(* *********************************************************************)
(*                                                                     *)
(*              The Compcert verified compiler                         *)
(*                                                                     *)
(*          Xavier Leroy, INRIA Paris-Rocquencourt                     *)
(*           Prashanth Mundkur, SRI International                      *)
(*                                                                     *)
(*  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.     *)
(*                                                                     *)
(*  The contributions by Prashanth Mundkur are reused and adapted      *)
(*  under the terms of a Contributor License Agreement between         *)
(*  SRI International and INRIA.                                       *)
(*                                                                     *)
(* *********************************************************************)
(** Function calling conventions and other conventions regarding the use of machine registers and stack slots. *)
(** * 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 RISC-V application binary interface (ABI) in our choice of callee- and caller-save registers. *)
Definition is_callee_save (r: mreg) : bool :=
match r with
| R5 | R6 | R7 => false
| R8 | R9 => true
| R10 | R11 | R12 | R13 | R14 | R15 | R16 | R17 => false
| R18 | R19 | R20 | R21 | R22 | R23 | R24 | R25 | R26 | R27 => true
| R28 | R29 | R30 => false
| F0 | F1 | F2 | F3 | F4 | F5 | F6 | F7 => false
| F8 | F9 => true
| F10 | F11 | F12 | F13 | F14 | F15 | F16 | F17 => false
| F18 | F19 | F20 | F21 | F22 | F23 | F24 | F25 | F26 | F27 => true
| F28 | F29 | F30 | F31 => false
end.
Definition int_caller_save_regs :=
R5  :: R6  :: R7 ::
R10 :: R11 :: R12 :: R13 :: R14 :: R15 :: R16 :: R17 ::
R28 :: R29 :: R30 ::
nil.
Definition float_caller_save_regs :=
F0  :: F1  :: F2  :: F3  :: F4  :: F5  :: F6  :: F7  ::
F10 :: F11 :: F12 :: F13 :: F14 :: F15 :: F16 :: F17 ::
F28 :: F29 :: F30 :: F31 ::
nil.
Definition int_callee_save_regs :=
R8  :: R9  ::
R18 :: R19 :: R20 :: R21 :: R22 :: R23 :: R24 :: R25 :: R26 :: R27 ::
nil.
Definition float_callee_save_regs :=
F8  :: F9  ::
F18 :: F19 :: F20 :: F21 :: F22 :: F23 :: F24 :: F25 :: F26 :: F27 ::
nil.
Definition destroyed_at_call :=
List.filter (fun r => negb (is_callee_save r)) all_mregs.
Definition dummy_int_reg   := R6.    (**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) :=
match r with
| R5  | R6  | R7  | R8  | R9  | R10 | R11
| R12 | R13 | R14 | R15 | R16 | R17 | R18 | R19
| R20 | R21 | R22 | R23 | R24 | R25 | R26 | R27
| R28 | R29 | R30 => 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.  To ensure binary interoperability of code generated by our compiler with libraries compiled by another compiler, we implement the standard RISC-V conventions as found here: https://github.com/riscv/riscv-elf-psabi-doc/blob/master/riscv-elf.md *)
(** ** Location of function result *)
(** The result value of a function is passed back to the caller in registers [R10] or [F10] or [R10,R11], 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 | Tany32 => One R10
| Tfloat | Tsingle | Tany64 => One F10
| Tlong => if Archi.ptr64 then One R10 else Twolong R11 R10
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. *)

Lemma loc_result_pair:
forall sg,
match loc_result sg with
| One _ => True
| Twolong r1 r2 =>
r1 <> r2 /\ proj_sig_res sg = Tlong
/\ subtype Tint (mreg_type r1) = true /\ subtype Tint (mreg_type r2) = true
/\ Archi.ptr64 = false
end.