Annotation of /sml/trunk/src/compiler/FLINT/opt/loopify.sml

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1 :	monnier	191	(* copyright 1998 YALE FLINT PROJECT *)
2 :			(* monnier@cs.yale.edu *)
3 :
4 :			signature LOOPIFY =
5 :			sig
6 :			val loopify : FLINT.prog -> FLINT.prog
7 :			end
8 :
9 :
10 :	monnier	199	structure Loopify :> LOOPIFY =
11 :	monnier	191	struct
12 :			local
13 :			structure F = FLINT
14 :			structure O = Option
15 :			structure M = IntmapF
16 :	monnier	199	structure S = IntSetF
17 :	monnier	191	structure LK = LtyKernel
18 :			in
19 :
20 :			fun bug msg = ErrorMsg.impossible ("Loopify: "^msg)
21 :			val cplv = LambdaVar.dupLvar
22 :
23 :	monnier	199	datatype info = I of {tails : int ref, calls: int ref, icalls: int ref, tcp: bool ref, parent: F.lvar}
24 :			exception NotFound
25 :
26 :	monnier	191	fun loopify (prog as (progkind,progname,progargs,progbody)) = let
27 :
28 :	monnier	199	val m : info Intmap.intmap = Intmap.new(128, NotFound)
29 :
30 :			(* tails: number of tail-recursive calls
31 :			* calls: number of other calls
32 :			* icalls: non-tail self-recursive subset of `calls'
33 :			* tcp: always called in tail-position
34 :			* parent: enclosing function *)
35 :			fun new (f,known,parent) =
36 :			let val i = I{tails=ref 0, calls=ref 0, icalls=ref 0,
37 :			tcp=ref known, parent=parent}
38 :			in Intmap.add m (f,i); i end
39 :
40 :			fun get f = Intmap.map m f
41 :
42 :			(* collect tries to determine what calls are tail recursive.
43 :			* If a function f is always called in tail position in a function g,
44 :			* then all tail calls to g from f are indeed tail recursive. *)
45 :			(* tfs: we are currently in tail position relative to those functions
46 :			* p: englobing function *)
47 :			fun collect p tfs le = let
48 :			val loop = collect p tfs
49 :			in case le
50 :			of F.RET _ => ()
51 :			| F.LET(_,body,le) => (collect p S.empty body; loop le)
52 :			| F.FIX([({isrec=(NONE | SOME(_,F.LK_TAIL)),known,...},f,_,body)],le) =>
53 :			let val I{tcp,calls,icalls,...} = new(f, known, p)
54 :			val _ = loop le
55 :			val ecalls = !calls
56 :			in collect f (if !tcp then S.add(f,tfs) else S.singleton f) body;
57 :			icalls := !calls - ecalls
58 :			end
59 :			| F.FIX(fdecs,le) =>
60 :			let (* create the new entries in the map *)
61 :			val fs = map (fn (fk as {known,...},f,_,body) =>
62 :			(fk, f, body, new(f, false, p)))
63 :			fdecs
64 :			fun cfun ({isrec,...}:F.fkind,f,body,I{calls,icalls,...}) =
65 :			let val ecalls = !calls
66 :			in collect f (S.singleton f) body;
67 :			icalls := !calls - ecalls
68 :			end
69 :			in loop le;
70 :			app cfun fs
71 :			end
72 :			| F.APP(F.VAR f,vs) =>
73 :			(let val I{tails,calls,tcp,parent,...} = get f
74 :			in if S.member tfs f then tails := !tails + 1
75 :			else (calls := !calls + 1;
76 :			if S.member tfs parent then () else tcp := false)
77 :			end handle NotFound => ())
78 :			| F.TFN((_,_,body),le) => (collect p S.empty body; loop le)
79 :			| F.TAPP _ => ()
80 :			| F.SWITCH(v,ac,arms,def) =>
81 :			let fun carm (_,body) = loop body
82 :			in app carm arms; case def of SOME le => loop le | _ => ()
83 :			end
84 :			| (F.CON(_,_,_,_,le) | F.RECORD(_,_,_,le) |
85 :			F.SELECT(_,_,_,le) | F.PRIMOP(_,_,_,le)) => loop le
86 :			| F.RAISE _ => ()
87 :			| F.HANDLE(le,v) => collect p S.empty le
88 :			| F.BRANCH(_,_,le1,le2) => (loop le1; loop le2)
89 :
90 :			| F.APP _ => bug "weird F.APP in collect"
91 :			end
92 :
93 :	monnier	191	(* m: int intmap renaming for function calls
94 :	monnier	199	* tf:(int,int) list the current functions (if any) and their tail version
95 :	monnier	191	* le: you get the idea *)
96 :	monnier	199	fun lexp m tfs le = let
97 :			val loop = lexp m tfs
98 :	monnier	191	in case le
99 :			of F.RET _ => le
100 :	monnier	199	| F.LET(lvs,body,le) => F.LET(lvs, lexp m [] body, loop le)
101 :	monnier	191	| F.FIX(fdecs,le) =>
102 :			let fun cfun (fk:F.fkind as {isrec=SOME(ltys,F.LK_UNKNOWN),cconv,...},
103 :			f,args,body) =
104 :	monnier	199	let val I{tcp=ref tcp,icalls=ref icalls,tails=ref tails,...} =
105 :			get f
106 :	monnier	191	(* cpsopt uses the following condition:
107 :			* escape = 0 andalso !unroll_call > 0
108 :			* andalso (!call - !unroll_call > 1
109 :			* orelse List.exists (fn t=>t) inv)
110 :			* `escape = 0': I don't quite see the need for it, though it
111 :			* probably won't change much since etasplit should have
112 :			* made "everything" known already.
113 :			* `!call - !unroll_call > 1 orelse List.exists (fn t=>t) inv)':
114 :			* loopification is only useful if there is more than one
115 :			* external call or if there are loop invariants.
116 :			* Note that we deal with invariants elsewhere, so it's
117 :			* not a good reason to loopify here. *)
118 :			(*** rationale behind the restrictions: ***
119 :			* `icallnb = 0': loopification is pointless and will be
120 :			* undone by fcontract.
121 :			* `C.callnb fi <= icallnb + 1': if there's only one external
122 :			* call, loopification will probably (?) not be of much use
123 :			* and the same benefit would be had by just moving f *)
124 :	monnier	199	in if icalls = 0 andalso tails = 0
125 :			then (fk, f, args, lexp m (if tcp then tfs else []) body)
126 :	monnier	191	else
127 :			let val fl = cplv f
128 :			val ft = cplv f
129 :			val largs = map (fn(v,t) => (cplv v, t)) args
130 :			val args' = map (fn(v,t) => (cplv v, t)) args
131 :			val cconv' =
132 :			case cconv
133 :			of (F.CC_FCT | F.CC_FUN(LK.FF_FIXED)) => cconv
134 :			| F.CC_FUN(LK.FF_VAR(f1,f2)) =>
135 :			F.CC_FUN(LK.FF_VAR(true,f2))
136 :			val nm = M.add(m, f, fl)
137 :	monnier	199	val tfs' = ((f,ft)::(if tcp then tfs else []))
138 :
139 :			(* make the new body *)
140 :			val (nargs,nbody) = (args, lexp nm tfs' body)
141 :			(* wrap into a tail loop if necessary *)
142 :			val (nargs,nbody) =
143 :			if tails = 0 then (nargs,nbody) else let
144 :			val args' = map (fn(v,t) => (cplv v, t)) args
145 :			in (args',
146 :			F.FIX([({isrec=SOME(ltys, F.LK_TAIL),
147 :			known=true, inline=F.IH_SAFE,
148 :			cconv=cconv'}, ft, nargs,
149 :			nbody)],
150 :			F.APP(F.VAR ft, map (F.VAR o #1) args')))
151 :			end
152 :			(* wrap into a non-tail loop if necessary *)
153 :			val (nargs,nbody) =
154 :			if icalls = 0 then (nargs,nbody) else let
155 :			val args' = map (fn(v,t) => (cplv v, t)) args
156 :			in (args',
157 :			F.FIX([({isrec=SOME(ltys, F.LK_LOOP),
158 :			known=true, inline=F.IH_SAFE,
159 :			cconv=cconv'}, fl, nargs,
160 :			nbody)],
161 :			F.APP(F.VAR fl, map (F.VAR o #1) args')))
162 :			end
163 :			in (fk, f, nargs, nbody)
164 :	monnier	191	end
165 :			end
166 :	monnier	199	| cfun (fk as {inline=F.IH_UNROLL,isrec=SOME _,...},f,args,body) =
167 :			let val I{tcp=ref tcp,...} = get f
168 :			in (fk, f, args, lexp m (if tcp then tfs else []) body)
169 :			end
170 :			| cfun (fk,f,args,body) =
171 :			let val I{tcp=ref tcp,...} = get f
172 :			in (fk, f, args, lexp m (if tcp then tfs else []) body)
173 :			end
174 :	monnier	191	in F.FIX(map cfun fdecs, loop le)
175 :			end
176 :			| F.APP(F.VAR f,vs) =>
177 :			(let val fl = M.lookup m f
178 :	monnier	199	in case List.find (fn (ft,ft') => ft = f) tfs
179 :			of SOME(ft, ft') => F.APP(F.VAR ft', vs)
180 :	monnier	191	| NONE => F.APP(F.VAR fl, vs)
181 :			end handle M.IntmapF => le)
182 :			| F.TFN((f,args,body),le) => F.TFN((f, args, loop body), loop le)
183 :			| F.TAPP(f,tycs) => le
184 :			| F.SWITCH(v,ac,arms,def) =>
185 :			let fun carm (con,le) = (con, loop le)
186 :			in F.SWITCH(v, ac, map carm arms, O.map loop def)
187 :			end
188 :			| F.CON(dc,tycs,v,lv,le) => F.CON(dc, tycs, v, lv, loop le)
189 :			| F.RECORD(rk,vs,lv,le) => F.RECORD(rk, vs, lv, loop le)
190 :			| F.SELECT(v,i,lv,le) => F.SELECT(v, i, lv, loop le)
191 :			| F.RAISE(v,ltys) => le
192 :	monnier	199	| F.HANDLE(le,v) => F.HANDLE(lexp m [] le, v)
193 :	monnier	191	| F.BRANCH(po,vs,le1,le2) => F.BRANCH(po, vs, loop le1, loop le2)
194 :			| F.PRIMOP(po,vs,lv,le) => F.PRIMOP(po, vs, lv, loop le)
195 :
196 :			| F.APP _ => bug "unexpected APP"
197 :			end
198 :
199 :			in
200 :	monnier	199	collect progname S.empty progbody;
201 :			(progkind, progname, progargs, lexp M.empty [] progbody)
202 :	monnier	191	end
203 :
204 :			end
205 :			end
206 :

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