[antlr-interest] Re: Perfomance question re bit iterator

lgcraymer lgc at mail1.jpl.nasa.gov
Tue Nov 16 15:00:27 PST 2004



--- In antlr-interest at yahoogroups.com, "ron_bennatan"
<ron_bennatan at g...> wrote:
> 
> 
> Hi,
> 
> We have fairly complex parsers with some (but not too much) 
> loookahead. We generate C++ code and we use codeGenBitsetThreshold=4.
> 
> We've been doing some performance testing and when running gprof we 
> see that around 40% of the time is in MismatchTokenException and 
> specifically in std::_Bit_iterator std::_copy. 
> 
> Can anyone shed some light as to what exactly MismatchTokenException 
> is, when it is raised (we think we know - but are not sure) and what 
> we can do to reduce the run time? Also, are there any tips as to how 
> to reduce the number of copies and anything else that can reduce the 
> number of these exceptions and copies.

It is raised in calls to Parser::match().  For this to happen without
being reported at the user level means that a syntactic predicate is
"failing".  Check your grammar and try to refactor it to remove
synpreds wherever possible.

--Loring

> Thanks.





 
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