Can gcc select vector mode instruction patterns itself?

["Ling-hua Tseng" <uranus at it dot muds dot net>]

I'm porting gcc to a new VLIW architecture.
There are 11 function units in the chip, and 4 of them are DSPs.
Now I'm designing the SIMD instruction patterns, and I wouldn't like use the built-in functions to support it.

If I wrote some instruction patterns which involved many V4QI packing/unpacking/arithmetic operations,
could gcc try to select them automatically and smartly?
(Of course I never wrote any define_expand/define_split to generate any V4QI operations myself.)

For example:
1. my packing instruction patterns ('D' means DSP register):
   (define_insn "*packqi_from_mem"
       [(set (vec_select:QI (match_operand:V4QI 0 "register_operand" "D")
                                       (parallel [(match_operand:SI 2 "const_int_operand" "i")]))
               (match_operand:QI 1 "memory_operand" "m"))]
       ""
       "ldub.b%2\\t%0, %1"
   )

2. my V4QI + V4QI SIMD operation
   (define_insn "*SIMD_addqi3"
       [(set (match_operand:V4QI 0 "register_operand" "=D")
               (plus:V4QI (match_operand:V4QI 1 "register_operand" "%D")
                                  (match_operand:V4QI 2 "register_operand" "D")))]
       ""
       "add.ub\\t%0, %1, %2"
   )

Is it possible that gcc can try to load 4 QImode value to a register by the pattern "*packqi_from_mem"
and perform the V4QI + V4QI SIMD add by the pattern "*SIMD_addqi3" itself?