Patch: #3 rs6000 specific (actually Darwin specific)

[David Edelsohn]

	Why does operand 1 use a register_operand predicate and not a
gpc_reg_operand predicate for constraint "b" in patterns like the
following?

(define_insn "movsi_low"
  [(set (match_operand:SI 0 "gpc_reg_operand" "=r")
        (mem:SI (lo_sum:SI (match_operand:SI 1 "register_operand" "b")
                           (match_operand 2 "" ""))))]
  "TARGET_MACHO && ! TARGET_64BIT"
  "{l|lwz} %0,lo16(%2)(%1)"
  [(set_attr "type" "load")
   (set_attr "length" "4")])


David