RISCVTargetTransformInfo.h

Go to the documentation of this file.

//===- RISCVTargetTransformInfo.h - RISC-V specific TTI ---------*- C++ -*-===//
//
// 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
/// This file defines a TargetTransformInfoImplBase conforming object specific
/// to the RISC-V target machine. It uses the target's detailed information to
/// provide more precise answers to certain TTI queries, while letting the
/// target independent and default TTI implementations handle the rest.
///
//===----------------------------------------------------------------------===//
 
#ifndef LLVM_LIB_TARGET_RISCV_RISCVTARGETTRANSFORMINFO_H
#define LLVM_LIB_TARGET_RISCV_RISCVTARGETTRANSFORMINFO_H
 
#include "RISCVSubtarget.h"
#include "RISCVTargetMachine.h"
#include "llvm/Analysis/TargetTransformInfo.h"
#include "llvm/CodeGen/BasicTTIImpl.h"
#include "llvm/IR/Function.h"
#include <optional>
 
namespace llvm {
 
class RISCVTTIImpl final : public BasicTTIImplBase<RISCVTTIImpl> {
  using BaseT = BasicTTIImplBase<RISCVTTIImpl>;
  using TTI = TargetTransformInfo;
 
  friend BaseT;
 
  const RISCVSubtarget *ST;
  const RISCVTargetLowering *TLI;
 
  const RISCVSubtarget *getST() const { return ST; }
  const RISCVTargetLowering *getTLI() const { return TLI; }
 
  /// This function returns an estimate for VL to be used in VL based terms
  /// of the cost model.  For fixed length vectors, this is simply the
  /// vector length.  For scalable vectors, we return results consistent
  /// with getVScaleForTuning under the assumption that clients are also
  /// using that when comparing costs between scalar and vector representation.
  /// This does unfortunately mean that we can both undershoot and overshot
  /// the true cost significantly if getVScaleForTuning is wildly off for the
  /// actual target hardware.
  unsigned getEstimatedVLFor(VectorType *Ty) const;
 
  /// This function calculates the costs for one or more RVV opcodes based
  /// on the vtype and the cost kind.
  /// \param Opcodes A list of opcodes of the RVV instruction to evaluate.
  /// \param VT The MVT of vtype associated with the RVV instructions.
  /// For widening/narrowing instructions where the result and source types
  /// differ, it is important to check the spec to determine whether the vtype
  /// refers to the result or source type.
  /// \param CostKind The type of cost to compute.
  InstructionCost getRISCVInstructionCost(ArrayRef<unsigned> OpCodes, MVT VT,
                                          TTI::TargetCostKind CostKind) const;
 
  /// Return the cost of accessing a constant pool entry of the specified
  /// type.
  InstructionCost getConstantPoolLoadCost(Type *Ty,
                                          TTI::TargetCostKind CostKind) const;
 
  /// If this shuffle can be lowered as a masked slide pair (at worst),
  /// return a cost for it.
  InstructionCost getSlideCost(FixedVectorType *Tp, ArrayRef<int> Mask,
                               TTI::TargetCostKind CostKind) const;
 
public:
  explicit RISCVTTIImpl(const RISCVTargetMachine *TM, const Function &F)
      : BaseT(TM, F.getDataLayout()), ST(TM->getSubtargetImpl(F)),
        TLI(ST->getTargetLowering()) {}
 
  /// Return the cost of materializing an immediate for a value operand of
  /// a store instruction.
  InstructionCost getStoreImmCost(Type *VecTy, TTI::OperandValueInfo OpInfo,
                                  TTI::TargetCostKind CostKind) const;
 
  InstructionCost getIntImmCost(const APInt &Imm, Type *Ty,
                                TTI::TargetCostKind CostKind) const override;
  InstructionCost getIntImmCostInst(unsigned Opcode, unsigned Idx,
                                    const APInt &Imm, Type *Ty,
                                    TTI::TargetCostKind CostKind,
                                    Instruction *Inst = nullptr) const override;
  InstructionCost
  getIntImmCostIntrin(Intrinsic::ID IID, unsigned Idx, const APInt &Imm,
                      Type *Ty, TTI::TargetCostKind CostKind) const override;
 
  /// \name EVL Support for predicated vectorization.
  /// Whether the target supports the %evl parameter of VP intrinsic efficiently
  /// in hardware. (see LLVM Language Reference - "Vector Predication
  /// Intrinsics",
  /// https://llvm.org/docs/LangRef.html#vector-predication-intrinsics and
  /// "IR-level VP intrinsics",
  /// https://llvm.org/docs/Proposals/VectorPredication.html#ir-level-vp-intrinsics).
  bool hasActiveVectorLength() const override;
 
  TargetTransformInfo::PopcntSupportKind
  getPopcntSupport(unsigned TyWidth) const override;
 
  InstructionCost getPartialReductionCost(
      unsigned Opcode, Type *InputTypeA, Type *InputTypeB, Type *AccumType,
      ElementCount VF, TTI::PartialReductionExtendKind OpAExtend,
      TTI::PartialReductionExtendKind OpBExtend, std::optional<unsigned> BinOp,
      TTI::TargetCostKind CostKind) const override;
 
  bool shouldExpandReduction(const IntrinsicInst *II) const override;
  bool supportsScalableVectors() const override {
    return ST->hasVInstructions();
  }
  bool enableOrderedReductions() const override { return true; }
  bool enableScalableVectorization() const override {
    return ST->hasVInstructions();
  }
  bool preferPredicateOverEpilogue(TailFoldingInfo *TFI) const override {
    return ST->hasVInstructions();
  }
  TailFoldingStyle
  getPreferredTailFoldingStyle(bool IVUpdateMayOverflow) const override {
    return ST->hasVInstructions() ? TailFoldingStyle::DataWithEVL
                                  : TailFoldingStyle::None;
  }
  std::optional<unsigned> getMaxVScale() const override;
  std::optional<unsigned> getVScaleForTuning() const override;
 
  TypeSize
  getRegisterBitWidth(TargetTransformInfo::RegisterKind K) const override;
 
  unsigned getRegUsageForType(Type *Ty) const override;
 
  unsigned getMaximumVF(unsigned ElemWidth, unsigned Opcode) const override;
 
  bool preferAlternateOpcodeVectorization() const override;
 
  bool preferEpilogueVectorization() const override {
    // Epilogue vectorization is usually unprofitable - tail folding or
    // a smaller VF would have been better.  This a blunt hammer - we
    // should re-examine this once vectorization is better tuned.
    return false;
  }
 
  bool shouldConsiderVectorizationRegPressure() const override { return true; }
 
  InstructionCost
  getMaskedMemoryOpCost(unsigned Opcode, Type *Src, Align Alignment,
                        unsigned AddressSpace,
                        TTI::TargetCostKind CostKind) const override;
 
  InstructionCost
  getPointersChainCost(ArrayRef<const Value *> Ptrs, const Value *Base,
                       const TTI::PointersChainInfo &Info, Type *AccessTy,
                       TTI::TargetCostKind CostKind) const override;
 
  void getUnrollingPreferences(Loop *L, ScalarEvolution &SE,
                               TTI::UnrollingPreferences &UP,
                               OptimizationRemarkEmitter *ORE) const override;
 
  void getPeelingPreferences(Loop *L, ScalarEvolution &SE,
                             TTI::PeelingPreferences &PP) const override;
 
  unsigned getMinVectorRegisterBitWidth() const override {
    return ST->useRVVForFixedLengthVectors() ? 16 : 0;
  }
 
  InstructionCost
  getShuffleCost(TTI::ShuffleKind Kind, VectorType *DstTy, VectorType *SrcTy,
                 ArrayRef<int> Mask, TTI::TargetCostKind CostKind, int Index,
                 VectorType *SubTp, ArrayRef<const Value *> Args = {},
                 const Instruction *CxtI = nullptr) const override;
 
  InstructionCost getScalarizationOverhead(
      VectorType *Ty, const APInt &DemandedElts, bool Insert, bool Extract,
      TTI::TargetCostKind CostKind, bool ForPoisonSrc = true,
      ArrayRef<Value *> VL = {}) const override;
 
  InstructionCost
  getIntrinsicInstrCost(const IntrinsicCostAttributes &ICA,
                        TTI::TargetCostKind CostKind) const override;
 
  InstructionCost
  getAddressComputationCost(Type *PTy, ScalarEvolution *SE, const SCEV *Ptr,
                            TTI::TargetCostKind CostKind) const override;
 
  InstructionCost getInterleavedMemoryOpCost(
      unsigned Opcode, Type *VecTy, unsigned Factor, ArrayRef<unsigned> Indices,
      Align Alignment, unsigned AddressSpace, TTI::TargetCostKind CostKind,
      bool UseMaskForCond = false, bool UseMaskForGaps = false) const override;
 
  InstructionCost getGatherScatterOpCost(unsigned Opcode, Type *DataTy,
                                         const Value *Ptr, bool VariableMask,
                                         Align Alignment,
                                         TTI::TargetCostKind CostKind,
                                         const Instruction *I) const override;
 
  InstructionCost
  getExpandCompressMemoryOpCost(unsigned Opcode, Type *Src, bool VariableMask,
                                Align Alignment, TTI::TargetCostKind CostKind,
                                const Instruction *I = nullptr) const override;
 
  InstructionCost getStridedMemoryOpCost(unsigned Opcode, Type *DataTy,
                                         const Value *Ptr, bool VariableMask,
                                         Align Alignment,
                                         TTI::TargetCostKind CostKind,
                                         const Instruction *I) const override;
 
  InstructionCost
  getCostOfKeepingLiveOverCall(ArrayRef<Type *> Tys) const override;
 
  InstructionCost
  getCastInstrCost(unsigned Opcode, Type *Dst, Type *Src,
                   TTI::CastContextHint CCH, TTI::TargetCostKind CostKind,
                   const Instruction *I = nullptr) const override;
 
  InstructionCost
  getMinMaxReductionCost(Intrinsic::ID IID, VectorType *Ty, FastMathFlags FMF,
                         TTI::TargetCostKind CostKind) const override;
 
  InstructionCost
  getArithmeticReductionCost(unsigned Opcode, VectorType *Ty,
                             std::optional<FastMathFlags> FMF,
                             TTI::TargetCostKind CostKind) const override;
 
  InstructionCost
  getExtendedReductionCost(unsigned Opcode, bool IsUnsigned, Type *ResTy,
                           VectorType *ValTy, std::optional<FastMathFlags> FMF,
                           TTI::TargetCostKind CostKind) const override;
 
  InstructionCost getMemoryOpCost(
      unsigned Opcode, Type *Src, Align Alignment, unsigned AddressSpace,
      TTI::TargetCostKind CostKind,
      TTI::OperandValueInfo OpdInfo = {TTI::OK_AnyValue, TTI::OP_None},
      const Instruction *I = nullptr) const override;
 
  InstructionCost getCmpSelInstrCost(
      unsigned Opcode, Type *ValTy, Type *CondTy, CmpInst::Predicate VecPred,
      TTI::TargetCostKind CostKind,
      TTI::OperandValueInfo Op1Info = {TTI::OK_AnyValue, TTI::OP_None},
      TTI::OperandValueInfo Op2Info = {TTI::OK_AnyValue, TTI::OP_None},
      const Instruction *I = nullptr) const override;
 
  InstructionCost getCFInstrCost(unsigned Opcode, TTI::TargetCostKind CostKind,
                                 const Instruction *I = nullptr) const override;
 
  using BaseT::getVectorInstrCost;
  InstructionCost getVectorInstrCost(unsigned Opcode, Type *Val,
                                     TTI::TargetCostKind CostKind,
                                     unsigned Index, const Value *Op0,
                                     const Value *Op1) const override;
 
  InstructionCost
  getIndexedVectorInstrCostFromEnd(unsigned Opcode, Type *Val,
                                   TTI::TargetCostKind CostKind,
                                   unsigned Index) const override;
 
  InstructionCost getArithmeticInstrCost(
      unsigned Opcode, Type *Ty, TTI::TargetCostKind CostKind,
      TTI::OperandValueInfo Op1Info = {TTI::OK_AnyValue, TTI::OP_None},
      TTI::OperandValueInfo Op2Info = {TTI::OK_AnyValue, TTI::OP_None},
      ArrayRef<const Value *> Args = {},
      const Instruction *CxtI = nullptr) const override;
 
  bool isElementTypeLegalForScalableVector(Type *Ty) const override {
    return TLI->isLegalElementTypeForRVV(TLI->getValueType(DL, Ty));
  }
 
  bool isLegalMaskedLoadStore(Type *DataType, Align Alignment) const {
    if (!ST->hasVInstructions())
      return false;
 
    EVT DataTypeVT = TLI->getValueType(DL, DataType);
 
    // Only support fixed vectors if we know the minimum vector size.
    if (DataTypeVT.isFixedLengthVector() && !ST->useRVVForFixedLengthVectors())
      return false;
 
    EVT ElemType = DataTypeVT.getScalarType();
    if (!ST->enableUnalignedVectorMem() && Alignment < ElemType.getStoreSize())
      return false;
 
    return TLI->isLegalElementTypeForRVV(ElemType);
  }
 
  bool isLegalMaskedLoad(Type *DataType, Align Alignment,
                         unsigned /*AddressSpace*/) const override {
    return isLegalMaskedLoadStore(DataType, Alignment);
  }
  bool isLegalMaskedStore(Type *DataType, Align Alignment,
                          unsigned /*AddressSpace*/) const override {
    return isLegalMaskedLoadStore(DataType, Alignment);
  }
 
  bool isLegalMaskedGatherScatter(Type *DataType, Align Alignment) const {
    if (!ST->hasVInstructions())
      return false;
 
    EVT DataTypeVT = TLI->getValueType(DL, DataType);
 
    // Only support fixed vectors if we know the minimum vector size.
    if (DataTypeVT.isFixedLengthVector() && !ST->useRVVForFixedLengthVectors())
      return false;
 
    // We also need to check if the vector of address is valid.
    EVT PointerTypeVT = EVT(TLI->getPointerTy(DL));
    if (DataTypeVT.isScalableVector() &&
        !TLI->isLegalElementTypeForRVV(PointerTypeVT))
      return false;
 
    EVT ElemType = DataTypeVT.getScalarType();
    if (!ST->enableUnalignedVectorMem() && Alignment < ElemType.getStoreSize())
      return false;
 
    return TLI->isLegalElementTypeForRVV(ElemType);
  }
 
  bool isLegalMaskedGather(Type *DataType, Align Alignment) const override {
    return isLegalMaskedGatherScatter(DataType, Alignment);
  }
  bool isLegalMaskedScatter(Type *DataType, Align Alignment) const override {
    return isLegalMaskedGatherScatter(DataType, Alignment);
  }
 
  bool forceScalarizeMaskedGather(VectorType *VTy,
                                  Align Alignment) const override {
    // Scalarize masked gather for RV64 if EEW=64 indices aren't supported.
    return ST->is64Bit() && !ST->hasVInstructionsI64();
  }
 
  bool forceScalarizeMaskedScatter(VectorType *VTy,
                                   Align Alignment) const override {
    // Scalarize masked scatter for RV64 if EEW=64 indices aren't supported.
    return ST->is64Bit() && !ST->hasVInstructionsI64();
  }
 
  bool isLegalStridedLoadStore(Type *DataType, Align Alignment) const override {
    EVT DataTypeVT = TLI->getValueType(DL, DataType);
    return TLI->isLegalStridedLoadStore(DataTypeVT, Alignment);
  }
 
  bool isLegalInterleavedAccessType(VectorType *VTy, unsigned Factor,
                                    Align Alignment,
                                    unsigned AddrSpace) const override {
    return TLI->isLegalInterleavedAccessType(VTy, Factor, Alignment, AddrSpace,
                                             DL);
  }
 
  bool isLegalMaskedExpandLoad(Type *DataType, Align Alignment) const override;
 
  bool isLegalMaskedCompressStore(Type *DataTy, Align Alignment) const override;
 
  bool isVScaleKnownToBeAPowerOfTwo() const override {
    return TLI->isVScaleKnownToBeAPowerOfTwo();
  }
 
  /// \returns How the target needs this vector-predicated operation to be
  /// transformed.
  TargetTransformInfo::VPLegalization
  getVPLegalizationStrategy(const VPIntrinsic &PI) const override {
    using VPLegalization = TargetTransformInfo::VPLegalization;
    if (!ST->hasVInstructions() ||
        (PI.getIntrinsicID() == Intrinsic::vp_reduce_mul &&
         cast<VectorType>(PI.getArgOperand(1)->getType())
                 ->getElementType()
                 ->getIntegerBitWidth() != 1))
      return VPLegalization(VPLegalization::Discard, VPLegalization::Convert);
    return VPLegalization(VPLegalization::Legal, VPLegalization::Legal);
  }
 
  bool isLegalToVectorizeReduction(const RecurrenceDescriptor &RdxDesc,
                                   ElementCount VF) const override {
    if (!VF.isScalable())
      return true;
 
    Type *Ty = RdxDesc.getRecurrenceType();
    if (!TLI->isLegalElementTypeForRVV(TLI->getValueType(DL, Ty)))
      return false;
 
    switch (RdxDesc.getRecurrenceKind()) {
    case RecurKind::Add:
    case RecurKind::Sub:
    case RecurKind::AddChainWithSubs:
    case RecurKind::And:
    case RecurKind::Or:
    case RecurKind::Xor:
    case RecurKind::SMin:
    case RecurKind::SMax:
    case RecurKind::UMin:
    case RecurKind::UMax:
    case RecurKind::FMin:
    case RecurKind::FMax:
      return true;
    case RecurKind::AnyOf:
    case RecurKind::FAdd:
    case RecurKind::FMulAdd:
      // We can't promote f16/bf16 fadd reductions and scalable vectors can't be
      // expanded.
      if (Ty->isBFloatTy() || (Ty->isHalfTy() && !ST->hasVInstructionsF16()))
        return false;
      return true;
    default:
      return false;
    }
  }
 
  unsigned getMaxInterleaveFactor(ElementCount VF) const override {
    // Don't interleave if the loop has been vectorized with scalable vectors.
    if (VF.isScalable())
      return 1;
    // If the loop will not be vectorized, don't interleave the loop.
    // Let regular unroll to unroll the loop.
    return VF.isScalar() ? 1 : ST->getMaxInterleaveFactor();
  }
 
  bool enableInterleavedAccessVectorization() const override { return true; }
 
  bool enableMaskedInterleavedAccessVectorization() const override {
    return ST->hasVInstructions();
  }
 
  unsigned getMinTripCountTailFoldingThreshold() const override;
 
  enum RISCVRegisterClass { GPRRC, FPRRC, VRRC };
  unsigned getNumberOfRegisters(unsigned ClassID) const override {
    switch (ClassID) {
    case RISCVRegisterClass::GPRRC:
      // 31 = 32 GPR - x0 (zero register)
      // FIXME: Should we exclude fixed registers like SP, TP or GP?
      return 31;
    case RISCVRegisterClass::FPRRC:
      if (ST->hasStdExtF())
        return 32;
      return 0;
    case RISCVRegisterClass::VRRC:
      // Although there are 32 vector registers, v0 is special in that it is the
      // only register that can be used to hold a mask.
      // FIXME: Should we conservatively return 31 as the number of usable
      // vector registers?
      return ST->hasVInstructions() ? 32 : 0;
    }
    llvm_unreachable("unknown register class");
  }
 
  TTI::AddressingModeKind
  getPreferredAddressingMode(const Loop *L, ScalarEvolution *SE) const override;
 
  unsigned getRegisterClassForType(bool Vector,
                                   Type *Ty = nullptr) const override {
    if (Vector)
      return RISCVRegisterClass::VRRC;
    if (!Ty)
      return RISCVRegisterClass::GPRRC;
 
    Type *ScalarTy = Ty->getScalarType();
    if ((ScalarTy->isHalfTy() && ST->hasStdExtZfhmin()) ||
        (ScalarTy->isFloatTy() && ST->hasStdExtF()) ||
        (ScalarTy->isDoubleTy() && ST->hasStdExtD())) {
      return RISCVRegisterClass::FPRRC;
    }
 
    return RISCVRegisterClass::GPRRC;
  }
 
  const char *getRegisterClassName(unsigned ClassID) const override {
    switch (ClassID) {
    case RISCVRegisterClass::GPRRC:
      return "RISCV::GPRRC";
    case RISCVRegisterClass::FPRRC:
      return "RISCV::FPRRC";
    case RISCVRegisterClass::VRRC:
      return "RISCV::VRRC";
    }
    llvm_unreachable("unknown register class");
  }
 
  bool isLSRCostLess(const TargetTransformInfo::LSRCost &C1,
                     const TargetTransformInfo::LSRCost &C2) const override;
 
  bool shouldConsiderAddressTypePromotion(
      const Instruction &I,
      bool &AllowPromotionWithoutCommonHeader) const override;
  std::optional<unsigned> getMinPageSize() const override { return 4096; }
  /// Return true if the (vector) instruction I will be lowered to an
  /// instruction with a scalar splat operand for the given Operand number.
  bool canSplatOperand(Instruction *I, int Operand) const;
  /// Return true if a vector instruction will lower to a target instruction
  /// able to splat the given operand.
  bool canSplatOperand(unsigned Opcode, int Operand) const;
 
  bool isProfitableToSinkOperands(Instruction *I,
                                  SmallVectorImpl<Use *> &Ops) const override;
 
  TTI::MemCmpExpansionOptions
  enableMemCmpExpansion(bool OptSize, bool IsZeroCmp) const override;
};
 
} // end namespace llvm
 
#endif // LLVM_LIB_TARGET_RISCV_RISCVTARGETTRANSFORMINFO_H