Re: Implementing OpenACC's Fortran module

[Thomas Schwinge <thomas at codesourcery dot com>]

Hi Tobias!

On Sat, 20 Sep 2014 13:51:58 +0200, Tobias Burnus <burnus@net-b.de> wrote:
> On 19.09.2014 11:03, Thomas Schwinge wrote:
> > Regarding linking the object file produced by Fortran openacc.f90 into 
> > libgomp: (with the version that Jim already has internally checked in) 
> > I find that libgomp then has undefined references to 
> > _gfortran_internal_unpack and _gfortran_internal_pack.
> 
> Internal pack and unpack appears when you a (potentially) noncontiguous 
> array is passed as argument to an argument which requires a contiguous 
> argument. Internal pack checks at run time whether the argument is 
> contiguous - and if not it creates a temporary and copies the data to 
> the temporary ('copy in') - internal unpack ensures for all arrays but 
> intent(in) that the data is propagated back to the original one.

Thanks for the explanation.

> I am pretty sure that copy-in will break the OpenACC functions.
> 
> One possibility would be to mark the dummy arguments in openacc.f90 as 
> CONTIGUOUS. That way, no internal pack/unpack is called by openacc.f90. 
> (If one has a noncontiguous array, the caller of openacc.f90 will do the 
> copy in/out.)
> 
> Thus, you could try to add ", contiguous" to all procedures which take 
> an assumed-rank array "(..)" as argument.

That works.  For avoidance of doubt: just tag to the actual
implementation (which is enough to avoid the references to
_gfortran_internal_unpack and _gfortran_internal_pack), or also the
interfaces, as detailed in the following "pseudo patch":

     [openacc.f90]

     module openacc_internal
       use openacc_kinds
       implicit none
     
       interface

         subroutine acc_delete_32_h (a, len)
           use iso_c_binding, only: c_int32_t, c_size_t
           !GCC$ ATTRIBUTES NO_ARG_CHECK :: a
           type(*), dimension(*) :: a
           integer(c_int32_t) len
         end subroutine
       
         subroutine acc_delete_64_h (a, len)
           use iso_c_binding, only: c_int64_t, c_size_t
           !GCC$ ATTRIBUTES NO_ARG_CHECK :: a
           type(*), dimension(*) :: a
           integer(c_int64_t) len
         end subroutine
       
         subroutine acc_delete_array_h (a)
           use iso_c_binding, only: c_size_t
    -      type(*), dimension(..) :: a
    +      type(*), dimension(..), contiguous :: a
         end subroutine

       end interface
     
       interface

         subroutine acc_delete_l (a, len) &
             bind(C, name="acc_delete")
           use iso_c_binding, only: c_size_t
           !GCC$ ATTRIBUTES NO_ARG_CHECK :: a
           type(*), dimension(*) :: a
           integer(c_size_t), value :: len
         end subroutine

       end interface
     end module
     
     module openacc
       use openacc_kinds
       use openacc_internal

       interface acc_delete
         procedure :: acc_delete_32_h
         procedure :: acc_delete_64_h
         procedure :: acc_delete_array_h
       end interface

     end module

     subroutine acc_delete_32_h (a, len)
       use iso_c_binding, only: c_int32_t, c_size_t
       use openacc_internal, only: acc_delete_l
       !GCC$ ATTRIBUTES NO_ARG_CHECK :: a
       type(*), dimension(*) :: a
       integer(c_int32_t) len
       call acc_delete_l (a, int (len, kind=c_size_t))
     end subroutine
     
     subroutine acc_delete_64_h (a, len)
       use iso_c_binding, only: c_int64_t, c_size_t
       use openacc_internal, only: acc_delete_l
       !GCC$ ATTRIBUTES NO_ARG_CHECK :: a
       type(*), dimension(*) :: a
       integer(c_int64_t) len
       call acc_delete_l (a, int (len, kind=c_size_t))
     end subroutine
     
     subroutine acc_delete_array_h (a)
       use iso_c_binding, only: c_size_t
       use openacc_internal, only: acc_delete_l
    -  type(*), dimension(..) :: a
    +  type(*), dimension(..), contiguous :: a
       call acc_delete_l (a, sizeof (a))
     end subroutine

     [openacc_lib.h]

           interface acc_delete
             subroutine acc_delete_32_h (a, len)
               use iso_c_binding, only: c_int32_t
               !GCC$ ATTRIBUTES NO_ARG_CHECK :: a
               type(*), dimension(*) :: a
               integer(c_int32_t) len
             end subroutine
       
             subroutine acc_delete_64_h (a, len)
               use iso_c_binding, only: c_int64_t
               !GCC$ ATTRIBUTES NO_ARG_CHECK :: a
               type(*), dimension(*) :: a
               integer(c_int64_t) len
             end subroutine
       
             subroutine acc_delete_array_h (a)
    -          class(*), dimension(..) :: a
    +          class(*), dimension(..), contiguous :: a
             end subroutine
           end interface


GrÃÃe,
 Thomas

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