C++ APInt::logBase2方法代码示例

void SeparateConstOffsetFromGEP::lowerToSingleIndexGEPs(
    GetElementPtrInst *Variadic, int64_t AccumulativeByteOffset) {
  IRBuilder<> Builder(Variadic);
  Type *IntPtrTy = DL->getIntPtrType(Variadic->getType());

  Type *I8PtrTy =
      Builder.getInt8PtrTy(Variadic->getType()->getPointerAddressSpace());
  Value *ResultPtr = Variadic->getOperand(0);
  if (ResultPtr->getType() != I8PtrTy)
    ResultPtr = Builder.CreateBitCast(ResultPtr, I8PtrTy);

  gep_type_iterator GTI = gep_type_begin(*Variadic);
  // Create an ugly GEP for each sequential index. We don't create GEPs for
  // structure indices, as they are accumulated in the constant offset index.
  for (unsigned I = 1, E = Variadic->getNumOperands(); I != E; ++I, ++GTI) {
    if (isa<SequentialType>(*GTI)) {
      Value *Idx = Variadic->getOperand(I);
      // Skip zero indices.
      if (ConstantInt *CI = dyn_cast<ConstantInt>(Idx))
        if (CI->isZero())
          continue;

      APInt ElementSize = APInt(IntPtrTy->getIntegerBitWidth(),
                                DL->getTypeAllocSize(GTI.getIndexedType()));
      // Scale the index by element size.
      if (ElementSize != 1) {
        if (ElementSize.isPowerOf2()) {
          Idx = Builder.CreateShl(
              Idx, ConstantInt::get(IntPtrTy, ElementSize.logBase2()));
        } else {
          Idx = Builder.CreateMul(Idx, ConstantInt::get(IntPtrTy, ElementSize));
        }
      }
      // Create an ugly GEP with a single index for each index.
      ResultPtr =
          Builder.CreateGEP(Builder.getInt8Ty(), ResultPtr, Idx, "uglygep");
    }
  }

  // Create a GEP with the constant offset index.
  if (AccumulativeByteOffset != 0) {
    Value *Offset = ConstantInt::get(IntPtrTy, AccumulativeByteOffset);
    ResultPtr =
        Builder.CreateGEP(Builder.getInt8Ty(), ResultPtr, Offset, "uglygep");
  }
  if (ResultPtr->getType() != Variadic->getType())
    ResultPtr = Builder.CreateBitCast(ResultPtr, Variadic->getType());

  Variadic->replaceAllUsesWith(ResultPtr);
  Variadic->eraseFromParent();
}

Value *StraightLineStrengthReduce::emitBump(const Candidate &Basis,
                                            const Candidate &C,
                                            IRBuilder<> &Builder,
                                            const DataLayout *DL,
                                            bool &BumpWithUglyGEP) {
  APInt Idx = C.Index->getValue(), BasisIdx = Basis.Index->getValue();
  unifyBitWidth(Idx, BasisIdx);
  APInt IndexOffset = Idx - BasisIdx;

  BumpWithUglyGEP = false;
  if (Basis.CandidateKind == Candidate::GEP) {
    APInt ElementSize(
        IndexOffset.getBitWidth(),
        DL->getTypeAllocSize(
            cast<GetElementPtrInst>(Basis.Ins)->getType()->getElementType()));
    APInt Q, R;
    APInt::sdivrem(IndexOffset, ElementSize, Q, R);
    if (R.getSExtValue() == 0)
      IndexOffset = Q;
    else
      BumpWithUglyGEP = true;
  }

  // Compute Bump = C - Basis = (i' - i) * S.
  // Common case 1: if (i' - i) is 1, Bump = S.
  if (IndexOffset.getSExtValue() == 1)
    return C.Stride;
  // Common case 2: if (i' - i) is -1, Bump = -S.
  if (IndexOffset.getSExtValue() == -1)
    return Builder.CreateNeg(C.Stride);

  // Otherwise, Bump = (i' - i) * sext/trunc(S). Note that (i' - i) and S may
  // have different bit widths.
  IntegerType *DeltaType =
      IntegerType::get(Basis.Ins->getContext(), IndexOffset.getBitWidth());
  Value *ExtendedStride = Builder.CreateSExtOrTrunc(C.Stride, DeltaType);
  if (IndexOffset.isPowerOf2()) {
    // If (i' - i) is a power of 2, Bump = sext/trunc(S) << log(i' - i).
    ConstantInt *Exponent = ConstantInt::get(DeltaType, IndexOffset.logBase2());
    return Builder.CreateShl(ExtendedStride, Exponent);
  }
  if ((-IndexOffset).isPowerOf2()) {
    // If (i - i') is a power of 2, Bump = -sext/trunc(S) << log(i' - i).
    ConstantInt *Exponent =
        ConstantInt::get(DeltaType, (-IndexOffset).logBase2());
    return Builder.CreateNeg(Builder.CreateShl(ExtendedStride, Exponent));
  }
  Constant *Delta = ConstantInt::get(DeltaType, IndexOffset);
  return Builder.CreateMul(ExtendedStride, Delta);
}

void
SeparateConstOffsetFromGEP::lowerToArithmetics(GetElementPtrInst *Variadic,
                                               int64_t AccumulativeByteOffset) {
  IRBuilder<> Builder(Variadic);
  const DataLayout &DL = Variadic->getModule()->getDataLayout();
  Type *IntPtrTy = DL.getIntPtrType(Variadic->getType());

  Value *ResultPtr = Builder.CreatePtrToInt(Variadic->getOperand(0), IntPtrTy);
  gep_type_iterator GTI = gep_type_begin(*Variadic);
  // Create ADD/SHL/MUL arithmetic operations for each sequential indices. We
  // don't create arithmetics for structure indices, as they are accumulated
  // in the constant offset index.
  for (unsigned I = 1, E = Variadic->getNumOperands(); I != E; ++I, ++GTI) {
    if (isa<SequentialType>(*GTI)) {
      Value *Idx = Variadic->getOperand(I);
      // Skip zero indices.
      if (ConstantInt *CI = dyn_cast<ConstantInt>(Idx))
        if (CI->isZero())
          continue;

      APInt ElementSize = APInt(IntPtrTy->getIntegerBitWidth(),
                                DL.getTypeAllocSize(GTI.getIndexedType()));
      // Scale the index by element size.
      if (ElementSize != 1) {
        if (ElementSize.isPowerOf2()) {
          Idx = Builder.CreateShl(
              Idx, ConstantInt::get(IntPtrTy, ElementSize.logBase2()));
        } else {
          Idx = Builder.CreateMul(Idx, ConstantInt::get(IntPtrTy, ElementSize));
        }
      }
      // Create an ADD for each index.
      ResultPtr = Builder.CreateAdd(ResultPtr, Idx);
    }
  }

  // Create an ADD for the constant offset index.
  if (AccumulativeByteOffset != 0) {
    ResultPtr = Builder.CreateAdd(
        ResultPtr, ConstantInt::get(IntPtrTy, AccumulativeByteOffset));
  }

  ResultPtr = Builder.CreateIntToPtr(ResultPtr, Variadic->getType());
  Variadic->replaceAllUsesWith(ResultPtr);
  Variadic->eraseFromParent();
}