[boost] Re: Spirit and slow compile (from gmane.comp.lib.boost.devel)

From: Vincent Finn (vincent_finn_at_[hidden])
Date: 2003-01-15 06:01:27

Joel de Guzman wrote:
> ----- Original Message ----- 
> From: <vincent_finn_at_[hidden]>
> 
> 
>>Hi,
>>
>>I was talking to you on the boost newsgroup about spirit being slow to compile
>>Here is a standalone section of code, it'll compile but you can't do anything with it
>>The compile takes about 15 mins on my machine 
>>(We are using spirit for a second file but that is smaller and only takes a minute or two)
>>
>>The Spec of my machine is P3 833, 512M RAM 
>>I'm using NT4 SP6a and VC6 SP4
>>
>>I split it into a lib and it works fine so the problem is less crucial than it was! 
> 
> []
> 
>>I have a feeling that the Grammar is just big so it's slow and there may not be
>>any getting around that but let me know if you see anything we are doing wrong
> 
> 
> []
> 
> Indeed! I counted 25 grammars. Wow I'm amazed, some grammars are
> quite elaborate, even :-)
> 
> After taking a peek at the grammars, I see one minor and one
> major code tweaks that should improve both the actual code size 
> and compile time speed.
> 
> minor: use chlit<> or strlit<> rather than rule<ScannerT> whenever possible.
> (e.g. m_CommaToken)
> 
> major: I see lots of code duplication. It would be best to factor out common 
> grammar definitions into base definition classes. Example:
> 
>     template<class ScannerT>
>     struct basic_definition
>     {
>         template<class GrammarT>
>         basic_definition(GrammarT const& self)
>         {
>             // common definitions
>         }
>     };
> 
> Then subclass your grammar definition from this. 
> 
>     struct my_grammar : public spirit::grammar<grammar>
>     {
>         template<class ScannerT>
>         struct definition : basic_definition<ScannerT>
>         {
>             typedef basic_definition<ScannerT> base_t;
>             definition(my_grammar const& self)
>             : base_t(self)
>             {
>             }    
>         };
>     };
> 
> It would help a lot to factor out the common grammars this way. You
> can even use multiple inheritance where necessary. 
> 
> I hope this helps. I took the liberty to re-post this to the list in the hope
> that this simple tip might be useful to others.
> 
> BTW, in the near future, productions such as:
> 
>     r = a | b | c | d | e...
> 
> where the alternatives have unambiguous prefixes, example:
> 
>     a = "LINEDESC:" >> ...
>     b = "PAINTDESC:" >> ...
> 
> can be optimized through Spirit style syntactic predicates. 
> 
> Ahh, finaly BTW,  you do not need to wrap str_p("...") inside
> a lexeme because strlits are implicit lexemes.
> 
> Regards,
> Joel de Guzman

I'll give it a go :-)

        Thanks, Vin