(* *********************************************************************)
(*                                                                     *)
(*              The Compcert verified compiler                         *)
(*                                                                     *)
(*          Xavier Leroy, INRIA Paris-Rocquencourt                     *)
(*                                                                     *)
(*  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 the following groups: - 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 PowerPC/EABI application binary interface (ABI) in our choice of callee- and caller-save registers. *)
Definition is_callee_save (r: mreg): bool :=
match r with
| R3  | R4  | R5  | R6  | R7  | R8  | R9  | R10  | R11 | R12 => false
| R14 | R15 | R16 | R17 | R18 | R19 | R20 | R21 | R22 | R23 | R24
| R25 | R26 | R27 | R28 | R29 | R30 | R31 => true
| F0  | F1  | F2  | F3  | F4  | F5  | F6  | F7
| F8  | F9  | F10 | F11 | F12 | F13 => false
| F14 | F15 | F16 | F17 | F18 | F19 | F20 | F21 | F22 | F23
| F24 | F25 | F26 | F27 | F28 | F29 | F30 | F31 => true
end.
Definition destroyed_at_call :=
List.filter (fun r => negb (is_callee_save r)) all_mregs.
(** The following definitions are used by the register allocator. *)
(** When a PPC64 processor is used with the PPC32 ABI, the high 32 bits of integer callee-save registers may not be preserved.  So, declare all integer registers as having size 32 bits for the purpose of determining which variables can go in callee-save registers. *)
Definition callee_save_type (r: mreg): typ :=
match r with
| R3  | R4  | R5  | R6  | R7  | R8  | R9  | R10  | R11 | R12
| R14 | R15 | R16 | R17 | R18 | R19 | R20 | R21 | R22 | R23 | R24
| R25 | R26 | R27 | R28 | R29 | R30 | R31 => Tany32
| 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 => Tany64
end.
Definition is_float_reg (r: mreg): bool :=
match r with
| R3  | R4  | R5  | R6  | R7  | R8  | R9  | R10  | R11 | R12
| R14 | R15 | R16 | R17 | R18 | R19 | R20 | R21 | R22 | R23 | R24
| R25 | R26 | R27 | R28 | R29 | R30 | R31 => 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.
Definition int_caller_save_regs :=
R3 :: R4 :: R5 :: R6 :: R7 :: R8 :: R9 :: R10 :: R11 :: R12 :: nil.
Definition float_caller_save_regs :=
F0 :: F1 :: F2 :: F3 :: F4 :: F5 :: F6 :: F7 :: F8 :: F9 :: F10 :: F11 :: F12 :: F13 :: nil.
Definition int_callee_save_regs :=
R31 :: R30 :: R29 :: R28 :: R27 :: R26 :: R25 :: R24 :: R23 ::
R22 :: R21 :: R20 :: R19 :: R18 :: R17 :: R16 :: R15 :: R14 :: nil.
Definition float_callee_save_regs :=
F31 :: F30 :: F29 :: F28 :: F27 :: F26 :: F25 :: F24 :: F23 ::
F22 :: F21 :: F20 :: F19 :: F18 :: F17 :: F16 :: F15 :: F14 :: nil.
Definition dummy_int_reg := R3.     (**r Used in [Coloring]. *)
Definition dummy_float_reg := F0.   (**r Used in [Coloring]. *)
(** * 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.  To ensure binary interoperability of code generated by our compiler with libraries compiled by another PowerPC compiler, we implement the standard conventions defined in the PowerPC/EABI application binary interface. *)
(** ** Location of function result *)
(** The result value of a function is passed back to the caller in registers [R3] or [F1] or [R3, R4], depending on the type of the returned value. We treat a function without result as a function with one integer result. *)
Definition loc_result_32 (s: signature) : rpair mreg :=
match proj_sig_res s with
| Tint | Tany32 => One R3
| Tfloat | Tsingle | Tany64 => One F1
| Tlong => Twolong R3 R4
end.
Definition loc_result_64 (s: signature) : rpair mreg :=
match proj_sig_res s with
| Tint | Tlong | Tany32 | Tany64 => One R3
| Tfloat | Tsingle => One F1
end.
Definition loc_result :=
if Archi.ptr64 then loc_result_64 else loc_result_32.
(** 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 PowerPC EABI states the following convention for passing arguments to a function: - The first 8 integer arguments are passed in registers [R3] to [R10]. - The first 8 float arguments are passed in registers [F1] to [F8]. - The first 4 long integer arguments are passed in register pairs [R3,R4] ... [R9,R10]. - Extra arguments are passed on the stack, in [Outgoing] slots, consecutively assigned (1 word for an integer argument, 2 words for a float), starting at word offset 0. - No stack space is reserved for the arguments that are passed in registers. *)
Definition int_param_regs :=
R3 :: R4 :: R5 :: R6 :: R7 :: R8 :: R9 :: R10 :: nil.
Definition float_param_regs :=
F1 :: F2 :: F3 :: F4 :: F5 :: F6 :: F7 :: F8 :: nil.
Fixpoint loc_arguments_rec
(tyl: list typ) (ir fr ofs: Z) {struct tyl} : list (rpair loc) :=
match tyl with
| nil => nil
| (Tint | Tany32) 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 + 1)
| Some ireg =>
One (R ireg) :: loc_arguments_rec tys (ir + 1) fr ofs
end
| Tsingle as ty :: tys =>
match list_nth_z float_param_regs fr with
| None =>
let ty := if Archi.single_passed_as_single then Tsingle else Tany64 in
let ofs := align ofs (typesize ty) in
One (S Outgoing ofs ty) :: loc_arguments_rec tys ir fr (ofs + (typesize ty))
| Some freg =>
One (R freg) :: loc_arguments_rec tys ir (fr + 1) ofs
end
| (Tfloat | Tany64) as ty :: tys =>
match list_nth_z float_param_regs fr with
| None =>
let ofs := align ofs 2 in
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
| Tlong :: tys =>
let ir := align ir 2 in
match list_nth_z int_param_regs ir, list_nth_z int_param_regs (ir + 1) with
| Some r1, Some r2 =>
Twolong (R r1) (R r2) :: loc_arguments_rec tys (ir + 2) fr ofs
| _, _ =>
let ofs := align ofs 2 in
(if Archi.ptr64
then One (S Outgoing ofs Tlong)
else Twolong (S Outgoing ofs Tint) (S Outgoing (ofs + 1) Tint)) ::
loc_arguments_rec tys ir fr (ofs + 2)
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 /\ (typealign ty | ofs')
| _ => False
end.
Remark loc_arguments_rec_charact:
forall tyl ir fr ofs p,
In p (loc_arguments_rec tyl ir fr ofs) ->
forall_rpair (loc_argument_charact ofs) p.

Lemma loc_arguments_acceptable:
forall (s: signature) (p: rpair loc),
In p (loc_arguments s) -> forall_rpair loc_argument_acceptable p.