http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60418
--- Comment #5 from H.J. Lu <hjl.tools at gmail dot com> --- Created attachment 32280 --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=32280&action=edit The assembly difference of good and bad executables Here is the assembly difference of good and bad executables due the removal of the single loop preheader.