http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50038
--- Comment #2 from tocarip.intel at gmail dot com 2011-09-27 10:15:15 UTC --- Created attachment 25369 --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=25369 Possible solution Here is an experimental patch which solves this problem. I modified implicit-zee pass to also eliminate useless zero-extensions from QImode to SImode. With this patch rgbyiqv test from EEMBC 2.0 benchmark showed 6% improvement. However after this patch implicit-zee may became useful for additional targets. For example it became beneficial to 32-bit x86 (+4% on rgbyiqv). Here is a Changelog: 2011-09-27 Ilya Tocar <ilya.to...@intel.com> * implicit-zee.c: Added 2011 to copyright. (combine_set_zero_extend): Add QImode. (merge_def_and_ze): Likewise. (add_removable_zero_extend): Likewise. (not_qi_to_si): New. (make_defs_and_copies_lists): Add check for QImode.