Suppose we have the following code to call a function foo:

$```$

movi r$12,4$

movi r$18,6$

movi r$20,0$x$5555$

call foo

add r$22,$ r$12,$ r$18$

xor r$22,$ r$22,$ r$20$

$```$

Which registers will we have to save before the call foo instruction?

aa

b$.18$

$.22$

d$.12$

e$20$