(** * 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.  *)

(** ** 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 s.(sig_res) with
  | None => One R10
  | Some (Tint | Tany32) => One R10
  | Some (Tfloat | Tsingle | Tany64) => One F10
  | Some Tlong => if Archi.ptr64 then One R10 else Twolong R11 R10
  end.

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