Re: [eigen] Performance difference icc <-> gcc, EIGEN_STRONG_INLINE

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On 14/03/2019 05.08, Michael Riesch wrote:
We could easily remove EIGEN_COMP_ICC from the cases where EIGEN_STRONG_INLINE is a __force_inline:

But I don't know the history of this, i.e., if it was necessary for older ICC versions. Or if it is necessary at other places.
Same here, hence I wanted to ask whether defining EIGEN_STRONG_INLINE has some disadvantages. According to the Intel profiling tools, my function that contains all the calculations actually calls the Eigen functions (e.g., Eigen::Matrix<...>::Matrix<...> and Eigen::Matrix<...>::operator=). I expected that those will be inlined. Is this something to worry about?

I think what you finally need to do is to look at the assembly generated from (the performance critical parts of) your program. Defining `EIGEN_STRONG_INLINE` as `inline` should be save regarding functionality, but I can't give any promises on the performance impact with ICC, especially with different compile flags.

Maybe I should add that I do not use the -inline-forceinline flag for the Intel compiler since this lead to incredibly long compilation times.

Interesting. It could be that (if inactive) this flag implies that `__forceinline` is essentially evaluated to nothing.
Perhaps for ICC we should do by default:
  #define EIGEN_STRONG_INLINE __forceinline inline

I think "Science" is the best fit, since mbsolve [1] "is an open-source solver tool for the Maxwell-Bloch equations, which are used to model light-matter interaction in nonlinear optics."



Thanks a lot for any comments!



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