Re: [Patch] OpenMP, libgomp: Add new runtime routine omp_target_is_accessible.

[Jakub Jelinek <jakub@redhat.com>]

On Thu, May 05, 2022 at 11:45:19AM +0200, Tobias Burnus wrote:
> > On Mon, Mar 14, 2022 at 04:42:14PM +0100, Marcel Vollweiler wrote:
> > > +        interface
> > > +          function omp_target_is_accessible (ptr, size, device_num) bind(c)
> > > +            use, intrinsic :: iso_c_binding, only : c_ptr, c_size_t, c_int
> > > +            integer(c_int) :: omp_target_is_accessible
> > The function returning integer(c_int) rather than logical seems like
> > a screw up in the standard, but too late to fix that :(.
> 
> I think the idea is that it can directly call the C function without
> needing a wrapper. And as default-kind 'logical' != 'integer(c_int)' in
> general, it cannot return logical. (In case of GCC, just claiming that
> it is logical would work. But some Fortran compilers use -1 for .true.
> and only flip a single bit for .not. For those,
> "if(.not.omp_target_is_accessible(..)) will not work properly, if the C
> function returns 1.
> 
> But I concur that requiring "/= 0" is ugly!

Yeah, but for the APIs that don't have any iso_c_binding arguments
we just use wrappers rather than bind(c) and it allows for more Fortran-like
callers.  So, if omp_target_is_accessible had the *_ wrapper (or alias if
we determine logical ir the same as c_int in the ABI passing), people could
avoid the /= 0 stuff.
Anyway, that is just a thought for future APIs that if they return
false/true only bind(c) isn't always a good idea.

	Jakub