Here is an example from the MIPS port. It defines the following modes and attributes (among others):
(define_mode_iterator GPR [SI (DI "TARGET_64BIT")]) (define_mode_attr d [(SI "") (DI "d")])
and uses the following template to define both subsi3
and subdi3:
(define_insn "sub<mode>3"
[(set (match_operand:GPR 0 "register_operand" "=d")
(minus:GPR (match_operand:GPR 1 "register_operand" "d")
(match_operand:GPR 2 "register_operand" "d")))]
""
"<d>subu\t%0,%1,%2"
[(set_attr "type" "arith")
(set_attr "mode" "<MODE>")])
This is exactly equivalent to:
(define_insn "subsi3"
[(set (match_operand:SI 0 "register_operand" "=d")
(minus:SI (match_operand:SI 1 "register_operand" "d")
(match_operand:SI 2 "register_operand" "d")))]
""
"subu\t%0,%1,%2"
[(set_attr "type" "arith")
(set_attr "mode" "SI")])
(define_insn "subdi3"
[(set (match_operand:DI 0 "register_operand" "=d")
(minus:DI (match_operand:DI 1 "register_operand" "d")
(match_operand:DI 2 "register_operand" "d")))]
""
"dsubu\t%0,%1,%2"
[(set_attr "type" "arith")
(set_attr "mode" "DI")])