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

[tschwinge at gcc dot gnu.org via Gcc-bugs]

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

Thomas Schwinge  changed:

   What|Removed |Added

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

[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  ---
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=0x7fffd79c, s=4
  ! NEW
  ! (gdb) print tgt
  ! $2 = (struct target_mem_desc *) 0xa7a690
  ! (gdb) print/x *tgt
  ! $3 = {refcount = 0x1, array = 0xb18570, tgt_start = 0x7fffcf00,
tgt_end = 0x7fffcf04, to_free = 0x7fffcf00, 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=0x7fffd79c, 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=0x7fffd79c, 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=0x7fffd79c, 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  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  ---
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=0x7fffd6d0, s=76
  ! NEW
  ! (gdb) print tgt
  ! $2 = (struct target_mem_desc *) 0xa7b690
  ! (gdb) print/x *tgt
  ! $3 = {refcount = 0x1, array = 0xb19480, tgt_start = 0x7fffcf00,
tgt_end = 0x7fffcf4c, to_free = 0x7fffcf00, 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