Re: Forwarding -foffload=[...] from the driver (compile-time) to libgomp (run-time)

[Jakub Jelinek <jakub@redhat.com>]

On Tue, Oct 20, 2015 at 01:45:37PM +0200, Bernd Schmidt wrote:
> Both of you can ignore me if you feel I'm not making sense, but what exactly
> is the use case for -foffload=disable? Isn't it slightly redundant with
> -fno-openacc? IMO it's not an option that alters the available devices,
> that's a question that is answered at run-time and doesn't (or shouldn't)
> really depend on compiler switches. As a user I'd expect -foffload=disable
> to just prevent generation of offloaded code for the things I'm compiling.
> As Jakub pointed out, shared libraries may still contain other pieces that
> are offloadable.
> 
> I guess I don't fully understand why you want to go to great lengths to
> disable devices at run-time based on a compile-time switch. What's the
> reasoning here?

At least for OpenMP, I'm also happy with what we do now (except for the
ability to configure offloading targets as optional, i.e. dynamically
configure the default based on what packages user install rather than
just on how it has been configured, so that e.g. just because it has been
configured for PTX offloading the host GCC itself doesn't have to have a
dependency on the proprietary CUDA stuff in any way).
I believe in OpenMP nobody says that if the device HW is available, but user
chose to not compile offloading code/variables for that particular device
that it can't show up among omp_get_num_devices ().  And I think it is
entirely fine if say target data map succeeds to that device, but then
target is offloaded, if that is caused by users configure or command line
choice.  Maybe OpenACC has different requirements, is it required to
terminate the program if it can't fulfill the requested offloading?

In any case, I'm fine with something I've noted in the last mail, or with
the status quo, but not with running constructors in TUs or even shared
libraries just because they have been compiled with -fopenmp (and either
haven't used any OpenMP code at all, or just the non-*target* directives).

	Jakub