(** * 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 s.(sig_res) with
  | None => One R3
  | Some (Tint | Tany32) => One R3
  | Some (Tfloat | Tsingle | Tany64) => One F1
  | Some Tlong => Twolong R3 R4
  end.Definition loc_result_64 (s: signature) : rpair mreg :=
  match s.(sig_res) with
  | None => One R3
  | Some (Tint | Tlong | Tany32 | Tany64) => One R3
  | Some (Tfloat | Tsingle) => One F1
  end.Definition loc_result :=
  if Archi.ptr64 then loc_result_64 else loc_result_32.

Lemma loc_result_caller_save: forall (s: signature), forall_rpair (fun r => is_callee_save r = false) (loc_result s).