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	190	val contract : FLINT.prog * Stats.counter -> 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	163	structure OU = OptUtils
189 :	monnier	159	structure CTRL = Control.FLINT
190 :	monnier	121	in
191 :
192 :			val say = Control.Print.say
193 :			fun bug msg = ErrorMsg.impossible ("FContract: "^msg)
194 :			fun buglexp (msg,le) = (say "\n"; PP.printLexp le; bug msg)
195 :			fun bugval (msg,v) = (say "\n"; PP.printSval v; bug msg)
196 :
197 :			(* fun sayexn e = app say (map (fn s => s^" <- ") (SMLofNJ.exnHistory e)) *)
198 :
199 :	monnier	159	val cplv = LambdaVar.dupLvar
200 :	monnier	121
201 :			datatype sval
202 :			= Val of F.value (* F.value should never be F.VAR lv *)
203 :	monnier	197	| Fun of F.lvar * F.lexp * (F.lvar * F.lty) list * F.fkind
204 :			| TFun of F.lvar * F.lexp * (F.tvar * F.tkind) list
205 :	monnier	189	| Record of F.lvar * sval list
206 :			| Con of F.lvar * sval * F.dcon * F.tyc list
207 :			| Decon of F.lvar * sval * F.dcon * F.tyc list
208 :			| Select of F.lvar * sval * int
209 :	monnier	121	| Var of F.lvar * F.lty option (* cop out case *)
210 :
211 :	monnier	159	fun sval2lty (Var(_,x)) = x
212 :			| sval2lty (Decon(_,_,(_,_,lty),tycs)) =
213 :			SOME(hd(#2 (LT.ltd_arrow (hd(LT.lt_inst(lty, tycs))))))
214 :	monnier	199	| sval2lty (Select(_,sv,i)) =
215 :			(case sval2lty sv of SOME lty => SOME(LT.lt_select(lty, i)) | _ => NONE)
216 :	monnier	159	| sval2lty _ = NONE
217 :	monnier	121
218 :	monnier	159	fun tycs_eq ([],[]) = true
219 :			| tycs_eq (tyc1::tycs1,tyc2::tycs2) =
220 :			LT.tc_eqv(tyc1,tyc2) andalso tycs_eq(tycs1,tycs2)
221 :			| tycs_eq _ = false
222 :	monnier	121
223 :	monnier	189	fun click s c = (if !CTRL.misc = 1 then say s else (); Stats.addCounter c 1)
224 :	monnier	185
225 :	monnier	189	(* val c_inline = Stats.newCounter[] *)
226 :			(* val c_deadval = Stats.newCounter[] *)
227 :			(* val c_deadlexp = Stats.newCounter[] *)
228 :			(* val c_select = Stats.newCounter[] *)
229 :			(* val c_record = Stats.newCounter[] *)
230 :			(* val c_lacktype = Stats.newCounter[] *)
231 :			(* val c_con = Stats.newCounter[] *)
232 :			(* val c_switch = Stats.newCounter[] *)
233 :			(* val c_eta = Stats.newCounter[] *)
234 :			(* val c_etasplit = Stats.newCounter[] *)
235 :			(* val c_branch = Stats.newCounter[] *)
236 :			(* val c_dropargs = Stats.newCounter[] *)
237 :	monnier	185
238 :	monnier	189	fun contract (fdec as (_,f,_,_), counter) = let
239 :
240 :			val c_dummy = Stats.newCounter[]
241 :			val c_miss = Stats.newCounter[]
242 :
243 :			fun click_deadval () = (click "d" counter)
244 :			fun click_deadlexp () = (click "D" counter)
245 :			fun click_select () = (click "s" counter)
246 :			fun click_record () = (click "r" counter)
247 :			fun click_con () = (click "c" counter)
248 :			fun click_switch () = (click "s" counter)
249 :			fun click_eta () = (click "e" counter)
250 :			fun click_etasplit () = (click "E" counter)
251 :			fun click_branch () = (click "b" counter)
252 :			fun click_dropargs () = (click "a" counter)
253 :
254 :			fun click_lacktype () = (click "t" c_miss)
255 :
256 :			(* this counters is actually *used* by fcontract.
257 :			* It's not used just for statistics. *)
258 :			val c_inline = Stats.newCounter[counter]
259 :			(* val c_inline1 = Stats.newCounter[c_inline] *)
260 :			(* val c_inline2 = Stats.newCounter[c_inline] *)
261 :			(* val c_unroll = Stats.newCounter[c_inline] *)
262 :			fun click_simpleinline () = (click "i" c_inline)
263 :			fun click_copyinline () = (click "I" c_inline)
264 :			fun click_unroll () = (click "u" c_inline)
265 :			fun inline_count () = Stats.getCounter c_inline
266 :
267 :	monnier	186	fun used lv = (C.usenb(C.get lv) > 0)
268 :	monnier	199	(* handle x =>
269 :	monnier	186	(say("while in FContract.used "^(C.LVarString lv)^"\n");
270 :	monnier	199	raise x) *)
271 :	monnier	121
272 :			fun impurePO po = true (* if a PrimOP is pure or not *)
273 :
274 :			fun eqConV (F.INTcon i1, F.INT i2) = i1 = i2
275 :			| eqConV (F.INT32con i1, F.INT32 i2) = i1 = i2
276 :			| eqConV (F.WORDcon i1, F.WORD i2) = i1 = i2
277 :			| eqConV (F.WORD32con i1, F.WORD32 i2) = i1 = i2
278 :			| eqConV (F.REALcon r1, F.REAL r2) = r1 = r2
279 :			| eqConV (F.STRINGcon s1, F.STRING s2) = s1 = s2
280 :			| eqConV (con,v) = bugval("unexpected comparison with val", v)
281 :
282 :			fun lookup m lv = (M.lookup m lv)
283 :			(* handle e as M.IntmapF =>
284 :			(say "\nlooking up unbound ";
285 :			say (!PP.LVarString lv);
286 :			raise e) *)
287 :
288 :			fun sval2val sv =
289 :			case sv
290 :	monnier	159	of (Fun{1=lv,...} | TFun{1=lv,...} | Record{1=lv,...} | Decon{1=lv,...}
291 :	monnier	121	| Con{1=lv,...} | Select{1=lv,...} | Var{1=lv,...}) => F.VAR lv
292 :			| Val v => v
293 :
294 :	monnier	163	fun val2sval m (F.VAR ov) =
295 :	monnier	199	((lookup m ov) (* handle x =>
296 :			(say("val2sval "^(C.LVarString ov)^"\n"); raise x) *) )
297 :	monnier	121	| val2sval m v = Val v
298 :
299 :			fun bugsv (msg,sv) = bugval(msg, sval2val sv)
300 :
301 :			fun subst m ov = sval2val (lookup m ov)
302 :	monnier	199	fun substval m = sval2val o (val2sval m)
303 :			fun substvar m lv =
304 :			case substval m (F.VAR lv)
305 :	monnier	121	of F.VAR lv => lv
306 :			| v => bugval ("unexpected val", v)
307 :
308 :			(* called when a variable becomes dead.
309 :			* it simply adjusts the use-counts *)
310 :			fun undertake m lv =
311 :			let val undertake = undertake m
312 :			in case lookup m lv
313 :	monnier	186	of Var {1=nlv,...} => ()
314 :	monnier	121	| Val v => ()
315 :	monnier	197	| Fun (lv,le,args,_) =>
316 :	monnier	187	C.unuselexp undertake
317 :			(F.LET(map #1 args,
318 :			F.RET (map (fn _ => F.INT 0) args),
319 :			le))
320 :			| TFun{1=lv,2=le,...} =>
321 :			C.unuselexp undertake le
322 :	monnier	189	| (Select {2=sv,...} | Con {2=sv,...}) => unusesval m sv
323 :			| Record {2=svs,...} => app (unusesval m) svs
324 :	monnier	159	(* decon's are implicit so we can't get rid of them *)
325 :			| Decon _ => ()
326 :	monnier	121	end
327 :			handle M.IntmapF =>
328 :	monnier	186	(say("Unable to undertake "^(C.LVarString lv)^"\n"))
329 :	monnier	121	| x =>
330 :	monnier	186	(say("while undertaking "^(C.LVarString lv)^"\n"); raise x)
331 :	monnier	121
332 :	monnier	189	and unusesval m sv = unuseval m (sval2val sv)
333 :	monnier	187	and unuseval m (F.VAR lv) =
334 :			if (C.unuse false (C.get lv)) then undertake m lv else ()
335 :			| unuseval f _ = ()
336 :			fun unusecall m lv =
337 :			if (C.unuse true (C.get lv)) then undertake m lv else ()
338 :
339 :
340 :	monnier	121	fun addbind (m,lv,sv) = M.add(m, lv, sv)
341 :
342 :	monnier	164	(* substitute a value sv for a variable lv and unuse value v. *)
343 :	monnier	121	fun substitute (m, lv1, sv, v) =
344 :			(case sval2val sv of F.VAR lv2 => C.transfer(lv1,lv2) | v2 => ();
345 :	monnier	187	unuseval m v;
346 :	monnier	199	addbind(m, lv1, sv)) (* handle x =>
347 :	monnier	186	(say ("while substituting "^
348 :	monnier	164	(C.LVarString lv1)^
349 :			" -> ");
350 :	monnier	121	PP.printSval (sval2val sv);
351 :	monnier	199	raise x) *)
352 :	monnier	121
353 :			(* common code for primops *)
354 :	monnier	199	fun cpo m (SOME{default,table},po,lty,tycs) =
355 :			(SOME{default=substvar m default,
356 :			table=map (fn (tycs,lv) => (tycs, substvar m lv)) table},
357 :	monnier	121	po,lty,tycs)
358 :	monnier	199	| cpo _ po = po
359 :	monnier	121
360 :	monnier	199	fun cdcon m (s,Access.EXN(Access.LVAR lv),lty) =
361 :			(s, Access.EXN(Access.LVAR(substvar m lv)), lty)
362 :			| cdcon _ dc = dc
363 :	monnier	121
364 :	monnier	199	(* cfg: is used for deBruijn renumbering when inlining at different depths
365 :			* ifs (inlined functions): records which functions we're currently inlining
366 :			* in order to detect loops
367 :			* m: is a map lvars to their defining expressions (svals) *)
368 :			fun cexp ifs m le cont = let
369 :			val loop = cexp ifs
370 :			val substval = substval m
371 :			val cdcon = cdcon m
372 :			val cpo = cpo m
373 :			in case le
374 :			of F.RET vs => cont(m, F.RET(map substval vs))
375 :	monnier	163
376 :	monnier	121	| F.LET (lvs,le,body) =>
377 :	monnier	184	let fun clet () =
378 :			loop m le
379 :			(fn (m,F.RET vs) =>
380 :	monnier	190	let fun simplesubst (lv,v,m) =
381 :	monnier	199	let val sv = val2sval m v
382 :	monnier	184	in substitute(m, lv, sv, sval2val sv)
383 :			end
384 :	monnier	190	val nm = (ListPair.foldl simplesubst m (lvs, vs))
385 :	monnier	184	in loop nm body cont
386 :			end
387 :			| (m,nle) =>
388 :			let val nm = (foldl (fn (lv,m) =>
389 :			addbind(m, lv, Var(lv, NONE)))
390 :			m lvs)
391 :			in case loop nm body cont
392 :			of F.RET vs => if vs = (map F.VAR lvs) then nle
393 :			else F.LET(lvs, nle, F.RET vs)
394 :			| nbody => F.LET(lvs, nle, nbody)
395 :			end)
396 :	monnier	199	in (* case le
397 :	monnier	184	of F.BRANCH (po,vs,le1,le2) =>
398 :			(* this is a hack originally meant to cleanup the BRANCH mess
399 :			* introduced in flintnm (where each branch returns just true or
400 :			* false which is generally only used as input to a SWITCH).
401 :			* The present code does slightly more than clean up this case *)
402 :	monnier	121	let fun known (F.RECORD(_,_,_,le)) = known le
403 :			| known (F.CON(_,_,_,v,F.RET[F.VAR v'])) = (v = v')
404 :			| known (F.RET[F.VAR v]) = false
405 :			| known (F.RET[_]) = true
406 :			| known _ = false
407 :	monnier	184	fun cassoc (lv,v,body,wrap) =
408 :	monnier	186	if lv = v andalso ((C.usenb(C.get lv)) handle x=> raise x) = 1 andalso
409 :	monnier	121	known le1 andalso known le2 then
410 :			(* here I should also check that le1 != le2 *)
411 :			let val nle1 = F.LET([lv], le1, body)
412 :	monnier	159	val nlv = cplv lv
413 :	monnier	164	val _ = C.new NONE nlv
414 :			val body2 = C.copylexp (M.add(M.empty, lv, nlv))
415 :			body
416 :	monnier	121	val nle2 = F.LET([nlv], le2, body2)
417 :	monnier	164	in
418 :	monnier	189	click_branch();
419 :	monnier	184	loop m (wrap(F.BRANCH(po, vs, nle1, nle2))) cont
420 :	monnier	121	end
421 :			else
422 :			clet()
423 :			in case (lvs,body)
424 :			of ([lv],le as F.SWITCH(F.VAR v,_,_,NONE)) =>
425 :	monnier	190	cassoc(lv, v, le, fn x => x)
426 :	monnier	121	| ([lv],F.LET(lvs,le as F.SWITCH(F.VAR v,_,_,NONE),rest)) =>
427 :	monnier	184	cassoc(lv, v, le, fn le => F.LET(lvs,le,rest))
428 :	monnier	121	| _ => clet()
429 :			end
430 :	monnier	199	| _ => *) clet()
431 :	monnier	121	end
432 :	monnier	184
433 :	monnier	121	| F.FIX (fs,le) =>
434 :	monnier	189	let (* The actual function contraction *)
435 :	monnier	164	fun cfun (m,[]:F.fundec list,acc) = acc
436 :	monnier	184	| cfun (m,fdec as ({inline,cconv,known,isrec},f,args,body)::fs,acc) =
437 :	monnier	189	let val fi = C.get f
438 :			in if C.dead fi then cfun(m, fs, acc)
439 :			else if C.iusenb fi = C.usenb fi then
440 :			(* we need to be careful that undertake not be called
441 :			* recursively *)
442 :			(C.use NONE fi; undertake m f; cfun(m, fs, acc))
443 :			else
444 :	monnier	164	let (* val _ = say ("\nEntering "^(C.LVarString f)) *)
445 :	monnier	189	val saved_ic = inline_count()
446 :	monnier	164	(* make up the bindings for args inside the body *)
447 :	monnier	121	fun addnobind ((lv,lty),m) =
448 :			addbind(m, lv, Var(lv, SOME lty))
449 :			val nm = foldl addnobind m args
450 :			(* contract the body and create the resulting fundec *)
451 :	monnier	197	val nbody = cexp (S.add(f, ifs)) nm body #2
452 :	monnier	185	(* if inlining took place, the body might be completely
453 :			* changed (read: bigger), so we have to reset the
454 :			* `inline' bit *)
455 :	monnier	184	val nfk = {isrec=isrec, cconv=cconv,
456 :	monnier	189	known=known orelse not(C.escaping fi),
457 :			inline=if inline_count() = saved_ic
458 :			then inline
459 :			else F.IH_SAFE}
460 :	monnier	199	(* update the binding in the map. This step is
461 :	monnier	121	* not just a mere optimization but is necessary
462 :			* because if we don't do it and the function
463 :			* gets inlined afterwards, the counts will reflect the
464 :			* new contracted code while we'll be working on the
465 :			* the old uncontracted code *)
466 :	monnier	197	val nm = addbind(m, f, Fun(f, nbody, args, nfk))
467 :	monnier	121	in cfun(nm, fs, (nfk, f, args, nbody)::acc)
468 :	monnier	164	(* before say ("\nExiting "^(C.LVarString f)) *)
469 :	monnier	121	end
470 :	monnier	189	end
471 :	monnier	121
472 :			(* check for eta redex *)
473 :	monnier	199	fun ceta (fdec as (fk,f,args,F.APP(F.VAR g,vs)):F.fundec,
474 :			(m,fs,hs)) =
475 :			if List.length args = List.length vs andalso
476 :			OU.ListPair_all (fn (v,(lv,t)) =>
477 :			case v of F.VAR v => v = lv andalso lv <> g
478 :			| _ => false)
479 :			(vs, args)
480 :	monnier	121	then
481 :	monnier	199	let val svg = lookup m g
482 :	monnier	121	val g = case sval2val svg
483 :			of F.VAR g => g
484 :			| v => bugval("not a variable", v)
485 :			(* NOTE: we don't want to turn a known function into an
486 :			* escaping one. It's dangerous for optimisations based
487 :			* on known functions (elimination of dead args, f.ex)
488 :			* and could generate cases where call>use in collect *)
489 :	monnier	189	in if (C.escaping(C.get f)) andalso not(C.escaping(C.get g))
490 :			(* the default case could ensure the inline *)
491 :			then (m, fdec::fs, hs)
492 :			else let
493 :	monnier	121	(* if an earlier function h has been eta-reduced
494 :			* to f, we have to be careful to update its
495 :			* binding to not refer to f any more since f
496 :			* will disappear *)
497 :			val nm = foldl (fn (h,m) =>
498 :			if sval2val(lookup m h) = F.VAR f
499 :			then addbind(m, h, svg) else m)
500 :			m hs
501 :	monnier	164	in
502 :			(* I could almost reuse `substitute' but the
503 :			* unuse in substitute assumes the val is escaping *)
504 :	monnier	189	click_eta();
505 :	monnier	164	C.transfer(f, g);
506 :	monnier	187	unusecall m g;
507 :	monnier	186	(addbind(m, f, svg), fs, f::hs)
508 :	monnier	121	end
509 :			end
510 :	monnier	186	else (m, fdec::fs, hs)
511 :			| ceta (fdec,(m,fs,hs)) = (m,fdec::fs,hs)
512 :	monnier	121
513 :	monnier	184	(* add wrapper for various purposes *)
514 :			fun wrap (f as ({inline=F.IH_ALWAYS,...},_,_,_):F.fundec,fs) = f::fs
515 :			| wrap (f as (fk as {isrec,...},g,args,body):F.fundec,fs) =
516 :	monnier	189	let val gi = C.get g
517 :			fun dropargs filter =
518 :	monnier	184	let val (nfk,nfk') = OU.fk_wrap(fk, O.map #1 isrec)
519 :	monnier	164	val args' = filter args
520 :	monnier	163	val ng = cplv g
521 :			val nargs = map (fn (v,t) => (cplv v, t)) args
522 :	monnier	164	val nargs' = map #1 (filter nargs)
523 :			val appargs = (map F.VAR nargs')
524 :	monnier	184	val nf = (nfk, g, nargs, F.APP(F.VAR ng, appargs))
525 :	monnier	164	val nf' = (nfk', ng, args', body)
526 :	monnier	186
527 :			val ngi = C.new (SOME(map #1 args')) ng
528 :	monnier	184	in
529 :	monnier	189	C.ireset gi;
530 :			app (ignore o (C.new NONE) o #1) nargs;
531 :	monnier	186	C.use (SOME appargs) ngi;
532 :	monnier	189	app (C.use NONE o C.get) nargs';
533 :	monnier	184	nf'::nf::fs
534 :	monnier	163	end
535 :	monnier	190	in
536 :	monnier	189	(* Don't introduce wrappers for escaping-only functions.
537 :			* This is debatable since although wrappers are useless
538 :			* on escaping-only functions, some of the escaping uses
539 :			* might turn into calls in the course of fcontract, so
540 :			* by not introducing wrappers here, we avoid useless work
541 :			* but we also postpone useful work to later invocations. *)
542 :	monnier	190	if C.dead gi then fs else
543 :			let val used = map (used o #1) args
544 :			in if C.called gi then
545 :			(* if some args are not used, let's drop them *)
546 :			if not (List.all (fn x => x) used) then
547 :			(click_dropargs();
548 :			dropargs (fn xs => OU.filter(used, xs)))
549 :
550 :			(* eta-split: add a wrapper for escaping uses *)
551 :			else if C.escaping gi then
552 :			(* like dropargs but keeping all args *)
553 :			(click_etasplit(); dropargs (fn x => x))
554 :
555 :			else f::fs
556 :			else f::fs
557 :			end
558 :	monnier	184	end
559 :	monnier	163
560 :	monnier	184	(* add various wrappers *)
561 :			val fs = foldl wrap [] fs
562 :
563 :	monnier	121	(* register the new bindings (uncontracted for now) *)
564 :			val nm = foldl (fn (fdec as (fk,f,args,body),m) =>
565 :	monnier	197	addbind(m, f, Fun(f, body, args, fk)))
566 :	monnier	121	m fs
567 :			(* check for eta redexes *)
568 :	monnier	186	val (nm,fs,_) = foldl ceta (nm,[],[]) fs
569 :	monnier	121
570 :			(* move the inlinable functions to the end of the list *)
571 :			val (f1s,f2s) =
572 :	monnier	184	List.partition (fn ({inline=F.IH_ALWAYS,...},_,_,_) => true
573 :	monnier	121	| _ => false) fs
574 :			val fs = f2s @ f1s
575 :
576 :			(* contract the main body *)
577 :	monnier	184	val nle = loop nm le cont
578 :	monnier	121	(* contract the functions *)
579 :			val fs = cfun(nm, fs, [])
580 :			(* junk newly unused funs *)
581 :			val fs = List.filter (used o #2) fs
582 :			in
583 :	monnier	163	case fs
584 :			of [] => nle
585 :	monnier	184	| [f1 as ({isrec=NONE,...},_,_,_),f2] =>
586 :	monnier	186	(* gross hack: `wrap' might have added a second
587 :	monnier	163	* non-recursive function. we need to split them into
588 :	monnier	184	* 2 FIXes. This is _very_ ad-hoc *)
589 :	monnier	163	F.FIX([f2], F.FIX([f1], nle))
590 :			| _ => F.FIX(fs, nle)
591 :	monnier	121	end
592 :
593 :			| F.APP (f,vs) =>
594 :	monnier	199	let val nvs = map substval vs
595 :			val svf = val2sval m f
596 :			(* F.APP inlining (if any) *)
597 :			in case svf
598 :			of Fun(g,body,args,{inline,...}) =>
599 :			if (C.usenb(C.get g)) = 1 andalso not(S.member ifs g) then
600 :
601 :			(* simple inlining: we should copy the body and then
602 :			* kill the function, but instead we just move the body
603 :			* and kill only the function name.
604 :			* This inlining strategy looks inoffensive enough,
605 :			* but still requires some care: see comments at the
606 :			* begining of this file and in cfun *)
607 :			(click_simpleinline();
608 :			ignore(C.unuse true (C.get g));
609 :			loop m (F.LET(map #1 args, F.RET vs, body)) cont)
610 :
611 :			(* aggressive (but safe) inlining. We allow pretty much
612 :			* any inlinling, but we detect and reject inlining
613 :			* recursively which would else lead to infinite loop *)
614 :			(* unrolling is not as straightforward as it seems:
615 :			* if you inline the function you're currently
616 :			* fcontracting, you're asking for trouble: there is a
617 :			* hidden assumption in the counting that the old code
618 :			* will be replaced by the new code (and is hence dead).
619 :			* If the function to be unrolled has the only call to
620 :			* function f, then f might get simpleinlined before
621 :			* unrolling, which means that unrolling will introduce
622 :			* a second occurence of the `only call' but at that point
623 :			* f has already been killed. *)
624 :			else if (inline = F.IH_ALWAYS andalso not(S.member ifs g)) then
625 :			let val nle =
626 :			C.copylexp M.empty (F.LET(map #1 args, F.RET vs, body))
627 :			in
628 :			click_copyinline();
629 :			(app (unuseval m) vs);
630 :			unusecall m g;
631 :			cexp (S.add(g, ifs)) m nle cont
632 :			end
633 :			else cont(m,F.APP(sval2val svf, nvs))
634 :			| sv => cont(m,F.APP(sval2val svf, nvs))
635 :	monnier	121	end
636 :
637 :			| F.TFN ((f,args,body),le) =>
638 :	monnier	189	let val fi = C.get f
639 :			in if C.dead fi then (click_deadlexp(); loop m le cont) else
640 :	monnier	197	let val nbody = cexp ifs m body #2
641 :			val nm = addbind(m, f, TFun(f, nbody, args))
642 :	monnier	186	val nle = loop nm le cont
643 :			in
644 :	monnier	189	if C.dead fi then nle else F.TFN((f, args, nbody), nle)
645 :	monnier	186	end
646 :	monnier	189	end
647 :	monnier	121
648 :	monnier	184	| F.TAPP(f,tycs) =>
649 :	monnier	189	(* (case val2sval m f
650 :			of TFun(g,body,args,od) =>
651 :			if d = od andalso C.usenb(C.get g) = 1 then
652 :			let val (_,_,_,le) =
653 :			({inline=false,isrec=NONE,known=false,cconv=F.CC_FCT},
654 :			LV.mkLvar(),[],
655 :			F.TFN((g,args,body),TAPP(g,tycs)))
656 :			in
657 :			inlineWitness := true;
658 :			ignore(C.unuse true (C.get g));
659 :			end *)
660 :	monnier	199	cont(m, F.TAPP(substval f, tycs))
661 :	monnier	121
662 :			| F.SWITCH (v,ac,arms,def) =>
663 :	monnier	199	(case val2sval m v
664 :	monnier	189	of sv as Con (lvc,svc,dc1,tycs1) =>
665 :	monnier	187	let fun killle le = C.unuselexp (undertake m) le
666 :	monnier	159	fun kill lv le =
667 :	monnier	187	C.unuselexp (undertake (addbind(m,lv,Var(lv,NONE)))) le
668 :	monnier	159	fun killarm (F.DATAcon(_,_,lv),le) = kill lv le
669 :			| killarm _ = buglexp("bad arm in switch(con)", le)
670 :
671 :			fun carm ((F.DATAcon(dc2,tycs2,lv),le)::tl) =
672 :	monnier	185	(* sometimes lty1 <> lty2 :-( so this doesn't work:
673 :			* FU.dcon_eq(dc1, dc2) andalso tycs_eq(tycs1,tycs2) *)
674 :			if #2 dc1 = #2 (cdcon dc2) then
675 :	monnier	159	(map killarm tl; (* kill the rest *)
676 :	monnier	185	O.map killle def; (* and the default case *)
677 :	monnier	189	loop (substitute(m, lv, svc, F.VAR lvc))
678 :	monnier	184	le cont)
679 :	monnier	159	else
680 :			(* kill this arm and continue with the rest *)
681 :			(kill lv le; carm tl)
682 :	monnier	185	| carm [] = loop m (O.valOf def) cont
683 :	monnier	121	| carm _ = buglexp("unexpected arm in switch(con,...)", le)
684 :	monnier	189	in click_switch(); carm arms
685 :	monnier	121	end
686 :
687 :	monnier	185	| sv as Val v =>
688 :	monnier	187	let fun kill le = C.unuselexp (undertake m) le
689 :	monnier	159	fun carm ((con,le)::tl) =
690 :			if eqConV(con, v) then
691 :	monnier	184	(map (kill o #2) tl;
692 :	monnier	185	O.map kill def;
693 :	monnier	184	loop m le cont)
694 :	monnier	159	else (kill le; carm tl)
695 :	monnier	185	| carm [] = loop m (O.valOf def) cont
696 :	monnier	189	in click_switch(); carm arms
697 :	monnier	121	end
698 :	monnier	185
699 :			| sv as (Var{1=lvc,...} | Select{1=lvc,...} | Decon{1=lvc, ...}
700 :			| (* will probably never happen *) Record{1=lvc,...}) =>
701 :			(case (arms,def)
702 :			of ([(F.DATAcon(dc,tycs,lv),le)],NONE) =>
703 :			(* this is a mere DECON, so we can push the let binding
704 :			* (hidden in cont) inside and maybe even drop the DECON *)
705 :			let val ndc = cdcon dc
706 :	monnier	189	val slv = Decon(lv, sv, ndc, tycs)
707 :			val nm = addbind(m, lv, slv)
708 :	monnier	185	(* see below *)
709 :	monnier	199	(* val nm = addbind(nm, lvc, Con(lvc, slv, ndc, tycs)) *)
710 :	monnier	185	val nle = loop nm le cont
711 :			val nv = sval2val sv
712 :			in
713 :			if used lv then
714 :			F.SWITCH(nv,ac,[(F.DATAcon(ndc,tycs,lv),nle)],NONE)
715 :	monnier	187	else (unuseval m nv; nle)
716 :	monnier	185	end
717 :			| (([(_,le)],NONE) | ([],SOME le)) =>
718 :			(* This should never happen, but we can optimize it away *)
719 :	monnier	189	(unuseval m (sval2val sv); loop m le cont)
720 :	monnier	185	| _ =>
721 :			let fun carm (F.DATAcon(dc,tycs,lv),le) =
722 :			let val ndc = cdcon dc
723 :	monnier	189	val slv = Decon(lv, sv, ndc, tycs)
724 :			val nm = addbind(m, lv, slv)
725 :	monnier	185	(* we can rebind lv to a more precise value
726 :			* !!BEWARE!! This rebinding is misleading:
727 :			* - it gives the impression that `lvc' is built
728 :			* from`lv' although the reverse is true:
729 :			* if `lvc' is undertaken, `lv's count should
730 :			* *not* be updated!
731 :			* Luckily, `lvc' will not become dead while
732 :			* rebound to Con(lv) because it's used by the
733 :			* SWITCH. All in all, it works fine, but it's
734 :			* not as straightforward as it seems.
735 :			* - it seems to be a good idea, but it can hide
736 :			* other opt-opportunities since it hides the
737 :			* previous binding. *)
738 :	monnier	199	(* val nm = addbind(nm, lvc, Con(lvc,slv,ndc,tycs)) *)
739 :	monnier	185	in (F.DATAcon(ndc, tycs, lv), loop nm le #2)
740 :			end
741 :			| carm (con,le) = (con, loop m le #2)
742 :			val narms = map carm arms
743 :			val ndef = Option.map (fn le => loop m le #2) def
744 :			in cont(m, F.SWITCH(sval2val sv, ac, narms, ndef))
745 :			end)
746 :
747 :	monnier	121	| sv as (Fun _ | TFun _) =>
748 :			bugval("unexpected switch arg", sval2val sv))
749 :
750 :	monnier	159	| F.CON (dc1,tycs1,v,lv,le) =>
751 :	monnier	189	let val lvi = C.get lv
752 :			in if C.dead lvi then (click_deadval(); loop m le cont) else
753 :	monnier	186	let val ndc = cdcon dc1
754 :			fun ccon sv =
755 :	monnier	189	let val nm = addbind(m, lv, Con(lv, sv, ndc, tycs1))
756 :	monnier	186	val nle = loop nm le cont
757 :	monnier	189	in if C.dead lvi then nle
758 :			else F.CON(ndc, tycs1, sval2val sv, lv, nle)
759 :	monnier	186	end
760 :	monnier	199	in case val2sval m v
761 :	monnier	189	of sv as (Decon (lvd,sv',dc2,tycs2)) =>
762 :	monnier	186	if FU.dcon_eq(dc1, dc2) andalso tycs_eq(tycs1,tycs2) then
763 :	monnier	189	(click_con();
764 :			loop (substitute(m, lv, sv', F.VAR lvd)) le cont)
765 :	monnier	186	else ccon sv
766 :			| sv => ccon sv
767 :			end
768 :	monnier	189	end
769 :	monnier	121
770 :			| F.RECORD (rk,vs,lv,le) =>
771 :	monnier	164	(* g: check whether the record already exists *)
772 :	monnier	189	let val lvi = C.get lv
773 :			in if C.dead lvi then (click_deadval(); loop m le cont) else
774 :			let fun g (Select(_,sv,0)::ss) =
775 :			let fun g' (n,Select(_,sv',i)::ss) =
776 :			if n = i andalso (sval2val sv) = (sval2val sv')
777 :			then g'(n+1,ss) else NONE
778 :			| g' (n,[]) =
779 :			(case sval2lty sv
780 :			of SOME lty =>
781 :			let val ltd = case rk
782 :			of F.RK_STRUCT => LT.ltd_str
783 :			| F.RK_TUPLE _ => LT.ltd_tuple
784 :			| _ => buglexp("bogus rk",le)
785 :			in if length(ltd lty) = n
786 :			then SOME sv else NONE
787 :			end
788 :			| _ => (click_lacktype(); NONE)) (* sad *)
789 :			| g' _ = NONE
790 :			in g'(1,ss)
791 :			end
792 :	monnier	186	| g _ = NONE
793 :	monnier	199	val svs = map (val2sval m) vs
794 :	monnier	189	in case g svs
795 :			of SOME sv => (click_record();
796 :			loop (substitute(m, lv, sv, F.INT 0)) le cont
797 :			before app (unuseval m) vs)
798 :			| _ =>
799 :			let val nm = addbind(m, lv, Record(lv, svs))
800 :	monnier	186	val nle = loop nm le cont
801 :	monnier	189	in if C.dead lvi then nle
802 :			else F.RECORD(rk, map sval2val svs, lv, nle)
803 :	monnier	186	end
804 :			end
805 :	monnier	189	end
806 :	monnier	121
807 :			| F.SELECT (v,i,lv,le) =>
808 :	monnier	189	let val lvi = C.get lv
809 :			in if C.dead lvi then (click_deadval(); loop m le cont) else
810 :	monnier	199	(case val2sval m v
811 :	monnier	189	of Record (lvr,svs) =>
812 :			let val sv = List.nth(svs, i)
813 :			in click_select();
814 :			loop (substitute(m, lv, sv, F.VAR lvr)) le cont
815 :	monnier	186	end
816 :			| sv =>
817 :	monnier	189	let val nm = addbind (m, lv, Select(lv, sv, i))
818 :	monnier	186	val nle = loop nm le cont
819 :	monnier	189	in if C.dead lvi then nle
820 :			else F.SELECT(sval2val sv, i, lv, nle)
821 :	monnier	186	end)
822 :	monnier	189	end
823 :	monnier	121
824 :	monnier	184	| F.RAISE (v,ltys) =>
825 :	monnier	199	cont(m, F.RAISE(substval v, ltys))
826 :	monnier	121
827 :	monnier	184	| F.HANDLE (le,v) =>
828 :	monnier	199	cont(m, F.HANDLE(loop m le #2, substval v))
829 :	monnier	121
830 :			| F.BRANCH (po,vs,le1,le2) =>
831 :	monnier	199	let val nvs = map substval vs
832 :	monnier	121	val npo = cpo po
833 :	monnier	184	val nle1 = loop m le1 #2
834 :			val nle2 = loop m le2 #2
835 :			in cont(m, F.BRANCH(npo, nvs, nle1, nle2))
836 :	monnier	121	end
837 :
838 :			| F.PRIMOP (po,vs,lv,le) =>
839 :	monnier	189	let val lvi = C.get lv
840 :			val pure = not(impurePO po)
841 :			in if pure andalso C.dead lvi then (click_deadval();loop m le cont) else
842 :	monnier	199	let val nvs = map substval vs
843 :	monnier	186	val npo = cpo po
844 :			val nm = addbind(m, lv, Var(lv,NONE))
845 :			val nle = loop nm le cont
846 :			in
847 :	monnier	189	if pure andalso C.dead lvi then nle
848 :			else F.PRIMOP(npo, nvs, lv, nle)
849 :	monnier	186	end
850 :	monnier	121	end
851 :			end
852 :
853 :	monnier	185	in
854 :			(* C.collect fdec; *)
855 :	monnier	197	case cexp S.empty
856 :	monnier	185	M.empty (F.FIX([fdec], F.RET[F.VAR f])) #2
857 :			of F.FIX([fdec], F.RET[F.VAR f]) => fdec
858 :			| fdec => bug "invalid return fundec"
859 :			end
860 :	monnier	121
861 :			end
862 :			end

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