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Re: PPC64 libmvec implementation of sincos


On Mon, Nov 25, 2019 at 5:53 PM GT <tnggil@protonmail.com> wrote:
>
> > >
> > > i wonder if gcc can auto-vectorize scalar sincos
> > > calls, the vectorizer seems to want the calls to
> > > have no side-effect, but attribute pure or const
> > > is not appropriate for sincos (which has no return
> > > value but takes writable pointer args)
> >
> > We have __builtin_cexpi for that but not sure if any of the mechanisms can provide a mapping to a vectorized variant.
> >
>
> 1. Using flags -fopt-info-all and -fopt-info-internals, the failure to vectorize sincos
> is reported as "unsupported data-type: complex double". The default GCC behavior is to
> replace sincos calls with calls to __builtin_cexpi.
>
> 2. Using flags -fno-builtin-sincos and -fno-builtin-cexpi, the failure to vectorize
> sincos is different. In this case, the failure to vectorize is due to "number of iterations
> could not be computed". No calls to __builtin_cexpi; sincos calls retained.
>
> Questions:
> 1. Should we aim to provide a vectorized version of __builtin_cexpi? If so, it would have
> to be a PPC64-only vector __builtin-cexpi, right?
>
> 2. Or should we require that vectorized sincos be available only when -fno-builtin-sincos flag
> is used in compilation?
>
> I don't think we need to fix both types of vectorization failures in order to obtain sincos
> vectorization.

I think we should have a vectorized cexpi since that's having a sane
ABI.  The complex
return type of cexpi makes it a little awkward for the vectorizer but
handling this should
be manageable.  It's a bit difficult to expose complex types to the
vectorizer since
most cases are lowered early.

Richard.

> Thanks.
> Bert.


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