2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1996
4 Taken quite directly from the Peyton Jones/Lester paper.
7 #include "HsVersions.h"
12 -- cheap and cheerful variant...
15 freeVarsOf, freeTyVarsOf,
16 FVCoreExpr(..), FVCoreBinding(..),
18 CoreExprWithFVs(..), -- For the above functions
19 AnnCoreExpr(..), -- Dito
20 FVInfo(..), LeakInfo(..)
25 import AnnCoreSyn -- output
28 import Id ( idType, getIdArity, isBottomingId,
29 emptyIdSet, unitIdSet, mkIdSet,
30 elementOfIdSet, minusIdSet, unionManyIdSets,
33 import IdInfo ( arityMaybe )
34 import PrimOp ( PrimOp(..) )
35 import Type ( tyVarsOfType )
36 import TyVar ( emptyTyVarSet, unitTyVarSet, minusTyVarSet,
40 import UniqSet ( unionUniqSets )
41 import Usage ( UVar(..) )
42 import Util ( panic, assertPanic )
45 %************************************************************************
47 \section[freevars-everywhere]{Attaching free variables to every sub-expression
49 %************************************************************************
51 The free variable pass annotates every node in the expression with its
52 NON-GLOBAL free variables and type variables.
54 The ``free type variables'' are defined to be those which are mentioned
55 in type applications, {\em not} ones which lie buried in the types of Ids.
57 *** ALAS: we *do* need to collect tyvars from lambda-bound ids. ***
58 I've half-convinced myself we don't for case- and letrec bound ids
59 but I might be wrong. (SLPJ, date unknown)
62 type CoreExprWithFVs = AnnCoreExpr Id Id TyVar UVar FVInfo
64 type TyVarCands = TyVarSet -- for when we carry around lists of
65 type IdCands = IdSet -- "candidate" TyVars/Ids.
66 noTyVarCands = emptyTyVarSet
67 noIdCands = emptyIdSet
70 = FVInfo IdSet -- Free ids
71 TyVarSet -- Free tyvars
74 noFreeIds = emptyIdSet
75 noFreeTyVars = emptyTyVarSet
76 noFreeAnything = (noFreeIds, noFreeTyVars)
77 aFreeId i = unitIdSet i
78 aFreeTyVar t = unitTyVarSet t
79 is_among = elementOfIdSet
80 munge_id_ty i = tyVarsOfType (idType i)
81 combine = unionUniqSets -- used both for {Id,TyVar}Sets
83 combineFVInfo (FVInfo fvs1 tfvs1 leak1) (FVInfo fvs2 tfvs2 leak2)
84 = FVInfo (fvs1 `combine` fvs2)
85 (tfvs1 `combine` tfvs2)
86 (leak1 `orLeak` leak2)
89 Leak-free-ness is based only on the value, not the type. In
90 particular, nested collections of constructors are guaranteed leak
91 free. Function applications are not, except for PAPs.
93 Applications of error gets (LeakFree bigArity) -- a hack!
98 | LeakFree Int -- Leak free, and guarantees to absorb this # of
99 -- args before becoming leaky.
101 lEAK_FREE_0 = LeakFree 0
102 lEAK_FREE_BIG = LeakFree bigArity
104 bigArity = 1000::Int -- NB: arbitrary
106 orLeak :: LeakInfo -> LeakInfo -> LeakInfo
107 orLeak MightLeak _ = MightLeak
108 orLeak _ MightLeak = MightLeak
109 orLeak (LeakFree n) (LeakFree m) = LeakFree (n `min` m)
112 Main public interface:
114 freeVars :: CoreExpr -> CoreExprWithFVs
116 freeVars expr = fvExpr noIdCands noTyVarCands expr
119 %************************************************************************
121 \subsection{Free variables (and types)}
123 %************************************************************************
125 We do the free-variable stuff by passing around ``candidates lists''
126 of @Ids@ and @TyVars@ that may be considered free. This is useful,
127 e.g., to avoid considering top-level binders as free variables---don't
128 put them on the candidates list.
132 fvExpr :: IdCands -- In-scope Ids
133 -> TyVarCands -- In-scope tyvars
137 fvExpr id_cands tyvar_cands (Var v)
138 = (FVInfo (if (v `is_among` id_cands)
146 | isBottomingId v = lEAK_FREE_BIG -- Hack
147 | otherwise = case arityMaybe (getIdArity v) of
148 Nothing -> lEAK_FREE_0
149 Just arity -> LeakFree arity
151 fvExpr id_cands tyvar_cands (Lit k)
152 = (FVInfo noFreeIds noFreeTyVars lEAK_FREE_0, AnnLit k)
154 fvExpr id_cands tyvar_cands (Con c args)
155 = (FVInfo args_fvs tfvs lEAK_FREE_0, AnnCon c args)
157 (args_fvs, tfvs) = freeArgs id_cands tyvar_cands args
159 fvExpr id_cands tyvar_cands (Prim op args)
160 = (FVInfo args_fvs tfvs lEAK_FREE_0, AnnPrim op args)
162 (args_fvs, tfvs) = freeArgs id_cands tyvar_cands args_to_use{-NB-}
165 CCallOp _ _ _ _ res_ty -> TyArg res_ty : args
168 -- this Lam stuff could probably be improved by rewriting (WDP 96/03)
170 fvExpr id_cands tyvar_cands (Lam (UsageBinder uvar) body)
171 = panic "fvExpr:Lam UsageBinder"
173 fvExpr id_cands tyvar_cands (Lam b@(ValBinder binder) body)
174 = (FVInfo (freeVarsOf body2 `minusIdSet` unitIdSet binder)
175 (freeTyVarsOf body2 `combine` munge_id_ty binder)
179 -- We need to collect free tyvars from the binders
180 body2 = fvExpr (unitIdSet binder `combine` id_cands) tyvar_cands body
182 leakiness = case leakinessOf body2 of
183 MightLeak -> LeakFree 1
184 LeakFree n -> LeakFree (n + 1)
186 fvExpr id_cands tyvar_cands (Lam b@(TyBinder tyvar) body)
187 = (FVInfo (freeVarsOf body2)
188 (freeTyVarsOf body2 `minusTyVarSet` aFreeTyVar tyvar)
192 body2 = fvExpr id_cands (aFreeTyVar tyvar `combine` tyvar_cands) body
194 -- ditto on rewriting this App stuff (WDP 96/03)
196 fvExpr id_cands tyvar_cands (App fun arg)
197 = (FVInfo (freeVarsOf fun2 `combine` fvs_arg)
198 (freeTyVarsOf fun2 `combine` tfvs_arg)
202 fun2 = fvExpr id_cands tyvar_cands fun
203 fun2_leakiness = leakinessOf fun2
205 (fvs_arg, tfvs_arg) = freeArgs id_cands tyvar_cands [arg]
207 leakiness = if (notValArg arg) then
210 case fun2_leakiness of
211 LeakFree n | n>1 -> LeakFree (n-1) -- Note > not >=
214 fvExpr id_cands tyvar_cands (Case expr alts)
215 = (combineFVInfo expr_fvinfo alts_fvinfo,
218 expr2@(expr_fvinfo,_) = fvExpr id_cands tyvar_cands expr
219 (alts_fvinfo, alts') = annotate_alts alts
221 annotate_alts (AlgAlts alts deflt)
222 = (fvinfo, AnnAlgAlts alts' deflt')
224 (alts_fvinfo_s, alts') = unzip (map ann_boxed_alt alts)
225 (deflt_fvinfo, deflt') = annotate_default deflt
226 fvinfo = foldr combineFVInfo deflt_fvinfo alts_fvinfo_s
228 ann_boxed_alt (con, params, rhs)
229 = (FVInfo (freeVarsOf rhs' `minusIdSet` mkIdSet params)
230 (freeTyVarsOf rhs' `combine` param_ftvs)
234 rhs' = fvExpr (mkIdSet params `combine` id_cands) tyvar_cands rhs
235 param_ftvs = foldr (combine . munge_id_ty) noFreeTyVars params
236 -- We need to collect free tyvars from the binders
238 annotate_alts (PrimAlts alts deflt)
239 = (fvinfo, AnnPrimAlts alts' deflt')
241 (alts_fvinfo_s, alts') = unzip (map ann_unboxed_alt alts)
242 (deflt_fvinfo, deflt') = annotate_default deflt
243 fvinfo = foldr combineFVInfo deflt_fvinfo alts_fvinfo_s
245 ann_unboxed_alt (lit, rhs) = (rhs_info, (lit, rhs'))
247 rhs'@(rhs_info,_) = fvExpr id_cands tyvar_cands rhs
249 annotate_default NoDefault = (FVInfo noFreeIds noFreeTyVars lEAK_FREE_BIG,
252 annotate_default (BindDefault binder rhs)
253 = (FVInfo (freeVarsOf rhs' `minusIdSet` aFreeId binder)
254 (freeTyVarsOf rhs' `combine` binder_ftvs)
256 AnnBindDefault binder rhs')
258 rhs' = fvExpr (aFreeId binder `combine` id_cands) tyvar_cands rhs
259 binder_ftvs = munge_id_ty binder
260 -- We need to collect free tyvars from the binder
262 fvExpr id_cands tyvar_cands (Let (NonRec binder rhs) body)
263 = (FVInfo (freeVarsOf rhs' `combine` body_fvs)
264 (freeTyVarsOf rhs' `combine` freeTyVarsOf body2 `combine` binder_ftvs)
265 (leakinessOf rhs' `orLeak` leakinessOf body2),
266 AnnLet (AnnNonRec binder rhs') body2)
268 rhs' = fvExpr id_cands tyvar_cands rhs
269 body2 = fvExpr (aFreeId binder `combine` id_cands) tyvar_cands body
270 body_fvs = freeVarsOf body2 `minusIdSet` aFreeId binder
271 binder_ftvs = munge_id_ty binder
272 -- We need to collect free tyvars from the binder
274 fvExpr id_cands tyvar_cands (Let (Rec binds) body)
275 = (FVInfo (binds_fvs `combine` body_fvs)
276 (rhss_tfvs `combine` freeTyVarsOf body2 `combine` binders_ftvs)
277 (leakiness_of_rhss `orLeak` leakinessOf body2),
278 AnnLet (AnnRec (binders `zip` rhss')) body2)
280 (binders, rhss) = unzip binds
281 new_id_cands = binders_set `combine` id_cands
282 binders_set = mkIdSet binders
283 rhss' = map (fvExpr new_id_cands tyvar_cands) rhss
285 FVInfo rhss_fvs rhss_tfvs leakiness_of_rhss
286 = foldr1 combineFVInfo [info | (info,_) <- rhss']
288 binds_fvs = rhss_fvs `minusIdSet` binders_set
289 body2 = fvExpr new_id_cands tyvar_cands body
290 body_fvs = freeVarsOf body2 `minusIdSet` binders_set
291 binders_ftvs = foldr (combine . munge_id_ty) noFreeTyVars binders
292 -- We need to collect free tyvars from the binders
294 fvExpr id_cands tyvar_cands (SCC label expr)
295 = (fvinfo, AnnSCC label expr2)
297 expr2@(fvinfo,_) = fvExpr id_cands tyvar_cands expr
301 freeArgs :: IdCands -> TyVarCands
305 freeArgs icands tcands [] = noFreeAnything
306 freeArgs icands tcands (arg:args)
307 -- this code is written this funny way only for "efficiency" purposes
309 free_first_arg@(arg_fvs, tfvs) = free_arg arg
314 case (freeArgs icands tcands args) of { (irest, trest) ->
315 (arg_fvs `combine` irest, tfvs `combine` trest) }
317 free_arg (LitArg _) = noFreeAnything
318 free_arg (UsageArg _) = noFreeAnything
319 free_arg (TyArg ty) = (noFreeIds, freeTy tcands ty)
321 | v `is_among` icands = (aFreeId v, noFreeTyVars)
322 | otherwise = noFreeAnything
325 freeTy :: TyVarCands -> Type -> TyVarSet
327 freeTy cands ty = tyVarsOfType ty `intersectTyVarSets` cands
329 freeVarsOf :: CoreExprWithFVs -> IdSet
330 freeVarsOf (FVInfo free_vars _ _, _) = free_vars
332 freeTyVarsOf :: CoreExprWithFVs -> TyVarSet
333 freeTyVarsOf (FVInfo _ free_tyvars _, _) = free_tyvars
335 leakinessOf :: CoreExprWithFVs -> LeakInfo
336 leakinessOf (FVInfo _ _ leakiness, _) = leakiness
340 %************************************************************************
342 \section[freevars-binders]{Attaching free variables to binders
344 %************************************************************************
347 Here's an variant of the free-variable pass, which pins free-variable
348 information on {\em binders} rather than every single jolly
352 The free vars attached to a lambda binder are the free vars of the
353 whole lambda abstraction. If there are multiple binders, they are
354 each given the same free-var set.
356 The free vars attached to a let(rec) binder are the free vars of the
357 rhs of the binding. In the case of letrecs, this set excludes the
360 The free vars attached to a case alternative binder are the free
361 vars of the alternative, excluding the alternative's binders.
364 There's a predicate carried in which tells what is a free-var
365 candidate. It is passed the Id and a set of in-scope Ids.
367 (Global) constructors used on the rhs in a Con are also treated as
368 potential free-var candidates (though they will not be recorded in the
369 in-scope set). The predicate must decide if they are to be recorded as
372 As it happens this is only ever used by the Specialiser!
375 type FVCoreBinder = (Id, IdSet)
376 type FVCoreExpr = GenCoreExpr FVCoreBinder Id TyVar UVar
377 type FVCoreBinding = GenCoreBinding FVCoreBinder Id TyVar UVar
379 type InterestingIdFun
380 = IdSet -- Non-top-level in-scope variables
381 -> Id -- The Id being looked at
382 -> Bool -- True <=> interesting
386 addExprFVs :: InterestingIdFun -- "Interesting id" predicate
387 -> IdSet -- In scope ids
389 -> (FVCoreExpr, IdSet)
391 addExprFVs fv_cand in_scope (Var v)
392 = (Var v, if fv_cand in_scope v
396 addExprFVs fv_cand in_scope (Lit lit) = (Lit lit, noFreeIds)
398 addExprFVs fv_cand in_scope (Con con args)
400 if fv_cand in_scope con
402 else noFreeIds `combine` fvsOfArgs fv_cand in_scope args)
404 addExprFVs fv_cand in_scope (Prim op args)
405 = (Prim op args, fvsOfArgs fv_cand in_scope args)
407 addExprFVs fv_cand in_scope (Lam binder body)
408 = (Lam new_binder new_body, lam_fvs)
410 (new_binder, binder_set)
412 TyBinder t -> (TyBinder t, emptyIdSet)
413 UsageBinder u -> (UsageBinder u, emptyIdSet)
414 ValBinder b -> (ValBinder (b, lam_fvs),
417 new_in_scope = in_scope `combine` binder_set
418 (new_body, body_fvs) = addExprFVs fv_cand new_in_scope body
419 lam_fvs = body_fvs `minusIdSet` binder_set
421 addExprFVs fv_cand in_scope (App fun arg)
422 = (App fun2 arg, fun_fvs `combine` fvsOfArgs fv_cand in_scope [arg])
424 (fun2, fun_fvs) = addExprFVs fv_cand in_scope fun
426 addExprFVs fv_cand in_scope (Case scrut alts)
427 = (Case scrut' alts', scrut_fvs `combine` alts_fvs)
429 (scrut', scrut_fvs) = addExprFVs fv_cand in_scope scrut
433 AlgAlts alg_alts deflt -> (AlgAlts alg_alts' deflt', fvs)
435 (alg_alts', alt_fvs) = unzip (map do_alg_alt alg_alts)
436 (deflt', deflt_fvs) = do_deflt deflt
437 fvs = unionManyIdSets (deflt_fvs : alt_fvs)
439 PrimAlts prim_alts deflt -> (PrimAlts prim_alts' deflt', fvs)
441 (prim_alts', alt_fvs) = unzip (map do_prim_alt prim_alts)
442 (deflt', deflt_fvs) = do_deflt deflt
443 fvs = unionManyIdSets (deflt_fvs : alt_fvs)
445 do_alg_alt :: (Id, [Id], CoreExpr)
446 -> ((Id, [FVCoreBinder], FVCoreExpr), IdSet)
448 do_alg_alt (con, args, rhs) = ((con, args `zip` (repeat fvs), rhs'), fvs)
450 new_in_scope = in_scope `combine` arg_set
451 (rhs', rhs_fvs) = addExprFVs fv_cand new_in_scope rhs
452 fvs = rhs_fvs `minusIdSet` arg_set
453 arg_set = mkIdSet args
455 do_prim_alt (lit, rhs) = ((lit, rhs'), rhs_fvs)
457 (rhs', rhs_fvs) = addExprFVs fv_cand in_scope rhs
459 do_deflt NoDefault = (NoDefault, noFreeIds)
460 do_deflt (BindDefault var rhs)
461 = (BindDefault (var,fvs) rhs', fvs)
463 new_in_scope = in_scope `combine` var_set
464 (rhs', rhs_fvs) = addExprFVs fv_cand new_in_scope rhs
465 fvs = rhs_fvs `minusIdSet` var_set
466 var_set = aFreeId var
468 addExprFVs fv_cand in_scope (Let binds body)
469 = (Let binds' body2, fvs_binds `combine` (fvs_body `minusIdSet` binder_set))
471 (binds', fvs_binds, new_in_scope, binder_set)
472 = addBindingFVs fv_cand in_scope binds
474 (body2, fvs_body) = addExprFVs fv_cand new_in_scope body
476 addExprFVs fv_cand in_scope (SCC label expr)
477 = (SCC label expr2, expr_fvs)
479 (expr2, expr_fvs) = addExprFVs fv_cand in_scope expr
484 :: InterestingIdFun -- "Interesting id" predicate
485 -> IdSet -- In scope ids
488 IdSet, -- Free vars of binding group
489 IdSet, -- Augmented in-scope Ids
490 IdSet) -- Set of Ids bound by this binding
492 addBindingFVs fv_cand in_scope (NonRec binder rhs)
493 = (NonRec binder' rhs', fvs, new_in_scope, binder_set)
495 ((binder', rhs'), fvs) = do_pair fv_cand in_scope binder_set (binder, rhs)
496 new_in_scope = in_scope `combine` binder_set
497 binder_set = aFreeId binder
499 addBindingFVs fv_cand in_scope (Rec pairs)
500 = (Rec pairs', unionManyIdSets fvs_s, new_in_scope, binder_set)
502 binders = [binder | (binder,_) <- pairs]
503 binder_set = mkIdSet binders
504 new_in_scope = in_scope `combine` binder_set
505 (pairs', fvs_s) = unzip (map (do_pair fv_cand new_in_scope binder_set) pairs)
510 :: InterestingIdFun -- "Interesting id" predicate
515 addTopBindsFVs fv_cand [] = ([], noFreeIds)
516 addTopBindsFVs fv_cand (b:bs)
518 (b', fvs_b, _, _) = addBindingFVs fv_cand noFreeIds b
519 (bs', fvs_bs) = addTopBindsFVs fv_cand bs
521 (b' : bs', fvs_b `combine` fvs_bs)
525 fvsOfArgs :: InterestingIdFun -- "Interesting id" predicate
526 -> IdSet -- In scope ids
530 fvsOfArgs _ _ [] = noFreeIds
532 fvsOfArgs fv_cand in_scope [VarArg v] -- this is only a short-cut...
533 = if (fv_cand in_scope v) then aFreeId v else noFreeIds
534 fvsOfArgs _ _ [ _ ] = noFreeIds
536 fvsOfArgs fv_cand in_scope args
537 = mkIdSet [ v | (VarArg v) <- args, fv_cand in_scope v ]
538 -- all other types of args are uninteresting here...
541 do_pair :: InterestingIdFun -- "Interesting id" predicate
542 -> IdSet -- In scope ids
545 -> ((FVCoreBinder, FVCoreExpr), IdSet)
547 do_pair fv_cand in_scope binder_set (binder,rhs)
548 = (((binder, fvs), rhs'), fvs)
550 (rhs', rhs_fvs) = addExprFVs fv_cand in_scope rhs
551 fvs = rhs_fvs `minusIdSet` binder_set