http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47449
--- Comment #2 from H.J. Lu <hjl.tools at gmail dot com> 2011-01-24 23:16:57 UTC --- fwprop1 turns: (insn 2 4 3 2 (set (reg/v/f:DI 61 [ trans ]) (zero_extend:DI (reg:SI 5 di [ trans ]))) x.c:4 115 {*zero_extendsidi2_r ex64} (nil)) (note 3 2 6 2 NOTE_INSN_FUNCTION_BEG) (insn 6 3 7 2 (parallel [ (set (reg:SI 62 [ ret ]) (asm_operands:SI ("negl %0 ") ("=D") 0 [] [] [] x.c:9)) (clobber (reg:QI 18 fpsr)) (clobber (reg:QI 17 flags)) ]) x.c:6 -1 (nil)) into (insn 6 3 9 2 (parallel [ (set (reg:SI 62 [ ret ]) (asm_operands:SI ("negl %0 ") ("=D") 0 [] [] [] x.c:9)) (clobber (reg:QI 18 fpsr)) (clobber (reg:QI 17 flags)) ]) x.c:6 -1 (expr_list:REG_UNUSED (reg:QI 18 fpsr) (expr_list:REG_UNUSED (reg:QI 17 flags) (nil)))) IRA can't deal with it.