[Bug libstdc++/59439] std::locale uses atomic instructions on construction

["ben.maurer at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59439

--- Comment #4 from Ben Maurer <ben.maurer at gmail dot com> ---
Also, here's where perf says time is being spent. While only 25% is shown as
being in the locale constructor/destructor, I suspect that the time spent in
other methods is actually related to the ping-ponging of cachelines caused by
the constructor -- all the time is being spent in memory access which should be
very hot in the CPU cache.

    16.77%  benchmark  libstdc++.so.6.0.18  [.] std::locale::locale()
    10.42%  benchmark  libstdc++.so.6.0.18  [.] std::locale::~locale()
     9.93%  benchmark  libstdc++.so.6.0.18  [.] bool
std::has_facet<std::num_put<char, std::ostreambuf_iterator<char,
std::char_traits<char> > > >(std::locale const&)
     9.84%  benchmark  libstdc++.so.6.0.18  [.] std::num_put<char,
std::ostreambuf_iterator<char, std::char_traits<char> > > const&
std::use_facet<std::num_put<char, std::ostreambuf_iterator<char,
std::char_traits<char> > > >(std::locale const&)
     9.26%  benchmark  libstdc++.so.6.0.18  [.] bool
std::has_facet<std::num_get<char, std::istreambuf_iterator<char,
std::char_traits<char> > > >(std::locale const&)
     9.10%  benchmark  libstdc++.so.6.0.18  [.] std::num_get<char,
std::istreambuf_iterator<char, std::char_traits<char> > > const&
std::use_facet<std::num_get<char, std::istreambuf_iterator<char,
std::char_traits<char> > > >(std::locale const&)
     8.78%  benchmark  libstdc++.so.6.0.18  [.] std::ctype<char> const&
std::use_facet<std::ctype<char> >(std::locale const&)
     6.14%  benchmark  libstdc++.so.6.0.18  [.]
std::locale::operator=(std::locale const&)
     3.71%  benchmark  libstdc++.so.6.0.18  [.]
std::__use_cache<std::__numpunct_cache<char> >::operator()(std::locale const&)
const
     3.66%  benchmark  libstdc++.so.6.0.18  [.] bool
std::has_facet<std::ctype<char> >(std::locale const&)
     3.42%  benchmark  libstdc++.so.6.0.18  [.] __dynamic_cast
     1.96%  benchmark  libstdc++.so.6.0.18  [.] std::locale::id::_M_id() const
     0.89%  benchmark  benchmark            [.] doIoStream()