Re: Reminder: Review for Zach's parsing library starts on Feb 19th

From: Zach Laine (whatwasthataddress_at_[hidden])
Date: 2024-03-01 03:26:05

On Thu, Feb 29, 2024 at 9:21 PM Peter Dimov via Boost
<boost_at_[hidden]> wrote:
>
> > Zach Laine wrote:
> > > I'm shocked too.  That's really crazy.  Believe me, I'm not interested
> > > in merging something with orders of magnitude of perf overhead into
> > > Boost.  I will be getting to the bottom of this long before a merge could take
> > place.
> >
> > My profiler (VS2022) says that the top performance problem is the
> > construction of a stringstream here
> >
> > https://github.com/tzlaine/parser/blob/f99ae3b94ad0acef0cc92166d5108aa
> > de41da4ea/include/boost/parser/detail/printing.hpp#L624
> >
> > This constructs a std::locale, which is apparently very slow.
> >
> > When I fix it
> >
> > diff --git a/include/boost/parser/detail/printing.hpp
> > b/include/boost/parser/detail/printing.hpp
> > index 1e204796..6cbec059 100644
> > --- a/include/boost/parser/detail/printing.hpp
> > +++ b/include/boost/parser/detail/printing.hpp
> > @@ -621,11 +621,19 @@ namespace boost { namespace parser { namespace
> > detail {
> >          flags f,
> >          Attribute const & attr)
> >      {
> > -        std::stringstream oss;
> >          if (detail::do_trace(f))
> > +        {
> > +            std::stringstream oss;
> >              detail::print_parser(context, parser, oss);
> > -        return scoped_trace_t<Iter, Sentinel, Context, Attribute>(
> > -            first, last, context, f, attr, oss.str());
> > +
> > +            return scoped_trace_t<Iter, Sentinel, Context, Attribute>(
> > +                first, last, context, f, attr, oss.str());
> > +        }
> > +        else
> > +        {
> > +            return scoped_trace_t<Iter, Sentinel, Context, Attribute>(
> > +                first, last, context, f, attr, {});
> > +        }
> >      }
> >
> >      template<typename Context, typename Attribute>
>
> This change takes me from ~6130ms to ~520ms.
>
> > the top function becomes the constructor of scoped_trace_t. (It's probably
> > not getting inlined.)
> >
> > Looks like the tracing functionality costs a lot even when off.
>
> Commenting out the bodies of scoped_trace_t and ~scoped_trace_t takes
> me to ~360ms.
>
> The top two functions are now `skip`
>
> https://github.com/tzlaine/parser/blob/f99ae3b94ad0acef0cc92166d5108aade41da4ea/include/boost/parser/parser.hpp#L1420
>
> and `omit_parser::call`
>
> https://github.com/tzlaine/parser/blob/f99ae3b94ad0acef0cc92166d5108aade41da4ea/include/boost/parser/parser.hpp#L4139
>
> both with 5.5%.
>
> The `SkipParser` of `skip` is
>
> ` boost::parser::rule<json::ws,boost::parser::detail::nope,boost::parser::detail::nope,boost::parser::detail::nope>`.

Thanks!  Template parameter it is then.

Zach