How to split mulsi3 pattern

[Mohamed Shafi]

Hello all,

I am doing a port for a 32bit target in GCC 4.4.0. In my target 32bit
multiply instruction is carried out in two instructions.

Dn = Da x Db is executed as

Dn = (Da.L * Db.H + Da.H * Db.L) << 16
Dn = Dn + (Da.L * Db.L)

Currently the pattern that i have for this is as follows:

(define_insn "mulsi3"
 [(set (match_operand:SI 0 "register_operand"           "=&d")
       (mult:SI (match_operand:SI 1 "register_operand"  "%d")
               (match_operand:SI 2 "register_operand" "d")))]

I would like to split this pattern into two (either after of before
reload). Currently i am doing something like this:

(define_insn_and_split "mulsi3"
 [(set (match_operand:SI 0 "register_operand"           "=&d")
       (mult:SI (match_operand:SI 1 "register_operand"  "%d")
                (match_operand:SI 2 "register_operand" "d")))]
 ""
 "#"
 "reload_completed"
 [(set (match_dup 0)
       (ashift:SI
        (plus:SI (mult:HI (unspec:HI [(match_dup 2)] UNSPEC_REG_LOW)
                          (unspec:HI [(match_dup 1)] UNSPEC_REG_HIGH))
                 (mult:HI (unspec:HI [(match_dup 2)] UNSPEC_REG_HIGH)
                          (unspec:HI [(match_dup 1)] UNSPEC_REG_LOW)))
        (const_int 16)))
  (set (match_dup 0)
       (plus:SI (match_dup 0)
                (mult:HI (unspec:HI [(match_dup 2)] UNSPEC_REG_LOW)
                         (unspec:HI [(match_dup 1)] UNSPEC_REG_LOW))))]
  ""
)

But in few testcases this is creating problems. So i would like to
know better patterns to split mulsi3 pattern.
Can someone help me out.

Regards,
Shafi