path: root/backend/Linearizeaux.ml

(* *********************************************************************)
(*                                                                     *)
(*              The Compcert verified compiler                         *)
(*                                                                     *)
(*          Xavier Leroy, INRIA Paris-Rocquencourt                     *)
(*                                                                     *)
(*  Copyright Institut National de Recherche en Informatique et en     *)
(*  Automatique.  All rights reserved.  This file is distributed       *)
(*  under the terms of the INRIA Non-Commercial License Agreement.     *)
(*                                                                     *)
(* *********************************************************************)

open LTL
open Maps

let debug_flag = ref false

let debug fmt =
  if !debug_flag then Printf.eprintf fmt
  else Printf.ifprintf stderr fmt

(* Trivial enumeration, in decreasing order of PC *)

(***
let enumerate_aux f reach =
  positive_rec
    Coq_nil
    (fun pc nodes ->
      if PMap.get pc reach
      then Coq_cons (pc, nodes)
      else nodes)
    f.fn_nextpc
***)

(* More clever enumeration that flattens basic blocks *)

open Camlcoq

module IntSet = Set.Make(struct type t = int let compare = compare end)

(* Determine join points: reachable nodes that have > 1 predecessor *)

let join_points f =
  let reached = ref IntSet.empty in
  let reached_twice = ref IntSet.empty in
  let rec traverse pc =
    let npc = P.to_int pc in
    if IntSet.mem npc !reached then begin
      if not (IntSet.mem npc !reached_twice) then
        reached_twice := IntSet.add npc !reached_twice
    end else begin
      reached := IntSet.add npc !reached;
      match PTree.get pc f.fn_code with
      | None -> ()
      | Some b -> traverse_succs (successors_block b)
    end
  and traverse_succs = function
    | [] -> ()
    | [pc] -> traverse pc
    | pc :: l -> traverse pc; traverse_succs l
  in traverse f.fn_entrypoint; !reached_twice

(* Cut into reachable basic blocks, annotated with the min value of the PC *)

let basic_blocks f joins =
  let blocks = ref [] in
  let visited = ref IntSet.empty in
  (* start_block:
       pc is the function entry point
          or a join point
          or the successor of a conditional test *)
  let rec start_block pc =
    let npc = P.to_int pc in
    if not (IntSet.mem npc !visited) then begin
      visited := IntSet.add npc !visited;
      in_block [] max_int pc
    end
  (* in_block: add pc to block and check successors *)
  and in_block blk minpc pc =
    let npc = P.to_int pc in
    let blk = pc :: blk in
    let minpc = min npc minpc in
    match PTree.get pc f.fn_code with
    | None -> assert false
    | Some b ->
       let rec do_instr_list = function
       | [] -> assert false
       | Lbranch s :: _ -> next_in_block blk minpc s
       | Ltailcall (sig0, ros) :: _ -> end_block blk minpc
       | Lcond (cond, args, ifso, ifnot, _) :: _ ->
             end_block blk minpc; start_block ifso; start_block ifnot
       | Ljumptable(arg, tbl) :: _ ->
             end_block blk minpc; List.iter start_block tbl
       | Lreturn :: _ -> end_block blk minpc
       | instr :: b' -> do_instr_list b' in
       do_instr_list b
  (* next_in_block: check if join point and either extend block
     or start block *)
  and next_in_block blk minpc pc =
    let npc = P.to_int pc in
    if IntSet.mem npc joins
    then (end_block blk minpc; start_block pc)
    else in_block blk minpc pc
  (* end_block: record block that we just discovered *)
  and end_block blk minpc =
    blocks := (minpc, List.rev blk) :: !blocks
  in
    start_block f.fn_entrypoint; !blocks

(* Flatten basic blocks in decreasing order of minpc *)

let flatten_blocks blks =
  let cmp_minpc (mpc1, _) (mpc2, _) =
    if mpc1 = mpc2 then 0 else if mpc1 > mpc2 then -1 else 1
  in
    List.flatten (List.map snd (List.sort cmp_minpc blks))

(* Build the enumeration *)

let enumerate_aux_flat f reach =
  flatten_blocks (basic_blocks f (join_points f))

(**
 * Alternate enumeration based on traces as identified by Duplicate.v 
 *
 * This is a slight alteration to the above heuristic, ensuring that any
 * superblock will be contiguous in memory, while still following the original
 * heuristic
 *)

let super_blocks f joins =
  let blocks = ref [] in
  let visited = ref IntSet.empty in
  (* start_block:
       pc is the function entry point
          or a join point
          or the successor of a conditional test *)
  let rec start_block pc =
    let npc = P.to_int pc in
    if not (IntSet.mem npc !visited) then begin
      visited := IntSet.add npc !visited;
      in_block [] max_int pc
    end
  (* in_block: add pc to block and check successors *)
  and in_block blk minpc pc =
    let npc = P.to_int pc in
    let blk = pc :: blk in
    let minpc = min npc minpc in
    match PTree.get pc f.fn_code with
    | None -> assert false
    | Some b ->
       let rec do_instr_list = function
       | [] -> assert false
       | Lbranch s :: _ -> next_in_block blk minpc s
       | Ltailcall (sig0, ros) :: _ -> end_block blk minpc
       | Lcond (cond, args, ifso, ifnot, pred) :: _ -> begin
            match pred with
            | None -> (end_block blk minpc; start_block ifso; start_block ifnot)
            | Some true -> (next_in_block blk minpc ifso; start_block ifnot)
            | Some false -> (next_in_block blk minpc ifnot; start_block ifso)
          end
       | Ljumptable(arg, tbl) :: _ ->
             end_block blk minpc; List.iter start_block tbl
       | Lreturn :: _ -> end_block blk minpc
       | instr :: b' -> do_instr_list b' in
       do_instr_list b
  (* next_in_block: check if join point and either extend block
     or start block *)
  and next_in_block blk minpc pc =
    let npc = P.to_int pc in
    if IntSet.mem npc joins
    then (end_block blk minpc; start_block pc)
    else in_block blk minpc pc
  (* end_block: record block that we just discovered *)
  and end_block blk minpc =
    blocks := (minpc, List.rev blk) :: !blocks
  in
    start_block f.fn_entrypoint; !blocks

(* Build the enumeration *)

let enumerate_aux_sb f reach =
  flatten_blocks (super_blocks f (join_points f))

(**
 * Alternate enumeration based on traces as identified by Duplicate.v 
 *
 * This is a slight alteration to the above heuristic, ensuring that any
 * superblock will be contiguous in memory, while still following the original
 * heuristic
 *)

let get_some = function
| None -> failwith "Did not get some"
| Some thing -> thing

exception EmptyList

let rec last_element = function
  | [] -> raise EmptyList
  | e :: [] -> e
  | e' :: e :: l -> last_element (e::l)

let print_plist l =
  let rec f = function
  | [] -> ()
  | n :: l -> Printf.printf "%d, " (P.to_int n); f l
  in begin
    if !debug_flag then begin
      Printf.printf "[";
      f l;
      Printf.printf "]"
    end
  end

(* adapted from the above join_points function, but with PTree *)
let get_join_points code entry =
  let reached = ref (PTree.map (fun n i -> false) code) in
  let reached_twice = ref (PTree.map (fun n i -> false) code) in
  let rec traverse pc =
    if get_some @@ PTree.get pc !reached then begin
      if not (get_some @@ PTree.get pc !reached_twice) then
        reached_twice := PTree.set pc true !reached_twice
    end else begin
      reached := PTree.set pc true !reached;
      traverse_succs (successors_block @@ get_some @@ PTree.get pc code)
    end
  and traverse_succs = function
    | [] -> ()
    | [pc] -> traverse pc
    | pc :: l -> traverse pc; traverse_succs l
  in traverse entry; !reached_twice

let forward_sequences code entry =
  let visited = ref (PTree.map (fun n i -> false) code) in
  let join_points = get_join_points code entry in
  (* returns the list of traversed nodes, and a list of nodes to start traversing next *)
  let rec traverse_fallthrough code node =
    (* debug "Traversing %d..\n" (P.to_int node); *)
    if not (get_some @@ PTree.get node !visited) then begin
      visited := PTree.set node true !visited;
      match PTree.get node code with
      | None -> failwith "No such node"
      | Some bb ->
          let ln, rem = match (last_element bb) with
          | Lop _ | Lload _ | Lgetstack _ | Lsetstack _ | Lstore _ | Lcall _
          | Lbuiltin _ -> assert false
          | Ltailcall _ | Lreturn -> begin (* debug "STOP tailcall/return\n"; *) ([], []) end
          | Lbranch n ->
              if get_some @@ PTree.get n join_points then ([], [n])
              else let ln, rem = traverse_fallthrough code n in (ln, rem)
          | Lcond (_, _, ifso, ifnot, info) -> (match info with
            | None -> begin (* debug "STOP Lcond None\n"; *) ([], [ifso; ifnot]) end
            | Some false ->
                if get_some @@ PTree.get ifnot join_points then ([], [ifso; ifnot])
                else let ln, rem = traverse_fallthrough code ifnot in (ln, [ifso] @ rem)
            | Some true ->
                if get_some @@ PTree.get ifso join_points then ([], [ifso; ifnot])
                else let ln, rem = traverse_fallthrough code ifso in (ln, [ifnot] @ rem)
            )
          | Ljumptable(_, ln) -> begin (* debug "STOP Ljumptable\n"; *) ([], ln) end
          in ([node] @ ln, rem)
      end
    else ([], [])
  in let rec f code = function
  | [] -> []
  | node :: ln ->
      let fs, rem_from_node = traverse_fallthrough code node
      in [fs] @ ((f code rem_from_node) @ (f code ln))
  in (f code [entry])

type pos = BinNums.positive

module PP = struct
  type t = pos * pos
  let compare a b =
    let ax, ay = a in
    let bx, by = b in
    let dx = compare ax bx in
    if (dx == 0) then compare ay by
    else dx
end

module PPMap = Map.Make(PP)

type vstate = Unvisited | Processed | Visited

let ppmap_is_true pp ppmap = PPMap.mem pp ppmap && PPMap.find pp ppmap

module Int = struct
  type t = int
  let compare x y = compare x y
end

module ISet = Set.Make(Int)

let print_iset s = begin
  if !debug_flag then begin
    Printf.printf "{";
    ISet.iter (fun e -> Printf.printf "%d, " e) s;
    Printf.printf "}"
  end
end

let print_sequence s =
  if !debug_flag then begin
    Printf.printf "[";
    List.iter (fun n -> Printf.printf "%d, " (P.to_int n)) s;
    Printf.printf "]\n"
  end

let print_ssequence ofs =
  if !debug_flag then begin
    Printf.printf "[";
    List.iter (fun s -> print_sequence s) ofs;
    Printf.printf "]\n"
  end

let rec minpc_of l =
  match l with
  | [] -> None
  | e::l -> begin
        let e_score = P.to_int e in
        let mpc = minpc_of l in 
        match mpc with
        | None -> Some e_score
        | Some e_score' -> if e_score < e_score' then Some e_score else Some e_score'
      end

let order_sequences code entry fs =
  let fs_a = Array.of_list fs in
  let fs_evaluated = Array.map (fun e -> false) fs_a in
  let ordered_fs = ref [] in
  let evaluate s_id =
    begin
      assert (not fs_evaluated.(s_id));
      ordered_fs := fs_a.(s_id) :: !ordered_fs;
      fs_evaluated.(s_id) <- true
    end
  in let choose_best_of candidates =
    let current_best_id = ref None in
    let current_best_score = ref None in
    begin
      List.iter (fun id ->
        match !current_best_id with
        | None -> begin
            current_best_id := Some id;
            match fs_a.(id) with
            | [] -> current_best_score := None
            | n::l -> current_best_score := Some (P.to_int n)
          end
        | Some b -> begin
            match fs_a.(id) with
            | [] -> ()
            | n::l -> let nscore = P.to_int n in
              match !current_best_score with
              | None -> (current_best_id := Some id; current_best_score := Some nscore)
              | Some bs -> if nscore > bs then (current_best_id := Some id; current_best_score := Some nscore)
          end
      ) candidates;
      !current_best_id
    end
  in let select_next () =
    let candidates = ref [] in
    begin
      Array.iteri (fun i _ ->
        begin
          if (not fs_evaluated.(i)) then
            candidates := i :: !candidates
        end
      ) fs_a;
      if not (List.length !candidates > 0) then begin
        Array.iteri (fun i _ ->
          if (not fs_evaluated.(i)) then candidates := i :: !candidates
        ) fs_a;
      end;
      get_some (choose_best_of !candidates)
    end
  in begin
    debug "-------------------------------\n";
    debug "forward sequences identified: "; print_ssequence fs;
    while List.length !ordered_fs != List.length fs do
      let next_id = select_next () in
      evaluate next_id
    done;
    debug "forward sequences ordered: "; print_ssequence (List.rev (!ordered_fs));
    List.rev (!ordered_fs)
  end

let enumerate_aux_trace f reach =
  let code = f.fn_code in
  let entry = f.fn_entrypoint in
  let fs = forward_sequences code entry in
  let ofs = order_sequences code entry fs in
  List.flatten ofs

let enumerate_aux f reach =
  if !Clflags.option_ftracelinearize then enumerate_aux_trace f reach
  else enumerate_aux_flat f reach