(** ** Location of function arguments *)

(** For the "hardfloat" configuration, we use the following calling conventions,
    adapted from the ARM EABI-HF:
- The first 4 integer arguments are passed in registers [R0] to [R3].
- The first 2 long integer arguments are passed in an aligned pair of
  two integer registers.
- The first 8 single- and double-precision float arguments are passed
  in registers [F0...F7]
- Extra arguments are passed on the stack, in [Outgoing] slots, consecutively
  assigned (1 word for an integer or single argument, 2 words for a float
  or a long), starting at word offset 0.

This convention is not quite that of the ARM EABI-HF, whereas single float
arguments are passed in 32-bit float registers.  Unfortunately,
this does not fit the data model of CompCert.  In [PrintAsm.ml]
we insert additional code around function calls that moves
data appropriately. *)

Definition int_param_regs :=
  R0 :: R1 :: R2 :: R3 :: nil.Definition float_param_regs :=
  F0 :: F1 :: F2 :: F3 :: F4 :: F5 :: F6 :: F7 :: nil.Definition ireg_param (n: Z) : mreg :=
  match list_nth_z int_param_regs n with Some r => r | None => R0 end.Definition freg_param (n: Z) : mreg :=
  match list_nth_z float_param_regs n with Some r => r | None => F0 end.Fixpoint loc_arguments_hf
     (tyl: list typ) (ir fr ofs: Z) {struct tyl} : list (rpair loc) :=
  match tyl with
  | nil => nil
  | (Tint | Tany32) as ty :: tys =>
      if zlt ir 4
      then One (R (ireg_param ir)) :: loc_arguments_hf tys (ir + 1) fr ofs
      else One (S Outgoing ofs ty) :: loc_arguments_hf tys ir fr (ofs + 1)
  | (Tfloat | Tany64) as ty :: tys =>
      if zlt fr 8
      then One (R (freg_param fr)) :: loc_arguments_hf tys ir (fr + 1) ofs
      else let ofs := align ofs 2 in
           One (S Outgoing ofs ty) :: loc_arguments_hf tys ir fr (ofs + 2)
  | Tsingle :: tys =>
      if zlt fr 8
      then One (R (freg_param fr)) :: loc_arguments_hf tys ir (fr + 1) ofs
      else One (S Outgoing ofs Tsingle) :: loc_arguments_hf tys ir fr (ofs + 1)
  | Tlong :: tys =>
      let ohi := if Archi.big_endian then 0 else 1 in
      let olo := if Archi.big_endian then 1 else 0 in
      let ir := align ir 2 in
      if zlt ir 4
      then Twolong (R (ireg_param (ir + ohi))) (R (ireg_param (ir + olo))) :: loc_arguments_hf tys (ir + 2) fr ofs
      else let ofs := align ofs 2 in
           Twolong (S Outgoing (ofs + ohi) Tint) (S Outgoing (ofs + olo) Tint) :: loc_arguments_hf tys ir fr (ofs + 2)
  end.(** For the "softfloat" configuration, as well as for variable-argument functions
  in the "hardfloat" configuration, we use the default ARM EABI (not HF)
  calling conventions:
- The first 4 integer arguments are passed in registers [R0] to [R3].
- The first 2 long integer arguments are passed in an aligned pair of
  two integer registers.
- The first 2 double-precision float arguments are passed in [F0] or [F2]
- The first 4 single-precision float arguments are passed in [F0...F3]
- Integer arguments and float arguments are kept in sync so that
  they can all be mapped back to [R0...R3] in [PrintAsm.ml].
- Extra arguments are passed on the stack, in [Outgoing] slots, consecutively
  assigned (1 word for an integer or single argument, 2 words for a float
  or a long), starting at word offset 0.

This convention is not quite that of the ARM EABI, whereas every float
argument are passed in one or two integer registers.  Unfortunately,
this does not fit the data model of CompCert.  In [PrintAsm.ml]
we insert additional code around function calls and returns that moves
data appropriately. *)

Fixpoint loc_arguments_sf
     (tyl: list typ) (ofs: Z) {struct tyl} : list (rpair loc) :=
  match tyl with
  | nil => nil
  | (Tint|Tany32) as ty :: tys =>
      One (if zlt ofs 0 then R (ireg_param (ofs + 4)) else S Outgoing ofs ty)
      :: loc_arguments_sf tys (ofs + 1)
  | (Tfloat|Tany64) as ty :: tys =>
      let ofs := align ofs 2 in
      One (if zlt ofs 0 then R (freg_param (ofs + 4)) else S Outgoing ofs ty)
      :: loc_arguments_sf tys (ofs + 2)
  | Tsingle :: tys =>
      One (if zlt ofs 0 then R (freg_param (ofs + 4)) else S Outgoing ofs Tsingle)
      :: loc_arguments_sf tys (ofs + 1)
  | Tlong :: tys =>
      let ohi := if Archi.big_endian then 0 else 1 in
      let olo := if Archi.big_endian then 1 else 0 in
      let ofs := align ofs 2 in
      Twolong (if zlt ofs 0 then R (ireg_param (ofs+ohi+4)) else S Outgoing (ofs+ohi) Tint)
              (if zlt ofs 0 then R (ireg_param (ofs+olo+4)) else S Outgoing (ofs+olo) Tint)
      :: loc_arguments_sf tys (ofs + 2)
  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) :=
  match Archi.abi with
  | Archi.Softfloat =>
      loc_arguments_sf s.(sig_args) (-4)
  | Archi.Hardfloat =>
      if s.(sig_cc).(cc_vararg)
      then loc_arguments_sf s.(sig_args) (-4)
      else loc_arguments_hf s.(sig_args) 0 0 0
  end.(** [size_arguments s] returns the number of [Outgoing] slots used
  to call a function with signature [s]. *)

Fixpoint size_arguments_hf (tyl: list typ) (ir fr ofs: Z) {struct tyl} : Z :=
  match tyl with
  | nil => ofs
  | (Tint|Tany32) :: tys =>
      if zlt ir 4
      then size_arguments_hf tys (ir + 1) fr ofs
      else size_arguments_hf tys ir fr (ofs + 1)
  | (Tfloat|Tany64) :: tys =>
      if zlt fr 8
      then size_arguments_hf tys ir (fr + 1) ofs
      else size_arguments_hf tys ir fr (align ofs 2 + 2)
  | Tsingle :: tys =>
      if zlt fr 8
      then size_arguments_hf tys ir (fr + 1) ofs
      else size_arguments_hf tys ir fr (ofs + 1)
  | Tlong :: tys =>
      let ir := align ir 2 in
      if zlt ir 4
      then size_arguments_hf tys (ir + 2) fr ofs
      else size_arguments_hf tys ir fr (align ofs 2 + 2)
  end.Fixpoint size_arguments_sf (tyl: list typ) (ofs: Z) {struct tyl} : Z :=
  match tyl with
  | nil => Z.max 0 ofs
  | (Tint | Tsingle | Tany32) :: tys => size_arguments_sf tys (ofs + 1)
  | (Tfloat | Tlong | Tany64) :: tys => size_arguments_sf tys (align ofs 2 + 2)
  end.Definition size_arguments (s: signature) : Z :=
  match Archi.abi with
  | Archi.Softfloat =>
      size_arguments_sf s.(sig_args) (-4)
  | Archi.Hardfloat =>
      if s.(sig_cc).(cc_vararg)
      then size_arguments_sf s.(sig_args) (-4)
      else size_arguments_hf s.(sig_args) 0 0 0
  end.Definition loc_argument_charact (ofs: Z) (l: loc) : Prop :=
  match l with
  | R r => is_callee_save r = false
  | S Outgoing ofs' ty => ofs' >= ofs /\ typealign ty = 1
  | _ => False
  end.Remark ireg_param_caller_save: forall n, is_callee_save (ireg_param n) = false.Remark freg_param_caller_save: forall n, is_callee_save (freg_param n) = false.Remark loc_arguments_hf_charact:
  forall tyl ir fr ofs p,
  In p (loc_arguments_hf tyl ir fr ofs) -> forall_rpair (loc_argument_charact ofs) p.Remark loc_arguments_sf_charact:
  forall tyl ofs p,
  In p (loc_arguments_sf tyl ofs) -> forall_rpair (loc_argument_charact (Z.max 0 ofs)) p.

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