Thank you for your help. Regarding your advice, I tried this implementation: ___________________________________________________ ;; movhi (define_expand "movhi" [(set (match_operand:HI 0 "nonimmediate_operand" "") (match_operand:HI 1 "general_operand" "") )] "" "" ) (define_insn "movhi1" [(set (match_operand:HI 0 "register_operand" "=r,r,m,r") (match_operand:HI 1 "general_operand" "r,m,r,i") )] "" "@ movew\t%1,%0 movew\t%1,%0 movew\t%1,%0 movew\t%1,%0" ) ____________________________________________________ But I get this error then: e.c:7: error: unrecognizable insn: (insn 7 6 8 3 e.c:4 (set (mem/c/i:HI (reg/f:HI 14) [0 i+0 S2 A16]) (const_int 3 [0x3])) -1 (nil)) I think GCC has to put immediate into memory. The arch can't do that directly. GCC should put the immediate in register and then register to memory. It succeded with old implementation (with a lot of define_insn). What should I change in the new implementation to get it right ? Another question, I wonder how to deal with access modes ? For example, to obtain such an ASM instruction movew r1,8(r2) should it come from a define_insn like movhi1 and then treated by print_operand ? Thank you. Regards. Florent