case "paddi":
		// There are several extended mnemonics.  Notably, "pla" is
		// the only valid mnemonic for paddi (R=1), In this case, RA must
		// always be 0.  Otherwise it is invalid.
		r := inst.Args[3].(Imm)
		ra := inst.Args[1].(Reg)
		str := opName
		if ra == R0 {
			name := []string{"pli", "pla"}
			str = fmt.Sprintf("%s %s,%s",
				name[r&1],
				gnuArg(&inst, 0, inst.Args[0], PC),

	                             add  r3,r31,r3

	MOVD $131073, R3             lis  r3, 2                 pli r3, 131073
	                             addi r3, 1

	MOVD $mypackage·foo(SB), R3  addis r2, r3, ...          pla r3, ...
	                             addi  r3, r3, ...
*/