Fortran LTO and array descriptors.

[Richard Biener]

On February 4, 2018 9:14:53 PM GMT+01:00, Thomas Koenig <tkoenig@netcologne.de> wrote:
>Hi Richard,
>> On February 3, 2018 6:17:15 PM GMT+01:00, Thomas Koenig
><tkoenig@netcologne.de> wrote:
>>> I wrote:
>>>
>>>> -  descriptor_dimension dim[r];\
>>>> +  descriptor_dimension dim[];\
>>>>    }
>>>
>>>> which works well
>>>
>>> ... up to a point, there are numerous dtio failures
>>> when regression testing this.
>>>
>>> So, clearly not ready for prime time :-)
>> 
>> As far as I remember libgfortran has function signatures with the
>array descriptor with the maximum number of dimensions and the frontend
>generates aliased function decls with descriptors of the number of
>dimensions of the actual argument?
>> 
>> I believe the solution to the problem is to have the frontend
>> emit only one declaration matching the library one
>
>That is definitely preferred.
>
>> and passing down pointers to descriptors that are accessed via the
>same full dimension type.
>> 
>> That can be achieved by either making all array descriptor instances
>full size
>
>Unfortunately, this is quite wasteful of memory. On a 64-bit system, we
>have 24 bytes per dimension; if we allocated a full rank 15
>descriptor for a rank one array, we would have 336 unused bytes
>on the stack.
>
>> or by doing _all_ actual accesses via that type. Like in pseudo C
>code:
>> 
>> Array2 two_dim;
>> ((arrayFullDim *) & two_dim) - >data =... ;
>
>Would it also be OK to make this a cast to a flexible member type?

Yes. I think that would even be preferred. 

Richard. 

>Regards
>
>	Thomas