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Subject: Re: [boost] [fusion] improving compile times
From: Joel de Guzman (joel_at_[hidden])
Date: 2009-06-02 10:45:14

Sebastian Redl wrote:
> Eric Niebler wrote:
>> Larry Evans wrote:
>>> On 06/01/09 20:26, Eric Niebler wrote:
>>>> I'm attaching a simple patch to vector_n_chooser.hpp that replaces
>>>> some template metaprogramming with preprocessor metaprogramming in
>>>> the interest of improving compile times. I found this hotspot
>>>> through profiling,
>>> [snip]
>>> Eric,
>>> Could you post your benchmark code that showed the improvement in
>>> compile speed? I'd like to eventually try it with a variadic template
>>> compiler version of fusion vector.
>> I confess that I'm not actually benchmarking compile speed; rather,
>> I'm benchmarking the number of template instantiations as reported by
>> Steven's template profiler. I'm profiling TMP-heavy code like some of
>> Proto's and xpressive's tests and cherry-picking the worst offenders.
>> The Fusion vector_n_chooser patch knocked off 100's of template
>> instantiations, for instance.
> That's not necessarily a good benchmark, especially if you replace it by
> preprocessor metaprogramming which leads to more non-template code. GCC
> is extremely slow at instantiating templates, but this is not
> necessarily true for other compilers - I believe, for example, that
> Clang will be faster at instantiating templates than parsing raw code.
> (No benchmarks - but I know the code.)

Agreed 100%


Joel de Guzman

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