2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1996
6 We attach binding levels to Core bindings, in preparation for floating
9 We also let-ify many applications (notably case scrutinees), so they
10 will have a fighting chance of being floated sensible.
13 #include "HsVersions.h"
20 incMinorLvl, ltMajLvl, ltLvl, isTopLvl
21 -- not exported: , incMajorLvl, isTopMajLvl, unTopify
29 import CoreUtils ( coreExprType, manifestlyWHNF, manifestlyBottom )
30 import FreeVars -- all of it
31 import Id ( idType, mkSysLocal, toplevelishId,
32 nullIdEnv, addOneToIdEnv, growIdEnvList,
33 unionManyIdSets, minusIdSet, mkIdSet,
35 lookupIdEnv, IdEnv(..)
37 import Pretty ( ppStr, ppBesides, ppChar, ppInt )
38 import SrcLoc ( mkUnknownSrcLoc )
39 import Type ( isPrimType, mkTyVarTys, mkForAllTys )
40 import TyVar ( nullTyVarEnv, addOneToTyVarEnv,
41 growTyVarEnvList, lookupTyVarEnv,
46 import UniqSupply ( thenUs, returnUs, mapUs, mapAndUnzipUs,
47 mapAndUnzip3Us, getUnique, UniqSM(..)
49 import Usage ( UVar(..) )
50 import Util ( mapAccumL, zipWithEqual, zipEqual, panic, assertPanic )
52 isLeakFreeType x y = False -- safe option; ToDo
55 %************************************************************************
57 \subsection{Level numbers}
59 %************************************************************************
63 = Top -- Means *really* the top level.
64 | Level Int -- Level number of enclosing lambdas
65 Int -- Number of big-lambda and/or case expressions between
66 -- here and the nearest enclosing lambda
69 The {\em level number} on a (type-)lambda-bound variable is the
70 nesting depth of the (type-)lambda which binds it. On an expression,
71 it's the maximum level number of its free (type-)variables. On a
72 let(rec)-bound variable, it's the level of its RHS. On a case-bound
73 variable, it's the number of enclosing lambdas.
75 Top-level variables: level~0. Those bound on the RHS of a top-level
76 definition but ``before'' a lambda; e.g., the \tr{x} in (levels shown
79 a_0 = let b_? = ... in
80 x_1 = ... b ... in ...
83 Level 0 0 will make something get floated to a top-level "equals",
84 @Top@ makes it go right to the top.
86 The main function @lvlExpr@ carries a ``context level'' (@ctxt_lvl@).
87 That's meant to be the level number of the enclosing binder in the
88 final (floated) program. If the level number of a sub-expression is
89 less than that of the context, then it might be worth let-binding the
90 sub-expression so that it will indeed float. This context level starts
91 at @Level 0 0@; it is never @Top@.
94 type LevelledExpr = GenCoreExpr (Id, Level) Id TyVar UVar
95 type LevelledArg = GenCoreArg Id TyVar UVar
96 type LevelledBind = GenCoreBinding (Id, Level) Id TyVar UVar
98 type LevelEnvs = (IdEnv Level, -- bind Ids to levels
99 TyVarEnv Level) -- bind type variables to levels
103 incMajorLvl :: Level -> Level
104 incMajorLvl Top = Level 1 0
105 incMajorLvl (Level major minor) = Level (major+1) 0
107 incMinorLvl :: Level -> Level
108 incMinorLvl Top = Level 0 1
109 incMinorLvl (Level major minor) = Level major (minor+1)
111 maxLvl :: Level -> Level -> Level
114 maxLvl l1@(Level maj1 min1) l2@(Level maj2 min2)
115 | (maj1 > maj2) || (maj1 == maj2 && min1 > min2) = l1
118 ltLvl :: Level -> Level -> Bool
120 ltLvl Top (Level _ _) = True
121 ltLvl (Level maj1 min1) (Level maj2 min2)
122 = (maj1 < maj2) || (maj1 == maj2 && min1 < min2)
124 ltMajLvl :: Level -> Level -> Bool
125 -- Tells if one level belongs to a difft *lambda* level to another
126 ltMajLvl l1 Top = False
127 ltMajLvl Top (Level 0 _) = False
128 ltMajLvl Top (Level _ _) = True
129 ltMajLvl (Level maj1 _) (Level maj2 _) = maj1 < maj2
131 isTopLvl :: Level -> Bool
133 isTopLvl other = False
135 isTopMajLvl :: Level -> Bool -- Tells if it's the top *lambda* level
136 isTopMajLvl Top = True
137 isTopMajLvl (Level maj _) = maj == 0
139 unTopify :: Level -> Level
140 unTopify Top = Level 0 0
143 instance Outputable Level where
144 ppr sty Top = ppStr "<Top>"
145 ppr sty (Level maj min) = ppBesides [ ppChar '<', ppInt maj, ppChar ',', ppInt min, ppChar '>' ]
148 %************************************************************************
150 \subsection{Main level-setting code}
152 %************************************************************************
155 setLevels :: [CoreBinding]
162 -- "do_them"'s main business is to thread the monad along
163 -- It gives each top binding the same empty envt, because
164 -- things unbound in the envt have level number zero implicitly
165 do_them :: [CoreBinding] -> LvlM [LevelledBind]
167 do_them [] = returnLvl []
169 = lvlTopBind b `thenLvl` \ (lvld_bind, _) ->
170 do_them bs `thenLvl` \ lvld_binds ->
171 returnLvl (lvld_bind ++ lvld_binds)
173 initial_envs = (nullIdEnv, nullTyVarEnv)
175 lvlTopBind (NonRec binder rhs)
176 = lvlBind (Level 0 0) initial_envs (AnnNonRec binder (freeVars rhs))
177 -- Rhs can have no free vars!
179 lvlTopBind (Rec pairs)
180 = lvlBind (Level 0 0) initial_envs (AnnRec [(b,freeVars rhs) | (b,rhs) <- pairs])
183 %************************************************************************
185 \subsection{Bindings}
187 %************************************************************************
189 The binding stuff works for top level too.
192 type CoreBindingWithFVs = AnnCoreBinding Id Id TyVar UVar FVInfo
196 -> CoreBindingWithFVs
197 -> LvlM ([LevelledBind], LevelEnvs)
199 lvlBind ctxt_lvl envs@(venv, tenv) (AnnNonRec name rhs)
200 = setFloatLevel True {- Already let-bound -}
201 ctxt_lvl envs rhs ty `thenLvl` \ (final_lvl, rhs') ->
203 new_envs = (addOneToIdEnv venv name final_lvl, tenv)
205 returnLvl ([NonRec (name, final_lvl) rhs'], new_envs)
210 lvlBind ctxt_lvl envs@(venv, tenv) (AnnRec pairs)
211 = decideRecFloatLevel ctxt_lvl envs binders rhss
212 `thenLvl` \ (final_lvl, extra_binds, rhss') ->
214 binders_w_lvls = binders `zip` repeat final_lvl
215 new_envs = (growIdEnvList venv binders_w_lvls, tenv)
217 returnLvl (extra_binds ++ [Rec (zipEqual "lvlBind" binders_w_lvls rhss')], new_envs)
219 (binders,rhss) = unzip pairs
222 %************************************************************************
224 \subsection{Setting expression levels}
226 %************************************************************************
229 lvlExpr :: Level -- ctxt_lvl: Level of enclosing expression
230 -> LevelEnvs -- Level of in-scope names/tyvars
231 -> CoreExprWithFVs -- input expression
232 -> LvlM LevelledExpr -- Result expression
235 The @ctxt_lvl@ is, roughly, the level of the innermost enclosing
240 v = \x -> ...\y -> let r = case (..x..) of
244 When looking at the rhs of @r@, @ctxt_lvl@ will be 1 because that's
245 the level of @r@, even though it's inside a level-2 @\y@. It's
246 important that @ctxt_lvl@ is 1 and not 2 in @r@'s rhs, because we
247 don't want @lvlExpr@ to turn the scrutinee of the @case@ into an MFE
248 --- because it isn't a *maximal* free expression.
250 If there were another lambda in @r@'s rhs, it would get level-2 as well.
253 lvlExpr _ _ (_, AnnVar v) = returnLvl (Var v)
254 lvlExpr _ _ (_, AnnLit l) = returnLvl (Lit l)
255 lvlExpr _ _ (_, AnnCon con args) = returnLvl (Con con args)
256 lvlExpr _ _ (_, AnnPrim op args) = returnLvl (Prim op args)
258 lvlExpr ctxt_lvl envs@(venv, tenv) (_, AnnApp fun arg)
259 = lvlExpr ctxt_lvl envs fun `thenLvl` \ fun' ->
260 returnLvl (App fun' arg)
262 lvlExpr ctxt_lvl envs (_, AnnSCC cc expr)
263 = lvlExpr ctxt_lvl envs expr `thenLvl` \ expr' ->
264 returnLvl (SCC cc expr')
266 lvlExpr ctxt_lvl envs (_, AnnCoerce c ty expr)
267 = lvlExpr ctxt_lvl envs expr `thenLvl` \ expr' ->
268 returnLvl (Coerce c ty expr')
270 lvlExpr ctxt_lvl envs@(venv, tenv) (_, AnnLam (ValBinder arg) rhs)
271 = lvlMFE incd_lvl (new_venv, tenv) rhs `thenLvl` \ rhs' ->
272 returnLvl (Lam (ValBinder (arg,incd_lvl)) rhs')
274 incd_lvl = incMajorLvl ctxt_lvl
275 new_venv = growIdEnvList venv [(arg,incd_lvl)]
277 lvlExpr ctxt_lvl (venv, tenv) (_, AnnLam (TyBinder tyvar) e)
278 = lvlExpr incd_lvl (venv, new_tenv) e `thenLvl` \ e' ->
279 returnLvl (Lam (TyBinder tyvar) e')
281 incd_lvl = incMinorLvl ctxt_lvl
282 new_tenv = addOneToTyVarEnv tenv tyvar incd_lvl
284 lvlExpr ctxt_lvl (venv, tenv) (_, AnnLam (UsageBinder u) e)
285 = panic "SetLevels.lvlExpr:AnnLam UsageBinder"
287 lvlExpr ctxt_lvl envs (_, AnnLet bind body)
288 = lvlBind ctxt_lvl envs bind `thenLvl` \ (binds', new_envs) ->
289 lvlExpr ctxt_lvl new_envs body `thenLvl` \ body' ->
290 returnLvl (foldr Let body' binds') -- mkCoLet* requires Core...
292 lvlExpr ctxt_lvl envs@(venv, tenv) (_, AnnCase expr alts)
293 = lvlMFE ctxt_lvl envs expr `thenLvl` \ expr' ->
294 lvl_alts alts `thenLvl` \ alts' ->
295 returnLvl (Case expr' alts')
297 expr_type = coreExprType (deAnnotate expr)
298 incd_lvl = incMinorLvl ctxt_lvl
300 lvl_alts (AnnAlgAlts alts deflt)
301 = mapLvl lvl_alt alts `thenLvl` \ alts' ->
302 lvl_deflt deflt `thenLvl` \ deflt' ->
303 returnLvl (AlgAlts alts' deflt')
307 bs' = [ (b, incd_lvl) | b <- bs ]
308 new_envs = (growIdEnvList venv bs', tenv)
310 lvlMFE incd_lvl new_envs e `thenLvl` \ e' ->
311 returnLvl (con, bs', e')
313 lvl_alts (AnnPrimAlts alts deflt)
314 = mapLvl lvl_alt alts `thenLvl` \ alts' ->
315 lvl_deflt deflt `thenLvl` \ deflt' ->
316 returnLvl (PrimAlts alts' deflt')
319 = lvlMFE incd_lvl envs e `thenLvl` \ e' ->
322 lvl_deflt AnnNoDefault = returnLvl NoDefault
324 lvl_deflt (AnnBindDefault b expr)
326 new_envs = (addOneToIdEnv venv b incd_lvl, tenv)
328 lvlMFE incd_lvl new_envs expr `thenLvl` \ expr' ->
329 returnLvl (BindDefault (b, incd_lvl) expr')
332 @lvlMFE@ is just like @lvlExpr@, except that it might let-bind
333 the expression, so that it can itself be floated.
336 lvlMFE :: Level -- Level of innermost enclosing lambda/tylam
337 -> LevelEnvs -- Level of in-scope names/tyvars
338 -> CoreExprWithFVs -- input expression
339 -> LvlM LevelledExpr -- Result expression
341 lvlMFE ctxt_lvl envs@(venv,_) ann_expr
342 | isPrimType ty -- Can't let-bind it
343 = lvlExpr ctxt_lvl envs ann_expr
345 | otherwise -- Not primitive type so could be let-bound
346 = setFloatLevel False {- Not already let-bound -}
347 ctxt_lvl envs ann_expr ty `thenLvl` \ (final_lvl, expr') ->
350 ty = coreExprType (deAnnotate ann_expr)
354 %************************************************************************
356 \subsection{Deciding floatability}
358 %************************************************************************
360 @setFloatLevel@ is used for let-bound right-hand-sides, or for MFEs which
361 are being created as let-bindings
365 YES. -> (a) try abstracting type variables.
366 If we abstract type variables it will go further, that is, past more
367 lambdas. same as asking if the level number given by the free
368 variables is less than the level number given by free variables
369 and type variables together.
370 Abstract offending type variables, e.g.
372 to let v = /\ty' -> f ty' a b
374 so that v' is not stopped by the level number of ty
375 tag the original let with its level number
376 (from its variables and type variables)
378 YES. -> No point in let binding to float a WHNF.
379 Pin (leave) expression here.
380 NO. -> Will float past a lambda?
381 (check using free variables only, not type variables)
382 YES. -> do the same as (a) above.
383 NO. -> No point in let binding if it is not going anywhere
384 Pin (leave) expression here.
387 setFloatLevel :: Bool -- True <=> the expression is already let-bound
388 -- False <=> it's a possible MFE
389 -> Level -- of context
392 -> CoreExprWithFVs -- Original rhs
393 -> Type -- Type of rhs
395 -> LvlM (Level, -- Level to attribute to this let-binding
396 LevelledExpr) -- Final rhs
398 setFloatLevel alreadyLetBound ctxt_lvl envs@(venv, tenv)
399 expr@(FVInfo fvs tfvs might_leak, _) ty
400 -- Invariant: ctxt_lvl is never = Top
401 -- Beautiful ASSERT, dudes (WDP 95/04)...
403 -- Now deal with (by not floating) trivial non-let-bound expressions
404 -- which just aren't worth let-binding in order to float. We always
405 -- choose to float even trivial let-bound things because it doesn't do
406 -- any harm, and not floating it may pin something important. For
413 -- Here, if we don't float v we won't float w, which is Bad News.
414 -- If this gives any problems we could restrict the idea to things destined
417 | not alreadyLetBound
418 && (manifestly_whnf || not will_float_past_lambda)
419 = -- Pin whnf non-let-bound expressions,
420 -- or ones which aren't going anywhere useful
421 lvlExpr ctxt_lvl envs expr `thenLvl` \ expr' ->
422 returnLvl (ctxt_lvl, expr')
424 | alreadyLetBound && not worth_type_abstraction
425 = -- Process the expression with a new ctxt_lvl, obtained from
426 -- the free vars of the expression itself
427 lvlExpr (unTopify expr_lvl) envs expr `thenLvl` \ expr' ->
428 returnLvl (maybe_unTopify expr_lvl, expr')
430 | otherwise -- This will create a let anyway, even if there is no
431 -- type variable to abstract, so we try to abstract anyway
432 = abstractWrtTyVars offending_tyvars ty envs lvl_after_ty_abstr expr
433 `thenLvl` \ final_expr ->
434 returnLvl (expr_lvl, final_expr)
435 -- OLD LIE: The body of the let, just a type application, isn't worth floating
436 -- so pin it with ctxt_lvl
437 -- The truth: better to give it expr_lvl in case it is pinning
438 -- something non-trivial which depends on it.
440 fv_list = idSetToList fvs
441 tv_list = tyVarSetToList tfvs
442 expr_lvl = ids_only_lvl `maxLvl` tyvars_only_lvl
443 ids_only_lvl = foldr (maxLvl . idLevel venv) tOP_LEVEL fv_list
444 tyvars_only_lvl = foldr (maxLvl . tyvarLevel tenv) tOP_LEVEL tv_list
445 lvl_after_ty_abstr = ids_only_lvl --`maxLvl` non_offending_tyvars_lvl
447 will_float_past_lambda = -- Will escape lambda if let-bound
448 ids_only_lvl `ltMajLvl` ctxt_lvl
450 worth_type_abstraction = -- Will escape (more) lambda(s)/type lambda(s)
451 -- if type abstracted
452 (ids_only_lvl `ltLvl` tyvars_only_lvl)
453 && not (is_trivial de_ann_expr) -- avoids abstracting trivial type applications
455 de_ann_expr = deAnnotate expr
458 | notValArg a = is_trivial e
459 is_trivial (Var _) = True
462 offending_tyvars = filter offending tv_list
463 --non_offending_tyvars = filter (not . offending) tv_list
464 --non_offending_tyvars_lvl = foldr (maxLvl . tyvarLevel tenv) tOP_LEVEL non_offending_tyvars
466 offending tyvar = ids_only_lvl `ltLvl` tyvarLevel tenv tyvar
468 manifestly_whnf = manifestlyWHNF de_ann_expr || manifestlyBottom de_ann_expr
470 maybe_unTopify Top | not (canFloatToTop (ty, expr)) = Level 0 0
471 maybe_unTopify lvl = lvl
472 {- ToDo [Andre]: the line above (maybe) should be Level 1 0,
473 -- so that the let will not go past the *last* lambda if it can
474 -- generate a space leak. If it is already in major level 0
475 -- It won't do any harm to give it a Level 1 0.
476 -- we should do the same test not only for things with level Top,
477 -- but also for anything that gets a major level 0.
479 f = \a -> let x = [1..1000]
482 f = let x = [1..1000]
484 is just as bad as floating x to the top level.
485 Notice it would be OK in cases like
486 f = \a -> let x = [1..1000]
490 f = let x = [1..1000]
493 as x will be gc'd after y is updated.
494 [We did not hit any problems with the above (Level 0 0) code
499 Abstract wrt tyvars, by making it just as if we had seen
504 instead of simply E. The idea is that v can be freely floated, since it
505 has no free type variables. Of course, if E has no free type
506 variables, then we just return E.
509 abstractWrtTyVars offending_tyvars ty (venv,tenv) lvl expr
510 = lvlExpr incd_lvl new_envs expr `thenLvl` \ expr' ->
511 newLvlVar poly_ty `thenLvl` \ poly_var ->
513 poly_var_rhs = mkTyLam offending_tyvars expr'
514 poly_var_binding = NonRec (poly_var, lvl) poly_var_rhs
515 poly_var_app = mkTyApp (Var poly_var) (mkTyVarTys offending_tyvars)
516 final_expr = Let poly_var_binding poly_var_app -- mkCoLet* requires Core
520 poly_ty = mkForAllTys offending_tyvars ty
522 -- These defns are just like those in the TyLam case of lvlExpr
523 (incd_lvl, tyvar_lvls) = mapAccumL next (unTopify lvl) offending_tyvars
525 next lvl tyvar = (lvl1, (tyvar,lvl1))
526 where lvl1 = incMinorLvl lvl
528 new_tenv = growTyVarEnvList tenv tyvar_lvls
529 new_envs = (venv, new_tenv)
532 Recursive definitions. We want to transform
544 x1' = /\ ab -> let D' in e1
546 xn' = /\ ab -> let D' in en
550 where ab are the tyvars pinning the defn further in than it
551 need be, and D is a bunch of simple type applications:
557 The "_cl" indicates that in D, the level numbers on the xi are the context level
558 number; type applications aren't worth floating. The D' decls are
565 but differ in their level numbers; here the ab are the newly-introduced
569 decideRecFloatLevel ctxt_lvl envs@(venv, tenv) ids rhss
570 | isTopMajLvl ids_only_lvl && -- Destination = top
571 not (all canFloatToTop (zipEqual "decideRec" tys rhss)) -- Some can't float to top
574 ids_w_lvls = ids `zip` repeat ctxt_lvl
575 new_envs = (growIdEnvList venv ids_w_lvls, tenv)
577 mapLvl (lvlExpr ctxt_lvl new_envs) rhss `thenLvl` \ rhss' ->
578 returnLvl (ctxt_lvl, [], rhss')
580 {- OMITTED; see comments above near isWorthFloatingExpr
582 | not (any (isWorthFloating True . deAnnotate) rhss)
584 mapLvl (lvlExpr ctxt_lvl envs) rhss `thenLvl` \ rhss' ->
585 returnLvl (ctxt_lvl, [], rhss')
589 | ids_only_lvl `ltLvl` tyvars_only_lvl
590 = -- Abstract wrt tyvars;
591 -- offending_tyvars is definitely non-empty
592 -- (I love the ASSERT to check this... WDP 95/02)
594 -- These defns are just like those in the TyLam case of lvlExpr
595 (incd_lvl, tyvar_lvls) = mapAccumL next (unTopify ids_only_lvl) offending_tyvars
597 next lvl tyvar = (lvl1, (tyvar,lvl1))
598 where lvl1 = incMinorLvl lvl
600 ids_w_incd_lvl = [(id,incd_lvl) | id <- ids]
601 new_tenv = growTyVarEnvList tenv tyvar_lvls
602 new_venv = growIdEnvList venv ids_w_incd_lvl
603 new_envs = (new_venv, new_tenv)
605 mapLvl (lvlExpr incd_lvl new_envs) rhss `thenLvl` \ rhss' ->
606 mapLvl newLvlVar poly_tys `thenLvl` \ poly_vars ->
608 ids_w_poly_vars = zipEqual "decideRec2" ids poly_vars
610 -- The "d_rhss" are the right-hand sides of "D" and "D'"
611 -- in the documentation above
612 d_rhss = [ mkTyApp (Var poly_var) offending_tyvar_tys | poly_var <- poly_vars]
614 -- "local_binds" are "D'" in the documentation above
615 local_binds = zipWithEqual "SetLevels" NonRec ids_w_incd_lvl d_rhss
617 poly_var_rhss = [ mkTyLam offending_tyvars (foldr Let rhs' local_binds)
618 | rhs' <- rhss' -- mkCoLet* requires Core...
621 poly_binds = zipEqual "poly_binds" [(poly_var, ids_only_lvl) | poly_var <- poly_vars] poly_var_rhss
624 returnLvl (ctxt_lvl, [Rec poly_binds], d_rhss)
625 -- The new right-hand sides, just a type application, aren't worth floating
626 -- so pin it with ctxt_lvl
629 = -- Let it float freely
631 ids_w_lvls = ids `zip` repeat expr_lvl
632 new_envs = (growIdEnvList venv ids_w_lvls, tenv)
634 mapLvl (lvlExpr (unTopify expr_lvl) new_envs) rhss `thenLvl` \ rhss' ->
635 returnLvl (expr_lvl, [], rhss')
640 fvs = unionManyIdSets [freeVarsOf rhs | rhs <- rhss] `minusIdSet` mkIdSet ids
641 tfvs = unionManyTyVarSets [freeTyVarsOf rhs | rhs <- rhss]
642 fv_list = idSetToList fvs
643 tv_list = tyVarSetToList tfvs
645 ids_only_lvl = foldr (maxLvl . idLevel venv) tOP_LEVEL fv_list
646 tyvars_only_lvl = foldr (maxLvl . tyvarLevel tenv) tOP_LEVEL tv_list
647 expr_lvl = ids_only_lvl `maxLvl` tyvars_only_lvl
650 | ids_only_lvl `ltLvl` tyvars_only_lvl = filter offending tv_list
653 offending_tyvar_tys = mkTyVarTys offending_tyvars
654 poly_tys = map (mkForAllTys offending_tyvars) tys
656 offending tyvar = ids_only_lvl `ltLvl` tyvarLevel tenv tyvar
661 {- ******** OMITTED NOW
663 isWorthFloating :: Bool -- True <=> already let-bound
664 -> CoreExpr -- The expression
667 isWorthFloating alreadyLetBound expr
669 | alreadyLetBound = isWorthFloatingExpr expr
671 | otherwise = -- No point in adding a fresh let-binding for a WHNF, because
672 -- floating it isn't beneficial enough.
673 isWorthFloatingExpr expr &&
674 not (manifestlyWHNF expr || manifestlyBottom expr)
677 isWorthFloatingExpr :: CoreExpr -> Bool
679 isWorthFloatingExpr (Var v) = False
680 isWorthFloatingExpr (Lit lit) = False
681 isWorthFloatingExpr (App e arg)
682 | notValArg arg = isWorthFloatingExpr e
683 isWorthFloatingExpr (Con con as)
684 | all notValArg as = False -- Just a type application
685 isWorthFloatingExpr _ = True
687 canFloatToTop :: (Type, CoreExprWithFVs) -> Bool
689 canFloatToTop (ty, (FVInfo _ _ (LeakFree _), expr)) = True
690 canFloatToTop (ty, (FVInfo _ _ MightLeak, expr)) = isLeakFreeType [] ty
692 valSuggestsLeakFree expr = manifestlyWHNF expr || manifestlyBottom expr
697 %************************************************************************
699 \subsection{Help functions}
701 %************************************************************************
704 idLevel :: IdEnv Level -> Id -> Level
706 = case lookupIdEnv venv v of
708 Nothing -> ASSERT(toplevelishId v)
711 tyvarLevel :: TyVarEnv Level -> TyVar -> Level
712 tyvarLevel tenv tyvar
713 = case lookupTyVarEnv tenv tyvar of
718 %************************************************************************
720 \subsection{Free-To-Level Monad}
722 %************************************************************************
725 type LvlM result = UniqSM result
730 mapAndUnzipLvl = mapAndUnzipUs
731 mapAndUnzip3Lvl = mapAndUnzip3Us
734 We create a let-binding for `interesting' (non-utterly-trivial)
735 applications, to give them a fighting chance of being floated.
738 newLvlVar :: Type -> LvlM Id
741 = mkSysLocal SLIT("lvl") (getUnique us) ty mkUnknownSrcLoc