On Wed, Apr 24, 2013 at 08:01:17AM +0200, Jakub Jelinek wrote: > On Tue, Apr 23, 2013 at 09:32:29PM +0000, Iyer, Balaji V wrote: > The documentation doesn't suggest that. Anyway, so > #pragma simd > should be equivalent to > #pragma omp simd > wrt. inter-iteration dependencies, and > #pragma simd vectorlength(a, b, c) > to > #pragma omp simd safelen(max (a, b, c)) > ? If so, then the FE could emit OMP_SIMD for #pragma simd, and if > vectorlength is present, add OMP_CLAUSE_SAFELEN with the maximum of the > values in all vectorlength clauses, and keep the vectorlength clauses around > too as CILK_CLAUSE_VECTORLENGTH as hints to the vectorizer? > > Also, Aldy said that #pragma simd loops allow != condition, how do you > compute number of iterations in that case if the increment isn't constant? > As conditional depending on whether increment is positive or negative? > != condition isn't allowed in OpenMP, so there it is always obvious which > direction it should iterate, and the expansion code will assume if it sees > NE_EXPR that it is just folded border test (comparison with maximum or > minimum value).
BTW, the semantics of private/firstprivate/lastprivate desribed in http://software.intel.com/sites/products/documentation/studio/composer/en-us/2011Update/compiler_c/cref_cls/common/cppref_pragma_simd.htm doesn't seem to match the semantics of those in #pragma omp simd. private in OpenMP I understand is private to the whole loop (or SIMD lane?; at least, that was the semantics of #pragma omp for too and there is no wording to suggest otherwise for #pragma omp simd or #pragma omp for simd), while the above html suggests in Cilk+ it is private to each iteration. #pragma omp simd doesn't support firstprivate. The lastprivate semantics wrt. returning the last iteration's value is the same. Jakub
