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, mkPiTypes )
60 import CoreFVs -- all of it
61 import CoreSubst ( Subst, emptySubst, extendInScope, extendIdSubst,
62 cloneIdBndr, cloneRecIdBndrs )
63 import Id ( Id, idType, mkSysLocal, isOneShotLambda,
64 zapDemandIdInfo, transferPolyIdInfo,
65 idSpecialisation, idWorkerInfo, setIdInfo
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
122 Note [FloatOut inside INLINE]
123 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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, iNLINE_CTXT :: Level
154 tOP_LEVEL = Level 0 0
155 iNLINE_CTXT = InlineCtxt
157 incMajorLvl :: Level -> Level
158 -- For InlineCtxt we ignore any inc's; we don't want
159 -- to do any floating at all; see notes above
160 incMajorLvl InlineCtxt = InlineCtxt
161 incMajorLvl (Level major _) = Level (major + 1) 0
163 incMinorLvl :: Level -> Level
164 incMinorLvl InlineCtxt = InlineCtxt
165 incMinorLvl (Level major minor) = Level major (minor+1)
167 maxLvl :: Level -> Level -> Level
168 maxLvl InlineCtxt l2 = l2
169 maxLvl l1 InlineCtxt = l1
170 maxLvl l1@(Level maj1 min1) l2@(Level maj2 min2)
171 | (maj1 > maj2) || (maj1 == maj2 && min1 > min2) = l1
174 ltLvl :: Level -> Level -> Bool
175 ltLvl _ InlineCtxt = False
176 ltLvl InlineCtxt (Level _ _) = True
177 ltLvl (Level maj1 min1) (Level maj2 min2)
178 = (maj1 < maj2) || (maj1 == maj2 && min1 < min2)
180 ltMajLvl :: Level -> Level -> Bool
181 -- Tells if one level belongs to a difft *lambda* level to another
182 ltMajLvl _ InlineCtxt = False
183 ltMajLvl InlineCtxt (Level maj2 _) = 0 < maj2
184 ltMajLvl (Level maj1 _) (Level maj2 _) = maj1 < maj2
186 isTopLvl :: Level -> Bool
187 isTopLvl (Level 0 0) = True
190 isInlineCtxt :: Level -> Bool
191 isInlineCtxt InlineCtxt = True
192 isInlineCtxt _ = False
194 instance Outputable Level where
195 ppr InlineCtxt = text "<INLINE>"
196 ppr (Level maj min) = hcat [ char '<', int maj, char ',', int min, char '>' ]
198 instance Eq Level where
199 InlineCtxt == InlineCtxt = True
200 (Level maj1 min1) == (Level maj2 min2) = maj1 == maj2 && min1 == min2
205 %************************************************************************
207 \subsection{Main level-setting code}
209 %************************************************************************
212 setLevels :: FloatOutSwitches
217 setLevels float_lams binds us
218 = initLvl us (do_them binds)
220 -- "do_them"'s main business is to thread the monad along
221 -- It gives each top binding the same empty envt, because
222 -- things unbound in the envt have level number zero implicitly
223 do_them :: [CoreBind] -> LvlM [LevelledBind]
225 do_them [] = return []
227 (lvld_bind, _) <- lvlTopBind init_env b
228 lvld_binds <- do_them bs
229 return (lvld_bind : lvld_binds)
231 init_env = initialEnv float_lams
233 lvlTopBind :: LevelEnv -> Bind Id -> LvlM (LevelledBind, LevelEnv)
234 lvlTopBind env (NonRec binder rhs)
235 = lvlBind TopLevel tOP_LEVEL env (AnnNonRec binder (freeVars rhs))
236 -- Rhs can have no free vars!
238 lvlTopBind env (Rec pairs)
239 = lvlBind TopLevel tOP_LEVEL env (AnnRec [(b,freeVars rhs) | (b,rhs) <- pairs])
242 %************************************************************************
244 \subsection{Setting expression levels}
246 %************************************************************************
249 lvlExpr :: Level -- ctxt_lvl: Level of enclosing expression
250 -> LevelEnv -- Level of in-scope names/tyvars
251 -> CoreExprWithFVs -- input expression
252 -> LvlM LevelledExpr -- Result expression
255 The @ctxt_lvl@ is, roughly, the level of the innermost enclosing
256 binder. Here's an example
258 v = \x -> ...\y -> let r = case (..x..) of
262 When looking at the rhs of @r@, @ctxt_lvl@ will be 1 because that's
263 the level of @r@, even though it's inside a level-2 @\y@. It's
264 important that @ctxt_lvl@ is 1 and not 2 in @r@'s rhs, because we
265 don't want @lvlExpr@ to turn the scrutinee of the @case@ into an MFE
266 --- because it isn't a *maximal* free expression.
268 If there were another lambda in @r@'s rhs, it would get level-2 as well.
271 lvlExpr _ _ ( _, AnnType ty) = return (Type ty)
272 lvlExpr _ env (_, AnnVar v) = return (lookupVar env v)
273 lvlExpr _ _ (_, AnnLit lit) = return (Lit lit)
275 lvlExpr ctxt_lvl env (_, AnnApp fun arg) = do
277 arg' <- lvlMFE False ctxt_lvl env arg
278 return (App fun' arg')
281 lvl_fun (_, AnnCase _ _ _ _) = lvlMFE True ctxt_lvl env fun
282 lvl_fun _ = lvlExpr ctxt_lvl env fun
283 -- We don't do MFE on partial applications generally,
284 -- but we do if the function is big and hairy, like a case
286 lvlExpr _ env (_, AnnNote InlineMe expr) = do
287 -- Don't float anything out of an InlineMe; hence the iNLINE_CTXT
288 expr' <- lvlExpr iNLINE_CTXT env expr
289 return (Note InlineMe expr')
291 lvlExpr ctxt_lvl env (_, AnnNote note expr) = do
292 expr' <- lvlExpr ctxt_lvl env expr
293 return (Note note expr')
295 lvlExpr ctxt_lvl env (_, AnnCast expr co) = do
296 expr' <- lvlExpr ctxt_lvl env expr
297 return (Cast expr' co)
299 -- We don't split adjacent lambdas. That is, given
301 -- we don't float to give
302 -- \x -> let v = x+y in \y -> (v,y)
303 -- Why not? Because partial applications are fairly rare, and splitting
304 -- lambdas makes them more expensive.
306 lvlExpr ctxt_lvl env expr@(_, AnnLam {}) = do
307 new_body <- lvlMFE True new_lvl new_env body
308 return (mkLams new_bndrs new_body)
310 (bndrs, body) = collectAnnBndrs expr
311 (new_lvl, new_bndrs) = lvlLamBndrs ctxt_lvl bndrs
312 new_env = extendLvlEnv env new_bndrs
313 -- At one time we called a special verion of collectBinders,
314 -- which ignored coercions, because we don't want to split
315 -- a lambda like this (\x -> coerce t (\s -> ...))
316 -- This used to happen quite a bit in state-transformer programs,
317 -- but not nearly so much now non-recursive newtypes are transparent.
318 -- [See SetLevels rev 1.50 for a version with this approach.]
320 lvlExpr ctxt_lvl env (_, AnnLet (AnnNonRec bndr rhs) body)
321 | isUnLiftedType (idType bndr) = do
322 -- Treat unlifted let-bindings (let x = b in e) just like (case b of x -> e)
323 -- That is, leave it exactly where it is
324 -- We used to float unlifted bindings too (e.g. to get a cheap primop
325 -- outside a lambda (to see how, look at lvlBind in rev 1.58)
326 -- but an unrelated change meant that these unlifed bindings
327 -- could get to the top level which is bad. And there's not much point;
328 -- unlifted bindings are always cheap, and so hardly worth floating.
329 rhs' <- lvlExpr ctxt_lvl env rhs
330 body' <- lvlExpr incd_lvl env' body
331 return (Let (NonRec bndr' rhs') body')
333 incd_lvl = incMinorLvl ctxt_lvl
334 bndr' = TB bndr incd_lvl
335 env' = extendLvlEnv env [bndr']
337 lvlExpr ctxt_lvl env (_, AnnLet bind body) = do
338 (bind', new_env) <- lvlBind NotTopLevel ctxt_lvl env bind
339 body' <- lvlExpr ctxt_lvl new_env body
340 return (Let bind' body')
342 lvlExpr ctxt_lvl env (_, AnnCase expr case_bndr ty alts) = do
343 expr' <- lvlMFE True ctxt_lvl env expr
344 let alts_env = extendCaseBndrLvlEnv env expr' case_bndr incd_lvl
345 alts' <- mapM (lvl_alt alts_env) alts
346 return (Case expr' (TB case_bndr incd_lvl) ty alts')
348 incd_lvl = incMinorLvl ctxt_lvl
350 lvl_alt alts_env (con, bs, rhs) = do
351 rhs' <- lvlMFE True incd_lvl new_env rhs
352 return (con, bs', rhs')
354 bs' = [ TB b incd_lvl | b <- bs ]
355 new_env = extendLvlEnv alts_env bs'
358 @lvlMFE@ is just like @lvlExpr@, except that it might let-bind
359 the expression, so that it can itself be floated.
362 ~~~~~~~~~~~~~~~~~~~~~
363 We don't float unlifted MFEs, which potentially loses big opportunites.
366 where h :: Int -> Int# is expensive. We'd like to float the (h y) outside
367 the \x, but we don't because it's unboxed. Possible solution: box it.
371 We don't float a case expression as an MFE from a strict context. Why not?
372 Because in doing so we share a tiny bit of computation (the switch) but
373 in exchange we build a thunk, which is bad. This case reduces allocation
374 by 7% in spectral/puzzle (a rather strange benchmark) and 1.2% in real/fem.
375 Doesn't change any other allocation at all.
378 lvlMFE :: Bool -- True <=> strict context [body of case or let]
379 -> Level -- Level of innermost enclosing lambda/tylam
380 -> LevelEnv -- Level of in-scope names/tyvars
381 -> CoreExprWithFVs -- input expression
382 -> LvlM LevelledExpr -- Result expression
384 lvlMFE _ _ _ (_, AnnType ty)
387 -- No point in floating out an expression wrapped in a coercion;
388 -- If we do we'll transform lvl = e |> co
389 -- to lvl' = e; lvl = lvl' |> co
390 -- and then inline lvl. Better just to float out the payload.
391 lvlMFE strict_ctxt ctxt_lvl env (_, AnnCast e co)
392 = do { expr' <- lvlMFE strict_ctxt ctxt_lvl env e
393 ; return (Cast expr' co) }
396 lvlMFE True ctxt_lvl env e@(_, AnnCase {})
397 = lvlExpr ctxt_lvl env e -- Don't share cases
399 lvlMFE strict_ctxt ctxt_lvl env ann_expr@(fvs, _)
400 | isUnLiftedType ty -- Can't let-bind it; see Note [Unlifted MFEs]
401 || isInlineCtxt ctxt_lvl -- Don't float out of an __inline__ context
402 || exprIsTrivial expr -- Never float if it's trivial
403 || not good_destination
404 = -- Don't float it out
405 lvlExpr ctxt_lvl env ann_expr
407 | otherwise -- Float it out!
408 = do expr' <- lvlFloatRhs abs_vars dest_lvl env ann_expr
409 var <- newLvlVar "lvl" abs_vars ty
410 return (Let (NonRec (TB var dest_lvl) expr')
411 (mkVarApps (Var var) abs_vars))
413 expr = deAnnotate ann_expr
415 dest_lvl = destLevel env fvs (isFunction ann_expr)
416 abs_vars = abstractVars dest_lvl env fvs
418 -- A decision to float entails let-binding this thing, and we only do
419 -- that if we'll escape a value lambda, or will go to the top level.
421 | dest_lvl `ltMajLvl` ctxt_lvl -- Escapes a value lambda
423 -- OLD CODE: not (exprIsCheap expr) || isTopLvl dest_lvl
424 -- see Note [Escaping a value lambda]
426 | otherwise -- Does not escape a value lambda
427 = isTopLvl dest_lvl -- Only float if we are going to the top level
428 && floatConsts env -- and the floatConsts flag is on
429 && not strict_ctxt -- Don't float from a strict context
430 -- We are keen to float something to the top level, even if it does not
431 -- escape a lambda, because then it needs no allocation. But it's controlled
432 -- by a flag, because doing this too early loses opportunities for RULES
433 -- which (needless to say) are important in some nofib programs
434 -- (gcd is an example).
437 -- concat = /\ a -> foldr ..a.. (++) []
438 -- was getting turned into
439 -- concat = /\ a -> lvl a
440 -- lvl = /\ a -> foldr ..a.. (++) []
441 -- which is pretty stupid. Hence the strict_ctxt test
444 Note [Escaping a value lambda]
445 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
446 We want to float even cheap expressions out of value lambdas,
447 because that saves allocation. Consider
448 f = \x. .. (\y.e) ...
449 Then we'd like to avoid allocating the (\y.e) every time we call f,
450 (assuming e does not mention x).
452 An example where this really makes a difference is simplrun009.
454 Another reason it's good is because it makes SpecContr fire on functions.
456 f = \x. ....(f (\y.e))....
457 After floating we get
459 f = \x. ....(f lvl)...
460 and that is much easier for SpecConstr to generate a robust specialisation for.
462 The OLD CODE (given where this Note is referred to) prevents floating
463 of the example above, so I just don't understand the old code. I
464 don't understand the old comment either (which appears below). I
465 measured the effect on nofib of changing OLD CODE to 'True', and got
466 zeros everywhere, but a 4% win for 'puzzle'. Very small 0.5% loss for
467 'cse'; turns out to be because our arity analysis isn't good enough
468 yet (mentioned in Simon-nofib-notes).
471 Even if it escapes a value lambda, we only
472 float if it's not cheap (unless it'll get all the
473 way to the top). I've seen cases where we
474 float dozens of tiny free expressions, which cost
475 more to allocate than to evaluate.
476 NB: exprIsCheap is also true of bottom expressions, which
477 is good; we don't want to share them
479 It's only Really Bad to float a cheap expression out of a
480 strict context, because that builds a thunk that otherwise
481 would never be built. So another alternative would be to
483 || (strict_ctxt && not (exprIsBottom expr))
484 to the condition above. We should really try this out.
487 %************************************************************************
489 \subsection{Bindings}
491 %************************************************************************
493 The binding stuff works for top level too.
496 lvlBind :: TopLevelFlag -- Used solely to decide whether to clone
497 -> Level -- Context level; might be Top even for bindings nested in the RHS
498 -- of a top level binding
501 -> LvlM (LevelledBind, LevelEnv)
503 lvlBind top_lvl ctxt_lvl env (AnnNonRec bndr rhs@(rhs_fvs,_))
504 | isTyVar bndr -- Don't do anything for TyVar binders
505 -- (simplifier gets rid of them pronto)
506 || isInlineCtxt ctxt_lvl -- Don't do anything inside InlineMe
507 = do rhs' <- lvlExpr ctxt_lvl env rhs
508 return (NonRec (TB bndr ctxt_lvl) rhs', env)
511 = do -- No type abstraction; clone existing binder
512 rhs' <- lvlExpr dest_lvl env rhs
513 (env', bndr') <- cloneVar top_lvl env bndr ctxt_lvl dest_lvl
514 return (NonRec (TB bndr' dest_lvl) rhs', env')
517 = do -- Yes, type abstraction; create a new binder, extend substitution, etc
518 rhs' <- lvlFloatRhs abs_vars dest_lvl env rhs
519 (env', [bndr']) <- newPolyBndrs dest_lvl env abs_vars [bndr]
520 return (NonRec (TB bndr' dest_lvl) rhs', env')
523 bind_fvs = rhs_fvs `unionVarSet` idFreeVars bndr
524 abs_vars = abstractVars dest_lvl env bind_fvs
525 dest_lvl = destLevel env bind_fvs (isFunction rhs)
530 lvlBind top_lvl ctxt_lvl env (AnnRec pairs)
531 | isInlineCtxt ctxt_lvl -- Don't do anything inside InlineMe
532 = do rhss' <- mapM (lvlExpr ctxt_lvl env) rhss
533 return (Rec ([TB b ctxt_lvl | b <- bndrs] `zip` rhss'), env)
536 = do (new_env, new_bndrs) <- cloneRecVars top_lvl env bndrs ctxt_lvl dest_lvl
537 new_rhss <- mapM (lvlExpr ctxt_lvl new_env) rhss
538 return (Rec ([TB b dest_lvl | b <- new_bndrs] `zip` new_rhss), new_env)
540 | isSingleton pairs && count isId abs_vars > 1
541 = do -- Special case for self recursion where there are
542 -- several variables carried around: build a local loop:
543 -- poly_f = \abs_vars. \lam_vars . letrec f = \lam_vars. rhs in f lam_vars
544 -- This just makes the closures a bit smaller. If we don't do
545 -- this, allocation rises significantly on some programs
547 -- We could elaborate it for the case where there are several
548 -- mutually functions, but it's quite a bit more complicated
550 -- This all seems a bit ad hoc -- sigh
552 (bndr,rhs) = head pairs
553 (rhs_lvl, abs_vars_w_lvls) = lvlLamBndrs dest_lvl abs_vars
554 rhs_env = extendLvlEnv env abs_vars_w_lvls
555 (rhs_env', new_bndr) <- cloneVar NotTopLevel rhs_env bndr rhs_lvl rhs_lvl
557 (lam_bndrs, rhs_body) = collectAnnBndrs rhs
558 (body_lvl, new_lam_bndrs) = lvlLamBndrs rhs_lvl lam_bndrs
559 body_env = extendLvlEnv rhs_env' new_lam_bndrs
560 new_rhs_body <- lvlExpr body_lvl body_env rhs_body
561 (poly_env, [poly_bndr]) <- newPolyBndrs dest_lvl env abs_vars [bndr]
562 return (Rec [(TB poly_bndr dest_lvl,
563 mkLams abs_vars_w_lvls $
564 mkLams new_lam_bndrs $
565 Let (Rec [(TB new_bndr rhs_lvl, mkLams new_lam_bndrs new_rhs_body)])
566 (mkVarApps (Var new_bndr) lam_bndrs))],
569 | otherwise = do -- Non-null abs_vars
570 (new_env, new_bndrs) <- newPolyBndrs dest_lvl env abs_vars bndrs
571 new_rhss <- mapM (lvlFloatRhs abs_vars dest_lvl new_env) rhss
572 return (Rec ([TB b dest_lvl | b <- new_bndrs] `zip` new_rhss), new_env)
575 (bndrs,rhss) = unzip pairs
577 -- Finding the free vars of the binding group is annoying
578 bind_fvs = (unionVarSets [ idFreeVars bndr `unionVarSet` rhs_fvs
579 | (bndr, (rhs_fvs,_)) <- pairs])
583 dest_lvl = destLevel env bind_fvs (all isFunction rhss)
584 abs_vars = abstractVars dest_lvl env bind_fvs
586 ----------------------------------------------------
587 -- Three help functons for the type-abstraction case
589 lvlFloatRhs :: [CoreBndr] -> Level -> LevelEnv -> CoreExprWithFVs
590 -> UniqSM (Expr (TaggedBndr Level))
591 lvlFloatRhs abs_vars dest_lvl env rhs = do
592 rhs' <- lvlExpr rhs_lvl rhs_env rhs
593 return (mkLams abs_vars_w_lvls rhs')
595 (rhs_lvl, abs_vars_w_lvls) = lvlLamBndrs dest_lvl abs_vars
596 rhs_env = extendLvlEnv env abs_vars_w_lvls
600 %************************************************************************
602 \subsection{Deciding floatability}
604 %************************************************************************
607 lvlLamBndrs :: Level -> [CoreBndr] -> (Level, [TaggedBndr Level])
608 -- Compute the levels for the binders of a lambda group
609 -- The binders returned are exactly the same as the ones passed,
610 -- but they are now paired with a level
614 lvlLamBndrs lvl bndrs
615 = go (incMinorLvl lvl)
616 False -- Havn't bumped major level in this group
619 go old_lvl bumped_major rev_lvld_bndrs (bndr:bndrs)
620 | isId bndr && -- Go to the next major level if this is a value binder,
621 not bumped_major && -- and we havn't already gone to the next level (one jump per group)
622 not (isOneShotLambda bndr) -- and it isn't a one-shot lambda
623 = go new_lvl True (TB bndr new_lvl : rev_lvld_bndrs) bndrs
626 = go old_lvl bumped_major (TB bndr old_lvl : rev_lvld_bndrs) bndrs
629 new_lvl = incMajorLvl old_lvl
631 go old_lvl _ rev_lvld_bndrs []
632 = (old_lvl, reverse rev_lvld_bndrs)
633 -- a lambda like this (\x -> coerce t (\s -> ...))
634 -- This happens quite a bit in state-transformer programs
638 -- Destintion level is the max Id level of the expression
639 -- (We'll abstract the type variables, if any.)
640 destLevel :: LevelEnv -> VarSet -> Bool -> Level
641 destLevel env fvs is_function
643 && is_function = tOP_LEVEL -- Send functions to top level; see
644 -- the comments with isFunction
645 | otherwise = maxIdLevel env fvs
647 isFunction :: CoreExprWithFVs -> Bool
648 -- The idea here is that we want to float *functions* to
649 -- the top level. This saves no work, but
650 -- (a) it can make the host function body a lot smaller,
651 -- and hence inlinable.
652 -- (b) it can also save allocation when the function is recursive:
653 -- h = \x -> letrec f = \y -> ...f...y...x...
656 -- f = \x y -> ...(f x)...y...x...
658 -- No allocation for f now.
659 -- We may only want to do this if there are sufficiently few free
660 -- variables. We certainly only want to do it for values, and not for
661 -- constructors. So the simple thing is just to look for lambdas
662 isFunction (_, AnnLam b e) | isId b = True
663 | otherwise = isFunction e
664 isFunction (_, AnnNote _ e) = isFunction e
669 %************************************************************************
671 \subsection{Free-To-Level Monad}
673 %************************************************************************
676 type LevelEnv = (FloatOutSwitches,
677 VarEnv Level, -- Domain is *post-cloned* TyVars and Ids
678 Subst, -- Domain is pre-cloned Ids; tracks the in-scope set
679 -- so that subtitution is capture-avoiding
680 IdEnv ([Var], LevelledExpr)) -- Domain is pre-cloned Ids
681 -- We clone let-bound variables so that they are still
682 -- distinct when floated out; hence the SubstEnv/IdEnv.
683 -- (see point 3 of the module overview comment).
684 -- We also use these envs when making a variable polymorphic
685 -- because we want to float it out past a big lambda.
687 -- The Subst and IdEnv always implement the same mapping, but the
688 -- Subst maps to CoreExpr and the IdEnv to LevelledExpr
689 -- Since the range is always a variable or type application,
690 -- there is never any difference between the two, but sadly
691 -- the types differ. The SubstEnv is used when substituting in
692 -- a variable's IdInfo; the IdEnv when we find a Var.
694 -- In addition the IdEnv records a list of tyvars free in the
695 -- type application, just so we don't have to call freeVars on
696 -- the type application repeatedly.
698 -- The domain of the both envs is *pre-cloned* Ids, though
700 -- The domain of the VarEnv Level is the *post-cloned* Ids
702 initialEnv :: FloatOutSwitches -> LevelEnv
703 initialEnv float_lams = (float_lams, emptyVarEnv, emptySubst, emptyVarEnv)
705 floatLams :: LevelEnv -> Bool
706 floatLams (fos, _, _, _) = floatOutLambdas fos
708 floatConsts :: LevelEnv -> Bool
709 floatConsts (fos, _, _, _) = floatOutConstants fos
711 extendLvlEnv :: LevelEnv -> [TaggedBndr Level] -> LevelEnv
712 -- Used when *not* cloning
713 extendLvlEnv (float_lams, lvl_env, subst, id_env) prs
715 foldl add_lvl lvl_env prs,
716 foldl del_subst subst prs,
717 foldl del_id id_env prs)
719 add_lvl env (TB v l) = extendVarEnv env v l
720 del_subst env (TB v _) = extendInScope env v
721 del_id env (TB v _) = delVarEnv env v
722 -- We must remove any clone for this variable name in case of
723 -- shadowing. This bit me in the following case
724 -- (in nofib/real/gg/Spark.hs):
727 -- ... -> case e of wild {
728 -- ... -> ... wild ...
732 -- The inside occurrence of @wild@ was being replaced with @ds@,
733 -- incorrectly, because the SubstEnv was still lying around. Ouch!
736 -- extendCaseBndrLvlEnv adds the mapping case-bndr->scrut-var if it can
737 -- (see point 4 of the module overview comment)
738 extendCaseBndrLvlEnv :: LevelEnv -> Expr (TaggedBndr Level) -> Var -> Level
740 extendCaseBndrLvlEnv (float_lams, lvl_env, subst, id_env) (Var scrut_var) case_bndr lvl
742 extendVarEnv lvl_env case_bndr lvl,
743 extendIdSubst subst case_bndr (Var scrut_var),
744 extendVarEnv id_env case_bndr ([scrut_var], Var scrut_var))
746 extendCaseBndrLvlEnv env _scrut case_bndr lvl
747 = extendLvlEnv env [TB case_bndr lvl]
749 extendPolyLvlEnv :: Level -> LevelEnv -> [Var] -> [(Var, Var)] -> LevelEnv
750 extendPolyLvlEnv dest_lvl (float_lams, lvl_env, subst, id_env) abs_vars bndr_pairs
752 foldl add_lvl lvl_env bndr_pairs,
753 foldl add_subst subst bndr_pairs,
754 foldl add_id id_env bndr_pairs)
756 add_lvl env (_, v') = extendVarEnv env v' dest_lvl
757 add_subst env (v, v') = extendIdSubst env v (mkVarApps (Var v') abs_vars)
758 add_id env (v, v') = extendVarEnv env v ((v':abs_vars), mkVarApps (Var v') abs_vars)
760 extendCloneLvlEnv :: Level -> LevelEnv -> Subst -> [(Var, Var)] -> LevelEnv
761 extendCloneLvlEnv lvl (float_lams, lvl_env, _, id_env) new_subst bndr_pairs
763 foldl add_lvl lvl_env bndr_pairs,
765 foldl add_id id_env bndr_pairs)
767 add_lvl env (_, v') = extendVarEnv env v' lvl
768 add_id env (v, v') = extendVarEnv env v ([v'], Var v')
771 maxIdLevel :: LevelEnv -> VarSet -> Level
772 maxIdLevel (_, lvl_env,_,id_env) var_set
773 = foldVarSet max_in tOP_LEVEL var_set
775 max_in in_var lvl = foldr max_out lvl (case lookupVarEnv id_env in_var of
776 Just (abs_vars, _) -> abs_vars
780 | isId out_var = case lookupVarEnv lvl_env out_var of
781 Just lvl' -> maxLvl lvl' lvl
783 | otherwise = lvl -- Ignore tyvars in *maxIdLevel*
785 lookupVar :: LevelEnv -> Id -> LevelledExpr
786 lookupVar (_, _, _, id_env) v = case lookupVarEnv id_env v of
787 Just (_, expr) -> expr
790 abstractVars :: Level -> LevelEnv -> VarSet -> [Var]
791 -- Find the variables in fvs, free vars of the target expresion,
792 -- whose level is greater than the destination level
793 -- These are the ones we are going to abstract out
794 abstractVars dest_lvl (_, lvl_env, _, id_env) fvs
795 = map zap $ uniq $ sortLe le
796 [var | fv <- varSetElems fvs
797 , var <- absVarsOf id_env fv
799 -- NB: it's important to call abstract_me only on the OutIds the
800 -- come from absVarsOf (not on fv, which is an InId)
802 -- Sort the variables so the true type variables come first;
803 -- the tyvars scope over Ids and coercion vars
804 v1 `le` v2 = case (is_tv v1, is_tv v2) of
805 (True, False) -> True
806 (False, True) -> False
807 _ -> v1 <= v2 -- Same family
809 is_tv v = isTyVar v && not (isCoVar v)
811 uniq :: [Var] -> [Var]
812 -- Remove adjacent duplicates; the sort will have brought them together
813 uniq (v1:v2:vs) | v1 == v2 = uniq (v2:vs)
814 | otherwise = v1 : uniq (v2:vs)
817 abstract_me v = case lookupVarEnv lvl_env v of
818 Just lvl -> dest_lvl `ltLvl` lvl
821 -- We are going to lambda-abstract, so nuke any IdInfo,
822 -- and add the tyvars of the Id (if necessary)
823 zap v | isId v = WARN( workerExists (idWorkerInfo v) ||
824 not (isEmptySpecInfo (idSpecialisation v)),
825 text "absVarsOf: discarding info on" <+> ppr v )
826 setIdInfo v vanillaIdInfo
829 absVarsOf :: IdEnv ([Var], LevelledExpr) -> Var -> [Var]
830 -- If f is free in the expression, and f maps to poly_f a b c in the
831 -- current substitution, then we must report a b c as candidate type
834 -- Also, if x::a is an abstracted variable, then so is a; that is,
835 -- we must look in x's type
836 -- And similarly if x is a coercion variable.
838 | isId v = [av2 | av1 <- lookup_avs v
839 , av2 <- add_tyvars av1]
840 | isCoVar v = add_tyvars v
844 lookup_avs v = case lookupVarEnv id_env v of
845 Just (abs_vars, _) -> abs_vars
848 add_tyvars v = v : varSetElems (varTypeTyVars v)
852 type LvlM result = UniqSM result
854 initLvl :: UniqSupply -> UniqSM a -> a
860 newPolyBndrs :: Level -> LevelEnv -> [Var] -> [Id] -> UniqSM (LevelEnv, [Id])
861 newPolyBndrs dest_lvl env abs_vars bndrs = do
863 let new_bndrs = zipWith mk_poly_bndr bndrs uniqs
864 return (extendPolyLvlEnv dest_lvl env abs_vars (bndrs `zip` new_bndrs), new_bndrs)
866 mk_poly_bndr bndr uniq = transferPolyIdInfo bndr abs_vars $ -- Note [transferPolyIdInfo] in Id.lhs
867 mkSysLocal (mkFastString str) uniq poly_ty
869 str = "poly_" ++ occNameString (getOccName bndr)
870 poly_ty = mkPiTypes abs_vars (idType bndr)
873 -> [CoreBndr] -> Type -- Abstract wrt these bndrs
875 newLvlVar str vars body_ty = do
877 return (mkSysLocal (mkFastString str) uniq (mkPiTypes vars body_ty))
879 -- The deeply tiresome thing is that we have to apply the substitution
880 -- to the rules inside each Id. Grr. But it matters.
882 cloneVar :: TopLevelFlag -> LevelEnv -> Id -> Level -> Level -> LvlM (LevelEnv, Id)
883 cloneVar TopLevel env v _ _
884 = return (env, v) -- Don't clone top level things
885 cloneVar NotTopLevel env@(_,_,subst,_) v ctxt_lvl dest_lvl
886 = ASSERT( isId v ) do
887 us <- getUniqueSupplyM
889 (subst', v1) = cloneIdBndr subst us v
890 v2 = zap_demand ctxt_lvl dest_lvl v1
891 env' = extendCloneLvlEnv dest_lvl env subst' [(v,v2)]
894 cloneRecVars :: TopLevelFlag -> LevelEnv -> [Id] -> Level -> Level -> LvlM (LevelEnv, [Id])
895 cloneRecVars TopLevel env vs _ _
896 = return (env, vs) -- Don't clone top level things
897 cloneRecVars NotTopLevel env@(_,_,subst,_) vs ctxt_lvl dest_lvl
898 = ASSERT( all isId vs ) do
899 us <- getUniqueSupplyM
901 (subst', vs1) = cloneRecIdBndrs subst us vs
902 vs2 = map (zap_demand ctxt_lvl dest_lvl) vs1
903 env' = extendCloneLvlEnv dest_lvl env subst' (vs `zip` vs2)
906 -- VERY IMPORTANT: we must zap the demand info
907 -- if the thing is going to float out past a lambda,
908 -- or if it's going to top level (where things can't be strict)
909 zap_demand :: Level -> Level -> Id -> Id
910 zap_demand dest_lvl ctxt_lvl id
911 | ctxt_lvl == dest_lvl,
912 not (isTopLvl dest_lvl) = id -- Stays, and not going to top level
913 | otherwise = zapDemandIdInfo id -- Floats out