(* copyright 1998 YALE FLINT PROJECT *)
(* monnier@cs.yale.edu *)
signature LOOPIFY =
sig
val loopify : FLINT.prog -> FLINT.prog
end
structure Loopify :> LOOPIFY =
struct
local
structure F = FLINT
structure O = Option
structure M = IntmapF
structure S = IntSetF
structure OU = OptUtils
structure LK = LtyKernel
structure CTRL = Control.FLINT
in
val say = Control.Print.say
fun bug msg = ErrorMsg.impossible ("Loopify: "^msg)
val cplv = LambdaVar.dupLvar
type al = F.value list list
datatype info = I of {tails : al ref, calls: al ref, icalls: al ref,
tcp: bool ref, parent: F.lvar}
exception NotFound
fun loopify (prog as (progkind,progname,progargs,progbody)) = let
val m : info Intmap.intmap = Intmap.new(128, NotFound)
(* tails: number of tail-recursive calls
* calls: number of other calls
* icalls: non-tail self-recursive subset of `calls'
* tcp: always called in tail-position
* parent: enclosing function *)
fun new (f,known,parent) =
let val i = I{tails=ref [], calls=ref [], icalls=ref [],
tcp=ref known, parent=parent}
in Intmap.add m (f,i); i end
fun get f = Intmap.map m f
(* collect tries to determine what calls are tail recursive.
* If a function f is always called in tail position in a function g,
* then all tail calls to g from f are indeed tail recursive. *)
(* tfs: we are currently in tail position relative to those functions
* p: englobing function *)
fun collect p tfs le = let
val loop = collect p tfs
in case le
of F.RET _ => ()
| F.LET(_,body,le) => (collect p S.empty body; loop le)
| F.FIX([({isrec=(NONE | SOME(_,F.LK_TAIL)),known,...},f,_,body)],le) =>
let val I{tcp,calls,icalls,...} = new(f, known, p)
val _ = loop le
val necalls = length(!calls)
in collect f (if !tcp then S.add(f,tfs) else S.singleton f) body;
icalls := List.take(!calls, length(!calls) - necalls)
end
| F.FIX(fdecs,le) =>
let (* create the new entries in the map *)
val fs = map (fn (fk as {known,...},f,_,body) =>
(fk, f, body, new(f, false, p)))
fdecs
fun cfun ({isrec,...}:F.fkind,f,body,I{calls,icalls,...}) =
let val necalls = length(!calls)
in collect f (S.singleton f) body;
icalls := List.take(!calls, length(!calls) - necalls)
end
in loop le;
app cfun fs
end
| F.APP(F.VAR f,vs) =>
(let val I{tails,calls,tcp,parent,...} = get f
in if S.member tfs f then tails := vs::(!tails)
else (calls := vs::(!calls);
if S.member tfs parent then () else tcp := false)
end handle NotFound => ())
| F.TFN((_,_,body),le) => (collect p S.empty body; loop le)
| F.TAPP _ => ()
| F.SWITCH(v,ac,arms,def) =>
let fun carm (_,body) = loop body
in app carm arms; case def of SOME le => loop le | _ => ()
end
| (F.CON(_,_,_,_,le) | F.RECORD(_,_,_,le) |
F.SELECT(_,_,_,le) | F.PRIMOP(_,_,_,le)) => loop le
| F.RAISE _ => ()
| F.HANDLE(le,v) => collect p S.empty le
| F.BRANCH(_,_,le1,le2) => (loop le1; loop le2)
| F.APP _ => bug "weird F.APP in collect"
end
(* (intended as a `foldr' argument).
* `filt' is the bool list indicating if the arg is kept
* `func' is the list of arguments for the FIX
* `call' is the list of arguments for the APP
* `free' is the list of resulting free variables *)
fun drop_invariant ((v,t),actuals,(filt,func,call,free)) =
if !CTRL.dropinvariant andalso List.all (fn a => F.VAR v = a) actuals then
(* drop the argument: the free list is unchanged *)
(false::filt, func, call, (v,t)::free)
else
(* keep the argument: create a new var (used in the call)
* which will replace the old in the free vars *)
let val nv = cplv v
in (true::filt, (v,t)::func, (F.VAR nv)::call, (nv,t)::free)
end
(* m: int intmap renaming for function calls
* tf:(int,int) list the current functions (if any) and their tail version
* le: you get the idea *)
fun lexp m tfs le = let
val loop = lexp m tfs
in case le
of F.RET _ => le
| F.LET(lvs,body,le) => F.LET(lvs, lexp m [] body, loop le)
| F.FIX(fdecs,le) =>
let fun cfun (fk:F.fkind as {isrec=SOME(ltys,F.LK_UNKNOWN),cconv,...},
f,args,body) =
let val I{tcp=ref tcp,icalls=ref icalls,tails=ref tails,...} =
get f
(* cpsopt uses the following condition:
* escape = 0 andalso !unroll_call > 0
* andalso (!call - !unroll_call > 1
* orelse List.exists (fn t=>t) inv)
* `escape = 0': I don't quite see the need for it, though it
* probably won't change much since etasplit should have
* made "everything" known already.
* `!call - !unroll_call > 1 orelse List.exists (fn t=>t) inv)':
* loopification is only useful if there is more than one
* external call or if there are loop invariants.
* Note that we deal with invariants elsewhere, so it's
* not a good reason to loopify here. *)
(*** rationale behind the restrictions: ***
* `icallnb = 0': loopification is pointless and will be
* undone by fcontract.
* `C.callnb fi <= icallnb + 1': if there's only one external
* call, loopification will probably (?) not be of much use
* and the same benefit would be had by just moving f *)
in if null icalls andalso null tails
then (fk, f, args, lexp m (if tcp then tfs else []) body)
else
let val cconv' =
case cconv
of (F.CC_FCT | F.CC_FUN(LK.FF_FIXED)) => cconv
| F.CC_FUN(LK.FF_VAR(f1,f2)) =>
F.CC_FUN(LK.FF_VAR(true,f2))
(* figure out what arguments of the tail loop
* are invariants and create the corresponding
* function args, call args, filter
* function for the actual calls, ... *)
val (tfs',atfun,atcall,args,ft) =
if null tails then (tfs,[],[],args,f) else let
val ft = cplv f
val actuals = OU.transpose tails
val (fcall,afun,acall,afree) =
ListPair.foldr drop_invariant
([],[],[],[])
(args, actuals)
in ((f,ft,fcall)::(if tcp then tfs else []),
afun, acall, afree, ft)
end
(* Do the same for the non-tail loop *)
val (nm,alfun,alcall,args,fl) =
if null icalls then (m,[],[],args,f) else let
val fl = cplv f
val actuals = OU.transpose icalls
val (fcall,afun,acall,afree) =
ListPair.foldr drop_invariant
([],[],[],[])
(args, actuals)
in (M.add(m, f, (fl, fcall)),
afun, acall, afree, fl)
end
(* make the new body *)
val nbody = lexp nm tfs' body
(* wrap into a tail loop if necessary *)
val nbody =
if null tails then nbody else
F.FIX([({isrec=SOME(ltys, F.LK_TAIL),
known=true, inline=F.IH_SAFE,
cconv=cconv'}, ft, atfun,
nbody)],
F.APP(F.VAR ft, atcall))
(* wrap into a non-tail loop if necessary *)
val nbody =
if null icalls then nbody else
F.FIX([({isrec=SOME(ltys, F.LK_LOOP),
known=true, inline=F.IH_SAFE,
cconv=cconv'}, fl, alfun,
nbody)],
F.APP(F.VAR fl, alcall))
in (fk, f, args, nbody)
end
end
| cfun (fk as {inline=F.IH_UNROLL,isrec=SOME _,...},f,args,body) =
let val I{tcp=ref tcp,...} = get f
in (fk, f, args, lexp m (if tcp then tfs else []) body)
end
| cfun (fk,f,args,body) =
let val I{tcp=ref tcp,...} = get f
in (fk, f, args, lexp m (if tcp then tfs else []) body)
end
in F.FIX(map cfun fdecs, loop le)
end
| F.APP(F.VAR f,vs) =>
(case List.find (fn (ft,ft',filt) => ft = f) tfs
of SOME(ft, ft', filt) => F.APP(F.VAR ft', OU.filter filt vs)
| NONE => let val (fl,filt) = M.lookup m f
in F.APP(F.VAR fl, OU.filter filt vs)
end handle M.IntmapF => le)
| F.TFN((f,args,body),le) => F.TFN((f, args, loop body), loop le)
| F.TAPP(f,tycs) => le
| F.SWITCH(v,ac,arms,def) =>
let fun carm (con,le) = (con, loop le)
in F.SWITCH(v, ac, map carm arms, O.map loop def)
end
| F.CON(dc,tycs,v,lv,le) => F.CON(dc, tycs, v, lv, loop le)
| F.RECORD(rk,vs,lv,le) => F.RECORD(rk, vs, lv, loop le)
| F.SELECT(v,i,lv,le) => F.SELECT(v, i, lv, loop le)
| F.RAISE(v,ltys) => le
| F.HANDLE(le,v) => F.HANDLE(lexp m [] le, v)
| F.BRANCH(po,vs,le1,le2) => F.BRANCH(po, vs, loop le1, loop le2)
| F.PRIMOP(po,vs,lv,le) => F.PRIMOP(po, vs, lv, loop le)
| F.APP _ => bug "unexpected APP"
end
in
collect progname S.empty progbody;
(progkind, progname, progargs, lexp M.empty [] progbody)
end
end
end