Target/RISCV/RISCVInsertVSETVLI.cpp

//===- RISCVInsertVSETVLI.cpp - Insert VSETVLI instructions ---------------===//
//
// 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 a function pass that inserts VSETVLI instructions where
// needed.
//
// This pass consists of 3 phases:
//
// Phase 1 collects how each basic block affects VL/VTYPE.
//
// Phase 2 uses the information from phase 1 to do a data flow analysis to
// propagate the VL/VTYPE changes through the function. This gives us the
// VL/VTYPE at the start of each basic block.
//
// Phase 3 inserts VSETVLI instructions in each basic block. Information from
// phase 2 is used to prevent inserting a VSETVLI before the first vector
// instruction in the block if possible.
//
//===----------------------------------------------------------------------===//

#include "RISCV.h"
#include "RISCVSubtarget.h"
#include "llvm/CodeGen/LiveIntervals.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include <queue>
using namespace llvm;

#define DEBUG_TYPE "riscv-insert-vsetvli"
#define RISCV_INSERT_VSETVLI_NAME "RISCV Insert VSETVLI pass"

static cl::opt<bool> DisableInsertVSETVLPHIOpt(
    "riscv-disable-insert-vsetvl-phi-opt", cl::init(false), cl::Hidden,
    cl::desc("Disable looking through phis when inserting vsetvlis."));

static cl::opt<bool> UseStrictAsserts(
    "riscv-insert-vsetvl-strict-asserts", cl::init(false), cl::Hidden,
    cl::desc("Enable strict assertion checking for the dataflow algorithm"));

namespace {

class VSETVLIInfo {
  union {
    Register AVLReg;
    unsigned AVLImm;
  };

  enum : uint8_t {
    Uninitialized,
    AVLIsReg,
    AVLIsImm,
    Unknown,
  } State = Uninitialized;

  // Fields from VTYPE.
  RISCVII::VLMUL VLMul = RISCVII::LMUL_1;
  uint8_t SEW = 0;
  uint8_t TailAgnostic : 1;
  uint8_t MaskAgnostic : 1;
  uint8_t MaskRegOp : 1;
  uint8_t StoreOp : 1;
  uint8_t ScalarMovOp : 1;
  uint8_t SEWLMULRatioOnly : 1;

public:
  VSETVLIInfo()
      : AVLImm(0), TailAgnostic(false), MaskAgnostic(false), MaskRegOp(false),
        StoreOp(false), ScalarMovOp(false), SEWLMULRatioOnly(false) {}

  static VSETVLIInfo getUnknown() {
    VSETVLIInfo Info;
    Info.setUnknown();
    return Info;
  }

  bool isValid() const { return State != Uninitialized; }
  void setUnknown() { State = Unknown; }
  bool isUnknown() const { return State == Unknown; }

  void setAVLReg(Register Reg) {
    AVLReg = Reg;
    State = AVLIsReg;
  }

  void setAVLImm(unsigned Imm) {
    AVLImm = Imm;
    State = AVLIsImm;
  }

  bool hasAVLImm() const { return State == AVLIsImm; }
  bool hasAVLReg() const { return State == AVLIsReg; }
  Register getAVLReg() const {
    assert(hasAVLReg());
    return AVLReg;
  }
  unsigned getAVLImm() const {
    assert(hasAVLImm());
    return AVLImm;
  }
  bool hasZeroAVL() const {
    if (hasAVLImm())
      return getAVLImm() == 0;
    return false;
  }
  bool hasNonZeroAVL() const {
    if (hasAVLImm())
      return getAVLImm() > 0;
    if (hasAVLReg())
      return getAVLReg() == RISCV::X0;
    return false;
  }

  bool hasSameAVL(const VSETVLIInfo &Other) const {
    assert(isValid() && Other.isValid() &&
           "Can't compare invalid VSETVLIInfos");
    assert(!isUnknown() && !Other.isUnknown() &&
           "Can't compare AVL in unknown state");
    if (hasAVLReg() && Other.hasAVLReg())
      return getAVLReg() == Other.getAVLReg();

    if (hasAVLImm() && Other.hasAVLImm())
      return getAVLImm() == Other.getAVLImm();

    return false;
  }

  void setVTYPE(unsigned VType) {
    assert(isValid() && !isUnknown() &&
           "Can't set VTYPE for uninitialized or unknown");
    VLMul = RISCVVType::getVLMUL(VType);
    SEW = RISCVVType::getSEW(VType);
    TailAgnostic = RISCVVType::isTailAgnostic(VType);
    MaskAgnostic = RISCVVType::isMaskAgnostic(VType);
  }
  void setVTYPE(RISCVII::VLMUL L, unsigned S, bool TA, bool MA, bool MRO,
                bool IsStore, bool IsScalarMovOp) {
    assert(isValid() && !isUnknown() &&
           "Can't set VTYPE for uninitialized or unknown");
    VLMul = L;
    SEW = S;
    TailAgnostic = TA;
    MaskAgnostic = MA;
    MaskRegOp = MRO;
    StoreOp = IsStore;
    ScalarMovOp = IsScalarMovOp;
  }

  unsigned encodeVTYPE() const {
    assert(isValid() && !isUnknown() && !SEWLMULRatioOnly &&
           "Can't encode VTYPE for uninitialized or unknown");
    return RISCVVType::encodeVTYPE(VLMul, SEW, TailAgnostic, MaskAgnostic);
  }

  bool hasSEWLMULRatioOnly() const { return SEWLMULRatioOnly; }

  bool hasSameSEW(const VSETVLIInfo &Other) const {
    assert(isValid() && Other.isValid() &&
           "Can't compare invalid VSETVLIInfos");
    assert(!isUnknown() && !Other.isUnknown() &&
           "Can't compare VTYPE in unknown state");
    assert(!SEWLMULRatioOnly && !Other.SEWLMULRatioOnly &&
           "Can't compare when only LMUL/SEW ratio is valid.");
    return SEW == Other.SEW;
  }

  bool hasSameVTYPE(const VSETVLIInfo &Other) const {
    assert(isValid() && Other.isValid() &&
           "Can't compare invalid VSETVLIInfos");
    assert(!isUnknown() && !Other.isUnknown() &&
           "Can't compare VTYPE in unknown state");
    assert(!SEWLMULRatioOnly && !Other.SEWLMULRatioOnly &&
           "Can't compare when only LMUL/SEW ratio is valid.");
    return std::tie(VLMul, SEW, TailAgnostic, MaskAgnostic) ==
           std::tie(Other.VLMul, Other.SEW, Other.TailAgnostic,
                    Other.MaskAgnostic);
  }

  static unsigned getSEWLMULRatio(unsigned SEW, RISCVII::VLMUL VLMul) {
    unsigned LMul;
    bool Fractional;
    std::tie(LMul, Fractional) = RISCVVType::decodeVLMUL(VLMul);

    // Convert LMul to a fixed point value with 3 fractional bits.
    LMul = Fractional ? (8 / LMul) : (LMul * 8);

    assert(SEW >= 8 && "Unexpected SEW value");
    return (SEW * 8) / LMul;
  }

  unsigned getSEWLMULRatio() const {
    assert(isValid() && !isUnknown() &&
           "Can't use VTYPE for uninitialized or unknown");
    return getSEWLMULRatio(SEW, VLMul);
  }

  // Check if the VTYPE for these two VSETVLIInfos produce the same VLMAX.
  bool hasSameVLMAX(const VSETVLIInfo &Other) const {
    assert(isValid() && Other.isValid() &&
           "Can't compare invalid VSETVLIInfos");
    assert(!isUnknown() && !Other.isUnknown() &&
           "Can't compare VTYPE in unknown state");
    return getSEWLMULRatio() == Other.getSEWLMULRatio();
  }

  bool hasSamePolicy(const VSETVLIInfo &Other) const {
    assert(isValid() && Other.isValid() &&
           "Can't compare invalid VSETVLIInfos");
    assert(!isUnknown() && !Other.isUnknown() &&
           "Can't compare VTYPE in unknown state");
    return TailAgnostic == Other.TailAgnostic &&
           MaskAgnostic == Other.MaskAgnostic;
  }

  bool hasCompatibleVTYPE(const VSETVLIInfo &Require, bool Strict) const {
    // Simple case, see if full VTYPE matches.
    if (hasSameVTYPE(Require))
      return true;

    if (Strict)
      return false;

    // If this is a mask reg operation, it only cares about VLMAX.
    // FIXME: Mask reg operations are probably ok if "this" VLMAX is larger
    // than "Require".
    // FIXME: The policy bits can probably be ignored for mask reg operations.
    if (Require.MaskRegOp && hasSameVLMAX(Require) &&
        TailAgnostic == Require.TailAgnostic &&
        MaskAgnostic == Require.MaskAgnostic)
      return true;

    return false;
  }

  // Determine whether the vector instructions requirements represented by
  // Require are compatible with the previous vsetvli instruction represented
  // by this.
  bool isCompatible(const VSETVLIInfo &Require, bool Strict) const {
    assert(isValid() && Require.isValid() &&
           "Can't compare invalid VSETVLIInfos");
    assert(!Require.SEWLMULRatioOnly &&
           "Expected a valid VTYPE for instruction!");
    // Nothing is compatible with Unknown.
    if (isUnknown() || Require.isUnknown())
      return false;

    // If only our VLMAX ratio is valid, then this isn't compatible.
    if (SEWLMULRatioOnly)
      return false;

    // If the instruction doesn't need an AVLReg and the SEW matches, consider
    // it compatible.
    if (!Strict && Require.hasAVLReg() &&
        Require.AVLReg == RISCV::NoRegister) {
      if (SEW == Require.SEW)
        return true;
    }

    // For vmv.s.x and vfmv.s.f, there is only two behaviors, VL = 0 and VL > 0.
    // So it's compatible when we could make sure that both VL be the same
    // situation.
    if (!Strict && Require.ScalarMovOp && Require.hasAVLImm() &&
        ((hasNonZeroAVL() && Require.hasNonZeroAVL()) ||
         (hasZeroAVL() && Require.hasZeroAVL())) &&
        hasSameSEW(Require) && hasSamePolicy(Require))
      return true;

    // The AVL must match.
    if (!hasSameAVL(Require))
      return false;

    if (hasCompatibleVTYPE(Require, Strict))
      return true;

    // Strict matches must ensure a full VTYPE match.
    if (Strict)
      return false;

    // Store instructions don't use the policy fields.
    // TODO: Move into hasCompatibleVTYPE?
    if (Require.StoreOp && VLMul == Require.VLMul && SEW == Require.SEW)
      return true;

    // Anything else is not compatible.
    return false;
  }

  bool isCompatibleWithLoadStoreEEW(unsigned EEW,
                                    const VSETVLIInfo &Require) const {
    assert(isValid() && Require.isValid() &&
           "Can't compare invalid VSETVLIInfos");
    assert(!Require.SEWLMULRatioOnly &&
           "Expected a valid VTYPE for instruction!");
    assert(EEW == Require.SEW && "Mismatched EEW/SEW for store");

    if (isUnknown() || hasSEWLMULRatioOnly())
      return false;

    if (!hasSameAVL(Require))
      return false;

    // Stores can ignore the tail and mask policies.
    if (!Require.StoreOp && (TailAgnostic != Require.TailAgnostic ||
                               MaskAgnostic != Require.MaskAgnostic))
      return false;

    return getSEWLMULRatio() == getSEWLMULRatio(EEW, Require.VLMul);
  }

  bool operator==(const VSETVLIInfo &Other) const {
    // Uninitialized is only equal to another Uninitialized.
    if (!isValid())
      return !Other.isValid();
    if (!Other.isValid())
      return !isValid();

    // Unknown is only equal to another Unknown.
    if (isUnknown())
      return Other.isUnknown();
    if (Other.isUnknown())
      return isUnknown();

    if (!hasSameAVL(Other))
      return false;

    // If only the VLMAX is valid, check that it is the same.
    if (SEWLMULRatioOnly && Other.SEWLMULRatioOnly)
      return hasSameVLMAX(Other);

    // If the full VTYPE is valid, check that it is the same.
    if (!SEWLMULRatioOnly && !Other.SEWLMULRatioOnly)
      return hasSameVTYPE(Other);

    // If the SEWLMULRatioOnly bits are different, then they aren't equal.
    return false;
  }

  bool operator!=(const VSETVLIInfo &Other) const {
    return !(*this == Other);
  }

  // Calculate the VSETVLIInfo visible to a block assuming this and Other are
  // both predecessors.
  VSETVLIInfo intersect(const VSETVLIInfo &Other) const {
    // If the new value isn't valid, ignore it.
    if (!Other.isValid())
      return *this;

    // If this value isn't valid, this must be the first predecessor, use it.
    if (!isValid())
      return Other;

    // If either is unknown, the result is unknown.
    if (isUnknown() || Other.isUnknown())
      return VSETVLIInfo::getUnknown();

    // If we have an exact, match return this.
    if (*this == Other)
      return *this;

    // Not an exact match, but maybe the AVL and VLMAX are the same. If so,
    // return an SEW/LMUL ratio only value.
    if (hasSameAVL(Other) && hasSameVLMAX(Other)) {
      VSETVLIInfo MergeInfo = *this;
      MergeInfo.SEWLMULRatioOnly = true;
      return MergeInfo;
    }

    // Otherwise the result is unknown.
    return VSETVLIInfo::getUnknown();
  }

  // Calculate the VSETVLIInfo visible at the end of the block assuming this
  // is the predecessor value, and Other is change for this block.
  VSETVLIInfo merge(const VSETVLIInfo &Other) const {
    assert(isValid() && "Can only merge with a valid VSETVLInfo");

    // Nothing changed from the predecessor, keep it.
    if (!Other.isValid())
      return *this;

    // If the change is compatible with the input, we won't create a VSETVLI
    // and should keep the predecessor.
    if (isCompatible(Other, /*Strict*/ true))
      return *this;

    // Otherwise just use whatever is in this block.
    return Other;
  }

#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
  /// Support for debugging, callable in GDB: V->dump()
  LLVM_DUMP_METHOD void dump() const {
    print(dbgs());
    dbgs() << "\n";
  }

  /// Implement operator<<.
  /// @{
  void print(raw_ostream &OS) const {
    OS << "{";
    if (!isValid())
      OS << "Uninitialized";
    if (isUnknown())
      OS << "unknown";;
    if (hasAVLReg())
      OS << "AVLReg=" << (unsigned)AVLReg;
    if (hasAVLImm())
      OS << "AVLImm=" << (unsigned)AVLImm;
    OS << ", "
       << "VLMul=" << (unsigned)VLMul << ", "
       << "SEW=" << (unsigned)SEW << ", "
       << "TailAgnostic=" << (bool)TailAgnostic << ", "
       << "MaskAgnostic=" << (bool)MaskAgnostic << ", "
       << "MaskRegOp=" << (bool)MaskRegOp << ", "
       << "StoreOp=" << (bool)StoreOp << ", "
       << "ScalarMovOp=" << (bool)ScalarMovOp << ", "
       << "SEWLMULRatioOnly=" << (bool)SEWLMULRatioOnly << "}";
  }
#endif
};

#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
LLVM_ATTRIBUTE_USED
inline raw_ostream &operator<<(raw_ostream &OS, const VSETVLIInfo &V) {
  V.print(OS);
  return OS;
}
#endif

struct BlockData {
  // The VSETVLIInfo that represents the net changes to the VL/VTYPE registers
  // made by this block. Calculated in Phase 1.
  VSETVLIInfo Change;

  // The VSETVLIInfo that represents the VL/VTYPE settings on exit from this
  // block. Calculated in Phase 2.
  VSETVLIInfo Exit;

  // The VSETVLIInfo that represents the VL/VTYPE settings from all predecessor
  // blocks. Calculated in Phase 2, and used by Phase 3.
  VSETVLIInfo Pred;

  // Keeps track of whether the block is already in the queue.
  bool InQueue = false;

  BlockData() = default;
};

class RISCVInsertVSETVLI : public MachineFunctionPass {
  const TargetInstrInfo *TII;
  MachineRegisterInfo *MRI;

  std::vector<BlockData> BlockInfo;
  std::queue<const MachineBasicBlock *> WorkList;

public:
  static char ID;

  RISCVInsertVSETVLI() : MachineFunctionPass(ID) {
    initializeRISCVInsertVSETVLIPass(*PassRegistry::getPassRegistry());
  }
  bool runOnMachineFunction(MachineFunction &MF) override;

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

  StringRef getPassName() const override { return RISCV_INSERT_VSETVLI_NAME; }

private:
  bool needVSETVLI(const VSETVLIInfo &Require, const VSETVLIInfo &CurInfo);
  bool needVSETVLIPHI(const VSETVLIInfo &Require, const MachineBasicBlock &MBB);
  void insertVSETVLI(MachineBasicBlock &MBB, MachineInstr &MI,
                     const VSETVLIInfo &Info, const VSETVLIInfo &PrevInfo);
  void insertVSETVLI(MachineBasicBlock &MBB,
                     MachineBasicBlock::iterator InsertPt, DebugLoc DL,
                     const VSETVLIInfo &Info, const VSETVLIInfo &PrevInfo);

  bool computeVLVTYPEChanges(const MachineBasicBlock &MBB);
  void computeIncomingVLVTYPE(const MachineBasicBlock &MBB);
  void emitVSETVLIs(MachineBasicBlock &MBB);
  void doLocalPrepass(MachineBasicBlock &MBB);
};

} // end anonymous namespace

char RISCVInsertVSETVLI::ID = 0;

INITIALIZE_PASS(RISCVInsertVSETVLI, DEBUG_TYPE, RISCV_INSERT_VSETVLI_NAME,
                false, false)

static bool isVectorConfigInstr(const MachineInstr &MI) {
  return MI.getOpcode() == RISCV::PseudoVSETVLI ||
         MI.getOpcode() == RISCV::PseudoVSETVLIX0 ||
         MI.getOpcode() == RISCV::PseudoVSETIVLI;
}

static MachineInstr *elideCopies(MachineInstr *MI,
                                 const MachineRegisterInfo *MRI) {
  while (true) {
    if (!MI->isFullCopy())
      return MI;
    if (!Register::isVirtualRegister(MI->getOperand(1).getReg()))
      return nullptr;
    MI = MRI->getVRegDef(MI->getOperand(1).getReg());
    if (!MI)
      return nullptr;
  }
}

static bool isScalarMoveInstr(const MachineInstr &MI) {
  switch (MI.getOpcode()) {
  default:
    return false;
  case RISCV::PseudoVMV_S_X_M1:
  case RISCV::PseudoVMV_S_X_M2:
  case RISCV::PseudoVMV_S_X_M4:
  case RISCV::PseudoVMV_S_X_M8:
  case RISCV::PseudoVMV_S_X_MF2:
  case RISCV::PseudoVMV_S_X_MF4:
  case RISCV::PseudoVMV_S_X_MF8:
  case RISCV::PseudoVFMV_S_F16_M1:
  case RISCV::PseudoVFMV_S_F16_M2:
  case RISCV::PseudoVFMV_S_F16_M4:
  case RISCV::PseudoVFMV_S_F16_M8:
  case RISCV::PseudoVFMV_S_F16_MF2:
  case RISCV::PseudoVFMV_S_F16_MF4:
  case RISCV::PseudoVFMV_S_F32_M1:
  case RISCV::PseudoVFMV_S_F32_M2:
  case RISCV::PseudoVFMV_S_F32_M4:
  case RISCV::PseudoVFMV_S_F32_M8:
  case RISCV::PseudoVFMV_S_F32_MF2:
  case RISCV::PseudoVFMV_S_F64_M1:
  case RISCV::PseudoVFMV_S_F64_M2:
  case RISCV::PseudoVFMV_S_F64_M4:
  case RISCV::PseudoVFMV_S_F64_M8:
    return true;
  }
}

static unsigned getVLOpNum(const MachineInstr &MI) {
  return RISCVII::getVLOpNum(MI.getDesc());
}

static unsigned getSEWOpNum(const MachineInstr &MI) {
  return RISCVII::getSEWOpNum(MI.getDesc());
}

static VSETVLIInfo computeInfoForInstr(const MachineInstr &MI, uint64_t TSFlags,
                                       const MachineRegisterInfo *MRI) {
  VSETVLIInfo InstrInfo;

  // If the instruction has policy argument, use the argument.
  // If there is no policy argument, default to tail agnostic unless the
  // destination is tied to a source. Unless the source is undef. In that case
  // the user would have some control over the policy values.
  bool TailAgnostic = true;
  bool UsesMaskPolicy = RISCVII::usesMaskPolicy(TSFlags);
  // FIXME: Could we look at the above or below instructions to choose the
  // matched mask policy to reduce vsetvli instructions? Default mask policy is
  // agnostic if instructions use mask policy, otherwise is undisturbed. Because
  // most mask operations are mask undisturbed, so we could possibly reduce the
  // vsetvli between mask and nomasked instruction sequence.
  bool MaskAgnostic = UsesMaskPolicy;
  unsigned UseOpIdx;
  if (RISCVII::hasVecPolicyOp(TSFlags)) {
    const MachineOperand &Op = MI.getOperand(MI.getNumExplicitOperands() - 1);
    uint64_t Policy = Op.getImm();
    assert(Policy <= (RISCVII::TAIL_AGNOSTIC | RISCVII::MASK_AGNOSTIC) &&
           "Invalid Policy Value");
    // Although in some cases, mismatched passthru/maskedoff with policy value
    // does not make sense (ex. tied operand is IMPLICIT_DEF with non-TAMA
    // policy, or tied operand is not IMPLICIT_DEF with TAMA policy), but users
    // have set the policy value explicitly, so compiler would not fix it.
    TailAgnostic = Policy & RISCVII::TAIL_AGNOSTIC;
    MaskAgnostic = Policy & RISCVII::MASK_AGNOSTIC;
  } else if (MI.isRegTiedToUseOperand(0, &UseOpIdx)) {
    TailAgnostic = false;
    if (UsesMaskPolicy)
      MaskAgnostic = false;
    // If the tied operand is an IMPLICIT_DEF we can keep TailAgnostic.
    const MachineOperand &UseMO = MI.getOperand(UseOpIdx);
    MachineInstr *UseMI = MRI->getVRegDef(UseMO.getReg());
    if (UseMI) {
      UseMI = elideCopies(UseMI, MRI);
      if (UseMI && UseMI->isImplicitDef()) {
        TailAgnostic = true;
        if (UsesMaskPolicy)
          MaskAgnostic = true;
      }
    }
    // Some pseudo instructions force a tail agnostic policy despite having a
    // tied def.
    if (RISCVII::doesForceTailAgnostic(TSFlags))
      TailAgnostic = true;
  }

  RISCVII::VLMUL VLMul = RISCVII::getLMul(TSFlags);

  unsigned Log2SEW = MI.getOperand(getSEWOpNum(MI)).getImm();
  // A Log2SEW of 0 is an operation on mask registers only.
  bool MaskRegOp = Log2SEW == 0;
  unsigned SEW = Log2SEW ? 1 << Log2SEW : 8;
  assert(RISCVVType::isValidSEW(SEW) && "Unexpected SEW");

  // If there are no explicit defs, this is a store instruction which can
  // ignore the tail and mask policies.
  bool StoreOp = MI.getNumExplicitDefs() == 0;
  bool ScalarMovOp = isScalarMoveInstr(MI);

  if (RISCVII::hasVLOp(TSFlags)) {
    const MachineOperand &VLOp = MI.getOperand(getVLOpNum(MI));
    if (VLOp.isImm()) {
      int64_t Imm = VLOp.getImm();
      // Conver the VLMax sentintel to X0 register.
      if (Imm == RISCV::VLMaxSentinel)
        InstrInfo.setAVLReg(RISCV::X0);
      else
        InstrInfo.setAVLImm(Imm);
    } else {
      InstrInfo.setAVLReg(VLOp.getReg());
    }
  } else
    InstrInfo.setAVLReg(RISCV::NoRegister);
  InstrInfo.setVTYPE(VLMul, SEW, TailAgnostic, MaskAgnostic, MaskRegOp, StoreOp,
                     ScalarMovOp);

  return InstrInfo;
}

void RISCVInsertVSETVLI::insertVSETVLI(MachineBasicBlock &MBB, MachineInstr &MI,
                                       const VSETVLIInfo &Info,
                                       const VSETVLIInfo &PrevInfo) {
  DebugLoc DL = MI.getDebugLoc();
  insertVSETVLI(MBB, MachineBasicBlock::iterator(&MI), DL, Info, PrevInfo);
}

void RISCVInsertVSETVLI::insertVSETVLI(MachineBasicBlock &MBB,
                     MachineBasicBlock::iterator InsertPt, DebugLoc DL,
                     const VSETVLIInfo &Info, const VSETVLIInfo &PrevInfo) {

  // Use X0, X0 form if the AVL is the same and the SEW+LMUL gives the same
  // VLMAX.
  if (PrevInfo.isValid() && !PrevInfo.isUnknown() &&
      Info.hasSameAVL(PrevInfo) && Info.hasSameVLMAX(PrevInfo)) {
    BuildMI(MBB, InsertPt, DL, TII->get(RISCV::PseudoVSETVLIX0))
        .addReg(RISCV::X0, RegState::Define | RegState::Dead)
        .addReg(RISCV::X0, RegState::Kill)
        .addImm(Info.encodeVTYPE())
        .addReg(RISCV::VL, RegState::Implicit);
    return;
  }

  if (Info.hasAVLImm()) {
    BuildMI(MBB, InsertPt, DL, TII->get(RISCV::PseudoVSETIVLI))
        .addReg(RISCV::X0, RegState::Define | RegState::Dead)
        .addImm(Info.getAVLImm())
        .addImm(Info.encodeVTYPE());
    return;
  }

  Register AVLReg = Info.getAVLReg();
  if (AVLReg == RISCV::NoRegister) {
    // We can only use x0, x0 if there's no chance of the vtype change causing
    // the previous vl to become invalid.
    if (PrevInfo.isValid() && !PrevInfo.isUnknown() &&
        Info.hasSameVLMAX(PrevInfo)) {
      BuildMI(MBB, InsertPt, DL, TII->get(RISCV::PseudoVSETVLIX0))
          .addReg(RISCV::X0, RegState::Define | RegState::Dead)
          .addReg(RISCV::X0, RegState::Kill)
          .addImm(Info.encodeVTYPE())
          .addReg(RISCV::VL, RegState::Implicit);
      return;
    }
    // Otherwise use an AVL of 0 to avoid depending on previous vl.
    BuildMI(MBB, InsertPt, DL, TII->get(RISCV::PseudoVSETIVLI))
        .addReg(RISCV::X0, RegState::Define | RegState::Dead)
        .addImm(0)
        .addImm(Info.encodeVTYPE());
    return;
  }

  if (AVLReg.isVirtual())
    MRI->constrainRegClass(AVLReg, &RISCV::GPRNoX0RegClass);

  // Use X0 as the DestReg unless AVLReg is X0. We also need to change the
  // opcode if the AVLReg is X0 as they have different register classes for
  // the AVL operand.
  Register DestReg = RISCV::X0;
  unsigned Opcode = RISCV::PseudoVSETVLI;
  if (AVLReg == RISCV::X0) {
    DestReg = MRI->createVirtualRegister(&RISCV::GPRRegClass);
    Opcode = RISCV::PseudoVSETVLIX0;
  }
  BuildMI(MBB, InsertPt, DL, TII->get(Opcode))
      .addReg(DestReg, RegState::Define | RegState::Dead)
      .addReg(AVLReg)
      .addImm(Info.encodeVTYPE());
}

// Return a VSETVLIInfo representing the changes made by this VSETVLI or
// VSETIVLI instruction.
static VSETVLIInfo getInfoForVSETVLI(const MachineInstr &MI) {
  VSETVLIInfo NewInfo;
  if (MI.getOpcode() == RISCV::PseudoVSETIVLI) {
    NewInfo.setAVLImm(MI.getOperand(1).getImm());
  } else {
    assert(MI.getOpcode() == RISCV::PseudoVSETVLI ||
           MI.getOpcode() == RISCV::PseudoVSETVLIX0);
    Register AVLReg = MI.getOperand(1).getReg();
    assert((AVLReg != RISCV::X0 || MI.getOperand(0).getReg() != RISCV::X0) &&
           "Can't handle X0, X0 vsetvli yet");
    NewInfo.setAVLReg(AVLReg);
  }
  NewInfo.setVTYPE(MI.getOperand(2).getImm());

  return NewInfo;
}

bool RISCVInsertVSETVLI::needVSETVLI(const VSETVLIInfo &Require,
                                     const VSETVLIInfo &CurInfo) {
  if (CurInfo.isCompatible(Require, /*Strict*/ false))
    return false;

  // We didn't find a compatible value. If our AVL is a virtual register,
  // it might be defined by a VSET(I)VLI. If it has the same VTYPE we need
  // and the last VL/VTYPE we observed is the same, we don't need a
  // VSETVLI here.
  if (!CurInfo.isUnknown() && Require.hasAVLReg() &&
      Require.getAVLReg().isVirtual() && !CurInfo.hasSEWLMULRatioOnly() &&
      CurInfo.hasCompatibleVTYPE(Require, /*Strict*/ false)) {
    if (MachineInstr *DefMI = MRI->getVRegDef(Require.getAVLReg())) {
      if (isVectorConfigInstr(*DefMI)) {
        VSETVLIInfo DefInfo = getInfoForVSETVLI(*DefMI);
        if (DefInfo.hasSameAVL(CurInfo) && DefInfo.hasSameVTYPE(CurInfo))
          return false;
      }
    }
  }

  return true;
}

bool canSkipVSETVLIForLoadStore(const MachineInstr &MI,
                                const VSETVLIInfo &Require,
                                const VSETVLIInfo &CurInfo) {
  unsigned EEW;
  switch (MI.getOpcode()) {
  default:
    return false;
  case RISCV::PseudoVLE8_V_M1:
  case RISCV::PseudoVLE8_V_M1_MASK:
  case RISCV::PseudoVLE8_V_M2:
  case RISCV::PseudoVLE8_V_M2_MASK:
  case RISCV::PseudoVLE8_V_M4:
  case RISCV::PseudoVLE8_V_M4_MASK:
  case RISCV::PseudoVLE8_V_M8:
  case RISCV::PseudoVLE8_V_M8_MASK:
  case RISCV::PseudoVLE8_V_MF2:
  case RISCV::PseudoVLE8_V_MF2_MASK:
  case RISCV::PseudoVLE8_V_MF4:
  case RISCV::PseudoVLE8_V_MF4_MASK:
  case RISCV::PseudoVLE8_V_MF8:
  case RISCV::PseudoVLE8_V_MF8_MASK:
  case RISCV::PseudoVLSE8_V_M1:
  case RISCV::PseudoVLSE8_V_M1_MASK:
  case RISCV::PseudoVLSE8_V_M2:
  case RISCV::PseudoVLSE8_V_M2_MASK:
  case RISCV::PseudoVLSE8_V_M4:
  case RISCV::PseudoVLSE8_V_M4_MASK:
  case RISCV::PseudoVLSE8_V_M8:
  case RISCV::PseudoVLSE8_V_M8_MASK:
  case RISCV::PseudoVLSE8_V_MF2:
  case RISCV::PseudoVLSE8_V_MF2_MASK:
  case RISCV::PseudoVLSE8_V_MF4:
  case RISCV::PseudoVLSE8_V_MF4_MASK:
  case RISCV::PseudoVLSE8_V_MF8:
  case RISCV::PseudoVLSE8_V_MF8_MASK:
  case RISCV::PseudoVSE8_V_M1:
  case RISCV::PseudoVSE8_V_M1_MASK:
  case RISCV::PseudoVSE8_V_M2:
  case RISCV::PseudoVSE8_V_M2_MASK:
  case RISCV::PseudoVSE8_V_M4:
  case RISCV::PseudoVSE8_V_M4_MASK:
  case RISCV::PseudoVSE8_V_M8:
  case RISCV::PseudoVSE8_V_M8_MASK:
  case RISCV::PseudoVSE8_V_MF2:
  case RISCV::PseudoVSE8_V_MF2_MASK:
  case RISCV::PseudoVSE8_V_MF4:
  case RISCV::PseudoVSE8_V_MF4_MASK:
  case RISCV::PseudoVSE8_V_MF8:
  case RISCV::PseudoVSE8_V_MF8_MASK:
  case RISCV::PseudoVSSE8_V_M1:
  case RISCV::PseudoVSSE8_V_M1_MASK:
  case RISCV::PseudoVSSE8_V_M2:
  case RISCV::PseudoVSSE8_V_M2_MASK:
  case RISCV::PseudoVSSE8_V_M4:
  case RISCV::PseudoVSSE8_V_M4_MASK:
  case RISCV::PseudoVSSE8_V_M8:
  case RISCV::PseudoVSSE8_V_M8_MASK:
  case RISCV::PseudoVSSE8_V_MF2:
  case RISCV::PseudoVSSE8_V_MF2_MASK:
  case RISCV::PseudoVSSE8_V_MF4:
  case RISCV::PseudoVSSE8_V_MF4_MASK:
  case RISCV::PseudoVSSE8_V_MF8:
  case RISCV::PseudoVSSE8_V_MF8_MASK:
    EEW = 8;
    break;
  case RISCV::PseudoVLE16_V_M1:
  case RISCV::PseudoVLE16_V_M1_MASK:
  case RISCV::PseudoVLE16_V_M2:
  case RISCV::PseudoVLE16_V_M2_MASK:
  case RISCV::PseudoVLE16_V_M4:
  case RISCV::PseudoVLE16_V_M4_MASK:
  case RISCV::PseudoVLE16_V_M8:
  case RISCV::PseudoVLE16_V_M8_MASK:
  case RISCV::PseudoVLE16_V_MF2:
  case RISCV::PseudoVLE16_V_MF2_MASK:
  case RISCV::PseudoVLE16_V_MF4:
  case RISCV::PseudoVLE16_V_MF4_MASK:
  case RISCV::PseudoVLSE16_V_M1:
  case RISCV::PseudoVLSE16_V_M1_MASK:
  case RISCV::PseudoVLSE16_V_M2:
  case RISCV::PseudoVLSE16_V_M2_MASK:
  case RISCV::PseudoVLSE16_V_M4:
  case RISCV::PseudoVLSE16_V_M4_MASK:
  case RISCV::PseudoVLSE16_V_M8:
  case RISCV::PseudoVLSE16_V_M8_MASK:
  case RISCV::PseudoVLSE16_V_MF2:
  case RISCV::PseudoVLSE16_V_MF2_MASK:
  case RISCV::PseudoVLSE16_V_MF4:
  case RISCV::PseudoVLSE16_V_MF4_MASK:
  case RISCV::PseudoVSE16_V_M1:
  case RISCV::PseudoVSE16_V_M1_MASK:
  case RISCV::PseudoVSE16_V_M2:
  case RISCV::PseudoVSE16_V_M2_MASK:
  case RISCV::PseudoVSE16_V_M4:
  case RISCV::PseudoVSE16_V_M4_MASK:
  case RISCV::PseudoVSE16_V_M8:
  case RISCV::PseudoVSE16_V_M8_MASK:
  case RISCV::PseudoVSE16_V_MF2:
  case RISCV::PseudoVSE16_V_MF2_MASK:
  case RISCV::PseudoVSE16_V_MF4:
  case RISCV::PseudoVSE16_V_MF4_MASK:
  case RISCV::PseudoVSSE16_V_M1:
  case RISCV::PseudoVSSE16_V_M1_MASK:
  case RISCV::PseudoVSSE16_V_M2:
  case RISCV::PseudoVSSE16_V_M2_MASK:
  case RISCV::PseudoVSSE16_V_M4:
  case RISCV::PseudoVSSE16_V_M4_MASK:
  case RISCV::PseudoVSSE16_V_M8:
  case RISCV::PseudoVSSE16_V_M8_MASK:
  case RISCV::PseudoVSSE16_V_MF2:
  case RISCV::PseudoVSSE16_V_MF2_MASK:
  case RISCV::PseudoVSSE16_V_MF4:
  case RISCV::PseudoVSSE16_V_MF4_MASK:
    EEW = 16;
    break;
  case RISCV::PseudoVLE32_V_M1:
  case RISCV::PseudoVLE32_V_M1_MASK:
  case RISCV::PseudoVLE32_V_M2:
  case RISCV::PseudoVLE32_V_M2_MASK:
  case RISCV::PseudoVLE32_V_M4:
  case RISCV::PseudoVLE32_V_M4_MASK:
  case RISCV::PseudoVLE32_V_M8:
  case RISCV::PseudoVLE32_V_M8_MASK:
  case RISCV::PseudoVLE32_V_MF2:
  case RISCV::PseudoVLE32_V_MF2_MASK:
  case RISCV::PseudoVLSE32_V_M1:
  case RISCV::PseudoVLSE32_V_M1_MASK:
  case RISCV::PseudoVLSE32_V_M2:
  case RISCV::PseudoVLSE32_V_M2_MASK:
  case RISCV::PseudoVLSE32_V_M4:
  case RISCV::PseudoVLSE32_V_M4_MASK:
  case RISCV::PseudoVLSE32_V_M8:
  case RISCV::PseudoVLSE32_V_M8_MASK:
  case RISCV::PseudoVLSE32_V_MF2:
  case RISCV::PseudoVLSE32_V_MF2_MASK:
  case RISCV::PseudoVSE32_V_M1:
  case RISCV::PseudoVSE32_V_M1_MASK:
  case RISCV::PseudoVSE32_V_M2:
  case RISCV::PseudoVSE32_V_M2_MASK:
  case RISCV::PseudoVSE32_V_M4:
  case RISCV::PseudoVSE32_V_M4_MASK:
  case RISCV::PseudoVSE32_V_M8:
  case RISCV::PseudoVSE32_V_M8_MASK:
  case RISCV::PseudoVSE32_V_MF2:
  case RISCV::PseudoVSE32_V_MF2_MASK:
  case RISCV::PseudoVSSE32_V_M1:
  case RISCV::PseudoVSSE32_V_M1_MASK:
  case RISCV::PseudoVSSE32_V_M2:
  case RISCV::PseudoVSSE32_V_M2_MASK:
  case RISCV::PseudoVSSE32_V_M4:
  case RISCV::PseudoVSSE32_V_M4_MASK:
  case RISCV::PseudoVSSE32_V_M8:
  case RISCV::PseudoVSSE32_V_M8_MASK:
  case RISCV::PseudoVSSE32_V_MF2:
  case RISCV::PseudoVSSE32_V_MF2_MASK:
    EEW = 32;
    break;
  case RISCV::PseudoVLE64_V_M1:
  case RISCV::PseudoVLE64_V_M1_MASK:
  case RISCV::PseudoVLE64_V_M2:
  case RISCV::PseudoVLE64_V_M2_MASK:
  case RISCV::PseudoVLE64_V_M4:
  case RISCV::PseudoVLE64_V_M4_MASK:
  case RISCV::PseudoVLE64_V_M8:
  case RISCV::PseudoVLE64_V_M8_MASK:
  case RISCV::PseudoVLSE64_V_M1:
  case RISCV::PseudoVLSE64_V_M1_MASK:
  case RISCV::PseudoVLSE64_V_M2:
  case RISCV::PseudoVLSE64_V_M2_MASK:
  case RISCV::PseudoVLSE64_V_M4:
  case RISCV::PseudoVLSE64_V_M4_MASK:
  case RISCV::PseudoVLSE64_V_M8:
  case RISCV::PseudoVLSE64_V_M8_MASK:
  case RISCV::PseudoVSE64_V_M1:
  case RISCV::PseudoVSE64_V_M1_MASK:
  case RISCV::PseudoVSE64_V_M2:
  case RISCV::PseudoVSE64_V_M2_MASK:
  case RISCV::PseudoVSE64_V_M4:
  case RISCV::PseudoVSE64_V_M4_MASK:
  case RISCV::PseudoVSE64_V_M8:
  case RISCV::PseudoVSE64_V_M8_MASK:
  case RISCV::PseudoVSSE64_V_M1:
  case RISCV::PseudoVSSE64_V_M1_MASK:
  case RISCV::PseudoVSSE64_V_M2:
  case RISCV::PseudoVSSE64_V_M2_MASK:
  case RISCV::PseudoVSSE64_V_M4:
  case RISCV::PseudoVSSE64_V_M4_MASK:
  case RISCV::PseudoVSSE64_V_M8:
  case RISCV::PseudoVSSE64_V_M8_MASK:
    EEW = 64;
    break;
  }

  return CurInfo.isCompatibleWithLoadStoreEEW(EEW, Require);
}

bool RISCVInsertVSETVLI::computeVLVTYPEChanges(const MachineBasicBlock &MBB) {
  bool HadVectorOp = false;

  BlockData &BBInfo = BlockInfo[MBB.getNumber()];
  for (const MachineInstr &MI : MBB) {
    // If this is an explicit VSETVLI or VSETIVLI, update our state.
    if (isVectorConfigInstr(MI)) {
      HadVectorOp = true;
      BBInfo.Change = getInfoForVSETVLI(MI);
      continue;
    }

    uint64_t TSFlags = MI.getDesc().TSFlags;
    if (RISCVII::hasSEWOp(TSFlags)) {
      HadVectorOp = true;

      VSETVLIInfo NewInfo = computeInfoForInstr(MI, TSFlags, MRI);

      if (!BBInfo.Change.isValid()) {
        BBInfo.Change = NewInfo;
      } else {
        // If this instruction isn't compatible with the previous VL/VTYPE
        // we need to insert a VSETVLI.
        // If this is a unit-stride or strided load/store, we may be able to use
        // the EMUL=(EEW/SEW)*LMUL relationship to avoid changing vtype.
        // NOTE: We only do this if the vtype we're comparing against was
        // created in this block. We need the first and third phase to treat
        // the store the same way.
        if (!canSkipVSETVLIForLoadStore(MI, NewInfo, BBInfo.Change) &&
            needVSETVLI(NewInfo, BBInfo.Change))
          BBInfo.Change = NewInfo;
      }
    }

    // If this is something that updates VL/VTYPE that we don't know about, set
    // the state to unknown.
    if (MI.isCall() || MI.isInlineAsm() || MI.modifiesRegister(RISCV::VL) ||
        MI.modifiesRegister(RISCV::VTYPE))
      BBInfo.Change = VSETVLIInfo::getUnknown();
  }

  // Initial exit state is whatever change we found in the block.
  BBInfo.Exit = BBInfo.Change;
  LLVM_DEBUG(dbgs() << "Initial exit state of " << printMBBReference(MBB)
                    << " is " << BBInfo.Exit << "\n");

  return HadVectorOp;
}

void RISCVInsertVSETVLI::computeIncomingVLVTYPE(const MachineBasicBlock &MBB) {
  BlockData &BBInfo = BlockInfo[MBB.getNumber()];

  BBInfo.InQueue = false;

  VSETVLIInfo InInfo;
  if (MBB.pred_empty()) {
    // There are no predecessors, so use the default starting status.
    InInfo.setUnknown();
  } else {
    for (MachineBasicBlock *P : MBB.predecessors())
      InInfo = InInfo.intersect(BlockInfo[P->getNumber()].Exit);
  }

  // If we don't have any valid predecessor value, wait until we do.
  if (!InInfo.isValid())
    return;

  // If no change, no need to rerun block
  if (InInfo == BBInfo.Pred)
    return;

  BBInfo.Pred = InInfo;
  LLVM_DEBUG(dbgs() << "Entry state of " << printMBBReference(MBB)
                    << " changed to " << BBInfo.Pred << "\n");

  VSETVLIInfo TmpStatus = BBInfo.Pred.merge(BBInfo.Change);

  // If the new exit value matches the old exit value, we don't need to revisit
  // any blocks.
  if (BBInfo.Exit == TmpStatus)
    return;

  BBInfo.Exit = TmpStatus;
  LLVM_DEBUG(dbgs() << "Exit state of " << printMBBReference(MBB)
                    << " changed to " << BBInfo.Exit << "\n");

  // Add the successors to the work list so we can propagate the changed exit
  // status.
  for (MachineBasicBlock *S : MBB.successors())
    if (!BlockInfo[S->getNumber()].InQueue)
      WorkList.push(S);
}

// If we weren't able to prove a vsetvli was directly unneeded, it might still
// be/ unneeded if the AVL is a phi node where all incoming values are VL
// outputs from the last VSETVLI in their respective basic blocks.
bool RISCVInsertVSETVLI::needVSETVLIPHI(const VSETVLIInfo &Require,
                                        const MachineBasicBlock &MBB) {
  if (DisableInsertVSETVLPHIOpt)
    return true;

  if (!Require.hasAVLReg())
    return true;

  Register AVLReg = Require.getAVLReg();
  if (!AVLReg.isVirtual())
    return true;

  // We need the AVL to be produce by a PHI node in this basic block.
  MachineInstr *PHI = MRI->getVRegDef(AVLReg);
  if (!PHI || PHI->getOpcode() != RISCV::PHI || PHI->getParent() != &MBB)
    return true;

  for (unsigned PHIOp = 1, NumOps = PHI->getNumOperands(); PHIOp != NumOps;
       PHIOp += 2) {
    Register InReg = PHI->getOperand(PHIOp).getReg();
    MachineBasicBlock *PBB = PHI->getOperand(PHIOp + 1).getMBB();
    const BlockData &PBBInfo = BlockInfo[PBB->getNumber()];
    // If the exit from the predecessor has the VTYPE we are looking for
    // we might be able to avoid a VSETVLI.
    if (PBBInfo.Exit.isUnknown() ||
        !PBBInfo.Exit.hasCompatibleVTYPE(Require, /*Strict*/ false))
      return true;

    // We need the PHI input to the be the output of a VSET(I)VLI.
    MachineInstr *DefMI = MRI->getVRegDef(InReg);
    if (!DefMI || !isVectorConfigInstr(*DefMI))
      return true;

    // We found a VSET(I)VLI make sure it matches the output of the
    // predecessor block.
    VSETVLIInfo DefInfo = getInfoForVSETVLI(*DefMI);
    if (!DefInfo.hasSameAVL(PBBInfo.Exit) ||
        !DefInfo.hasSameVTYPE(PBBInfo.Exit))
      return true;
  }

  // If all the incoming values to the PHI checked out, we don't need
  // to insert a VSETVLI.
  return false;
}

void RISCVInsertVSETVLI::emitVSETVLIs(MachineBasicBlock &MBB) {
  VSETVLIInfo CurInfo;
  // Only be set if current VSETVLIInfo is from an explicit VSET(I)VLI.
  MachineInstr *PrevVSETVLIMI = nullptr;

  for (MachineInstr &MI : MBB) {
    // If this is an explicit VSETVLI or VSETIVLI, update our state.
    if (isVectorConfigInstr(MI)) {
      // Conservatively, mark the VL and VTYPE as live.
      assert(MI.getOperand(3).getReg() == RISCV::VL &&
             MI.getOperand(4).getReg() == RISCV::VTYPE &&
             "Unexpected operands where VL and VTYPE should be");
      MI.getOperand(3).setIsDead(false);
      MI.getOperand(4).setIsDead(false);
      CurInfo = getInfoForVSETVLI(MI);
      PrevVSETVLIMI = &MI;
      continue;
    }

    uint64_t TSFlags = MI.getDesc().TSFlags;
    if (RISCVII::hasSEWOp(TSFlags)) {
      VSETVLIInfo NewInfo = computeInfoForInstr(MI, TSFlags, MRI);
      if (RISCVII::hasVLOp(TSFlags)) {
        MachineOperand &VLOp = MI.getOperand(getVLOpNum(MI));
        if (VLOp.isReg()) {
          // Erase the AVL operand from the instruction.
          VLOp.setReg(RISCV::NoRegister);
          VLOp.setIsKill(false);
        }
        MI.addOperand(MachineOperand::CreateReg(RISCV::VL, /*isDef*/ false,
                                                /*isImp*/ true));
      }
      MI.addOperand(MachineOperand::CreateReg(RISCV::VTYPE, /*isDef*/ false,
                                              /*isImp*/ true));

      if (!CurInfo.isValid()) {
        // We haven't found any vector instructions or VL/VTYPE changes yet,
        // use the predecessor information.
        assert(BlockInfo[MBB.getNumber()].Pred.isValid() &&
               "Expected a valid predecessor state.");
        if (needVSETVLI(NewInfo, BlockInfo[MBB.getNumber()].Pred)) {
          // If this is the first implicit state change, and the state change
          // requested can be proven to produce the same register contents, we
          // can skip emitting the actual state change and continue as if we
          // had since we know the GPR result of the implicit state change
          // wouldn't be used and VL/VTYPE registers are correct.  Note that
          // we *do* need to model the state as if it changed as while the
          // register contents are unchanged, the abstract model can change.
          if (needVSETVLIPHI(NewInfo, MBB))
            insertVSETVLI(MBB, MI, NewInfo, BlockInfo[MBB.getNumber()].Pred);
          CurInfo = NewInfo;
        }
      } else {
        // If this instruction isn't compatible with the previous VL/VTYPE
        // we need to insert a VSETVLI.
        // If this is a unit-stride or strided load/store, we may be able to use
        // the EMUL=(EEW/SEW)*LMUL relationship to avoid changing vtype.
        // NOTE: We can't use predecessor information for the store. We must
        // treat it the same as the first phase so that we produce the correct
        // vl/vtype for succesor blocks.
        if (!canSkipVSETVLIForLoadStore(MI, NewInfo, CurInfo) &&
            needVSETVLI(NewInfo, CurInfo)) {
          // If the previous VL/VTYPE is set by VSETVLI and do not use, Merge it
          // with current VL/VTYPE.
          bool NeedInsertVSETVLI = true;
          if (PrevVSETVLIMI) {
            // If these two VSETVLI have the same AVL and the same VLMAX,
            // we could merge these two VSETVLI.
            // TODO: If we remove this, we get a `vsetvli x0, x0, vtype'
            // here.  We could simply let this be emitted, then remove
            // the unused vsetvlis in a post-pass.
            if (CurInfo.hasSameAVL(NewInfo) && CurInfo.hasSameVLMAX(NewInfo)) {
              // WARNING: For correctness, it is essential the contents of VL
              // and VTYPE stay the same after MI.  This greatly limits the
              // mutation we can legally do here.
              PrevVSETVLIMI->getOperand(2).setImm(NewInfo.encodeVTYPE());
              NeedInsertVSETVLI = false;
            }
          }
          if (NeedInsertVSETVLI)
            insertVSETVLI(MBB, MI, NewInfo, CurInfo);
          CurInfo = NewInfo;
        }
      }
      PrevVSETVLIMI = nullptr;
    }

    // If this is something that updates VL/VTYPE that we don't know about, set
    // the state to unknown.
    if (MI.isCall() || MI.isInlineAsm() || MI.modifiesRegister(RISCV::VL) ||
        MI.modifiesRegister(RISCV::VTYPE)) {
      CurInfo = VSETVLIInfo::getUnknown();
      PrevVSETVLIMI = nullptr;
    }
  }

  // If we reach the end of the block and our current info doesn't match the
  // expected info, insert a vsetvli to correct.
  if (!UseStrictAsserts) {
    const VSETVLIInfo &ExitInfo = BlockInfo[MBB.getNumber()].Exit;
    if (CurInfo.isValid() && ExitInfo.isValid() && !ExitInfo.isUnknown() &&
        CurInfo != ExitInfo) {
      // Note there's an implicit assumption here that terminators never use
      // or modify VL or VTYPE.  Also, fallthrough will return end().
      auto InsertPt = MBB.getFirstTerminator().getInstrIterator();
      insertVSETVLI(MBB, InsertPt, MBB.findDebugLoc(InsertPt), ExitInfo, CurInfo);
      CurInfo = ExitInfo;
    }
  }

  if (UseStrictAsserts && CurInfo.isValid()) {
    const auto &Info = BlockInfo[MBB.getNumber()];
    if (CurInfo != Info.Exit) {
      LLVM_DEBUG(dbgs() << "in block " << printMBBReference(MBB) << "\n");
      LLVM_DEBUG(dbgs() << "  begin        state: " << Info.Pred << "\n");
      LLVM_DEBUG(dbgs() << "  expected end state: " << Info.Exit << "\n");
      LLVM_DEBUG(dbgs() << "  actual   end state: " << CurInfo << "\n");
    }
    assert(CurInfo == Info.Exit &&
           "InsertVSETVLI dataflow invariant violated");
  }
}

void RISCVInsertVSETVLI::doLocalPrepass(MachineBasicBlock &MBB) {
  VSETVLIInfo CurInfo = VSETVLIInfo::getUnknown();
  for (MachineInstr &MI : MBB) {
    // If this is an explicit VSETVLI or VSETIVLI, update our state.
    if (isVectorConfigInstr(MI)) {
      CurInfo = getInfoForVSETVLI(MI);
      continue;
    }

    const uint64_t TSFlags = MI.getDesc().TSFlags;
    if (isScalarMoveInstr(MI)) {
      assert(RISCVII::hasSEWOp(TSFlags) && RISCVII::hasVLOp(TSFlags));
      const VSETVLIInfo NewInfo = computeInfoForInstr(MI, TSFlags, MRI);

      // For vmv.s.x and vfmv.s.f, there are only two behaviors, VL = 0 and
      // VL > 0. We can discard the user requested AVL and just use the last
      // one if we can prove it equally zero.  This removes a vsetvli entirely
      // if the types match or allows use of cheaper avl preserving variant
      // if VLMAX doesn't change.  If VLMAX might change, we couldn't use
      // the 'vsetvli x0, x0, vtype" variant, so we avoid the transform to
      // prevent extending live range of an avl register operand.
      // TODO: We can probably relax this for immediates.
      if (((CurInfo.hasNonZeroAVL() && NewInfo.hasNonZeroAVL()) ||
           (CurInfo.hasZeroAVL() && NewInfo.hasZeroAVL())) &&
          NewInfo.hasSameVLMAX(CurInfo)) {
        MachineOperand &VLOp = MI.getOperand(getVLOpNum(MI));
        if (CurInfo.hasAVLImm())
          VLOp.ChangeToImmediate(CurInfo.getAVLImm());
        else
          VLOp.ChangeToRegister(CurInfo.getAVLReg(), /*IsDef*/ false);
        CurInfo = computeInfoForInstr(MI, TSFlags, MRI);
        continue;
      }
    }

    if (RISCVII::hasSEWOp(TSFlags)) {
      if (RISCVII::hasVLOp(TSFlags)) {
        const auto Require = computeInfoForInstr(MI, TSFlags, MRI);
        // If the AVL is the result of a previous vsetvli which has the
        // same AVL and VLMAX as our current state, we can reuse the AVL
        // from the current state for the new one.  This allows us to
        // generate 'vsetvli x0, x0, vtype" or possible skip the transition
        // entirely.
        if (!CurInfo.isUnknown() && Require.hasAVLReg() &&
            Require.getAVLReg().isVirtual()) {
          if (MachineInstr *DefMI = MRI->getVRegDef(Require.getAVLReg())) {
            if (isVectorConfigInstr(*DefMI)) {
              VSETVLIInfo DefInfo = getInfoForVSETVLI(*DefMI);
              if (DefInfo.hasSameAVL(CurInfo) &&
                  DefInfo.hasSameVLMAX(CurInfo)) {
                MachineOperand &VLOp = MI.getOperand(getVLOpNum(MI));
                if (CurInfo.hasAVLImm())
                  VLOp.ChangeToImmediate(CurInfo.getAVLImm());
                else
                  VLOp.ChangeToRegister(CurInfo.getAVLReg(), /*IsDef*/ false);
                CurInfo = computeInfoForInstr(MI, TSFlags, MRI);
                continue;
              }
            }
          }
        }
      }
      CurInfo = computeInfoForInstr(MI, TSFlags, MRI);
      continue;
    }

    // If this is something that updates VL/VTYPE that we don't know about,
    // set the state to unknown.
    if (MI.isCall() || MI.isInlineAsm() || MI.modifiesRegister(RISCV::VL) ||
        MI.modifiesRegister(RISCV::VTYPE))
      CurInfo = VSETVLIInfo::getUnknown();
  }
}

bool RISCVInsertVSETVLI::runOnMachineFunction(MachineFunction &MF) {
  // Skip if the vector extension is not enabled.
  const RISCVSubtarget &ST = MF.getSubtarget<RISCVSubtarget>();
  if (!ST.hasVInstructions())
    return false;

  LLVM_DEBUG(dbgs() << "Entering InsertVSETVLI for " << MF.getName() << "\n");

  TII = ST.getInstrInfo();
  MRI = &MF.getRegInfo();

  assert(BlockInfo.empty() && "Expect empty block infos");
  BlockInfo.resize(MF.getNumBlockIDs());

  // Scan the block locally for cases where we can mutate the operands
  // of the instructions to reduce state transitions.  Critically, this
  // must be done before we start propagating data flow states as these
  // transforms are allowed to change the contents of VTYPE and VL so
  // long as the semantics of the program stays the same.
  for (MachineBasicBlock &MBB : MF)
    doLocalPrepass(MBB);

  bool HaveVectorOp = false;

  // Phase 1 - determine how VL/VTYPE are affected by the each block.
  for (const MachineBasicBlock &MBB : MF)
    HaveVectorOp |= computeVLVTYPEChanges(MBB);

  // If we didn't find any instructions that need VSETVLI, we're done.
  if (!HaveVectorOp) {
    BlockInfo.clear();
    return false;
  }

  // Phase 2 - determine the exit VL/VTYPE from each block. We add all
  // blocks to the list here, but will also add any that need to be revisited
  // during Phase 2 processing.
  for (const MachineBasicBlock &MBB : MF) {
    WorkList.push(&MBB);
    BlockInfo[MBB.getNumber()].InQueue = true;
  }
  while (!WorkList.empty()) {
    const MachineBasicBlock &MBB = *WorkList.front();
    WorkList.pop();
    computeIncomingVLVTYPE(MBB);
  }

  // Phase 3 - add any vsetvli instructions needed in the block. Use the
  // Phase 2 information to avoid adding vsetvlis before the first vector
  // instruction in the block if the VL/VTYPE is satisfied by its
  // predecessors.
  for (MachineBasicBlock &MBB : MF)
    emitVSETVLIs(MBB);

  // Once we're fully done rewriting all the instructions, do a final pass
  // through to check for VSETVLIs which write to an unused destination.
  // For the non X0, X0 variant, we can replace the destination register
  // with X0 to reduce register pressure.  This is really a generic
  // optimization which can be applied to any dead def (TODO: generalize).
  for (MachineBasicBlock &MBB : MF) {
    for (MachineInstr &MI : MBB) {
      if (MI.getOpcode() == RISCV::PseudoVSETVLI ||
          MI.getOpcode() == RISCV::PseudoVSETIVLI) {
        Register VRegDef = MI.getOperand(0).getReg();
        if (VRegDef != RISCV::X0 && MRI->use_nodbg_empty(VRegDef))
          MI.getOperand(0).setReg(RISCV::X0);
      }
    }
  }

  BlockInfo.clear();
  return HaveVectorOp;
}

/// Returns an instance of the Insert VSETVLI pass.
FunctionPass *llvm::createRISCVInsertVSETVLIPass() {
  return new RISCVInsertVSETVLI();
}