[Bug libstdc++/24704] New: __gnu_cxx::__exchange_and_add is out of line and called even for single threaded applications using std::string

["ahu at ds9a dot nl" <gcc-bugzilla at gcc dot gnu dot org>]

__gnu_cxx::__exchange_and_add shows up in profiles of the PowerDNS recursor,
which is single threaded. I'm somewhat amazed this is an out-of-line function
(there are 40 cycles to be gained by inlining it, and this function gets called
a lot), but I'm worried more about the 1000 cycle overhead even in a
single-threaded program!

I think it would be good to teach std::string to use a non-atomic
exchange_and_add  (or even just 'add') for non-REENTRANT applications, plus it
would be good to be able to inline the function, but I understand this is of
far smaller importance.

The code exhibiting prominent profiled use of __gnu_cxx::__exchange_and_add can
be found via the repository described on http://wiki.powerdn.somc.

Thanks!


-- 
           Summary: __gnu_cxx::__exchange_and_add is out of line and called
                    even for single threaded applications using std::string
           Product: gcc
           Version: 4.0.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: ahu at ds9a dot nl
 GCC build triplet: i486-linux-gnu
  GCC host triplet: i486-linux-gnu
GCC target triplet: i486-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24704