[Bug testsuite/104423] [libgomp, testsuite] Add means to do accelerator-only testing in libgomp

["tschwinge at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104423

Thomas Schwinge <tschwinge at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |tschwinge at gcc dot gnu.org
     Ever confirmed|0                           |1
           Keywords|                            |openacc, openmp
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2022-02-08
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=66005

--- Comment #2 from Thomas Schwinge <tschwinge at gcc dot gnu.org> ---
(In reply to Tom de Vries from comment #0)
> I noticed that a lot of time is spent running libgomp tests that do not use the accelerator, and which are not needed for my purposes.

We can assume that effectively all OpenACC test cases use any available GPUs.

For OpenMP test cases indeed there is no clear answer.

> It would be nice if libgomp provided a mode to run only tests that use the accelerator, to drive down the test-board.sh execution time.

We may add a knob to skip the OpenACC '-foffload=disable' testing.

For OpenMP test cases, we'd either have to manually mark them up (error prone
and generally ugly), or scan the source file(s) (error prone and generally
ugly), or use some kind of marker that gets set during compilation if any
offloading code has been generated.

Regarding the latter, you also reported:

(In reply to Tom de Vries from comment #1)
> Looking at f.i. test-case for-3.c, compilation takes 3 minutes

We should be able to at least mitigate that problem via my PR66005 idea.

> and execution a few seconds.  It would make sense to reuse the executable.

I suppose you mean re-use across what currently are independent libgomp
testsuite invocations:

(In reply to Tom de Vries from comment #1)
> One of the dimensions that I test is env var GOMP_NVPTX_JIT, with values:
> - -O0, and
> - default (using unset GOMP_NVPTX_JIT), which supposedly is -O4.

For OpenACC, we'd hook that into the existing looping over any available GPUs
(plus host fallback).

For OpenMP, there currently is no such looping.

If paralellizing compilation via PR66005 is not sufficient then indeed we have
to think about switching OpenACC testing to a mode where only once we do
compile (without any '-foffload=[...]), and then loop over 'ACC_DEVICE_TYPE'
etc.