Source file deadcodeelim.ml

(* Eliminate assignment instructions whose results are not
   used *)
open GoblintCil
open Expcompare
open Liveness

module E = Errormsg
module RD = Reachingdefs
module UD = Usedef
module IH = Inthash
module S = Stats

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

let debug = RD.debug


let doTime = ref false

let time s f a =
  if !doTime then
    S.time s f a
  else f a

(* This function should be set by the client if it
   knows of functions returning a result that have
   no side effects. If the result is not used, then
   the call will be eliminated. *)
let callHasNoSideEffects : (instr -> bool) ref =
  ref (fun _ -> false)


(* the set of used definition ids *)
let usedDefsSet = ref IS.empty

(* a mapping d -> {u_1,...,u_n} where d is a
   definition id, and the u's are definition
   ids corresponding to definitions in which
   d was used *)
let defUseSetHash = IH.create 100

(* a mapping d -> {sid_1,...,sid_n} where d is
   a definition id and the sids are statement ids
   corresponding to non-Instr statements where d
   was used *)
let sidUseSetHash = IH.create 100

(* put used def ids into usedDefsSet *)
(* assumes reaching definitions have already been computed *)
class usedDefsCollectorClass = object(self)
    inherit RD.rdVisitorClass as super

  method add_defids iosh e u =
    UD.VS.iter (fun vi ->
      if IH.mem iosh vi.vid then
	let ios = IH.find iosh vi.vid in
	if !debug then ignore(E.log "DCE: IOS size for vname=%s at stmt=%d: %d\n"
				vi.vname sid (RD.IOS.cardinal ios));
	RD.IOS.iter (function
	    Some(i) ->
	      if !debug then ignore(E.log "DCE: def %d used: %a\n" i d_exp e);
	      usedDefsSet := IS.add i (!usedDefsSet)
	  | None -> ()) ios
      else if !debug then ignore(E.log "DCE: vid %d:%s not in stm:%d iosh at %a\n"
				   vi.vid vi.vname sid d_plainexp e)) u

  method! vexpr e =
    let u = UD.computeUseExp e in
    match self#get_cur_iosh() with
      Some(iosh) -> self#add_defids iosh e u; DoChildren
    | None ->
	if !debug then ignore(E.log "DCE: use but no rd data: %a\n" d_plainexp e);
	DoChildren

  method! vstmt s =
    ignore(super#vstmt s);
    match s.skind with
    | Instr _ -> DoChildren
    | _ -> begin
	let u,d = UD.computeUseDefStmtKind s.skind in
	match self#get_cur_iosh() with
	| Some iosh ->
	    UD.VS.iter (fun vi ->
	      if IH.mem iosh vi.vid then
		let ios = IH.find iosh vi.vid in
		RD.IOS.iter (function
		  | Some i -> begin (* add s.sid to set for i *)
		      try
			let set = IH.find sidUseSetHash i in
			IH.replace sidUseSetHash i (IS.add s.sid set)
		      with Not_found ->
			IH.add sidUseSetHash i (IS.singleton s.sid)
		  end
		  | None -> ()) ios) u;
	    DoChildren
	| None -> DoChildren
    end

  method! vinst i =
    let handle_inst iosh i = match i with
    | Asm(_,_,slvl,_,_,_) -> List.iter (fun (_,s,lv) ->
	match lv with (Var v, off) ->
	  if s.[0] = '+' then
	    self#add_defids iosh (Lval(Var v, off)) (UD.VS.singleton v)
	| _ -> ()) slvl
    | Call(_,ce,el,_,_) when not (!callHasNoSideEffects i) ->
	List.iter (fun e ->
	  let u = UD.computeUseExp e in
	  UD.VS.iter (fun vi ->
	    if IH.mem iosh vi.vid then
	      let ios = IH.find iosh vi.vid in
	      RD.IOS.iter (function
		| Some i -> begin (* add sid to set for i *)
		    try
		      let set = IH.find sidUseSetHash i in
		      IH.replace sidUseSetHash i (IS.add sid set)
		    with Not_found ->
		      IH.add sidUseSetHash i (IS.singleton sid)
		end
		| None -> ()) ios) u) (ce::el)
    | Set((Mem _,_) as lh, rhs,l,el) ->
	List.iter (fun e ->
	  let u = UD.computeUseExp e in
	  UD.VS.iter (fun vi ->
	    if IH.mem iosh vi.vid then
	      let ios = IH.find iosh vi.vid in
	      RD.IOS.iter (function
		| Some i -> begin (* add sid to set for i *)
		    try
		      let set = IH.find sidUseSetHash i in
		      IH.replace sidUseSetHash i (IS.add sid set)
		    with Not_found ->
		      IH.add sidUseSetHash i (IS.singleton sid)
		end
		| None -> ()) ios) u) ([Lval(lh);rhs])
    | _ -> ()
    in
    ignore(super#vinst i);
    match cur_rd_dat with
    | None -> begin
	if !debug then ignore(E.log "DCE: instr with no cur_rd_dat\n");
	(* handle_inst *)
	DoChildren
    end
    | Some(_,s,iosh) -> begin
	let u,d = UD.computeUseDefInstr i in
	(* add things in d to the U sets for things in u *)
	let rec loop n =
	  if n < 0 then () else begin
	    UD.VS.iter (fun vi ->
	      if IH.mem iosh vi.vid then
		let ios = IH.find iosh vi.vid in
		RD.IOS.iter (function
		  | Some i -> begin (* add n + s to set for i *)
		      try
			let set = IH.find defUseSetHash i in
			IH.replace defUseSetHash i (IS.add (n+s) set)
		      with Not_found ->
			IH.add defUseSetHash i (IS.singleton (n+s))
		  end
		  | None -> ()) ios
	      else ()) u;
	    loop (n-1)
	  end
	in
	loop (UD.VS.cardinal d - 1);
	handle_inst iosh i;
	DoChildren
    end

end

(***************************************************
   Also need to find reads from volatiles
   uses two functions I've put in ciltools which
   are basically what Zach wrote, except one is for
   types and one is for vars. Another difference is
   they filter out pointers to volatiles. This
   handles DMA
 ***************************************************)
class hasVolatile flag = object (self)
  inherit nopCilVisitor
  method! vlval l =
    let tp = typeOfLval l in
    if (Ciltools.is_volatile_tp tp) then flag := true;
    DoChildren
  method! vexpr e =
    DoChildren
end

let exp_has_volatile e =
  let flag = ref false in
  ignore (visitCilExpr (new hasVolatile flag) e);
  !flag

let el_has_volatile =
  List.fold_left (fun b e ->
    b || (exp_has_volatile e)) false
 (***************************************************)

(*
let rec compareExp (e1: exp) (e2: exp) : bool =
(*   log "CompareExp %a and %a.\n" d_plainexp e1 d_plainexp e2; *)
  e1 == e2 ||
  match e1, e2 with
  | Lval lv1, Lval lv2
  | StartOf lv1, StartOf lv2
  | AddrOf lv1, AddrOf lv2 -> compareLval lv1 lv2
  | BinOp(bop1, l1, r1, _), BinOp(bop2, l2, r2, _) ->
      bop1 = bop2 && compareExp l1 l2 && compareExp r1 r2
  | _ -> begin
      match getInteger (constFold true e1), getInteger (constFold true e2) with
        Some i1, Some i2 -> compare_cilint i1 i2 = 0
      | _ -> false
    end

and compareLval (lv1: lval) (lv2: lval) : bool =
  let rec compareOffset (off1: offset) (off2: offset) : bool =
    match off1, off2 with
    | Field (fld1, off1'), Field (fld2, off2') ->
        fld1 == fld2 && compareOffset off1' off2'
    | Index (e1, off1'), Index (e2, off2') ->
        compareExp e1 e2 && compareOffset off1' off2'
    | NoOffset, NoOffset -> true
    | _ -> false
  in
  lv1 == lv2 ||
  match lv1, lv2 with
  | (Var vi1, off1), (Var vi2, off2) ->
      vi1 == vi2 && compareOffset off1 off2
  | (Mem e1, off1), (Mem e2, off2) ->
      compareExp e1 e2 && compareOffset off1 off2
  | _ -> false

let rec stripNopCasts (e:exp): exp =
  match e with
    CastE(t, e') -> begin
      match unrollType (typeOf e'), unrollType t  with
        TPtr _, TPtr _ -> (* okay to strip *)
          stripNopCasts e'
      (* strip casts from pointers to unsigned int/long*)
      | (TPtr _ as t1), (TInt(ik,_) as t2)
          when bitsSizeOf t1 = bitsSizeOf t2
            && not (isSigned ik) ->
          stripNopCasts e'
      | (TInt _ as t1), (TInt _ as t2)
          when bitsSizeOf t1 = bitsSizeOf t2 -> (* Okay to strip.*)
          stripNopCasts e'
      |  _ -> e
    end
  | _ -> e

let compareExpStripCasts (e1: exp) (e2: exp) : bool =
  compareExp (stripNopCasts e1) (stripNopCasts e2)
*)

let removedCount = ref 0
(* Filter out instructions whose definition ids are not
   in usedDefsSet *)
class uselessInstrElim : cilVisitor = object(self)
  inherit nopCilVisitor

  method! vstmt stm =

    (* give a set of varinfos and an iosh and get
       the set of definition ids definining the vars *)
    let viSetToDefIdSet iosh vis =
      UD.VS.fold (fun vi s ->
	if IH.mem iosh vi.vid then
	  let ios = IH.find iosh vi.vid in
	  RD.IOS.fold (fun io s ->
	    match io with None -> s
	    | Some i -> IS.add i s) ios s
	else s) vis IS.empty
    in

    (* false when U(defid)\subeq instruses and SU(d) = empty *)
    let check_defid i instruses iosh defid =
      IS.mem defid (!usedDefsSet) &&
      try
	let defuses = IH.find defUseSetHash defid in
	(*let siduses = IH.find sidUseSetHash defid in*)
	if IH.mem sidUseSetHash defid then begin
	  if !debug then ignore(E.log "siduses not empty: %a\n" d_instr i);
	  true
	end else begin
	  (* true if there is something in defuses not in instruses or when
	     something from defuses is in instruses and is also used somewhere else *)
	  if UD.VS.exists (fun vi -> vi.vglob) instruses then true else
	  let instruses = viSetToDefIdSet iosh instruses in
	  IS.fold (fun i' b ->
	    if not(IS.mem i' instruses) then begin
	      if !debug then ignore(E.log "i not in instruses: %a\n" d_instr i);
	      true
	    end else
	      (* can only use the definition i' at the definition defid *)
	      let i'_uses = IH.find defUseSetHash i' in
	      IH.mem sidUseSetHash i' ||
	      if not(IS.equal i'_uses (IS.singleton defid)) then begin
		IS.iter (fun iu -> match RD.getSimpRhs iu with
		| Some(RD.RDExp e) ->
		    if !debug then ignore(E.log "i' had other than one use: %d: %a\n"
			     (IS.cardinal i'_uses) d_exp e)
		| Some(RD.RDCall i) ->
		    if !debug then ignore(E.log "i' had other than one use: %d: %a\n"
			     (IS.cardinal i'_uses) d_instr i)
		| None -> ()) i'_uses;
		true
	      end else b) defuses false
	end
      with Not_found -> true
    in

    let test (i,(_,s,iosh)) =
      match i with
      | Call(Some(Var vi,NoOffset),Lval(Var vf,NoOffset),el,l,eloc) ->
	  if not(!callHasNoSideEffects i) then begin
	    if !debug then ignore(E.log "found call w/ side effects: %a\n" d_instr i);
	    true
	  end else begin
	    if !debug then ignore(E.log "found call w/o side effects: %a\n" d_instr i);
	    (vi.vglob || (Ciltools.is_volatile_vi vi) || (el_has_volatile el) ||
	    let uses, defd = UD.computeUseDefInstr i in
	    let rec loop n =
	      n >= 0 &&
	      (check_defid i uses iosh (n+s) || loop (n-1))
	    in
	    loop (UD.VS.cardinal defd - 1) || (incr removedCount; false))
	  end
      |	Call _ -> true
      | Set(lh,e,_,_) when compareExpStripCasts (Lval lh) e -> false (* filter x = x *)
      | Set((Var vi,NoOffset),e,_,_) ->
	  vi.vglob || (Ciltools.is_volatile_vi vi) || (exp_has_volatile e) ||
	  let uses, defd = UD.computeUseDefInstr i in
	  let rec loop n =
	    n >= 0 &&
	    (check_defid i uses iosh (n+s) || loop (n-1))
	  in
	  loop (UD.VS.cardinal defd - 1) || (incr removedCount; false)
      | _ -> true
    in

    let filter il stmdat =
      let rd_dat_lst = RD.instrRDs il stm.sid stmdat false in
      let ildatlst = List.combine il rd_dat_lst in
      let ildatlst' = List.filter test ildatlst in
      let (newil,_) = List.split ildatlst' in
      newil
    in

    match RD.getRDs stm.sid with
      None -> DoChildren
    | Some(_,s,iosh) ->
	match stm.skind with
	  Instr il ->
	    stm.skind <- Instr(filter il ((),s,iosh));
	    SkipChildren
	| _ -> DoChildren

end

(* until fixed point is reached *)
let elim_dead_code_fp (fd : fundec) :  fundec =
  (* fundec -> fundec *)
  let rec loop fd =
    usedDefsSet := IS.empty;
    IH.clear defUseSetHash;
    IH.clear sidUseSetHash;
    removedCount := 0;
    time "reaching definitions" RD.computeRDs fd;
    ignore(time "ud-collector"
	     (visitCilFunction (new usedDefsCollectorClass :> cilVisitor)) fd);
    let fd' = time "useless-elim" (visitCilFunction (new uselessInstrElim)) fd in
    if !removedCount = 0 then fd' else loop fd'
  in
  loop fd

(* just once *)
let elim_dead_code (fd : fundec) :  fundec =
  (* fundec -> fundec *)
  usedDefsSet := IS.empty;
  IH.clear defUseSetHash;
  IH.clear sidUseSetHash;
  removedCount := 0;
  time "reaching definitions" RD.computeRDs fd;
  if !debug then ignore(E.log "DCE: collecting used definitions\n");
  ignore(time "ud-collector"
	   (visitCilFunction (new usedDefsCollectorClass :> cilVisitor)) fd);
  if !debug then ignore(E.log "DCE: eliminating useless instructions\n");
  let fd' = time "useless-elim" (visitCilFunction (new uselessInstrElim)) fd in
  fd'

class deadCodeElimClass : cilVisitor = object(self)
    inherit nopCilVisitor

  method! vfunc fd =
    let fd' = elim_dead_code(*_fp*) fd in
    ChangeTo(fd')

end

let dce f =
  if !debug then ignore(E.log "DCE: starting dead code elimination\n");
  visitCilFile (new deadCodeElimClass) f