Method ComputeBitMapsForExpr

cpp/src/gandiva/llvm_generator.cc:494–530

Extract the bitmap addresses, and do an intersection.

/// Extract the bitmap addresses, and do an intersection.
void LLVMGenerator::ComputeBitMapsForExpr(const CompiledExpr& compiled_expr,
                                          const SelectionVector* selection_vector,
                                          EvalBatch* eval_batch) const {
  auto validities = compiled_expr.value_validity()->validity_exprs();

  // Extract all the source bitmap addresses.
  BitMapAccumulator accumulator(*eval_batch);
  for (auto& validity_dex : validities) {
    validity_dex->Accept(accumulator);
  }

  // Extract the destination bitmap address.
  int out_idx = compiled_expr.output()->validity_idx();
  uint8_t* dst_bitmap = eval_batch->GetBuffer(out_idx);
  // Compute the destination bitmap.
  if (selection_vector == nullptr) {
    accumulator.ComputeResult(dst_bitmap);
  } else {
    /// The output bitmap is an intersection of some input/local bitmaps. However, with a
    /// selection vector, only the bits corresponding to the indices in the selection
    /// vector need to set in the output bitmap. This is done in two steps :
    ///
    /// 1. Do the intersection of input/local bitmaps to generate a temporary bitmap.
    /// 2. copy just the relevant bits from the temporary bitmap to the output bitmap.
    LocalBitMapsHolder bit_map_holder(eval_batch->num_records(), 1);
    uint8_t* temp_bitmap = bit_map_holder.GetLocalBitMap(0);
    accumulator.ComputeResult(temp_bitmap);

    auto num_out_records = selection_vector->GetNumSlots();
    // the memset isn't required, doing it just for valgrind.
    memset(dst_bitmap, 0, arrow::bit_util::BytesForBits(num_out_records));
    for (auto i = 0; i < num_out_records; ++i) {
      auto bit = arrow::bit_util::GetBit(temp_bitmap, selection_vector->GetIndex(i));
      arrow::bit_util::SetBitTo(dst_bitmap, i, bit);
    }
  }
}

llvm::Value* LLVMGenerator::AddFunctionCall(const std::string& full_name,
                                            llvm::Type* ret_type,