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

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1 :	monnier	121	(* copyright 1998 YALE FLINT PROJECT *)
2 :	monnier	159	(* monnier@cs.yale.edu *)
3 :	monnier	121
4 :			signature FCONTRACT =
5 :			sig
6 :
7 :			(* needs Collect to be setup properly *)
8 :	monnier	213	val contract : FLINT.prog -> FLINT.prog
9 :	monnier	121
10 :			end
11 :
12 :			(* All kinds of beta-reductions. In order to do as much work per pass as
13 :			* possible, the usage counts of each variable (maintained by the Collect
14 :			* module) is kept as much uptodate as possible. For instance as soon as a
15 :			* variable becomes dead, all the variables that were referenced have their
16 :			* usage counts decremented correspondingly. This means that we have to
17 :			* be careful to make sure that a dead variable will indeed not appear
18 :			* in the output lexp since it might else reference other dead variables *)
19 :
20 :	monnier	159	(* things that fcontract does:
21 :			* - several things not mentioned
22 :			* - elimination of Con(Decon x)
23 :			* - update counts when selecting a SWITCH alternative
24 :	monnier	162	* - contracting RECORD(R.1,R.2) => R (only if the type is easily available)
25 :	monnier	184	* - dropping of dead arguments
26 :	monnier	159	*)
27 :
28 :	monnier	121	(* things that lcontract.sml does that fcontract doesn't do (yet):
29 :	monnier	159	* - inline across DeBruijn depths (will be solved by named-tvar)
30 :	monnier	121	* - elimination of let [dead-vs] = pure in body
31 :			*)
32 :
33 :			(* things that cpsopt/eta.sml did that fcontract doesn't do:
34 :	monnier	159	* - let f vs = select(v,i,g,g vs)
35 :	monnier	121	*)
36 :
37 :			(* things that cpsopt/contract.sml did that fcontract doesn't do:
38 :	monnier	159	* - IF-idiom (I still don't know what it is)
39 :	monnier	121	* - unifying branches
40 :			* - Handler operations
41 :			* - primops expressions
42 :			* - branch expressions
43 :			*)
44 :
45 :			(* things that could also be added:
46 :	monnier	184	* - elimination of dead vars in let
47 :	monnier	191	* - elimination of constant arguments
48 :	monnier	121	*)
49 :
50 :			(* things that would require some type info:
51 :			* - dropping foo in LET vs = RAISE v IN foo
52 :			*)
53 :
54 :			(* eta-reduction is tricky:
55 :			* - recognition of eta-redexes and introduction of the corresponding
56 :			* substitution in the table has to be done at the very beginning of
57 :			* the processing of the FIX
58 :			* - eta-reduction can turn a known function into an escaping function
59 :			* - fun f (g,v2,v3) = g(g,v2,v3) looks tremendously like an eta-redex
60 :			*)
61 :
62 :			(* order of contraction is important:
63 :			* - the body of a FIX is contracted before the functions because the
64 :			* functions might end up being inlined in the body in which case they
65 :			* could be contracted twice.
66 :			*)
67 :
68 :			(* When creating substitution f->g (as happens with eta redexes or with
69 :			* code like `LET [f] = RET[g]'), we need to make sure that the usage cout
70 :			* of f gets properly transfered to g. One way to do that is to make the
71 :			* transfer incremental: each time we apply the substitution, we decrement
72 :			* f's count and increment g's count. But this can be tricky since the
73 :			* elimination of the eta-redex (or the trivial binding) eliminates one of the
74 :	monnier	159	* references to g and if this is the only one, we might trigger the killing
75 :	monnier	121	* of g even though its count would be later incremented. Similarly, inlining
76 :			* of g would be dangerous as long as some references to f exist.
77 :			* So instead we do the transfer once and for all when we see the eta-redex,
78 :			* which frees us from those two problems but forces us to make sure that
79 :			* every existing reference to f will be substituted with g.
80 :			* Also, the transfer of counts from f to g is not quite straightforward
81 :			* since some of the references to f might be from inside g and without doing
82 :			* the transfer incrementally, we can't easily know which of the usage counts
83 :			* of f should be transfered to the internal counts of g and which to the
84 :			* external counts.
85 :			*)
86 :
87 :	monnier	159	(* Preventing infinite inlining:
88 :			* - inlining a function in its own body amounts to unrolling which has
89 :			* to be controlled (you only want to unroll some number of times).
90 :			* It's currently simply not allowed.
91 :			* - inlining a recursive function outside of tis body amounts to `peeling'
92 :			* one iteration. Here also, since the inlined body will have yet another
93 :			* call, the inlining risks non-termination. It's hence also
94 :			* not allowed.
95 :			* - inlining a mutually recursive function is just a more general form
96 :			* of the problem above although it can be safe and desirable in some cases.
97 :			* To be safe, you simply need that one of the functions forming the
98 :			* mutual-recursion loop cannot be inlined (to break the loop). This cannot
99 :			* be trivially checked. So we (foolishly?) trust the `inline' bit in
100 :			* those cases. This is mostly used to inline wrappers inside the
101 :			* function they wrap.
102 :			* - even if one only allows inlining of funtions showing no sign of
103 :			* recursion, we can be bitten by a program creating its own Y combinator:
104 :			* datatype dt = F of dt -> int -> int
105 :			* let fun f (F g) x = g (F g) x in f (F f) end
106 :			* To solve this problem, `cexp' has an `ifs' parameter containing the set
107 :			* of funtions that we are inlining in order to detect (and break) cycles.
108 :			* - funnily enough, if we allow inlining recursive functions the cycle
109 :			* detection will ensure that the unrolling (or peeling) will only be done
110 :			* once. In the future, maybe.
111 :			*)
112 :
113 :	monnier	184	(* Dropping useless arguments.
114 :			* Arguments whose value is constant (i.e. the function is known and each
115 :			* call site provides the same value for that argument (or the argument
116 :			* itself in the case of recursive calls) can be safely removed and replaced
117 :			* inside the body by a simple let binding. The only problem is that the
118 :			* constant argument might be out of scope at the function definition site.
119 :			* It is obviously always possible to move the function to bring the argument
120 :			* in scope, but since we don't do any code motion here, we're stuck.
121 :			* If it wasn't for this little problem, we could do the cst-arg removal in
122 :			* collect (we don't gain anything from doing it here).
123 :			* The removal of dead arguments (args not used in the body) on the other
124 :			* hand can quite well be done in collect, the only problem being that it
125 :			* is convenient to do it after the cst-arg removal so that we can rely
126 :			* on deadarg to do the actual removal of the cst-arg.
127 :			*)
128 :
129 :	monnier	121	(* Simple inlining (inlining called-once functions, which doesn't require
130 :			* alpha-renaming) seems inoffensive enough but is not always desirable.
131 :	monnier	159	* The typical example is wrapper functions introduced by eta-expand: they
132 :			* usually (until inlined) contain the only call to the main function,
133 :	monnier	121	* but inlining the main function in the wrapper defeats the purpose of the
134 :			* wrapper.
135 :			* cpsopt dealt with this problem by adding a `NO_INLINE_INTO' hint to the
136 :	monnier	159	* wrapper function. In this file, the idea is the following:
137 :			* If you have a function declaration like `let f x = body in exp', first
138 :			* contract `exp' and only contract `body' afterwards. This ensures that
139 :			* the eta-wrapper gets a chance to be inlined before it is (potentially)
140 :			* eta-reduced away. Interesting details:
141 :	monnier	121	* - all functions (even the ones that would have a `NO_INLINE_INTO') are
142 :			* contracted, because the "aggressive usage count maintenance" makes any
143 :			* alternative painful (the collect phase has already assumed that dead code
144 :			* will be eliminated, which means that fcontract should at the very least
145 :	monnier	159	* do the dead-code elimination, so you can only avoid fcontracting a
146 :			* a function if you can be sure that the body doesn't contain any dead-code,
147 :			* which is generally not known).
148 :	monnier	190	* - once a function is fcontracted, its inlinable status is re-examined.
149 :			* More specifically, if no inlining occured during its fcontraction, then
150 :			* we assume that the code has just become smaller and should hence
151 :			* still be considered inlinable. On another hand, if inlining took place,
152 :			* then we have to reset the inline-bit because the new body might
153 :			* be completely different (i.e. much bigger) and inlining it might be
154 :			* undesirable.
155 :	monnier	159	* This means that in the case of
156 :			* let fwrap x = body1 and f y = body2 in exp
157 :	monnier	190	* if fwrap is fcontracted before f and something gets inlined into it,
158 :			* then fwrap cannot be inlined in f.
159 :	monnier	159	* To minimize the impact of this problem, we make sure that we fcontract
160 :			* inlinable functions only after fcontracting other mutually recursive
161 :	monnier	190	* functions. One way to solve the problem more thoroughly would be
162 :			* to keep the uncontracted fwrap around until f has been contracted.
163 :			* Such a trick hasn't seemed necessary yet.
164 :	monnier	121	* - at the very end of the optimization phase, cpsopt had a special pass
165 :			* that ignored the `NO_INLINE_INTO' hint (since at this stage, inlining
166 :			* into it doesn't have any undesirable side effects any more). The present
167 :			* code doesn't need such a thing. On another hand, the cpsopt approach
168 :			* had the advantage of keeping the `inline' bit from one contract phase to
169 :	monnier	159	* the next. If this ends up being important, one could add a global
170 :	monnier	121	* "noinline" flag that could be set to true whenever fcontracting an
171 :	monnier	159	* inlinable function (this would ensure that fcontracting such an inlinable
172 :			* function can only reduce its size, which would allow keeping the `inline'
173 :			* bit set after fcontracting).
174 :	monnier	121	*)
175 :
176 :			structure FContract :> FCONTRACT =
177 :			struct
178 :			local
179 :			structure F = FLINT
180 :			structure M = IntmapF
181 :	monnier	159	structure S = IntSetF
182 :	monnier	121	structure C = Collect
183 :	monnier	184	structure O = Option
184 :	monnier	121	structure DI = DebIndex
185 :			structure PP = PPFlint
186 :	monnier	159	structure FU = FlintUtil
187 :			structure LT = LtyExtern
188 :	monnier	200	structure LK = LtyKernel
189 :	monnier	163	structure OU = OptUtils
190 :	monnier	202	structure PO = PrimOp
191 :	monnier	159	structure CTRL = Control.FLINT
192 :	monnier	121	in
193 :
194 :			val say = Control.Print.say
195 :			fun bug msg = ErrorMsg.impossible ("FContract: "^msg)
196 :			fun buglexp (msg,le) = (say "\n"; PP.printLexp le; bug msg)
197 :			fun bugval (msg,v) = (say "\n"; PP.printSval v; bug msg)
198 :
199 :			(* fun sayexn e = app say (map (fn s => s^" <- ") (SMLofNJ.exnHistory e)) *)
200 :
201 :	monnier	159	val cplv = LambdaVar.dupLvar
202 :	monnier	200	val mklv = LambdaVar.mkLvar
203 :	monnier	121
204 :			datatype sval
205 :			= Val of F.value (* F.value should never be F.VAR lv *)
206 :	monnier	202	| Fun of F.lvar * F.lexp * (F.lvar * F.lty) list * F.fkind * sval list list ref
207 :	monnier	197	| TFun of F.lvar * F.lexp * (F.tvar * F.tkind) list
208 :	monnier	189	| Record of F.lvar * sval list
209 :			| Con of F.lvar * sval * F.dcon * F.tyc list
210 :			| Decon of F.lvar * sval * F.dcon * F.tyc list
211 :			| Select of F.lvar * sval * int
212 :	monnier	121	| Var of F.lvar * F.lty option (* cop out case *)
213 :
214 :	monnier	159	fun sval2lty (Var(_,x)) = x
215 :			| sval2lty (Decon(_,_,(_,_,lty),tycs)) =
216 :			SOME(hd(#2 (LT.ltd_arrow (hd(LT.lt_inst(lty, tycs))))))
217 :	monnier	199	| sval2lty (Select(_,sv,i)) =
218 :			(case sval2lty sv of SOME lty => SOME(LT.lt_select(lty, i)) | _ => NONE)
219 :	monnier	159	| sval2lty _ = NONE
220 :	monnier	121
221 :	monnier	159	fun tycs_eq ([],[]) = true
222 :			| tycs_eq (tyc1::tycs1,tyc2::tycs2) =
223 :			LT.tc_eqv(tyc1,tyc2) andalso tycs_eq(tycs1,tycs2)
224 :			| tycs_eq _ = false
225 :	monnier	121
226 :	monnier	200	(* calls `code' to append a lexp to each leaf of `le'.
227 :			* Typically used to transform `let lvs = le in code' so that
228 :			* `code' is now copied at the end of each branch of `le'.
229 :			* `lvs' is a list of lvars that should be used if the result of `le'
230 :			* needs to be bound before calling `code'. *)
231 :			fun append lvs code le =
232 :			let fun l (F.RET vs) = code vs
233 :			| l (le as (F.APP _ | F.TAPP _ | F.RAISE _ | F.HANDLE _)) =
234 :			let val lvs = map (fn lv => let val nlv = cplv lv
235 :			in C.new NONE nlv; nlv end)
236 :			lvs
237 :			in F.LET(lvs, le, code(map F.VAR lvs))
238 :			end
239 :			| l (F.LET (lvs,body,le)) = F.LET(lvs,body, l le)
240 :			| l (F.FIX (fdecs,le)) = F.FIX(fdecs, l le)
241 :			| l (F.TFN (tfdec,le)) = F.TFN(tfdec, l le)
242 :			| l (F.SWITCH (v,ac,arms,def)) =
243 :			let fun larm (con,le) = (con, l le)
244 :			in F.SWITCH(v, ac, map larm arms, O.map l def)
245 :			end
246 :			| l (F.CON (dc,tycs,v,lv,le)) = F.CON(dc, tycs, v, lv, l le)
247 :			| l (F.RECORD (rk,vs,lv,le)) = F.RECORD(rk, vs, lv, l le)
248 :			| l (F.SELECT (v,i,lv,le)) = F.SELECT(v, i, lv, l le)
249 :			| l (F.BRANCH (po,vs,le1,le2)) = F.BRANCH(po, vs, l le1, l le2)
250 :			| l (F.PRIMOP (po,vs,lv,le)) = F.PRIMOP(po, vs, lv, l le)
251 :			in l le
252 :			end
253 :
254 :	monnier	201	(* `extract' extracts the code of a switch arm into a function
255 :			* and replaces it with a call to that function *)
256 :			fun extract (con,le) =
257 :			let val f = mklv()
258 :			val fk = {isrec=NONE,known=true,inline=F.IH_SAFE,
259 :			cconv=F.CC_FUN(LK.FF_FIXED)}
260 :			in case con of
261 :			F.DATAcon(dc as (_,_,lty),tycs,lv) =>
262 :			let val nlv = cplv lv
263 :			val _ = C.new (SOME[lv]) f
264 :			val _ = C.use NONE (C.new NONE nlv)
265 :			val (lty,_) = LT.ltd_parrow(hd(LT.lt_inst(lty, tycs)))
266 :			in ((F.DATAcon(dc, tycs, nlv),
267 :			F.APP(F.VAR f, [F.VAR nlv])),
268 :			(fk, f, [(lv, lty)], le))
269 :			end
270 :			| con =>
271 :			let val _ = C.new (SOME[]) f
272 :			in ((con, F.APP(F.VAR f, [])),
273 :			(fk, f, [], le))
274 :			end
275 :			end
276 :
277 :	monnier	202	fun inScope m lv = (M.lookup m lv; true) handle M.IntmapF => false
278 :
279 :	monnier	213	fun click s c = (if !CTRL.misc = 1 then say s else ();
280 :			c := !c + 1 (* Stats.addCounter c 1 *) )
281 :	monnier	185
282 :	monnier	213	fun contract (fdec as (_,f,_,_)) = let
283 :	monnier	185
284 :	monnier	213	val c_dummy = ref 0 (* Stats.newCounter[] *)
285 :			val c_miss = ref 0 (* Stats.newCounter[] *)
286 :	monnier	189
287 :	monnier	213	val counter = c_dummy
288 :	monnier	189
289 :			fun click_deadval () = (click "d" counter)
290 :			fun click_deadlexp () = (click "D" counter)
291 :			fun click_select () = (click "s" counter)
292 :			fun click_record () = (click "r" counter)
293 :			fun click_con () = (click "c" counter)
294 :			fun click_switch () = (click "s" counter)
295 :			fun click_eta () = (click "e" counter)
296 :			fun click_etasplit () = (click "E" counter)
297 :			fun click_branch () = (click "b" counter)
298 :			fun click_dropargs () = (click "a" counter)
299 :
300 :			fun click_lacktype () = (click "t" c_miss)
301 :
302 :			(* this counters is actually *used* by fcontract.
303 :			* It's not used just for statistics. *)
304 :	monnier	213	val c_inline = ref 0 (* Stats.newCounter[counter] *)
305 :	monnier	189	fun click_simpleinline () = (click "i" c_inline)
306 :			fun click_copyinline () = (click "I" c_inline)
307 :			fun click_unroll () = (click "u" c_inline)
308 :	monnier	213	fun inline_count () = (* Stats.getCounter *) !c_inline
309 :	monnier	189
310 :	monnier	186	fun used lv = (C.usenb(C.get lv) > 0)
311 :	monnier	199	(* handle x =>
312 :	monnier	186	(say("while in FContract.used "^(C.LVarString lv)^"\n");
313 :	monnier	199	raise x) *)
314 :	monnier	121
315 :			fun eqConV (F.INTcon i1, F.INT i2) = i1 = i2
316 :			| eqConV (F.INT32con i1, F.INT32 i2) = i1 = i2
317 :			| eqConV (F.WORDcon i1, F.WORD i2) = i1 = i2
318 :			| eqConV (F.WORD32con i1, F.WORD32 i2) = i1 = i2
319 :			| eqConV (F.REALcon r1, F.REAL r2) = r1 = r2
320 :			| eqConV (F.STRINGcon s1, F.STRING s2) = s1 = s2
321 :			| eqConV (con,v) = bugval("unexpected comparison with val", v)
322 :
323 :			fun lookup m lv = (M.lookup m lv)
324 :	monnier	202	handle e as M.IntmapF =>
325 :	monnier	121	(say "\nlooking up unbound ";
326 :			say (!PP.LVarString lv);
327 :	monnier	202	raise e)
328 :	monnier	121
329 :			fun sval2val sv =
330 :			case sv
331 :	monnier	159	of (Fun{1=lv,...} | TFun{1=lv,...} | Record{1=lv,...} | Decon{1=lv,...}
332 :	monnier	121	| Con{1=lv,...} | Select{1=lv,...} | Var{1=lv,...}) => F.VAR lv
333 :			| Val v => v
334 :
335 :	monnier	163	fun val2sval m (F.VAR ov) =
336 :	monnier	199	((lookup m ov) (* handle x =>
337 :			(say("val2sval "^(C.LVarString ov)^"\n"); raise x) *) )
338 :	monnier	121	| val2sval m v = Val v
339 :
340 :			fun bugsv (msg,sv) = bugval(msg, sval2val sv)
341 :
342 :			fun subst m ov = sval2val (lookup m ov)
343 :	monnier	199	fun substval m = sval2val o (val2sval m)
344 :			fun substvar m lv =
345 :			case substval m (F.VAR lv)
346 :	monnier	121	of F.VAR lv => lv
347 :			| v => bugval ("unexpected val", v)
348 :
349 :			(* called when a variable becomes dead.
350 :			* it simply adjusts the use-counts *)
351 :			fun undertake m lv =
352 :			let val undertake = undertake m
353 :			in case lookup m lv
354 :	monnier	186	of Var {1=nlv,...} => ()
355 :	monnier	121	| Val v => ()
356 :	monnier	202	| Fun (lv,le,args,_,_) =>
357 :	monnier	187	C.unuselexp undertake
358 :			(F.LET(map #1 args,
359 :			F.RET (map (fn _ => F.INT 0) args),
360 :			le))
361 :			| TFun{1=lv,2=le,...} =>
362 :			C.unuselexp undertake le
363 :	monnier	189	| (Select {2=sv,...} | Con {2=sv,...}) => unusesval m sv
364 :			| Record {2=svs,...} => app (unusesval m) svs
365 :	monnier	159	(* decon's are implicit so we can't get rid of them *)
366 :			| Decon _ => ()
367 :	monnier	121	end
368 :			handle M.IntmapF =>
369 :	monnier	186	(say("Unable to undertake "^(C.LVarString lv)^"\n"))
370 :	monnier	121	| x =>
371 :	monnier	186	(say("while undertaking "^(C.LVarString lv)^"\n"); raise x)
372 :	monnier	121
373 :	monnier	189	and unusesval m sv = unuseval m (sval2val sv)
374 :	monnier	187	and unuseval m (F.VAR lv) =
375 :			if (C.unuse false (C.get lv)) then undertake m lv else ()
376 :			| unuseval f _ = ()
377 :			fun unusecall m lv =
378 :			if (C.unuse true (C.get lv)) then undertake m lv else ()
379 :
380 :
381 :	monnier	121	fun addbind (m,lv,sv) = M.add(m, lv, sv)
382 :
383 :	monnier	164	(* substitute a value sv for a variable lv and unuse value v. *)
384 :	monnier	121	fun substitute (m, lv1, sv, v) =
385 :			(case sval2val sv of F.VAR lv2 => C.transfer(lv1,lv2) | v2 => ();
386 :	monnier	187	unuseval m v;
387 :	monnier	199	addbind(m, lv1, sv)) (* handle x =>
388 :	monnier	186	(say ("while substituting "^
389 :	monnier	164	(C.LVarString lv1)^
390 :			" -> ");
391 :	monnier	121	PP.printSval (sval2val sv);
392 :	monnier	199	raise x) *)
393 :	monnier	121
394 :			(* common code for primops *)
395 :	monnier	199	fun cpo m (SOME{default,table},po,lty,tycs) =
396 :			(SOME{default=substvar m default,
397 :			table=map (fn (tycs,lv) => (tycs, substvar m lv)) table},
398 :	monnier	121	po,lty,tycs)
399 :	monnier	199	| cpo _ po = po
400 :	monnier	121
401 :	monnier	199	fun cdcon m (s,Access.EXN(Access.LVAR lv),lty) =
402 :			(s, Access.EXN(Access.LVAR(substvar m lv)), lty)
403 :			| cdcon _ dc = dc
404 :	monnier	121
405 :	monnier	201	(* ifs (inlined functions): records which functions we're currently inlining
406 :	monnier	199	* in order to detect loops
407 :			* m: is a map lvars to their defining expressions (svals) *)
408 :	monnier	201	fun fcexp ifs m le cont = let
409 :			val loop = fcexp ifs
410 :	monnier	199	val substval = substval m
411 :			val cdcon = cdcon m
412 :			val cpo = cpo m
413 :	monnier	163
414 :	monnier	201	fun fcLet (lvs,le,body) =
415 :			loop m le
416 :			(fn (nm,nle) =>
417 :			let fun cbody () =
418 :			let val nm = (foldl (fn (lv,m) =>
419 :			addbind(m, lv, Var(lv, NONE)))
420 :			nm lvs)
421 :			in case loop nm body cont
422 :			of F.RET vs => if vs = (map F.VAR lvs) then nle
423 :			else F.LET(lvs, nle, F.RET vs)
424 :			| nbody => F.LET(lvs, nle, nbody)
425 :			end
426 :			in case nle
427 :			of F.RET vs =>
428 :			let fun simplesubst (lv,v,m) =
429 :			let val sv = val2sval m v
430 :			in substitute(m, lv, sv, sval2val sv)
431 :			end
432 :			val nm = (ListPair.foldl simplesubst nm (lvs, vs))
433 :			in loop nm body cont
434 :			end
435 :			| F.TAPP _ =>
436 :			if List.all (C.dead o C.get) lvs
437 :			then loop nm body cont
438 :			else cbody()
439 :			| (F.BRANCH _ | F.SWITCH _) =>
440 :			(* this is a hack originally meant to cleanup the BRANCH
441 :			* mess introduced in flintnm (where each branch returns
442 :			* just true or false which is generally only used as
443 :			* input to a SWITCH).
444 :			* The present code does more than clean up this case.
445 :			* It has one serious shortcoming: it ends up making
446 :			* three fcontract passes through the same code (plus
447 :			* one cheap traversal). *)
448 :			let fun cassoc (lv,F.SWITCH(F.VAR v,ac,arms,NONE),wrap) =
449 :			if lv <> v orelse C.usenb(C.get lv) > 1
450 :			then cbody() else
451 :			let val (narms,fdecs) =
452 :			ListPair.unzip (map extract arms)
453 :			fun addswitch [v] =
454 :			C.copylexp
455 :			IntmapF.empty
456 :			(F.SWITCH(v,ac,narms,NONE))
457 :			| addswitch _ = bug "prob in addswitch"
458 :			(* replace each leaf `ret' with a copy
459 :			* of the switch *)
460 :			val nle = append [lv] addswitch nle
461 :			(* decorate with the functions extracted
462 :			* from the switch arms *)
463 :			val nle =
464 :			foldl (fn (f,le) => F.FIX([f],le))
465 :			(wrap nle) fdecs
466 :			(* Ugly hack: force one more traversal *)
467 :			val nle = loop nm nle #2
468 :			in click_branch();
469 :			loop nm nle cont
470 :			end
471 :			| cassoc _ = cbody()
472 :			in case (lvs,body)
473 :			of ([lv],le as F.SWITCH _) =>
474 :			cassoc(lv, le, fn x => x)
475 :			| ([lv],F.LET(lvs,le as F.SWITCH _,rest)) =>
476 :			cassoc(lv, le, fn le => F.LET(lvs,le,rest))
477 :			| _ => cbody()
478 :			end
479 :			| _ => cbody()
480 :			end)
481 :	monnier	200
482 :	monnier	201	fun fcFix (fs,le) =
483 :	monnier	202	let (* merge actual arguments to extract the constant subpart *)
484 :			fun merge_actuals ((lv,lty),[],m) = addbind(m, lv, Var(lv, SOME lty))
485 :			| merge_actuals ((lv,lty),a::bs,m) = addbind(m, lv, Var(lv, SOME lty))
486 :			(* FIXME: there's a bug here, but it's not caught by chkflint
487 :			let fun f (b::bs) =
488 :			if sval2val a = sval2val b then f bs
489 :			else addbind(m, lv, Var(lv, SOME lty))
490 :			| f [] =
491 :			(click "C" c_cstarg;
492 :			case sval2val a
493 :			of v as F.VAR lv' =>
494 :			(* FIXME: this inScope check is wrong for non-recursive
495 :			* functions. But it only matters if the function is
496 :			* passed itself as a parameter which cannot happen
497 :			* with the current type system I believe. *)
498 :			if inScope m lv' then
499 :			let val sv =
500 :			case a of Var (v,NONE) => Var(v, SOME lty)
501 :			| _ => a
502 :			in substitute(m, lv, sv, v)
503 :			end
504 :			else (click "O" c_outofscope;
505 :
506 :			addbind(m, lv, Var(lv, SOME lty)))
507 :			| v => substitute(m, lv, a, v))
508 :			in f bs
509 :			end *)
510 :			(* The actual function contraction *)
511 :	monnier	203	fun fcFun ((f,body,args,fk as {inline,cconv,known,isrec},actuals),
512 :			(m,fs)) =
513 :	monnier	201	let val fi = C.get f
514 :	monnier	203	in if C.dead fi then (m,fs)
515 :	monnier	201	else if C.iusenb fi = C.usenb fi then
516 :			(* we need to be careful that undertake not be called
517 :			* recursively *)
518 :	monnier	203	(C.use NONE fi; undertake m f; (m,fs))
519 :	monnier	201	else
520 :	monnier	213	let (* val _ = say ("\nEntering "^(C.LVarString f)) *)
521 :	monnier	201	val saved_ic = inline_count()
522 :			(* make up the bindings for args inside the body *)
523 :	monnier	202	val actuals = if isSome isrec orelse
524 :			C.escaping fi orelse
525 :			null(!actuals)
526 :			then map (fn _ => []) args
527 :			else OU.transpose(!actuals)
528 :			val nm = ListPair.foldl merge_actuals m (args, actuals)
529 :	monnier	201	(* contract the body and create the resulting fundec *)
530 :			val nbody = fcexp (S.add(f, ifs)) nm body #2
531 :			(* if inlining took place, the body might be completely
532 :			* changed (read: bigger), so we have to reset the
533 :			* `inline' bit *)
534 :			val nfk = {isrec=isrec, cconv=cconv,
535 :			known=known orelse not(C.escaping fi),
536 :			inline=if inline_count() = saved_ic
537 :			then inline
538 :			else F.IH_SAFE}
539 :			(* update the binding in the map. This step is
540 :			* not just a mere optimization but is necessary
541 :			* because if we don't do it and the function
542 :			* gets inlined afterwards, the counts will reflect the
543 :			* new contracted code while we'll be working on the
544 :			* the old uncontracted code *)
545 :	monnier	203	val nm = addbind(m, f, Fun(f, nbody, args, nfk, ref []))
546 :			in (nm, (nfk, f, args, nbody)::fs)
547 :	monnier	213	(* before say ("\nExiting "^(C.LVarString f)) *)
548 :	monnier	201	end
549 :			end
550 :
551 :			(* check for eta redex *)
552 :	monnier	202	fun fcEta (fdec as (f,F.APP(F.VAR g,vs),args,_,_),(m,fs,hs)) =
553 :	monnier	201	if List.length args = List.length vs andalso
554 :			OU.ListPair_all (fn (v,(lv,t)) =>
555 :			case v of F.VAR v => v = lv andalso lv <> g
556 :			| _ => false)
557 :			(vs, args)
558 :			then
559 :			let val svg = lookup m g
560 :			val g = case sval2val svg
561 :			of F.VAR g => g
562 :			| v => bugval("not a variable", v)
563 :			(* NOTE: we don't want to turn a known function into an
564 :			* escaping one. It's dangerous for optimisations based
565 :			* on known functions (elimination of dead args, f.ex)
566 :	monnier	217	* and could generate cases where call>use in collect.
567 :			* Of course, if g is not a locally defined function (it's
568 :			* bound by a LET or as an argument), then knownness is
569 :			* irrelevant. *)
570 :	monnier	215	in if f = g orelse
571 :	monnier	217	((C.escaping(C.get f)) andalso
572 :			not(C.escaping(C.get g)) andalso
573 :			(case svg of Fun _ => true | _ => false))
574 :	monnier	201	(* the default case could ensure the inline *)
575 :			then (m, fdec::fs, hs)
576 :			else let
577 :			(* if an earlier function h has been eta-reduced
578 :			* to f, we have to be careful to update its
579 :			* binding to not refer to f any more since f
580 :			* will disappear *)
581 :			val nm = foldl (fn (h,m) =>
582 :			if sval2val(lookup m h) = F.VAR f
583 :			then addbind(m, h, svg) else m)
584 :			m hs
585 :			in
586 :			(* I could almost reuse `substitute' but the
587 :			* unuse in substitute assumes the val is escaping *)
588 :			click_eta();
589 :			C.transfer(f, g);
590 :			unusecall m g;
591 :			(addbind(m, f, svg), fs, f::hs)
592 :			end
593 :	monnier	189	end
594 :	monnier	201	else (m, fdec::fs, hs)
595 :			| fcEta (fdec,(m,fs,hs)) = (m,fdec::fs,hs)
596 :
597 :			(* add wrapper for various purposes *)
598 :	monnier	217	fun wrap (f as (fk as {isrec,inline,...},g,args,body):F.fundec,fs) =
599 :	monnier	201	let val gi = C.get g
600 :			fun dropargs filter =
601 :			let val (nfk,nfk') = OU.fk_wrap(fk, O.map #1 isrec)
602 :			val args' = filter args
603 :			val ng = cplv g
604 :			val nargs = map (fn (v,t) => (cplv v, t)) args
605 :			val nargs' = map #1 (filter nargs)
606 :			val appargs = (map F.VAR nargs')
607 :			val nf = (nfk, g, nargs, F.APP(F.VAR ng, appargs))
608 :			val nf' = (nfk', ng, args', body)
609 :
610 :			val ngi = C.new (SOME(map #1 args')) ng
611 :			in
612 :			C.ireset gi;
613 :			app (ignore o (C.new NONE) o #1) nargs;
614 :			C.use (SOME appargs) ngi;
615 :			app (C.use NONE o C.get) nargs';
616 :			nf'::nf::fs
617 :	monnier	121	end
618 :	monnier	201	in
619 :			(* Don't introduce wrappers for escaping-only functions.
620 :			* This is debatable since although wrappers are useless
621 :			* on escaping-only functions, some of the escaping uses
622 :			* might turn into calls in the course of fcontract, so
623 :			* by not introducing wrappers here, we avoid useless work
624 :			* but we also postpone useful work to later invocations. *)
625 :	monnier	217	if C.dead gi then fs
626 :			else if inline=F.IH_ALWAYS then f::fs else
627 :	monnier	201	let val used = map (used o #1) args
628 :			in if C.called gi then
629 :			(* if some args are not used, let's drop them *)
630 :			if not (List.all (fn x => x) used) then
631 :			(click_dropargs();
632 :	monnier	203	dropargs (fn xs => OU.filter used xs))
633 :	monnier	190
634 :	monnier	201	(* eta-split: add a wrapper for escaping uses *)
635 :			else if C.escaping gi then
636 :			(* like dropargs but keeping all args *)
637 :			(click_etasplit(); dropargs (fn x => x))
638 :
639 :			else f::fs
640 :			else f::fs
641 :			end
642 :			end
643 :
644 :			(* add various wrappers *)
645 :			val fs = foldl wrap [] fs
646 :
647 :			(* register the new bindings (uncontracted for now) *)
648 :	monnier	202	val (nm,fs) = foldl (fn (fdec as (fk,f,args,body),(m,fs)) =>
649 :			let val nf = (f, body, args, fk, ref [])
650 :			in (addbind(m, f, Fun nf), nf::fs) end)
651 :			(m,[]) fs
652 :	monnier	201	(* check for eta redexes *)
653 :			val (nm,fs,_) = foldl fcEta (nm,[],[]) fs
654 :
655 :	monnier	204	val (wrappers,funs) =
656 :	monnier	202	List.partition (fn (_,_,_,{inline=F.IH_ALWAYS,...},_) => true
657 :	monnier	201	| _ => false) fs
658 :	monnier	204	val (maybes,funs) =
659 :	monnier	203	List.partition (fn (_,_,_,{inline=F.IH_MAYBE _,...},_) => true
660 :			| _ => false) funs
661 :	monnier	213
662 :	monnier	204	(* First contract the big inlinable functions. This might make them
663 :			* non-inlinable and we'd rather know that before we inline them.
664 :			* Then we inline the body (so that we won't go through the inline-once
665 :			* functions twice), then the normal functions and finally the wrappers
666 :			* (which need to come last to make sure that they get inlined if
667 :			* at all possible) *)
668 :			val fs = []
669 :			val (nm,fs) = foldl fcFun (nm,fs) maybes
670 :	monnier	201	val nle = loop nm le cont
671 :	monnier	203	val (nm,fs) = foldl fcFun (nm,fs) funs
672 :			val (nm,fs) = foldl fcFun (nm,fs) wrappers
673 :	monnier	201	(* junk newly unused funs *)
674 :			val fs = List.filter (used o #2) fs
675 :			in
676 :			case fs
677 :			of [] => nle
678 :			| [f1 as ({isrec=NONE,...},_,_,_),f2] =>
679 :			(* gross hack: `wrap' might have added a second
680 :			* non-recursive function. we need to split them into
681 :	monnier	203	* 2 FIXes. This is _very_ ad-hoc. *)
682 :	monnier	204	F.FIX([f2], F.FIX([f1], nle))
683 :	monnier	201	| _ => F.FIX(fs, nle)
684 :			end
685 :	monnier	163
686 :	monnier	201	fun fcApp (f,vs) =
687 :	monnier	202	let val svs = map (val2sval m) vs
688 :	monnier	201	val svf = val2sval m f
689 :			(* F.APP inlining (if any) *)
690 :	monnier	202
691 :	monnier	201	in case svf
692 :	monnier	202	of Fun(g,body,args,{inline,...},actuals) =>
693 :			let val gi = C.get g
694 :			fun noinline () =
695 :			(actuals := svs :: (!actuals);
696 :			cont(m,F.APP(sval2val svf, map sval2val svs)))
697 :			fun simpleinline () =
698 :			(* simple inlining: we should copy the body and then
699 :			* kill the function, but instead we just move the body
700 :			* and kill only the function name.
701 :			* This inlining strategy looks inoffensive enough,
702 :			* but still requires some care: see comments at the
703 :			* begining of this file and in cfun *)
704 :	monnier	213	(click_simpleinline();
705 :	monnier	202	ignore(C.unuse true gi);
706 :			loop m (F.LET(map #1 args, F.RET vs, body)) cont)
707 :			fun copyinline () =
708 :			(* aggressive inlining. We allow pretty much
709 :			* any inlinling, but we detect and reject inlining
710 :			* recursively which would else lead to infinite loop *)
711 :			(* unrolling is not as straightforward as it seems:
712 :			* if you inline the function you're currently
713 :			* fcontracting, you're asking for trouble: there is a
714 :			* hidden assumption in the counting that the old code
715 :			* will be replaced by the new code (and is hence dead).
716 :			* If the function to be unrolled has the only call to
717 :			* function f, then f might get simpleinlined before
718 :			* unrolling, which means that unrolling will introduce
719 :			* a second occurence of the `only call' but at that point
720 :			* f has already been killed. *)
721 :			let val nle = (F.LET(map #1 args, F.RET vs, body))
722 :			val nle = C.copylexp M.empty nle
723 :			in
724 :			click_copyinline();
725 :			(app (unuseval m) vs);
726 :			unusecall m g;
727 :			fcexp (S.add(g, ifs)) m nle cont
728 :			end
729 :
730 :			in if C.usenb gi = 1 andalso not(S.member ifs g) then simpleinline()
731 :			else case inline of
732 :			F.IH_SAFE => noinline()
733 :			| F.IH_UNROLL => noinline()
734 :			| F.IH_ALWAYS =>
735 :			if S.member ifs g then noinline() else copyinline()
736 :			| F.IH_MAYBE(min,ws) =>
737 :			if S.member ifs g then noinline() else let
738 :			fun value w _ (Val _ | Con _ | Record _) = w
739 :			| value w v (Fun (f,_,args,_,_)) =
740 :			if C.usenb(C.get v) = 1 then w * 2 else w
741 :			| value w _ _ = 0
742 :			val s = (OU.foldl3 (fn (sv,w,(v,t),s) => value w v sv + s)
743 :			0 (svs,ws,args))
744 :			handle OU.Unbalanced => 0
745 :			in if s > min then copyinline() else noinline()
746 :			end
747 :			end
748 :			| sv => cont(m,F.APP(sval2val svf, map sval2val svs))
749 :	monnier	201	end
750 :	monnier	184
751 :	monnier	201	fun fcTfn ((f,args,body),le) =
752 :			let val fi = C.get f
753 :			in if C.dead fi then (click_deadlexp(); loop m le cont) else
754 :			let val nbody = fcexp ifs m body #2
755 :			val nm = addbind(m, f, TFun(f, nbody, args))
756 :	monnier	184	val nle = loop nm le cont
757 :	monnier	121	in
758 :	monnier	201	if C.dead fi then nle else F.TFN((f, args, nbody), nle)
759 :	monnier	121	end
760 :	monnier	201	end
761 :
762 :			fun fcSwitch (v,ac,arms,def) =
763 :			let fun fcsCon (lvc,svc,dc1:F.dcon,tycs1) =
764 :			let fun killle le = C.unuselexp (undertake m) le
765 :			fun kill lv le =
766 :			C.unuselexp (undertake (addbind(m,lv,Var(lv,NONE)))) le
767 :			fun killarm (F.DATAcon(_,_,lv),le) = kill lv le
768 :			| killarm _ = buglexp("bad arm in switch(con)", le)
769 :
770 :			fun carm ((F.DATAcon(dc2,tycs2,lv),le)::tl) =
771 :			(* sometimes lty1 <> lty2 :-( so this doesn't work:
772 :			* FU.dcon_eq(dc1, dc2) andalso tycs_eq(tycs1,tycs2) *)
773 :			if #2 dc1 = #2 (cdcon dc2) then
774 :			(map killarm tl; (* kill the rest *)
775 :			O.map killle def; (* and the default case *)
776 :			loop (substitute(m, lv, svc, F.VAR lvc))
777 :			le cont)
778 :			else
779 :			(* kill this arm and continue with the rest *)
780 :			(kill lv le; carm tl)
781 :			| carm [] = loop m (O.valOf def) cont
782 :			| carm _ = buglexp("unexpected arm in switch(con,...)", le)
783 :			in click_switch(); carm arms
784 :	monnier	186	end
785 :	monnier	121
786 :	monnier	201	fun fcsVal v =
787 :			let fun kill le = C.unuselexp (undertake m) le
788 :			fun carm ((con,le)::tl) =
789 :			if eqConV(con, v) then
790 :			(map (kill o #2) tl;
791 :			O.map kill def;
792 :			loop m le cont)
793 :			else (kill le; carm tl)
794 :			| carm [] = loop m (O.valOf def) cont
795 :			in click_switch(); carm arms
796 :			end
797 :
798 :			fun fcsDefault (sv,lvc) =
799 :			case (arms,def)
800 :			of ([(F.DATAcon(dc,tycs,lv),le)],NONE) =>
801 :			(* this is a mere DECON, so we can push the let binding
802 :			* (hidden in cont) inside and maybe even drop the DECON *)
803 :			let val ndc = cdcon dc
804 :			val slv = Decon(lv, sv, ndc, tycs)
805 :			val nm = addbind(m, lv, slv)
806 :			(* see below *)
807 :			(* val nm = addbind(nm, lvc, Con(lvc, slv, ndc, tycs)) *)
808 :			val nle = loop nm le cont
809 :			val nv = sval2val sv
810 :			in
811 :			if used lv then
812 :			F.SWITCH(nv,ac,[(F.DATAcon(ndc,tycs,lv),nle)],NONE)
813 :			else (unuseval m nv; nle)
814 :			end
815 :			| (([(_,le)],NONE) | ([],SOME le)) =>
816 :			(* This should never happen, but we can optimize it away *)
817 :			(unuseval m (sval2val sv); loop m le cont)
818 :			| _ =>
819 :			let fun carm (F.DATAcon(dc,tycs,lv),le) =
820 :			let val ndc = cdcon dc
821 :			val slv = Decon(lv, sv, ndc, tycs)
822 :			val nm = addbind(m, lv, slv)
823 :			(* we can rebind lv to a more precise value
824 :			* !!BEWARE!! This rebinding is misleading:
825 :			* - it gives the impression that `lvc' is built
826 :			* from`lv' although the reverse is true:
827 :			* if `lvc' is undertaken, `lv's count should
828 :			* *not* be updated!
829 :			* Luckily, `lvc' will not become dead while
830 :			* rebound to Con(lv) because it's used by the
831 :			* SWITCH. All in all, it works fine, but it's
832 :			* not as straightforward as it seems.
833 :			* - it seems to be a good idea, but it can hide
834 :			* other opt-opportunities since it hides the
835 :			* previous binding. *)
836 :			(* val nm = addbind(nm, lvc, Con(lvc,slv,ndc,tycs)) *)
837 :			in (F.DATAcon(ndc, tycs, lv), loop nm le #2)
838 :			end
839 :			| carm (con,le) = (con, loop m le #2)
840 :			val narms = map carm arms
841 :			val ndef = Option.map (fn le => loop m le #2) def
842 :			in cont(m, F.SWITCH(sval2val sv, ac, narms, ndef))
843 :			end
844 :	monnier	121
845 :	monnier	201	in case val2sval m v
846 :			of sv as Con x => fcsCon x
847 :			| sv as Val v => fcsVal v
848 :			| sv as (Var{1=lvc,...} | Select{1=lvc,...} | Decon{1=lvc, ...}
849 :			| (* will probably never happen *) Record{1=lvc,...}) =>
850 :			fcsDefault(sv, lvc)
851 :			| sv as (Fun _ | TFun _) =>
852 :			bugval("unexpected switch arg", sval2val sv)
853 :			end
854 :	monnier	159
855 :	monnier	201	fun fcCon (dc1,tycs1,v,lv,le) =
856 :			let val lvi = C.get lv
857 :			in if C.dead lvi then (click_deadval(); loop m le cont) else
858 :			let val ndc = cdcon dc1
859 :			fun ccon sv =
860 :			let val nm = addbind(m, lv, Con(lv, sv, ndc, tycs1))
861 :			val nle = loop nm le cont
862 :			in if C.dead lvi then nle
863 :			else F.CON(ndc, tycs1, sval2val sv, lv, nle)
864 :			end
865 :			in case val2sval m v
866 :			of sv as (Decon (lvd,sv',dc2,tycs2)) =>
867 :			if FU.dcon_eq(dc1, dc2) andalso tycs_eq(tycs1,tycs2) then
868 :			(click_con();
869 :			loop (substitute(m, lv, sv', F.VAR lvd)) le cont)
870 :			else ccon sv
871 :			| sv => ccon sv
872 :	monnier	189	end
873 :	monnier	201	end
874 :	monnier	121
875 :	monnier	201	fun fcRecord (rk,vs,lv,le) =
876 :			(* g: check whether the record already exists *)
877 :			let val lvi = C.get lv
878 :			in if C.dead lvi then (click_deadval(); loop m le cont) else
879 :			let fun g (Select(_,sv,0)::ss) =
880 :			let fun g' (n,Select(_,sv',i)::ss) =
881 :			if n = i andalso (sval2val sv) = (sval2val sv')
882 :			then g'(n+1,ss) else NONE
883 :	monnier	204	| g' (n,[]) =
884 :	monnier	201	(case sval2lty sv
885 :			of SOME lty =>
886 :	monnier	204	let val ltd =
887 :			case (rk, LT.ltp_tyc lty)
888 :			of (F.RK_STRUCT,false) => LT.ltd_str
889 :			| (F.RK_TUPLE _,true) => LT.ltd_tuple
890 :			(* we might select out of a struct
891 :			* into a tuple or vice-versa *)
892 :			| _ => (fn _ => [])
893 :	monnier	201	in if length(ltd lty) = n
894 :			then SOME sv else NONE
895 :			end
896 :			| _ => (click_lacktype(); NONE)) (* sad *)
897 :			| g' _ = NONE
898 :			in g'(1,ss)
899 :			end
900 :			| g _ = NONE
901 :			val svs = map (val2sval m) vs
902 :			in case g svs
903 :			of SOME sv => (click_record();
904 :			loop (substitute(m, lv, sv, F.INT 0)) le cont
905 :			before app (unuseval m) vs)
906 :			| _ =>
907 :			let val nm = addbind(m, lv, Record(lv, svs))
908 :			val nle = loop nm le cont
909 :			in if C.dead lvi then nle
910 :			else F.RECORD(rk, map sval2val svs, lv, nle)
911 :			end
912 :	monnier	189	end
913 :	monnier	201	end
914 :	monnier	121
915 :	monnier	201	fun fcSelect (v,i,lv,le) =
916 :			let val lvi = C.get lv
917 :			in if C.dead lvi then (click_deadval(); loop m le cont) else
918 :			(case val2sval m v
919 :			of Record (lvr,svs) =>
920 :			let val sv = List.nth(svs, i)
921 :			in click_select();
922 :			loop (substitute(m, lv, sv, F.VAR lvr)) le cont
923 :			end
924 :			| sv =>
925 :			let val nm = addbind (m, lv, Select(lv, sv, i))
926 :			val nle = loop nm le cont
927 :			in if C.dead lvi then nle
928 :			else F.SELECT(sval2val sv, i, lv, nle)
929 :			end)
930 :			end
931 :	monnier	121
932 :	monnier	201	fun fcBranch (po,vs,le1,le2) =
933 :			let val nvs = map substval vs
934 :			val npo = cpo po
935 :			val nle1 = loop m le1 #2
936 :			val nle2 = loop m le2 #2
937 :			in cont(m, F.BRANCH(npo, nvs, nle1, nle2))
938 :			end
939 :	monnier	121
940 :	monnier	201	fun fcPrimop (po,vs,lv,le) =
941 :			let val lvi = C.get lv
942 :	monnier	204	val pure = not(PO.effect(#2 po))
943 :	monnier	201	in if pure andalso C.dead lvi then (click_deadval();loop m le cont) else
944 :	monnier	199	let val nvs = map substval vs
945 :	monnier	121	val npo = cpo po
946 :	monnier	201	val nm = addbind(m, lv, Var(lv,NONE))
947 :			val nle = loop nm le cont
948 :			in
949 :			if pure andalso C.dead lvi then nle
950 :			else F.PRIMOP(npo, nvs, lv, nle)
951 :	monnier	121	end
952 :	monnier	201	end
953 :	monnier	121
954 :	monnier	201	in case le
955 :			of F.RET vs => cont(m, F.RET(map substval vs))
956 :			| F.LET x => fcLet x
957 :			| F.FIX x => fcFix x
958 :			| F.APP x => fcApp x
959 :			| F.TFN x => fcTfn x
960 :			| F.TAPP (f,tycs) => cont(m, F.TAPP(substval f, tycs))
961 :			| F.SWITCH x => fcSwitch x
962 :			| F.CON x => fcCon x
963 :			| F.RECORD x => fcRecord x
964 :			| F.SELECT x => fcSelect x
965 :			| F.RAISE (v,ltys) => cont(m, F.RAISE(substval v, ltys))
966 :			| F.HANDLE (le,v) => cont(m, F.HANDLE(loop m le #2, substval v))
967 :			| F.BRANCH x => fcBranch x
968 :			| F.PRIMOP x => fcPrimop x
969 :	monnier	121	end
970 :
971 :	monnier	185	in
972 :			(* C.collect fdec; *)
973 :	monnier	201	case fcexp S.empty
974 :	monnier	185	M.empty (F.FIX([fdec], F.RET[F.VAR f])) #2
975 :			of F.FIX([fdec], F.RET[F.VAR f]) => fdec
976 :			| fdec => bug "invalid return fundec"
977 :			end
978 :	monnier	121
979 :			end
980 :			end

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