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Re: [gomp4 simd, RFC] Simple fix to override vectorization cost estimation.
- From: Sergey Ostanevich <sergos dot gnu at gmail dot com>
- To: Jakub Jelinek <jakub at redhat dot com>
- Cc: Richard Biener <rguenther at suse dot de>, Yuri Rumyantsev <ysrumyan at gmail dot com>, gcc-patches <gcc-patches at gcc dot gnu dot org>, Igor Zamyatin <izamyatin at gmail dot com>, Areg Melik-Adamyan <areg dot melikadamyan at gmail dot com>
- Date: Tue, 12 Nov 2013 16:45:17 +0400
- Subject: Re: [gomp4 simd, RFC] Simple fix to override vectorization cost estimation.
- Authentication-results: sourceware.org; auth=none
- References: <CAEoMCqRPF8h_h0FU=+YHiizio-axzwx77q5gw-ewgbLRhv=cjQ at mail dot gmail dot com> <20131031151528 dot GS27813 at tucnak dot zalov dot cz> <c7dffd79-1947-4722-a75a-a25fdaafdeed at email dot android dot com> <CAGYS_T+m==Vu-bvWNUV0e3q2ZUZwSFSR526QiOiEsOoy_mnzQg at mail dot gmail dot com> <20131112110551 dot GP27813 at tucnak dot zalov dot cz>
yes, ICC ignores cost analysis and follows user request on introduction of
simd parallelism in the loop.they follow the omp parallel semantics.
On Tue, Nov 12, 2013 at 3:05 PM, Jakub Jelinek <jakub@redhat.com> wrote:
> On Tue, Nov 12, 2013 at 02:48:46PM +0400, Sergey Ostanevich wrote:
>> You are right regarding the cost model if we talk about vectorizer alone.
>> But the #pragma omp simd goes beyond the vectorizer - it introduces
>> parallel context in a place user defines, similar to #pragma omp parallel.
>> Are we applying any cost model for omp parallel region?
>>
>> You can consider this pragma as a helper for developer for 'easily'
>> introduce parallelism in his code, hence any type of cost model -
>> whatever quality it is - will plays against this paradigm, forcing user
>> to play around our cost model to let it make the loop simd-parallel.
>
> So what do other compilers do here? Does icc also totally ignore all
> cost analysis for #pragma omp simd or #pragma simd and vectorizes even when
> it would be obviously undesirable?
>
> Jakub