Re: [eigen] Eigen containers cannot be vectorized |

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*To*: eigen@xxxxxxxxxxxxxxxxxxx*Subject*: Re: [eigen] Eigen containers cannot be vectorized*From*: Joseph Mirabel <joseph.mirabel@xxxxxxx>*Date*: Thu, 8 Dec 2016 15:28:07 +0100

Actually, my code can't work. I realize it just now. A(i,j) returns something like (A.data_ + i * A.cols_ + j) As it does not know that A.cols_ is constant, it does not vectorize... On 12/08/2016 03:03 PM, Francois Fayard wrote: > Hi Joseph, > >> what about this: >> >> #include <Eigen/Dense> >> >> void f(Eigen::Matrix<Eigen::Index, Eigen::Dynamic, Eigen::Dynamic>& A) { >> const Eigen::Index cols = A.cols(); >> const Eigen::Index rows = A.rows(); >> for (Eigen::Index j = 0; j < cols; ++j) { >> for(Eigen::Index i = 0; i < rows; ++i) { >> A(i, j) = i + j; >> } >> } >> } > > I was too quick to reply. It does not work, compiled with > > icpc -c -std=c++11 -O3 -xHost -DNDEBUG > > I can’t really explain what is going on. I have tried to walk the > accessor (A(i, j)) through the debugger, and it is not straightforward > code for the compiler. There is a pointer cast that might disconnect any > optimizer. So, I can’t easily provide you with a solution. > > I was also surprised to see that in debug mode, bounds checking is done > with: assert(i >=0 && i < n). This can be optimized into > assert(static_cast<std::size_t>(i) < static_cast<std::size_t>(n)). > > François Fayard > Founder & Consultant - Inside Loop > Applied Mathematics & High Performance Computing > Tel: +33 (0)6 01 44 06 93 > Web: www.insideloop.io <http://www.insideloop.io>

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**References**:**[eigen] Eigen containers cannot be vectorized***From:*Francois Fayard

**Re: [eigen] Eigen containers cannot be vectorized***From:*Joseph Mirabel

**Re: [eigen] Eigen containers cannot be vectorized***From:*Francois Fayard

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