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Re: PPC64 libmvec implementation of sincos


On September 30, 2019 3:52:52 PM GMT+02:00, 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)

We have __builtin_cexpi for that but not sure if any of the mechanisms can provide a mapping to a vectorized variant. 

>"#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?)


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