[Bug fortran/96080] New: [OpenACC] 'acc_is_present' for Fortran 'pointer'

[Bug fortran/96080] New: [OpenACC] 'acc_is_present' for Fortran 'pointer'

[tschwinge at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96080

            Bug ID: 96080
           Summary: [OpenACC] 'acc_is_present' for Fortran 'pointer'
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Keywords: openacc
          Severity: normal
          Priority: P3
         Component: fortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: tschwinge at gcc dot gnu.org
                CC: burnus at gcc dot gnu.org
  Target Milestone: ---

Do we have to clarify what 'acc_is_present' on a pointer means: whether the
data it points to is present, or whether the pointer object itself is present
-- or invalid?

    program main
      use openacc
      implicit none
      integer, dimension (:), allocatable, target :: a
      integer, dimension (:), pointer :: p

      allocate (a(10))
      !$acc enter data create(a)
      if (.not. acc_is_present (a)) stop 1

      p => a
      ! At this point, the data it points to is present, but the 'p' object
itself isn't.
      if (acc_is_present (p)) stop 2

      !$acc enter data create(p)
      ! At this point, both the data it points to, and the 'p' object are
present.
      if (.not. acc_is_present (p)) stop 3 !TODO This fails -- unexpectedly?

    end program main

[Bug fortran/96080] OpenACC/Fortran runtime library routines vs. Fortran 'pointer'

[tschwinge at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96080

Thomas Schwinge <tschwinge at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[OpenACC] 'acc_is_present'  |OpenACC/Fortran runtime
                   |for Fortran 'pointer'       |library routines vs.
                   |                            |Fortran 'pointer'
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1
                 CC|                            |jakub at gcc dot gnu.org
   Last reconfirmed|                            |2020-07-09

--- Comment #1 from Thomas Schwinge <tschwinge at gcc dot gnu.org> ---
This problem does *not* seem to be specific to just 'acc_is_present', but
probably all (?) OpenACC/Fortran runtime library routines?  Consider the
following transcript, where we see the directives behave as expected for
Fortran 'pointer' to 'dimension(:)', but the runtime library routines do not.

    program main
      use openacc
      implicit none
      integer, dimension(:), target :: data(19) ! 19 * 4 = 76 = 0x4c
      integer, dimension(:), pointer :: data_p

      call acc_create(data) ! h=0x7fffffffd6d0, s=76
      ! NEW
      ! (gdb) print tgt
      ! $2 = (struct target_mem_desc *) 0xa7b690
      ! (gdb) print/x *tgt
      ! $3 = {refcount = 0x1, array = 0xb19480, tgt_start = 0x7fffcf000000,
tgt_end = 0x7fffcf00004c, to_free = 0x7fffcf000000, prev = 0x0, list_count =
0x1, device_descr = 0x80bae0, list = 0xa7b6d0}
      ! (gdb) print/x tgt->list[0]
      ! $4 = {key = 0xb19480, copy_from = 0x0, always_copy_from = 0x0,
do_detach = 0x0, offset = 0x0, length = 0x4c}

      data_p => data

      call acc_copyin(data_p) ! h=0xb191b0, s=76
      ! NEW
      ! (gdb) print tgt
      ! $7 = (struct target_mem_desc *) 0xa7abc0
      ! (gdb) print/x *tgt
      ! $8 = {refcount = 0x1, array = 0xc21cd0, tgt_start = 0x7fffcf000200,
tgt_end = 0x7fffcf00024c, to_free = 0x7fffcf000200, prev = 0x0, list_count =
0x1, device_descr = 0x80bae0, list = 0xa7ac00}
      ! (gdb) print/x tgt->list[0]
      ! $9 = {key = 0xc21cd0, copy_from = 0x0, always_copy_from = 0x0,
do_detach = 0x0, offset = 0x0, length = 0x4c}
      ! That means, this creates a new mapping, 'acc_copyin(data_p)' does *not*
dereference 'data_p => data'.  So far, so good?  But:

      print *, acc_is_present(data_p) ! h=0xb18db0, s=76
      ! Not mapped; this neither looks up the 'acc_create(data)', nor the
'acc_copyin(data_p)'.

      !$acc enter data copyin(data_p)
      ! 0 ("to" '*data_p.data')
      !   (gdb) print n
      !   $12 = (splay_tree_prefix_splay_tree_key) 0xb19480
      !     OLD 'data' -- expected
      !     '++dynamic_refcount'
      ! 1 ("pset" 'data_p'), 2 ("pointer assign" 'data_p.data')
      !   NEW
      !     Was somewhat expecting this would look up what 'acc_copyin(data_p)'
mapped?
      !   (gdb) print tgt
      !   $4 = (struct target_mem_desc *) 0xc38000
      !   (gdb) print/x *tgt
      !   $5 = {refcount = 0x1, array = 0xc38770, tgt_start = 0x7fffcf000400,
tgt_end = 0x7fffcf000440, to_free = 0x7fffcf000400, prev = 0x0, list_count =
0x2, device_descr = 0x80bae0, list = 0xc38040}
      !   (gdb) print/x tgt->list[0]
      !   $6 = {key = 0xc38770, copy_from = 0x0, always_copy_from = 0x0,
do_detach = 0x0, offset = 0x0, length = 0x40}
      !   (gdb) print/x tgt->list[1] 
      !   $7 = {key = 0xc38770, copy_from = 0x0, always_copy_from = 0x0,
do_detach = 0x0, offset = 0x0, length = 0x0}

      print *, acc_is_present(data_p) ! h=0xb18db0, s=76
      ! Same as above; still isn't mapped.

      !$acc serial present(data_p)
      ! 0 ("force_present" '*data_p.data')
      !   (gdb) print n
      !   $14 = (splay_tree_prefix_splay_tree_key) 0xb19480
      !     OLD 'data' -- expected
      ! 1 ("pset" 'data_p'), 2 ("pointer assign" 'data_p.data')
      !   (gdb) print n
      !   $10 = (splay_tree_prefix_splay_tree_key) 0xc38770
      !     OLD "pset" 'data_p' (from 'enter data copyin(data_p)') -- expected
      data_p(5) = 55
      !$acc end serial
    end program main

[Bug fortran/96080] OpenACC/Fortran runtime library routines vs. Fortran 'pointer'

[tschwinge at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96080

--- Comment #2 from Thomas Schwinge <tschwinge at gcc dot gnu.org> ---
In contrast, see the same example with 'dimension(:)' removed, that is, scalar
data.  Here, we see the directives and the runtime library routines behave in
the same way for Fortran 'pointer'.

    program main
      use openacc
      implicit none
      integer, target :: data
      integer, pointer :: data_p

      call acc_create(data) ! h=0x7fffffffd79c, s=4
      ! NEW
      ! (gdb) print tgt
      ! $2 = (struct target_mem_desc *) 0xa7a690
      ! (gdb) print/x *tgt
      ! $3 = {refcount = 0x1, array = 0xb18570, tgt_start = 0x7fffcf000000,
tgt_end = 0x7fffcf000004, to_free = 0x7fffcf000000, prev = 0x0, list_count =
0x1, device_descr = 0x80aae0, list = 0xa7a6d0}
      ! (gdb) print/x tgt->list[0]
      ! $4 = {key = 0xb18570, copy_from = 0x0, always_copy_from = 0x0,
do_detach = 0x0, offset = 0x0, length = 0x4}

      data_p => data

      call acc_copyin(data_p) ! h=0x7fffffffd79c, s=4
      ! This is 'data'!
      ! (gdb) print n
      ! $5 = (splay_tree_prefix_splay_tree_key) 0xb18570
      !   OLD 'data'
      !     '++dynamic_refcount'
      ! That means, this does *not* create a new mapping, 'acc_copyin(data_p)'
*does* dereference 'data_p => data'.
      ! That means, we cannot use this to create a "pointer object 'data_p'" on
the device.

      print *, acc_is_present(data_p) ! h=0x7fffffffd79c, s=4
      ! This is 'data'!
      ! (gdb) print n
      ! $6 = (splay_tree_prefix_splay_tree_key) 0xb18570
      ! Mapped.

      !$acc enter data copyin(data_p)
      ! 0 ("to" '*data_p'), 1 ("pointer assign" 'data_p')
      !   (gdb) print n
      !   $8 = (splay_tree_prefix_splay_tree_key) 0xb18570
      !     OLD 'data'
      !       '++dynamic_refcount'

      print *, acc_is_present(data_p) ! h=0x7fffffffd79c, s=4
      ! Same as above; mapped.

      !$acc serial present(data_p)
      ! 0 ("force_present" '*data_p')
      !   (gdb) print n
      !   $10 = (splay_tree_prefix_splay_tree_key) 0xb18570
      !     OLD 'data' -- expected
      ! 1 ("pointer assign" 'data_p')
      !   [...]
      data_p = 55
      !$acc end serial
    end program main

In contrast to an 'integer, dimension(:), pointer :: data_p', we cannot use an
'integer, pointer :: data_p' to create a "pointer object 'data_p'" on the
device.  That's confusing (at least for me).  Plus the original confusion about
'acc_on_device' etc. behaving differently (non-sensical?).

[Bug fortran/96080] OpenACC/Fortran runtime library routines vs. Fortran 'pointer'

[tschwinge at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96080

Thomas Schwinge <tschwinge at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://github.com/OpenACC/
                   |                            |openacc-spec/issues/57
             Status|NEW                         |WAITING