package goblint-cil
A front-end for the C programming language that facilitates program analysis and transformation
Install
Dune Dependency
Authors
Maintainers
Sources
goblint-cil-2.0.6.tbz
sha256=5577007bfac63c3f0609abdb74119fe674c9bc8529d790e90ef73a85964aa07a
sha512=f1a393fa92614ceaf857bec4df474d3e152c578d0ab5fdf791e9129668861ccaa37efae2f18aa539965d6c2ed4dabb47b4a5262aab55112e181935def06f18da
doc/src/goblint-cil.zrapp/deadcodeelim.ml.html
Source file deadcodeelim.ml
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(* 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
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