C++ APInt::countTrailingOnes方法代码示例

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    // Output known-0 bits are only known if clear in both the LHS & RHS.
    KnownZero &= KnownZero2;
    // Output known-1 are known to be set if set in either the LHS | RHS.
    KnownOne |= KnownOne2;
    return;
  }
  case Instruction::Xor: {
    ComputeMaskedBits(I->getOperand(1), Mask, KnownZero, KnownOne, TD, Depth+1);
    ComputeMaskedBits(I->getOperand(0), Mask, KnownZero2, KnownOne2, TD,
                      Depth+1);
    assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); 
    assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?"); 
    
    // Output known-0 bits are known if clear or set in both the LHS & RHS.
    APInt KnownZeroOut = (KnownZero & KnownZero2) | (KnownOne & KnownOne2);
    // Output known-1 are known to be set if set in only one of the LHS, RHS.
    KnownOne = (KnownZero & KnownOne2) | (KnownOne & KnownZero2);
    KnownZero = KnownZeroOut;
    return;
  }
  case Instruction::Mul: {
    APInt Mask2 = APInt::getAllOnesValue(BitWidth);
    ComputeMaskedBits(I->getOperand(1), Mask2, KnownZero, KnownOne, TD,Depth+1);
    ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero2, KnownOne2, TD,
                      Depth+1);
    assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); 
    assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?"); 
    
    // If low bits are zero in either operand, output low known-0 bits.
    // Also compute a conserative estimate for high known-0 bits.
    // More trickiness is possible, but this is sufficient for the
    // interesting case of alignment computation.
    KnownOne.clear();
    unsigned TrailZ = KnownZero.countTrailingOnes() +
                      KnownZero2.countTrailingOnes();
    unsigned LeadZ =  std::max(KnownZero.countLeadingOnes() +
                               KnownZero2.countLeadingOnes(),
                               BitWidth) - BitWidth;

    TrailZ = std::min(TrailZ, BitWidth);
    LeadZ = std::min(LeadZ, BitWidth);
    KnownZero = APInt::getLowBitsSet(BitWidth, TrailZ) |
                APInt::getHighBitsSet(BitWidth, LeadZ);
    KnownZero &= Mask;
    return;
  }
  case Instruction::UDiv: {
    // For the purposes of computing leading zeros we can conservatively
    // treat a udiv as a logical right shift by the power of 2 known to
    // be less than the denominator.
    APInt AllOnes = APInt::getAllOnesValue(BitWidth);
    ComputeMaskedBits(I->getOperand(0),
                      AllOnes, KnownZero2, KnownOne2, TD, Depth+1);
    unsigned LeadZ = KnownZero2.countLeadingOnes();

    KnownOne2.clear();
    KnownZero2.clear();
    ComputeMaskedBits(I->getOperand(1),
                      AllOnes, KnownZero2, KnownOne2, TD, Depth+1);
    unsigned RHSUnknownLeadingOnes = KnownOne2.countLeadingZeros();
    if (RHSUnknownLeadingOnes != BitWidth)
      LeadZ = std::min(BitWidth,
                       LeadZ + BitWidth - RHSUnknownLeadingOnes - 1);

    KnownZero = APInt::getHighBitsSet(BitWidth, LeadZ) & Mask;
    return;

bool HexagonGenExtract::convert(Instruction *In) {
  using namespace PatternMatch;

  Value *BF = nullptr;
  ConstantInt *CSL = nullptr, *CSR = nullptr, *CM = nullptr;
  BasicBlock *BB = In->getParent();
  LLVMContext &Ctx = BB->getContext();
  bool LogicalSR;

  // (and (shl (lshr x, #sr), #sl), #m)
  LogicalSR = true;
  bool Match = match(In, m_And(m_Shl(m_LShr(m_Value(BF), m_ConstantInt(CSR)),
                               m_ConstantInt(CSL)),
                         m_ConstantInt(CM)));

  if (!Match) {
    // (and (shl (ashr x, #sr), #sl), #m)
    LogicalSR = false;
    Match = match(In, m_And(m_Shl(m_AShr(m_Value(BF), m_ConstantInt(CSR)),
                            m_ConstantInt(CSL)),
                      m_ConstantInt(CM)));
  }
  if (!Match) {
    // (and (shl x, #sl), #m)
    LogicalSR = true;
    CSR = ConstantInt::get(Type::getInt32Ty(Ctx), 0);
    Match = match(In, m_And(m_Shl(m_Value(BF), m_ConstantInt(CSL)),
                      m_ConstantInt(CM)));
    if (Match && NoSR0)
      return false;
  }
  if (!Match) {
    // (and (lshr x, #sr), #m)
    LogicalSR = true;
    CSL = ConstantInt::get(Type::getInt32Ty(Ctx), 0);
    Match = match(In, m_And(m_LShr(m_Value(BF), m_ConstantInt(CSR)),
                            m_ConstantInt(CM)));
  }
  if (!Match) {
    // (and (ashr x, #sr), #m)
    LogicalSR = false;
    CSL = ConstantInt::get(Type::getInt32Ty(Ctx), 0);
    Match = match(In, m_And(m_AShr(m_Value(BF), m_ConstantInt(CSR)),
                            m_ConstantInt(CM)));
  }
  if (!Match) {
    CM = nullptr;
    // (shl (lshr x, #sr), #sl)
    LogicalSR = true;
    Match = match(In, m_Shl(m_LShr(m_Value(BF), m_ConstantInt(CSR)),
                            m_ConstantInt(CSL)));
  }
  if (!Match) {
    CM = nullptr;
    // (shl (ashr x, #sr), #sl)
    LogicalSR = false;
    Match = match(In, m_Shl(m_AShr(m_Value(BF), m_ConstantInt(CSR)),
                            m_ConstantInt(CSL)));
  }
  if (!Match)
    return false;

  Type *Ty = BF->getType();
  if (!Ty->isIntegerTy())
    return false;
  unsigned BW = Ty->getPrimitiveSizeInBits();
  if (BW != 32 && BW != 64)
    return false;

  uint32_t SR = CSR->getZExtValue();
  uint32_t SL = CSL->getZExtValue();

  if (!CM) {
    // If there was no and, and the shift left did not remove all potential
    // sign bits created by the shift right, then extractu cannot reproduce
    // this value.
    if (!LogicalSR && (SR > SL))
      return false;
    APInt A = APInt(BW, ~0ULL).lshr(SR).shl(SL);
    CM = ConstantInt::get(Ctx, A);
  }

  // CM is the shifted-left mask. Shift it back right to remove the zero
  // bits on least-significant positions.
  APInt M = CM->getValue().lshr(SL);
  uint32_t T = M.countTrailingOnes();

  // During the shifts some of the bits will be lost. Calculate how many
  // of the original value will remain after shift right and then left.
  uint32_t U = BW - std::max(SL, SR);
  // The width of the extracted field is the minimum of the original bits
  // that remain after the shifts and the number of contiguous 1s in the mask.
  uint32_t W = std::min(U, T);
  if (W == 0)
    return false;

  // Check if the extracted bits are contained within the mask that it is
  // and-ed with. The extract operation will copy these bits, and so the
  // mask cannot any holes in it that would clear any of the bits of the
  // extracted field.
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