[PATCH] D128911: Emit table lookup from TargetLowering::expandCTTZ()

[Shubham Narlawar via Phabricator via llvm-commits]

gsocshubham added a comment.

I am generating table at end of `TargetLowering::expandCTTZ()` as below -

  // Create a table in constant data pool
  std::vector<Constant *> Elt;
  unsigned int RshrArr[NumBitsPerElt];
  unsigned int DeBrujin = 0x077CB531U;
  
  for (unsigned int i = 0; i < NumBitsPerElt; i++) {
    unsigned int Lshr = DeBrujin << i;
    unsigned int Rshr = Lshr >> 27;
    RshrArr[Rshr] = i;
  }
  
  for (unsigned int i = 0; i < NumBitsPerElt; i++) {
    SDValue Index = DAG.getConstant(RshrArr[i], dl, VT);
    ConstantSDNode *IndexNode = dyn_cast<ConstantSDNode>(Index);
    ConstantInt *temp = const_cast<ConstantInt *>(IndexNode->getConstantIntValue());
    Constant *ConstantData =  dyn_cast<Constant >(temp);
    Elt.push_back(ConstantData);
  }
  ArrayRef<Constant *> Elts = Elt;

...code for indexing into above table

I will post update patch within a while.

Note - I will change RshrArr from variable length array to vector.


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  https://reviews.llvm.org/D128911/new/

https://reviews.llvm.org/D128911