Re: [PATCH v3 06/11] OpenMP: Pointers and member mappings

[Tobias Burnus <tobias@codesourcery.com>]

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On 30.09.22 15:30, Julian Brown wrote:
On Fri, 23 Sep 2022 14:10:51 +0200 Tobias Burnus <tobias@codesourcery.com><mailto:tobias@codesourcery.com> wrote:
...

I added n->expr->expr_type == EXPR_VARIABLE to the condition -- I think
that should suffice for now?

Yes.


A similar mean way to write code would be:

integer, target :: A(5)
integer, pointer :: p(:), p2(:)
type(t) :: var

allocate(p2(1:20))
p => A
var%p2 => p2
!$omp target map(A(3:4), p2(4:8), p, var%p2)
  ....
!$omp end target

which has a similar issue – it is not clear from the syntax whether
p's or var%p2's pointer target has been mapped or not.


Again, I don't think you're allowed to write that: that's "different
list items" sharing the same "original storage", IIUC. (It'd be nice to
diagnose it at compile time, but that's probably not that easy...)

Hmm, isn't that implied to be valid per:

"[Fortran] If a list item in a map clause is an associated pointer and the pointer
 is not the base pointer of another list item in a map clause on the same
 construct, then it is treated as if its pointer target is implicitly
 mapped in the same clause."
(OpenMP 5.2, 5.8.3 map Clause [152:1-4]; seems to be identical to
 OpenMP 5.1, 2.21.7.1 map Clause [349:9-12])

Admittedly, in 5.0 I only see the wording (OpenMP 5.0, [316:22-25]),
which is also not handled - but different:

"[Fortran] Each pointer component that is a list item that results from
 a mapped derived type variable is treated as if its association status
 is undefined, unless the pointer component appears as another list
 item or as the base pointer of another list item in a map clause on
 the same construct."

I think the that's for the following case (which is also covered by the
more general 5.1/5.2 wording):
type t

  integer, pointer :: p(:)
  integer, pointer :: p2(:)
end type t
type(t) :: var
integer, target :: tgt(5), tgt2(1000)
var%p => tgt
var%p => tgt2

!$omp target map(tgt, tgt2(4:6), var)
  var%p(1) = 5
  var%p2(5) = 7
!$omp end target

and I think GCC does not handled this, but I might be wrong.

Tobias


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