//===-- SIFoldOperands.cpp - Fold operands --- ----------------------------===//
//
// 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
//
/// \file
//===----------------------------------------------------------------------===//
//

#include "SIFoldOperands.h"
#include "AMDGPU.h"
#include "GCNSubtarget.h"
#include "MCTargetDesc/AMDGPUMCTargetDesc.h"
#include "SIInstrInfo.h"
#include "SIMachineFunctionInfo.h"
#include "SIRegisterInfo.h"
#include "llvm/ADT/DepthFirstIterator.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineOperand.h"

#define DEBUG_TYPE "si-fold-operands"
using namespace llvm;

namespace {

struct FoldCandidate {
  MachineInstr *UseMI;
  union {
    MachineOperand *OpToFold;
    uint64_t ImmToFold;
    int FrameIndexToFold;
  };
  int ShrinkOpcode;
  unsigned UseOpNo;
  MachineOperand::MachineOperandType Kind;
  bool Commuted;

  FoldCandidate(MachineInstr *MI, unsigned OpNo, MachineOperand *FoldOp,
                bool Commuted_ = false,
                int ShrinkOp = -1) :
    UseMI(MI), OpToFold(nullptr), ShrinkOpcode(ShrinkOp), UseOpNo(OpNo),
    Kind(FoldOp->getType()),
    Commuted(Commuted_) {
    if (FoldOp->isImm()) {
      ImmToFold = FoldOp->getImm();
    } else if (FoldOp->isFI()) {
      FrameIndexToFold = FoldOp->getIndex();
    } else {
      assert(FoldOp->isReg() || FoldOp->isGlobal());
      OpToFold = FoldOp;
    }
  }

  FoldCandidate(MachineInstr *MI, unsigned OpNo, int64_t FoldImm,
                bool Commuted_ = false, int ShrinkOp = -1)
      : UseMI(MI), ImmToFold(FoldImm), ShrinkOpcode(ShrinkOp), UseOpNo(OpNo),
        Kind(MachineOperand::MO_Immediate), Commuted(Commuted_) {}

  bool isFI() const {
    return Kind == MachineOperand::MO_FrameIndex;
  }

  bool isImm() const {
    return Kind == MachineOperand::MO_Immediate;
  }

  bool isReg() const {
    return Kind == MachineOperand::MO_Register;
  }

  bool isGlobal() const { return Kind == MachineOperand::MO_GlobalAddress; }

  bool needsShrink() const { return ShrinkOpcode != -1; }
};

class SIFoldOperandsImpl {
public:
  MachineRegisterInfo *MRI;
  const SIInstrInfo *TII;
  const SIRegisterInfo *TRI;
  const GCNSubtarget *ST;
  const SIMachineFunctionInfo *MFI;

  bool frameIndexMayFold(const MachineInstr &UseMI, int OpNo,
                         const MachineOperand &OpToFold) const;

  // TODO: Just use TII::getVALUOp
  unsigned convertToVALUOp(unsigned Opc, bool UseVOP3 = false) const {
    switch (Opc) {
    case AMDGPU::S_ADD_I32: {
      if (ST->hasAddNoCarry())
        return UseVOP3 ? AMDGPU::V_ADD_U32_e64 : AMDGPU::V_ADD_U32_e32;
      return UseVOP3 ? AMDGPU::V_ADD_CO_U32_e64 : AMDGPU::V_ADD_CO_U32_e32;
    }
    case AMDGPU::S_OR_B32:
      return UseVOP3 ? AMDGPU::V_OR_B32_e64 : AMDGPU::V_OR_B32_e32;
    case AMDGPU::S_AND_B32:
      return UseVOP3 ? AMDGPU::V_AND_B32_e64 : AMDGPU::V_AND_B32_e32;
    case AMDGPU::S_MUL_I32:
      return AMDGPU::V_MUL_LO_U32_e64;
    default:
      return AMDGPU::INSTRUCTION_LIST_END;
    }
  }

  bool foldCopyToVGPROfScalarAddOfFrameIndex(Register DstReg, Register SrcReg,
                                             MachineInstr &MI) const;

  bool updateOperand(FoldCandidate &Fold) const;

  bool canUseImmWithOpSel(FoldCandidate &Fold) const;

  bool tryFoldImmWithOpSel(FoldCandidate &Fold) const;

  bool tryAddToFoldList(SmallVectorImpl<FoldCandidate> &FoldList,
                        MachineInstr *MI, unsigned OpNo,
                        MachineOperand *OpToFold) const;
  bool isUseSafeToFold(const MachineInstr &MI,
                       const MachineOperand &UseMO) const;
  bool
  getRegSeqInit(SmallVectorImpl<std::pair<MachineOperand *, unsigned>> &Defs,
                Register UseReg, uint8_t OpTy) const;
  bool tryToFoldACImm(MachineOperand &OpToFold, MachineInstr *UseMI,
                      unsigned UseOpIdx,
                      SmallVectorImpl<FoldCandidate> &FoldList) const;
  void foldOperand(MachineOperand &OpToFold,
                   MachineInstr *UseMI,
                   int UseOpIdx,
                   SmallVectorImpl<FoldCandidate> &FoldList,
                   SmallVectorImpl<MachineInstr *> &CopiesToReplace) const;

  std::optional<int64_t> getImmOrMaterializedImm(MachineOperand &Op) const;
  bool tryConstantFoldOp(MachineInstr *MI) const;
  bool tryFoldCndMask(MachineInstr &MI) const;
  bool tryFoldZeroHighBits(MachineInstr &MI) const;
  bool foldInstOperand(MachineInstr &MI, MachineOperand &OpToFold) const;

  bool foldCopyToAGPRRegSequence(MachineInstr *CopyMI) const;
  bool tryFoldFoldableCopy(MachineInstr &MI,
                           MachineOperand *&CurrentKnownM0Val) const;

  const MachineOperand *isClamp(const MachineInstr &MI) const;
  bool tryFoldClamp(MachineInstr &MI);

  std::pair<const MachineOperand *, int> isOMod(const MachineInstr &MI) const;
  bool tryFoldOMod(MachineInstr &MI);
  bool tryFoldRegSequence(MachineInstr &MI);
  bool tryFoldPhiAGPR(MachineInstr &MI);
  bool tryFoldLoad(MachineInstr &MI);

  bool tryOptimizeAGPRPhis(MachineBasicBlock &MBB);

public:
  SIFoldOperandsImpl() = default;

  bool run(MachineFunction &MF);
};

class SIFoldOperandsLegacy : public MachineFunctionPass {
public:
  static char ID;

  SIFoldOperandsLegacy() : MachineFunctionPass(ID) {}

  bool runOnMachineFunction(MachineFunction &MF) override {
    if (skipFunction(MF.getFunction()))
      return false;
    return SIFoldOperandsImpl().run(MF);
  }

  StringRef getPassName() const override { return "SI Fold Operands"; }

  void getAnalysisUsage(AnalysisUsage &AU) const override {
    AU.setPreservesCFG();
    MachineFunctionPass::getAnalysisUsage(AU);
  }

  MachineFunctionProperties getRequiredProperties() const override {
    return MachineFunctionProperties().set(
        MachineFunctionProperties::Property::IsSSA);
  }
};

} // End anonymous namespace.

INITIALIZE_PASS(SIFoldOperandsLegacy, DEBUG_TYPE, "SI Fold Operands", false,
                false)

char SIFoldOperandsLegacy::ID = 0;

char &llvm::SIFoldOperandsLegacyID = SIFoldOperandsLegacy::ID;

static const TargetRegisterClass *getRegOpRC(const MachineRegisterInfo &MRI,
                                             const TargetRegisterInfo &TRI,
                                             const MachineOperand &MO) {
  const TargetRegisterClass *RC = MRI.getRegClass(MO.getReg());
  if (const TargetRegisterClass *SubRC =
          TRI.getSubRegisterClass(RC, MO.getSubReg()))
    RC = SubRC;
  return RC;
}

// Map multiply-accumulate opcode to corresponding multiply-add opcode if any.
static unsigned macToMad(unsigned Opc) {
  switch (Opc) {
  case AMDGPU::V_MAC_F32_e64:
    return AMDGPU::V_MAD_F32_e64;
  case AMDGPU::V_MAC_F16_e64:
    return AMDGPU::V_MAD_F16_e64;
  case AMDGPU::V_FMAC_F32_e64:
    return AMDGPU::V_FMA_F32_e64;
  case AMDGPU::V_FMAC_F16_e64:
    return AMDGPU::V_FMA_F16_gfx9_e64;
  case AMDGPU::V_FMAC_F16_t16_e64:
    return AMDGPU::V_FMA_F16_gfx9_t16_e64;
  case AMDGPU::V_FMAC_F16_fake16_e64:
    return AMDGPU::V_FMA_F16_gfx9_fake16_e64;
  case AMDGPU::V_FMAC_LEGACY_F32_e64:
    return AMDGPU::V_FMA_LEGACY_F32_e64;
  case AMDGPU::V_FMAC_F64_e64:
    return AMDGPU::V_FMA_F64_e64;
  }
  return AMDGPU::INSTRUCTION_LIST_END;
}

// TODO: Add heuristic that the frame index might not fit in the addressing mode
// immediate offset to avoid materializing in loops.
bool SIFoldOperandsImpl::frameIndexMayFold(
    const MachineInstr &UseMI, int OpNo, const MachineOperand &OpToFold) const {
  if (!OpToFold.isFI())
    return false;

  const unsigned Opc = UseMI.getOpcode();
  switch (Opc) {
  case AMDGPU::S_ADD_I32:
  case AMDGPU::S_ADD_U32:
  case AMDGPU::V_ADD_U32_e32:
  case AMDGPU::V_ADD_CO_U32_e32:
    // TODO: Possibly relax hasOneUse. It matters more for mubuf, since we have
    // to insert the wave size shift at every point we use the index.
    // TODO: Fix depending on visit order to fold immediates into the operand
    return UseMI.getOperand(OpNo == 1 ? 2 : 1).isImm() &&
           MRI->hasOneNonDBGUse(UseMI.getOperand(OpNo).getReg());
  case AMDGPU::V_ADD_U32_e64:
  case AMDGPU::V_ADD_CO_U32_e64:
    return UseMI.getOperand(OpNo == 2 ? 3 : 2).isImm() &&
           MRI->hasOneNonDBGUse(UseMI.getOperand(OpNo).getReg());
  default:
    break;
  }

  if (TII->isMUBUF(UseMI))
    return OpNo == AMDGPU::getNamedOperandIdx(Opc, AMDGPU::OpName::vaddr);
  if (!TII->isFLATScratch(UseMI))
    return false;

  int SIdx = AMDGPU::getNamedOperandIdx(Opc, AMDGPU::OpName::saddr);
  if (OpNo == SIdx)
    return true;

  int VIdx = AMDGPU::getNamedOperandIdx(Opc, AMDGPU::OpName::vaddr);
  return OpNo == VIdx && SIdx == -1;
}

/// Fold %vgpr = COPY (S_ADD_I32 x, frameindex)
///
///   => %vgpr = V_ADD_U32 x, frameindex
bool SIFoldOperandsImpl::foldCopyToVGPROfScalarAddOfFrameIndex(
    Register DstReg, Register SrcReg, MachineInstr &MI) const {
  if (TRI->isVGPR(*MRI, DstReg) && TRI->isSGPRReg(*MRI, SrcReg) &&
      MRI->hasOneNonDBGUse(SrcReg)) {
    MachineInstr *Def = MRI->getVRegDef(SrcReg);
    if (!Def || Def->getNumOperands() != 4)
      return false;

    MachineOperand *Src0 = &Def->getOperand(1);
    MachineOperand *Src1 = &Def->getOperand(2);

    // TODO: This is profitable with more operand types, and for more
    // opcodes. But ultimately this is working around poor / nonexistent
    // regbankselect.
    if (!Src0->isFI() && !Src1->isFI())
      return false;

    if (Src0->isFI())
      std::swap(Src0, Src1);

    const bool UseVOP3 = !Src0->isImm() || TII->isInlineConstant(*Src0);
    unsigned NewOp = convertToVALUOp(Def->getOpcode(), UseVOP3);
    if (NewOp == AMDGPU::INSTRUCTION_LIST_END ||
        !Def->getOperand(3).isDead()) // Check if scc is dead
      return false;

    MachineBasicBlock *MBB = Def->getParent();
    const DebugLoc &DL = Def->getDebugLoc();
    if (NewOp != AMDGPU::V_ADD_CO_U32_e32) {
      MachineInstrBuilder Add =
          BuildMI(*MBB, *Def, DL, TII->get(NewOp), DstReg);

      if (Add->getDesc().getNumDefs() == 2) {
        Register CarryOutReg = MRI->createVirtualRegister(TRI->getBoolRC());
        Add.addDef(CarryOutReg, RegState::Dead);
        MRI->setRegAllocationHint(CarryOutReg, 0, TRI->getVCC());
      }

      Add.add(*Src0).add(*Src1).setMIFlags(Def->getFlags());
      if (AMDGPU::hasNamedOperand(NewOp, AMDGPU::OpName::clamp))
        Add.addImm(0);

      Def->eraseFromParent();
      MI.eraseFromParent();
      return true;
    }

    assert(NewOp == AMDGPU::V_ADD_CO_U32_e32);

    MachineBasicBlock::LivenessQueryResult Liveness =
        MBB->computeRegisterLiveness(TRI, AMDGPU::VCC, *Def, 16);
    if (Liveness == MachineBasicBlock::LQR_Dead) {
      // TODO: If src1 satisfies operand constraints, use vop3 version.
      BuildMI(*MBB, *Def, DL, TII->get(NewOp), DstReg)
          .add(*Src0)
          .add(*Src1)
          .setOperandDead(3) // implicit-def $vcc
          .setMIFlags(Def->getFlags());
      Def->eraseFromParent();
      MI.eraseFromParent();
      return true;
    }
  }

  return false;
}

FunctionPass *llvm::createSIFoldOperandsLegacyPass() {
  return new SIFoldOperandsLegacy();
}

bool SIFoldOperandsImpl::canUseImmWithOpSel(FoldCandidate &Fold) const {
  MachineInstr *MI = Fold.UseMI;
  MachineOperand &Old = MI->getOperand(Fold.UseOpNo);
  const uint64_t TSFlags = MI->getDesc().TSFlags;

  assert(Old.isReg() && Fold.isImm());

  if (!(TSFlags & SIInstrFlags::IsPacked) || (TSFlags & SIInstrFlags::IsMAI) ||
      (TSFlags & SIInstrFlags::IsWMMA) || (TSFlags & SIInstrFlags::IsSWMMAC) ||
      (ST->hasDOTOpSelHazard() && (TSFlags & SIInstrFlags::IsDOT)))
    return false;

  unsigned Opcode = MI->getOpcode();
  int OpNo = MI->getOperandNo(&Old);
  uint8_t OpType = TII->get(Opcode).operands()[OpNo].OperandType;
  switch (OpType) {
  default:
    return false;
  case AMDGPU::OPERAND_REG_IMM_V2FP16:
  case AMDGPU::OPERAND_REG_IMM_V2BF16:
  case AMDGPU::OPERAND_REG_IMM_V2INT16:
  case AMDGPU::OPERAND_REG_INLINE_C_V2FP16:
  case AMDGPU::OPERAND_REG_INLINE_C_V2BF16:
  case AMDGPU::OPERAND_REG_INLINE_C_V2INT16:
    break;
  }

  return true;
}

bool SIFoldOperandsImpl::tryFoldImmWithOpSel(FoldCandidate &Fold) const {
  MachineInstr *MI = Fold.UseMI;
  MachineOperand &Old = MI->getOperand(Fold.UseOpNo);
  unsigned Opcode = MI->getOpcode();
  int OpNo = MI->getOperandNo(&Old);
  uint8_t OpType = TII->get(Opcode).operands()[OpNo].OperandType;

  // If the literal can be inlined as-is, apply it and short-circuit the
  // tests below. The main motivation for this is to avoid unintuitive
  // uses of opsel.
  if (AMDGPU::isInlinableLiteralV216(Fold.ImmToFold, OpType)) {
    Old.ChangeToImmediate(Fold.ImmToFold);
    return true;
  }

  // Refer to op_sel/op_sel_hi and check if we can change the immediate and
  // op_sel in a way that allows an inline constant.
  AMDGPU::OpName ModName = AMDGPU::OpName::NUM_OPERAND_NAMES;
  unsigned SrcIdx = ~0;
  if (OpNo == AMDGPU::getNamedOperandIdx(Opcode, AMDGPU::OpName::src0)) {
    ModName = AMDGPU::OpName::src0_modifiers;
    SrcIdx = 0;
  } else if (OpNo == AMDGPU::getNamedOperandIdx(Opcode, AMDGPU::OpName::src1)) {
    ModName = AMDGPU::OpName::src1_modifiers;
    SrcIdx = 1;
  } else if (OpNo == AMDGPU::getNamedOperandIdx(Opcode, AMDGPU::OpName::src2)) {
    ModName = AMDGPU::OpName::src2_modifiers;
    SrcIdx = 2;
  }
  assert(ModName != AMDGPU::OpName::NUM_OPERAND_NAMES);
  int ModIdx = AMDGPU::getNamedOperandIdx(Opcode, ModName);
  MachineOperand &Mod = MI->getOperand(ModIdx);
  unsigned ModVal = Mod.getImm();

  uint16_t ImmLo = static_cast<uint16_t>(
      Fold.ImmToFold >> (ModVal & SISrcMods::OP_SEL_0 ? 16 : 0));
  uint16_t ImmHi = static_cast<uint16_t>(
      Fold.ImmToFold >> (ModVal & SISrcMods::OP_SEL_1 ? 16 : 0));
  uint32_t Imm = (static_cast<uint32_t>(ImmHi) << 16) | ImmLo;
  unsigned NewModVal = ModVal & ~(SISrcMods::OP_SEL_0 | SISrcMods::OP_SEL_1);

  // Helper function that attempts to inline the given value with a newly
  // chosen opsel pattern.
  auto tryFoldToInline = [&](uint32_t Imm) -> bool {
    if (AMDGPU::isInlinableLiteralV216(Imm, OpType)) {
      Mod.setImm(NewModVal | SISrcMods::OP_SEL_1);
      Old.ChangeToImmediate(Imm);
      return true;
    }

    // Try to shuffle the halves around and leverage opsel to get an inline
    // constant.
    uint16_t Lo = static_cast<uint16_t>(Imm);
    uint16_t Hi = static_cast<uint16_t>(Imm >> 16);
    if (Lo == Hi) {
      if (AMDGPU::isInlinableLiteralV216(Lo, OpType)) {
        Mod.setImm(NewModVal);
        Old.ChangeToImmediate(Lo);
        return true;
      }

      if (static_cast<int16_t>(Lo) < 0) {
        int32_t SExt = static_cast<int16_t>(Lo);
        if (AMDGPU::isInlinableLiteralV216(SExt, OpType)) {
          Mod.setImm(NewModVal);
          Old.ChangeToImmediate(SExt);
          return true;
        }
      }

      // This check is only useful for integer instructions
      if (OpType == AMDGPU::OPERAND_REG_IMM_V2INT16 ||
          OpType == AMDGPU::OPERAND_REG_INLINE_AC_V2INT16) {
        if (AMDGPU::isInlinableLiteralV216(Lo << 16, OpType)) {
          Mod.setImm(NewModVal | SISrcMods::OP_SEL_0 | SISrcMods::OP_SEL_1);
          Old.ChangeToImmediate(static_cast<uint32_t>(Lo) << 16);
          return true;
        }
      }
    } else {
      uint32_t Swapped = (static_cast<uint32_t>(Lo) << 16) | Hi;
      if (AMDGPU::isInlinableLiteralV216(Swapped, OpType)) {
        Mod.setImm(NewModVal | SISrcMods::OP_SEL_0);
        Old.ChangeToImmediate(Swapped);
        return true;
      }
    }

    return false;
  };

  if (tryFoldToInline(Imm))
    return true;

  // Replace integer addition by subtraction and vice versa if it allows
  // folding the immediate to an inline constant.
  //
  // We should only ever get here for SrcIdx == 1 due to canonicalization
  // earlier in the pipeline, but we double-check here to be safe / fully
  // general.
  bool IsUAdd = Opcode == AMDGPU::V_PK_ADD_U16;
  bool IsUSub = Opcode == AMDGPU::V_PK_SUB_U16;
  if (SrcIdx == 1 && (IsUAdd || IsUSub)) {
    unsigned ClampIdx =
        AMDGPU::getNamedOperandIdx(Opcode, AMDGPU::OpName::clamp);
    bool Clamp = MI->getOperand(ClampIdx).getImm() != 0;

    if (!Clamp) {
      uint16_t NegLo = -static_cast<uint16_t>(Imm);
      uint16_t NegHi = -static_cast<uint16_t>(Imm >> 16);
      uint32_t NegImm = (static_cast<uint32_t>(NegHi) << 16) | NegLo;

      if (tryFoldToInline(NegImm)) {
        unsigned NegOpcode =
            IsUAdd ? AMDGPU::V_PK_SUB_U16 : AMDGPU::V_PK_ADD_U16;
        MI->setDesc(TII->get(NegOpcode));
        return true;
      }
    }
  }

  return false;
}

bool SIFoldOperandsImpl::updateOperand(FoldCandidate &Fold) const {
  MachineInstr *MI = Fold.UseMI;
  MachineOperand &Old = MI->getOperand(Fold.UseOpNo);
  assert(Old.isReg());

  if (Fold.isImm() && canUseImmWithOpSel(Fold)) {
    if (tryFoldImmWithOpSel(Fold))
      return true;

    // We can't represent the candidate as an inline constant. Try as a literal
    // with the original opsel, checking constant bus limitations.
    MachineOperand New = MachineOperand::CreateImm(Fold.ImmToFold);
    int OpNo = MI->getOperandNo(&Old);
    if (!TII->isOperandLegal(*MI, OpNo, &New))
      return false;
    Old.ChangeToImmediate(Fold.ImmToFold);
    return true;
  }

  if ((Fold.isImm() || Fold.isFI() || Fold.isGlobal()) && Fold.needsShrink()) {
    MachineBasicBlock *MBB = MI->getParent();
    auto Liveness = MBB->computeRegisterLiveness(TRI, AMDGPU::VCC, MI, 16);
    if (Liveness != MachineBasicBlock::LQR_Dead) {
      LLVM_DEBUG(dbgs() << "Not shrinking " << MI << " due to vcc liveness\n");
      return false;
    }

    int Op32 = Fold.ShrinkOpcode;
    MachineOperand &Dst0 = MI->getOperand(0);
    MachineOperand &Dst1 = MI->getOperand(1);
    assert(Dst0.isDef() && Dst1.isDef());

    bool HaveNonDbgCarryUse = !MRI->use_nodbg_empty(Dst1.getReg());

    const TargetRegisterClass *Dst0RC = MRI->getRegClass(Dst0.getReg());
    Register NewReg0 = MRI->createVirtualRegister(Dst0RC);

    MachineInstr *Inst32 = TII->buildShrunkInst(*MI, Op32);

    if (HaveNonDbgCarryUse) {
      BuildMI(*MBB, MI, MI->getDebugLoc(), TII->get(AMDGPU::COPY),
              Dst1.getReg())
        .addReg(AMDGPU::VCC, RegState::Kill);
    }

    // Keep the old instruction around to avoid breaking iterators, but
    // replace it with a dummy instruction to remove uses.
    //
    // FIXME: We should not invert how this pass looks at operands to avoid
    // this. Should track set of foldable movs instead of looking for uses
    // when looking at a use.
    Dst0.setReg(NewReg0);
    for (unsigned I = MI->getNumOperands() - 1; I > 0; --I)
      MI->removeOperand(I);
    MI->setDesc(TII->get(AMDGPU::IMPLICIT_DEF));

    if (Fold.Commuted)
      TII->commuteInstruction(*Inst32, false);
    return true;
  }

  assert(!Fold.needsShrink() && "not handled");

  if (Fold.isImm()) {
    if (Old.isTied()) {
      int NewMFMAOpc = AMDGPU::getMFMAEarlyClobberOp(MI->getOpcode());
      if (NewMFMAOpc == -1)
        return false;
      MI->setDesc(TII->get(NewMFMAOpc));
      MI->untieRegOperand(0);
    }
    Old.ChangeToImmediate(Fold.ImmToFold);
    return true;
  }

  if (Fold.isGlobal()) {
    Old.ChangeToGA(Fold.OpToFold->getGlobal(), Fold.OpToFold->getOffset(),
                   Fold.OpToFold->getTargetFlags());
    return true;
  }

  if (Fold.isFI()) {
    Old.ChangeToFrameIndex(Fold.FrameIndexToFold);
    return true;
  }

  MachineOperand *New = Fold.OpToFold;
  // Rework once the VS_16 register class is updated to include proper
  // 16-bit SGPRs instead of 32-bit ones.
  if (Old.getSubReg() == AMDGPU::lo16 && TRI->isSGPRReg(*MRI, New->getReg()))
    Old.setSubReg(AMDGPU::NoSubRegister);
  Old.substVirtReg(New->getReg(), New->getSubReg(), *TRI);
  Old.setIsUndef(New->isUndef());
  return true;
}

static void appendFoldCandidate(SmallVectorImpl<FoldCandidate> &FoldList,
                                FoldCandidate &&Entry) {
  // Skip additional folding on the same operand.
  for (FoldCandidate &Fold : FoldList)
    if (Fold.UseMI == Entry.UseMI && Fold.UseOpNo == Entry.UseOpNo)
      return;
  LLVM_DEBUG(dbgs() << "Append " << (Entry.Commuted ? "commuted" : "normal")
                    << " operand " << Entry.UseOpNo << "\n  " << *Entry.UseMI);
  FoldList.push_back(Entry);
}

static void appendFoldCandidate(SmallVectorImpl<FoldCandidate> &FoldList,
                                MachineInstr *MI, unsigned OpNo,
                                MachineOperand *FoldOp, bool Commuted = false,
                                int ShrinkOp = -1) {
  appendFoldCandidate(FoldList,
                      FoldCandidate(MI, OpNo, FoldOp, Commuted, ShrinkOp));
}

static void appendFoldCandidate(SmallVectorImpl<FoldCandidate> &FoldList,
                                MachineInstr *MI, unsigned OpNo, int64_t ImmVal,
                                bool Commuted = false, int ShrinkOp = -1) {
  appendFoldCandidate(FoldList,
                      FoldCandidate(MI, OpNo, ImmVal, Commuted, ShrinkOp));
}

bool SIFoldOperandsImpl::tryAddToFoldList(
    SmallVectorImpl<FoldCandidate> &FoldList, MachineInstr *MI, unsigned OpNo,
    MachineOperand *OpToFold) const {
  const unsigned Opc = MI->getOpcode();

  auto tryToFoldAsFMAAKorMK = [&]() {
    if (!OpToFold->isImm())
      return false;

    const bool TryAK = OpNo == 3;
    const unsigned NewOpc = TryAK ? AMDGPU::S_FMAAK_F32 : AMDGPU::S_FMAMK_F32;
    MI->setDesc(TII->get(NewOpc));

    // We have to fold into operand which would be Imm not into OpNo.
    bool FoldAsFMAAKorMK =
        tryAddToFoldList(FoldList, MI, TryAK ? 3 : 2, OpToFold);
    if (FoldAsFMAAKorMK) {
      // Untie Src2 of fmac.
      MI->untieRegOperand(3);
      // For fmamk swap operands 1 and 2 if OpToFold was meant for operand 1.
      if (OpNo == 1) {
        MachineOperand &Op1 = MI->getOperand(1);
        MachineOperand &Op2 = MI->getOperand(2);
        Register OldReg = Op1.getReg();
        // Operand 2 might be an inlinable constant
        if (Op2.isImm()) {
          Op1.ChangeToImmediate(Op2.getImm());
          Op2.ChangeToRegister(OldReg, false);
        } else {
          Op1.setReg(Op2.getReg());
          Op2.setReg(OldReg);
        }
      }
      return true;
    }
    MI->setDesc(TII->get(Opc));
    return false;
  };

  bool IsLegal = TII->isOperandLegal(*MI, OpNo, OpToFold);
  if (!IsLegal && OpToFold->isImm()) {
    FoldCandidate Fold(MI, OpNo, OpToFold);
    IsLegal = canUseImmWithOpSel(Fold);
  }

  if (!IsLegal) {
    // Special case for v_mac_{f16, f32}_e64 if we are trying to fold into src2
    unsigned NewOpc = macToMad(Opc);
    if (NewOpc != AMDGPU::INSTRUCTION_LIST_END) {
      // Check if changing this to a v_mad_{f16, f32} instruction will allow us
      // to fold the operand.
      MI->setDesc(TII->get(NewOpc));
      bool AddOpSel = !AMDGPU::hasNamedOperand(Opc, AMDGPU::OpName::op_sel) &&
                      AMDGPU::hasNamedOperand(NewOpc, AMDGPU::OpName::op_sel);
      if (AddOpSel)
        MI->addOperand(MachineOperand::CreateImm(0));
      bool FoldAsMAD = tryAddToFoldList(FoldList, MI, OpNo, OpToFold);
      if (FoldAsMAD) {
        MI->untieRegOperand(OpNo);
        return true;
      }
      if (AddOpSel)
        MI->removeOperand(MI->getNumExplicitOperands() - 1);
      MI->setDesc(TII->get(Opc));
    }

    // Special case for s_fmac_f32 if we are trying to fold into Src2.
    // By transforming into fmaak we can untie Src2 and make folding legal.
    if (Opc == AMDGPU::S_FMAC_F32 && OpNo == 3) {
      if (tryToFoldAsFMAAKorMK())
        return true;
    }

    // Special case for s_setreg_b32
    if (OpToFold->isImm()) {
      unsigned ImmOpc = 0;
      if (Opc == AMDGPU::S_SETREG_B32)
        ImmOpc = AMDGPU::S_SETREG_IMM32_B32;
      else if (Opc == AMDGPU::S_SETREG_B32_mode)
        ImmOpc = AMDGPU::S_SETREG_IMM32_B32_mode;
      if (ImmOpc) {
        MI->setDesc(TII->get(ImmOpc));
        appendFoldCandidate(FoldList, MI, OpNo, OpToFold);
        return true;
      }
    }

    // Operand is not legal, so try to commute the instruction to
    // see if this makes it possible to fold.
    unsigned CommuteOpNo = TargetInstrInfo::CommuteAnyOperandIndex;
    bool CanCommute = TII->findCommutedOpIndices(*MI, OpNo, CommuteOpNo);
    if (!CanCommute)
      return false;

    MachineOperand &Op = MI->getOperand(OpNo);
    MachineOperand &CommutedOp = MI->getOperand(CommuteOpNo);

    // One of operands might be an Imm operand, and OpNo may refer to it after
    // the call of commuteInstruction() below. Such situations are avoided
    // here explicitly as OpNo must be a register operand to be a candidate
    // for memory folding.
    if (!Op.isReg() || !CommutedOp.isReg())
      return false;

    // The same situation with an immediate could reproduce if both inputs are
    // the same register.
    if (Op.isReg() && CommutedOp.isReg() &&
        (Op.getReg() == CommutedOp.getReg() &&
         Op.getSubReg() == CommutedOp.getSubReg()))
      return false;

    if (!TII->commuteInstruction(*MI, false, OpNo, CommuteOpNo))
      return false;

    int Op32 = -1;
    if (!TII->isOperandLegal(*MI, CommuteOpNo, OpToFold)) {
      if ((Opc != AMDGPU::V_ADD_CO_U32_e64 && Opc != AMDGPU::V_SUB_CO_U32_e64 &&
           Opc != AMDGPU::V_SUBREV_CO_U32_e64) || // FIXME
          (!OpToFold->isImm() && !OpToFold->isFI() && !OpToFold->isGlobal())) {
        TII->commuteInstruction(*MI, false, OpNo, CommuteOpNo);
        return false;
      }

      // Verify the other operand is a VGPR, otherwise we would violate the
      // constant bus restriction.
      MachineOperand &OtherOp = MI->getOperand(OpNo);
      if (!OtherOp.isReg() ||
          !TII->getRegisterInfo().isVGPR(*MRI, OtherOp.getReg()))
        return false;

      assert(MI->getOperand(1).isDef());

      // Make sure to get the 32-bit version of the commuted opcode.
      unsigned MaybeCommutedOpc = MI->getOpcode();
      Op32 = AMDGPU::getVOPe32(MaybeCommutedOpc);
    }

    appendFoldCandidate(FoldList, MI, CommuteOpNo, OpToFold, true, Op32);
    return true;
  }

  // Inlineable constant might have been folded into Imm operand of fmaak or
  // fmamk and we are trying to fold a non-inlinable constant.
  if ((Opc == AMDGPU::S_FMAAK_F32 || Opc == AMDGPU::S_FMAMK_F32) &&
      !OpToFold->isReg() && !TII->isInlineConstant(*OpToFold)) {
    unsigned ImmIdx = Opc == AMDGPU::S_FMAAK_F32 ? 3 : 2;
    MachineOperand &OpImm = MI->getOperand(ImmIdx);
    if (!OpImm.isReg() &&
        TII->isInlineConstant(*MI, MI->getOperand(OpNo), OpImm))
      return tryToFoldAsFMAAKorMK();
  }

  // Special case for s_fmac_f32 if we are trying to fold into Src0 or Src1.
  // By changing into fmamk we can untie Src2.
  // If folding for Src0 happens first and it is identical operand to Src1 we
  // should avoid transforming into fmamk which requires commuting as it would
  // cause folding into Src1 to fail later on due to wrong OpNo used.
  if (Opc == AMDGPU::S_FMAC_F32 &&
      (OpNo != 1 || !MI->getOperand(1).isIdenticalTo(MI->getOperand(2)))) {
    if (tryToFoldAsFMAAKorMK())
      return true;
  }

  // Check the case where we might introduce a second constant operand to a
  // scalar instruction
  if (TII->isSALU(MI->getOpcode())) {
    const MCInstrDesc &InstDesc = MI->getDesc();
    const MCOperandInfo &OpInfo = InstDesc.operands()[OpNo];

    // Fine if the operand can be encoded as an inline constant
    if (!OpToFold->isReg() && !TII->isInlineConstant(*OpToFold, OpInfo)) {
      // Otherwise check for another constant
      for (unsigned i = 0, e = InstDesc.getNumOperands(); i != e; ++i) {
        auto &Op = MI->getOperand(i);
        if (OpNo != i && !Op.isReg() &&
            !TII->isInlineConstant(Op, InstDesc.operands()[i]))
          return false;
      }
    }
  }

  appendFoldCandidate(FoldList, MI, OpNo, OpToFold);
  return true;
}

bool SIFoldOperandsImpl::isUseSafeToFold(const MachineInstr &MI,
                                         const MachineOperand &UseMO) const {
  // Operands of SDWA instructions must be registers.
  return !TII->isSDWA(MI);
}

static MachineOperand *lookUpCopyChain(const SIInstrInfo &TII,
                                       const MachineRegisterInfo &MRI,
                                       Register SrcReg) {
  MachineOperand *Sub = nullptr;
  for (MachineInstr *SubDef = MRI.getVRegDef(SrcReg);
       SubDef && TII.isFoldableCopy(*SubDef);
       SubDef = MRI.getVRegDef(Sub->getReg())) {
    MachineOperand &SrcOp = SubDef->getOperand(1);
    if (SrcOp.isImm())
      return &SrcOp;
    if (!SrcOp.isReg() || SrcOp.getReg().isPhysical())
      break;
    Sub = &SrcOp;
    // TODO: Support compose
    if (SrcOp.getSubReg())
      break;
  }

  return Sub;
}

// Find a def of the UseReg, check if it is a reg_sequence and find initializers
// for each subreg, tracking it to foldable inline immediate if possible.
// Returns true on success.
bool SIFoldOperandsImpl::getRegSeqInit(
    SmallVectorImpl<std::pair<MachineOperand *, unsigned>> &Defs,
    Register UseReg, uint8_t OpTy) const {
  MachineInstr *Def = MRI->getVRegDef(UseReg);
  if (!Def || !Def->isRegSequence())
    return false;

  for (unsigned I = 1, E = Def->getNumExplicitOperands(); I != E; I += 2) {
    MachineOperand &SrcOp = Def->getOperand(I);
    unsigned SubRegIdx = Def->getOperand(I + 1).getImm();

    if (SrcOp.getSubReg()) {
      // TODO: Handle subregister compose
      Defs.emplace_back(&SrcOp, SubRegIdx);
      continue;
    }

    MachineOperand *DefSrc = lookUpCopyChain(*TII, *MRI, SrcOp.getReg());
    if (DefSrc && (DefSrc->isReg() ||
                   (DefSrc->isImm() && TII->isInlineConstant(*DefSrc, OpTy)))) {
      Defs.emplace_back(DefSrc, SubRegIdx);
      continue;
    }

    Defs.emplace_back(&SrcOp, SubRegIdx);
  }

  return true;
}

bool SIFoldOperandsImpl::tryToFoldACImm(
    MachineOperand &OpToFold, MachineInstr *UseMI, unsigned UseOpIdx,
    SmallVectorImpl<FoldCandidate> &FoldList) const {
  const MCInstrDesc &Desc = UseMI->getDesc();
  if (UseOpIdx >= Desc.getNumOperands())
    return false;

  // Filter out unhandled pseudos.
  if (!AMDGPU::isSISrcOperand(Desc, UseOpIdx))
    return false;

  uint8_t OpTy = Desc.operands()[UseOpIdx].OperandType;
  MachineOperand &UseOp = UseMI->getOperand(UseOpIdx);
  if (OpToFold.isImm()) {
    if (unsigned UseSubReg = UseOp.getSubReg()) {
      std::optional<int64_t> SubImm =
          SIInstrInfo::extractSubregFromImm(OpToFold.getImm(), UseSubReg);
      if (!SubImm)
        return false;

      // TODO: Avoid the temporary MachineOperand
      MachineOperand TmpOp = MachineOperand::CreateImm(*SubImm);
      if (TII->isOperandLegal(*UseMI, UseOpIdx, &TmpOp)) {
        appendFoldCandidate(FoldList, UseMI, UseOpIdx, *SubImm);
        return true;
      }

      return false;
    }

    if (TII->isOperandLegal(*UseMI, UseOpIdx, &OpToFold)) {
      appendFoldCandidate(FoldList, UseMI, UseOpIdx, &OpToFold);
      return true;
    }
  }

  // TODO: Verify the following code handles subregisters correctly.
  // TODO: Handle extract of global reference
  if (UseOp.getSubReg())
    return false;

  if (!OpToFold.isReg())
    return false;

  Register UseReg = OpToFold.getReg();
  if (!UseReg.isVirtual())
    return false;

  // Maybe it is just a COPY of an immediate itself.
  MachineInstr *Def = MRI->getVRegDef(UseReg);
  if (Def && TII->isFoldableCopy(*Def)) {
    MachineOperand &DefOp = Def->getOperand(1);
    if (DefOp.isImm() && TII->isOperandLegal(*UseMI, UseOpIdx, &DefOp)) {
      appendFoldCandidate(FoldList, UseMI, UseOpIdx, &DefOp);
      return true;
    }
  }

  SmallVector<std::pair<MachineOperand*, unsigned>, 32> Defs;
  if (!getRegSeqInit(Defs, UseReg, OpTy))
    return false;

  int32_t Imm;
  for (unsigned I = 0, E = Defs.size(); I != E; ++I) {
    const MachineOperand *Op = Defs[I].first;
    if (!Op->isImm())
      return false;

    auto SubImm = Op->getImm();
    if (!I) {
      Imm = SubImm;
      if (!TII->isInlineConstant(*Op, OpTy) ||
          !TII->isOperandLegal(*UseMI, UseOpIdx, Op))
        return false;

      continue;
    }
    if (Imm != SubImm)
      return false; // Can only fold splat constants
  }

  appendFoldCandidate(FoldList, UseMI, UseOpIdx, Defs[0].first);
  return true;
}

void SIFoldOperandsImpl::foldOperand(
    MachineOperand &OpToFold, MachineInstr *UseMI, int UseOpIdx,
    SmallVectorImpl<FoldCandidate> &FoldList,
    SmallVectorImpl<MachineInstr *> &CopiesToReplace) const {
  const MachineOperand *UseOp = &UseMI->getOperand(UseOpIdx);

  if (!isUseSafeToFold(*UseMI, *UseOp))
    return;

  // FIXME: Fold operands with subregs.
  if (UseOp->isReg() && OpToFold.isReg()) {
    if (UseOp->isImplicit())
      return;
    // Allow folding from SGPRs to 16-bit VGPRs.
    if (UseOp->getSubReg() != AMDGPU::NoSubRegister &&
        (UseOp->getSubReg() != AMDGPU::lo16 ||
         !TRI->isSGPRReg(*MRI, OpToFold.getReg())))
      return;
  }

  // Special case for REG_SEQUENCE: We can't fold literals into
  // REG_SEQUENCE instructions, so we have to fold them into the
  // uses of REG_SEQUENCE.
  if (UseMI->isRegSequence()) {
    Register RegSeqDstReg = UseMI->getOperand(0).getReg();
    unsigned RegSeqDstSubReg = UseMI->getOperand(UseOpIdx + 1).getImm();

    // Grab the use operands first
    SmallVector<MachineOperand *, 4> UsesToProcess;
    for (auto &Use : MRI->use_nodbg_operands(RegSeqDstReg))
      UsesToProcess.push_back(&Use);
    for (auto *RSUse : UsesToProcess) {
      MachineInstr *RSUseMI = RSUse->getParent();

      if (tryToFoldACImm(UseMI->getOperand(0), RSUseMI,
                         RSUseMI->getOperandNo(RSUse), FoldList))
        continue;

      if (RSUse->getSubReg() != RegSeqDstSubReg)
        continue;

      foldOperand(OpToFold, RSUseMI, RSUseMI->getOperandNo(RSUse), FoldList,
                  CopiesToReplace);
    }
    return;
  }

  if (tryToFoldACImm(OpToFold, UseMI, UseOpIdx, FoldList))
    return;

  if (frameIndexMayFold(*UseMI, UseOpIdx, OpToFold)) {
    // Verify that this is a stack access.
    // FIXME: Should probably use stack pseudos before frame lowering.

    if (TII->isMUBUF(*UseMI)) {
      if (TII->getNamedOperand(*UseMI, AMDGPU::OpName::srsrc)->getReg() !=
          MFI->getScratchRSrcReg())
        return;

      // Ensure this is either relative to the current frame or the current
      // wave.
      MachineOperand &SOff =
          *TII->getNamedOperand(*UseMI, AMDGPU::OpName::soffset);
      if (!SOff.isImm() || SOff.getImm() != 0)
        return;
    }

    // A frame index will resolve to a positive constant, so it should always be
    // safe to fold the addressing mode, even pre-GFX9.
    UseMI->getOperand(UseOpIdx).ChangeToFrameIndex(OpToFold.getIndex());

    const unsigned Opc = UseMI->getOpcode();
    if (TII->isFLATScratch(*UseMI) &&
        AMDGPU::hasNamedOperand(Opc, AMDGPU::OpName::vaddr) &&
        !AMDGPU::hasNamedOperand(Opc, AMDGPU::OpName::saddr)) {
      unsigned NewOpc = AMDGPU::getFlatScratchInstSSfromSV(Opc);
      UseMI->setDesc(TII->get(NewOpc));
    }

    return;
  }

  bool FoldingImmLike =
      OpToFold.isImm() || OpToFold.isFI() || OpToFold.isGlobal();

  if (FoldingImmLike && UseMI->isCopy()) {
    Register DestReg = UseMI->getOperand(0).getReg();
    Register SrcReg = UseMI->getOperand(1).getReg();
    assert(SrcReg.isVirtual());

    const TargetRegisterClass *SrcRC = MRI->getRegClass(SrcReg);

    // Don't fold into a copy to a physical register with the same class. Doing
    // so would interfere with the register coalescer's logic which would avoid
    // redundant initializations.
    if (DestReg.isPhysical() && SrcRC->contains(DestReg))
      return;

    const TargetRegisterClass *DestRC = TRI->getRegClassForReg(*MRI, DestReg);
    if (!DestReg.isPhysical()) {
      if (DestRC == &AMDGPU::AGPR_32RegClass &&
          TII->isInlineConstant(OpToFold, AMDGPU::OPERAND_REG_INLINE_C_INT32)) {
        UseMI->setDesc(TII->get(AMDGPU::V_ACCVGPR_WRITE_B32_e64));
        UseMI->getOperand(1).ChangeToImmediate(OpToFold.getImm());
        CopiesToReplace.push_back(UseMI);
        return;
      }
    }

    // Allow immediates COPYd into sgpr_lo16 to be further folded while
    // still being legal if not further folded
    if (DestRC == &AMDGPU::SGPR_LO16RegClass) {
      assert(ST->useRealTrue16Insts());
      MRI->setRegClass(DestReg, &AMDGPU::SGPR_32RegClass);
      DestRC = &AMDGPU::SGPR_32RegClass;
    }

    // In order to fold immediates into copies, we need to change the
    // copy to a MOV.

    unsigned MovOp = TII->getMovOpcode(DestRC);
    if (MovOp == AMDGPU::COPY)
      return;

    MachineInstr::mop_iterator ImpOpI = UseMI->implicit_operands().begin();
    MachineInstr::mop_iterator ImpOpE = UseMI->implicit_operands().end();
    while (ImpOpI != ImpOpE) {
      MachineInstr::mop_iterator Tmp = ImpOpI;
      ImpOpI++;
      UseMI->removeOperand(UseMI->getOperandNo(Tmp));
    }
    UseMI->setDesc(TII->get(MovOp));

    if (MovOp == AMDGPU::V_MOV_B16_t16_e64) {
      const auto &SrcOp = UseMI->getOperand(UseOpIdx);
      MachineOperand NewSrcOp(SrcOp);
      MachineFunction *MF = UseMI->getParent()->getParent();
      UseMI->removeOperand(1);
      UseMI->addOperand(*MF, MachineOperand::CreateImm(0)); // src0_modifiers
      UseMI->addOperand(NewSrcOp);                          // src0
      UseMI->addOperand(*MF, MachineOperand::CreateImm(0)); // op_sel
      UseOpIdx = 2;
      UseOp = &UseMI->getOperand(UseOpIdx);
    }
    CopiesToReplace.push_back(UseMI);
  } else {
    if (UseMI->isCopy() && OpToFold.isReg() &&
        UseMI->getOperand(0).getReg().isVirtual() &&
        !UseMI->getOperand(1).getSubReg()) {
      LLVM_DEBUG(dbgs() << "Folding " << OpToFold << "\n into " << *UseMI);
      unsigned Size = TII->getOpSize(*UseMI, 1);
      Register UseReg = OpToFold.getReg();
      UseMI->getOperand(1).setReg(UseReg);
      unsigned SubRegIdx = OpToFold.getSubReg();
      // Hack to allow 32-bit SGPRs to be folded into True16 instructions
      // Remove this if 16-bit SGPRs (i.e. SGPR_LO16) are added to the
      // VS_16RegClass
      //
      // Excerpt from AMDGPUGenRegisterInfo.inc
      // NoSubRegister, //0
      // hi16, // 1
      // lo16, // 2
      // sub0, // 3
      // ...
      // sub1, // 11
      // sub1_hi16, // 12
      // sub1_lo16, // 13
      static_assert(AMDGPU::sub1_hi16 == 12, "Subregister layout has changed");
      if (Size == 2 && TRI->isVGPR(*MRI, UseMI->getOperand(0).getReg()) &&
          TRI->isSGPRReg(*MRI, UseReg)) {
        // Produce the 32 bit subregister index to which the 16-bit subregister
        // is aligned.
        if (SubRegIdx > AMDGPU::sub1) {
          LaneBitmask M = TRI->getSubRegIndexLaneMask(SubRegIdx);
          M |= M.getLane(M.getHighestLane() - 1);
          SmallVector<unsigned, 4> Indexes;
          TRI->getCoveringSubRegIndexes(TRI->getRegClassForReg(*MRI, UseReg), M,
                                        Indexes);
          assert(Indexes.size() == 1 && "Expected one 32-bit subreg to cover");
          SubRegIdx = Indexes[0];
          // 32-bit registers do not have a sub0 index
        } else if (TII->getOpSize(*UseMI, 1) == 4)
          SubRegIdx = 0;
        else
          SubRegIdx = AMDGPU::sub0;
      }
      UseMI->getOperand(1).setSubReg(SubRegIdx);
      UseMI->getOperand(1).setIsKill(false);
      CopiesToReplace.push_back(UseMI);
      OpToFold.setIsKill(false);

      // Remove kill flags as kills may now be out of order with uses.
      MRI->clearKillFlags(UseReg);
      if (foldCopyToAGPRRegSequence(UseMI))
        return;
    }

    unsigned UseOpc = UseMI->getOpcode();
    if (UseOpc == AMDGPU::V_READFIRSTLANE_B32 ||
        (UseOpc == AMDGPU::V_READLANE_B32 &&
         (int)UseOpIdx ==
         AMDGPU::getNamedOperandIdx(UseOpc, AMDGPU::OpName::src0))) {
      // %vgpr = V_MOV_B32 imm
      // %sgpr = V_READFIRSTLANE_B32 %vgpr
      // =>
      // %sgpr = S_MOV_B32 imm
      if (FoldingImmLike) {
        if (execMayBeModifiedBeforeUse(*MRI,
                                       UseMI->getOperand(UseOpIdx).getReg(),
                                       *OpToFold.getParent(),
                                       *UseMI))
          return;

        UseMI->setDesc(TII->get(AMDGPU::S_MOV_B32));

        if (OpToFold.isImm())
          UseMI->getOperand(1).ChangeToImmediate(OpToFold.getImm());
        else
          UseMI->getOperand(1).ChangeToFrameIndex(OpToFold.getIndex());
        UseMI->removeOperand(2); // Remove exec read (or src1 for readlane)
        return;
      }

      if (OpToFold.isReg() && TRI->isSGPRReg(*MRI, OpToFold.getReg())) {
        if (execMayBeModifiedBeforeUse(*MRI,
                                       UseMI->getOperand(UseOpIdx).getReg(),
                                       *OpToFold.getParent(),
                                       *UseMI))
          return;

        // %vgpr = COPY %sgpr0
        // %sgpr1 = V_READFIRSTLANE_B32 %vgpr
        // =>
        // %sgpr1 = COPY %sgpr0
        UseMI->setDesc(TII->get(AMDGPU::COPY));
        UseMI->getOperand(1).setReg(OpToFold.getReg());
        UseMI->getOperand(1).setSubReg(OpToFold.getSubReg());
        UseMI->getOperand(1).setIsKill(false);
        UseMI->removeOperand(2); // Remove exec read (or src1 for readlane)
        return;
      }
    }

    const MCInstrDesc &UseDesc = UseMI->getDesc();

    // Don't fold into target independent nodes.  Target independent opcodes
    // don't have defined register classes.
    if (UseDesc.isVariadic() || UseOp->isImplicit() ||
        UseDesc.operands()[UseOpIdx].RegClass == -1)
      return;
  }

  if (!FoldingImmLike) {
    if (OpToFold.isReg() && ST->needsAlignedVGPRs()) {
      // Don't fold if OpToFold doesn't hold an aligned register.
      const TargetRegisterClass *RC =
          TRI->getRegClassForReg(*MRI, OpToFold.getReg());
      assert(RC);
      if (TRI->hasVectorRegisters(RC) && OpToFold.getSubReg()) {
        unsigned SubReg = OpToFold.getSubReg();
        if (const TargetRegisterClass *SubRC =
                TRI->getSubRegisterClass(RC, SubReg))
          RC = SubRC;
      }

      if (!RC || !TRI->isProperlyAlignedRC(*RC))
        return;
    }

    tryAddToFoldList(FoldList, UseMI, UseOpIdx, &OpToFold);

    // FIXME: We could try to change the instruction from 64-bit to 32-bit
    // to enable more folding opportunities.  The shrink operands pass
    // already does this.
    return;
  }


  const MCInstrDesc &FoldDesc = OpToFold.getParent()->getDesc();
  const TargetRegisterClass *FoldRC =
      TRI->getRegClass(FoldDesc.operands()[0].RegClass);

  // Split 64-bit constants into 32-bits for folding.
  if (UseOp->getSubReg() && AMDGPU::getRegBitWidth(*FoldRC) == 64) {
    Register UseReg = UseOp->getReg();
    const TargetRegisterClass *UseRC = MRI->getRegClass(UseReg);
    if (AMDGPU::getRegBitWidth(*UseRC) != 64)
      return;

    APInt Imm(64, OpToFold.getImm());
    if (UseOp->getSubReg() == AMDGPU::sub0) {
      Imm = Imm.getLoBits(32);
    } else {
      assert(UseOp->getSubReg() == AMDGPU::sub1);
      Imm = Imm.getHiBits(32);
    }

    MachineOperand ImmOp = MachineOperand::CreateImm(Imm.getSExtValue());
    tryAddToFoldList(FoldList, UseMI, UseOpIdx, &ImmOp);
    return;
  }

  tryAddToFoldList(FoldList, UseMI, UseOpIdx, &OpToFold);
}

static bool evalBinaryInstruction(unsigned Opcode, int32_t &Result,
                                  uint32_t LHS, uint32_t RHS) {
  switch (Opcode) {
  case AMDGPU::V_AND_B32_e64:
  case AMDGPU::V_AND_B32_e32:
  case AMDGPU::S_AND_B32:
    Result = LHS & RHS;
    return true;
  case AMDGPU::V_OR_B32_e64:
  case AMDGPU::V_OR_B32_e32:
  case AMDGPU::S_OR_B32:
    Result = LHS | RHS;
    return true;
  case AMDGPU::V_XOR_B32_e64:
  case AMDGPU::V_XOR_B32_e32:
  case AMDGPU::S_XOR_B32:
    Result = LHS ^ RHS;
    return true;
  case AMDGPU::S_XNOR_B32:
    Result = ~(LHS ^ RHS);
    return true;
  case AMDGPU::S_NAND_B32:
    Result = ~(LHS & RHS);
    return true;
  case AMDGPU::S_NOR_B32:
    Result = ~(LHS | RHS);
    return true;
  case AMDGPU::S_ANDN2_B32:
    Result = LHS & ~RHS;
    return true;
  case AMDGPU::S_ORN2_B32:
    Result = LHS | ~RHS;
    return true;
  case AMDGPU::V_LSHL_B32_e64:
  case AMDGPU::V_LSHL_B32_e32:
  case AMDGPU::S_LSHL_B32:
    // The instruction ignores the high bits for out of bounds shifts.
    Result = LHS << (RHS & 31);
    return true;
  case AMDGPU::V_LSHLREV_B32_e64:
  case AMDGPU::V_LSHLREV_B32_e32:
    Result = RHS << (LHS & 31);
    return true;
  case AMDGPU::V_LSHR_B32_e64:
  case AMDGPU::V_LSHR_B32_e32:
  case AMDGPU::S_LSHR_B32:
    Result = LHS >> (RHS & 31);
    return true;
  case AMDGPU::V_LSHRREV_B32_e64:
  case AMDGPU::V_LSHRREV_B32_e32:
    Result = RHS >> (LHS & 31);
    return true;
  case AMDGPU::V_ASHR_I32_e64:
  case AMDGPU::V_ASHR_I32_e32:
  case AMDGPU::S_ASHR_I32:
    Result = static_cast<int32_t>(LHS) >> (RHS & 31);
    return true;
  case AMDGPU::V_ASHRREV_I32_e64:
  case AMDGPU::V_ASHRREV_I32_e32:
    Result = static_cast<int32_t>(RHS) >> (LHS & 31);
    return true;
  default:
    return false;
  }
}

static unsigned getMovOpc(bool IsScalar) {
  return IsScalar ? AMDGPU::S_MOV_B32 : AMDGPU::V_MOV_B32_e32;
}

static void mutateCopyOp(MachineInstr &MI, const MCInstrDesc &NewDesc) {
  MI.setDesc(NewDesc);

  // Remove any leftover implicit operands from mutating the instruction. e.g.
  // if we replace an s_and_b32 with a copy, we don't need the implicit scc def
  // anymore.
  const MCInstrDesc &Desc = MI.getDesc();
  unsigned NumOps = Desc.getNumOperands() + Desc.implicit_uses().size() +
                    Desc.implicit_defs().size();

  for (unsigned I = MI.getNumOperands() - 1; I >= NumOps; --I)
    MI.removeOperand(I);
}

std::optional<int64_t>
SIFoldOperandsImpl::getImmOrMaterializedImm(MachineOperand &Op) const {
  if (Op.isImm())
    return Op.getImm();

  if (!Op.isReg() || !Op.getReg().isVirtual())
    return std::nullopt;

  const MachineInstr *Def = MRI->getVRegDef(Op.getReg());
  if (Def && Def->isMoveImmediate()) {
    const MachineOperand &ImmSrc = Def->getOperand(1);
    if (ImmSrc.isImm())
      return TII->extractSubregFromImm(ImmSrc.getImm(), Op.getSubReg());
  }

  return std::nullopt;
}

// Try to simplify operations with a constant that may appear after instruction
// selection.
// TODO: See if a frame index with a fixed offset can fold.
bool SIFoldOperandsImpl::tryConstantFoldOp(MachineInstr *MI) const {
  if (!MI->allImplicitDefsAreDead())
    return false;

  unsigned Opc = MI->getOpcode();

  int Src0Idx = AMDGPU::getNamedOperandIdx(Opc, AMDGPU::OpName::src0);
  if (Src0Idx == -1)
    return false;

  MachineOperand *Src0 = &MI->getOperand(Src0Idx);
  std::optional<int64_t> Src0Imm = getImmOrMaterializedImm(*Src0);

  if ((Opc == AMDGPU::V_NOT_B32_e64 || Opc == AMDGPU::V_NOT_B32_e32 ||
       Opc == AMDGPU::S_NOT_B32) &&
      Src0Imm) {
    MI->getOperand(1).ChangeToImmediate(~*Src0Imm);
    mutateCopyOp(*MI, TII->get(getMovOpc(Opc == AMDGPU::S_NOT_B32)));
    return true;
  }

  int Src1Idx = AMDGPU::getNamedOperandIdx(Opc, AMDGPU::OpName::src1);
  if (Src1Idx == -1)
    return false;

  MachineOperand *Src1 = &MI->getOperand(Src1Idx);
  std::optional<int64_t> Src1Imm = getImmOrMaterializedImm(*Src1);

  if (!Src0Imm && !Src1Imm)
    return false;

  // and k0, k1 -> v_mov_b32 (k0 & k1)
  // or k0, k1 -> v_mov_b32 (k0 | k1)
  // xor k0, k1 -> v_mov_b32 (k0 ^ k1)
  if (Src0Imm && Src1Imm) {
    int32_t NewImm;
    if (!evalBinaryInstruction(Opc, NewImm, *Src0Imm, *Src1Imm))
      return false;

    bool IsSGPR = TRI->isSGPRReg(*MRI, MI->getOperand(0).getReg());

    // Be careful to change the right operand, src0 may belong to a different
    // instruction.
    MI->getOperand(Src0Idx).ChangeToImmediate(NewImm);
    MI->removeOperand(Src1Idx);
    mutateCopyOp(*MI, TII->get(getMovOpc(IsSGPR)));
    return true;
  }

  if (!MI->isCommutable())
    return false;

  if (Src0Imm && !Src1Imm) {
    std::swap(Src0, Src1);
    std::swap(Src0Idx, Src1Idx);
    std::swap(Src0Imm, Src1Imm);
  }

  int32_t Src1Val = static_cast<int32_t>(*Src1Imm);
  if (Opc == AMDGPU::V_OR_B32_e64 ||
      Opc == AMDGPU::V_OR_B32_e32 ||
      Opc == AMDGPU::S_OR_B32) {
    if (Src1Val == 0) {
      // y = or x, 0 => y = copy x
      MI->removeOperand(Src1Idx);
      mutateCopyOp(*MI, TII->get(AMDGPU::COPY));
    } else if (Src1Val == -1) {
      // y = or x, -1 => y = v_mov_b32 -1
      MI->removeOperand(Src1Idx);
      mutateCopyOp(*MI, TII->get(getMovOpc(Opc == AMDGPU::S_OR_B32)));
    } else
      return false;

    return true;
  }

  if (Opc == AMDGPU::V_AND_B32_e64 || Opc == AMDGPU::V_AND_B32_e32 ||
      Opc == AMDGPU::S_AND_B32) {
    if (Src1Val == 0) {
      // y = and x, 0 => y = v_mov_b32 0
      MI->removeOperand(Src0Idx);
      mutateCopyOp(*MI, TII->get(getMovOpc(Opc == AMDGPU::S_AND_B32)));
    } else if (Src1Val == -1) {
      // y = and x, -1 => y = copy x
      MI->removeOperand(Src1Idx);
      mutateCopyOp(*MI, TII->get(AMDGPU::COPY));
    } else
      return false;

    return true;
  }

  if (Opc == AMDGPU::V_XOR_B32_e64 || Opc == AMDGPU::V_XOR_B32_e32 ||
      Opc == AMDGPU::S_XOR_B32) {
    if (Src1Val == 0) {
      // y = xor x, 0 => y = copy x
      MI->removeOperand(Src1Idx);
      mutateCopyOp(*MI, TII->get(AMDGPU::COPY));
      return true;
    }
  }

  return false;
}

// Try to fold an instruction into a simpler one
bool SIFoldOperandsImpl::tryFoldCndMask(MachineInstr &MI) const {
  unsigned Opc = MI.getOpcode();
  if (Opc != AMDGPU::V_CNDMASK_B32_e32 && Opc != AMDGPU::V_CNDMASK_B32_e64 &&
      Opc != AMDGPU::V_CNDMASK_B64_PSEUDO)
    return false;

  MachineOperand *Src0 = TII->getNamedOperand(MI, AMDGPU::OpName::src0);
  MachineOperand *Src1 = TII->getNamedOperand(MI, AMDGPU::OpName::src1);
  if (!Src1->isIdenticalTo(*Src0)) {
    std::optional<int64_t> Src1Imm = getImmOrMaterializedImm(*Src1);
    if (!Src1Imm)
      return false;

    std::optional<int64_t> Src0Imm = getImmOrMaterializedImm(*Src0);
    if (!Src0Imm || *Src0Imm != *Src1Imm)
      return false;
  }

  int Src1ModIdx =
      AMDGPU::getNamedOperandIdx(Opc, AMDGPU::OpName::src1_modifiers);
  int Src0ModIdx =
      AMDGPU::getNamedOperandIdx(Opc, AMDGPU::OpName::src0_modifiers);
  if ((Src1ModIdx != -1 && MI.getOperand(Src1ModIdx).getImm() != 0) ||
      (Src0ModIdx != -1 && MI.getOperand(Src0ModIdx).getImm() != 0))
    return false;

  LLVM_DEBUG(dbgs() << "Folded " << MI << " into ");
  auto &NewDesc =
      TII->get(Src0->isReg() ? (unsigned)AMDGPU::COPY : getMovOpc(false));
  int Src2Idx = AMDGPU::getNamedOperandIdx(Opc, AMDGPU::OpName::src2);
  if (Src2Idx != -1)
    MI.removeOperand(Src2Idx);
  MI.removeOperand(AMDGPU::getNamedOperandIdx(Opc, AMDGPU::OpName::src1));
  if (Src1ModIdx != -1)
    MI.removeOperand(Src1ModIdx);
  if (Src0ModIdx != -1)
    MI.removeOperand(Src0ModIdx);
  mutateCopyOp(MI, NewDesc);
  LLVM_DEBUG(dbgs() << MI);
  return true;
}

bool SIFoldOperandsImpl::tryFoldZeroHighBits(MachineInstr &MI) const {
  if (MI.getOpcode() != AMDGPU::V_AND_B32_e64 &&
      MI.getOpcode() != AMDGPU::V_AND_B32_e32)
    return false;

  std::optional<int64_t> Src0Imm = getImmOrMaterializedImm(MI.getOperand(1));
  if (!Src0Imm || *Src0Imm != 0xffff || !MI.getOperand(2).isReg())
    return false;

  Register Src1 = MI.getOperand(2).getReg();
  MachineInstr *SrcDef = MRI->getVRegDef(Src1);
  if (!ST->zeroesHigh16BitsOfDest(SrcDef->getOpcode()))
    return false;

  Register Dst = MI.getOperand(0).getReg();
  MRI->replaceRegWith(Dst, Src1);
  if (!MI.getOperand(2).isKill())
    MRI->clearKillFlags(Src1);
  MI.eraseFromParent();
  return true;
}

bool SIFoldOperandsImpl::foldInstOperand(MachineInstr &MI,
                                         MachineOperand &OpToFold) const {
  // We need mutate the operands of new mov instructions to add implicit
  // uses of EXEC, but adding them invalidates the use_iterator, so defer
  // this.
  SmallVector<MachineInstr *, 4> CopiesToReplace;
  SmallVector<FoldCandidate, 4> FoldList;
  MachineOperand &Dst = MI.getOperand(0);
  bool Changed = false;

  if (OpToFold.isImm()) {
    for (auto &UseMI :
         make_early_inc_range(MRI->use_nodbg_instructions(Dst.getReg()))) {
      // Folding the immediate may reveal operations that can be constant
      // folded or replaced with a copy. This can happen for example after
      // frame indices are lowered to constants or from splitting 64-bit
      // constants.
      //
      // We may also encounter cases where one or both operands are
      // immediates materialized into a register, which would ordinarily not
      // be folded due to multiple uses or operand constraints.
      if (tryConstantFoldOp(&UseMI)) {
        LLVM_DEBUG(dbgs() << "Constant folded " << UseMI);
        Changed = true;
      }
    }
  }

  SmallVector<MachineOperand *, 4> UsesToProcess;
  for (auto &Use : MRI->use_nodbg_operands(Dst.getReg()))
    UsesToProcess.push_back(&Use);
  for (auto *U : UsesToProcess) {
    MachineInstr *UseMI = U->getParent();
    foldOperand(OpToFold, UseMI, UseMI->getOperandNo(U), FoldList,
                CopiesToReplace);
  }

  if (CopiesToReplace.empty() && FoldList.empty())
    return Changed;

  MachineFunction *MF = MI.getParent()->getParent();
  // Make sure we add EXEC uses to any new v_mov instructions created.
  for (MachineInstr *Copy : CopiesToReplace)
    Copy->addImplicitDefUseOperands(*MF);

  for (FoldCandidate &Fold : FoldList) {
    assert(!Fold.isReg() || Fold.OpToFold);
    if (Fold.isReg() && Fold.OpToFold->getReg().isVirtual()) {
      Register Reg = Fold.OpToFold->getReg();
      MachineInstr *DefMI = Fold.OpToFold->getParent();
      if (DefMI->readsRegister(AMDGPU::EXEC, TRI) &&
          execMayBeModifiedBeforeUse(*MRI, Reg, *DefMI, *Fold.UseMI))
        continue;
    }
    if (updateOperand(Fold)) {
      // Clear kill flags.
      if (Fold.isReg()) {
        assert(Fold.OpToFold && Fold.OpToFold->isReg());
        // FIXME: Probably shouldn't bother trying to fold if not an
        // SGPR. PeepholeOptimizer can eliminate redundant VGPR->VGPR
        // copies.
        MRI->clearKillFlags(Fold.OpToFold->getReg());
      }
      LLVM_DEBUG(dbgs() << "Folded source from " << MI << " into OpNo "
                        << static_cast<int>(Fold.UseOpNo) << " of "
                        << *Fold.UseMI);
    } else if (Fold.Commuted) {
      // Restoring instruction's original operand order if fold has failed.
      TII->commuteInstruction(*Fold.UseMI, false);
    }
  }
  return true;
}

/// Fold %agpr = COPY (REG_SEQUENCE x_MOV_B32, ...) into REG_SEQUENCE
///  (V_ACCVGPR_WRITE_B32_e64) ... depending on the reg_sequence input values.
bool SIFoldOperandsImpl::foldCopyToAGPRRegSequence(MachineInstr *CopyMI) const {
  // It is very tricky to store a value into an AGPR. v_accvgpr_write_b32 can
  // only accept VGPR or inline immediate. Recreate a reg_sequence with its
  // initializers right here, so we will rematerialize immediates and avoid
  // copies via different reg classes.
  const TargetRegisterClass *DefRC =
      MRI->getRegClass(CopyMI->getOperand(0).getReg());
  if (!TRI->isAGPRClass(DefRC))
    return false;

  Register UseReg = CopyMI->getOperand(1).getReg();
  MachineInstr *RegSeq = MRI->getVRegDef(UseReg);
  if (!RegSeq || !RegSeq->isRegSequence())
    return false;

  const DebugLoc &DL = CopyMI->getDebugLoc();
  MachineBasicBlock &MBB = *CopyMI->getParent();

  MachineInstrBuilder B(*MBB.getParent(), CopyMI);
  DenseMap<TargetInstrInfo::RegSubRegPair, Register> VGPRCopies;
  SmallSetVector<TargetInstrInfo::RegSubRegPair, 32> SeenInputs;

  const TargetRegisterClass *UseRC =
      MRI->getRegClass(CopyMI->getOperand(1).getReg());

  // Value, subregindex for new REG_SEQUENCE
  SmallVector<std::pair<MachineOperand *, unsigned>, 32> NewDefs;

  unsigned NumRegSeqOperands = RegSeq->getNumOperands();
  unsigned NumFoldable = 0;

  for (unsigned I = 1; I != NumRegSeqOperands; I += 2) {
    MachineOperand &RegOp = RegSeq->getOperand(I);
    unsigned SubRegIdx = RegSeq->getOperand(I + 1).getImm();

    if (RegOp.getSubReg()) {
      // TODO: Handle subregister compose
      NewDefs.emplace_back(&RegOp, SubRegIdx);
      continue;
    }

    MachineOperand *Lookup = lookUpCopyChain(*TII, *MRI, RegOp.getReg());
    if (!Lookup)
      Lookup = &RegOp;

    if (Lookup->isImm()) {
      // Check if this is an agpr_32 subregister.
      const TargetRegisterClass *DestSuperRC = TRI->getMatchingSuperRegClass(
          DefRC, &AMDGPU::AGPR_32RegClass, SubRegIdx);
      if (DestSuperRC &&
          TII->isInlineConstant(*Lookup, AMDGPU::OPERAND_REG_INLINE_C_INT32)) {
        ++NumFoldable;
        NewDefs.emplace_back(Lookup, SubRegIdx);
        continue;
      }
    }

    const TargetRegisterClass *InputRC =
        Lookup->isReg() ? MRI->getRegClass(Lookup->getReg())
                        : MRI->getRegClass(RegOp.getReg());

    // TODO: Account for Lookup->getSubReg()

    // If we can't find a matching super class, this is an SGPR->AGPR or
    // VGPR->AGPR subreg copy (or something constant-like we have to materialize
    // in the AGPR). We can't directly copy from SGPR to AGPR on gfx908, so we
    // want to rewrite to copy to an intermediate VGPR class.
    const TargetRegisterClass *MatchRC =
        TRI->getMatchingSuperRegClass(DefRC, InputRC, SubRegIdx);
    if (!MatchRC) {
      ++NumFoldable;
      NewDefs.emplace_back(&RegOp, SubRegIdx);
      continue;
    }

    NewDefs.emplace_back(&RegOp, SubRegIdx);
  }

  // Do not clone a reg_sequence and merely change the result register class.
  if (NumFoldable == 0)
    return false;

  CopyMI->setDesc(TII->get(AMDGPU::REG_SEQUENCE));
  for (unsigned I = CopyMI->getNumOperands() - 1; I > 0; --I)
    CopyMI->removeOperand(I);

  for (auto [Def, DestSubIdx] : NewDefs) {
    if (!Def->isReg()) {
      // TODO: Should we use single write for each repeated value like in
      // register case?
      Register Tmp = MRI->createVirtualRegister(&AMDGPU::AGPR_32RegClass);
      BuildMI(MBB, CopyMI, DL, TII->get(AMDGPU::V_ACCVGPR_WRITE_B32_e64), Tmp)
          .add(*Def);
      B.addReg(Tmp);
    } else {
      TargetInstrInfo::RegSubRegPair Src = getRegSubRegPair(*Def);
      Def->setIsKill(false);

      Register &VGPRCopy = VGPRCopies[Src];
      if (!VGPRCopy) {
        const TargetRegisterClass *VGPRUseSubRC =
            TRI->getSubRegisterClass(UseRC, DestSubIdx);

        // We cannot build a reg_sequence out of the same registers, they
        // must be copied. Better do it here before copyPhysReg() created
        // several reads to do the AGPR->VGPR->AGPR copy.

        // Direct copy from SGPR to AGPR is not possible on gfx908. To avoid
        // creation of exploded copies SGPR->VGPR->AGPR in the copyPhysReg()
        // later, create a copy here and track if we already have such a copy.
        if (TRI->getSubRegisterClass(MRI->getRegClass(Src.Reg), Src.SubReg) !=
            VGPRUseSubRC) {
          VGPRCopy = MRI->createVirtualRegister(VGPRUseSubRC);
          BuildMI(MBB, CopyMI, DL, TII->get(AMDGPU::COPY), VGPRCopy).add(*Def);
          B.addReg(VGPRCopy);
        } else {
          // If it is already a VGPR, do not copy the register.
          B.add(*Def);
        }
      } else {
        B.addReg(VGPRCopy);
      }
    }

    B.addImm(DestSubIdx);
  }

  LLVM_DEBUG(dbgs() << "Folded " << *CopyMI);
  return true;
}

bool SIFoldOperandsImpl::tryFoldFoldableCopy(
    MachineInstr &MI, MachineOperand *&CurrentKnownM0Val) const {
  Register DstReg = MI.getOperand(0).getReg();
  // Specially track simple redefs of m0 to the same value in a block, so we
  // can erase the later ones.
  if (DstReg == AMDGPU::M0) {
    MachineOperand &NewM0Val = MI.getOperand(1);
    if (CurrentKnownM0Val && CurrentKnownM0Val->isIdenticalTo(NewM0Val)) {
      MI.eraseFromParent();
      return true;
    }

    // We aren't tracking other physical registers
    CurrentKnownM0Val = (NewM0Val.isReg() && NewM0Val.getReg().isPhysical())
                            ? nullptr
                            : &NewM0Val;
    return false;
  }

  MachineOperand *OpToFoldPtr;
  if (MI.getOpcode() == AMDGPU::V_MOV_B16_t16_e64) {
    // Folding when any src_modifiers are non-zero is unsupported
    if (TII->hasAnyModifiersSet(MI))
      return false;
    OpToFoldPtr = &MI.getOperand(2);
  } else
    OpToFoldPtr = &MI.getOperand(1);
  MachineOperand &OpToFold = *OpToFoldPtr;
  bool FoldingImm = OpToFold.isImm() || OpToFold.isFI() || OpToFold.isGlobal();

  // FIXME: We could also be folding things like TargetIndexes.
  if (!FoldingImm && !OpToFold.isReg())
    return false;

  if (OpToFold.isReg() && !OpToFold.getReg().isVirtual())
    return false;

  // True16: Fix malformed 16-bit sgpr COPY produced by peephole-opt
  // Can remove this code if proper 16-bit SGPRs are implemented
  // Example: Pre-peephole-opt
  // %29:sgpr_lo16 = COPY %16.lo16:sreg_32
  // %32:sreg_32 = COPY %29:sgpr_lo16
  // %30:sreg_32 = S_PACK_LL_B32_B16 killed %31:sreg_32, killed %32:sreg_32
  // Post-peephole-opt and DCE
  // %32:sreg_32 = COPY %16.lo16:sreg_32
  // %30:sreg_32 = S_PACK_LL_B32_B16 killed %31:sreg_32, killed %32:sreg_32
  // After this transform
  // %32:sreg_32 = COPY %16:sreg_32
  // %30:sreg_32 = S_PACK_LL_B32_B16 killed %31:sreg_32, killed %32:sreg_32
  // After the fold operands pass
  // %30:sreg_32 = S_PACK_LL_B32_B16 killed %31:sreg_32, killed %16:sreg_32
  if (MI.getOpcode() == AMDGPU::COPY && OpToFold.isReg() &&
      OpToFold.getSubReg()) {
    const TargetRegisterClass *DstRC =
        MRI->getRegClass(MI.getOperand(0).getReg());
    if (DstRC == &AMDGPU::SReg_32RegClass &&
        DstRC == MRI->getRegClass(OpToFold.getReg())) {
      assert(OpToFold.getSubReg() == AMDGPU::lo16);
      OpToFold.setSubReg(0);
    }
  }

  // Prevent folding operands backwards in the function. For example,
  // the COPY opcode must not be replaced by 1 in this example:
  //
  //    %3 = COPY %vgpr0; VGPR_32:%3
  //    ...
  //    %vgpr0 = V_MOV_B32_e32 1, implicit %exec
  if (!DstReg.isVirtual())
    return false;

  if (OpToFold.isReg() &&
      foldCopyToVGPROfScalarAddOfFrameIndex(DstReg, OpToFold.getReg(), MI))
    return true;

  // Fold copy to AGPR through reg_sequence
  // TODO: Handle with subregister extract
  if (OpToFold.isReg() && MI.isCopy() && !MI.getOperand(1).getSubReg()) {
    if (foldCopyToAGPRRegSequence(&MI))
      return true;
  }

  bool Changed = foldInstOperand(MI, OpToFold);

  // If we managed to fold all uses of this copy then we might as well
  // delete it now.
  // The only reason we need to follow chains of copies here is that
  // tryFoldRegSequence looks forward through copies before folding a
  // REG_SEQUENCE into its eventual users.
  auto *InstToErase = &MI;
  while (MRI->use_nodbg_empty(InstToErase->getOperand(0).getReg())) {
    auto &SrcOp = InstToErase->getOperand(1);
    auto SrcReg = SrcOp.isReg() ? SrcOp.getReg() : Register();
    InstToErase->eraseFromParent();
    Changed = true;
    InstToErase = nullptr;
    if (!SrcReg || SrcReg.isPhysical())
      break;
    InstToErase = MRI->getVRegDef(SrcReg);
    if (!InstToErase || !TII->isFoldableCopy(*InstToErase))
      break;
  }

  if (InstToErase && InstToErase->isRegSequence() &&
      MRI->use_nodbg_empty(InstToErase->getOperand(0).getReg())) {
    InstToErase->eraseFromParent();
    Changed = true;
  }

  return Changed;
}

// Clamp patterns are canonically selected to v_max_* instructions, so only
// handle them.
const MachineOperand *
SIFoldOperandsImpl::isClamp(const MachineInstr &MI) const {
  unsigned Op = MI.getOpcode();
  switch (Op) {
  case AMDGPU::V_MAX_F32_e64:
  case AMDGPU::V_MAX_F16_e64:
  case AMDGPU::V_MAX_F16_t16_e64:
  case AMDGPU::V_MAX_F16_fake16_e64:
  case AMDGPU::V_MAX_F64_e64:
  case AMDGPU::V_MAX_NUM_F64_e64:
  case AMDGPU::V_PK_MAX_F16: {
    if (MI.mayRaiseFPException())
      return nullptr;

    if (!TII->getNamedOperand(MI, AMDGPU::OpName::clamp)->getImm())
      return nullptr;

    // Make sure sources are identical.
    const MachineOperand *Src0 = TII->getNamedOperand(MI, AMDGPU::OpName::src0);
    const MachineOperand *Src1 = TII->getNamedOperand(MI, AMDGPU::OpName::src1);
    if (!Src0->isReg() || !Src1->isReg() ||
        Src0->getReg() != Src1->getReg() ||
        Src0->getSubReg() != Src1->getSubReg() ||
        Src0->getSubReg() != AMDGPU::NoSubRegister)
      return nullptr;

    // Can't fold up if we have modifiers.
    if (TII->hasModifiersSet(MI, AMDGPU::OpName::omod))
      return nullptr;

    unsigned Src0Mods
      = TII->getNamedOperand(MI, AMDGPU::OpName::src0_modifiers)->getImm();
    unsigned Src1Mods
      = TII->getNamedOperand(MI, AMDGPU::OpName::src1_modifiers)->getImm();

    // Having a 0 op_sel_hi would require swizzling the output in the source
    // instruction, which we can't do.
    unsigned UnsetMods = (Op == AMDGPU::V_PK_MAX_F16) ? SISrcMods::OP_SEL_1
                                                      : 0u;
    if (Src0Mods != UnsetMods && Src1Mods != UnsetMods)
      return nullptr;
    return Src0;
  }
  default:
    return nullptr;
  }
}

// FIXME: Clamp for v_mad_mixhi_f16 handled during isel.
bool SIFoldOperandsImpl::tryFoldClamp(MachineInstr &MI) {
  const MachineOperand *ClampSrc = isClamp(MI);
  if (!ClampSrc || !MRI->hasOneNonDBGUser(ClampSrc->getReg()))
    return false;

  if (!ClampSrc->getReg().isVirtual())
    return false;

  // Look through COPY. COPY only observed with True16.
  Register DefSrcReg = TRI->lookThruCopyLike(ClampSrc->getReg(), MRI);
  MachineInstr *Def =
      MRI->getVRegDef(DefSrcReg.isVirtual() ? DefSrcReg : ClampSrc->getReg());

  // The type of clamp must be compatible.
  if (TII->getClampMask(*Def) != TII->getClampMask(MI))
    return false;

  if (Def->mayRaiseFPException())
    return false;

  MachineOperand *DefClamp = TII->getNamedOperand(*Def, AMDGPU::OpName::clamp);
  if (!DefClamp)
    return false;

  LLVM_DEBUG(dbgs() << "Folding clamp " << *DefClamp << " into " << *Def);

  // Clamp is applied after omod, so it is OK if omod is set.
  DefClamp->setImm(1);

  Register DefReg = Def->getOperand(0).getReg();
  Register MIDstReg = MI.getOperand(0).getReg();
  if (TRI->isSGPRReg(*MRI, DefReg)) {
    // Pseudo scalar instructions have a SGPR for dst and clamp is a v_max*
    // instruction with a VGPR dst.
    BuildMI(*MI.getParent(), MI, MI.getDebugLoc(), TII->get(AMDGPU::COPY),
            MIDstReg)
        .addReg(DefReg);
  } else {
    MRI->replaceRegWith(MIDstReg, DefReg);
  }
  MI.eraseFromParent();

  // Use of output modifiers forces VOP3 encoding for a VOP2 mac/fmac
  // instruction, so we might as well convert it to the more flexible VOP3-only
  // mad/fma form.
  if (TII->convertToThreeAddress(*Def, nullptr, nullptr))
    Def->eraseFromParent();

  return true;
}

static int getOModValue(unsigned Opc, int64_t Val) {
  switch (Opc) {
  case AMDGPU::V_MUL_F64_e64:
  case AMDGPU::V_MUL_F64_pseudo_e64: {
    switch (Val) {
    case 0x3fe0000000000000: // 0.5
      return SIOutMods::DIV2;
    case 0x4000000000000000: // 2.0
      return SIOutMods::MUL2;
    case 0x4010000000000000: // 4.0
      return SIOutMods::MUL4;
    default:
      return SIOutMods::NONE;
    }
  }
  case AMDGPU::V_MUL_F32_e64: {
    switch (static_cast<uint32_t>(Val)) {
    case 0x3f000000: // 0.5
      return SIOutMods::DIV2;
    case 0x40000000: // 2.0
      return SIOutMods::MUL2;
    case 0x40800000: // 4.0
      return SIOutMods::MUL4;
    default:
      return SIOutMods::NONE;
    }
  }
  case AMDGPU::V_MUL_F16_e64:
  case AMDGPU::V_MUL_F16_t16_e64:
  case AMDGPU::V_MUL_F16_fake16_e64: {
    switch (static_cast<uint16_t>(Val)) {
    case 0x3800: // 0.5
      return SIOutMods::DIV2;
    case 0x4000: // 2.0
      return SIOutMods::MUL2;
    case 0x4400: // 4.0
      return SIOutMods::MUL4;
    default:
      return SIOutMods::NONE;
    }
  }
  default:
    llvm_unreachable("invalid mul opcode");
  }
}

// FIXME: Does this really not support denormals with f16?
// FIXME: Does this need to check IEEE mode bit? SNaNs are generally not
// handled, so will anything other than that break?
std::pair<const MachineOperand *, int>
SIFoldOperandsImpl::isOMod(const MachineInstr &MI) const {
  unsigned Op = MI.getOpcode();
  switch (Op) {
  case AMDGPU::V_MUL_F64_e64:
  case AMDGPU::V_MUL_F64_pseudo_e64:
  case AMDGPU::V_MUL_F32_e64:
  case AMDGPU::V_MUL_F16_t16_e64:
  case AMDGPU::V_MUL_F16_fake16_e64:
  case AMDGPU::V_MUL_F16_e64: {
    // If output denormals are enabled, omod is ignored.
    if ((Op == AMDGPU::V_MUL_F32_e64 &&
         MFI->getMode().FP32Denormals.Output != DenormalMode::PreserveSign) ||
        ((Op == AMDGPU::V_MUL_F64_e64 || Op == AMDGPU::V_MUL_F64_pseudo_e64 ||
          Op == AMDGPU::V_MUL_F16_e64 || Op == AMDGPU::V_MUL_F16_t16_e64 ||
          Op == AMDGPU::V_MUL_F16_fake16_e64) &&
         MFI->getMode().FP64FP16Denormals.Output !=
             DenormalMode::PreserveSign) ||
        MI.mayRaiseFPException())
      return std::pair(nullptr, SIOutMods::NONE);

    const MachineOperand *RegOp = nullptr;
    const MachineOperand *ImmOp = nullptr;
    const MachineOperand *Src0 = TII->getNamedOperand(MI, AMDGPU::OpName::src0);
    const MachineOperand *Src1 = TII->getNamedOperand(MI, AMDGPU::OpName::src1);
    if (Src0->isImm()) {
      ImmOp = Src0;
      RegOp = Src1;
    } else if (Src1->isImm()) {
      ImmOp = Src1;
      RegOp = Src0;
    } else
      return std::pair(nullptr, SIOutMods::NONE);

    int OMod = getOModValue(Op, ImmOp->getImm());
    if (OMod == SIOutMods::NONE ||
        TII->hasModifiersSet(MI, AMDGPU::OpName::src0_modifiers) ||
        TII->hasModifiersSet(MI, AMDGPU::OpName::src1_modifiers) ||
        TII->hasModifiersSet(MI, AMDGPU::OpName::omod) ||
        TII->hasModifiersSet(MI, AMDGPU::OpName::clamp))
      return std::pair(nullptr, SIOutMods::NONE);

    return std::pair(RegOp, OMod);
  }
  case AMDGPU::V_ADD_F64_e64:
  case AMDGPU::V_ADD_F64_pseudo_e64:
  case AMDGPU::V_ADD_F32_e64:
  case AMDGPU::V_ADD_F16_e64:
  case AMDGPU::V_ADD_F16_t16_e64:
  case AMDGPU::V_ADD_F16_fake16_e64: {
    // If output denormals are enabled, omod is ignored.
    if ((Op == AMDGPU::V_ADD_F32_e64 &&
         MFI->getMode().FP32Denormals.Output != DenormalMode::PreserveSign) ||
        ((Op == AMDGPU::V_ADD_F64_e64 || Op == AMDGPU::V_ADD_F64_pseudo_e64 ||
          Op == AMDGPU::V_ADD_F16_e64 || Op == AMDGPU::V_ADD_F16_t16_e64 ||
          Op == AMDGPU::V_ADD_F16_fake16_e64) &&
         MFI->getMode().FP64FP16Denormals.Output != DenormalMode::PreserveSign))
      return std::pair(nullptr, SIOutMods::NONE);

    // Look through the DAGCombiner canonicalization fmul x, 2 -> fadd x, x
    const MachineOperand *Src0 = TII->getNamedOperand(MI, AMDGPU::OpName::src0);
    const MachineOperand *Src1 = TII->getNamedOperand(MI, AMDGPU::OpName::src1);

    if (Src0->isReg() && Src1->isReg() && Src0->getReg() == Src1->getReg() &&
        Src0->getSubReg() == Src1->getSubReg() &&
        !TII->hasModifiersSet(MI, AMDGPU::OpName::src0_modifiers) &&
        !TII->hasModifiersSet(MI, AMDGPU::OpName::src1_modifiers) &&
        !TII->hasModifiersSet(MI, AMDGPU::OpName::clamp) &&
        !TII->hasModifiersSet(MI, AMDGPU::OpName::omod))
      return std::pair(Src0, SIOutMods::MUL2);

    return std::pair(nullptr, SIOutMods::NONE);
  }
  default:
    return std::pair(nullptr, SIOutMods::NONE);
  }
}

// FIXME: Does this need to check IEEE bit on function?
bool SIFoldOperandsImpl::tryFoldOMod(MachineInstr &MI) {
  const MachineOperand *RegOp;
  int OMod;
  std::tie(RegOp, OMod) = isOMod(MI);
  if (OMod == SIOutMods::NONE || !RegOp->isReg() ||
      RegOp->getSubReg() != AMDGPU::NoSubRegister ||
      !MRI->hasOneNonDBGUser(RegOp->getReg()))
    return false;

  MachineInstr *Def = MRI->getVRegDef(RegOp->getReg());
  MachineOperand *DefOMod = TII->getNamedOperand(*Def, AMDGPU::OpName::omod);
  if (!DefOMod || DefOMod->getImm() != SIOutMods::NONE)
    return false;

  if (Def->mayRaiseFPException())
    return false;

  // Clamp is applied after omod. If the source already has clamp set, don't
  // fold it.
  if (TII->hasModifiersSet(*Def, AMDGPU::OpName::clamp))
    return false;

  LLVM_DEBUG(dbgs() << "Folding omod " << MI << " into " << *Def);

  DefOMod->setImm(OMod);
  MRI->replaceRegWith(MI.getOperand(0).getReg(), Def->getOperand(0).getReg());
  // Kill flags can be wrong if we replaced a def inside a loop with a def
  // outside the loop.
  MRI->clearKillFlags(Def->getOperand(0).getReg());
  MI.eraseFromParent();

  // Use of output modifiers forces VOP3 encoding for a VOP2 mac/fmac
  // instruction, so we might as well convert it to the more flexible VOP3-only
  // mad/fma form.
  if (TII->convertToThreeAddress(*Def, nullptr, nullptr))
    Def->eraseFromParent();

  return true;
}

// Try to fold a reg_sequence with vgpr output and agpr inputs into an
// instruction which can take an agpr. So far that means a store.
bool SIFoldOperandsImpl::tryFoldRegSequence(MachineInstr &MI) {
  assert(MI.isRegSequence());
  auto Reg = MI.getOperand(0).getReg();

  if (!ST->hasGFX90AInsts() || !TRI->isVGPR(*MRI, Reg) ||
      !MRI->hasOneNonDBGUse(Reg))
    return false;

  SmallVector<std::pair<MachineOperand*, unsigned>, 32> Defs;
  if (!getRegSeqInit(Defs, Reg, MCOI::OPERAND_REGISTER))
    return false;

  for (auto &[Op, SubIdx] : Defs) {
    if (!Op->isReg())
      return false;
    if (TRI->isAGPR(*MRI, Op->getReg()))
      continue;
    // Maybe this is a COPY from AREG
    const MachineInstr *SubDef = MRI->getVRegDef(Op->getReg());
    if (!SubDef || !SubDef->isCopy() || SubDef->getOperand(1).getSubReg())
      return false;
    if (!TRI->isAGPR(*MRI, SubDef->getOperand(1).getReg()))
      return false;
  }

  MachineOperand *Op = &*MRI->use_nodbg_begin(Reg);
  MachineInstr *UseMI = Op->getParent();
  while (UseMI->isCopy() && !Op->getSubReg()) {
    Reg = UseMI->getOperand(0).getReg();
    if (!TRI->isVGPR(*MRI, Reg) || !MRI->hasOneNonDBGUse(Reg))
      return false;
    Op = &*MRI->use_nodbg_begin(Reg);
    UseMI = Op->getParent();
  }

  if (Op->getSubReg())
    return false;

  unsigned OpIdx = Op - &UseMI->getOperand(0);
  const MCInstrDesc &InstDesc = UseMI->getDesc();
  const TargetRegisterClass *OpRC =
      TII->getRegClass(InstDesc, OpIdx, TRI, *MI.getMF());
  if (!OpRC || !TRI->isVectorSuperClass(OpRC))
    return false;

  const auto *NewDstRC = TRI->getEquivalentAGPRClass(MRI->getRegClass(Reg));
  auto Dst = MRI->createVirtualRegister(NewDstRC);
  auto RS = BuildMI(*MI.getParent(), MI, MI.getDebugLoc(),
                    TII->get(AMDGPU::REG_SEQUENCE), Dst);

  for (auto &[Def, SubIdx] : Defs) {
    Def->setIsKill(false);
    if (TRI->isAGPR(*MRI, Def->getReg())) {
      RS.add(*Def);
    } else { // This is a copy
      MachineInstr *SubDef = MRI->getVRegDef(Def->getReg());
      SubDef->getOperand(1).setIsKill(false);
      RS.addReg(SubDef->getOperand(1).getReg(), 0, Def->getSubReg());
    }
    RS.addImm(SubIdx);
  }

  Op->setReg(Dst);
  if (!TII->isOperandLegal(*UseMI, OpIdx, Op)) {
    Op->setReg(Reg);
    RS->eraseFromParent();
    return false;
  }

  LLVM_DEBUG(dbgs() << "Folded " << *RS << " into " << *UseMI);

  // Erase the REG_SEQUENCE eagerly, unless we followed a chain of COPY users,
  // in which case we can erase them all later in runOnMachineFunction.
  if (MRI->use_nodbg_empty(MI.getOperand(0).getReg()))
    MI.eraseFromParent();
  return true;
}

/// Checks whether \p Copy is a AGPR -> VGPR copy. Returns `true` on success and
/// stores the AGPR register in \p OutReg and the subreg in \p OutSubReg
static bool isAGPRCopy(const SIRegisterInfo &TRI,
                       const MachineRegisterInfo &MRI, const MachineInstr &Copy,
                       Register &OutReg, unsigned &OutSubReg) {
  assert(Copy.isCopy());

  const MachineOperand &CopySrc = Copy.getOperand(1);
  Register CopySrcReg = CopySrc.getReg();
  if (!CopySrcReg.isVirtual())
    return false;

  // Common case: copy from AGPR directly, e.g.
  //  %1:vgpr_32 = COPY %0:agpr_32
  if (TRI.isAGPR(MRI, CopySrcReg)) {
    OutReg = CopySrcReg;
    OutSubReg = CopySrc.getSubReg();
    return true;
  }

  // Sometimes it can also involve two copies, e.g.
  //  %1:vgpr_256 = COPY %0:agpr_256
  //  %2:vgpr_32 = COPY %1:vgpr_256.sub0
  const MachineInstr *CopySrcDef = MRI.getVRegDef(CopySrcReg);
  if (!CopySrcDef || !CopySrcDef->isCopy())
    return false;

  const MachineOperand &OtherCopySrc = CopySrcDef->getOperand(1);
  Register OtherCopySrcReg = OtherCopySrc.getReg();
  if (!OtherCopySrcReg.isVirtual() ||
      CopySrcDef->getOperand(0).getSubReg() != AMDGPU::NoSubRegister ||
      OtherCopySrc.getSubReg() != AMDGPU::NoSubRegister ||
      !TRI.isAGPR(MRI, OtherCopySrcReg))
    return false;

  OutReg = OtherCopySrcReg;
  OutSubReg = CopySrc.getSubReg();
  return true;
}

// Try to hoist an AGPR to VGPR copy across a PHI.
// This should allow folding of an AGPR into a consumer which may support it.
//
// Example 1: LCSSA PHI
//      loop:
//        %1:vreg = COPY %0:areg
//      exit:
//        %2:vreg = PHI %1:vreg, %loop
//  =>
//      loop:
//      exit:
//        %1:areg = PHI %0:areg, %loop
//        %2:vreg = COPY %1:areg
//
// Example 2: PHI with multiple incoming values:
//      entry:
//        %1:vreg = GLOBAL_LOAD(..)
//      loop:
//        %2:vreg = PHI %1:vreg, %entry, %5:vreg, %loop
//        %3:areg = COPY %2:vreg
//        %4:areg = (instr using %3:areg)
//        %5:vreg = COPY %4:areg
//  =>
//      entry:
//        %1:vreg = GLOBAL_LOAD(..)
//        %2:areg = COPY %1:vreg
//      loop:
//        %3:areg = PHI %2:areg, %entry, %X:areg,
//        %4:areg = (instr using %3:areg)
bool SIFoldOperandsImpl::tryFoldPhiAGPR(MachineInstr &PHI) {
  assert(PHI.isPHI());

  Register PhiOut = PHI.getOperand(0).getReg();
  if (!TRI->isVGPR(*MRI, PhiOut))
    return false;

  // Iterate once over all incoming values of the PHI to check if this PHI is
  // eligible, and determine the exact AGPR RC we'll target.
  const TargetRegisterClass *ARC = nullptr;
  for (unsigned K = 1; K < PHI.getNumExplicitOperands(); K += 2) {
    MachineOperand &MO = PHI.getOperand(K);
    MachineInstr *Copy = MRI->getVRegDef(MO.getReg());
    if (!Copy || !Copy->isCopy())
      continue;

    Register AGPRSrc;
    unsigned AGPRRegMask = AMDGPU::NoSubRegister;
    if (!isAGPRCopy(*TRI, *MRI, *Copy, AGPRSrc, AGPRRegMask))
      continue;

    const TargetRegisterClass *CopyInRC = MRI->getRegClass(AGPRSrc);
    if (const auto *SubRC = TRI->getSubRegisterClass(CopyInRC, AGPRRegMask))
      CopyInRC = SubRC;

    if (ARC && !ARC->hasSubClassEq(CopyInRC))
      return false;
    ARC = CopyInRC;
  }

  if (!ARC)
    return false;

  bool IsAGPR32 = (ARC == &AMDGPU::AGPR_32RegClass);

  // Rewrite the PHI's incoming values to ARC.
  LLVM_DEBUG(dbgs() << "Folding AGPR copies into: " << PHI);
  for (unsigned K = 1; K < PHI.getNumExplicitOperands(); K += 2) {
    MachineOperand &MO = PHI.getOperand(K);
    Register Reg = MO.getReg();

    MachineBasicBlock::iterator InsertPt;
    MachineBasicBlock *InsertMBB = nullptr;

    // Look at the def of Reg, ignoring all copies.
    unsigned CopyOpc = AMDGPU::COPY;
    if (MachineInstr *Def = MRI->getVRegDef(Reg)) {

      // Look at pre-existing COPY instructions from ARC: Steal the operand. If
      // the copy was single-use, it will be removed by DCE later.
      if (Def->isCopy()) {
        Register AGPRSrc;
        unsigned AGPRSubReg = AMDGPU::NoSubRegister;
        if (isAGPRCopy(*TRI, *MRI, *Def, AGPRSrc, AGPRSubReg)) {
          MO.setReg(AGPRSrc);
          MO.setSubReg(AGPRSubReg);
          continue;
        }

        // If this is a multi-use SGPR -> VGPR copy, use V_ACCVGPR_WRITE on
        // GFX908 directly instead of a COPY. Otherwise, SIFoldOperand may try
        // to fold the sgpr -> vgpr -> agpr copy into a sgpr -> agpr copy which
        // is unlikely to be profitable.
        //
        // Note that V_ACCVGPR_WRITE is only used for AGPR_32.
        MachineOperand &CopyIn = Def->getOperand(1);
        if (IsAGPR32 && !ST->hasGFX90AInsts() && !MRI->hasOneNonDBGUse(Reg) &&
            TRI->isSGPRReg(*MRI, CopyIn.getReg()))
          CopyOpc = AMDGPU::V_ACCVGPR_WRITE_B32_e64;
      }

      InsertMBB = Def->getParent();
      InsertPt = InsertMBB->SkipPHIsLabelsAndDebug(++Def->getIterator());
    } else {
      InsertMBB = PHI.getOperand(MO.getOperandNo() + 1).getMBB();
      InsertPt = InsertMBB->getFirstTerminator();
    }

    Register NewReg = MRI->createVirtualRegister(ARC);
    MachineInstr *MI = BuildMI(*InsertMBB, InsertPt, PHI.getDebugLoc(),
                               TII->get(CopyOpc), NewReg)
                           .addReg(Reg);
    MO.setReg(NewReg);

    (void)MI;
    LLVM_DEBUG(dbgs() << "  Created COPY: " << *MI);
  }

  // Replace the PHI's result with a new register.
  Register NewReg = MRI->createVirtualRegister(ARC);
  PHI.getOperand(0).setReg(NewReg);

  // COPY that new register back to the original PhiOut register. This COPY will
  // usually be folded out later.
  MachineBasicBlock *MBB = PHI.getParent();
  BuildMI(*MBB, MBB->getFirstNonPHI(), PHI.getDebugLoc(),
          TII->get(AMDGPU::COPY), PhiOut)
      .addReg(NewReg);

  LLVM_DEBUG(dbgs() << "  Done: Folded " << PHI);
  return true;
}

// Attempt to convert VGPR load to an AGPR load.
bool SIFoldOperandsImpl::tryFoldLoad(MachineInstr &MI) {
  assert(MI.mayLoad());
  if (!ST->hasGFX90AInsts() || MI.getNumExplicitDefs() != 1)
    return false;

  MachineOperand &Def = MI.getOperand(0);
  if (!Def.isDef())
    return false;

  Register DefReg = Def.getReg();

  if (DefReg.isPhysical() || !TRI->isVGPR(*MRI, DefReg))
    return false;

  SmallVector<const MachineInstr*, 8> Users;
  SmallVector<Register, 8> MoveRegs;
  for (const MachineInstr &I : MRI->use_nodbg_instructions(DefReg))
    Users.push_back(&I);

  if (Users.empty())
    return false;

  // Check that all uses a copy to an agpr or a reg_sequence producing an agpr.
  while (!Users.empty()) {
    const MachineInstr *I = Users.pop_back_val();
    if (!I->isCopy() && !I->isRegSequence())
      return false;
    Register DstReg = I->getOperand(0).getReg();
    // Physical registers may have more than one instruction definitions
    if (DstReg.isPhysical())
      return false;
    if (TRI->isAGPR(*MRI, DstReg))
      continue;
    MoveRegs.push_back(DstReg);
    for (const MachineInstr &U : MRI->use_nodbg_instructions(DstReg))
      Users.push_back(&U);
  }

  const TargetRegisterClass *RC = MRI->getRegClass(DefReg);
  MRI->setRegClass(DefReg, TRI->getEquivalentAGPRClass(RC));
  if (!TII->isOperandLegal(MI, 0, &Def)) {
    MRI->setRegClass(DefReg, RC);
    return false;
  }

  while (!MoveRegs.empty()) {
    Register Reg = MoveRegs.pop_back_val();
    MRI->setRegClass(Reg, TRI->getEquivalentAGPRClass(MRI->getRegClass(Reg)));
  }

  LLVM_DEBUG(dbgs() << "Folded " << MI);

  return true;
}

// tryFoldPhiAGPR will aggressively try to create AGPR PHIs.
// For GFX90A and later, this is pretty much always a good thing, but for GFX908
// there's cases where it can create a lot more AGPR-AGPR copies, which are
// expensive on this architecture due to the lack of V_ACCVGPR_MOV.
//
// This function looks at all AGPR PHIs in a basic block and collects their
// operands. Then, it checks for register that are used more than once across
// all PHIs and caches them in a VGPR. This prevents ExpandPostRAPseudo from
// having to create one VGPR temporary per use, which can get very messy if
// these PHIs come from a broken-up large PHI (e.g. 32 AGPR phis, one per vector
// element).
//
// Example
//      a:
//        %in:agpr_256 = COPY %foo:vgpr_256
//      c:
//        %x:agpr_32 = ..
//      b:
//        %0:areg = PHI %in.sub0:agpr_32, %a, %x, %c
//        %1:areg = PHI %in.sub0:agpr_32, %a, %y, %c
//        %2:areg = PHI %in.sub0:agpr_32, %a, %z, %c
//  =>
//      a:
//        %in:agpr_256 = COPY %foo:vgpr_256
//        %tmp:vgpr_32 = V_ACCVGPR_READ_B32_e64 %in.sub0:agpr_32
//        %tmp_agpr:agpr_32 = COPY %tmp
//      c:
//        %x:agpr_32 = ..
//      b:
//        %0:areg = PHI %tmp_agpr, %a, %x, %c
//        %1:areg = PHI %tmp_agpr, %a, %y, %c
//        %2:areg = PHI %tmp_agpr, %a, %z, %c
bool SIFoldOperandsImpl::tryOptimizeAGPRPhis(MachineBasicBlock &MBB) {
  // This is only really needed on GFX908 where AGPR-AGPR copies are
  // unreasonably difficult.
  if (ST->hasGFX90AInsts())
    return false;

  // Look at all AGPR Phis and collect the register + subregister used.
  DenseMap<std::pair<Register, unsigned>, std::vector<MachineOperand *>>
      RegToMO;

  for (auto &MI : MBB) {
    if (!MI.isPHI())
      break;

    if (!TRI->isAGPR(*MRI, MI.getOperand(0).getReg()))
      continue;

    for (unsigned K = 1; K < MI.getNumOperands(); K += 2) {
      MachineOperand &PhiMO = MI.getOperand(K);
      if (!PhiMO.getSubReg())
        continue;
      RegToMO[{PhiMO.getReg(), PhiMO.getSubReg()}].push_back(&PhiMO);
    }
  }

  // For all (Reg, SubReg) pair that are used more than once, cache the value in
  // a VGPR.
  bool Changed = false;
  for (const auto &[Entry, MOs] : RegToMO) {
    if (MOs.size() == 1)
      continue;

    const auto [Reg, SubReg] = Entry;
    MachineInstr *Def = MRI->getVRegDef(Reg);
    MachineBasicBlock *DefMBB = Def->getParent();

    // Create a copy in a VGPR using V_ACCVGPR_READ_B32_e64 so it's not folded
    // out.
    const TargetRegisterClass *ARC = getRegOpRC(*MRI, *TRI, *MOs.front());
    Register TempVGPR =
        MRI->createVirtualRegister(TRI->getEquivalentVGPRClass(ARC));
    MachineInstr *VGPRCopy =
        BuildMI(*DefMBB, ++Def->getIterator(), Def->getDebugLoc(),
                TII->get(AMDGPU::V_ACCVGPR_READ_B32_e64), TempVGPR)
            .addReg(Reg, /* flags */ 0, SubReg);

    // Copy back to an AGPR and use that instead of the AGPR subreg in all MOs.
    Register TempAGPR = MRI->createVirtualRegister(ARC);
    BuildMI(*DefMBB, ++VGPRCopy->getIterator(), Def->getDebugLoc(),
            TII->get(AMDGPU::COPY), TempAGPR)
        .addReg(TempVGPR);

    LLVM_DEBUG(dbgs() << "Caching AGPR into VGPR: " << *VGPRCopy);
    for (MachineOperand *MO : MOs) {
      MO->setReg(TempAGPR);
      MO->setSubReg(AMDGPU::NoSubRegister);
      LLVM_DEBUG(dbgs() << "  Changed PHI Operand: " << *MO << "\n");
    }

    Changed = true;
  }

  return Changed;
}

bool SIFoldOperandsImpl::run(MachineFunction &MF) {
  MRI = &MF.getRegInfo();
  ST = &MF.getSubtarget<GCNSubtarget>();
  TII = ST->getInstrInfo();
  TRI = &TII->getRegisterInfo();
  MFI = MF.getInfo<SIMachineFunctionInfo>();

  // omod is ignored by hardware if IEEE bit is enabled. omod also does not
  // correctly handle signed zeros.
  //
  // FIXME: Also need to check strictfp
  bool IsIEEEMode = MFI->getMode().IEEE;
  bool HasNSZ = MFI->hasNoSignedZerosFPMath();

  bool Changed = false;
  for (MachineBasicBlock *MBB : depth_first(&MF)) {
    MachineOperand *CurrentKnownM0Val = nullptr;
    for (auto &MI : make_early_inc_range(*MBB)) {
      Changed |= tryFoldCndMask(MI);

      if (tryFoldZeroHighBits(MI)) {
        Changed = true;
        continue;
      }

      if (MI.isRegSequence() && tryFoldRegSequence(MI)) {
        Changed = true;
        continue;
      }

      if (MI.isPHI() && tryFoldPhiAGPR(MI)) {
        Changed = true;
        continue;
      }

      if (MI.mayLoad() && tryFoldLoad(MI)) {
        Changed = true;
        continue;
      }

      if (TII->isFoldableCopy(MI)) {
        Changed |= tryFoldFoldableCopy(MI, CurrentKnownM0Val);
        continue;
      }

      // Saw an unknown clobber of m0, so we no longer know what it is.
      if (CurrentKnownM0Val && MI.modifiesRegister(AMDGPU::M0, TRI))
        CurrentKnownM0Val = nullptr;

      // TODO: Omod might be OK if there is NSZ only on the source
      // instruction, and not the omod multiply.
      if (IsIEEEMode || (!HasNSZ && !MI.getFlag(MachineInstr::FmNsz)) ||
          !tryFoldOMod(MI))
        Changed |= tryFoldClamp(MI);
    }

    Changed |= tryOptimizeAGPRPhis(*MBB);
  }

  return Changed;
}

PreservedAnalyses SIFoldOperandsPass::run(MachineFunction &MF,
                                          MachineFunctionAnalysisManager &) {
  MFPropsModifier _(*this, MF);

  bool Changed = SIFoldOperandsImpl().run(MF);
  if (!Changed) {
    return PreservedAnalyses::all();
  }
  auto PA = getMachineFunctionPassPreservedAnalyses();
  PA.preserveSet<CFGAnalyses>();
  return PA;
}