GCC compiler porting to new architecture : Call external library function

I'm porting GCC compiler to a new processor architecture. It is similer to v850 architecture ("/gcc/config/v850") and almost done. But I have a problem in multiplication arithmetic operation. Architecture supports only unsigned multiplication. In signed case, I have to use "__mulsi3" library function from lib1funcs.asm. So I need to call library function when it is signed. Implemented "mulsi3" instruction as follows. Does anybody know how can call any library functions from {target}.md file or {target}.c file? help me...

I followed "sh" architecture ("/gcc/config/sh") and implemented like sh architecture. GCC build ok. but when I compile test code on target, there is a bug message. (file => emit-rtl.c:862)

---

mulsi3 instruction

    (define_insn "mulsi3"
        [(set (match_operand:SI 0 "register_operand" "=r,r")
            (mult:SI (match_operand:SI 1 "nonmemory_operand" "r,r")
                (match_operand:SI 2 "nonmemory_operand" "r,i")))]
        ""
        "*
        {
        /* REG */
        if(GET_CODE (operands[2]) == REG)
        {
            return \"mul %0,%1,%2\";
        }
        /* IMMEDIATE */
        else
        {
            /* unsigned case */
            if(CONST_OK_FOR_M(INTVAL(operands[2])))
            {
                return \"muli %0,%1,%2\";
            }
            /* signed case */
            else
            {
                /******************************************/
                /* need to call __mulsi3 library function */
                /******************************************/
            }
        }
    }
    "
    [(set_attr "length" "6,6")
    (set_attr "cc" "none_0hit,none_0hit")
    (set_attr "type" "mult")])

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