http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57994
--- Comment #2 from joseph at codesourcery dot com <joseph at codesourcery dot com> --- There are no errno issues - this is an exact zero result, not underflow. But I'm not confident that MPFR follows all the Annex F special cases for infinities and NaNs (and even less confident in MPC following Annex G), and in cases that are errors and should produce exceptions / errno (e.g. sin (Inf)) you do of course need to avoid folding.
