(** Preservation of register agreement under various assignments. *)

Lemma agree_undef_regs2:
forall ms sp rl rs rs',
agree (Mach.undef_regs rl ms) sp rs ->
(forall r', data_preg r' = true -> preg_notin r' rl -> rs'#r' = rs#r') ->
agree (Mach.undef_regs rl ms) sp rs'.