http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51494
--- Comment #3 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-05-03 23:04:35 UTC --- A slightly improved patch is available here: http://gcc.gnu.org/ml/gcc-patches/2012-02/msg00429.html but see the comments. I'm not sure I will be able soon enough to address the non-trivial comments and post a new version.
