heptagon/compiler/global/static.ml

(**************************************************************************)
(*                                                                        *)
(*  Heptagon                                                              *)
(*                                                                        *)
(*  Author : Marc Pouzet                                                  *)
(*  Organization : Demons, LRI, University of Paris-Sud, Orsay            *)
(*                                                                        *)
(**************************************************************************)

(** This module defines static expressions, used in params and for constants.

    const n: int = 3;
    var x : int^n; var y : int^(n + 2);
    x[n - 1], x[1 + 3],...
*)

open Names
open Format


(** Constraints on size expressions. *)
type size_constraint =
  | Cequal of static_exp * static_exp (* e1 = e2*)
  | Clequal of static_exp * static_exp (* e1 <= e2 *)
  | Cfalse

(* unsatisfiable constraint *)
exception Instanciation_failed

exception Not_static

(** Returns the op from an operator full name. *)
let op_from_app_name ln =
  match ln with
    | Modname { qual = "Pervasives" } -> ln
    | _ -> raise Not_static

(** Applies the operator [op] to the two integers [n1] and [n2]
    and returns the reslt as a static exp. *)
let apply_int_op op n1 n2 =
  match op with
    | Modname { qual = "Pervasives"; id = "+" } -> Sint (n1 + n2)
    | Modname { qual = "Pervasives"; id = "-" } -> Sint (n1 - n2)
    | Modname { qual = "Pervasives"; id = "*" } -> Sint (n1 * n2)
    | Modname { qual = "Pervasives"; id = "/" } ->
        let n = if n2 = 0 then raise Instanciation_failed else n1 / n2 in
          Sint n
    | _ -> (* unknown operator, reconstrcut the op *)
        Sop (op, Sint n1, Sint n2)

(** [simplify env e] returns e simplified with the
    variables values taken from env (mapping vars to integers).
    Variables are replaced with their values and every operator
    that can be computed is replaced with the value of the result. *)
let rec simplify env se =
  match se with
    | Sint _ | Sfloat _ | Sbool _ | Sconstructor -> se
    | Svar id -> (try simplify env (NamesEnv.find id env) with | _ -> Svar id)
    | Sop (op, [e1; e2]) ->
        (match simplify env e1, simplify env e2 with
           | Sint n1, Sint n2 -> apply_int_op op n1 n2
           | e1, e2 -> Sop (op, [e1; e2])
        )
    | Sop (op, se_list) -> Sop (op, List.map (simplify env) se_list)
    | Sarray se_list -> Sarray (List.map (simplify env) se_list)
    | Sarray_power (se, n) -> Sarray_power (simplify env se, simplify env n)
    | Stuple se_list -> Stuple (List.map (simplify env) se_list)

(** [int_of_static_exp env e] returns the value of the expression
    [e] in the environment [env], mapping vars to integers. Raises
    Instanciation_failed if it cannot be computed (if a var has no value).*)
let int_of_static_exp env e =
  match simplify env e with | Sint n -> n | _ -> raise Instanciation_failed

(** [is_true env constr] returns whether the constraint is satisfied
    in the environment (or None if this can be decided)
    and a simplified constraint. *)
let is_true env =
  function
    | Cequal e1, e2 when e1 = e2 ->
        Some true, Cequal (simplify env e1, simplify env e2)
    | Cequal (e1, e2) ->
        let e1 = simplify env e1 in
        let e2 = simplify env e2
        in
        (match e1, e2 with
           | SConst n1, SConst n2 -> Some (n1 = n2), Cequal (e1, e2)
           | (_, _) -> None, Cequal (e1, e2))
    | Clequal (e1, e2) ->
        let e1 = simplify env e1 in
        let e2 = simplify env e2
        in
        (match e1, e2 with
           | SConst n1, SConst n2 -> Some (n1 <= n2), Clequal (e1, e2)
           | _, _ -> None, Clequal (e1, e2))
    | Cfalse -> None, Cfalse

exception Solve_failed of size_constraint

(** [solve env constr_list solves a list of constraints. It
    removes equations that can be decided and simplify others.
    If one equation cannot be satisfied, it raises Solve_failed. ]*)
let rec solve const_env =
  function
    | [] -> []
    | c :: l ->
        let l = solve const_env l in
        let (res, c) = is_true const_env c
        in
        (match res with
           | None -> c :: l
           | Some v -> if not v then raise (Solve_failed c) else l)

(** Substitutes variables in the size exp with their value
    in the map (mapping vars to size exps). *)
let rec static_exp_subst m = function
  | Svar n -> (try List.assoc n m with | Not_found -> Svar n)
  | Sop (op, se_list) -> Sop (op, List.map (static_exp_subst m) se_list)
  | Sarray_power (se, n) -> Sarray_power (static_exp_subst m se,
                                          static_exp_subst m n)
  | Sarray se_list -> Sarray (List.map (static_exp_subst env) se_list)
  | Stuple se_list -> Stuple (List.map (static_exp_subst env) se_list)
  | s -> s

(** Substitutes variables in the constraint list with their value
    in the map (mapping vars to size exps). *)
let instanciate_constr m constr =
  let replace_one m = function
    | Cequal (e1, e2) -> Cequal (static_exp_subst m e1, static_exp_subst m e2)
    | Clequal (e1, e2) -> Clequal (static_exp_subst m e1, static_exp_subst m e2)
    | Cfalse -> Cfalse
  in List.map (replace_one m) constr

let rec print_static_exp ff = function
  | Sint i -> fprintf ff "%d" i
  | Sbool b -> fprintf ff "%b" b
  | Sfloat f -> fprintf ff "%f" f
  | Sconstructor ln -> print_longname ff ln
  | Svar id -> fprintf ff "%s" id
  | Sop (op, se_list) ->
      fprintf ff "@[<2>%a@,%a@]"
        print_longname op  print_static_exp_tuple se_list
  | Sarray_power (se, n) ->
      fprintf ff "%a^%a" print_static_exp se  print_static_exp n
  | Sarray se_list ->
      fprintf ff "@[<2>%a@]" (print_list_r print_static_exp "["";""]") se_list
  | Stuple se_list -> print_static_exp_tuple se_list

and print_static_exp_tuple ff l =
  fprintf ff "@[<2>%a@]" (print_list_r print_static_exp "("","")") l

let print_size_constraint ff = function
  | Cequal (e1, e2) ->
      fprintf ff "@[%a = %a@]" print_static_exp e1 print_static_exp e2
  | Clequal (e1, e2) ->
      fprintf ff "@[%a <= %a@]" print_static_exp e1 print_static_exp e2
  | Cfalse -> fprintf ff "Cfalse"

let psize_constraint oc c =
  let ff = formatter_of_out_channel oc
  in (print_size_constraint ff c; fprintf ff "@?")