Re: PPC64 libmvec implementation of sincos

[GT <tnggil@protonmail.com>]

‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
On Monday, September 30, 2019 9:52 AM, Szabolcs Nagy <Szabolcs.Nagy@arm.com> wrote:

> On 27/09/2019 20:23, GT wrote:
>
> > I am attempting to create a vector version of sincos for PPC64.
> > The relevant discussion thread is on the GLIBC libc-alpha mailing list.
> > Navigate it beginning at https://sourceware.org/ml/libc-alpha/2019-09/msg00334.html
> > The intention is to reuse as much as possible from the existing GCC implementation of other libmvec functions.
> > My questions are: Which function(s) in GCC;
> >
> > 1.  Gather scalar function input arguments, from multiple loop iterations, into a single vector input argument for the vector function version?
> > 2.  Distribute scalar function outputs, to appropriate loop iteration result, from the single vector function output result?
> >
> > I am referring especially to vectorization of sin and cos.
>
> 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)

1.  Do you mean whether x86_64 already does auto-vectorize sincos?
2.  Where in the code do you see the vectorizer require no side-effect?

> "#pragma omp simd" on a loop seems to work but i
> could not get unannotated sincos loops to vectorize.
>
> it seems it would be nice if we could add pure/const
> somehow (maybe to the simd variant only? afaik openmp
> requires no sideeffects for simd variants, but that's
> probably only for explicitly marked loops?)

1. Example 1 and Example 2 at https://sourceware.org/glibc/wiki/libmvec show the 2 different
ways to activate auto-vectorization. When you refer to "unannotated sincos", which of
the 2 techniques do you mean?
2. Which function was auto-vectorized by "pragma omp simd" in the loop?