HexagonTargetTransformInfo.cpp

Go to the documentation of this file.

//===- HexagonTargetTransformInfo.cpp - Hexagon specific TTI pass ---------===//
//
// 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 implements a TargetTransformInfo analysis pass specific to the
/// Hexagon 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.
///
//===----------------------------------------------------------------------===//

#include "HexagonTargetTransformInfo.h"
#include "HexagonSubtarget.h"
#include "llvm/Analysis/TargetTransformInfo.h"
#include "llvm/CodeGen/ValueTypes.h"
#include "llvm/IR/InstrTypes.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/User.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Transforms/Utils/UnrollLoop.h"

using namespace llvm;

#define DEBUG_TYPE "hexagontti"

static cl::opt<bool> HexagonAutoHVX("hexagon-autohvx", cl::init(false),
  cl::Hidden, cl::desc("Enable loop vectorizer for HVX"));

static cl::opt<bool> EmitLookupTables("hexagon-emit-lookup-tables",
  cl::init(true), cl::Hidden,
  cl::desc("Control lookup table emission on Hexagon target"));

// Constant "cost factor" to make floating point operations more expensive
// in terms of vectorization cost. This isn't the best way, but it should
// do. Ultimately, the cost should use cycles.
static const unsigned FloatFactor = 4;

bool HexagonTTIImpl::useHVX() const {
  return ST.useHVXOps() && HexagonAutoHVX;
}

bool HexagonTTIImpl::isTypeForHVX(Type *VecTy) const {
  assert(VecTy->isVectorTy());
  if (isa<ScalableVectorType>(VecTy))
    return false;
  // Avoid types like <2 x i32*>.
  if (!cast<VectorType>(VecTy)->getElementType()->isIntegerTy())
    return false;
  EVT VecVT = EVT::getEVT(VecTy);
  if (!VecVT.isSimple() || VecVT.getSizeInBits() <= 64)
    return false;
  if (ST.isHVXVectorType(VecVT.getSimpleVT()))
    return true;
  auto Action = TLI.getPreferredVectorAction(VecVT.getSimpleVT());
  return Action == TargetLoweringBase::TypeWidenVector;
}

unsigned HexagonTTIImpl::getTypeNumElements(Type *Ty) const {
  if (auto *VTy = dyn_cast<FixedVectorType>(Ty))
    return VTy->getNumElements();
  assert((Ty->isIntegerTy() || Ty->isFloatingPointTy()) &&
         "Expecting scalar type");
  return 1;
}

TargetTransformInfo::PopcntSupportKind
HexagonTTIImpl::getPopcntSupport(unsigned IntTyWidthInBit) const {
  // Return fast hardware support as every input < 64 bits will be promoted
  // to 64 bits.
  return TargetTransformInfo::PSK_FastHardware;
}

// The Hexagon target can unroll loops with run-time trip counts.
void HexagonTTIImpl::getUnrollingPreferences(Loop *L, ScalarEvolution &SE,
                                             TTI::UnrollingPreferences &UP) {
  UP.Runtime = UP.Partial = true;
}

void HexagonTTIImpl::getPeelingPreferences(Loop *L, ScalarEvolution &SE,
                                           TTI::PeelingPreferences &PP) {
  BaseT::getPeelingPreferences(L, SE, PP);
  // Only try to peel innermost loops with small runtime trip counts.
  if (L && L->empty() && canPeel(L) &&
      SE.getSmallConstantTripCount(L) == 0 &&
      SE.getSmallConstantMaxTripCount(L) > 0 &&
      SE.getSmallConstantMaxTripCount(L) <= 5) {
    PP.PeelCount = 2;
  }
}

bool HexagonTTIImpl::shouldFavorPostInc() const {
  return true;
}

/// --- Vector TTI begin ---

unsigned HexagonTTIImpl::getNumberOfRegisters(bool Vector) const {
  if (Vector)
    return useHVX() ? 32 : 0;
  return 32;
}

unsigned HexagonTTIImpl::getMaxInterleaveFactor(unsigned VF) {
  return useHVX() ? 2 : 0;
}

unsigned HexagonTTIImpl::getRegisterBitWidth(bool Vector) const {
  return Vector ? getMinVectorRegisterBitWidth() : 32;
}

unsigned HexagonTTIImpl::getMinVectorRegisterBitWidth() const {
  return useHVX() ? ST.getVectorLength()*8 : 0;
}

unsigned HexagonTTIImpl::getMinimumVF(unsigned ElemWidth) const {
  return (8 * ST.getVectorLength()) / ElemWidth;
}

unsigned HexagonTTIImpl::getScalarizationOverhead(VectorType *Ty,
                                                  const APInt &DemandedElts,
                                                  bool Insert, bool Extract) {
  return BaseT::getScalarizationOverhead(Ty, DemandedElts, Insert, Extract);
}

unsigned HexagonTTIImpl::getOperandsScalarizationOverhead(
      ArrayRef<const Value*> Args, unsigned VF) {
  return BaseT::getOperandsScalarizationOverhead(Args, VF);
}

unsigned HexagonTTIImpl::getCallInstrCost(Function *F, Type *RetTy,
      ArrayRef<Type*> Tys, TTI::TargetCostKind CostKind) {
  return BaseT::getCallInstrCost(F, RetTy, Tys, CostKind);
}

unsigned
HexagonTTIImpl::getIntrinsicInstrCost(const IntrinsicCostAttributes &ICA,
                                      TTI::TargetCostKind CostKind) {
  if (ICA.getID() == Intrinsic::bswap) {
    std::pair<int, MVT> LT = TLI.getTypeLegalizationCost(DL, ICA.getReturnType());
    return LT.first + 2;
  }
  return BaseT::getIntrinsicInstrCost(ICA, CostKind);
}

unsigned HexagonTTIImpl::getAddressComputationCost(Type *Tp,
      ScalarEvolution *SE, const SCEV *S) {
  return 0;
}

unsigned HexagonTTIImpl::getMemoryOpCost(unsigned Opcode, Type *Src,
                                         MaybeAlign Alignment,
                                         unsigned AddressSpace,
                                         TTI::TargetCostKind CostKind,
                                         const Instruction *I) {
  assert(Opcode == Instruction::Load || Opcode == Instruction::Store);
  // TODO: Handle other cost kinds.
  if (CostKind != TTI::TCK_RecipThroughput)
    return 1;

  if (Opcode == Instruction::Store)
    return BaseT::getMemoryOpCost(Opcode, Src, Alignment, AddressSpace,
                                  CostKind, I);

  if (Src->isVectorTy()) {
    VectorType *VecTy = cast<VectorType>(Src);
    unsigned VecWidth = VecTy->getPrimitiveSizeInBits().getFixedSize();
    if (useHVX() && isTypeForHVX(VecTy)) {
      unsigned RegWidth = getRegisterBitWidth(true);
      assert(RegWidth && "Non-zero vector register width expected");
      // Cost of HVX loads.
      if (VecWidth % RegWidth == 0)
        return VecWidth / RegWidth;
      // Cost of constructing HVX vector from scalar loads
      const Align RegAlign(RegWidth / 8);
      if (!Alignment || *Alignment > RegAlign)
        Alignment = RegAlign;
      assert(Alignment);
      unsigned AlignWidth = 8 * Alignment->value();
      unsigned NumLoads = alignTo(VecWidth, AlignWidth) / AlignWidth;
      return 3 * NumLoads;
    }

    // Non-HVX vectors.
    // Add extra cost for floating point types.
    unsigned Cost =
        VecTy->getElementType()->isFloatingPointTy() ? FloatFactor : 1;

    // At this point unspecified alignment is considered as Align(1).
    const Align BoundAlignment = std::min(Alignment.valueOrOne(), Align(8));
    unsigned AlignWidth = 8 * BoundAlignment.value();
    unsigned NumLoads = alignTo(VecWidth, AlignWidth) / AlignWidth;
    if (Alignment == Align(4) || Alignment == Align(8))
      return Cost * NumLoads;
    // Loads of less than 32 bits will need extra inserts to compose a vector.
    assert(BoundAlignment <= Align(8));
    unsigned LogA = Log2(BoundAlignment);
    return (3 - LogA) * Cost * NumLoads;
  }

  return BaseT::getMemoryOpCost(Opcode, Src, Alignment, AddressSpace,
                                CostKind, I);
}

unsigned HexagonTTIImpl::getMaskedMemoryOpCost(unsigned Opcode, Type *Src,
                                               Align Alignment,
                                               unsigned AddressSpace,
                                               TTI::TargetCostKind CostKind) {
  return BaseT::getMaskedMemoryOpCost(Opcode, Src, Alignment, AddressSpace,
                                      CostKind);
}

unsigned HexagonTTIImpl::getShuffleCost(TTI::ShuffleKind Kind, Type *Tp,
      int Index, Type *SubTp) {
  return 1;
}

unsigned HexagonTTIImpl::getGatherScatterOpCost(
    unsigned Opcode, Type *DataTy, const Value *Ptr, bool VariableMask,
    Align Alignment, TTI::TargetCostKind CostKind, const Instruction *I) {
  return BaseT::getGatherScatterOpCost(Opcode, DataTy, Ptr, VariableMask,
                                       Alignment, CostKind, I);
}

unsigned HexagonTTIImpl::getInterleavedMemoryOpCost(
    unsigned Opcode, Type *VecTy, unsigned Factor, ArrayRef<unsigned> Indices,
    Align Alignment, unsigned AddressSpace, TTI::TargetCostKind CostKind,
    bool UseMaskForCond, bool UseMaskForGaps) {
  if (Indices.size() != Factor || UseMaskForCond || UseMaskForGaps)
    return BaseT::getInterleavedMemoryOpCost(Opcode, VecTy, Factor, Indices,
                                             Alignment, AddressSpace,
                                             CostKind,
                                             UseMaskForCond, UseMaskForGaps);
  return getMemoryOpCost(Opcode, VecTy, MaybeAlign(Alignment), AddressSpace,
                         CostKind);
}

unsigned HexagonTTIImpl::getCmpSelInstrCost(unsigned Opcode, Type *ValTy,
      Type *CondTy, TTI::TargetCostKind CostKind, const Instruction *I) {
  if (ValTy->isVectorTy() && CostKind == TTI::TCK_RecipThroughput) {
    std::pair<int, MVT> LT = TLI.getTypeLegalizationCost(DL, ValTy);
    if (Opcode == Instruction::FCmp)
      return LT.first + FloatFactor * getTypeNumElements(ValTy);
  }
  return BaseT::getCmpSelInstrCost(Opcode, ValTy, CondTy, CostKind, I);
}

unsigned HexagonTTIImpl::getArithmeticInstrCost(
    unsigned Opcode, Type *Ty, TTI::TargetCostKind CostKind,
    TTI::OperandValueKind Opd1Info,
    TTI::OperandValueKind Opd2Info, TTI::OperandValueProperties Opd1PropInfo,
    TTI::OperandValueProperties Opd2PropInfo, ArrayRef<const Value *> Args,
    const Instruction *CxtI) {
  // TODO: Handle more cost kinds.
  if (CostKind != TTI::TCK_RecipThroughput)
    return BaseT::getArithmeticInstrCost(Opcode, Ty, CostKind, Opd1Info,
                                         Opd2Info, Opd1PropInfo,
                                         Opd2PropInfo, Args, CxtI);

  if (Ty->isVectorTy()) {
    std::pair<int, MVT> LT = TLI.getTypeLegalizationCost(DL, Ty);
    if (LT.second.isFloatingPoint())
      return LT.first + FloatFactor * getTypeNumElements(Ty);
  }
  return BaseT::getArithmeticInstrCost(Opcode, Ty, CostKind, Opd1Info, Opd2Info,
                                       Opd1PropInfo, Opd2PropInfo, Args, CxtI);
}

unsigned HexagonTTIImpl::getCastInstrCost(unsigned Opcode, Type *DstTy,
      Type *SrcTy, TTI::TargetCostKind CostKind, const Instruction *I) {
  if (SrcTy->isFPOrFPVectorTy() || DstTy->isFPOrFPVectorTy()) {
    unsigned SrcN = SrcTy->isFPOrFPVectorTy() ? getTypeNumElements(SrcTy) : 0;
    unsigned DstN = DstTy->isFPOrFPVectorTy() ? getTypeNumElements(DstTy) : 0;

    std::pair<int, MVT> SrcLT = TLI.getTypeLegalizationCost(DL, SrcTy);
    std::pair<int, MVT> DstLT = TLI.getTypeLegalizationCost(DL, DstTy);
    unsigned Cost = std::max(SrcLT.first, DstLT.first) + FloatFactor * (SrcN + DstN);
    // TODO: Allow non-throughput costs that aren't binary.
    if (CostKind != TTI::TCK_RecipThroughput)
      return Cost == 0 ? 0 : 1;
    return Cost;
  }
  return 1;
}

unsigned HexagonTTIImpl::getVectorInstrCost(unsigned Opcode, Type *Val,
      unsigned Index) {
  Type *ElemTy = Val->isVectorTy() ? cast<VectorType>(Val)->getElementType()
                                   : Val;
  if (Opcode == Instruction::InsertElement) {
    // Need two rotations for non-zero index.
    unsigned Cost = (Index != 0) ? 2 : 0;
    if (ElemTy->isIntegerTy(32))
      return Cost;
    // If it's not a 32-bit value, there will need to be an extract.
    return Cost + getVectorInstrCost(Instruction::ExtractElement, Val, Index);
  }

  if (Opcode == Instruction::ExtractElement)
    return 2;

  return 1;
}

/// --- Vector TTI end ---

unsigned HexagonTTIImpl::getPrefetchDistance() const {
  return ST.getL1PrefetchDistance();
}

unsigned HexagonTTIImpl::getCacheLineSize() const {
  return ST.getL1CacheLineSize();
}

int
HexagonTTIImpl::getUserCost(const User *U,
                            ArrayRef<const Value *> Operands,
                            TTI::TargetCostKind CostKind) {
  auto isCastFoldedIntoLoad = [this](const CastInst *CI) -> bool {
    if (!CI->isIntegerCast())
      return false;
    // Only extensions from an integer type shorter than 32-bit to i32
    // can be folded into the load.
    const DataLayout &DL = getDataLayout();
    unsigned SBW = DL.getTypeSizeInBits(CI->getSrcTy());
    unsigned DBW = DL.getTypeSizeInBits(CI->getDestTy());
    if (DBW != 32 || SBW >= DBW)
      return false;

    const LoadInst *LI = dyn_cast<const LoadInst>(CI->getOperand(0));
    // Technically, this code could allow multiple uses of the load, and
    // check if all the uses are the same extension operation, but this
    // should be sufficient for most cases.
    return LI && LI->hasOneUse();
  };

  if (const CastInst *CI = dyn_cast<const CastInst>(U))
    if (isCastFoldedIntoLoad(CI))
      return TargetTransformInfo::TCC_Free;
  return BaseT::getUserCost(U, Operands, CostKind);
}

bool HexagonTTIImpl::shouldBuildLookupTables() const {
  return EmitLookupTables;
}