dolfin team mailing list archive

["Robert C. Kirby" <kirby@xxxxxxxxxxxx>]

The situation in which templating versus nontemplating will matter is  
when the compiler is capable of inlining away a lot of function calls  
in templated code.  For example, indexing into a matrix is sometimes  
done virtually so that you can access a matrix, sum of matrices, etc  
with the same syntax.  If it's templated instead (and correct  
optimizations happen), you'll get a big win.  This is the basic  
technical contribution of expression templating.  Virtual functions  
can never be inlined (this is a "theorem") in C++.


On May 8, 2006, at 6:24 AM, Anders Logg wrote:

> I have added a benchmark to src/test/main.cpp. It compares the speed
> of assemblhy for 2D Poisson on a 128 x 128 mesh repeated 100
> times. Here are some typical timings:
>
> Time with template:    4.23
> Time without template: 4.24
>
> Time with template:    4.24
> Time without template: 4.21
>
> Time with template:    4.2
> Time without template: 4.29
>
> Time with template:    4.22
> Time without template: 4.24
>
> Time with template:    4.22
> Time without template: 4.15
>
> Sometimes the templated version wins and sometimes the non-templated
> wins, so I'd say there is no overhead of removing the templating. The
> advantage would be that FEM and other implementations can be
> simplified and more code moved to .cpp from .h.
>
> Garth, maybe you can check the benchmark and see if you agree with the
> results. I've compiled with --enable-optimization.
>
> /Anders
>
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