Method InitAggSlots

be/src/exec/aggregator.cc:144–179

TODO: codegen this function.

// TODO: codegen this function.
void Aggregator::InitAggSlots(
    const vector<AggFnEvaluator*>& agg_fn_evals, Tuple* intermediate_tuple) {
  vector<SlotDescriptor*>::const_iterator slot_desc =
      intermediate_tuple_desc_->slots().begin() + GetNumGroupingExprs();
  for (int i = 0; i < agg_fn_evals.size(); ++i, ++slot_desc) {
    // To minimize branching on the UpdateTuple path, initialize the result value so that
    // the Add() UDA function can ignore the NULL bit of its destination value. E.g. for
    // SUM(), if we initialize the destination value to 0 (with the NULL bit set), we can
    // just start adding to the destination value (rather than repeatedly checking the
    // destination NULL bit. The codegen'd version of UpdateSlot() exploits this to
    // eliminate a branch per value.
    //
    // For boolean and numeric types, the default values are false/0, so the nullable
    // aggregate functions SUM() and AVG() produce the correct result. For MIN()/MAX(),
    // initialize the value to max/min possible value for the same effect.
    AggFnEvaluator* eval = agg_fn_evals[i];
    eval->Init(intermediate_tuple);

    DCHECK(agg_fns_[i] == &(eval->agg_fn()));
    const AggFn* agg_fn = agg_fns_[i];
    const AggFn::AggregationOp agg_op = agg_fn->agg_op();
    if ((agg_op == AggFn::MIN || agg_op == AggFn::MAX)
        && !agg_fn->intermediate_type().IsStringType()
        && !agg_fn->intermediate_type().IsTimestampType()) {
      ExprValue default_value;
      void* default_value_ptr = nullptr;
      if (agg_op == AggFn::MIN) {
        default_value_ptr = default_value.SetToMax((*slot_desc)->type());
      } else {
        DCHECK_EQ(agg_op, AggFn::MAX);
        default_value_ptr = default_value.SetToMin((*slot_desc)->type());
      }
      RawValue::Write(default_value_ptr, intermediate_tuple, *slot_desc, nullptr);
    }
  }
}

void Aggregator::UpdateTuple(
    AggFnEvaluator** agg_fn_evals, Tuple* tuple, TupleRow* row, bool is_merge) noexcept {