http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60847
--- Comment #1 from Sanjay Patel <spatel at rotateright dot com> --- It looks like an extra leading underscore is required to recognize the BMI intrinsics. This is not happening with other (BMI2, SSE4) intrinsics. According to the Intel reference docs and previous versions of gcc, a single underscore is the correct usage.
