && ValC->isZero())
                 ? DAG.getTargetLoweringInfo().getLibcallName(RTLIB::BZERO)
                 : nullptr) {
       const TargetLowering &TLI = DAG.getTargetLoweringInfo();
       EVT IntPtr = TLI.getPointerTy(DAG.getDataLayout());
       Type *IntPtrTy = DAG.getDataLayout().getIntPtrType(*DAG.getContext());
       TargetLowering::ArgListTy Args;
       TargetLowering::ArgListEntry Entry;
       Entry.Node = Dst;
       Entry.Ty = IntPtrTy;
       Args.push_back(Entry);
       Entry.Node = Size;
       Args.push_back(Entry);

       TargetLowering::CallLoweringInfo CLI(DAG);
       CLI.setDebugLoc(dl)
           .setChain(Chain)
           .setLibCallee(CallingConv::C, Type::getVoidTy(*DAG.getContext()),
                         DAG.getExternalSymbol(bzeroName, IntPtr),
                         std::move(Args))
           .setDiscardResult();

       std::pair<SDValue,SDValue> CallResult = TLI.LowerCallTo(CLI);
       return CallResult.second;
     }

     // Otherwise have the target-independent code call memset.
     return SDValue();
   }

   uint64_t SizeVal = ConstantSize->getZExtValue();
   SDValue InFlag;
   EVT AVT;
   SDValue Count;
   ConstantSDNode *ValC = dyn_cast<ConstantSDNode>(Val);
   unsigned BytesLeft = 0;
   if (ValC) {
     unsigned ValReg;
     uint64_t Val = ValC->getZExtValue() & 255;

     // If the value is a constant, then we can potentially use larger sets.
     if (Alignment > Align(2)) {
       // DWORD aligned
       AVT = MVT::i32;
       ValReg = X86::EAX;
       Val = (Val << 8)  | Val;
       Val = (Val << 16) | Val;
       if (Subtarget.is64Bit() && Alignment > Align(8)) { // QWORD aligned
         AVT = MVT::i64;
         ValReg = X86::RAX;
         Val = (Val << 32) | Val;
       }
     } else if (Alignment == Align(2)) {
       // WORD aligned
       AVT = MVT::i16;
       ValReg = X86::AX;
       Val = (Val << 8) | Val;
     } else {
       // Byte aligned
       AVT = MVT::i8;
       ValReg = X86::AL;
       Count = DAG.getIntPtrConstant(SizeVal, dl);
     }

     if (AVT.bitsGT(MVT::i8)) {
       unsigned UBytes = AVT.getSizeInBits() / 8;
       Count = DAG.getIntPtrConstant(SizeVal / UBytes, dl);
       BytesLeft = SizeVal % UBytes;
     }

     Chain = DAG.getCopyToReg(Chain, dl, ValReg, DAG.getConstant(Val, dl, AVT),
                              InFlag);
     InFlag = Chain.getValue(1);
   } else {
     AVT = MVT::i8;
     Count  = DAG.getIntPtrConstant(SizeVal, dl);
     Chain  = DAG.getCopyToReg(Chain, dl, X86::AL, Val, InFlag);
     InFlag = Chain.getValue(1);
   }

   bool Use64BitRegs = Subtarget.isTarget64BitLP64();
   Chain = DAG.getCopyToReg(Chain, dl, Use64BitRegs ? X86::RCX : X86::ECX,
                            Count, InFlag);
   InFlag = Chain.getValue(1);
   Chain = DAG.getCopyToReg(Chain, dl, Use64BitRegs ? X86::RDI : X86::EDI,
                            Dst, InFlag);
   InFlag = Chain.getValue(1);

   SDVTList Tys = DAG.getVTList(MVT::Other, MVT::Glue);
   SDValue Ops[] = { Chain, DAG.getValueType(AVT), InFlag };
   Chain = DAG.getNode(X86ISD::REP_STOS, dl, Tys, Ops);

   if (BytesLeft) {
     // Handle the last 1 - 7 bytes.
     unsigned Offset = SizeVal - BytesLeft;
     EVT AddrVT = Dst.getValueType();
     EVT SizeVT = Size.getValueType();

     Chain =
         DAG.getMemset(Chain, dl,
                       DAG.getNode(ISD::ADD, dl, AddrVT, Dst,
                                   DAG.getConstant(Offset, dl, AddrVT)),
                       Val, DAG.getConstant(BytesLeft, dl, SizeVT), Alignment,
                       isVolatile, false, DstPtrInfo.getWithOffset(Offset));
   }

   // TODO: Use a Tokenfactor, as in memcpy, instead of a single chain.
   return Chain;
 }

 /// Emit a single REP MOVS{B,W,D,Q} instruction.
 static SDValue emitRepmovs(const X86Subtarget &Subtarget, SelectionDAG &DAG,
                            const SDLoc &dl, SDValue Chain, SDValue Dst,
                            SDValue Src, SDValue Size, MVT AVT) {
   const bool Use64BitRegs = Subtarget.isTarget64BitLP64();
   const unsigned CX = Use64BitRegs ? X86::RCX : X86::ECX;
   const unsigned DI = Use64BitRegs ? X86::RDI : X86::EDI;
   const unsigned SI = Use64BitRegs ? X86::RSI : X86::ESI;

   SDValue InFlag;
   Chain = DAG.getCopyToReg(Chain, dl, CX, Size, InFlag);
   InFlag = Chain.getValue(1);
   Chain = DAG.getCopyToReg(Chain, dl, DI, Dst, InFlag);
   InFlag = Chain.getValue(1);
   Chain = DAG.getCopyToReg(Chain, dl, SI, Src, InFlag);
   InFlag = Chain.getValue(1);

   SDVTList Tys = DAG.getVTList(MVT::Other, MVT::Glue);
   SDValue Ops[] = {Chain, DAG.getValueType(AVT), InFlag};
   return DAG.getNode(X86ISD::REP_MOVS, dl, Tys, Ops);
 }

 /// Emit a single REP MOVSB instruction for a particular constant size.
 static SDValue emitRepmovsB(const X86Subtarget &Subtarget, SelectionDAG &DAG,
                             const SDLoc &dl, SDValue Chain, SDValue Dst,
                             SDValue Src, uint64_t Size) {
   return emitRepmovs(Subtarget, DAG, dl, Chain, Dst, Src,
                      DAG.getIntPtrConstant(Size, dl), MVT::i8);
 }

 /// Returns the best type to use with repmovs depending on alignment.
 static MVT getOptimalRepmovsType(const X86Subtarget &Subtarget,
                                  uint64_t Align) {
   assert((Align != 0) && "Align is normalized");
   assert(isPowerOf2_64(Align) && "Align is a power of 2");
   switch (Align) {
   case 1:
     return MVT::i8;
   case 2:
     return MVT::i16;
   case 4:
     return MVT::i32;
   default:
     return Subtarget.is64Bit() ? MVT::i64 : MVT::i32;
   }
 }

 /// Returns a REP MOVS instruction, possibly with a few load/stores to implement
 /// a constant size memory copy. In some cases where we know REP MOVS is
 /// inefficient we return an empty SDValue so the calling code can either
 /// generate a load/store sequence or call the runtime memcpy function.
 static SDValue emitConstantSizeRepmov(
     SelectionDAG &DAG, const X86Subtarget &Subtarget, const SDLoc &dl,
     SDValue Chain, SDValue Dst, SDValue Src, uint64_t Size, EVT SizeVT,
     unsigned Align, bool isVolatile, bool AlwaysInline,
     MachinePointerInfo DstPtrInfo, MachinePointerInfo SrcPtrInfo) {

   /// TODO: Revisit next line: big copy with ERMSB on march >= haswell are very
   /// efficient.
   if (!AlwaysInline && Size > Subtarget.getMaxInlineSizeThreshold())
     return SDValue();

   /// If we have enhanced repmovs we use it.
   if (Subtarget.hasERMSB())
     return emitRepmovsB(Subtarget, DAG, dl, Chain, Dst, Src, Size);

   assert(!Subtarget.hasERMSB() && "No efficient RepMovs");
   /// We assume runtime memcpy will do a better job for unaligned copies when
   /// ERMS is not present.
   if (!AlwaysInline && (Align & 3) != 0)
     return SDValue();

   const MVT BlockType = getOptimalRepmovsType(Subtarget, Align);
   const uint64_t BlockBytes = BlockType.getSizeInBits() / 8;
   const uint64_t BlockCount = Size / BlockBytes;
   const uint64_t BytesLeft = Size % BlockBytes;
   SDValue RepMovs =
       emitRepmovs(Subtarget, DAG, dl, Chain, Dst, Src,
                   DAG.getIntPtrConstant(BlockCount, dl), BlockType);

   /// RepMov can process the whole length.
   if (BytesLeft == 0)
     return RepMovs;

   assert(BytesLeft && "We have leftover at this point");

   /// In case we optimize for size we use repmovsb even if it's less efficient
   /// so we can save the loads/stores of the leftover.
   if (DAG.getMachineFunction().getFunction().hasMinSize())
     return emitRepmovsB(Subtarget, DAG, dl, Chain, Dst, Src, Size);

   // Handle the last 1 - 7 bytes.
   SmallVector<SDValue, 4> Results;
   Results.push_back(RepMovs);
   unsigned Offset = Size - BytesLeft;
   EVT DstVT = Dst.getValueType();
   EVT SrcVT = Src.getValueType();
   Results.push_back(DAG.getMemcpy(
       Chain, dl,
       DAG.getNode(ISD::ADD, dl, DstVT, Dst, DAG.getConstant(Offset, dl, DstVT)),
       DAG.getNode(ISD::ADD, dl, SrcVT, Src, DAG.getConstant(Offset, dl, SrcVT)),
       DAG.getConstant(BytesLeft, dl, SizeVT), llvm::Align(Align), isVolatile,
       /*AlwaysInline*/ true, /*isTailCall*/ false,
       DstPtrInfo.getWithOffset(Offset), SrcPtrInfo.getWithOffset(Offset)));
   return DAG.getNode(ISD::TokenFactor, dl, MVT::Other, Results);
 }

 SDValue X86SelectionDAGInfo::EmitTargetCodeForMemcpy(
     SelectionDAG &DAG, const SDLoc &dl, SDValue Chain, SDValue Dst, SDValue Src,
     SDValue Size, Align Alignment, bool isVolatile, bool AlwaysInline,
     MachinePointerInfo DstPtrInfo, MachinePointerInfo SrcPtrInfo) const {
   // If to a segment-relative address space, use the default lowering.
   if (DstPtrInfo.getAddrSpace() >= 256 || SrcPtrInfo.getAddrSpace() >= 256)
     return SDValue();

   // If the base registers conflict with our physical registers, use the default
   // lowering.
   const MCPhysReg ClobberSet[] = {X86::RCX, X86::RSI, X86::RDI,
                                   X86::ECX, X86::ESI, X86::EDI};
   if (isBaseRegConflictPossible(DAG, ClobberSet))
     return SDValue();

   const X86Subtarget &Subtarget =
       DAG.getMachineFunction().getSubtarget<X86Subtarget>();

   // If enabled and available, use fast short rep mov.
   if (UseFSRMForMemcpy && Subtarget.hasFSRM())
     return emitRepmovs(Subtarget, DAG, dl, Chain, Dst, Src, Size, MVT::i8);

   /// Handle constant sizes,
   if (ConstantSDNode *ConstantSize = dyn_cast<ConstantSDNode>(Size))
     return emitConstantSizeRepmov(
         DAG, Subtarget, dl, Chain, Dst, Src, ConstantSize->getZExtValue(),
         Size.getValueType(), Alignment.value(), isVolatile, AlwaysInline,
         DstPtrInfo, SrcPtrInfo);

   return SDValue();
 }
	//===-- X86SelectionDAGInfo.cpp - X86 SelectionDAG Info -------------------===//
	//
	// 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 implements the X86SelectionDAGInfo class.
	//
	//===----------------------------------------------------------------------===//

	#include "X86SelectionDAGInfo.h"
	#include "X86ISelLowering.h"
	#include "X86InstrInfo.h"
	#include "X86RegisterInfo.h"
	#include "X86Subtarget.h"
	#include "llvm/CodeGen/MachineFrameInfo.h"
	#include "llvm/CodeGen/SelectionDAG.h"
	#include "llvm/CodeGen/TargetLowering.h"
	#include "llvm/IR/DerivedTypes.h"

	using namespace llvm;

	#define DEBUG_TYPE "x86-selectiondag-info"

	static cl::opt<bool>
	UseFSRMForMemcpy("x86-use-fsrm-for-memcpy", cl::Hidden, cl::init(false),
	cl::desc("Use fast short rep mov in memcpy lowering"));

	bool X86SelectionDAGInfo::isBaseRegConflictPossible(
	SelectionDAG &DAG, ArrayRef<MCPhysReg> ClobberSet) const {
	// We cannot use TRI->hasBasePointer() until after we select all basic
	// blocks. Legalization may introduce new stack temporaries with large
	// alignment requirements. Fall back to generic code if there are any
	// dynamic stack adjustments (hopefully rare) and the base pointer would
	// conflict if we had to use it.
	MachineFrameInfo &MFI = DAG.getMachineFunction().getFrameInfo();
	if (!MFI.hasVarSizedObjects() && !MFI.hasOpaqueSPAdjustment())
	return false;

	const X86RegisterInfo TRI = static_cast<const X86RegisterInfo >(
	DAG.getSubtarget().getRegisterInfo());
	return llvm::is_contained(ClobberSet, TRI->getBaseRegister());
	}

	SDValue X86SelectionDAGInfo::EmitTargetCodeForMemset(
	SelectionDAG &DAG, const SDLoc &dl, SDValue Chain, SDValue Dst, SDValue Val,
	SDValue Size, Align Alignment, bool isVolatile,
	MachinePointerInfo DstPtrInfo) const {
	ConstantSDNode *ConstantSize = dyn_cast<ConstantSDNode>(Size);
	const X86Subtarget &Subtarget =
	DAG.getMachineFunction().getSubtarget<X86Subtarget>();

	#ifndef NDEBUG
	// If the base register might conflict with our physical registers, bail out.
	const MCPhysReg ClobberSet[] = {X86::RCX, X86::RAX, X86::RDI,
	X86::ECX, X86::EAX, X86::EDI};
	assert(!isBaseRegConflictPossible(DAG, ClobberSet));
	#endif

	// If to a segment-relative address space, use the default lowering.
	if (DstPtrInfo.getAddrSpace() >= 256)
	return SDValue();

	// If not DWORD aligned or size is more than the threshold, call the library.
	// The libc version is likely to be faster for these cases. It can use the
	// address value and run time information about the CPU.
	if (Alignment < Align(4) \|\| !ConstantSize \|\|
	ConstantSize->getZExtValue() > Subtarget.getMaxInlineSizeThreshold()) {
	// Check to see if there is a specialized entry-point for memory zeroing.
	ConstantSDNode *ValC = dyn_cast<ConstantSDNode>(Val);

	if (const char *bzeroName =
	(ValC && ValC->isZero())
	? DAG.getTargetLoweringInfo().getLibcallName(RTLIB::BZERO)
	: nullptr) {
	const TargetLowering &TLI = DAG.getTargetLoweringInfo();
	EVT IntPtr = TLI.getPointerTy(DAG.getDataLayout());
	Type IntPtrTy = DAG.getDataLayout().getIntPtrType(DAG.getContext());
	TargetLowering::ArgListTy Args;
	TargetLowering::ArgListEntry Entry;
	Entry.Node = Dst;
	Entry.Ty = IntPtrTy;
	Args.push_back(Entry);
	Entry.Node = Size;
	Args.push_back(Entry);

	TargetLowering::CallLoweringInfo CLI(DAG);
	CLI.setDebugLoc(dl)
	.setChain(Chain)
	.setLibCallee(CallingConv::C, Type::getVoidTy(*DAG.getContext()),
	DAG.getExternalSymbol(bzeroName, IntPtr),
	std::move(Args))
	.setDiscardResult();

	std::pair<SDValue,SDValue> CallResult = TLI.LowerCallTo(CLI);
	return CallResult.second;
	}

	// Otherwise have the target-independent code call memset.
	return SDValue();
	}

	uint64_t SizeVal = ConstantSize->getZExtValue();
	SDValue InFlag;
	EVT AVT;
	SDValue Count;
	ConstantSDNode *ValC = dyn_cast<ConstantSDNode>(Val);
	unsigned BytesLeft = 0;
	if (ValC) {
	unsigned ValReg;
	uint64_t Val = ValC->getZExtValue() & 255;

	// If the value is a constant, then we can potentially use larger sets.
	if (Alignment > Align(2)) {
	// DWORD aligned
	AVT = MVT::i32;
	ValReg = X86::EAX;
	Val = (Val << 8) \| Val;
	Val = (Val << 16) \| Val;
	if (Subtarget.is64Bit() && Alignment > Align(8)) { // QWORD aligned
	AVT = MVT::i64;
	ValReg = X86::RAX;
	Val = (Val << 32) \| Val;
	}
	} else if (Alignment == Align(2)) {
	// WORD aligned
	AVT = MVT::i16;
	ValReg = X86::AX;
	Val = (Val << 8) \| Val;
	} else {
	// Byte aligned
	AVT = MVT::i8;
	ValReg = X86::AL;
	Count = DAG.getIntPtrConstant(SizeVal, dl);
	}

	if (AVT.bitsGT(MVT::i8)) {
	unsigned UBytes = AVT.getSizeInBits() / 8;
	Count = DAG.getIntPtrConstant(SizeVal / UBytes, dl);
	BytesLeft = SizeVal % UBytes;
	}

	Chain = DAG.getCopyToReg(Chain, dl, ValReg, DAG.getConstant(Val, dl, AVT),
	InFlag);
	InFlag = Chain.getValue(1);
	} else {
	AVT = MVT::i8;
	Count = DAG.getIntPtrConstant(SizeVal, dl);
	Chain = DAG.getCopyToReg(Chain, dl, X86::AL, Val, InFlag);
	InFlag = Chain.getValue(1);
	}

	bool Use64BitRegs = Subtarget.isTarget64BitLP64();
	Chain = DAG.getCopyToReg(Chain, dl, Use64BitRegs ? X86::RCX : X86::ECX,
	Count, InFlag);
	InFlag = Chain.getValue(1);
	Chain = DAG.getCopyToReg(Chain, dl, Use64BitRegs ? X86::RDI : X86::EDI,
	Dst, InFlag);
	InFlag = Chain.getValue(1);

	SDVTList Tys = DAG.getVTList(MVT::Other, MVT::Glue);
	SDValue Ops[] = { Chain, DAG.getValueType(AVT), InFlag };
	Chain = DAG.getNode(X86ISD::REP_STOS, dl, Tys, Ops);

	if (BytesLeft) {
	// Handle the last 1 - 7 bytes.
	unsigned Offset = SizeVal - BytesLeft;
	EVT AddrVT = Dst.getValueType();
	EVT SizeVT = Size.getValueType();

	Chain =
	DAG.getMemset(Chain, dl,
	DAG.getNode(ISD::ADD, dl, AddrVT, Dst,
	DAG.getConstant(Offset, dl, AddrVT)),
	Val, DAG.getConstant(BytesLeft, dl, SizeVT), Alignment,
	isVolatile, false, DstPtrInfo.getWithOffset(Offset));
	}

	// TODO: Use a Tokenfactor, as in memcpy, instead of a single chain.
	return Chain;
	}

	/// Emit a single REP MOVS{B,W,D,Q} instruction.
	static SDValue emitRepmovs(const X86Subtarget &Subtarget, SelectionDAG &DAG,
	const SDLoc &dl, SDValue Chain, SDValue Dst,
	SDValue Src, SDValue Size, MVT AVT) {
	const bool Use64BitRegs = Subtarget.isTarget64BitLP64();
	const unsigned CX = Use64BitRegs ? X86::RCX : X86::ECX;
	const unsigned DI = Use64BitRegs ? X86::RDI : X86::EDI;
	const unsigned SI = Use64BitRegs ? X86::RSI : X86::ESI;

	SDValue InFlag;
	Chain = DAG.getCopyToReg(Chain, dl, CX, Size, InFlag);
	InFlag = Chain.getValue(1);
	Chain = DAG.getCopyToReg(Chain, dl, DI, Dst, InFlag);
	InFlag = Chain.getValue(1);
	Chain = DAG.getCopyToReg(Chain, dl, SI, Src, InFlag);
	InFlag = Chain.getValue(1);

	SDVTList Tys = DAG.getVTList(MVT::Other, MVT::Glue);
	SDValue Ops[] = {Chain, DAG.getValueType(AVT), InFlag};
	return DAG.getNode(X86ISD::REP_MOVS, dl, Tys, Ops);
	}

	/// Emit a single REP MOVSB instruction for a particular constant size.
	static SDValue emitRepmovsB(const X86Subtarget &Subtarget, SelectionDAG &DAG,
	const SDLoc &dl, SDValue Chain, SDValue Dst,
	SDValue Src, uint64_t Size) {
	return emitRepmovs(Subtarget, DAG, dl, Chain, Dst, Src,
	DAG.getIntPtrConstant(Size, dl), MVT::i8);
	}

	/// Returns the best type to use with repmovs depending on alignment.
	static MVT getOptimalRepmovsType(const X86Subtarget &Subtarget,
	uint64_t Align) {
	assert((Align != 0) && "Align is normalized");
	assert(isPowerOf2_64(Align) && "Align is a power of 2");
	switch (Align) {
	case 1:
	return MVT::i8;
	case 2:
	return MVT::i16;
	case 4:
	return MVT::i32;
	default:
	return Subtarget.is64Bit() ? MVT::i64 : MVT::i32;
	}
	}

	/// Returns a REP MOVS instruction, possibly with a few load/stores to implement
	/// a constant size memory copy. In some cases where we know REP MOVS is
	/// inefficient we return an empty SDValue so the calling code can either
	/// generate a load/store sequence or call the runtime memcpy function.
	static SDValue emitConstantSizeRepmov(
	SelectionDAG &DAG, const X86Subtarget &Subtarget, const SDLoc &dl,
	SDValue Chain, SDValue Dst, SDValue Src, uint64_t Size, EVT SizeVT,
	unsigned Align, bool isVolatile, bool AlwaysInline,
	MachinePointerInfo DstPtrInfo, MachinePointerInfo SrcPtrInfo) {

	/// TODO: Revisit next line: big copy with ERMSB on march >= haswell are very
	/// efficient.
	if (!AlwaysInline && Size > Subtarget.getMaxInlineSizeThreshold())
	return SDValue();

	/// If we have enhanced repmovs we use it.
	if (Subtarget.hasERMSB())
	return emitRepmovsB(Subtarget, DAG, dl, Chain, Dst, Src, Size);

	assert(!Subtarget.hasERMSB() && "No efficient RepMovs");
	/// We assume runtime memcpy will do a better job for unaligned copies when
	/// ERMS is not present.
	if (!AlwaysInline && (Align & 3) != 0)
	return SDValue();

	const MVT BlockType = getOptimalRepmovsType(Subtarget, Align);
	const uint64_t BlockBytes = BlockType.getSizeInBits() / 8;
	const uint64_t BlockCount = Size / BlockBytes;
	const uint64_t BytesLeft = Size % BlockBytes;
	SDValue RepMovs =
	emitRepmovs(Subtarget, DAG, dl, Chain, Dst, Src,
	DAG.getIntPtrConstant(BlockCount, dl), BlockType);

	/// RepMov can process the whole length.
	if (BytesLeft == 0)
	return RepMovs;

	assert(BytesLeft && "We have leftover at this point");

	/// In case we optimize for size we use repmovsb even if it's less efficient
	/// so we can save the loads/stores of the leftover.
	if (DAG.getMachineFunction().getFunction().hasMinSize())
	return emitRepmovsB(Subtarget, DAG, dl, Chain, Dst, Src, Size);

	// Handle the last 1 - 7 bytes.
	SmallVector<SDValue, 4> Results;
	Results.push_back(RepMovs);
	unsigned Offset = Size - BytesLeft;
	EVT DstVT = Dst.getValueType();
	EVT SrcVT = Src.getValueType();
	Results.push_back(DAG.getMemcpy(
	Chain, dl,
	DAG.getNode(ISD::ADD, dl, DstVT, Dst, DAG.getConstant(Offset, dl, DstVT)),
	DAG.getNode(ISD::ADD, dl, SrcVT, Src, DAG.getConstant(Offset, dl, SrcVT)),
	DAG.getConstant(BytesLeft, dl, SizeVT), llvm::Align(Align), isVolatile,
	/AlwaysInline/ true, /isTailCall/ false,
	DstPtrInfo.getWithOffset(Offset), SrcPtrInfo.getWithOffset(Offset)));
	return DAG.getNode(ISD::TokenFactor, dl, MVT::Other, Results);
	}

	SDValue X86SelectionDAGInfo::EmitTargetCodeForMemcpy(
	SelectionDAG &DAG, const SDLoc &dl, SDValue Chain, SDValue Dst, SDValue Src,
	SDValue Size, Align Alignment, bool isVolatile, bool AlwaysInline,
	MachinePointerInfo DstPtrInfo, MachinePointerInfo SrcPtrInfo) const {
	// If to a segment-relative address space, use the default lowering.
	if (DstPtrInfo.getAddrSpace() >= 256 \|\| SrcPtrInfo.getAddrSpace() >= 256)
	return SDValue();

	// If the base registers conflict with our physical registers, use the default
	// lowering.
	const MCPhysReg ClobberSet[] = {X86::RCX, X86::RSI, X86::RDI,
	X86::ECX, X86::ESI, X86::EDI};
	if (isBaseRegConflictPossible(DAG, ClobberSet))
	return SDValue();

	const X86Subtarget &Subtarget =
	DAG.getMachineFunction().getSubtarget<X86Subtarget>();

	// If enabled and available, use fast short rep mov.
	if (UseFSRMForMemcpy && Subtarget.hasFSRM())
	return emitRepmovs(Subtarget, DAG, dl, Chain, Dst, Src, Size, MVT::i8);

	/// Handle constant sizes,
	if (ConstantSDNode *ConstantSize = dyn_cast<ConstantSDNode>(Size))
	return emitConstantSizeRepmov(
	DAG, Subtarget, dl, Chain, Dst, Src, ConstantSize->getZExtValue(),
	Size.getValueType(), Alignment.value(), isVolatile, AlwaysInline,
	DstPtrInfo, SrcPtrInfo);

	return SDValue();
	}