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 CmdLineOpts ( FloatOutSwitches(..) )
59 import CoreUtils ( exprType, exprIsTrivial, exprIsCheap, mkPiTypes )
60 import CoreFVs -- all of it
62 import Id ( Id, idType, mkSysLocalUnencoded,
63 isOneShotLambda, zapDemandIdInfo,
64 idSpecialisation, idWorkerInfo, setIdInfo
66 import IdInfo ( workerExists, vanillaIdInfo, )
70 import Name ( getOccName )
71 import OccName ( occNameUserString )
72 import Type ( isUnLiftedType, Type )
73 import BasicTypes ( TopLevelFlag(..) )
75 import Util ( sortLt, isSingleton, count )
80 %************************************************************************
82 \subsection{Level numbers}
84 %************************************************************************
87 data Level = InlineCtxt -- A level that's used only for
88 -- the context parameter ctxt_lvl
89 | Level Int -- Level number of enclosing lambdas
90 Int -- Number of big-lambda and/or case expressions between
91 -- here and the nearest enclosing lambda
94 The {\em level number} on a (type-)lambda-bound variable is the
95 nesting depth of the (type-)lambda which binds it. The outermost lambda
96 has level 1, so (Level 0 0) means that the variable is bound outside any lambda.
98 On an expression, it's the maximum level number of its free
99 (type-)variables. On a let(rec)-bound variable, it's the level of its
100 RHS. On a case-bound variable, it's the number of enclosing lambdas.
102 Top-level variables: level~0. Those bound on the RHS of a top-level
103 definition but ``before'' a lambda; e.g., the \tr{x} in (levels shown
104 as ``subscripts'')...
106 a_0 = let b_? = ... in
107 x_1 = ... b ... in ...
110 The main function @lvlExpr@ carries a ``context level'' (@ctxt_lvl@).
111 That's meant to be the level number of the enclosing binder in the
112 final (floated) program. If the level number of a sub-expression is
113 less than that of the context, then it might be worth let-binding the
114 sub-expression so that it will indeed float.
116 If you can float to level @Level 0 0@ worth doing so because then your
117 allocation becomes static instead of dynamic. We always start with
123 @InlineCtxt@ very similar to @Level 0 0@, but is used for one purpose:
124 to say "don't float anything out of here". That's exactly what we
125 want for the body of an INLINE, where we don't want to float anything
126 out at all. See notes with lvlMFE below.
130 -- At one time I tried the effect of not float anything out of an InlineMe,
131 -- but it sometimes works badly. For example, consider PrelArr.done. It
132 -- has the form __inline (\d. e)
133 -- where e doesn't mention d. If we float this to
134 -- __inline (let x = e in \d. x)
135 -- things are bad. The inliner doesn't even inline it because it doesn't look
136 -- like a head-normal form. So it seems a lesser evil to let things float.
137 -- In SetLevels we do set the context to (Level 0 0) when we get to an InlineMe
138 -- which discourages floating out.
140 So the conclusion is: don't do any floating at all inside an InlineMe.
141 (In the above example, don't float the {x=e} out of the \d.)
143 One particular case is that of workers: we don't want to float the
144 call to the worker outside the wrapper, otherwise the worker might get
145 inlined into the floated expression, and an importing module won't see
149 type LevelledExpr = TaggedExpr Level
150 type LevelledBind = TaggedBind Level
152 tOP_LEVEL = Level 0 0
153 iNLINE_CTXT = InlineCtxt
155 incMajorLvl :: Level -> Level
156 -- For InlineCtxt we ignore any inc's; we don't want
157 -- to do any floating at all; see notes above
158 incMajorLvl InlineCtxt = InlineCtxt
159 incMajorLvl (Level major minor) = Level (major+1) 0
161 incMinorLvl :: Level -> Level
162 incMinorLvl InlineCtxt = InlineCtxt
163 incMinorLvl (Level major minor) = Level major (minor+1)
165 maxLvl :: Level -> Level -> Level
166 maxLvl InlineCtxt l2 = l2
167 maxLvl l1 InlineCtxt = l1
168 maxLvl l1@(Level maj1 min1) l2@(Level maj2 min2)
169 | (maj1 > maj2) || (maj1 == maj2 && min1 > min2) = l1
172 ltLvl :: Level -> Level -> Bool
173 ltLvl any_lvl InlineCtxt = False
174 ltLvl InlineCtxt (Level _ _) = True
175 ltLvl (Level maj1 min1) (Level maj2 min2)
176 = (maj1 < maj2) || (maj1 == maj2 && min1 < min2)
178 ltMajLvl :: Level -> Level -> Bool
179 -- Tells if one level belongs to a difft *lambda* level to another
180 ltMajLvl any_lvl InlineCtxt = False
181 ltMajLvl InlineCtxt (Level maj2 _) = 0 < maj2
182 ltMajLvl (Level maj1 _) (Level maj2 _) = maj1 < maj2
184 isTopLvl :: Level -> Bool
185 isTopLvl (Level 0 0) = True
186 isTopLvl other = False
188 isInlineCtxt :: Level -> Bool
189 isInlineCtxt InlineCtxt = True
190 isInlineCtxt other = False
192 instance Outputable Level where
193 ppr InlineCtxt = text "<INLINE>"
194 ppr (Level maj min) = hcat [ char '<', int maj, char ',', int min, char '>' ]
196 instance Eq Level where
197 InlineCtxt == InlineCtxt = True
198 (Level maj1 min1) == (Level maj2 min2) = maj1==maj2 && min1==min2
203 %************************************************************************
205 \subsection{Main level-setting code}
207 %************************************************************************
210 setLevels :: FloatOutSwitches
215 setLevels float_lams binds us
216 = initLvl us (do_them binds)
218 -- "do_them"'s main business is to thread the monad along
219 -- It gives each top binding the same empty envt, because
220 -- things unbound in the envt have level number zero implicitly
221 do_them :: [CoreBind] -> LvlM [LevelledBind]
223 do_them [] = returnLvl []
225 = lvlTopBind init_env b `thenLvl` \ (lvld_bind, _) ->
226 do_them bs `thenLvl` \ lvld_binds ->
227 returnLvl (lvld_bind : lvld_binds)
229 init_env = initialEnv float_lams
231 lvlTopBind env (NonRec binder rhs)
232 = lvlBind TopLevel tOP_LEVEL env (AnnNonRec binder (freeVars rhs))
233 -- Rhs can have no free vars!
235 lvlTopBind env (Rec pairs)
236 = lvlBind TopLevel tOP_LEVEL env (AnnRec [(b,freeVars rhs) | (b,rhs) <- pairs])
239 %************************************************************************
241 \subsection{Setting expression levels}
243 %************************************************************************
246 lvlExpr :: Level -- ctxt_lvl: Level of enclosing expression
247 -> LevelEnv -- Level of in-scope names/tyvars
248 -> CoreExprWithFVs -- input expression
249 -> LvlM LevelledExpr -- Result expression
252 The @ctxt_lvl@ is, roughly, the level of the innermost enclosing
253 binder. Here's an example
255 v = \x -> ...\y -> let r = case (..x..) of
259 When looking at the rhs of @r@, @ctxt_lvl@ will be 1 because that's
260 the level of @r@, even though it's inside a level-2 @\y@. It's
261 important that @ctxt_lvl@ is 1 and not 2 in @r@'s rhs, because we
262 don't want @lvlExpr@ to turn the scrutinee of the @case@ into an MFE
263 --- because it isn't a *maximal* free expression.
265 If there were another lambda in @r@'s rhs, it would get level-2 as well.
268 lvlExpr _ _ (_, AnnType ty) = returnLvl (Type ty)
269 lvlExpr _ env (_, AnnVar v) = returnLvl (lookupVar env v)
270 lvlExpr _ env (_, AnnLit lit) = returnLvl (Lit lit)
272 lvlExpr ctxt_lvl env (_, AnnApp fun arg)
273 = lvl_fun fun `thenLvl` \ fun' ->
274 lvlMFE False ctxt_lvl env arg `thenLvl` \ arg' ->
275 returnLvl (App fun' arg')
277 lvl_fun (_, AnnCase _ _ _) = lvlMFE True ctxt_lvl env fun
278 lvl_fun other = lvlExpr ctxt_lvl env fun
279 -- We don't do MFE on partial applications generally,
280 -- but we do if the function is big and hairy, like a case
282 lvlExpr ctxt_lvl env (_, AnnNote InlineMe expr)
283 -- Don't float anything out of an InlineMe; hence the iNLINE_CTXT
284 = lvlExpr iNLINE_CTXT env expr `thenLvl` \ expr' ->
285 returnLvl (Note InlineMe expr')
287 lvlExpr ctxt_lvl env (_, AnnNote note expr)
288 = lvlExpr ctxt_lvl env expr `thenLvl` \ expr' ->
289 returnLvl (Note note expr')
291 -- We don't split adjacent lambdas. That is, given
293 -- we don't float to give
294 -- \x -> let v = x+y in \y -> (v,y)
295 -- Why not? Because partial applications are fairly rare, and splitting
296 -- lambdas makes them more expensive.
298 lvlExpr ctxt_lvl env expr@(_, AnnLam bndr rhs)
299 = lvlMFE True new_lvl new_env body `thenLvl` \ new_body ->
300 returnLvl (mkLams new_bndrs new_body)
302 (bndrs, body) = collectAnnBndrs expr
303 (new_lvl, new_bndrs) = lvlLamBndrs ctxt_lvl bndrs
304 new_env = extendLvlEnv env new_bndrs
305 -- At one time we called a special verion of collectBinders,
306 -- which ignored coercions, because we don't want to split
307 -- a lambda like this (\x -> coerce t (\s -> ...))
308 -- This used to happen quite a bit in state-transformer programs,
309 -- but not nearly so much now non-recursive newtypes are transparent.
310 -- [See SetLevels rev 1.50 for a version with this approach.]
312 lvlExpr ctxt_lvl env (_, AnnLet (AnnNonRec bndr rhs) body)
313 | isUnLiftedType (idType bndr)
314 -- Treat unlifted let-bindings (let x = b in e) just like (case b of x -> e)
315 -- That is, leave it exactly where it is
316 -- We used to float unlifted bindings too (e.g. to get a cheap primop
317 -- outside a lambda (to see how, look at lvlBind in rev 1.58)
318 -- but an unrelated change meant that these unlifed bindings
319 -- could get to the top level which is bad. And there's not much point;
320 -- unlifted bindings are always cheap, and so hardly worth floating.
321 = lvlExpr ctxt_lvl env rhs `thenLvl` \ rhs' ->
322 lvlExpr incd_lvl env' body `thenLvl` \ body' ->
323 returnLvl (Let (NonRec bndr' rhs') body')
325 incd_lvl = incMinorLvl ctxt_lvl
326 bndr' = TB bndr incd_lvl
327 env' = extendLvlEnv env [bndr']
329 lvlExpr ctxt_lvl env (_, AnnLet bind body)
330 = lvlBind NotTopLevel ctxt_lvl env bind `thenLvl` \ (bind', new_env) ->
331 lvlExpr ctxt_lvl new_env body `thenLvl` \ body' ->
332 returnLvl (Let bind' body')
334 lvlExpr ctxt_lvl env (_, AnnCase expr case_bndr alts)
335 = lvlMFE True ctxt_lvl env expr `thenLvl` \ expr' ->
337 alts_env = extendCaseBndrLvlEnv env expr' case_bndr incd_lvl
339 mapLvl (lvl_alt alts_env) alts `thenLvl` \ alts' ->
340 returnLvl (Case expr' (TB case_bndr incd_lvl) alts')
342 incd_lvl = incMinorLvl ctxt_lvl
344 lvl_alt alts_env (con, bs, rhs)
345 = lvlMFE True incd_lvl new_env rhs `thenLvl` \ rhs' ->
346 returnLvl (con, bs', rhs')
348 bs' = [ TB b incd_lvl | b <- bs ]
349 new_env = extendLvlEnv alts_env bs'
352 @lvlMFE@ is just like @lvlExpr@, except that it might let-bind
353 the expression, so that it can itself be floated.
355 [NOTE: unlifted MFEs]
356 We don't float unlifted MFEs, which potentially loses big opportunites.
359 where h :: Int -> Int# is expensive. We'd like to float the (h y) outside
360 the \x, but we don't because it's unboxed. Possible solution: box it.
363 lvlMFE :: Bool -- True <=> strict context [body of case or let]
364 -> Level -- Level of innermost enclosing lambda/tylam
365 -> LevelEnv -- Level of in-scope names/tyvars
366 -> CoreExprWithFVs -- input expression
367 -> LvlM LevelledExpr -- Result expression
369 lvlMFE strict_ctxt ctxt_lvl env (_, AnnType ty)
370 = returnLvl (Type ty)
373 lvlMFE strict_ctxt ctxt_lvl env ann_expr@(fvs, _)
374 | isUnLiftedType ty -- Can't let-bind it; see [NOTE: unlifted MFEs]
375 || isInlineCtxt ctxt_lvl -- Don't float out of an __inline__ context
376 || exprIsTrivial expr -- Never float if it's trivial
377 || not good_destination
378 = -- Don't float it out
379 lvlExpr ctxt_lvl env ann_expr
381 | otherwise -- Float it out!
382 = lvlFloatRhs abs_vars dest_lvl env ann_expr `thenLvl` \ expr' ->
383 newLvlVar "lvl" abs_vars ty `thenLvl` \ var ->
384 returnLvl (Let (NonRec (TB var dest_lvl) expr')
385 (mkVarApps (Var var) abs_vars))
387 expr = deAnnotate ann_expr
389 dest_lvl = destLevel env fvs (isFunction ann_expr)
390 abs_vars = abstractVars dest_lvl env fvs
392 -- A decision to float entails let-binding this thing, and we only do
393 -- that if we'll escape a value lambda, or will go to the top level.
395 | dest_lvl `ltMajLvl` ctxt_lvl -- Escapes a value lambda
396 = not (exprIsCheap expr) || isTopLvl dest_lvl
397 -- Even if it escapes a value lambda, we only
398 -- float if it's not cheap (unless it'll get all the
399 -- way to the top). I've seen cases where we
400 -- float dozens of tiny free expressions, which cost
401 -- more to allocate than to evaluate.
402 -- NB: exprIsCheap is also true of bottom expressions, which
403 -- is good; we don't want to share them
405 -- It's only Really Bad to float a cheap expression out of a
406 -- strict context, because that builds a thunk that otherwise
407 -- would never be built. So another alternative would be to
409 -- || (strict_ctxt && not (exprIsBottom expr))
410 -- to the condition above. We should really try this out.
412 | otherwise -- Does not escape a value lambda
413 = isTopLvl dest_lvl -- Only float if we are going to the top level
414 && floatConsts env -- and the floatConsts flag is on
415 && not strict_ctxt -- Don't float from a strict context
416 -- We are keen to float something to the top level, even if it does not
417 -- escape a lambda, because then it needs no allocation. But it's controlled
418 -- by a flag, because doing this too early loses opportunities for RULES
419 -- which (needless to say) are important in some nofib programs
420 -- (gcd is an example).
423 -- concat = /\ a -> foldr ..a.. (++) []
424 -- was getting turned into
425 -- concat = /\ a -> lvl a
426 -- lvl = /\ a -> foldr ..a.. (++) []
427 -- which is pretty stupid. Hence the strict_ctxt test
431 %************************************************************************
433 \subsection{Bindings}
435 %************************************************************************
437 The binding stuff works for top level too.
440 lvlBind :: TopLevelFlag -- Used solely to decide whether to clone
441 -> Level -- Context level; might be Top even for bindings nested in the RHS
442 -- of a top level binding
445 -> LvlM (LevelledBind, LevelEnv)
447 lvlBind top_lvl ctxt_lvl env (AnnNonRec bndr rhs@(rhs_fvs,_))
448 | isInlineCtxt ctxt_lvl -- Don't do anything inside InlineMe
449 = lvlExpr ctxt_lvl env rhs `thenLvl` \ rhs' ->
450 returnLvl (NonRec (TB bndr ctxt_lvl) rhs', env)
453 = -- No type abstraction; clone existing binder
454 lvlExpr dest_lvl env rhs `thenLvl` \ rhs' ->
455 cloneVar top_lvl env bndr ctxt_lvl dest_lvl `thenLvl` \ (env', bndr') ->
456 returnLvl (NonRec (TB bndr' dest_lvl) rhs', env')
459 = -- Yes, type abstraction; create a new binder, extend substitution, etc
460 lvlFloatRhs abs_vars dest_lvl env rhs `thenLvl` \ rhs' ->
461 newPolyBndrs dest_lvl env abs_vars [bndr] `thenLvl` \ (env', [bndr']) ->
462 returnLvl (NonRec (TB bndr' dest_lvl) rhs', env')
465 bind_fvs = rhs_fvs `unionVarSet` idFreeVars bndr
466 abs_vars = abstractVars dest_lvl env bind_fvs
467 dest_lvl = destLevel env bind_fvs (isFunction rhs)
472 lvlBind top_lvl ctxt_lvl env (AnnRec pairs)
473 | isInlineCtxt ctxt_lvl -- Don't do anything inside InlineMe
474 = mapLvl (lvlExpr ctxt_lvl env) rhss `thenLvl` \ rhss' ->
475 returnLvl (Rec ([TB b ctxt_lvl | b <- bndrs] `zip` rhss'), env)
478 = cloneRecVars top_lvl env bndrs ctxt_lvl dest_lvl `thenLvl` \ (new_env, new_bndrs) ->
479 mapLvl (lvlExpr ctxt_lvl new_env) rhss `thenLvl` \ new_rhss ->
480 returnLvl (Rec ([TB b dest_lvl | b <- new_bndrs] `zip` new_rhss), new_env)
482 | isSingleton pairs && count isId abs_vars > 1
483 = -- Special case for self recursion where there are
484 -- several variables carried around: build a local loop:
485 -- poly_f = \abs_vars. \lam_vars . letrec f = \lam_vars. rhs in f lam_vars
486 -- This just makes the closures a bit smaller. If we don't do
487 -- this, allocation rises significantly on some programs
489 -- We could elaborate it for the case where there are several
490 -- mutually functions, but it's quite a bit more complicated
492 -- This all seems a bit ad hoc -- sigh
494 (bndr,rhs) = head pairs
495 (rhs_lvl, abs_vars_w_lvls) = lvlLamBndrs dest_lvl abs_vars
496 rhs_env = extendLvlEnv env abs_vars_w_lvls
498 cloneVar NotTopLevel rhs_env bndr rhs_lvl rhs_lvl `thenLvl` \ (rhs_env', new_bndr) ->
500 (lam_bndrs, rhs_body) = collectAnnBndrs rhs
501 (body_lvl, new_lam_bndrs) = lvlLamBndrs rhs_lvl lam_bndrs
502 body_env = extendLvlEnv rhs_env' new_lam_bndrs
504 lvlExpr body_lvl body_env rhs_body `thenLvl` \ new_rhs_body ->
505 newPolyBndrs dest_lvl env abs_vars [bndr] `thenLvl` \ (poly_env, [poly_bndr]) ->
506 returnLvl (Rec [(TB poly_bndr dest_lvl,
507 mkLams abs_vars_w_lvls $
508 mkLams new_lam_bndrs $
509 Let (Rec [(TB new_bndr rhs_lvl, mkLams new_lam_bndrs new_rhs_body)])
510 (mkVarApps (Var new_bndr) lam_bndrs))],
513 | otherwise -- Non-null abs_vars
514 = newPolyBndrs dest_lvl env abs_vars bndrs `thenLvl` \ (new_env, new_bndrs) ->
515 mapLvl (lvlFloatRhs abs_vars dest_lvl new_env) rhss `thenLvl` \ new_rhss ->
516 returnLvl (Rec ([TB b dest_lvl | b <- new_bndrs] `zip` new_rhss), new_env)
519 (bndrs,rhss) = unzip pairs
521 -- Finding the free vars of the binding group is annoying
522 bind_fvs = (unionVarSets [ idFreeVars bndr `unionVarSet` rhs_fvs
523 | (bndr, (rhs_fvs,_)) <- pairs])
527 dest_lvl = destLevel env bind_fvs (all isFunction rhss)
528 abs_vars = abstractVars dest_lvl env bind_fvs
530 ----------------------------------------------------
531 -- Three help functons for the type-abstraction case
533 lvlFloatRhs abs_vars dest_lvl env rhs
534 = lvlExpr rhs_lvl rhs_env rhs `thenLvl` \ rhs' ->
535 returnLvl (mkLams abs_vars_w_lvls rhs')
537 (rhs_lvl, abs_vars_w_lvls) = lvlLamBndrs dest_lvl abs_vars
538 rhs_env = extendLvlEnv env abs_vars_w_lvls
542 %************************************************************************
544 \subsection{Deciding floatability}
546 %************************************************************************
549 lvlLamBndrs :: Level -> [CoreBndr] -> (Level, [TaggedBndr Level])
550 -- Compute the levels for the binders of a lambda group
551 -- The binders returned are exactly the same as the ones passed,
552 -- but they are now paired with a level
556 lvlLamBndrs lvl bndrs
557 = go (incMinorLvl lvl)
558 False -- Havn't bumped major level in this group
561 go old_lvl bumped_major rev_lvld_bndrs (bndr:bndrs)
562 | isId bndr && -- Go to the next major level if this is a value binder,
563 not bumped_major && -- and we havn't already gone to the next level (one jump per group)
564 not (isOneShotLambda bndr) -- and it isn't a one-shot lambda
565 = go new_lvl True (TB bndr new_lvl : rev_lvld_bndrs) bndrs
568 = go old_lvl bumped_major (TB bndr old_lvl : rev_lvld_bndrs) bndrs
571 new_lvl = incMajorLvl old_lvl
573 go old_lvl _ rev_lvld_bndrs []
574 = (old_lvl, reverse rev_lvld_bndrs)
575 -- a lambda like this (\x -> coerce t (\s -> ...))
576 -- This happens quite a bit in state-transformer programs
580 -- Destintion level is the max Id level of the expression
581 -- (We'll abstract the type variables, if any.)
582 destLevel :: LevelEnv -> VarSet -> Bool -> Level
583 destLevel env fvs is_function
585 && is_function = tOP_LEVEL -- Send functions to top level; see
586 -- the comments with isFunction
587 | otherwise = maxIdLevel env fvs
589 isFunction :: CoreExprWithFVs -> Bool
590 -- The idea here is that we want to float *functions* to
591 -- the top level. This saves no work, but
592 -- (a) it can make the host function body a lot smaller,
593 -- and hence inlinable.
594 -- (b) it can also save allocation when the function is recursive:
595 -- h = \x -> letrec f = \y -> ...f...y...x...
598 -- f = \x y -> ...(f x)...y...x...
600 -- No allocation for f now.
601 -- We may only want to do this if there are sufficiently few free
602 -- variables. We certainly only want to do it for values, and not for
603 -- constructors. So the simple thing is just to look for lambdas
604 isFunction (_, AnnLam b e) | isId b = True
605 | otherwise = isFunction e
606 isFunction (_, AnnNote n e) = isFunction e
607 isFunction other = False
611 %************************************************************************
613 \subsection{Free-To-Level Monad}
615 %************************************************************************
618 type LevelEnv = (FloatOutSwitches,
619 VarEnv Level, -- Domain is *post-cloned* TyVars and Ids
620 Subst, -- Domain is pre-cloned Ids; tracks the in-scope set
621 -- so that subtitution is capture-avoiding
622 IdEnv ([Var], LevelledExpr)) -- Domain is pre-cloned Ids
623 -- We clone let-bound variables so that they are still
624 -- distinct when floated out; hence the SubstEnv/IdEnv.
625 -- (see point 3 of the module overview comment).
626 -- We also use these envs when making a variable polymorphic
627 -- because we want to float it out past a big lambda.
629 -- The SubstEnv and IdEnv always implement the same mapping, but the
630 -- SubstEnv maps to CoreExpr and the IdEnv to LevelledExpr
631 -- Since the range is always a variable or type application,
632 -- there is never any difference between the two, but sadly
633 -- the types differ. The SubstEnv is used when substituting in
634 -- a variable's IdInfo; the IdEnv when we find a Var.
636 -- In addition the IdEnv records a list of tyvars free in the
637 -- type application, just so we don't have to call freeVars on
638 -- the type application repeatedly.
640 -- The domain of the both envs is *pre-cloned* Ids, though
642 -- The domain of the VarEnv Level is the *post-cloned* Ids
644 initialEnv :: FloatOutSwitches -> LevelEnv
645 initialEnv float_lams = (float_lams, emptyVarEnv, emptySubst, emptyVarEnv)
647 floatLams :: LevelEnv -> Bool
648 floatLams (FloatOutSw float_lams _, _, _, _) = float_lams
650 floatConsts :: LevelEnv -> Bool
651 floatConsts (FloatOutSw _ float_consts, _, _, _) = float_consts
653 extendLvlEnv :: LevelEnv -> [TaggedBndr Level] -> LevelEnv
654 -- Used when *not* cloning
655 extendLvlEnv (float_lams, lvl_env, subst, id_env) prs
657 foldl add_lvl lvl_env prs,
658 foldl del_subst subst prs,
659 foldl del_id id_env prs)
661 add_lvl env (TB v l) = extendVarEnv env v l
662 del_subst env (TB v _) = extendInScope env v
663 del_id env (TB v _) = delVarEnv env v
664 -- We must remove any clone for this variable name in case of
665 -- shadowing. This bit me in the following case
666 -- (in nofib/real/gg/Spark.hs):
669 -- ... -> case e of wild {
670 -- ... -> ... wild ...
674 -- The inside occurrence of @wild@ was being replaced with @ds@,
675 -- incorrectly, because the SubstEnv was still lying around. Ouch!
678 -- extendCaseBndrLvlEnv adds the mapping case-bndr->scrut-var if it can
679 -- (see point 4 of the module overview comment)
680 extendCaseBndrLvlEnv (float_lams, lvl_env, subst, id_env) (Var scrut_var) case_bndr lvl
682 extendVarEnv lvl_env case_bndr lvl,
683 extendSubst subst case_bndr (DoneEx (Var scrut_var)),
684 extendVarEnv id_env case_bndr ([scrut_var], Var scrut_var))
686 extendCaseBndrLvlEnv env scrut case_bndr lvl
687 = extendLvlEnv env [TB case_bndr lvl]
689 extendPolyLvlEnv dest_lvl (float_lams, lvl_env, subst, id_env) abs_vars bndr_pairs
691 foldl add_lvl lvl_env bndr_pairs,
692 foldl add_subst subst bndr_pairs,
693 foldl add_id id_env bndr_pairs)
695 add_lvl env (v,v') = extendVarEnv env v' dest_lvl
696 add_subst env (v,v') = extendSubst env v (DoneEx (mkVarApps (Var v') abs_vars))
697 add_id env (v,v') = extendVarEnv env v ((v':abs_vars), mkVarApps (Var v') abs_vars)
699 extendCloneLvlEnv lvl (float_lams, lvl_env, _, id_env) new_subst bndr_pairs
701 foldl add_lvl lvl_env bndr_pairs,
703 foldl add_id id_env bndr_pairs)
705 add_lvl env (v,v') = extendVarEnv env v' lvl
706 add_id env (v,v') = extendVarEnv env v ([v'], Var v')
709 maxIdLevel :: LevelEnv -> VarSet -> Level
710 maxIdLevel (_, lvl_env,_,id_env) var_set
711 = foldVarSet max_in tOP_LEVEL var_set
713 max_in in_var lvl = foldr max_out lvl (case lookupVarEnv id_env in_var of
714 Just (abs_vars, _) -> abs_vars
718 | isId out_var = case lookupVarEnv lvl_env out_var of
719 Just lvl' -> maxLvl lvl' lvl
721 | otherwise = lvl -- Ignore tyvars in *maxIdLevel*
723 lookupVar :: LevelEnv -> Id -> LevelledExpr
724 lookupVar (_, _, _, id_env) v = case lookupVarEnv id_env v of
725 Just (_, expr) -> expr
728 abstractVars :: Level -> LevelEnv -> VarSet -> [Var]
729 -- Find the variables in fvs, free vars of the target expresion,
730 -- whose level is greater than the destination level
731 -- These are the ones we are going to abstract out
732 abstractVars dest_lvl env fvs
733 = uniq (sortLt lt [var | fv <- varSetElems fvs, var <- absVarsOf dest_lvl env fv])
735 -- Sort the variables so we don't get
736 -- mixed-up tyvars and Ids; it's just messy
737 v1 `lt` v2 = case (isId v1, isId v2) of
738 (True, False) -> False
739 (False, True) -> True
740 other -> v1 < v2 -- Same family
742 uniq :: [Var] -> [Var]
743 -- Remove adjacent duplicates; the sort will have brought them together
744 uniq (v1:v2:vs) | v1 == v2 = uniq (v2:vs)
745 | otherwise = v1 : uniq (v2:vs)
748 absVarsOf :: Level -> LevelEnv -> Var -> [Var]
749 -- If f is free in the expression, and f maps to poly_f a b c in the
750 -- current substitution, then we must report a b c as candidate type
752 absVarsOf dest_lvl (_, lvl_env, _, id_env) v
754 = [zap av2 | av1 <- lookup_avs v, av2 <- add_tyvars av1, abstract_me av2]
757 = if abstract_me v then [v] else []
760 abstract_me v = case lookupVarEnv lvl_env v of
761 Just lvl -> dest_lvl `ltLvl` lvl
764 lookup_avs v = case lookupVarEnv id_env v of
765 Just (abs_vars, _) -> abs_vars
768 add_tyvars v | isId v = v : varSetElems (idFreeTyVars v)
771 -- We are going to lambda-abstract, so nuke any IdInfo,
772 -- and add the tyvars of the Id (if necessary)
773 zap v | isId v = WARN( workerExists (idWorkerInfo v) ||
774 not (isEmptyCoreRules (idSpecialisation v)),
775 text "absVarsOf: discarding info on" <+> ppr v )
776 setIdInfo v vanillaIdInfo
781 type LvlM result = UniqSM result
790 newPolyBndrs dest_lvl env abs_vars bndrs
791 = getUniquesUs `thenLvl` \ uniqs ->
793 new_bndrs = zipWith mk_poly_bndr bndrs uniqs
795 returnLvl (extendPolyLvlEnv dest_lvl env abs_vars (bndrs `zip` new_bndrs), new_bndrs)
797 mk_poly_bndr bndr uniq = mkSysLocalUnencoded (mkFastString str) uniq poly_ty
799 str = "poly_" ++ occNameUserString (getOccName bndr)
800 poly_ty = mkPiTypes abs_vars (idType bndr)
804 -> [CoreBndr] -> Type -- Abstract wrt these bndrs
806 newLvlVar str vars body_ty
807 = getUniqueUs `thenLvl` \ uniq ->
808 returnUs (mkSysLocalUnencoded (mkFastString str) uniq (mkPiTypes vars body_ty))
810 -- The deeply tiresome thing is that we have to apply the substitution
811 -- to the rules inside each Id. Grr. But it matters.
813 cloneVar :: TopLevelFlag -> LevelEnv -> Id -> Level -> Level -> LvlM (LevelEnv, Id)
814 cloneVar TopLevel env v ctxt_lvl dest_lvl
815 = returnUs (env, v) -- Don't clone top level things
816 cloneVar NotTopLevel env@(_,_,subst,_) v ctxt_lvl dest_lvl
818 getUs `thenLvl` \ us ->
820 (subst', v1) = substAndCloneId subst us v
821 v2 = zap_demand ctxt_lvl dest_lvl v1
822 env' = extendCloneLvlEnv dest_lvl env subst' [(v,v2)]
826 cloneRecVars :: TopLevelFlag -> LevelEnv -> [Id] -> Level -> Level -> LvlM (LevelEnv, [Id])
827 cloneRecVars TopLevel env vs ctxt_lvl dest_lvl
828 = returnUs (env, vs) -- Don't clone top level things
829 cloneRecVars NotTopLevel env@(_,_,subst,_) vs ctxt_lvl dest_lvl
830 = ASSERT( all isId vs )
831 getUs `thenLvl` \ us ->
833 (subst', vs1) = substAndCloneRecIds subst us vs
834 vs2 = map (zap_demand ctxt_lvl dest_lvl) vs1
835 env' = extendCloneLvlEnv dest_lvl env subst' (vs `zip` vs2)
839 -- VERY IMPORTANT: we must zap the demand info
840 -- if the thing is going to float out past a lambda
841 zap_demand dest_lvl ctxt_lvl id
842 | ctxt_lvl == dest_lvl = id -- Stays put
843 | otherwise = zapDemandIdInfo id -- Floats out