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,
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, 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
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 vanillaIdInfo = mkIdInfo VanillaId
213 constantIdInfo :: IdInfo
214 constantIdInfo = mkIdInfo ConstantId
216 mkIdInfo :: IdFlavour -> IdInfo
217 mkIdInfo flv = IdInfo {
219 arityInfo = UnknownArity,
221 specInfo = emptyCoreRules,
222 tyGenInfo = noTyGenInfo,
223 workerInfo = NoWorker,
224 strictnessInfo = NoStrictnessInfo,
225 unfoldingInfo = noUnfolding,
226 cafInfo = MayHaveCafRefs,
228 lbvarInfo = NoLBVarInfo,
229 inlinePragInfo = NoInlinePragInfo,
235 %************************************************************************
239 %************************************************************************
243 = VanillaId -- Locally defined, not exported
244 | ExportedId -- Locally defined, exported
245 | SpecPragmaId -- Locally defined, RHS holds specialised call
247 | ConstantId -- Imported from elsewhere, or a dictionary function,
248 -- default method Id.
250 | DataConId DataCon -- The Id for a data constructor *worker*
251 | DataConWrapId DataCon -- The Id for a data constructor *wrapper*
252 -- [the only reasons we need to know is so that
253 -- a) we can suppress printing a definition in the interface file
254 -- b) when typechecking a pattern we can get from the
255 -- Id back to the data con]
256 | PrimOpId PrimOp -- The Id for a primitive operator
257 | RecordSelId FieldLabel -- The Id for a record selector
260 ppFlavourInfo :: IdFlavour -> SDoc
261 ppFlavourInfo VanillaId = empty
262 ppFlavourInfo ExportedId = ptext SLIT("[Exported]")
263 ppFlavourInfo SpecPragmaId = ptext SLIT("[SpecPrag]")
264 ppFlavourInfo ConstantId = ptext SLIT("[Constant]")
265 ppFlavourInfo (DataConId _) = ptext SLIT("[DataCon]")
266 ppFlavourInfo (DataConWrapId _) = ptext SLIT("[DataConWrapper]")
267 ppFlavourInfo (PrimOpId _) = ptext SLIT("[PrimOp]")
268 ppFlavourInfo (RecordSelId _) = ptext SLIT("[RecSel]")
270 seqFlavour :: IdFlavour -> ()
271 seqFlavour f = f `seq` ()
274 The @SpecPragmaId@ exists only to make Ids that are
275 on the *LHS* of bindings created by SPECIALISE pragmas;
277 The SpecPragmaId is never itself mentioned; it
278 exists solely so that the specialiser will find
279 the call to f, and make specialised version of it.
280 The SpecPragmaId binding is discarded by the specialiser
281 when it gathers up overloaded calls.
282 Meanwhile, it is not discarded as dead code.
285 %************************************************************************
287 \subsection[arity-IdInfo]{Arity info about an @Id@}
289 %************************************************************************
291 For locally-defined Ids, the code generator maintains its own notion
292 of their arities; so it should not be asking... (but other things
293 besides the code-generator need arity info!)
297 = UnknownArity -- No idea
299 | ArityExactly Arity -- Arity is exactly this. We use this when importing a
300 -- function; it's already been compiled and we know its
303 | ArityAtLeast Arity -- A partial application of this Id to up to n-1 value arguments
304 -- does essentially no work. That is not necessarily the
305 -- same as saying that it has n leading lambdas, because coerces
306 -- may get in the way.
308 -- functions in the module being compiled. Their arity
309 -- might increase later in the compilation process, if
310 -- an extra lambda floats up to the binding site.
313 seqArity :: ArityInfo -> ()
314 seqArity a = arityLowerBound a `seq` ()
316 exactArity = ArityExactly
317 atLeastArity = ArityAtLeast
318 unknownArity = UnknownArity
320 arityLowerBound :: ArityInfo -> Arity
321 arityLowerBound UnknownArity = 0
322 arityLowerBound (ArityAtLeast n) = n
323 arityLowerBound (ArityExactly n) = n
325 hasArity :: ArityInfo -> Bool
326 hasArity UnknownArity = False
327 hasArity other = True
329 ppArityInfo UnknownArity = empty
330 ppArityInfo (ArityExactly arity) = hsep [ptext SLIT("__A"), int arity]
331 ppArityInfo (ArityAtLeast arity) = hsep [ptext SLIT("__AL"), int arity]
334 %************************************************************************
336 \subsection{Inline-pragma information}
338 %************************************************************************
343 | IMustNotBeINLINEd Bool -- True <=> came from an INLINE prag, False <=> came from a NOINLINE prag
344 (Maybe Int) -- Phase number from pragma, if any
346 -- The True, Nothing case doesn't need to be recorded
348 -- SEE COMMENTS WITH CoreUnfold.blackListed on the
349 -- exact significance of the IMustNotBeINLINEd pragma
351 isNeverInlinePrag :: InlinePragInfo -> Bool
352 isNeverInlinePrag (IMustNotBeINLINEd _ Nothing) = True
353 isNeverInlinePrag other = False
355 neverInlinePrag :: InlinePragInfo
356 neverInlinePrag = IMustNotBeINLINEd True{-should be False? --SDM -} Nothing
358 instance Outputable InlinePragInfo where
359 -- This is now parsed in interface files
360 ppr NoInlinePragInfo = empty
361 ppr other_prag = ptext SLIT("__U") <> pprInlinePragInfo other_prag
363 pprInlinePragInfo NoInlinePragInfo = empty
364 pprInlinePragInfo (IMustNotBeINLINEd True Nothing) = empty
365 pprInlinePragInfo (IMustNotBeINLINEd True (Just n)) = brackets (int n)
366 pprInlinePragInfo (IMustNotBeINLINEd False Nothing) = brackets (char '!')
367 pprInlinePragInfo (IMustNotBeINLINEd False (Just n)) = brackets (char '!' <> int n)
369 instance Show InlinePragInfo where
370 showsPrec p prag = showsPrecSDoc p (ppr prag)
374 %************************************************************************
376 \subsection[TyGen-IdInfo]{Type generalisation info about an @Id@}
378 %************************************************************************
380 Certain passes (notably usage inference) may change the type of an
381 identifier, modifying all in-scope uses of that identifier
382 appropriately to maintain type safety.
384 However, some identifiers must not have their types changed in this
385 way, because their types are conjured up in the front end of the
386 compiler rather than being read from the interface file. Default
387 methods, dictionary functions, record selectors, and others are in
388 this category. (see comment at TcClassDcl.tcClassSig).
390 To indicate this property, such identifiers are marked TyGenNever.
392 Furthermore, if the usage inference generates a usage-specialised
393 variant of a function, we must NOT re-infer a fully-generalised type
394 at the next inference. This finer property is indicated by a
395 TyGenUInfo on the identifier.
399 = NoTyGenInfo -- no restriction on type generalisation
401 | TyGenUInfo [Maybe Type] -- restrict generalisation of this Id to
402 -- preserve specified usage annotations
404 | TyGenNever -- never generalise the type of this Id
409 For TyGenUInfo, the list has one entry for each usage annotation on
410 the type of the Id, in left-to-right pre-order (annotations come
411 before the type they annotate). Nothing means no restriction; Just
412 usOnce or Just usMany forces that annotation to that value. Other
413 usage annotations are illegal.
416 seqTyGenInfo :: TyGenInfo -> ()
417 seqTyGenInfo NoTyGenInfo = ()
418 seqTyGenInfo (TyGenUInfo us) = seqList us ()
419 seqTyGenInfo TyGenNever = ()
421 noTyGenInfo :: TyGenInfo
422 noTyGenInfo = NoTyGenInfo
424 isNoTyGenInfo :: TyGenInfo -> Bool
425 isNoTyGenInfo NoTyGenInfo = True
426 isNoTyGenInfo _ = False
428 -- NB: There's probably no need to write this information out to the interface file.
429 -- Why? Simply because imported identifiers never get their types re-inferred.
430 -- But it's definitely nice to see in dumps, it for debugging purposes.
432 ppTyGenInfo :: TyGenInfo -> SDoc
433 ppTyGenInfo NoTyGenInfo = empty
434 ppTyGenInfo (TyGenUInfo us) = ptext SLIT("__G") <+> text (tyGenInfoString us)
435 ppTyGenInfo TyGenNever = ptext SLIT("__G N")
437 tyGenInfoString us = map go us
438 where go Nothing = 'x' -- for legibility, choose
439 go (Just u) | u == usOnce = '1' -- chars with identity
440 | u == usMany = 'M' -- Z-encoding.
441 go other = pprPanic "IdInfo.tyGenInfoString: unexpected annotation" (ppr other)
443 instance Outputable TyGenInfo where
446 instance Show TyGenInfo where
447 showsPrec p c = showsPrecSDoc p (ppr c)
451 %************************************************************************
453 \subsection[worker-IdInfo]{Worker info about an @Id@}
455 %************************************************************************
457 If this Id has a worker then we store a reference to it. Worker
458 functions are generated by the worker/wrapper pass. This uses
459 information from the strictness and CPR analyses.
461 There might not be a worker, even for a strict function, because:
462 (a) the function might be small enough to inline, so no need
464 (b) the strictness info might be "SSS" or something, so no w/w split.
468 data WorkerInfo = NoWorker
470 -- The Arity is the arity of the *wrapper* at the moment of the
471 -- w/w split. See comments in MkIface.ifaceId, with the 'Worker' code.
473 seqWorker :: WorkerInfo -> ()
474 seqWorker (HasWorker id _) = id `seq` ()
475 seqWorker NoWorker = ()
477 ppWorkerInfo NoWorker = empty
478 ppWorkerInfo (HasWorker wk_id _) = ptext SLIT("__P") <+> ppr wk_id
480 noWorkerInfo = NoWorker
482 workerExists :: WorkerInfo -> Bool
483 workerExists NoWorker = False
484 workerExists (HasWorker _ _) = True
486 workerId :: WorkerInfo -> Id
487 workerId (HasWorker id _) = id
489 wrapperArity :: WorkerInfo -> Arity
490 wrapperArity (HasWorker _ a) = a
494 %************************************************************************
496 \subsection[CAF-IdInfo]{CAF-related information}
498 %************************************************************************
500 This information is used to build Static Reference Tables (see
501 simplStg/ComputeSRT.lhs).
505 = MayHaveCafRefs -- either:
506 -- (1) A function or static constructor
507 -- that refers to one or more CAFs,
508 -- (2) A real live CAF
510 | NoCafRefs -- A function or static constructor
511 -- that refers to no CAFs.
513 -- LATER: not sure how easy this is...
517 seqCaf c = c `seq` ()
519 ppCafInfo NoCafRefs = ptext SLIT("__C")
520 ppCafInfo MayHaveCafRefs = empty
524 %************************************************************************
526 \subsection[cpr-IdInfo]{Constructed Product Result info about an @Id@}
528 %************************************************************************
530 If the @Id@ is a function then it may have CPR info. A CPR analysis
531 phase detects whether:
535 The function's return value has a product type, i.e. an algebraic type
536 with a single constructor. Examples of such types are tuples and boxed
539 The function always 'constructs' the value that it is returning. It
540 must do this on every path through, and it's OK if it calls another
541 function which constructs the result.
544 If this is the case then we store a template which tells us the
545 function has the CPR property and which components of the result are
551 | ReturnsCPR -- Yes, this function returns a constructed product
552 -- Implicitly, this means "after the function has been applied
553 -- to all its arguments", so the worker/wrapper builder in
554 -- WwLib.mkWWcpr checks that that it is indeed saturated before
555 -- making use of the CPR info
557 -- We used to keep nested info about sub-components, but
558 -- we never used it so I threw it away
562 seqCpr :: CprInfo -> ()
563 seqCpr ReturnsCPR = ()
564 seqCpr NoCPRInfo = ()
566 noCprInfo = NoCPRInfo
568 ppCprInfo NoCPRInfo = empty
569 ppCprInfo ReturnsCPR = ptext SLIT("__M")
571 instance Outputable CprInfo where
574 instance Show CprInfo where
575 showsPrec p c = showsPrecSDoc p (ppr c)
579 %************************************************************************
581 \subsection[lbvar-IdInfo]{Lambda-bound var info about an @Id@}
583 %************************************************************************
585 If the @Id@ is a lambda-bound variable then it may have lambda-bound
586 var info. The usage analysis (UsageSP) detects whether the lambda
587 binding this var is a ``one-shot'' lambda; that is, whether it is
588 applied at most once.
590 This information may be useful in optimisation, as computations may
591 safely be floated inside such a lambda without risk of duplicating
598 | LBVarInfo Type -- The lambda that binds this Id has this usage
599 -- annotation (i.e., if ==usOnce, then the
600 -- lambda is applied at most once).
601 -- The annotation's kind must be `$'
602 -- HACK ALERT! placing this info here is a short-term hack,
603 -- but it minimises changes to the rest of the compiler.
604 -- Hack agreed by SLPJ/KSW 1999-04.
606 seqLBVar l = l `seq` ()
610 noLBVarInfo = NoLBVarInfo
612 -- not safe to print or parse LBVarInfo because it is not really a
613 -- property of the definition, but a property of the context.
614 pprLBVarInfo NoLBVarInfo = empty
615 pprLBVarInfo (LBVarInfo u) | u == usOnce
616 = getPprStyle $ \ sty ->
619 else ptext SLIT("OneShot")
623 instance Outputable LBVarInfo where
626 instance Show LBVarInfo where
627 showsPrec p c = showsPrecSDoc p (ppr c)
631 %************************************************************************
633 \subsection{Bulk operations on IdInfo}
635 %************************************************************************
637 zapFragileInfo is used when cloning binders, mainly in the
638 simplifier. We must forget about used-once information because that
639 isn't necessarily correct in the transformed program.
640 Also forget specialisations and unfoldings because they would need
641 substitution to be correct. (They get pinned back on separately.)
644 zapFragileInfo :: IdInfo -> Maybe IdInfo
645 zapFragileInfo info@(IdInfo {occInfo = occ,
648 unfoldingInfo = unfolding})
649 | not (isFragileOcc occ)
650 -- We must forget about whether it was marked safe-to-inline,
651 -- because that isn't necessarily true in the simplified expression.
652 -- This is important because expressions may be re-simplified
653 -- We don't zap deadness or loop-breaker-ness.
654 -- The latter is important because it tells MkIface not to
655 -- spit out an inlining for the thing. The former doesn't
656 -- seem so important, but there's no harm.
658 && isEmptyCoreRules rules
659 -- Specialisations would need substituting. They get pinned
660 -- back on separately.
662 && not (workerExists wrkr)
664 && not (hasUnfolding unfolding)
665 -- This is very important; occasionally a let-bound binder is used
666 -- as a binder in some lambda, in which case its unfolding is utterly
667 -- bogus. Also the unfolding uses old binders so if we left it we'd
668 -- have to substitute it. Much better simply to give the Id a new
669 -- unfolding each time, which is what the simplifier does.
673 = Just (info {occInfo = robust_occ_info,
674 workerInfo = noWorkerInfo,
675 specInfo = emptyCoreRules,
676 unfoldingInfo = noUnfolding})
678 -- It's important to keep the loop-breaker info,
679 -- because the substitution doesn't remember it.
680 robust_occ_info = case occ of
681 OneOcc _ _ -> NoOccInfo
685 @zapLamInfo@ is used for lambda binders that turn out to to be
686 part of an unsaturated lambda
689 zapLamInfo :: IdInfo -> Maybe IdInfo
690 zapLamInfo info@(IdInfo {occInfo = occ, demandInfo = demand})
691 | is_safe_occ && not (isStrict demand)
694 = Just (info {occInfo = safe_occ,
695 demandInfo = wwLazy})
697 -- The "unsafe" occ info is the ones that say I'm not in a lambda
698 -- because that might not be true for an unsaturated lambda
699 is_safe_occ = case occ of
700 OneOcc in_lam once -> in_lam
703 safe_occ = case occ of
704 OneOcc _ once -> OneOcc insideLam once
709 copyIdInfo is used when shorting out a top-level binding
712 where f is exported. We are going to swizzle it around to
716 BUT (a) we must be careful about messing up rules
717 (b) we must ensure f's IdInfo ends up right
719 (a) Messing up the rules
721 The example that went bad on me was this one:
723 iterate :: (a -> a) -> a -> [a]
724 iterate = iterateList
726 iterateFB c f x = x `c` iterateFB c f (f x)
727 iterateList f x = x : iterateList f (f x)
730 "iterate" forall f x. iterate f x = build (\c _n -> iterateFB c f x)
731 "iterateFB" iterateFB (:) = iterateList
734 This got shorted out to:
736 iterateList :: (a -> a) -> a -> [a]
737 iterateList = iterate
739 iterateFB c f x = x `c` iterateFB c f (f x)
740 iterate f x = x : iterate f (f x)
743 "iterate" forall f x. iterate f x = build (\c _n -> iterateFB c f x)
744 "iterateFB" iterateFB (:) = iterate
747 And now we get an infinite loop in the rule system
748 iterate f x -> build (\cn -> iterateFB c f x
752 Tiresome solution: don't do shorting out if f has rewrite rules.
753 Hence shortableIdInfo.
755 (b) Keeping the IdInfo right
756 ~~~~~~~~~~~~~~~~~~~~~~~~
757 We want to move strictness/worker info from f_local to f, but keep the rest.
761 shortableIdInfo :: IdInfo -> Bool
762 shortableIdInfo info = isEmptyCoreRules (specInfo info)
764 copyIdInfo :: IdInfo -- f_local
765 -> IdInfo -- f (the exported one)
766 -> IdInfo -- New info for f
767 copyIdInfo f_local f = f { strictnessInfo = strictnessInfo f_local,
768 workerInfo = workerInfo f_local,
769 cprInfo = cprInfo f_local