2 % (c) The GRASP/AQUA Project, Glasgow University, 1993-1998
4 \section[IdInfo]{@IdInfos@: Non-essential information about @Ids@}
6 (And a pretty good illustration of quite a few things wrong with
13 vanillaIdInfo, constantIdInfo, mkIdInfo, seqIdInfo, megaSeqIdInfo,
16 zapFragileInfo, zapLamInfo, zapSpecPragInfo, shortableIdInfo, copyIdInfo,
19 IdFlavour(..), flavourInfo, makeConstantFlavour,
20 setNoDiscardInfo, setFlavourInfo,
25 exactArity, atLeastArity, unknownArity, hasArity,
26 arityInfo, setArityInfo, ppArityInfo, arityLowerBound,
28 -- Strictness; imported from Demand
30 mkStrictnessInfo, noStrictnessInfo,
31 ppStrictnessInfo,isBottomingStrictness,
32 strictnessInfo, setStrictnessInfo,
34 -- Usage generalisation
36 tyGenInfo, setTyGenInfo,
37 noTyGenInfo, isNoTyGenInfo, ppTyGenInfo, tyGenInfoString,
40 WorkerInfo(..), workerExists, wrapperArity, workerId,
41 workerInfo, setWorkerInfo, ppWorkerInfo,
44 unfoldingInfo, setUnfoldingInfo,
47 demandInfo, setDemandInfo,
51 inlinePragInfo, setInlinePragInfo, pprInlinePragInfo,
52 isNeverInlinePrag, neverInlinePrag,
55 OccInfo(..), isFragileOcc, isDeadOcc, isLoopBreaker,
56 InsideLam, OneBranch, insideLam, notInsideLam, oneBranch, notOneBranch,
60 specInfo, setSpecInfo,
63 CafInfo(..), cafInfo, setCafInfo, mayHaveCafRefs, ppCafInfo,
65 -- Constructed Product Result Info
66 CprInfo(..), cprInfo, setCprInfo, ppCprInfo, noCprInfo,
68 -- Lambda-bound variable info
69 LBVarInfo(..), lbvarInfo, setLBVarInfo, noLBVarInfo
72 #include "HsVersions.h"
76 import Type ( Type, usOnce )
77 import PrimOp ( PrimOp )
79 import BasicTypes ( OccInfo(..), isFragileOcc, isDeadOcc, seqOccInfo, isLoopBreaker,
80 InsideLam, insideLam, notInsideLam,
81 OneBranch, oneBranch, notOneBranch,
84 import DataCon ( DataCon )
85 import FieldLabel ( FieldLabel )
86 import Type ( usOnce, usMany )
87 import Demand -- Lots of stuff
89 import Util ( seqList )
91 infixl 1 `setDemandInfo`,
103 -- infixl so you can say (id `set` a `set` b)
106 An @IdInfo@ gives {\em optional} information about an @Id@. If
107 present it never lies, but it may not be present, in which case there
108 is always a conservative assumption which can be made.
110 There is one exception: the 'flavour' is *not* optional.
111 You must not discard it.
112 It used to be in Var.lhs, but that seems unclean.
114 Two @Id@s may have different info even though they have the same
115 @Unique@ (and are hence the same @Id@); for example, one might lack
116 the properties attached to the other.
118 The @IdInfo@ gives information about the value, or definition, of the
119 @Id@. It does {\em not} contain information about the @Id@'s usage
120 (except for @DemandInfo@? ToDo). (@lbvarInfo@ is also a marginal
126 flavourInfo :: IdFlavour, -- NOT OPTIONAL
127 arityInfo :: ArityInfo, -- Its arity
128 demandInfo :: Demand, -- Whether or not it is definitely demanded
129 specInfo :: CoreRules, -- Specialisations of this function which exist
130 tyGenInfo :: TyGenInfo, -- Restrictions on usage-generalisation of this Id
131 strictnessInfo :: StrictnessInfo, -- Strictness properties
132 workerInfo :: WorkerInfo, -- Pointer to Worker Function
133 unfoldingInfo :: Unfolding, -- Its unfolding
134 cafInfo :: CafInfo, -- whether it refers (indirectly) to any CAFs
135 cprInfo :: CprInfo, -- Function always constructs a product result
136 lbvarInfo :: LBVarInfo, -- Info about a lambda-bound variable
137 inlinePragInfo :: InlinePragInfo, -- Inline pragma
138 occInfo :: OccInfo -- How it occurs
141 seqIdInfo :: IdInfo -> ()
142 seqIdInfo (IdInfo {}) = ()
144 megaSeqIdInfo :: IdInfo -> ()
146 = seqFlavour (flavourInfo info) `seq`
147 seqArity (arityInfo info) `seq`
148 seqDemand (demandInfo info) `seq`
149 seqRules (specInfo info) `seq`
150 seqTyGenInfo (tyGenInfo info) `seq`
151 seqStrictnessInfo (strictnessInfo info) `seq`
152 seqWorker (workerInfo info) `seq`
154 -- seqUnfolding (unfoldingInfo info) `seq`
155 -- Omitting this improves runtimes a little, presumably because
156 -- some unfoldings are not calculated at all
158 seqCaf (cafInfo info) `seq`
159 seqCpr (cprInfo info) `seq`
160 seqLBVar (lbvarInfo info) `seq`
161 seqOccInfo (occInfo info)
167 setFlavourInfo info fl = fl `seq` info { flavourInfo = fl }
168 setWorkerInfo info wk = wk `seq` info { workerInfo = wk }
169 setSpecInfo info sp = PSEQ sp (info { specInfo = sp })
170 setTyGenInfo info tg = tg `seq` info { tyGenInfo = tg }
171 setInlinePragInfo info pr = pr `seq` info { inlinePragInfo = pr }
172 setOccInfo info oc = oc `seq` info { occInfo = oc }
173 setStrictnessInfo info st = st `seq` info { strictnessInfo = st }
174 -- Try to avoid spack leaks by seq'ing
176 setUnfoldingInfo info uf
177 | isEvaldUnfolding uf && isStrict (demandInfo info)
178 -- If the unfolding is a value, the demand info may
179 -- go pear-shaped, so we nuke it. Example:
181 -- case x of (p,q) -> h p q x
182 -- Here x is certainly demanded. But after we've nuked
183 -- the case, we'll get just
184 -- let x = (a,b) in h a b x
185 -- and now x is not demanded (I'm assuming h is lazy)
186 -- This really happens. The solution here is a bit ad hoc...
187 = info { unfoldingInfo = uf, demandInfo = wwLazy }
190 -- We do *not* seq on the unfolding info, For some reason, doing so
191 -- actually increases residency significantly.
192 = info { unfoldingInfo = uf }
194 setDemandInfo info dd = info { demandInfo = dd }
195 setArityInfo info ar = info { arityInfo = ar }
196 setCafInfo info cf = info { cafInfo = cf }
197 setCprInfo info cp = info { cprInfo = cp }
198 setLBVarInfo info lb = info { lbvarInfo = lb }
200 setNoDiscardInfo info = case flavourInfo info of
201 VanillaId -> info { flavourInfo = ExportedId }
203 zapSpecPragInfo info = case flavourInfo info of
204 SpecPragmaId -> info { flavourInfo = VanillaId }
210 vanillaIdInfo :: IdInfo
211 -- Used for locally-defined Ids
212 -- We are going to calculate correct CAF information at the end
213 vanillaIdInfo = mkIdInfo VanillaId NoCafRefs
215 constantIdInfo :: IdInfo
216 -- Used for imported Ids
217 -- The default is that they *do* have CAFs; an interface-file pragma
218 -- may say "oh no it doesn't", but in the absence of such a pragma
219 -- we'd better assume it does
220 constantIdInfo = mkIdInfo ConstantId MayHaveCafRefs
222 mkIdInfo :: IdFlavour -> CafInfo -> IdInfo
227 arityInfo = UnknownArity,
229 specInfo = emptyCoreRules,
230 tyGenInfo = noTyGenInfo,
231 workerInfo = NoWorker,
232 strictnessInfo = NoStrictnessInfo,
233 unfoldingInfo = noUnfolding,
235 lbvarInfo = NoLBVarInfo,
236 inlinePragInfo = NoInlinePragInfo,
242 %************************************************************************
246 %************************************************************************
250 = VanillaId -- Locally defined, not exported
251 | ExportedId -- Locally defined, exported
252 | SpecPragmaId -- Locally defined, RHS holds specialised call
254 | ConstantId -- Imported from elsewhere, or a default method Id.
256 | DictFunId -- We flag dictionary functions so that we can
257 -- conveniently extract the DictFuns from a set of
258 -- bindings when building a module's interface
260 | DataConId DataCon -- The Id for a data constructor *worker*
261 | DataConWrapId DataCon -- The Id for a data constructor *wrapper*
262 -- [the only reasons we need to know is so that
263 -- a) we can suppress printing a definition in the interface file
264 -- b) when typechecking a pattern we can get from the
265 -- Id back to the data con]
266 | PrimOpId PrimOp -- The Id for a primitive operator
267 | RecordSelId FieldLabel -- The Id for a record selector
270 makeConstantFlavour :: IdFlavour -> IdFlavour
271 makeConstantFlavour flavour = new_flavour
272 where new_flavour = case flavour of
273 VanillaId -> ConstantId
274 ExportedId -> ConstantId
275 ConstantId -> ConstantId -- e.g. Default methods
276 DictFunId -> DictFunId
277 flavour -> pprTrace "makeConstantFlavour"
278 (ppFlavourInfo flavour)
282 ppFlavourInfo :: IdFlavour -> SDoc
283 ppFlavourInfo VanillaId = empty
284 ppFlavourInfo ExportedId = ptext SLIT("[Exported]")
285 ppFlavourInfo SpecPragmaId = ptext SLIT("[SpecPrag]")
286 ppFlavourInfo ConstantId = ptext SLIT("[Constant]")
287 ppFlavourInfo DictFunId = ptext SLIT("[DictFun]")
288 ppFlavourInfo (DataConId _) = ptext SLIT("[DataCon]")
289 ppFlavourInfo (DataConWrapId _) = ptext SLIT("[DataConWrapper]")
290 ppFlavourInfo (PrimOpId _) = ptext SLIT("[PrimOp]")
291 ppFlavourInfo (RecordSelId _) = ptext SLIT("[RecSel]")
293 seqFlavour :: IdFlavour -> ()
294 seqFlavour f = f `seq` ()
297 The @SpecPragmaId@ exists only to make Ids that are
298 on the *LHS* of bindings created by SPECIALISE pragmas;
300 The SpecPragmaId is never itself mentioned; it
301 exists solely so that the specialiser will find
302 the call to f, and make specialised version of it.
303 The SpecPragmaId binding is discarded by the specialiser
304 when it gathers up overloaded calls.
305 Meanwhile, it is not discarded as dead code.
308 %************************************************************************
310 \subsection[arity-IdInfo]{Arity info about an @Id@}
312 %************************************************************************
314 For locally-defined Ids, the code generator maintains its own notion
315 of their arities; so it should not be asking... (but other things
316 besides the code-generator need arity info!)
320 = UnknownArity -- No idea
322 | ArityExactly Arity -- Arity is exactly this. We use this when importing a
323 -- function; it's already been compiled and we know its
326 | ArityAtLeast Arity -- A partial application of this Id to up to n-1 value arguments
327 -- does essentially no work. That is not necessarily the
328 -- same as saying that it has n leading lambdas, because coerces
329 -- may get in the way.
331 -- functions in the module being compiled. Their arity
332 -- might increase later in the compilation process, if
333 -- an extra lambda floats up to the binding site.
336 seqArity :: ArityInfo -> ()
337 seqArity a = arityLowerBound a `seq` ()
339 exactArity = ArityExactly
340 atLeastArity = ArityAtLeast
341 unknownArity = UnknownArity
343 arityLowerBound :: ArityInfo -> Arity
344 arityLowerBound UnknownArity = 0
345 arityLowerBound (ArityAtLeast n) = n
346 arityLowerBound (ArityExactly n) = n
348 hasArity :: ArityInfo -> Bool
349 hasArity UnknownArity = False
350 hasArity other = True
352 ppArityInfo UnknownArity = empty
353 ppArityInfo (ArityExactly arity) = hsep [ptext SLIT("__A"), int arity]
354 ppArityInfo (ArityAtLeast arity) = hsep [ptext SLIT("__AL"), int arity]
357 %************************************************************************
359 \subsection{Inline-pragma information}
361 %************************************************************************
366 | IMustNotBeINLINEd Bool -- True <=> came from an INLINE prag, False <=> came from a NOINLINE prag
367 (Maybe Int) -- Phase number from pragma, if any
369 -- The True, Nothing case doesn't need to be recorded
371 -- SEE COMMENTS WITH CoreUnfold.blackListed on the
372 -- exact significance of the IMustNotBeINLINEd pragma
374 isNeverInlinePrag :: InlinePragInfo -> Bool
375 isNeverInlinePrag (IMustNotBeINLINEd _ Nothing) = True
376 isNeverInlinePrag other = False
378 neverInlinePrag :: InlinePragInfo
379 neverInlinePrag = IMustNotBeINLINEd True{-should be False? --SDM -} Nothing
381 instance Outputable InlinePragInfo where
382 -- This is now parsed in interface files
383 ppr NoInlinePragInfo = empty
384 ppr other_prag = ptext SLIT("__U") <> pprInlinePragInfo other_prag
386 pprInlinePragInfo NoInlinePragInfo = empty
387 pprInlinePragInfo (IMustNotBeINLINEd True Nothing) = empty
388 pprInlinePragInfo (IMustNotBeINLINEd True (Just n)) = brackets (int n)
389 pprInlinePragInfo (IMustNotBeINLINEd False Nothing) = brackets (char '!')
390 pprInlinePragInfo (IMustNotBeINLINEd False (Just n)) = brackets (char '!' <> int n)
392 instance Show InlinePragInfo where
393 showsPrec p prag = showsPrecSDoc p (ppr prag)
397 %************************************************************************
399 \subsection[TyGen-IdInfo]{Type generalisation info about an @Id@}
401 %************************************************************************
403 Certain passes (notably usage inference) may change the type of an
404 identifier, modifying all in-scope uses of that identifier
405 appropriately to maintain type safety.
407 However, some identifiers must not have their types changed in this
408 way, because their types are conjured up in the front end of the
409 compiler rather than being read from the interface file. Default
410 methods, dictionary functions, record selectors, and others are in
411 this category. (see comment at TcClassDcl.tcClassSig).
413 To indicate this property, such identifiers are marked TyGenNever.
415 Furthermore, if the usage inference generates a usage-specialised
416 variant of a function, we must NOT re-infer a fully-generalised type
417 at the next inference. This finer property is indicated by a
418 TyGenUInfo on the identifier.
422 = NoTyGenInfo -- no restriction on type generalisation
424 | TyGenUInfo [Maybe Type] -- restrict generalisation of this Id to
425 -- preserve specified usage annotations
427 | TyGenNever -- never generalise the type of this Id
432 For TyGenUInfo, the list has one entry for each usage annotation on
433 the type of the Id, in left-to-right pre-order (annotations come
434 before the type they annotate). Nothing means no restriction; Just
435 usOnce or Just usMany forces that annotation to that value. Other
436 usage annotations are illegal.
439 seqTyGenInfo :: TyGenInfo -> ()
440 seqTyGenInfo NoTyGenInfo = ()
441 seqTyGenInfo (TyGenUInfo us) = seqList us ()
442 seqTyGenInfo TyGenNever = ()
444 noTyGenInfo :: TyGenInfo
445 noTyGenInfo = NoTyGenInfo
447 isNoTyGenInfo :: TyGenInfo -> Bool
448 isNoTyGenInfo NoTyGenInfo = True
449 isNoTyGenInfo _ = False
451 -- NB: There's probably no need to write this information out to the interface file.
452 -- Why? Simply because imported identifiers never get their types re-inferred.
453 -- But it's definitely nice to see in dumps, it for debugging purposes.
455 ppTyGenInfo :: TyGenInfo -> SDoc
456 ppTyGenInfo NoTyGenInfo = empty
457 ppTyGenInfo (TyGenUInfo us) = ptext SLIT("__G") <+> text (tyGenInfoString us)
458 ppTyGenInfo TyGenNever = ptext SLIT("__G N")
460 tyGenInfoString us = map go us
461 where go Nothing = 'x' -- for legibility, choose
462 go (Just u) | u == usOnce = '1' -- chars with identity
463 | u == usMany = 'M' -- Z-encoding.
464 go other = pprPanic "IdInfo.tyGenInfoString: unexpected annotation" (ppr other)
466 instance Outputable TyGenInfo where
469 instance Show TyGenInfo where
470 showsPrec p c = showsPrecSDoc p (ppr c)
474 %************************************************************************
476 \subsection[worker-IdInfo]{Worker info about an @Id@}
478 %************************************************************************
480 If this Id has a worker then we store a reference to it. Worker
481 functions are generated by the worker/wrapper pass. This uses
482 information from the strictness and CPR analyses.
484 There might not be a worker, even for a strict function, because:
485 (a) the function might be small enough to inline, so no need
487 (b) the strictness info might be "SSS" or something, so no w/w split.
491 data WorkerInfo = NoWorker
493 -- The Arity is the arity of the *wrapper* at the moment of the
494 -- w/w split. See comments in MkIface.ifaceId, with the 'Worker' code.
496 seqWorker :: WorkerInfo -> ()
497 seqWorker (HasWorker id _) = id `seq` ()
498 seqWorker NoWorker = ()
500 ppWorkerInfo NoWorker = empty
501 ppWorkerInfo (HasWorker wk_id _) = ptext SLIT("__P") <+> ppr wk_id
503 noWorkerInfo = NoWorker
505 workerExists :: WorkerInfo -> Bool
506 workerExists NoWorker = False
507 workerExists (HasWorker _ _) = True
509 workerId :: WorkerInfo -> Id
510 workerId (HasWorker id _) = id
512 wrapperArity :: WorkerInfo -> Arity
513 wrapperArity (HasWorker _ a) = a
517 %************************************************************************
519 \subsection[CAF-IdInfo]{CAF-related information}
521 %************************************************************************
523 This information is used to build Static Reference Tables (see
524 simplStg/ComputeSRT.lhs).
528 = MayHaveCafRefs -- either:
529 -- (1) A function or static constructor
530 -- that refers to one or more CAFs,
531 -- (2) A real live CAF
533 | NoCafRefs -- A function or static constructor
534 -- that refers to no CAFs.
536 -- LATER: not sure how easy this is...
540 mayHaveCafRefs MayHaveCafRefs = True
541 mayHaveCafRefs _ = False
543 seqCaf c = c `seq` ()
545 ppCafInfo NoCafRefs = ptext SLIT("__C")
546 ppCafInfo MayHaveCafRefs = empty
550 %************************************************************************
552 \subsection[cpr-IdInfo]{Constructed Product Result info about an @Id@}
554 %************************************************************************
556 If the @Id@ is a function then it may have CPR info. A CPR analysis
557 phase detects whether:
561 The function's return value has a product type, i.e. an algebraic type
562 with a single constructor. Examples of such types are tuples and boxed
565 The function always 'constructs' the value that it is returning. It
566 must do this on every path through, and it's OK if it calls another
567 function which constructs the result.
570 If this is the case then we store a template which tells us the
571 function has the CPR property and which components of the result are
577 | ReturnsCPR -- Yes, this function returns a constructed product
578 -- Implicitly, this means "after the function has been applied
579 -- to all its arguments", so the worker/wrapper builder in
580 -- WwLib.mkWWcpr checks that that it is indeed saturated before
581 -- making use of the CPR info
583 -- We used to keep nested info about sub-components, but
584 -- we never used it so I threw it away
588 seqCpr :: CprInfo -> ()
589 seqCpr ReturnsCPR = ()
590 seqCpr NoCPRInfo = ()
592 noCprInfo = NoCPRInfo
594 ppCprInfo NoCPRInfo = empty
595 ppCprInfo ReturnsCPR = ptext SLIT("__M")
597 instance Outputable CprInfo where
600 instance Show CprInfo where
601 showsPrec p c = showsPrecSDoc p (ppr c)
605 %************************************************************************
607 \subsection[lbvar-IdInfo]{Lambda-bound var info about an @Id@}
609 %************************************************************************
611 If the @Id@ is a lambda-bound variable then it may have lambda-bound
612 var info. The usage analysis (UsageSP) detects whether the lambda
613 binding this var is a ``one-shot'' lambda; that is, whether it is
614 applied at most once.
616 This information may be useful in optimisation, as computations may
617 safely be floated inside such a lambda without risk of duplicating
624 | LBVarInfo Type -- The lambda that binds this Id has this usage
625 -- annotation (i.e., if ==usOnce, then the
626 -- lambda is applied at most once).
627 -- The annotation's kind must be `$'
628 -- HACK ALERT! placing this info here is a short-term hack,
629 -- but it minimises changes to the rest of the compiler.
630 -- Hack agreed by SLPJ/KSW 1999-04.
632 seqLBVar l = l `seq` ()
636 noLBVarInfo = NoLBVarInfo
638 -- not safe to print or parse LBVarInfo because it is not really a
639 -- property of the definition, but a property of the context.
640 pprLBVarInfo NoLBVarInfo = empty
641 pprLBVarInfo (LBVarInfo u) | u == usOnce
642 = getPprStyle $ \ sty ->
645 else ptext SLIT("OneShot")
649 instance Outputable LBVarInfo where
652 instance Show LBVarInfo where
653 showsPrec p c = showsPrecSDoc p (ppr c)
657 %************************************************************************
659 \subsection{Bulk operations on IdInfo}
661 %************************************************************************
663 zapFragileInfo is used when cloning binders, mainly in the
664 simplifier. We must forget about used-once information because that
665 isn't necessarily correct in the transformed program.
666 Also forget specialisations and unfoldings because they would need
667 substitution to be correct. (They get pinned back on separately.)
669 Hoever, we REMEMBER loop-breaker and dead-variable information. The loop-breaker
670 information is used (for example) in MkIface to avoid exposing the unfolding of
674 zapFragileInfo :: IdInfo -> Maybe IdInfo
675 zapFragileInfo info@(IdInfo {occInfo = occ,
678 unfoldingInfo = unfolding})
679 | not (isFragileOcc occ)
680 -- We must forget about whether it was marked safe-to-inline,
681 -- because that isn't necessarily true in the simplified expression.
682 -- This is important because expressions may be re-simplified
683 -- We don't zap deadness or loop-breaker-ness.
684 -- The latter is important because it tells MkIface not to
685 -- spit out an inlining for the thing. The former doesn't
686 -- seem so important, but there's no harm.
688 && isEmptyCoreRules rules
689 -- Specialisations would need substituting. They get pinned
690 -- back on separately.
692 && not (workerExists wrkr)
694 && not (hasUnfolding unfolding)
695 -- This is very important; occasionally a let-bound binder is used
696 -- as a binder in some lambda, in which case its unfolding is utterly
697 -- bogus. Also the unfolding uses old binders so if we left it we'd
698 -- have to substitute it. Much better simply to give the Id a new
699 -- unfolding each time, which is what the simplifier does.
703 = Just (info {occInfo = robust_occ_info,
704 workerInfo = noWorkerInfo,
705 specInfo = emptyCoreRules,
706 unfoldingInfo = noUnfolding})
708 -- It's important to keep the loop-breaker info,
709 -- because the substitution doesn't remember it.
710 robust_occ_info = case occ of
711 OneOcc _ _ -> NoOccInfo
715 @zapLamInfo@ is used for lambda binders that turn out to to be
716 part of an unsaturated lambda
719 zapLamInfo :: IdInfo -> Maybe IdInfo
720 zapLamInfo info@(IdInfo {occInfo = occ, demandInfo = demand})
721 | is_safe_occ && not (isStrict demand)
724 = Just (info {occInfo = safe_occ,
725 demandInfo = wwLazy})
727 -- The "unsafe" occ info is the ones that say I'm not in a lambda
728 -- because that might not be true for an unsaturated lambda
729 is_safe_occ = case occ of
730 OneOcc in_lam once -> in_lam
733 safe_occ = case occ of
734 OneOcc _ once -> OneOcc insideLam once
739 copyIdInfo is used when shorting out a top-level binding
742 where f is exported. We are going to swizzle it around to
746 BUT (a) we must be careful about messing up rules
747 (b) we must ensure f's IdInfo ends up right
749 (a) Messing up the rules
751 The example that went bad on me was this one:
753 iterate :: (a -> a) -> a -> [a]
754 iterate = iterateList
756 iterateFB c f x = x `c` iterateFB c f (f x)
757 iterateList f x = x : iterateList f (f x)
760 "iterate" forall f x. iterate f x = build (\c _n -> iterateFB c f x)
761 "iterateFB" iterateFB (:) = iterateList
764 This got shorted out to:
766 iterateList :: (a -> a) -> a -> [a]
767 iterateList = iterate
769 iterateFB c f x = x `c` iterateFB c f (f x)
770 iterate f x = x : iterate f (f x)
773 "iterate" forall f x. iterate f x = build (\c _n -> iterateFB c f x)
774 "iterateFB" iterateFB (:) = iterate
777 And now we get an infinite loop in the rule system
778 iterate f x -> build (\cn -> iterateFB c f x
782 Tiresome solution: don't do shorting out if f has rewrite rules.
783 Hence shortableIdInfo.
785 (b) Keeping the IdInfo right
786 ~~~~~~~~~~~~~~~~~~~~~~~~
787 We want to move strictness/worker info from f_local to f, but keep the rest.
791 shortableIdInfo :: IdInfo -> Bool
792 shortableIdInfo info = isEmptyCoreRules (specInfo info)
794 copyIdInfo :: IdInfo -- f_local
795 -> IdInfo -- f (the exported one)
796 -> IdInfo -- New info for f
797 copyIdInfo f_local f = f { strictnessInfo = strictnessInfo f_local,
798 workerInfo = workerInfo f_local,
799 cprInfo = cprInfo f_local