From: Tobias Burnus <burnus@net-b.de>
To: Mikael Morin <mikael.morin@sfr.fr>
Cc: fortran@gcc.gnu.org, gcc patches <gcc-patches@gcc.gnu.org>
Subject: Re: [Patch, Fortran] Support allocatable *scalar* coarrays
Date: Sat, 16 Jul 2011 15:45:00 -0000 [thread overview]
Message-ID: <4E21AD70.2090508@net-b.de> (raw)
In-Reply-To: <201107161459.26836.mikael.morin@sfr.fr>
Mikael Morin wrote:
> let me understand one thing about coarray scalars: despite their name, they
> are arrays, right?
Yes and no. In terms of the language, they are scalars - but they have a
codimension, e.g.
integer, save :: A[4:6, 7:*]
is a scalar variable on each image, but it has a coarank of 2 with
lcobound(A) == [4, 7] and ucobound(A, dim=1) == 7. (The value of
cobound(A, dim=2) depends on the number of images, it's >= 7 in this
example.)
In terms of gfortran, nonallocatable coarrays are normal scalars - with
a lang-specific node attached to them, which contains the cobounds, i.e.,
GFC_ARRAY_TYPE_P (type) = 1;
GFC_TYPE_ARRAY_CORANK (type) = as->corank;
with
GFC_TYPE_ARRAY_LBOUND (type, dim)
containing the trees for dim = (rank + 1) ... (rank + corank).
The same scheme is used for assumed-type coarrays:
subroutine sub(B, n)
integer :: B(:)[5:7, n:*]
Note that here that contrary to the dimension, the codimension is not
":" (i.e. assumed shape) but that it is assumed-size.
For allocatable (scalar) coarrays, one has:
integer, allocatable :: B[:, :] ! Note: The coshape is deferred
...
allocate (B[2:3, 5:*])
Again, one has the actual data and the cobounds. For that case, I have
decided to store the information in the array descriptor of rank == 0
and dim[0 ... corank-1] for the bounds. Thus, "desc->data" contains the
scalar but the variable itself is a descriptor (GFC_DESCRIPTOR_TYPE_P).
The corank is not stored in the descriptor, but as one knows the number
of codimensions (an explicit interface is required for allocatable
coarray dummies), one knows the corank.
> Then when you do in gfc_conv_array_ref:
>
> + if (GFC_DESCRIPTOR_TYPE_P (TREE_TYPE (se->expr)))
> + se->expr = build_fold_indirect_ref (gfc_conv_array_data (se->expr));
> [...]
> return;
>
> you are returning scalar[1] instead of scalar (== scalar[this_image()]) or
> scalar[whatever_image_selector], aren't you?
Well, the current implementation supports effectively only a single
image - for -fcoarray=single on purpose and for -fcoarray=lib because it
has not yet been implemented.
Later, one has to add some function call for "scalar[<image_numer>]"
while "scalar" itself is the local variable and can be handled as above.
The expression of "scalar" ends up having expr->ref->type == REF_ARRAY
with dimen_type == DIMEN_THIS_IMAGE. That way one can distinguish a
reference to the local coarray and to a remote coarray (coindexed
variable); note that "coarray[this_image()]" also counts as
remote/coindexed.
> Sorry for the delay; it seems that the more it goes, the more you are the only
> one who can maintain coarray stuff. :-(
Well, Daniel Carrera develops into an trans*.c, allocate,
libgfortran/caf/ expert :-)
Tobias
PS: I should document somewhere how coarrays are implemented internally.
next prev parent reply other threads:[~2011-07-16 15:25 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-07-10 21:16 Tobias Burnus
2011-07-11 7:54 ` Tobias Burnus
2011-07-14 7:38 ` *ping* - " Tobias Burnus
2011-07-16 11:20 ` Tobias Burnus
2011-07-16 14:38 ` Mikael Morin
2011-07-16 15:45 ` Tobias Burnus [this message]
2011-07-16 17:05 ` Steve Kargl
2011-07-16 17:07 ` Mikael Morin
2011-07-16 19:59 ` Daniel Carrera
2011-07-16 22:57 ` Tobias Burnus
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