Method computeMetadata

bolt/expression/Expr.cpp:243–320

  } else {
    BOLT_CHECK(isSpecialForm());
    deterministic_ = true;
  }

  for (auto& input : inputs_) {
    deterministic_ &= input->deterministic_;
  }

  // (2) Compute distinctFields_ and multiplyReferencedFields_.
  computeDistinctFields();

  // (3) Compute propagatesNulls_.
  // propagatesNulls_ is true iff a null in any of the columns this
  // depends on makes the Expr null.
  if (isSpecialForm() && !is<ConstantExpr>() && !is<FieldReference>() &&
      !is<CastExpr>()) {
    as<SpecialForm>()->computePropagatesNulls();
  } else {
    if (vectorFunction_ && !vectorFunction_->isDefaultNullBehavior()) {
      propagatesNulls_ = false;
    } else {
      // Logic for handling default-null vector functions.
      // cast, constant and fieldReference expressions act as vector functions
      // with default null behavior.

      // If the function has default null behavior, the Expr propagates nulls if
      // the set of fields null-propagating arguments depend on is a superset of
      // the fields non null-propagating arguments depend on.
      std::unordered_set<FieldReference*> nullPropagating, nonNullPropagating;
      for (auto& input : inputs_) {
        if (input->propagatesNulls_) {
          nullPropagating.insert(
              input->distinctFields_.begin(), input->distinctFields_.end());
        } else {
          nonNullPropagating.insert(
              input->distinctFields_.begin(), input->distinctFields_.end());
        }
      }

      // propagatesNulls_ is true if nonNullPropagating is subset of
      // nullPropagating.
      propagatesNulls_ = true;
      for (auto* field : nonNullPropagating) {
        if (!nullPropagating.count(field)) {
          propagatesNulls_ = false;
          break;
        }
      }
    }
  }

  for (auto& input : inputs_) {
    if (isSameFields(distinctFields_, input->distinctFields_)) {
      input->sameAsParentDistinctFields_ = true;
    }
  }

  // (5) Compute hasConditionals_.
  hasConditionals_ = hasConditionals(this);