(* *********************************************************************)
(*                                                                     *)
(*              The Compcert verified compiler                         *)
(*                                                                     *)
(*         Xavier Leroy, Collège de France and INRIA Paris             *)
(*                                                                     *)
(*  Copyright Institut National de Recherche en Informatique et en     *)
(*  Automatique.  All rights reserved.  This file is distributed       *)
(*  under the terms of the INRIA Non-Commercial License Agreement.     *)
(*                                                                     *)
(* *********************************************************************)
(** Function calling conventions and other conventions regarding the use of machine registers and stack slots. *)
Require Archi.
(** * Classification of machine registers *)
(** Machine registers (type [mreg] in module [Locations]) are divided in: - Callee-save registers, whose value is preserved across a function call. - Caller-save registers that can be modified during a function call.  We follow the Procedure Call Standard for the ARM 64-bit Architecture (AArch64) document: R19-R28 and F8-F15 are callee-save. *)
Definition is_callee_save (r: mreg): bool :=
match r with
| R0  | R1  | R2  | R3  | R4  | R5  | R6  | R7 => false
| R8  | R9  | R10 | R11 | R12 | R13 | R14 | R15 => false
| R17 => false
| R19 | R20 | R21 |  R22 | R23 => true
| R24 | R25 | R26 | R27 | R28 => true
| R29 => false
| F0  | F1  | F2  | F3  | F4  | F5  | F6  | F7 => false
| F8  | F9  | F10 | F11 | F12 | F13 | F14 | F15 => true
| F16 | F17 | F18 | F19 | F20 | F21 | F22 | F23 => false
| F24 | F25 | F26 | F27 | F28 | F29 | F30 | F31 => false
end.
Definition int_caller_save_regs :=
R0  :: R1  :: R2  :: R3  :: R4  :: R5  :: R6  :: R7
:: R8  :: R9  :: R10 :: R11 :: R12 :: R13 :: R14 :: R15
:: R17 :: R29 :: nil.
Definition float_caller_save_regs :=
F0  :: F1  :: F2  :: F3  :: F4  :: F5  :: F6  :: F7
:: F16 :: F17 :: F18 :: F19 :: F20 :: F21 :: F22 :: F23
:: F24 :: F25 :: F26 :: F27 :: F28 :: F29 :: F30 :: F31 :: nil.
Definition int_callee_save_regs :=
R19 :: R20 :: R21 ::  R22 :: R23
:: R24 :: R25 :: R26 :: R27 :: R28 :: nil.
Definition float_callee_save_regs :=
F8  :: F9  :: F10 :: F11 :: F12 :: F13 :: F14 :: F15 :: nil.
Definition destroyed_at_call :=
List.filter (fun r => negb (is_callee_save r)) all_mregs.
Definition dummy_int_reg := R0.     (**r Used in [Coloring]. *)
Definition dummy_float_reg := F0.   (**r Used in [Coloring]. *)
Definition callee_save_type := mreg_type.
Definition is_float_reg (r: mreg): bool :=
match r with
| R0  | R1  | R2  | R3  | R4  | R5  | R6  | R7
| R8  | R9  | R10 | R11 | R12 | R13 | R14 | R15
| R17 | R19 | R20 | R21 |  R22 | R23
| R24 | R25 | R26 | R27 | R28
| R29 => false
| F0  | F1  | F2  | F3  | F4  | F5  | F6  | F7
| F8  | F9  | F10 | F11 | F12 | F13 | F14 | F15
| F16 | F17 | F18 | F19 | F20 | F21 | F22 | F23
| F24 | F25 | F26 | F27 | F28 | F29 | F30 | F31 => true
end.
(** * Function calling conventions *)
(** The functions in this section determine the locations (machine registers and stack slots) used to communicate arguments and results between the caller and the callee during function calls.  These locations are functions of the signature of the function and of the call instruction. Agreement between the caller and the callee on the locations to use is guaranteed by our dynamic semantics for Cminor and RTL, which demand that the signature of the call instruction is identical to that of the called function.  Calling conventions are largely arbitrary: they must respect the properties proved in this section (such as no overlapping between the locations of function arguments), but this leaves much liberty in choosing actual locations.  *)
(** ** Location of function result *)
(** The result value of a function is passed back to the caller in registers [R0] or [F0], depending on the type of the returned value.  We treat a function without result as a function with one integer result. *)
Definition loc_result (s: signature) : rpair mreg :=
match proj_sig_res s with
| Tint | Tlong | Tany32 | Tany64 => One R0
| Tfloat | Tsingle => One F0
end.
(** The result registers have types compatible with that given in the signature. *)
(** The result locations are caller-save registers *)
(** If the result is in a pair of registers, those registers are distinct and have type [Tint] at least. *)
(** The location of the result depends only on the result part of the signature *)
(** ** Location of function arguments *)
(** - The first 8 integer arguments are passed in registers [R0...R7]. - The first 8 FP arguments are passed in registers [F0...F7]. - Extra arguments are passed on the stack, in [Outgoing] slots of size 64 bits (2 words), consecutively assigned, starting at word offset 0. **)
Definition int_param_regs :=
R0  :: R1  :: R2  :: R3  :: R4  :: R5  :: R6  :: R7 :: nil.
Definition float_param_regs :=
F0  :: F1  :: F2  :: F3  :: F4  :: F5  :: F6  :: F7 :: nil.
Fixpoint loc_arguments_rec
(tyl: list typ) (ir fr ofs: Z) {struct tyl} : list (rpair loc) :=
match tyl with
| nil => nil
| (Tint | Tlong | Tany32 | Tany64) as ty :: tys =>
match list_nth_z int_param_regs ir with
| None =>
One (S Outgoing ofs ty) :: loc_arguments_rec tys ir fr (ofs + 2)
| Some ireg =>
One (R ireg) :: loc_arguments_rec tys (ir + 1) fr ofs
end
| (Tfloat | Tsingle) as ty :: tys =>
match list_nth_z float_param_regs fr with
| None =>
One (S Outgoing ofs ty) :: loc_arguments_rec tys ir fr (ofs + 2)
| Some freg =>
One (R freg) :: loc_arguments_rec tys ir (fr + 1) ofs
end
end.
(** [loc_arguments s] returns the list of locations where to store arguments when calling a function with signature [s].  *)
Definition loc_arguments (s: signature) : list (rpair loc) :=
loc_arguments_rec s.(sig_args) 0 0 0.
(** Argument locations are either caller-save registers or [Outgoing] stack slots at nonnegative offsets. *)
Definition loc_argument_acceptable (l: loc) : Prop :=
match l with
| R r => is_callee_save r = false
| S Outgoing ofs ty => ofs >= 0 /\ (typealign ty | ofs)
| _ => False
end.
Definition loc_argument_charact (ofs: Z) (l: loc) : Prop :=
match l with
| R r => In r int_param_regs \/ In r float_param_regs
| S Outgoing ofs' ty => ofs' >= ofs /\ (2 | ofs')
| _ => False
end.
Remark loc_arguments_rec_charact:
forall tyl ir fr ofs p,
In p (loc_arguments_rec tyl ir fr ofs) -> (2 | ofs) -> forall_rpair (loc_argument_charact ofs) p.
Hint Resolve loc_arguments_acceptable: locs.

Lemma loc_arguments_main:
loc_arguments signature_main = nil.