Definition if_preg (r: preg) : bool :=
match r with
| IR _ => true
| FR _ => true
| CR _ => false
| PC   => false
end.

(* Specifications: *)
Lemma data_if_preg: forall r, data_preg r = true -> if_preg r = true.
Lemma if_preg_not_PC: forall r, if_preg r = true -> r <> PC.
Hint Resolve data_if_preg if_preg_not_PC: asmgen.
Lemma nextinstr_nf_inv:
forall r rs, if_preg r = true -> (nextinstr_nf rs)#r = rs#r.
Lemma nextinstr_nf_inv1:
forall r rs, data_preg r = true -> (nextinstr_nf rs)#r = rs#r.