[Patch, v2] OpenMP/Fortran: Fix handling of 'declare target' with 'link' clause [PR11555]

[Tobias Burnus]

Updated patch - only change is to the testcase:

* With the just posted patch for PR116107, array sections with offset 
work for 'link', hence, I updated the testcase.

* For 'arr2', I added ref to the associated PR.

I intent to commit it once PR116107 has been committed.

Tobias

Tobias Burnus wrote:
> Hi all,
>
> it turned out that 'declare target' with 'link' clause was broken in multiple ways.
>
> The main fix is the attached patch, i.e. namely pushing the variables already to
> the offload-vars list already in the FE.
>
> When implementing it, I noticed:
> * C has a similar issue when using nested functions, which is
>    a GNU extension →https://gcc.gnu.org/115574
>
> * When doing partial mapping of arrays (which is one of the reasons for 'link'),
>    offsets are mishandled in Fortran (not tested in C), see FIXME in the patch)
>    There: arr2(10) should print 10 but with map(arr2(10:)) it prints 19.
>    (I will file a PR about this).
>
> * It might happen that linked variables do not get linked. I have not investigated
>    why, but 'arr2' gives link errors – while 'arr' works.
>    See FIXME in the patch. (I will file a PR about this)
>
> * For COMMON blocks, map(/common/) is rejected,https://gcc.gnu.org/PR115577
>
> * When then mapping map(a,b,c) which is identical for 'common /mycom/ a,b,c',
>    it fails to link the device side as the 'mycom_' symbol cannot be found on the
>    device side.  (I will file a PR about this)
>
> As COMMON as issues, an alternative would be to defer the trans-common.cc
> changes to a later patch.
>
> Comments, questions, concerns?
>
> Tobias
>
> PS: Tested with nvptx offloading with a page-migration supporting system with
> nvptx and GCN offloading configured and no new fails observed.
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