[4.8, Fortran, Patch] PR 48820 - Support TYPE(*) of TS29113

[Tobias Burnus]

TYPE(*) is Fortran's equivalent to C's "void *buffer". It may only be 
used for dummy arguments and essentially might only either be passed on, 
or appear in PRESENT, LBOUND/UBOUND/SHAPE/SIZE/IS_CONTIGUOUS - and most 
useful: in C_LOC.


Note: For scalar TYPE(*) and for assumed-size dummies, only the address 
is passed on. But for dimension(:) and TS29113's new (but unimplemented) 
dimension(..) an array descriptor is passed. In that case, one might 
recover the type from the array descriptor - at least for intrinsic types.


TYPE(*) is useful for, e.g., MPI (and used in the MPI v3 draft spec): 
There, one simply takes an argument of any type and transfers some bytes 
from it - without needing to know the type. TYPE(*) avoids to create 
hundreds of useless explicit interfaces for all kind of data types (and 
missing derived types that way) - or TS29113 avoids the alternative: Not 
using explicit interfaces (causing argument checking issues and prevents 
the use of BIND(C).)


See PR (or first test case) for a usage example. For a pure Fortran use, 
one could imagine:

subroutine send(buf, size)
   use iso_c_binding, only: c_signed_char, c_size_t
   type(*) :: buf(*)
   integer(c_size_t) :: size
   integer(c_signed_char) :: ibuf(size)
   call c_f_pointer (c_loc(buf), ibuf, shape=[size])
   ! ... use ibuf ...
end

[This example currently fails as "c_loc(buf)" is rejected. Several 
BIND(C) restrictions were removed in F2008 and especially in TS29113, 
but gfortran has not yet removed them.]


For more details, see:

* TS 29113 draft: ftp://ftp.nag.co.uk/sc22wg5/N1901-N1950/N1904.pdf
(Status: Went as PDTR through one round of voting by the ISO members, 
was updated at the last J3 meeting and is now the subject of a one-month 
WG5 ballot that ends on 19 March 2012. The schedule is that it will then 
be forwarded to SC22, which initiates a DTS ballot such that the final 
version will be published in September by ISO.)

* MPIv3 draft (of 2011-12-15):
https://svn.mpi-forum.org/trac/mpi-forum-web/attachment/ticket/229/mpi-report-F2008-2011-12-15-changeonlyplustickets_majorpages.pdf

Build and regtested on x86-64-linux.
OK for the 4.8 trunk?

Tobias
-------------- next part --------------
A non-text attachment was scrubbed...
Name: assumed-type.diff
Type: text/x-patch
Size: 24815 bytes
Desc: not available
URL: <http://gcc.gnu.org/pipermail/fortran/attachments/20120302/38c12746/attachment.bin>