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

From: Peter Dimov (pdimov_at_[hidden])
Date: 2024-03-01 02:44:49

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/f99ae3b94ad0acef0cc92166d5108aade41da4ea/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>

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.