Re: Implementing OpenACC's Fortran module

[Tobias Burnus <burnus at net-b dot de>]

On 22.09.2014 17:17, Thomas Schwinge wrote:
> That works.  For avoidance of doubt: just tag to the actual
> implementation (which is enough to avoid the references to
> _gfortran_internal_unpack and _gfortran_internal_pack), or also the
> interfaces, as detailed in the following "pseudo patch":

Well, the standard mandates that those match, thus, I think one should 
do it.

If one passes a noncontiguous array to a CONTIGUOUS dummy argument, the 
caller ensures that the argument is truly packed by creating a temporary 
and packing it, iff it is not contiguous. (If it is known at compile 
time that the array is contiguous, no run-time test is inserted.) The 
idea is to avoid wrong code, if one passes something noncontiguous. 
Hence, the caller has to see the attribute - and if it only sees the 
interface block and not the function itself, it must be in the interface 
block.

In case of OpenACC, the OpenACC semantics require that the argument is 
contiguous. If users gets it wrong, it will be wrong either way: If the 
variable is not packed and when it is packed (and the temporary removed 
after the function call).

Tobias