Hi Thomas, hi all,

(Updated patch attached – only changes the goacc testcases.
I intent to commit the patch tomorrow, unless more comments come up.)

On 10.03.22 10:00, Thomas Schwinge wrote:

[OpenACC testcases:]

> I recently added that checking in ... [...] to document the status quo.
> (1), as you have proposed, add '-O0' (but with source code comment, please); [...]
> ..., or (2): update the test cases [...] (rationale: the test cases
> haven't originally been written for the '-Wuninitialized' diagnostics; [...]
> (3): duplicate the test cases to account for both (1) and (2)
> [...] (3), would be my approach.

Attached patch does (3). I also remove the code tweaking, added in previous
patch. - But added a bunch of comments.

And I have to admit that I did not realize that the -Wuninitialized was only
added later. (I did not expect that new flags get added to existing patches.)

>> ** I am actually not sure whether 'acc update(b)' will/should map a
>> previous allocated variable - or whether it should. [...]
>> testcases.

Should be: "previously *un*allocated" (+ Thomas s%...%.. comments).

> I don't quickly dig that, sorry.  Do we need to first clarify that with
> OpenACC Technical Committee, or is this just a GCC/OpenACC implementation
> issue?

That's mostly an OpenACC spec question.
But I did not check what the spec says. Thus, I don't know
* whether the spec needs to be improved
* what the implications are on the implementation.

I assume that the implementation for OpenMP does also make sense for
OpenACC (i.e. either works as required or does more but in a sensible
way) - but I don't know.

I think either/both of us should check the OpenACC spec.

  * * *

On the OpenMP side (clarified in 5.1 or 5.2):
* Map first an unallocated allocatable
=> That one is regarded as mapped/present
* Allocate it and map it again (e.g. implicit/explicit
   mapping for a target region)
=> Spec: Implementation may or may not update the item.
    However, (only) with 'always' the spec guarantees that it
    will also show up as allocated on the device.
=> Sentiment: should also work without 'always' modifier
    if previously unallocated. (Discussion postponed.)
* I have not checked 'update' but I think it behaves
   like 'map(always,to/from:' (except for ref counting)

OpenMP GCC implementation: there is a known issue for
scalar allocatables (PR96668). It does work for arrays
(also without 'always') - and 'omp update' has not been
checked. (Ref counting issues?)

OpenACC GCC implementation: I think this code is shared
with OpenMP and, thus, works likewise. But I have have
also not checked this.

Tobias
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