(** * Callee-save locations *)

(** We classify locations as either
- callee-save, i.e. preserved across function calls:
  callee-save registers, [Local] and [Incoming] stack slots;
- caller-save, i.e. possibly modified by a function call:
  non-callee-save registers, [Outgoing] stack slots.

Concerning [Outgoing] stack slots: several ABIs allow a function to modify
the stack slots used for passing parameters to this function.
The code currently generated by CompCert never does so, but the code
generated by other compilers often does so (e.g. GCC for x86-32).
Hence, CompCert-generated code must not assume that [Outgoing] stack slots
are preserved across function calls, because they might not be preserved
if the called function was compiled by another compiler. 
*)

Definition callee_save_loc (l: loc) :=
  match l with
  | R r => is_callee_save r = true
  | S sl ofs ty => sl <> Outgoing
  end.Definition agree_callee_save (ls1 ls2: Locmap.t) : Prop :=
  forall l, callee_save_loc l -> ls1 l = ls2 l.

Lemma locmap_get_set_loc_result: forall sg v rs l, match l with R r => is_callee_save r = true | S _ _ _ => True end -> Locmap.setpair (loc_result sg) v rs l = rs l.