http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60847
--- Comment #10 from Sanjay Patel <spatel at rotateright dot com> --- Ah - thank you for the explanation! I found the original checkin from AMD: http://gcc.gnu.org/ml/gcc-patches/2010-10/msg01356.html Strangely, I can't find any documentation for those double-underscores from AMD though.