if (terminator->getOperand(index) != returned_val) return failure();
      }
      result_to_extern_value[result] = returned_val;
    }

    // If no pass through values are found, no change is required.
    if (result_to_extern_value.empty()) return failure();

    // Create new case/if region op.
    auto new_op = CreateTfOp<CaseOrIfRegionOp>(rewriter, op, new_result_types,