Re: Small grammar, long compilation time

On 10/26/2017 09:03 AM, Søren Enevoldsen wrote:
> The following program takes about 10s to compile. However, the rule 
> currently used in parenProcess, 'nullProcess' should actually be 
> 'process'. However, when I make the change, compilation does not finish. 
> Instead CPU keeps spinning hot, and memory usage gradually increases. 
> Since it is a rather small grammar, I am guessing I am doing something 
> wrong. How do I make the grammar work then I correct it by changing 
> parenProcess to '(' > process > ')' ?  (Note I cannot reduce the number 
> of rules between process and parenProcess for a smaller example, since 
> then the compile time immediately decreases).
> 
> - Søren
> 
> ====================================================================
> 
> #include <boost/config/warning_disable.hpp>
> #include <boost/spirit/home/x3.hpp>
> #include <boost/spirit/home/x3/support/ast/variant.hpp>
> #include <boost/spirit/include/qi_char_class.hpp>
> #include <boost/fusion/include/adapt_struct.hpp>
[snip]
> x3::rule<struct processRule, AstAnyProcess> process{"process"};
> 
> ///  Here be compile time dragons.
> auto const parenProcess = '(' > nullProcess > ')';
> 
> auto const primitive = rule<AstAnyProcess>("primitive")
>      = parenProcess
>      | nullProcess
>      | constant;
[snip]
With this "convenience" change:

#define USE_PROCESS_IN_PAREN
auto const parenProcess
   = '('
#ifdef USE_PROCESS_IN_PAREN
   ///  Here be compile time dragons.
   > process
#else
   > nullProcess
#endif
   > ')'
   ;

and when compiled, it did take more than 10s (way more)
and I did see my memory use go up and 100% of some of
my cpu's.  However, when the get_rhs branch of a spirit
fork here:

https://github.com/cppljevans/spirit/tree/get_rhs

was -I included in front of the standard boost,
it compiled in a flash.

This problem has been reported before; however, I've
been advised that it needs more documentation before
submitting it as a pull request.  I'm working slowly
on that.

HTH.

-regards,
Larry



------------------------------------------------------------------------------
Check out the vibrant tech community on one of the world's most
engaging tech sites, Slashdot.org! http://sdm.link/slashdot
_______________________________________________
Spirit-general mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/spirit-general