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RE: [gomp4] Some progress on #pragma omp simd

> -----Original Message-----
> From: [mailto:gcc-patches-
>] On Behalf Of Aldy Hernandez
> Sent: Saturday, April 27, 2013 1:30 PM
> To: Iyer, Balaji V
> Cc: Jakub Jelinek; Richard Henderson;
> Subject: Re: [gomp4] Some progress on #pragma omp simd
> Hi Balaji.
> >> "The syntax and semantics of the various simd-openmp-data-clauses are
> >> detailed in the OpenMP specification.
> >> (, Section 2.9.3)."
> >>
> >> Balaji, can you verify which is correct?  For that matter, which are
> >> the official specs from which we should be basing this work?
> >
> > Privatization clause makes a variable private for the simd lane. In
> > general,  I would follow the spec. If you have further questions,
> > please feel free to ask.
> Ok, so the Cilk Plus 1.1 spec is incorrectly pointing to the OpenMP 3.0 spec,
> because the OpenMP 3.0 spec has the private clause being task/thread private.
> Since the OpenMP 4.0rc2 explicitly says that the private clause is for the SIMD
> lane (as you've stated), can we assume that when the Cilk Plus 1.1 spec mentions
> OpenMP, it is talking about the OpenMP 4.0 spec?

I don't know of all the references to the OMP manual in the spec, so I will be a bit hesitant to make a blanket assumption like that. In this case, I think you can assume that it behaves in the same way as 4.0. If you have further questions, please feel free to ask. In general, #pragma simd, array notation and elemental functions deal with vectorization, not threading. But, Cilk part (Cilk keywords and reducers) deal with threading. All these parts can be mixed and matched (with restrictions) to take advantage of both threading and vectorization.

> One more question Balaji, the Cilk Plus spec says that for #pragma simd, the
> private, firstprivate, lastprivate, and reduction clauses are as OpenMP.
> However, for <#omp simd>, there is no firstprivate in the OpenMP 4.0rc2 spec.
> Is the firstprivate clause valid for Cilk Plus'
> <#pragma simd>?

> Thanks.
> Aldy

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