2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
6 ***************************
8 ***************************
10 1. We attach binding levels to Core bindings, in preparation for floating
11 outwards (@FloatOut@).
13 2. We also let-ify many expressions (notably case scrutinees), so they
14 will have a fighting chance of being floated sensible.
16 3. We clone the binders of any floatable let-binding, so that when it is
17 floated out it will be unique. (This used to be done by the simplifier
18 but the latter now only ensures that there's no shadowing; indeed, even
19 that may not be true.)
21 NOTE: this can't be done using the uniqAway idea, because the variable
22 must be unique in the whole program, not just its current scope,
23 because two variables in different scopes may float out to the
26 NOTE: Very tiresomely, we must apply this substitution to
27 the rules stored inside a variable too.
29 We do *not* clone top-level bindings, because some of them must not change,
30 but we *do* clone bindings that are heading for the top level
33 case x of wild { p -> ...wild... }
34 we substitute x for wild in the RHS of the case alternatives:
35 case x of wild { p -> ...x... }
36 This means that a sub-expression involving x is not "trapped" inside the RHS.
37 And it's not inconvenient because we already have a substitution.
39 Note that this is EXACTLY BACKWARDS from the what the simplifier does.
40 The simplifier tries to get rid of occurrences of x, in favour of wild,
41 in the hope that there will only be one remaining occurrence of x, namely
42 the scrutinee of the case, and we can inline it.
49 LevelledBind, LevelledExpr,
51 incMinorLvl, ltMajLvl, ltLvl, isTopLvl, isInlineCtxt
54 #include "HsVersions.h"
58 import DynFlags ( FloatOutSwitches(..) )
59 import CoreUtils ( exprType, exprIsTrivial, exprIsCheap, mkPiTypes )
60 import CoreFVs -- all of it
61 import CoreSubst ( Subst, emptySubst, extendInScope, extendIdSubst,
62 cloneIdBndr, cloneRecIdBndrs )
63 import Id ( Id, idType, mkSysLocal, isOneShotLambda,
65 idSpecialisation, idWorkerInfo, setIdInfo
67 import IdInfo ( workerExists, vanillaIdInfo, isEmptySpecInfo )
71 import Name ( getOccName )
72 import OccName ( occNameString )
73 import Type ( isUnLiftedType, Type )
74 import BasicTypes ( TopLevelFlag(..) )
76 import Util ( sortLe, isSingleton, count )
81 %************************************************************************
83 \subsection{Level numbers}
85 %************************************************************************
88 data Level = InlineCtxt -- A level that's used only for
89 -- the context parameter ctxt_lvl
90 | Level Int -- Level number of enclosing lambdas
91 Int -- Number of big-lambda and/or case expressions between
92 -- here and the nearest enclosing lambda
95 The {\em level number} on a (type-)lambda-bound variable is the
96 nesting depth of the (type-)lambda which binds it. The outermost lambda
97 has level 1, so (Level 0 0) means that the variable is bound outside any lambda.
99 On an expression, it's the maximum level number of its free
100 (type-)variables. On a let(rec)-bound variable, it's the level of its
101 RHS. On a case-bound variable, it's the number of enclosing lambdas.
103 Top-level variables: level~0. Those bound on the RHS of a top-level
104 definition but ``before'' a lambda; e.g., the \tr{x} in (levels shown
105 as ``subscripts'')...
107 a_0 = let b_? = ... in
108 x_1 = ... b ... in ...
111 The main function @lvlExpr@ carries a ``context level'' (@ctxt_lvl@).
112 That's meant to be the level number of the enclosing binder in the
113 final (floated) program. If the level number of a sub-expression is
114 less than that of the context, then it might be worth let-binding the
115 sub-expression so that it will indeed float.
117 If you can float to level @Level 0 0@ worth doing so because then your
118 allocation becomes static instead of dynamic. We always start with
124 @InlineCtxt@ very similar to @Level 0 0@, but is used for one purpose:
125 to say "don't float anything out of here". That's exactly what we
126 want for the body of an INLINE, where we don't want to float anything
127 out at all. See notes with lvlMFE below.
131 -- At one time I tried the effect of not float anything out of an InlineMe,
132 -- but it sometimes works badly. For example, consider PrelArr.done. It
133 -- has the form __inline (\d. e)
134 -- where e doesn't mention d. If we float this to
135 -- __inline (let x = e in \d. x)
136 -- things are bad. The inliner doesn't even inline it because it doesn't look
137 -- like a head-normal form. So it seems a lesser evil to let things float.
138 -- In SetLevels we do set the context to (Level 0 0) when we get to an InlineMe
139 -- which discourages floating out.
141 So the conclusion is: don't do any floating at all inside an InlineMe.
142 (In the above example, don't float the {x=e} out of the \d.)
144 One particular case is that of workers: we don't want to float the
145 call to the worker outside the wrapper, otherwise the worker might get
146 inlined into the floated expression, and an importing module won't see
150 type LevelledExpr = TaggedExpr Level
151 type LevelledBind = TaggedBind Level
153 tOP_LEVEL = Level 0 0
154 iNLINE_CTXT = InlineCtxt
156 incMajorLvl :: Level -> Level
157 -- For InlineCtxt we ignore any inc's; we don't want
158 -- to do any floating at all; see notes above
159 incMajorLvl InlineCtxt = InlineCtxt
160 incMajorLvl (Level major minor) = Level (major+1) 0
162 incMinorLvl :: Level -> Level
163 incMinorLvl InlineCtxt = InlineCtxt
164 incMinorLvl (Level major minor) = Level major (minor+1)
166 maxLvl :: Level -> Level -> Level
167 maxLvl InlineCtxt l2 = l2
168 maxLvl l1 InlineCtxt = l1
169 maxLvl l1@(Level maj1 min1) l2@(Level maj2 min2)
170 | (maj1 > maj2) || (maj1 == maj2 && min1 > min2) = l1
173 ltLvl :: Level -> Level -> Bool
174 ltLvl any_lvl InlineCtxt = False
175 ltLvl InlineCtxt (Level _ _) = True
176 ltLvl (Level maj1 min1) (Level maj2 min2)
177 = (maj1 < maj2) || (maj1 == maj2 && min1 < min2)
179 ltMajLvl :: Level -> Level -> Bool
180 -- Tells if one level belongs to a difft *lambda* level to another
181 ltMajLvl any_lvl InlineCtxt = False
182 ltMajLvl InlineCtxt (Level maj2 _) = 0 < maj2
183 ltMajLvl (Level maj1 _) (Level maj2 _) = maj1 < maj2
185 isTopLvl :: Level -> Bool
186 isTopLvl (Level 0 0) = True
187 isTopLvl other = False
189 isInlineCtxt :: Level -> Bool
190 isInlineCtxt InlineCtxt = True
191 isInlineCtxt other = False
193 instance Outputable Level where
194 ppr InlineCtxt = text "<INLINE>"
195 ppr (Level maj min) = hcat [ char '<', int maj, char ',', int min, char '>' ]
197 instance Eq Level where
198 InlineCtxt == InlineCtxt = True
199 (Level maj1 min1) == (Level maj2 min2) = maj1==maj2 && min1==min2
204 %************************************************************************
206 \subsection{Main level-setting code}
208 %************************************************************************
211 setLevels :: FloatOutSwitches
216 setLevels float_lams binds us
217 = initLvl us (do_them binds)
219 -- "do_them"'s main business is to thread the monad along
220 -- It gives each top binding the same empty envt, because
221 -- things unbound in the envt have level number zero implicitly
222 do_them :: [CoreBind] -> LvlM [LevelledBind]
224 do_them [] = returnLvl []
226 = lvlTopBind init_env b `thenLvl` \ (lvld_bind, _) ->
227 do_them bs `thenLvl` \ lvld_binds ->
228 returnLvl (lvld_bind : lvld_binds)
230 init_env = initialEnv float_lams
232 lvlTopBind env (NonRec binder rhs)
233 = lvlBind TopLevel tOP_LEVEL env (AnnNonRec binder (freeVars rhs))
234 -- Rhs can have no free vars!
236 lvlTopBind env (Rec pairs)
237 = lvlBind TopLevel tOP_LEVEL env (AnnRec [(b,freeVars rhs) | (b,rhs) <- pairs])
240 %************************************************************************
242 \subsection{Setting expression levels}
244 %************************************************************************
247 lvlExpr :: Level -- ctxt_lvl: Level of enclosing expression
248 -> LevelEnv -- Level of in-scope names/tyvars
249 -> CoreExprWithFVs -- input expression
250 -> LvlM LevelledExpr -- Result expression
253 The @ctxt_lvl@ is, roughly, the level of the innermost enclosing
254 binder. Here's an example
256 v = \x -> ...\y -> let r = case (..x..) of
260 When looking at the rhs of @r@, @ctxt_lvl@ will be 1 because that's
261 the level of @r@, even though it's inside a level-2 @\y@. It's
262 important that @ctxt_lvl@ is 1 and not 2 in @r@'s rhs, because we
263 don't want @lvlExpr@ to turn the scrutinee of the @case@ into an MFE
264 --- because it isn't a *maximal* free expression.
266 If there were another lambda in @r@'s rhs, it would get level-2 as well.
269 lvlExpr _ _ (_, AnnType ty) = returnLvl (Type ty)
270 lvlExpr _ env (_, AnnVar v) = returnLvl (lookupVar env v)
271 lvlExpr _ env (_, AnnLit lit) = returnLvl (Lit lit)
273 lvlExpr ctxt_lvl env (_, AnnApp fun arg)
274 = lvl_fun fun `thenLvl` \ fun' ->
275 lvlMFE False ctxt_lvl env arg `thenLvl` \ arg' ->
276 returnLvl (App fun' arg')
279 lvl_fun (_, AnnCase _ _ _ _) = lvlMFE True ctxt_lvl env fun
280 lvl_fun other = lvlExpr ctxt_lvl env fun
281 -- We don't do MFE on partial applications generally,
282 -- but we do if the function is big and hairy, like a case
284 lvlExpr ctxt_lvl env (_, AnnNote InlineMe expr)
285 -- Don't float anything out of an InlineMe; hence the iNLINE_CTXT
286 = lvlExpr iNLINE_CTXT env expr `thenLvl` \ expr' ->
287 returnLvl (Note InlineMe expr')
289 lvlExpr ctxt_lvl env (_, AnnNote note expr)
290 = lvlExpr ctxt_lvl env expr `thenLvl` \ expr' ->
291 returnLvl (Note note expr')
293 -- We don't split adjacent lambdas. That is, given
295 -- we don't float to give
296 -- \x -> let v = x+y in \y -> (v,y)
297 -- Why not? Because partial applications are fairly rare, and splitting
298 -- lambdas makes them more expensive.
300 lvlExpr ctxt_lvl env expr@(_, AnnLam bndr rhs)
301 = lvlMFE True new_lvl new_env body `thenLvl` \ new_body ->
302 returnLvl (mkLams new_bndrs new_body)
304 (bndrs, body) = collectAnnBndrs expr
305 (new_lvl, new_bndrs) = lvlLamBndrs ctxt_lvl bndrs
306 new_env = extendLvlEnv env new_bndrs
307 -- At one time we called a special verion of collectBinders,
308 -- which ignored coercions, because we don't want to split
309 -- a lambda like this (\x -> coerce t (\s -> ...))
310 -- This used to happen quite a bit in state-transformer programs,
311 -- but not nearly so much now non-recursive newtypes are transparent.
312 -- [See SetLevels rev 1.50 for a version with this approach.]
314 lvlExpr ctxt_lvl env (_, AnnLet (AnnNonRec bndr rhs) body)
315 | isUnLiftedType (idType bndr)
316 -- Treat unlifted let-bindings (let x = b in e) just like (case b of x -> e)
317 -- That is, leave it exactly where it is
318 -- We used to float unlifted bindings too (e.g. to get a cheap primop
319 -- outside a lambda (to see how, look at lvlBind in rev 1.58)
320 -- but an unrelated change meant that these unlifed bindings
321 -- could get to the top level which is bad. And there's not much point;
322 -- unlifted bindings are always cheap, and so hardly worth floating.
323 = lvlExpr ctxt_lvl env rhs `thenLvl` \ rhs' ->
324 lvlExpr incd_lvl env' body `thenLvl` \ body' ->
325 returnLvl (Let (NonRec bndr' rhs') body')
327 incd_lvl = incMinorLvl ctxt_lvl
328 bndr' = TB bndr incd_lvl
329 env' = extendLvlEnv env [bndr']
331 lvlExpr ctxt_lvl env (_, AnnLet bind body)
332 = lvlBind NotTopLevel ctxt_lvl env bind `thenLvl` \ (bind', new_env) ->
333 lvlExpr ctxt_lvl new_env body `thenLvl` \ body' ->
334 returnLvl (Let bind' body')
336 lvlExpr ctxt_lvl env (_, AnnCase expr case_bndr ty alts)
337 = lvlMFE True ctxt_lvl env expr `thenLvl` \ expr' ->
339 alts_env = extendCaseBndrLvlEnv env expr' case_bndr incd_lvl
341 mapLvl (lvl_alt alts_env) alts `thenLvl` \ alts' ->
342 returnLvl (Case expr' (TB case_bndr incd_lvl) ty alts')
344 incd_lvl = incMinorLvl ctxt_lvl
346 lvl_alt alts_env (con, bs, rhs)
347 = lvlMFE True incd_lvl new_env rhs `thenLvl` \ rhs' ->
348 returnLvl (con, bs', rhs')
350 bs' = [ TB b incd_lvl | b <- bs ]
351 new_env = extendLvlEnv alts_env bs'
354 @lvlMFE@ is just like @lvlExpr@, except that it might let-bind
355 the expression, so that it can itself be floated.
357 [NOTE: unlifted MFEs]
358 We don't float unlifted MFEs, which potentially loses big opportunites.
361 where h :: Int -> Int# is expensive. We'd like to float the (h y) outside
362 the \x, but we don't because it's unboxed. Possible solution: box it.
365 lvlMFE :: Bool -- True <=> strict context [body of case or let]
366 -> Level -- Level of innermost enclosing lambda/tylam
367 -> LevelEnv -- Level of in-scope names/tyvars
368 -> CoreExprWithFVs -- input expression
369 -> LvlM LevelledExpr -- Result expression
371 lvlMFE strict_ctxt ctxt_lvl env (_, AnnType ty)
372 = returnLvl (Type ty)
375 lvlMFE strict_ctxt ctxt_lvl env ann_expr@(fvs, _)
376 | isUnLiftedType ty -- Can't let-bind it; see [NOTE: unlifted MFEs]
377 || isInlineCtxt ctxt_lvl -- Don't float out of an __inline__ context
378 || exprIsTrivial expr -- Never float if it's trivial
379 || not good_destination
380 = -- Don't float it out
381 lvlExpr ctxt_lvl env ann_expr
383 | otherwise -- Float it out!
384 = lvlFloatRhs abs_vars dest_lvl env ann_expr `thenLvl` \ expr' ->
385 newLvlVar "lvl" abs_vars ty `thenLvl` \ var ->
386 returnLvl (Let (NonRec (TB var dest_lvl) expr')
387 (mkVarApps (Var var) abs_vars))
389 expr = deAnnotate ann_expr
391 dest_lvl = destLevel env fvs (isFunction ann_expr)
392 abs_vars = abstractVars dest_lvl env fvs
394 -- A decision to float entails let-binding this thing, and we only do
395 -- that if we'll escape a value lambda, or will go to the top level.
397 | dest_lvl `ltMajLvl` ctxt_lvl -- Escapes a value lambda
398 = not (exprIsCheap expr) || isTopLvl dest_lvl
399 -- Even if it escapes a value lambda, we only
400 -- float if it's not cheap (unless it'll get all the
401 -- way to the top). I've seen cases where we
402 -- float dozens of tiny free expressions, which cost
403 -- more to allocate than to evaluate.
404 -- NB: exprIsCheap is also true of bottom expressions, which
405 -- is good; we don't want to share them
407 -- It's only Really Bad to float a cheap expression out of a
408 -- strict context, because that builds a thunk that otherwise
409 -- would never be built. So another alternative would be to
411 -- || (strict_ctxt && not (exprIsBottom expr))
412 -- to the condition above. We should really try this out.
414 | otherwise -- Does not escape a value lambda
415 = isTopLvl dest_lvl -- Only float if we are going to the top level
416 && floatConsts env -- and the floatConsts flag is on
417 && not strict_ctxt -- Don't float from a strict context
418 -- We are keen to float something to the top level, even if it does not
419 -- escape a lambda, because then it needs no allocation. But it's controlled
420 -- by a flag, because doing this too early loses opportunities for RULES
421 -- which (needless to say) are important in some nofib programs
422 -- (gcd is an example).
425 -- concat = /\ a -> foldr ..a.. (++) []
426 -- was getting turned into
427 -- concat = /\ a -> lvl a
428 -- lvl = /\ a -> foldr ..a.. (++) []
429 -- which is pretty stupid. Hence the strict_ctxt test
433 %************************************************************************
435 \subsection{Bindings}
437 %************************************************************************
439 The binding stuff works for top level too.
442 lvlBind :: TopLevelFlag -- Used solely to decide whether to clone
443 -> Level -- Context level; might be Top even for bindings nested in the RHS
444 -- of a top level binding
447 -> LvlM (LevelledBind, LevelEnv)
449 lvlBind top_lvl ctxt_lvl env (AnnNonRec bndr rhs@(rhs_fvs,_))
450 | isInlineCtxt ctxt_lvl -- Don't do anything inside InlineMe
451 = lvlExpr ctxt_lvl env rhs `thenLvl` \ rhs' ->
452 returnLvl (NonRec (TB bndr ctxt_lvl) rhs', env)
455 = -- No type abstraction; clone existing binder
456 lvlExpr dest_lvl env rhs `thenLvl` \ rhs' ->
457 cloneVar top_lvl env bndr ctxt_lvl dest_lvl `thenLvl` \ (env', bndr') ->
458 returnLvl (NonRec (TB bndr' dest_lvl) rhs', env')
461 = -- Yes, type abstraction; create a new binder, extend substitution, etc
462 lvlFloatRhs abs_vars dest_lvl env rhs `thenLvl` \ rhs' ->
463 newPolyBndrs dest_lvl env abs_vars [bndr] `thenLvl` \ (env', [bndr']) ->
464 returnLvl (NonRec (TB bndr' dest_lvl) rhs', env')
467 bind_fvs = rhs_fvs `unionVarSet` idFreeVars bndr
468 abs_vars = abstractVars dest_lvl env bind_fvs
469 dest_lvl = destLevel env bind_fvs (isFunction rhs)
474 lvlBind top_lvl ctxt_lvl env (AnnRec pairs)
475 | isInlineCtxt ctxt_lvl -- Don't do anything inside InlineMe
476 = mapLvl (lvlExpr ctxt_lvl env) rhss `thenLvl` \ rhss' ->
477 returnLvl (Rec ([TB b ctxt_lvl | b <- bndrs] `zip` rhss'), env)
480 = cloneRecVars top_lvl env bndrs ctxt_lvl dest_lvl `thenLvl` \ (new_env, new_bndrs) ->
481 mapLvl (lvlExpr ctxt_lvl new_env) rhss `thenLvl` \ new_rhss ->
482 returnLvl (Rec ([TB b dest_lvl | b <- new_bndrs] `zip` new_rhss), new_env)
484 | isSingleton pairs && count isId abs_vars > 1
485 = -- Special case for self recursion where there are
486 -- several variables carried around: build a local loop:
487 -- poly_f = \abs_vars. \lam_vars . letrec f = \lam_vars. rhs in f lam_vars
488 -- This just makes the closures a bit smaller. If we don't do
489 -- this, allocation rises significantly on some programs
491 -- We could elaborate it for the case where there are several
492 -- mutually functions, but it's quite a bit more complicated
494 -- This all seems a bit ad hoc -- sigh
496 (bndr,rhs) = head pairs
497 (rhs_lvl, abs_vars_w_lvls) = lvlLamBndrs dest_lvl abs_vars
498 rhs_env = extendLvlEnv env abs_vars_w_lvls
500 cloneVar NotTopLevel rhs_env bndr rhs_lvl rhs_lvl `thenLvl` \ (rhs_env', new_bndr) ->
502 (lam_bndrs, rhs_body) = collectAnnBndrs rhs
503 (body_lvl, new_lam_bndrs) = lvlLamBndrs rhs_lvl lam_bndrs
504 body_env = extendLvlEnv rhs_env' new_lam_bndrs
506 lvlExpr body_lvl body_env rhs_body `thenLvl` \ new_rhs_body ->
507 newPolyBndrs dest_lvl env abs_vars [bndr] `thenLvl` \ (poly_env, [poly_bndr]) ->
508 returnLvl (Rec [(TB poly_bndr dest_lvl,
509 mkLams abs_vars_w_lvls $
510 mkLams new_lam_bndrs $
511 Let (Rec [(TB new_bndr rhs_lvl, mkLams new_lam_bndrs new_rhs_body)])
512 (mkVarApps (Var new_bndr) lam_bndrs))],
515 | otherwise -- Non-null abs_vars
516 = newPolyBndrs dest_lvl env abs_vars bndrs `thenLvl` \ (new_env, new_bndrs) ->
517 mapLvl (lvlFloatRhs abs_vars dest_lvl new_env) rhss `thenLvl` \ new_rhss ->
518 returnLvl (Rec ([TB b dest_lvl | b <- new_bndrs] `zip` new_rhss), new_env)
521 (bndrs,rhss) = unzip pairs
523 -- Finding the free vars of the binding group is annoying
524 bind_fvs = (unionVarSets [ idFreeVars bndr `unionVarSet` rhs_fvs
525 | (bndr, (rhs_fvs,_)) <- pairs])
529 dest_lvl = destLevel env bind_fvs (all isFunction rhss)
530 abs_vars = abstractVars dest_lvl env bind_fvs
532 ----------------------------------------------------
533 -- Three help functons for the type-abstraction case
535 lvlFloatRhs abs_vars dest_lvl env rhs
536 = lvlExpr rhs_lvl rhs_env rhs `thenLvl` \ rhs' ->
537 returnLvl (mkLams abs_vars_w_lvls rhs')
539 (rhs_lvl, abs_vars_w_lvls) = lvlLamBndrs dest_lvl abs_vars
540 rhs_env = extendLvlEnv env abs_vars_w_lvls
544 %************************************************************************
546 \subsection{Deciding floatability}
548 %************************************************************************
551 lvlLamBndrs :: Level -> [CoreBndr] -> (Level, [TaggedBndr Level])
552 -- Compute the levels for the binders of a lambda group
553 -- The binders returned are exactly the same as the ones passed,
554 -- but they are now paired with a level
558 lvlLamBndrs lvl bndrs
559 = go (incMinorLvl lvl)
560 False -- Havn't bumped major level in this group
563 go old_lvl bumped_major rev_lvld_bndrs (bndr:bndrs)
564 | isId bndr && -- Go to the next major level if this is a value binder,
565 not bumped_major && -- and we havn't already gone to the next level (one jump per group)
566 not (isOneShotLambda bndr) -- and it isn't a one-shot lambda
567 = go new_lvl True (TB bndr new_lvl : rev_lvld_bndrs) bndrs
570 = go old_lvl bumped_major (TB bndr old_lvl : rev_lvld_bndrs) bndrs
573 new_lvl = incMajorLvl old_lvl
575 go old_lvl _ rev_lvld_bndrs []
576 = (old_lvl, reverse rev_lvld_bndrs)
577 -- a lambda like this (\x -> coerce t (\s -> ...))
578 -- This happens quite a bit in state-transformer programs
582 -- Destintion level is the max Id level of the expression
583 -- (We'll abstract the type variables, if any.)
584 destLevel :: LevelEnv -> VarSet -> Bool -> Level
585 destLevel env fvs is_function
587 && is_function = tOP_LEVEL -- Send functions to top level; see
588 -- the comments with isFunction
589 | otherwise = maxIdLevel env fvs
591 isFunction :: CoreExprWithFVs -> Bool
592 -- The idea here is that we want to float *functions* to
593 -- the top level. This saves no work, but
594 -- (a) it can make the host function body a lot smaller,
595 -- and hence inlinable.
596 -- (b) it can also save allocation when the function is recursive:
597 -- h = \x -> letrec f = \y -> ...f...y...x...
600 -- f = \x y -> ...(f x)...y...x...
602 -- No allocation for f now.
603 -- We may only want to do this if there are sufficiently few free
604 -- variables. We certainly only want to do it for values, and not for
605 -- constructors. So the simple thing is just to look for lambdas
606 isFunction (_, AnnLam b e) | isId b = True
607 | otherwise = isFunction e
608 isFunction (_, AnnNote n e) = isFunction e
609 isFunction other = False
613 %************************************************************************
615 \subsection{Free-To-Level Monad}
617 %************************************************************************
620 type LevelEnv = (FloatOutSwitches,
621 VarEnv Level, -- Domain is *post-cloned* TyVars and Ids
622 Subst, -- Domain is pre-cloned Ids; tracks the in-scope set
623 -- so that subtitution is capture-avoiding
624 IdEnv ([Var], LevelledExpr)) -- Domain is pre-cloned Ids
625 -- We clone let-bound variables so that they are still
626 -- distinct when floated out; hence the SubstEnv/IdEnv.
627 -- (see point 3 of the module overview comment).
628 -- We also use these envs when making a variable polymorphic
629 -- because we want to float it out past a big lambda.
631 -- The SubstEnv and IdEnv always implement the same mapping, but the
632 -- SubstEnv maps to CoreExpr and the IdEnv to LevelledExpr
633 -- Since the range is always a variable or type application,
634 -- there is never any difference between the two, but sadly
635 -- the types differ. The SubstEnv is used when substituting in
636 -- a variable's IdInfo; the IdEnv when we find a Var.
638 -- In addition the IdEnv records a list of tyvars free in the
639 -- type application, just so we don't have to call freeVars on
640 -- the type application repeatedly.
642 -- The domain of the both envs is *pre-cloned* Ids, though
644 -- The domain of the VarEnv Level is the *post-cloned* Ids
646 initialEnv :: FloatOutSwitches -> LevelEnv
647 initialEnv float_lams = (float_lams, emptyVarEnv, emptySubst, emptyVarEnv)
649 floatLams :: LevelEnv -> Bool
650 floatLams (FloatOutSw float_lams _, _, _, _) = float_lams
652 floatConsts :: LevelEnv -> Bool
653 floatConsts (FloatOutSw _ float_consts, _, _, _) = float_consts
655 extendLvlEnv :: LevelEnv -> [TaggedBndr Level] -> LevelEnv
656 -- Used when *not* cloning
657 extendLvlEnv (float_lams, lvl_env, subst, id_env) prs
659 foldl add_lvl lvl_env prs,
660 foldl del_subst subst prs,
661 foldl del_id id_env prs)
663 add_lvl env (TB v l) = extendVarEnv env v l
664 del_subst env (TB v _) = extendInScope env v
665 del_id env (TB v _) = delVarEnv env v
666 -- We must remove any clone for this variable name in case of
667 -- shadowing. This bit me in the following case
668 -- (in nofib/real/gg/Spark.hs):
671 -- ... -> case e of wild {
672 -- ... -> ... wild ...
676 -- The inside occurrence of @wild@ was being replaced with @ds@,
677 -- incorrectly, because the SubstEnv was still lying around. Ouch!
680 -- extendCaseBndrLvlEnv adds the mapping case-bndr->scrut-var if it can
681 -- (see point 4 of the module overview comment)
682 extendCaseBndrLvlEnv (float_lams, lvl_env, subst, id_env) (Var scrut_var) case_bndr lvl
684 extendVarEnv lvl_env case_bndr lvl,
685 extendIdSubst subst case_bndr (Var scrut_var),
686 extendVarEnv id_env case_bndr ([scrut_var], Var scrut_var))
688 extendCaseBndrLvlEnv env scrut case_bndr lvl
689 = extendLvlEnv env [TB case_bndr lvl]
691 extendPolyLvlEnv dest_lvl (float_lams, lvl_env, subst, id_env) abs_vars bndr_pairs
693 foldl add_lvl lvl_env bndr_pairs,
694 foldl add_subst subst bndr_pairs,
695 foldl add_id id_env bndr_pairs)
697 add_lvl env (v,v') = extendVarEnv env v' dest_lvl
698 add_subst env (v,v') = extendIdSubst env v (mkVarApps (Var v') abs_vars)
699 add_id env (v,v') = extendVarEnv env v ((v':abs_vars), mkVarApps (Var v') abs_vars)
701 extendCloneLvlEnv lvl (float_lams, lvl_env, _, id_env) new_subst bndr_pairs
703 foldl add_lvl lvl_env bndr_pairs,
705 foldl add_id id_env bndr_pairs)
707 add_lvl env (v,v') = extendVarEnv env v' lvl
708 add_id env (v,v') = extendVarEnv env v ([v'], Var v')
711 maxIdLevel :: LevelEnv -> VarSet -> Level
712 maxIdLevel (_, lvl_env,_,id_env) var_set
713 = foldVarSet max_in tOP_LEVEL var_set
715 max_in in_var lvl = foldr max_out lvl (case lookupVarEnv id_env in_var of
716 Just (abs_vars, _) -> abs_vars
720 | isId out_var = case lookupVarEnv lvl_env out_var of
721 Just lvl' -> maxLvl lvl' lvl
723 | otherwise = lvl -- Ignore tyvars in *maxIdLevel*
725 lookupVar :: LevelEnv -> Id -> LevelledExpr
726 lookupVar (_, _, _, id_env) v = case lookupVarEnv id_env v of
727 Just (_, expr) -> expr
730 abstractVars :: Level -> LevelEnv -> VarSet -> [Var]
731 -- Find the variables in fvs, free vars of the target expresion,
732 -- whose level is greater than the destination level
733 -- These are the ones we are going to abstract out
734 abstractVars dest_lvl env fvs
735 = uniq (sortLe le [var | fv <- varSetElems fvs, var <- absVarsOf dest_lvl env fv])
737 -- Sort the variables so we don't get
738 -- mixed-up tyvars and Ids; it's just messy
739 v1 `le` v2 = case (isId v1, isId v2) of
740 (True, False) -> False
741 (False, True) -> True
742 other -> v1 <= v2 -- Same family
744 uniq :: [Var] -> [Var]
745 -- Remove adjacent duplicates; the sort will have brought them together
746 uniq (v1:v2:vs) | v1 == v2 = uniq (v2:vs)
747 | otherwise = v1 : uniq (v2:vs)
750 absVarsOf :: Level -> LevelEnv -> Var -> [Var]
751 -- If f is free in the expression, and f maps to poly_f a b c in the
752 -- current substitution, then we must report a b c as candidate type
754 absVarsOf dest_lvl (_, lvl_env, _, id_env) v
756 = [zap av2 | av1 <- lookup_avs v, av2 <- add_tyvars av1, abstract_me av2]
759 = if abstract_me v then [v] else []
762 abstract_me v = case lookupVarEnv lvl_env v of
763 Just lvl -> dest_lvl `ltLvl` lvl
766 lookup_avs v = case lookupVarEnv id_env v of
767 Just (abs_vars, _) -> abs_vars
770 add_tyvars v | isId v = v : varSetElems (idFreeTyVars v)
773 -- We are going to lambda-abstract, so nuke any IdInfo,
774 -- and add the tyvars of the Id (if necessary)
775 zap v | isId v = WARN( workerExists (idWorkerInfo v) ||
776 not (isEmptySpecInfo (idSpecialisation v)),
777 text "absVarsOf: discarding info on" <+> ppr v )
778 setIdInfo v vanillaIdInfo
783 type LvlM result = UniqSM result
792 newPolyBndrs dest_lvl env abs_vars bndrs
793 = getUniquesUs `thenLvl` \ uniqs ->
795 new_bndrs = zipWith mk_poly_bndr bndrs uniqs
797 returnLvl (extendPolyLvlEnv dest_lvl env abs_vars (bndrs `zip` new_bndrs), new_bndrs)
799 mk_poly_bndr bndr uniq = mkSysLocal (mkFastString str) uniq poly_ty
801 str = "poly_" ++ occNameString (getOccName bndr)
802 poly_ty = mkPiTypes abs_vars (idType bndr)
806 -> [CoreBndr] -> Type -- Abstract wrt these bndrs
808 newLvlVar str vars body_ty
809 = getUniqueUs `thenLvl` \ uniq ->
810 returnUs (mkSysLocal (mkFastString str) uniq (mkPiTypes vars body_ty))
812 -- The deeply tiresome thing is that we have to apply the substitution
813 -- to the rules inside each Id. Grr. But it matters.
815 cloneVar :: TopLevelFlag -> LevelEnv -> Id -> Level -> Level -> LvlM (LevelEnv, Id)
816 cloneVar TopLevel env v ctxt_lvl dest_lvl
817 = returnUs (env, v) -- Don't clone top level things
818 cloneVar NotTopLevel env@(_,_,subst,_) v ctxt_lvl dest_lvl
820 getUs `thenLvl` \ us ->
822 (subst', v1) = cloneIdBndr subst us v
823 v2 = zap_demand ctxt_lvl dest_lvl v1
824 env' = extendCloneLvlEnv dest_lvl env subst' [(v,v2)]
828 cloneRecVars :: TopLevelFlag -> LevelEnv -> [Id] -> Level -> Level -> LvlM (LevelEnv, [Id])
829 cloneRecVars TopLevel env vs ctxt_lvl dest_lvl
830 = returnUs (env, vs) -- Don't clone top level things
831 cloneRecVars NotTopLevel env@(_,_,subst,_) vs ctxt_lvl dest_lvl
832 = ASSERT( all isId vs )
833 getUs `thenLvl` \ us ->
835 (subst', vs1) = cloneRecIdBndrs subst us vs
836 vs2 = map (zap_demand ctxt_lvl dest_lvl) vs1
837 env' = extendCloneLvlEnv dest_lvl env subst' (vs `zip` vs2)
841 -- VERY IMPORTANT: we must zap the demand info
842 -- if the thing is going to float out past a lambda
843 zap_demand dest_lvl ctxt_lvl id
844 | ctxt_lvl == dest_lvl = id -- Stays put
845 | otherwise = zapDemandIdInfo id -- Floats out