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(********************************************************************)
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(*                                                                  *)
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(*  The LustreC compiler toolset   /  The LustreC Development Team  *)
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(*  Copyright 2012 -    --   ONERA - CNRS - INPT                    *)
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(*                                                                  *)
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(*  LustreC is free software, distributed WITHOUT ANY WARRANTY      *)
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(*  under the terms of the GNU Lesser General Public License        *)
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(*  version 2.1.                                                    *)
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(*                                                                  *)
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(********************************************************************)
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open Utils
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open LustreSpec
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open Corelang
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open Graph
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open Causality
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type context =
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{
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  mutable evaluated : Disjunction.CISet.t;
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  dep_graph : IdentDepGraph.t;
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  disjoint : (ident, Disjunction.CISet.t) Hashtbl.t;
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  policy : (ident, var_decl) Hashtbl.t;
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}
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(* computes the in-degree for each local variable of node [n], according to dep graph [g].
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*)
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let compute_fanin n g =
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  let locals = ISet.diff (ExprDep.node_local_variables n) (ExprDep.node_memory_variables n) in
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  let fanin = Hashtbl.create 23 in
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  begin
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    IdentDepGraph.iter_vertex (fun v -> if ISet.mem v locals then Hashtbl.add fanin v (IdentDepGraph.in_degree g v)) g;
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    fanin
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  end
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let pp_fanin fmt fanin =
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  begin
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    Format.fprintf fmt "{ /* locals fanin: */@.";
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    Hashtbl.iter (fun s t -> Format.fprintf fmt "%s -> %d@." s t) fanin;
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    Format.fprintf fmt "}@."
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  end
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(* computes the cone of influence of a given [var] wrt a dependency graph [g].
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*)
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let cone_of_influence g var =
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 (*Format.printf "coi: %s@." var;*)
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 let frontier = ref (ISet.add var ISet.empty) in
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 let coi = ref ISet.empty in
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 while not (ISet.is_empty !frontier)
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 do
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   let head = ISet.min_elt !frontier in
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   (*Format.printf "head: %s@." head;*)
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   frontier := ISet.remove head !frontier;
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   if ExprDep.is_read_var head then coi := ISet.add (ExprDep.undo_read_var head) !coi;
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   List.iter (fun s -> frontier := ISet.add s !frontier) (IdentDepGraph.succ g head);
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 done;
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 !coi
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let compute_unused_variables n g =
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  let inputs = ExprDep.node_input_variables n in
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  let mems = ExprDep.node_memory_variables n in
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  let outputs = ExprDep.node_output_variables n in
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  ISet.fold
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    (fun var unused -> ISet.diff unused (cone_of_influence g var))
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    (ISet.union outputs mems)
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    (ISet.union inputs mems)
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(* computes the set of potentially reusable variables.
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   We don't reuse input variables, due to possible aliasing *)
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let node_reusable_variables node =
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  let mems = ExprDep.node_memory_variables node in
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  List.fold_left
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    (fun acc l ->
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      if ISet.mem l.var_id mems then acc else Disjunction.CISet.add l acc)
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    Disjunction.CISet.empty
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    node.node_locals
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let kill_root ctx head =
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  IdentDepGraph.iter_succ (IdentDepGraph.remove_edge ctx.dep_graph head.var_id) ctx.dep_graph head.var_id
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(* Recursively removes useless variables,
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   i.e. [ctx.evaluated] variables that are current roots of the dep graph [ctx.dep_graph]
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   - [evaluated] is the set of already evaluated variables,
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     wrt the scheduling
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   - does only remove edges, not variables themselves
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*)
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let remove_roots ctx =
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  let rem = ref true in
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  let remaining = ref ctx.evaluated in
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  while !rem
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  do
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    rem := false;
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    let all_roots = graph_roots ctx.dep_graph in
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    let frontier_roots = Disjunction.CISet.filter (fun v -> List.mem v.var_id all_roots) !remaining in
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    if not (Disjunction.CISet.is_empty frontier_roots) then
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      begin
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	rem := true;
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	Disjunction.CISet.iter (kill_root ctx) frontier_roots;
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	remaining := Disjunction.CISet.diff !remaining frontier_roots
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      end
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  done
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(* checks whether a variable is aliasable,
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   depending on its (address) type *)
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let is_aliasable var =
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 Types.is_address_type var.var_type
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(* checks whether a variable [v] is an input of the [var] equation, with an address type.
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   if so, [var] could not safely reuse/alias [v], should [v] be dead in the caller node,
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   because [v] may not be dead in the callee node when [var] is assigned *)
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let is_aliasable_input node var =
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  let eq_var = get_node_eq var node in
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  let inputs_var =
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    match NodeDep.get_callee eq_var.eq_rhs with
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    | None           -> []
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    | Some (_, args) -> List.fold_right (fun e r -> match e.expr_desc with Expr_ident id -> id::r | _ -> r) args [] in
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  fun v -> is_aliasable v && List.mem v.var_id inputs_var
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(* replace variable [v] by [v'] in graph [g].
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   [v'] is a dead variable
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*)
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let replace_in_dep_graph v v' g =
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  begin
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    IdentDepGraph.add_vertex g v';
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    IdentDepGraph.iter_succ (fun s -> IdentDepGraph.add_edge g v' s) g v;
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    IdentDepGraph.iter_pred (fun p -> IdentDepGraph.add_edge g p v') g v;
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    IdentDepGraph.remove_vertex g v
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  end
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let pp_reuse_policy fmt policy =
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  begin
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    Format.fprintf fmt "{ /* reuse policy */@.";
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    Hashtbl.iter (fun s t -> Format.fprintf fmt "%s -> %s@." s t.var_id) policy;
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    Format.fprintf fmt "}@."
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  end
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let pp_context fmt ctx =
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  begin
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    Format.fprintf fmt "{ /*BEGIN context */@.";
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    Format.fprintf fmt "eval=%a;@." Disjunction.pp_ciset ctx.evaluated;
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    Format.fprintf fmt "graph=%a;@." pp_dep_graph ctx.dep_graph;
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    Format.fprintf fmt "disjoint=%a;@." Disjunction.pp_disjoint_map ctx.disjoint;
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    Format.fprintf fmt "policy=%a;@." pp_reuse_policy ctx.policy;
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    Format.fprintf fmt "/* END context */ }@.";
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  end
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(* computes the reusable dependencies of variable [var] in graph [g],
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   once [var] has been evaluated
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   - [locals] is the set of potentially reusable variables
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   - [evaluated] is the set of evaluated variables
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   - [quasi] is the set of quasi-reusable variables
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   - [reusable] is the set of dead/reusable dependencies of [var] in graph [g]
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   - [policy] is the reuse map (which domain is [evaluated])
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*)
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let compute_dependencies heads ctx =
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  begin
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    (*Log.report ~level:6 (fun fmt -> Format.fprintf fmt "compute_reusable_dependencies %a %a %a@." Disjunction.pp_ciset locals Printers.pp_var_name var pp_context ctx);*)
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    List.iter (kill_root ctx) heads;
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    remove_roots ctx;
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  end
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let compute_evaluated heads ctx =
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  begin
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    List.iter (fun head -> ctx.evaluated <- Disjunction.CISet.add head ctx.evaluated) heads;
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  end
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let compute_reuse node ctx var =
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  let aliasable = is_aliasable_input node var.var_id in
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  let disjoint = Hashtbl.find ctx.disjoint var.var_id in
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  let eligible v =
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       Typing.eq_ground var.var_type v.var_type
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    && not (aliasable v) in
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  let locally_reusable v =
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    IdentDepGraph.fold_pred (fun p r -> r && Disjunction.CISet.exists (fun d -> p = d.var_id) disjoint) ctx.dep_graph v.var_id true in
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  let eligibles = Disjunction.CISet.filter eligible ctx.evaluated in
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  let dead, live = Disjunction.CISet.partition locally_reusable eligibles in
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  try
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    let disjoint_live = Disjunction.CISet.inter disjoint live in
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    let reuse = Disjunction.CISet.max_elt disjoint_live in
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    begin
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      IdentDepGraph.add_edge ctx.dep_graph var.var_id reuse.var_id;
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      Hashtbl.add ctx.policy var.var_id (Hashtbl.find ctx.policy reuse.var_id);
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    end
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  with Not_found ->
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  try
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    let reuse = Disjunction.CISet.choose dead in
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    begin
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      IdentDepGraph.add_edge ctx.dep_graph var.var_id reuse.var_id;
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      Hashtbl.add ctx.policy var.var_id (Hashtbl.find ctx.policy reuse.var_id);
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    end
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      with Not_found ->
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    begin
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      Hashtbl.add ctx.policy var.var_id var;
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    end
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let compute_reuse_policy node schedule disjoint g =
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  let sort = ref schedule in
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  let ctx = { evaluated = Disjunction.CISet.empty;
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	      dep_graph = g;
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	      disjoint  = disjoint;
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	      policy    = Hashtbl.create 23; } in
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  while !sort <> []
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  do
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    Log.report ~level:6 (fun fmt -> Format.fprintf fmt "new context:%a@." pp_context ctx);
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    let heads = List.map (fun v -> get_node_var v node) (List.hd !sort) in
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    Log.report ~level:6 (fun fmt -> Format.fprintf fmt "NEW HEADS:");
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    List.iter (fun head -> Log.report ~level:6 (fun fmt -> Format.fprintf fmt "%s " head.var_id)) heads;
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    Log.report ~level:6 (fun fmt -> Format.fprintf fmt "@.");
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    Log.report ~level:6 (fun fmt -> Format.fprintf fmt "COMPUTE_DEPENDENCIES@.");
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    compute_dependencies heads ctx;
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    Log.report ~level:6 (fun fmt -> Format.fprintf fmt "new context:%a@." pp_context ctx);
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    Log.report ~level:6 (fun fmt -> Format.fprintf fmt "COMPUTE_REUSE@.");
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    List.iter (compute_reuse node ctx) heads;
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    compute_evaluated heads ctx;
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    List.iter (fun head -> Log.report ~level:6 (fun fmt -> Format.fprintf fmt "reuse %s instead of %s@." (Hashtbl.find ctx.policy head.var_id).var_id head.var_id)) heads;
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    sort := List.tl !sort;
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  done;
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  IdentDepGraph.clear ctx.dep_graph;
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  ctx.policy
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(* Reuse policy:
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   - could reuse variables with the same type exactly only (simple).
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   - reusing variables with different types would involve:
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     - either dirty castings
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     - or complex inclusion expression (for instance: array <-> array cell, struct <-> struct field) to be able to reuse only some parts of structured data.
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     ... it seems too complex and potentially unsafe
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   - for node instance calls: output variables could NOT reuse aliasable input variables, 
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     even if inputs become dead, because the correctness would depend on the scheduling
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     of the callee (so, the compiling strategy could NOT be modular anymore).
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   - once a policy is set, we need to:
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     - replace each variable by its reuse alias.
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     - simplify resulting equations, as we may now have:
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        x = x;                     --> ;           for scalar vars
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       or:
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        x = &{ f1 = x->f1; f2 = t; } --> x->f2 = t;   for struct vars
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 *)
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(* the reuse policy seeks to use less local variables
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   by replacing local variables, applying the rules
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   in the following order:
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    1) use another clock disjoint still live variable,
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       with the greatest possible disjoint clock
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    2) reuse a dead variable
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   For the sake of safety, we replace variables by others:
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    - with the same type
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    - not aliasable (i.e. address type)
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*)
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(* Local Variables: *)
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(* compile-command:"make -C .." *)
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(* End: *)