Why is this not allowed?
!$acc data region if (.not. openshell)
!$acc> copyin(ca_acc_t(1:l1,1:na))
C
!$acc data region if (openshell)
!$acc> copyin(ca_acc_t(1:l1,1:na))
!$acc> copyin(cb_acc_t(1:l1,1:na))
... some code ...
!$acc end data region
!$acc end data region