gcc porting - machine description for realizing multiplication with a routine call

[Diego Bernini <diego dot bernini at gmail dot com>]

Hi to all,
I am porting GCC to a custom architecture.

The custom architecture has not a "mul" instruction. Hence I am
working to generate a proper routine call. The external routine ("
__mulqi3") expect to have the first parameter inside the reg #0, the
second parameter inside the reg #1 and then it puts the result inside
the reg #0.

Starting from the porting for AVR, I tried to add the following
machine description definitions:

define_expand "mulqi3"
  [(set (match_operand:QI 0 "register_operand" "")
(mult:QI (match_operand:QI 1 "register_operand" "")
 (match_operand:QI 2 "register_operand" "")))]
  ""
  "
      emit_insn (gen_mulqi3_call (operands[0], operands[1], operands[2]));
      DONE;
  ")

(define_expand "mulqi3_call"
  [(set (reg:QI 0) (match_operand:QI 1 "register_operand" ""))
   (set (reg:QI 1) (match_operand:QI 2 "register_operand" ""))
   (parallel [(set (reg:QI 0) (mult:QI (reg:QI 0) (reg:QI 1)))
      (clobber (reg:QI 1))
  ])
   (set (match_operand:QI 0 "register_operand" "") (reg:QI 0))]
  ""
  "")

(define_insn "*mulqi3_call"
  [(set (reg:QI 0) (mult:QI (reg:QI 0) (reg:QI 1)))
   (clobber (reg:QI 1))
   ]
  ""
  "call __mulqi3"
)

There is something wrong with these definitions, because trying to
compile a simple multiplication I obtain

error: insn does not satisfy its constraints:
(insn 51 25 26 (set (reg:QI 0 A0 [orig:51 a ] [51])
        (reg:QI 2 A2)) 5 {*move_regs} (nil)
    (nil))


Any advice?

Best,
Diego