See http://gcc.gnu.org/ml/gcc-patches/2005-12/msg01815.html. New libgcc2.c code results in a couple of functions that are well over twice as slow.
-- Summary: libgcc2.c __floattisf code quality regression Product: gcc Version: 4.2.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: target AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: amodra at bigpond dot net dot au GCC target triplet: powerpc64-linux http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25668