Boost::multi_array performance question

Question

I am trying to compare the performance of boost::multi_array to native dynamically allocated arrays, with the following test program:

#include 

        

Answer 1

I've compiled the code (with slight modifications) under VC++ 2010 with optimisation turned on ("Maximize Speed" together with inlining "Any Suitable" functions and "Favoring fast code") and got times 0.015/0.391. I've generated assembly listing and, though I'm a terrible assembly noob, there's one line inside the boost-measuring loop which doesn't look good to me:

call    ??A?$multi_array_ref@N$01@boost@@QAE?AV?$sub_array@N$00@multi_array@detail@1@H@Z ; boost::multi_array_ref::operator[]

One of the [] operators didn't get inlined! The called procedure makes another call, this time to multi_array::value_accessor_n<...>::access<...>():

call    ??$access@V?$sub_array@N$00@multi_array@detail@boost@@PAN@?$value_accessor_n@N$01@multi_array@detail@boost@@IBE?AV?$sub_array@N$00@123@U?$type@V?$sub_array@N$00@multi_array@detail@boost@@@3@HPANPBIPBH3@Z ; boost::detail::multi_array::value_accessor_n::access,double *>

Altogether, the two procedures are quite a lot of code for simply accessing a single element in the array. My general impression is that the library is so complex and high-level that Visual Studio is unable to optimise it as much as we would like (posters using gcc apparently have got better results).

IMHO, a good compiler really should have inlined and optimised the two procedures - both are pretty short and straight-forward, don't contain any loops etc. A lot of time may be wasted simply on passing their arguments and results.