Re: [RFC 0/X] Implement GCC support for AArch64 libmvec

[Jakub Jelinek <jakub@redhat.com>]

On Thu, Apr 20, 2023 at 04:22:50PM +0100, Andre Vieira (lists) wrote:
> > I don't see a good reason for dropping the extension("scalable").
> > The problem is that since the base spec requires a simdlen clause,
> > GCC should in general raise an error if simdlen is omitted.
> Where can you find this in the specs? I tried to find it but couldn't.
> 
> Leaving out simdlen in a 'omp declare simd' I assume is OK, our vector ABI
> defines behaviour for this. But I couldn't find what it meant for a omp
> declare variant, obviously can't be the same as for declare simd, as that is
> defined to mean 'define a set of clones' and only one clone can be
> associated to a declare variant.

For missing simdlen on omp declare simd, OpenMP 5.2 says [202:14-15]:
"If a SIMD version is created and the simdlen clause is not specified, the number of concurrent
arguments for the function is implementation defined."
Nobody says it must be a constant when not specified, when specified it has
to be a constant.
declare variant is function call specialization based on lots of different
aspects.  If you specify simd among construct selectors, then the
implementation is allowed (and kind of expected but not currently implemented in
GCC) to change the calling convention based on the declare simd ABIs, but
again, simdlen might be specified (then it has to have constant number in
it) or not, then I bet it is supposed to be derived from the actual
differences in the calling convention to which match it is.
But as I said, this part isn't implemented yet even on other targets.

	Jakub