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
54 #include "HsVersions.h"
58 import DynFlags ( FloatOutSwitches(..) )
59 import CoreUtils ( exprType, exprIsTrivial, exprBotStrictness_maybe, mkPiTypes )
60 import CoreFVs -- all of it
61 import CoreSubst ( Subst, emptySubst, extendInScope, extendInScopeList,
62 extendIdSubst, cloneIdBndr, cloneRecIdBndrs )
63 import Id ( Id, idType, mkSysLocal, isOneShotLambda,
64 zapDemandIdInfo, transferPolyIdInfo,
65 idSpecialisation, idUnfolding, setIdInfo,
66 setIdNewStrictness, setIdArity
72 import Name ( getOccName )
73 import OccName ( occNameString )
74 import Type ( isUnLiftedType, Type )
75 import BasicTypes ( TopLevelFlag(..) )
77 import Util ( sortLe, isSingleton, count )
82 %************************************************************************
84 \subsection{Level numbers}
86 %************************************************************************
89 data Level = 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
121 Note [FloatOut inside INLINE]
122 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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
153 tOP_LEVEL = Level 0 0
155 incMajorLvl :: Level -> Level
156 incMajorLvl (Level major _) = Level (major + 1) 0
158 incMinorLvl :: Level -> Level
159 incMinorLvl (Level major minor) = Level major (minor+1)
161 maxLvl :: Level -> Level -> Level
162 maxLvl l1@(Level maj1 min1) l2@(Level maj2 min2)
163 | (maj1 > maj2) || (maj1 == maj2 && min1 > min2) = l1
166 ltLvl :: Level -> Level -> Bool
167 ltLvl (Level maj1 min1) (Level maj2 min2)
168 = (maj1 < maj2) || (maj1 == maj2 && min1 < min2)
170 ltMajLvl :: Level -> Level -> Bool
171 -- Tells if one level belongs to a difft *lambda* level to another
172 ltMajLvl (Level maj1 _) (Level maj2 _) = maj1 < maj2
174 isTopLvl :: Level -> Bool
175 isTopLvl (Level 0 0) = True
178 instance Outputable Level where
179 ppr (Level maj min) = hcat [ char '<', int maj, char ',', int min, char '>' ]
181 instance Eq Level where
182 (Level maj1 min1) == (Level maj2 min2) = maj1 == maj2 && min1 == min2
186 %************************************************************************
188 \subsection{Main level-setting code}
190 %************************************************************************
193 setLevels :: FloatOutSwitches
198 setLevels float_lams binds us
199 = initLvl us (do_them init_env binds)
201 init_env = initialEnv float_lams
203 do_them :: LevelEnv -> [CoreBind] -> LvlM [LevelledBind]
204 do_them _ [] = return []
206 = do { (lvld_bind, env') <- lvlTopBind env b
207 ; lvld_binds <- do_them env' bs
208 ; return (lvld_bind : lvld_binds) }
210 lvlTopBind :: LevelEnv -> Bind Id -> LvlM (LevelledBind, LevelEnv)
211 lvlTopBind env (NonRec binder rhs)
212 = lvlBind TopLevel tOP_LEVEL env (AnnNonRec binder (freeVars rhs))
213 -- Rhs can have no free vars!
215 lvlTopBind env (Rec pairs)
216 = lvlBind TopLevel tOP_LEVEL env (AnnRec [(b,freeVars rhs) | (b,rhs) <- pairs])
219 %************************************************************************
221 \subsection{Setting expression levels}
223 %************************************************************************
226 lvlExpr :: Level -- ctxt_lvl: Level of enclosing expression
227 -> LevelEnv -- Level of in-scope names/tyvars
228 -> CoreExprWithFVs -- input expression
229 -> LvlM LevelledExpr -- Result expression
232 The @ctxt_lvl@ is, roughly, the level of the innermost enclosing
233 binder. Here's an example
235 v = \x -> ...\y -> let r = case (..x..) of
239 When looking at the rhs of @r@, @ctxt_lvl@ will be 1 because that's
240 the level of @r@, even though it's inside a level-2 @\y@. It's
241 important that @ctxt_lvl@ is 1 and not 2 in @r@'s rhs, because we
242 don't want @lvlExpr@ to turn the scrutinee of the @case@ into an MFE
243 --- because it isn't a *maximal* free expression.
245 If there were another lambda in @r@'s rhs, it would get level-2 as well.
248 lvlExpr _ _ ( _, AnnType ty) = return (Type ty)
249 lvlExpr _ env (_, AnnVar v) = return (lookupVar env v)
250 lvlExpr _ _ (_, AnnLit lit) = return (Lit lit)
252 lvlExpr ctxt_lvl env (_, AnnApp fun arg) = do
254 arg' <- lvlMFE False ctxt_lvl env arg
255 return (App fun' arg')
258 lvl_fun (_, AnnCase _ _ _ _) = lvlMFE True ctxt_lvl env fun
259 lvl_fun _ = lvlExpr ctxt_lvl env fun
260 -- We don't do MFE on partial applications generally,
261 -- but we do if the function is big and hairy, like a case
263 lvlExpr ctxt_lvl env (_, AnnNote note expr) = do
264 expr' <- lvlExpr ctxt_lvl env expr
265 return (Note note expr')
267 lvlExpr ctxt_lvl env (_, AnnCast expr co) = do
268 expr' <- lvlExpr ctxt_lvl env expr
269 return (Cast expr' co)
271 -- We don't split adjacent lambdas. That is, given
273 -- we don't float to give
274 -- \x -> let v = x+y in \y -> (v,y)
275 -- Why not? Because partial applications are fairly rare, and splitting
276 -- lambdas makes them more expensive.
278 lvlExpr ctxt_lvl env expr@(_, AnnLam {}) = do
279 new_body <- lvlMFE True new_lvl new_env body
280 return (mkLams new_bndrs new_body)
282 (bndrs, body) = collectAnnBndrs expr
283 (new_lvl, new_bndrs) = lvlLamBndrs ctxt_lvl bndrs
284 new_env = extendLvlEnv env new_bndrs
285 -- At one time we called a special verion of collectBinders,
286 -- which ignored coercions, because we don't want to split
287 -- a lambda like this (\x -> coerce t (\s -> ...))
288 -- This used to happen quite a bit in state-transformer programs,
289 -- but not nearly so much now non-recursive newtypes are transparent.
290 -- [See SetLevels rev 1.50 for a version with this approach.]
292 lvlExpr ctxt_lvl env (_, AnnLet (AnnNonRec bndr rhs) body)
293 | isUnLiftedType (idType bndr) = do
294 -- Treat unlifted let-bindings (let x = b in e) just like (case b of x -> e)
295 -- That is, leave it exactly where it is
296 -- We used to float unlifted bindings too (e.g. to get a cheap primop
297 -- outside a lambda (to see how, look at lvlBind in rev 1.58)
298 -- but an unrelated change meant that these unlifed bindings
299 -- could get to the top level which is bad. And there's not much point;
300 -- unlifted bindings are always cheap, and so hardly worth floating.
301 rhs' <- lvlExpr ctxt_lvl env rhs
302 body' <- lvlExpr incd_lvl env' body
303 return (Let (NonRec bndr' rhs') body')
305 incd_lvl = incMinorLvl ctxt_lvl
306 bndr' = TB bndr incd_lvl
307 env' = extendLvlEnv env [bndr']
309 lvlExpr ctxt_lvl env (_, AnnLet bind body) = do
310 (bind', new_env) <- lvlBind NotTopLevel ctxt_lvl env bind
311 body' <- lvlExpr ctxt_lvl new_env body
312 return (Let bind' body')
314 lvlExpr ctxt_lvl env (_, AnnCase expr case_bndr ty alts) = do
315 expr' <- lvlMFE True ctxt_lvl env expr
316 let alts_env = extendCaseBndrLvlEnv env expr' case_bndr incd_lvl
317 alts' <- mapM (lvl_alt alts_env) alts
318 return (Case expr' (TB case_bndr incd_lvl) ty alts')
320 incd_lvl = incMinorLvl ctxt_lvl
322 lvl_alt alts_env (con, bs, rhs) = do
323 rhs' <- lvlMFE True incd_lvl new_env rhs
324 return (con, bs', rhs')
326 bs' = [ TB b incd_lvl | b <- bs ]
327 new_env = extendLvlEnv alts_env bs'
330 @lvlMFE@ is just like @lvlExpr@, except that it might let-bind
331 the expression, so that it can itself be floated.
335 We don't float unlifted MFEs, which potentially loses big opportunites.
338 where h :: Int -> Int# is expensive. We'd like to float the (h y) outside
339 the \x, but we don't because it's unboxed. Possible solution: box it.
341 Note [Bottoming floats]
342 ~~~~~~~~~~~~~~~~~~~~~~~
344 f = \x. g (error "urk")
345 we'd like to float the call to error, to get
348 But, it's very helpful for lvl to get a strictness signature, so that,
349 for example, its unfolding is not exposed in interface files (unnecessary).
350 But this float-out might occur after strictness analysis. So we use the
351 cheap-and-cheerful exprBotStrictness_maybe function.
354 lvlMFE :: Bool -- True <=> strict context [body of case or let]
355 -> Level -- Level of innermost enclosing lambda/tylam
356 -> LevelEnv -- Level of in-scope names/tyvars
357 -> CoreExprWithFVs -- input expression
358 -> LvlM LevelledExpr -- Result expression
360 lvlMFE _ _ _ (_, AnnType ty)
363 -- No point in floating out an expression wrapped in a coercion or note
364 -- If we do we'll transform lvl = e |> co
365 -- to lvl' = e; lvl = lvl' |> co
366 -- and then inline lvl. Better just to float out the payload.
367 lvlMFE strict_ctxt ctxt_lvl env (_, AnnNote n e)
368 = do { e' <- lvlMFE strict_ctxt ctxt_lvl env e
369 ; return (Note n e') }
371 lvlMFE strict_ctxt ctxt_lvl env (_, AnnCast e co)
372 = do { e' <- lvlMFE strict_ctxt ctxt_lvl env e
373 ; return (Cast e' co) }
375 lvlMFE strict_ctxt ctxt_lvl env ann_expr@(fvs, _)
376 | isUnLiftedType ty -- Can't let-bind it; see Note [Unlifted MFEs]
377 || exprIsTrivial expr -- Never float if it's trivial
378 || not good_destination
379 = -- Don't float it out
380 lvlExpr ctxt_lvl env ann_expr
382 | otherwise -- Float it out!
383 = do expr' <- lvlFloatRhs abs_vars dest_lvl env ann_expr
384 var <- newLvlVar "lvl" abs_vars ty
385 -- Note [Bottoming floats]
386 let var_w_str = case exprBotStrictness_maybe expr of
387 Just (arity,str) -> var `setIdArity` arity
388 `setIdNewStrictness` str
390 return (Let (NonRec (TB var_w_str dest_lvl) expr')
391 (mkVarApps (Var var_w_str) abs_vars))
393 expr = deAnnotate ann_expr
395 dest_lvl = destLevel env fvs (isFunction ann_expr)
396 abs_vars = abstractVars dest_lvl env fvs
398 -- A decision to float entails let-binding this thing, and we only do
399 -- that if we'll escape a value lambda, or will go to the top level.
401 | dest_lvl `ltMajLvl` ctxt_lvl -- Escapes a value lambda
403 -- OLD CODE: not (exprIsCheap expr) || isTopLvl dest_lvl
404 -- see Note [Escaping a value lambda]
406 | otherwise -- Does not escape a value lambda
407 = isTopLvl dest_lvl -- Only float if we are going to the top level
408 && floatConsts env -- and the floatConsts flag is on
409 && not strict_ctxt -- Don't float from a strict context
410 -- We are keen to float something to the top level, even if it does not
411 -- escape a lambda, because then it needs no allocation. But it's controlled
412 -- by a flag, because doing this too early loses opportunities for RULES
413 -- which (needless to say) are important in some nofib programs
414 -- (gcd is an example).
417 -- concat = /\ a -> foldr ..a.. (++) []
418 -- was getting turned into
419 -- concat = /\ a -> lvl a
420 -- lvl = /\ a -> foldr ..a.. (++) []
421 -- which is pretty stupid. Hence the strict_ctxt test
424 Note [Escaping a value lambda]
425 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
426 We want to float even cheap expressions out of value lambdas,
427 because that saves allocation. Consider
428 f = \x. .. (\y.e) ...
429 Then we'd like to avoid allocating the (\y.e) every time we call f,
430 (assuming e does not mention x).
432 An example where this really makes a difference is simplrun009.
434 Another reason it's good is because it makes SpecContr fire on functions.
436 f = \x. ....(f (\y.e))....
437 After floating we get
439 f = \x. ....(f lvl)...
440 and that is much easier for SpecConstr to generate a robust specialisation for.
442 The OLD CODE (given where this Note is referred to) prevents floating
443 of the example above, so I just don't understand the old code. I
444 don't understand the old comment either (which appears below). I
445 measured the effect on nofib of changing OLD CODE to 'True', and got
446 zeros everywhere, but a 4% win for 'puzzle'. Very small 0.5% loss for
447 'cse'; turns out to be because our arity analysis isn't good enough
448 yet (mentioned in Simon-nofib-notes).
451 Even if it escapes a value lambda, we only
452 float if it's not cheap (unless it'll get all the
453 way to the top). I've seen cases where we
454 float dozens of tiny free expressions, which cost
455 more to allocate than to evaluate.
456 NB: exprIsCheap is also true of bottom expressions, which
457 is good; we don't want to share them
459 It's only Really Bad to float a cheap expression out of a
460 strict context, because that builds a thunk that otherwise
461 would never be built. So another alternative would be to
463 || (strict_ctxt && not (exprIsBottom expr))
464 to the condition above. We should really try this out.
467 %************************************************************************
469 \subsection{Bindings}
471 %************************************************************************
473 The binding stuff works for top level too.
476 lvlBind :: TopLevelFlag -- Used solely to decide whether to clone
477 -> Level -- Context level; might be Top even for bindings nested in the RHS
478 -- of a top level binding
481 -> LvlM (LevelledBind, LevelEnv)
483 lvlBind top_lvl ctxt_lvl env (AnnNonRec bndr rhs@(rhs_fvs,_))
484 | isTyVar bndr -- Don't do anything for TyVar binders
485 -- (simplifier gets rid of them pronto)
486 = do rhs' <- lvlExpr ctxt_lvl env rhs
487 return (NonRec (TB bndr ctxt_lvl) rhs', env)
490 = do -- No type abstraction; clone existing binder
491 rhs' <- lvlExpr dest_lvl env rhs
492 (env', bndr') <- cloneVar top_lvl env bndr ctxt_lvl dest_lvl
493 return (NonRec (TB bndr' dest_lvl) rhs', env')
496 = do -- Yes, type abstraction; create a new binder, extend substitution, etc
497 rhs' <- lvlFloatRhs abs_vars dest_lvl env rhs
498 (env', [bndr']) <- newPolyBndrs dest_lvl env abs_vars [bndr]
499 return (NonRec (TB bndr' dest_lvl) rhs', env')
502 bind_fvs = rhs_fvs `unionVarSet` idFreeVars bndr
503 abs_vars = abstractVars dest_lvl env bind_fvs
504 dest_lvl = destLevel env bind_fvs (isFunction rhs)
509 lvlBind top_lvl ctxt_lvl env (AnnRec pairs)
511 = do (new_env, new_bndrs) <- cloneRecVars top_lvl env bndrs ctxt_lvl dest_lvl
512 new_rhss <- mapM (lvlExpr ctxt_lvl new_env) rhss
513 return (Rec ([TB b dest_lvl | b <- new_bndrs] `zip` new_rhss), new_env)
515 | isSingleton pairs && count isIdVar abs_vars > 1
516 = do -- Special case for self recursion where there are
517 -- several variables carried around: build a local loop:
518 -- poly_f = \abs_vars. \lam_vars . letrec f = \lam_vars. rhs in f lam_vars
519 -- This just makes the closures a bit smaller. If we don't do
520 -- this, allocation rises significantly on some programs
522 -- We could elaborate it for the case where there are several
523 -- mutually functions, but it's quite a bit more complicated
525 -- This all seems a bit ad hoc -- sigh
527 (bndr,rhs) = head pairs
528 (rhs_lvl, abs_vars_w_lvls) = lvlLamBndrs dest_lvl abs_vars
529 rhs_env = extendLvlEnv env abs_vars_w_lvls
530 (rhs_env', new_bndr) <- cloneVar NotTopLevel rhs_env bndr rhs_lvl rhs_lvl
532 (lam_bndrs, rhs_body) = collectAnnBndrs rhs
533 (body_lvl, new_lam_bndrs) = lvlLamBndrs rhs_lvl lam_bndrs
534 body_env = extendLvlEnv rhs_env' new_lam_bndrs
535 new_rhs_body <- lvlExpr body_lvl body_env rhs_body
536 (poly_env, [poly_bndr]) <- newPolyBndrs dest_lvl env abs_vars [bndr]
537 return (Rec [(TB poly_bndr dest_lvl,
538 mkLams abs_vars_w_lvls $
539 mkLams new_lam_bndrs $
540 Let (Rec [(TB new_bndr rhs_lvl, mkLams new_lam_bndrs new_rhs_body)])
541 (mkVarApps (Var new_bndr) lam_bndrs))],
544 | otherwise = do -- Non-null abs_vars
545 (new_env, new_bndrs) <- newPolyBndrs dest_lvl env abs_vars bndrs
546 new_rhss <- mapM (lvlFloatRhs abs_vars dest_lvl new_env) rhss
547 return (Rec ([TB b dest_lvl | b <- new_bndrs] `zip` new_rhss), new_env)
550 (bndrs,rhss) = unzip pairs
552 -- Finding the free vars of the binding group is annoying
553 bind_fvs = (unionVarSets [ idFreeVars bndr `unionVarSet` rhs_fvs
554 | (bndr, (rhs_fvs,_)) <- pairs])
558 dest_lvl = destLevel env bind_fvs (all isFunction rhss)
559 abs_vars = abstractVars dest_lvl env bind_fvs
561 ----------------------------------------------------
562 -- Three help functons for the type-abstraction case
564 lvlFloatRhs :: [CoreBndr] -> Level -> LevelEnv -> CoreExprWithFVs
565 -> UniqSM (Expr (TaggedBndr Level))
566 lvlFloatRhs abs_vars dest_lvl env rhs = do
567 rhs' <- lvlExpr rhs_lvl rhs_env rhs
568 return (mkLams abs_vars_w_lvls rhs')
570 (rhs_lvl, abs_vars_w_lvls) = lvlLamBndrs dest_lvl abs_vars
571 rhs_env = extendLvlEnv env abs_vars_w_lvls
575 %************************************************************************
577 \subsection{Deciding floatability}
579 %************************************************************************
582 lvlLamBndrs :: Level -> [CoreBndr] -> (Level, [TaggedBndr Level])
583 -- Compute the levels for the binders of a lambda group
584 -- The binders returned are exactly the same as the ones passed,
585 -- but they are now paired with a level
589 lvlLamBndrs lvl bndrs
590 = go (incMinorLvl lvl)
591 False -- Havn't bumped major level in this group
594 go old_lvl bumped_major rev_lvld_bndrs (bndr:bndrs)
595 | isIdVar bndr && -- Go to the next major level if this is a value binder,
596 not bumped_major && -- and we havn't already gone to the next level (one jump per group)
597 not (isOneShotLambda bndr) -- and it isn't a one-shot lambda
598 = go new_lvl True (TB bndr new_lvl : rev_lvld_bndrs) bndrs
601 = go old_lvl bumped_major (TB bndr old_lvl : rev_lvld_bndrs) bndrs
604 new_lvl = incMajorLvl old_lvl
606 go old_lvl _ rev_lvld_bndrs []
607 = (old_lvl, reverse rev_lvld_bndrs)
608 -- a lambda like this (\x -> coerce t (\s -> ...))
609 -- This happens quite a bit in state-transformer programs
613 -- Destintion level is the max Id level of the expression
614 -- (We'll abstract the type variables, if any.)
615 destLevel :: LevelEnv -> VarSet -> Bool -> Level
616 destLevel env fvs is_function
618 && is_function = tOP_LEVEL -- Send functions to top level; see
619 -- the comments with isFunction
620 | otherwise = maxIdLevel env fvs
622 isFunction :: CoreExprWithFVs -> Bool
623 -- The idea here is that we want to float *functions* to
624 -- the top level. This saves no work, but
625 -- (a) it can make the host function body a lot smaller,
626 -- and hence inlinable.
627 -- (b) it can also save allocation when the function is recursive:
628 -- h = \x -> letrec f = \y -> ...f...y...x...
631 -- f = \x y -> ...(f x)...y...x...
633 -- No allocation for f now.
634 -- We may only want to do this if there are sufficiently few free
635 -- variables. We certainly only want to do it for values, and not for
636 -- constructors. So the simple thing is just to look for lambdas
637 isFunction (_, AnnLam b e) | isIdVar b = True
638 | otherwise = isFunction e
639 isFunction (_, AnnNote _ e) = isFunction e
644 %************************************************************************
646 \subsection{Free-To-Level Monad}
648 %************************************************************************
651 type LevelEnv = (FloatOutSwitches,
652 VarEnv Level, -- Domain is *post-cloned* TyVars and Ids
653 Subst, -- Domain is pre-cloned Ids; tracks the in-scope set
654 -- so that subtitution is capture-avoiding
655 IdEnv ([Var], LevelledExpr)) -- Domain is pre-cloned Ids
656 -- We clone let-bound variables so that they are still
657 -- distinct when floated out; hence the SubstEnv/IdEnv.
658 -- (see point 3 of the module overview comment).
659 -- We also use these envs when making a variable polymorphic
660 -- because we want to float it out past a big lambda.
662 -- The Subst and IdEnv always implement the same mapping, but the
663 -- Subst maps to CoreExpr and the IdEnv to LevelledExpr
664 -- Since the range is always a variable or type application,
665 -- there is never any difference between the two, but sadly
666 -- the types differ. The SubstEnv is used when substituting in
667 -- a variable's IdInfo; the IdEnv when we find a Var.
669 -- In addition the IdEnv records a list of tyvars free in the
670 -- type application, just so we don't have to call freeVars on
671 -- the type application repeatedly.
673 -- The domain of the both envs is *pre-cloned* Ids, though
675 -- The domain of the VarEnv Level is the *post-cloned* Ids
677 initialEnv :: FloatOutSwitches -> LevelEnv
678 initialEnv float_lams = (float_lams, emptyVarEnv, emptySubst, emptyVarEnv)
680 floatLams :: LevelEnv -> Bool
681 floatLams (fos, _, _, _) = floatOutLambdas fos
683 floatConsts :: LevelEnv -> Bool
684 floatConsts (fos, _, _, _) = floatOutConstants fos
686 extendLvlEnv :: LevelEnv -> [TaggedBndr Level] -> LevelEnv
687 -- Used when *not* cloning
688 extendLvlEnv (float_lams, lvl_env, subst, id_env) prs
690 foldl add_lvl lvl_env prs,
691 foldl del_subst subst prs,
692 foldl del_id id_env prs)
694 add_lvl env (TB v l) = extendVarEnv env v l
695 del_subst env (TB v _) = extendInScope env v
696 del_id env (TB v _) = delVarEnv env v
697 -- We must remove any clone for this variable name in case of
698 -- shadowing. This bit me in the following case
699 -- (in nofib/real/gg/Spark.hs):
702 -- ... -> case e of wild {
703 -- ... -> ... wild ...
707 -- The inside occurrence of @wild@ was being replaced with @ds@,
708 -- incorrectly, because the SubstEnv was still lying around. Ouch!
711 extendInScopeEnv :: LevelEnv -> Var -> LevelEnv
712 extendInScopeEnv (fl, le, subst, ids) v = (fl, le, extendInScope subst v, ids)
714 extendInScopeEnvList :: LevelEnv -> [Var] -> LevelEnv
715 extendInScopeEnvList (fl, le, subst, ids) vs = (fl, le, extendInScopeList subst vs, ids)
717 -- extendCaseBndrLvlEnv adds the mapping case-bndr->scrut-var if it can
718 -- (see point 4 of the module overview comment)
719 extendCaseBndrLvlEnv :: LevelEnv -> Expr (TaggedBndr Level) -> Var -> Level
721 extendCaseBndrLvlEnv (float_lams, lvl_env, subst, id_env) (Var scrut_var) case_bndr lvl
723 extendVarEnv lvl_env case_bndr lvl,
724 extendIdSubst subst case_bndr (Var scrut_var),
725 extendVarEnv id_env case_bndr ([scrut_var], Var scrut_var))
727 extendCaseBndrLvlEnv env _scrut case_bndr lvl
728 = extendLvlEnv env [TB case_bndr lvl]
730 extendPolyLvlEnv :: Level -> LevelEnv -> [Var] -> [(Var, Var)] -> LevelEnv
731 extendPolyLvlEnv dest_lvl (float_lams, lvl_env, subst, id_env) abs_vars bndr_pairs
733 foldl add_lvl lvl_env bndr_pairs,
734 foldl add_subst subst bndr_pairs,
735 foldl add_id id_env bndr_pairs)
737 add_lvl env (_, v') = extendVarEnv env v' dest_lvl
738 add_subst env (v, v') = extendIdSubst env v (mkVarApps (Var v') abs_vars)
739 add_id env (v, v') = extendVarEnv env v ((v':abs_vars), mkVarApps (Var v') abs_vars)
741 extendCloneLvlEnv :: Level -> LevelEnv -> Subst -> [(Var, Var)] -> LevelEnv
742 extendCloneLvlEnv lvl (float_lams, lvl_env, _, id_env) new_subst bndr_pairs
744 foldl add_lvl lvl_env bndr_pairs,
746 foldl add_id id_env bndr_pairs)
748 add_lvl env (_, v') = extendVarEnv env v' lvl
749 add_id env (v, v') = extendVarEnv env v ([v'], Var v')
752 maxIdLevel :: LevelEnv -> VarSet -> Level
753 maxIdLevel (_, lvl_env,_,id_env) var_set
754 = foldVarSet max_in tOP_LEVEL var_set
756 max_in in_var lvl = foldr max_out lvl (case lookupVarEnv id_env in_var of
757 Just (abs_vars, _) -> abs_vars
761 | isIdVar out_var = case lookupVarEnv lvl_env out_var of
762 Just lvl' -> maxLvl lvl' lvl
764 | otherwise = lvl -- Ignore tyvars in *maxIdLevel*
766 lookupVar :: LevelEnv -> Id -> LevelledExpr
767 lookupVar (_, _, _, id_env) v = case lookupVarEnv id_env v of
768 Just (_, expr) -> expr
771 abstractVars :: Level -> LevelEnv -> VarSet -> [Var]
772 -- Find the variables in fvs, free vars of the target expresion,
773 -- whose level is greater than the destination level
774 -- These are the ones we are going to abstract out
775 abstractVars dest_lvl (_, lvl_env, _, id_env) fvs
776 = map zap $ uniq $ sortLe le
777 [var | fv <- varSetElems fvs
778 , var <- absVarsOf id_env fv
780 -- NB: it's important to call abstract_me only on the OutIds the
781 -- come from absVarsOf (not on fv, which is an InId)
783 -- Sort the variables so the true type variables come first;
784 -- the tyvars scope over Ids and coercion vars
785 v1 `le` v2 = case (is_tv v1, is_tv v2) of
786 (True, False) -> True
787 (False, True) -> False
788 _ -> v1 <= v2 -- Same family
790 is_tv v = isTyVar v && not (isCoVar v)
792 uniq :: [Var] -> [Var]
793 -- Remove adjacent duplicates; the sort will have brought them together
794 uniq (v1:v2:vs) | v1 == v2 = uniq (v2:vs)
795 | otherwise = v1 : uniq (v2:vs)
798 abstract_me v = case lookupVarEnv lvl_env v of
799 Just lvl -> dest_lvl `ltLvl` lvl
802 -- We are going to lambda-abstract, so nuke any IdInfo,
803 -- and add the tyvars of the Id (if necessary)
804 zap v | isIdVar v = WARN( isInlineRule (idUnfolding v) ||
805 not (isEmptySpecInfo (idSpecialisation v)),
806 text "absVarsOf: discarding info on" <+> ppr v )
807 setIdInfo v vanillaIdInfo
810 absVarsOf :: IdEnv ([Var], LevelledExpr) -> Var -> [Var]
811 -- If f is free in the expression, and f maps to poly_f a b c in the
812 -- current substitution, then we must report a b c as candidate type
815 -- Also, if x::a is an abstracted variable, then so is a; that is,
816 -- we must look in x's type
817 -- And similarly if x is a coercion variable.
819 | isIdVar v = [av2 | av1 <- lookup_avs v
820 , av2 <- add_tyvars av1]
821 | isCoVar v = add_tyvars v
825 lookup_avs v = case lookupVarEnv id_env v of
826 Just (abs_vars, _) -> abs_vars
829 add_tyvars v = v : varSetElems (varTypeTyVars v)
833 type LvlM result = UniqSM result
835 initLvl :: UniqSupply -> UniqSM a -> a
841 newPolyBndrs :: Level -> LevelEnv -> [Var] -> [Id] -> UniqSM (LevelEnv, [Id])
842 newPolyBndrs dest_lvl env abs_vars bndrs = do
844 let new_bndrs = zipWith mk_poly_bndr bndrs uniqs
845 return (extendPolyLvlEnv dest_lvl env abs_vars (bndrs `zip` new_bndrs), new_bndrs)
847 mk_poly_bndr bndr uniq = transferPolyIdInfo bndr $ -- Note [transferPolyIdInfo] in Id.lhs
848 mkSysLocal (mkFastString str) uniq poly_ty
850 str = "poly_" ++ occNameString (getOccName bndr)
851 poly_ty = mkPiTypes abs_vars (idType bndr)
854 -> [CoreBndr] -> Type -- Abstract wrt these bndrs
856 newLvlVar str vars body_ty = do
858 return (mkSysLocal (mkFastString str) uniq (mkPiTypes vars body_ty))
860 -- The deeply tiresome thing is that we have to apply the substitution
861 -- to the rules inside each Id. Grr. But it matters.
863 cloneVar :: TopLevelFlag -> LevelEnv -> Id -> Level -> Level -> LvlM (LevelEnv, Id)
864 cloneVar TopLevel env v _ _
865 = return (extendInScopeEnv env v, v) -- Don't clone top level things
866 -- But do extend the in-scope env, to satisfy the in-scope invariant
868 cloneVar NotTopLevel env@(_,_,subst,_) v ctxt_lvl dest_lvl
869 = ASSERT( isIdVar v ) do
870 us <- getUniqueSupplyM
872 (subst', v1) = cloneIdBndr subst us v
873 v2 = zap_demand ctxt_lvl dest_lvl v1
874 env' = extendCloneLvlEnv dest_lvl env subst' [(v,v2)]
877 cloneRecVars :: TopLevelFlag -> LevelEnv -> [Id] -> Level -> Level -> LvlM (LevelEnv, [Id])
878 cloneRecVars TopLevel env vs _ _
879 = return (extendInScopeEnvList env vs, vs) -- Don't clone top level things
880 cloneRecVars NotTopLevel env@(_,_,subst,_) vs ctxt_lvl dest_lvl
881 = ASSERT( all isIdVar vs ) do
882 us <- getUniqueSupplyM
884 (subst', vs1) = cloneRecIdBndrs subst us vs
885 vs2 = map (zap_demand ctxt_lvl dest_lvl) vs1
886 env' = extendCloneLvlEnv dest_lvl env subst' (vs `zip` vs2)
889 -- VERY IMPORTANT: we must zap the demand info
890 -- if the thing is going to float out past a lambda,
891 -- or if it's going to top level (where things can't be strict)
892 zap_demand :: Level -> Level -> Id -> Id
893 zap_demand dest_lvl ctxt_lvl id
894 | ctxt_lvl == dest_lvl,
895 not (isTopLvl dest_lvl) = id -- Stays, and not going to top level
896 | otherwise = zapDemandIdInfo id -- Floats out