[Bug fortran/37577] New: Change internal array descriptor format for better syntax, C interop TR, rank 15

["burnus at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org>]

There are a couple of issues with regards to the internal representation of
arrays in gfortran.

The solution is to revamp the internal format.

The main format should match the "Further Interoperability with C" technical
report (TR) which is currently developed.

It further more needs to:
- Support the distinction between pointer/allocatable targets and
nondeallocatable targets -> PR 35718
- It could support a flag to store the contiguous status. Ifort has and it
might make more sense than having to check it everytime when needed explicitly.
(Or is this faster on average?) Need also to check CONTIGIOUS flag of F2008
- A storage allocated flag (as ifort has) for zero-sized arrays; currently a
single item is allocated.
- Be prepared for coarrays - they can be handled by the normal dim etc., but
one might want to store information none the less.
- Possibly save some space for extensions

Internal format of ifort:

http://www.intel.com/software/products/compilers/docs/flin/main_for/mergedProjects/bldaps_for/common/bldaps_hndl_arrdesc.htm


"SC 22 N 4146, New Work Item Proposal for Further Interoperability with C, TR
Type 2": Not yet publicly available; check status or ask your TR/WG5 contact
;-)
The original proposal is available at
http://j3-fortran.org/doc/year/06/06-171.txt


For subref arrays, a byte-based approach should replace the span:

> > Is there a plan to do it right with the next major ABI change (i.e.
> > represent strides in bytes rather than elements and kill this span stuff)?
> > I think there are comments about intending to go from 7 to 15 maximum rank
> > and that will need ABI changes to the array descriptors anyway.
>
> At the time that subref array pointers were implemented, there was a
> discussion on the list on how to do this.  Changing the ABI for array
> descriptors was favoured but nobody had the time to carry out the
> necessary surgery.  Therefore, I came up with the span kludge, which
> arguably is worse than nothing:-(


-- 
           Summary: Change internal array descriptor format for better
                    syntax, C interop TR, rank 15
           Product: gcc
           Version: 4.4.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: burnus at gcc dot gnu dot org
OtherBugsDependingO 20923,34528,35718,36825
             nThis:


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37577