PPC64 libmvec implementation of sincos

[GT]

> >
> > 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.

Thanks.
Bert.