Re: [PATCH v5 2/4] OpenMP/OpenACC: Rework clause expansion and nested struct handling

[Julian Brown <julian@codesourcery.com>]

On Wed, 7 Dec 2022 15:54:42 +0100
Tobias Burnus <tobias@codesourcery.com> wrote:

> Hi Julian,
> 
> If I understand Deepak's comment (on OpenMP.org's omp-lang list, sorry
> it is a nonpublic list) correctly, the following wording implies that
> a 'from: s.w[z:4]' for a pointer 's.w' also implies a mapping of
> 's.w' - if 's' is used inside the target region and, thus, gets
> implicitly mapped.
> 
> [TR11 157:21-26] (approx. [5.2 154:22-27], [5.1 352:17-22], [5.0
> 320:22-27])
> 
> "If a list item with an implicit data-mapping attribute does not have
> any corresponding storage in the device data environment prior to a
> task encountering the construct associated with the map clause, and
> one or more contiguous parts of the original storage are either list
> items or base pointers to list items that are explicitly mapped on
> the construct, only those parts of the original storage will have
> corresponding storage in the device data environment as a result of
> the map clauses on the construct."

Hmmm... IIRC that is a different conclusion than the one we have
understood previously, leading to e.g. the patch here (Chung-Lin CC'ed):

https://gcc.gnu.org/pipermail/gcc-patches/2021-May/570075.html

Follow-on discussion then questioned whether the change was really the
intention of the spec, but we thought it was.  Has that changed now?

(I think actually changing the behaviour is a matter of flipping a
switch, but let's make sure we choose the right setting!)

Thanks,

Julian