X86SelectionDAGInfo.cpp

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//===-- 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"
 
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"));
 
/// Returns the best type to use with repmovs/repstos depending on alignment.
static MVT getOptimalRepType(const X86Subtarget &Subtarget, Align Alignment) {
  uint64_t Align = Alignment.value();
  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;
  }
}
 
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());
}
 
/// Emit a single REP STOSB instruction for a particular constant size.
static SDValue emitRepstos(const X86Subtarget &Subtarget, SelectionDAG &DAG,
                           const SDLoc &dl, SDValue Chain, SDValue Dst,
                           SDValue Val, SDValue Size, MVT AVT) {
  const bool Use64BitRegs = Subtarget.isTarget64BitLP64();
  unsigned AX = X86::AL;
  switch (AVT.getSizeInBits()) {
  case 8:
    AX = X86::AL;
    break;
  case 16:
    AX = X86::AX;
    break;
  case 32:
    AX = X86::EAX;
    break;
  default:
    AX = X86::RAX;
    break;
  }
 
  const unsigned CX = Use64BitRegs ? X86::RCX : X86::ECX;
  const unsigned DI = Use64BitRegs ? X86::RDI : X86::EDI;
 
  SDValue InGlue;
  Chain = DAG.getCopyToReg(Chain, dl, AX, Val, InGlue);
  InGlue = Chain.getValue(1);
  Chain = DAG.getCopyToReg(Chain, dl, CX, Size, InGlue);
  InGlue = Chain.getValue(1);
  Chain = DAG.getCopyToReg(Chain, dl, DI, Dst, InGlue);
  InGlue = Chain.getValue(1);
 
  SDVTList Tys = DAG.getVTList(MVT::Other, MVT::Glue);
  SDValue Ops[] = {Chain, DAG.getValueType(AVT), InGlue};
  return DAG.getNode(X86ISD::REP_STOS, dl, Tys, Ops);
}
 
/// Emit a single REP STOSB instruction for a particular constant size.
static SDValue emitRepstosB(const X86Subtarget &Subtarget, SelectionDAG &DAG,
                            const SDLoc &dl, SDValue Chain, SDValue Dst,
                            SDValue Val, uint64_t Size) {
  return emitRepstos(Subtarget, DAG, dl, Chain, Dst, Val,
                     DAG.getIntPtrConstant(Size, dl), MVT::i8);
}
 
/// Returns a REP STOS instruction, possibly with a few load/stores to implement
/// a constant size memory set. In some cases where we know REP MOVS is
/// inefficient we return an empty SDValue so the calling code can either
/// generate a store sequence or call the runtime memset function.
static SDValue emitConstantSizeRepstos(SelectionDAG &DAG,
                                       const X86Subtarget &Subtarget,
                                       const SDLoc &dl, SDValue Chain,
                                       SDValue Dst, SDValue Val, uint64_t Size,
                                       EVT SizeVT, Align Alignment,
                                       bool isVolatile, bool AlwaysInline,
                                       MachinePointerInfo DstPtrInfo) {
  /// In case we optimize for size, we use repstosb even if it's less efficient
  /// so we can save the loads/stores of the leftover.
  if (DAG.getMachineFunction().getFunction().hasMinSize()) {
    if (auto *ValC = dyn_cast<ConstantSDNode>(Val)) {
      // Special case 0 because otherwise we get large literals,
      // which causes larger encoding.
      if ((Size & 31) == 0 && (ValC->getZExtValue() & 255) == 0) {
        MVT BlockType = MVT::i32;
        const uint64_t BlockBits = BlockType.getSizeInBits();
        const uint64_t BlockBytes = BlockBits / 8;
        const uint64_t BlockCount = Size / BlockBytes;
 
        Val = DAG.getConstant(0, dl, BlockType);
        // repstosd is same size as repstosb
        return emitRepstos(Subtarget, DAG, dl, Chain, Dst, Val,
                           DAG.getIntPtrConstant(BlockCount, dl), BlockType);
      }
    }
    return emitRepstosB(Subtarget, DAG, dl, Chain, Dst, Val, Size);
  }
 
  if (Size > Subtarget.getMaxInlineSizeThreshold())
    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))
    return SDValue();
 
  MVT BlockType = MVT::i8;
  uint64_t BlockCount = Size;
  uint64_t BytesLeft = 0;
 
  SDValue OriginalVal = Val;
  if (auto *ValC = dyn_cast<ConstantSDNode>(Val)) {
    BlockType = getOptimalRepType(Subtarget, Alignment);
    uint64_t Value = ValC->getZExtValue() & 255;
    const uint64_t BlockBits = BlockType.getSizeInBits();
 
    if (BlockBits >= 16)
      Value = (Value << 8) | Value;
 
    if (BlockBits >= 32)
      Value = (Value << 16) | Value;
 
    if (BlockBits >= 64)
      Value = (Value << 32) | Value;
 
    const uint64_t BlockBytes = BlockBits / 8;
    BlockCount = Size / BlockBytes;
    BytesLeft = Size % BlockBytes;
    Val = DAG.getConstant(Value, dl, BlockType);
  }
 
  SDValue RepStos =
      emitRepstos(Subtarget, DAG, dl, Chain, Dst, Val,
                  DAG.getIntPtrConstant(BlockCount, dl), BlockType);
  /// RepStos can process the whole length.
  if (BytesLeft == 0)
    return RepStos;
 
  // Handle the last 1 - 7 bytes.
  SmallVector<SDValue, 4> Results;
  Results.push_back(RepStos);
  unsigned Offset = Size - BytesLeft;
  EVT AddrVT = Dst.getValueType();
 
  Results.push_back(
      DAG.getMemset(Chain, dl,
                    DAG.getNode(ISD::ADD, dl, AddrVT, Dst,
                                DAG.getConstant(Offset, dl, AddrVT)),
                    OriginalVal, DAG.getConstant(BytesLeft, dl, SizeVT),
                    Alignment, isVolatile, AlwaysInline,
                    /* CI */ nullptr, DstPtrInfo.getWithOffset(Offset)));
 
  return DAG.getNode(ISD::TokenFactor, dl, MVT::Other, Results);
}
 
SDValue X86SelectionDAGInfo::EmitTargetCodeForMemset(
    SelectionDAG &DAG, const SDLoc &dl, SDValue Chain, SDValue Dst, SDValue Val,
    SDValue Size, Align Alignment, bool isVolatile, bool AlwaysInline,
    MachinePointerInfo DstPtrInfo) const {
  // If to a segment-relative address space, use the default lowering.
  if (DstPtrInfo.getAddrSpace() >= 256)
    return SDValue();
 
  // 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};
  if (isBaseRegConflictPossible(DAG, ClobberSet))
    return SDValue();
 
  ConstantSDNode *ConstantSize = dyn_cast<ConstantSDNode>(Size);
  if (!ConstantSize)
    return SDValue();
 
  const X86Subtarget &Subtarget =
      DAG.getMachineFunction().getSubtarget<X86Subtarget>();
  return emitConstantSizeRepstos(
      DAG, Subtarget, dl, Chain, Dst, Val, ConstantSize->getZExtValue(),
      Size.getValueType(), Alignment, isVolatile, AlwaysInline, DstPtrInfo);
}
 
/// 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 InGlue;
  Chain = DAG.getCopyToReg(Chain, dl, CX, Size, InGlue);
  InGlue = Chain.getValue(1);
  Chain = DAG.getCopyToReg(Chain, dl, DI, Dst, InGlue);
  InGlue = Chain.getValue(1);
  Chain = DAG.getCopyToReg(Chain, dl, SI, Src, InGlue);
  InGlue = Chain.getValue(1);
 
  SDVTList Tys = DAG.getVTList(MVT::Other, MVT::Glue);
  SDValue Ops[] = {Chain, DAG.getValueType(AVT), InGlue};
  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 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,
    Align Alignment, bool isVolatile, bool AlwaysInline,
    MachinePointerInfo DstPtrInfo, MachinePointerInfo SrcPtrInfo) {
  /// 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);
 
  /// 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 && (Alignment < Align(4)))
    return SDValue();
 
  const MVT BlockType = getOptimalRepType(Subtarget, Alignment);
  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");
 
  // 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), Alignment, isVolatile,
      /*AlwaysInline*/ true, /*CI=*/nullptr, std::nullopt,
      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, isVolatile,
                                  AlwaysInline, DstPtrInfo, SrcPtrInfo);
 
  return SDValue();
}