X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=ghc%2Fcompiler%2FbasicTypes%2FIdInfo.lhs;h=9e1a3f0668d7df3ffde5a7fa59cf4fd501687d82;hb=9541ef3440f89f5f275509b1cc64fb9c498dcf73;hp=f486614afff46b0979ac4440b21072d4d0998767;hpb=27f395a7289a5c944b135345d9c956e03d5317a2;p=ghc-hetmet.git diff --git a/ghc/compiler/basicTypes/IdInfo.lhs b/ghc/compiler/basicTypes/IdInfo.lhs index f486614..9e1a3f0 100644 --- a/ghc/compiler/basicTypes/IdInfo.lhs +++ b/ghc/compiler/basicTypes/IdInfo.lhs @@ -8,54 +8,266 @@ Haskell. [WDP 94/11]) \begin{code} module IdInfo ( + GlobalIdDetails(..), notGlobalId, -- Not abstract + IdInfo, -- Abstract + vanillaIdInfo, noCafIdInfo, + seqIdInfo, megaSeqIdInfo, - noIdInfo, + -- Zapping + zapLamInfo, zapDemandInfo, + shortableIdInfo, copyIdInfo, -- Arity - ArityInfo(..), - exactArity, atLeastArity, unknownArity, - arityInfo, setArityInfo, ppArityInfo, arityLowerBound, - - -- Strictness - StrictnessInfo(..), -- Non-abstract - workerExists, mkStrictnessInfo, - noStrictnessInfo, strictnessInfo, - ppStrictnessInfo, setStrictnessInfo, - isBottomingStrictness, appIsBottom, + ArityInfo, + unknownArity, + arityInfo, setArityInfo, ppArityInfo, + + -- New demand and strictness info + newStrictnessInfo, setNewStrictnessInfo, + newDemandInfo, setNewDemandInfo, pprNewStrictness, + setAllStrictnessInfo, + +#ifdef OLD_STRICTNESS + -- Strictness; imported from Demand + StrictnessInfo(..), + mkStrictnessInfo, noStrictnessInfo, + ppStrictnessInfo,isBottomingStrictness, +#endif + + -- Worker + WorkerInfo(..), workerExists, wrapperArity, workerId, + workerInfo, setWorkerInfo, ppWorkerInfo, -- Unfolding - unfoldingInfo, setUnfoldingInfo, + unfoldingInfo, setUnfoldingInfo, setUnfoldingInfoLazily, - -- DemandInfo +#ifdef OLD_STRICTNESS + -- Old DemandInfo and StrictnessInfo demandInfo, setDemandInfo, + strictnessInfo, setStrictnessInfo, + cprInfoFromNewStrictness, + oldStrictnessFromNew, newStrictnessFromOld, + oldDemand, newDemand, + + -- Constructed Product Result Info + CprInfo(..), cprInfo, setCprInfo, ppCprInfo, noCprInfo, +#endif -- Inline prags - InlinePragInfo(..), OccInfo(..), - inlinePragInfo, setInlinePragInfo, notInsideLambda, + InlinePragInfo, + inlinePragInfo, setInlinePragInfo, - -- Specialisation - IdSpecEnv, specInfo, setSpecInfo, + -- Occurrence info + OccInfo(..), isFragileOcc, isDeadOcc, isLoopBreaker, + InsideLam, OneBranch, insideLam, notInsideLam, oneBranch, notOneBranch, + occInfo, setOccInfo, - -- Update - UpdateInfo, UpdateSpec, - mkUpdateInfo, updateInfo, updateInfoMaybe, ppUpdateInfo, setUpdateInfo, + -- Specialisation + specInfo, setSpecInfo, -- CAF info - CafInfo(..), cafInfo, setCafInfo, ppCafInfo, + CafInfo(..), cafInfo, ppCafInfo, setCafInfo, mayHaveCafRefs, + + -- Lambda-bound variable info + LBVarInfo(..), lbvarInfo, setLBVarInfo, noLBVarInfo, hasNoLBVarInfo ) where #include "HsVersions.h" -import {-# SOURCE #-} CoreUnfold ( Unfolding, noUnfolding ) -import {-# SOURCE #-} CoreSyn ( CoreExpr ) - -import SpecEnv ( SpecEnv, emptySpecEnv ) -import Demand ( Demand, isLazy, wwLazy, pprDemands ) +import CoreSyn +import TyCon ( TyCon ) +import Class ( Class ) +import PrimOp ( PrimOp ) +import Var ( Id ) +import BasicTypes ( OccInfo(..), isFragileOcc, isDeadOcc, seqOccInfo, isLoopBreaker, + InsideLam, insideLam, notInsideLam, + OneBranch, oneBranch, notOneBranch, + Arity, + Activation(..) + ) +import DataCon ( DataCon ) +import ForeignCall ( ForeignCall ) +import FieldLabel ( FieldLabel ) +import NewDemand import Outputable +import Maybe ( isJust ) + +#ifdef OLD_STRICTNESS +import Name ( Name ) +import Demand hiding( Demand, seqDemand ) +import qualified Demand +import Util ( listLengthCmp ) +import List ( replicate ) +#endif + +-- infixl so you can say (id `set` a `set` b) +infixl 1 `setSpecInfo`, + `setArityInfo`, + `setInlinePragInfo`, + `setUnfoldingInfo`, + `setWorkerInfo`, + `setLBVarInfo`, + `setOccInfo`, + `setCafInfo`, + `setNewStrictnessInfo`, + `setAllStrictnessInfo`, + `setNewDemandInfo` +#ifdef OLD_STRICTNESS + , `setCprInfo` + , `setDemandInfo` + , `setStrictnessInfo` +#endif +\end{code} + +%************************************************************************ +%* * +\subsection{New strictness info} +%* * +%************************************************************************ + +To be removed later + +\begin{code} +-- setAllStrictnessInfo :: IdInfo -> Maybe StrictSig -> IdInfo +-- Set old and new strictness info +setAllStrictnessInfo info Nothing + = info { newStrictnessInfo = Nothing +#ifdef OLD_STRICTNESS + , strictnessInfo = NoStrictnessInfo + , cprInfo = NoCPRInfo +#endif + } + +setAllStrictnessInfo info (Just sig) + = info { newStrictnessInfo = Just sig +#ifdef OLD_STRICTNESS + , strictnessInfo = oldStrictnessFromNew sig + , cprInfo = cprInfoFromNewStrictness sig +#endif + } + +seqNewStrictnessInfo Nothing = () +seqNewStrictnessInfo (Just ty) = seqStrictSig ty + +pprNewStrictness Nothing = empty +pprNewStrictness (Just sig) = ftext FSLIT("Str:") <+> ppr sig + +#ifdef OLD_STRICTNESS +oldStrictnessFromNew :: StrictSig -> Demand.StrictnessInfo +oldStrictnessFromNew sig = mkStrictnessInfo (map oldDemand dmds, isBotRes res_info) + where + (dmds, res_info) = splitStrictSig sig + +cprInfoFromNewStrictness :: StrictSig -> CprInfo +cprInfoFromNewStrictness sig = case strictSigResInfo sig of + RetCPR -> ReturnsCPR + other -> NoCPRInfo + +newStrictnessFromOld :: Name -> Arity -> Demand.StrictnessInfo -> CprInfo -> StrictSig +newStrictnessFromOld name arity (Demand.StrictnessInfo ds res) cpr + | listLengthCmp ds arity /= GT -- length ds <= arity + -- Sometimes the old strictness analyser has more + -- demands than the arity justifies + = mk_strict_sig name arity $ + mkTopDmdType (map newDemand ds) (newRes res cpr) + +newStrictnessFromOld name arity other cpr + = -- Either no strictness info, or arity is too small + -- In either case we can't say anything useful + mk_strict_sig name arity $ + mkTopDmdType (replicate arity lazyDmd) (newRes False cpr) + +mk_strict_sig name arity dmd_ty + = WARN( arity /= dmdTypeDepth dmd_ty, ppr name <+> (ppr arity $$ ppr dmd_ty) ) + mkStrictSig dmd_ty + +newRes True _ = BotRes +newRes False ReturnsCPR = retCPR +newRes False NoCPRInfo = TopRes + +newDemand :: Demand.Demand -> NewDemand.Demand +newDemand (WwLazy True) = Abs +newDemand (WwLazy False) = lazyDmd +newDemand WwStrict = evalDmd +newDemand (WwUnpack unpk ds) = Eval (Prod (map newDemand ds)) +newDemand WwPrim = lazyDmd +newDemand WwEnum = evalDmd + +oldDemand :: NewDemand.Demand -> Demand.Demand +oldDemand Abs = WwLazy True +oldDemand Top = WwLazy False +oldDemand Bot = WwStrict +oldDemand (Box Bot) = WwStrict +oldDemand (Box Abs) = WwLazy False +oldDemand (Box (Eval _)) = WwStrict -- Pass box only +oldDemand (Defer d) = WwLazy False +oldDemand (Eval (Prod ds)) = WwUnpack True (map oldDemand ds) +oldDemand (Eval (Poly _)) = WwStrict +oldDemand (Call _) = WwStrict + +#endif /* OLD_STRICTNESS */ +\end{code} + + +\begin{code} +seqNewDemandInfo Nothing = () +seqNewDemandInfo (Just dmd) = seqDemand dmd \end{code} + +%************************************************************************ +%* * +\subsection{GlobalIdDetails +%* * +%************************************************************************ + +This type is here (rather than in Id.lhs) mainly because there's +an IdInfo.hi-boot, but no Id.hi-boot, and GlobalIdDetails is imported +(recursively) by Var.lhs. + +\begin{code} +data GlobalIdDetails + = VanillaGlobal -- Imported from elsewhere, a default method Id. + + | GenericOpId TyCon -- The to/from operations of a + | RecordSelId FieldLabel -- The Id for a record selector + | DataConWorkId DataCon -- The Id for a data constructor *worker* + | DataConWrapId DataCon -- The Id for a data constructor *wrapper* + -- [the only reasons we need to know is so that + -- a) we can suppress printing a definition in the interface file + -- b) when typechecking a pattern we can get from the + -- Id back to the data con] + + | ClassOpId Class -- An operation of a class + + | PrimOpId PrimOp -- The Id for a primitive operator + | FCallId ForeignCall -- The Id for a foreign call + + | NotGlobalId -- Used as a convenient extra return value from globalIdDetails + +notGlobalId = NotGlobalId + +instance Outputable GlobalIdDetails where + ppr NotGlobalId = ptext SLIT("[***NotGlobalId***]") + ppr VanillaGlobal = ptext SLIT("[GlobalId]") + ppr (GenericOpId _) = ptext SLIT("[GenericOp]") + ppr (DataConWorkId _) = ptext SLIT("[DataCon]") + ppr (DataConWrapId _) = ptext SLIT("[DataConWrapper]") + ppr (ClassOpId _) = ptext SLIT("[ClassOp]") + ppr (PrimOpId _) = ptext SLIT("[PrimOp]") + ppr (FCallId _) = ptext SLIT("[ForeignCall]") + ppr (RecordSelId _) = ptext SLIT("[RecSel]") +\end{code} + + +%************************************************************************ +%* * +\subsection{The main IdInfo type} +%* * +%************************************************************************ + An @IdInfo@ gives {\em optional} information about an @Id@. If present it never lies, but it may not be present, in which case there is always a conservative assumption which can be made. @@ -66,49 +278,137 @@ the properties attached to the other. The @IdInfo@ gives information about the value, or definition, of the @Id@. It does {\em not} contain information about the @Id@'s usage -(except for @DemandInfo@? ToDo). +(except for @DemandInfo@? ToDo). (@lbvarInfo@ is also a marginal +case. KSW 1999-04). \begin{code} data IdInfo = IdInfo { - arityInfo :: ArityInfo, -- Its arity - demandInfo :: Demand, -- Whether or not it is definitely demanded - specInfo :: IdSpecEnv, -- Specialisations of this function which exist - strictnessInfo :: StrictnessInfo, -- Strictness properties - unfoldingInfo :: Unfolding, -- Its unfolding - updateInfo :: UpdateInfo, -- Which args should be updated - cafInfo :: CafInfo, - inlinePragInfo :: !InlinePragInfo -- Inline pragmas + arityInfo :: !ArityInfo, -- Its arity + specInfo :: CoreRules, -- Specialisations of this function which exist +#ifdef OLD_STRICTNESS + cprInfo :: CprInfo, -- Function always constructs a product result + demandInfo :: Demand.Demand, -- Whether or not it is definitely demanded + strictnessInfo :: StrictnessInfo, -- Strictness properties +#endif + workerInfo :: WorkerInfo, -- Pointer to Worker Function + unfoldingInfo :: Unfolding, -- Its unfolding + cafInfo :: CafInfo, -- CAF info + lbvarInfo :: LBVarInfo, -- Info about a lambda-bound variable + inlinePragInfo :: InlinePragInfo, -- Inline pragma + occInfo :: OccInfo, -- How it occurs + + newStrictnessInfo :: Maybe StrictSig, -- Reason for Maybe: the DmdAnal phase needs to + -- know whether whether this is the first visit, + -- so it can assign botSig. Other customers want + -- topSig. So Nothing is good. + + newDemandInfo :: Maybe Demand -- Similarly we want to know if there's no + -- known demand yet, for when we are looking for + -- CPR info } + +seqIdInfo :: IdInfo -> () +seqIdInfo (IdInfo {}) = () + +megaSeqIdInfo :: IdInfo -> () +megaSeqIdInfo info + = seqRules (specInfo info) `seq` + seqWorker (workerInfo info) `seq` + +-- Omitting this improves runtimes a little, presumably because +-- some unfoldings are not calculated at all +-- seqUnfolding (unfoldingInfo info) `seq` + + seqNewDemandInfo (newDemandInfo info) `seq` + seqNewStrictnessInfo (newStrictnessInfo info) `seq` + +#ifdef OLD_STRICTNESS + Demand.seqDemand (demandInfo info) `seq` + seqStrictnessInfo (strictnessInfo info) `seq` + seqCpr (cprInfo info) `seq` +#endif + + seqCaf (cafInfo info) `seq` + seqLBVar (lbvarInfo info) `seq` + seqOccInfo (occInfo info) \end{code} Setters \begin{code} -setUpdateInfo ud info = info { updateInfo = ud } -setDemandInfo dd info = info { demandInfo = dd } -setStrictnessInfo st info = info { strictnessInfo = st } -setSpecInfo sp info = info { specInfo = sp } -setArityInfo ar info = info { arityInfo = ar } -setInlinePragInfo pr info = info { inlinePragInfo = pr } -setUnfoldingInfo uf info = info { unfoldingInfo = uf } -setCafInfo cf info = info { cafInfo = cf } +setWorkerInfo info wk = wk `seq` info { workerInfo = wk } +setSpecInfo info sp = sp `seq` info { specInfo = sp } +setInlinePragInfo info pr = pr `seq` info { inlinePragInfo = pr } +setOccInfo info oc = oc `seq` info { occInfo = oc } +#ifdef OLD_STRICTNESS +setStrictnessInfo info st = st `seq` info { strictnessInfo = st } +#endif + -- Try to avoid spack leaks by seq'ing + +setUnfoldingInfoLazily info uf -- Lazy variant to avoid looking at the + = -- unfolding of an imported Id unless necessary + info { unfoldingInfo = uf } -- (In this case the demand-zapping is redundant.) + +setUnfoldingInfo info uf + | isEvaldUnfolding uf + -- If the unfolding is a value, the demand info may + -- go pear-shaped, so we nuke it. Example: + -- let x = (a,b) in + -- case x of (p,q) -> h p q x + -- Here x is certainly demanded. But after we've nuked + -- the case, we'll get just + -- let x = (a,b) in h a b x + -- and now x is not demanded (I'm assuming h is lazy) + -- This really happens. The solution here is a bit ad hoc... + = info { unfoldingInfo = uf, newDemandInfo = Nothing } + + | otherwise + -- We do *not* seq on the unfolding info, For some reason, doing so + -- actually increases residency significantly. + = info { unfoldingInfo = uf } + +#ifdef OLD_STRICTNESS +setDemandInfo info dd = info { demandInfo = dd } +setCprInfo info cp = info { cprInfo = cp } +#endif + +setArityInfo info ar = info { arityInfo = ar } +setCafInfo info caf = info { cafInfo = caf } + +setLBVarInfo info lb = {-lb `seq`-} info { lbvarInfo = lb } + +setNewDemandInfo info dd = dd `seq` info { newDemandInfo = dd } +setNewStrictnessInfo info dd = dd `seq` info { newStrictnessInfo = dd } \end{code} \begin{code} -noIdInfo = IdInfo { - arityInfo = UnknownArity, - demandInfo = wwLazy, - specInfo = emptySpecEnv, - strictnessInfo = NoStrictnessInfo, - unfoldingInfo = noUnfolding, - updateInfo = NoUpdateInfo, - cafInfo = MayHaveCafRefs, - inlinePragInfo = NoInlinePragInfo +vanillaIdInfo :: IdInfo +vanillaIdInfo + = IdInfo { + cafInfo = vanillaCafInfo, + arityInfo = unknownArity, +#ifdef OLD_STRICTNESS + cprInfo = NoCPRInfo, + demandInfo = wwLazy, + strictnessInfo = NoStrictnessInfo, +#endif + specInfo = emptyCoreRules, + workerInfo = NoWorker, + unfoldingInfo = noUnfolding, + lbvarInfo = NoLBVarInfo, + inlinePragInfo = AlwaysActive, + occInfo = NoOccInfo, + newDemandInfo = Nothing, + newStrictnessInfo = Nothing } + +noCafIdInfo = vanillaIdInfo `setCafInfo` NoCafRefs + -- Used for built-in type Ids in MkId. \end{code} + %************************************************************************ %* * \subsection[arity-IdInfo]{Arity info about an @Id@} @@ -120,24 +420,19 @@ of their arities; so it should not be asking... (but other things besides the code-generator need arity info!) \begin{code} -data ArityInfo - = UnknownArity -- No idea - | ArityExactly Int -- Arity is exactly this - | ArityAtLeast Int -- Arity is this or greater +type ArityInfo = Arity + -- A partial application of this Id to up to n-1 value arguments + -- does essentially no work. That is not necessarily the + -- same as saying that it has n leading lambdas, because coerces + -- may get in the way. -exactArity = ArityExactly -atLeastArity = ArityAtLeast -unknownArity = UnknownArity + -- The arity might increase later in the compilation process, if + -- an extra lambda floats up to the binding site. -arityLowerBound :: ArityInfo -> Int -arityLowerBound UnknownArity = 0 -arityLowerBound (ArityAtLeast n) = n -arityLowerBound (ArityExactly n) = n +unknownArity = 0 :: Arity - -ppArityInfo UnknownArity = empty -ppArityInfo (ArityExactly arity) = hsep [ptext SLIT("__A"), int arity] -ppArityInfo (ArityAtLeast arity) = hsep [ptext SLIT("__AL"), int arity] +ppArityInfo 0 = empty +ppArityInfo n = hsep [ptext SLIT("Arity"), int n] \end{code} %************************************************************************ @@ -147,240 +442,297 @@ ppArityInfo (ArityAtLeast arity) = hsep [ptext SLIT("__AL"), int arity] %************************************************************************ \begin{code} -data InlinePragInfo - = NoInlinePragInfo - - | IAmASpecPragmaId -- Used for spec-pragma Ids; don't discard or inline - - | IWantToBeINLINEd -- User INLINE pragma - | IMustNotBeINLINEd -- User NOINLINE pragma - - | IAmALoopBreaker -- Used by the occurrence analyser to mark loop-breakers - -- in a group of recursive definitions - - | ICanSafelyBeINLINEd -- Used by the occurrence analyser to mark things - -- that manifesly occur once, not inside SCCs, - -- not in constructor arguments +type InlinePragInfo = Activation + -- Tells when the inlining is active + -- When it is active the thing may be inlined, depending on how + -- big it is. + -- + -- If there was an INLINE pragma, then as a separate matter, the + -- RHS will have been made to look small with a CoreSyn Inline Note +\end{code} - OccInfo -- Says whether the occurrence is inside a lambda - -- If so, must only substitute WHNFs - Bool -- False <=> occurs in more than one case branch - -- If so, there's a code-duplication issue +%************************************************************************ +%* * +\subsection[worker-IdInfo]{Worker info about an @Id@} +%* * +%************************************************************************ - | IAmDead -- Marks unused variables. Sometimes useful for - -- lambda and case-bound variables. +If this Id has a worker then we store a reference to it. Worker +functions are generated by the worker/wrapper pass. This uses +information from strictness analysis. - | IMustBeINLINEd -- Absolutely must inline; used for PrimOps and - -- constructors only. +There might not be a worker, even for a strict function, because: +(a) the function might be small enough to inline, so no need + for w/w split +(b) the strictness info might be "SSS" or something, so no w/w split. -instance Outputable InlinePragInfo where - ppr NoInlinePragInfo = empty - ppr IMustBeINLINEd = ptext SLIT("__UU") - ppr IWantToBeINLINEd = ptext SLIT("__U") - ppr IMustNotBeINLINEd = ptext SLIT("__Unot") - ppr IAmALoopBreaker = ptext SLIT("__Ux") - ppr IAmDead = ptext SLIT("__Ud") - ppr (ICanSafelyBeINLINEd InsideLam _) = ptext SLIT("__Ul") - ppr (ICanSafelyBeINLINEd _ _) = ptext SLIT("__Us") - ppr IAmASpecPragmaId = ptext SLIT("__US") +Sometimes the arity of a wrapper changes from the original arity from +which it was generated, so we always emit the "original" arity into +the interface file, as part of the worker info. -instance Show InlinePragInfo where - showsPrec p prag = showsPrecSDoc p (ppr prag) -\end{code} +How can this happen? Sometimes we get + f = coerce t (\x y -> $wf x y) +at the moment of w/w split; but the eta reducer turns it into + f = coerce t $wf +which is perfectly fine except that the exposed arity so far as +the code generator is concerned (zero) differs from the arity +when we did the split (2). -The @IMustNotBeDiscarded@ exists only to make Ids that are -on the *LHS* of bindings created by SPECIALISE pragmas; -eg: s = f Int d -The SpecPragmaId is never itself mentioned; it -exists solely so that the specialiser will find -the call to f, and make specialised version of it. -The SpecPragmaId binding is discarded by the specialiser -when it gathers up overloaded calls. -Meanwhile, it is not discarded as dead code. +All this arises because we use 'arity' to mean "exactly how many +top level lambdas are there" in interface files; but during the +compilation of this module it means "how many things can I apply +this to". \begin{code} -data OccInfo - = StrictOcc -- Occurs syntactically strictly; - -- i.e. in a function position or case scrutinee - | LazyOcc -- Not syntactically strict (*even* that of a strict function) - -- or in a case branch where there's more than one alternative +data WorkerInfo = NoWorker + | HasWorker Id Arity + -- The Arity is the arity of the *wrapper* at the moment of the + -- w/w split. See comments in MkIface.ifaceId, with the 'Worker' code. - | InsideLam -- Inside a non-linear lambda (that is, a lambda which - -- is sure to be instantiated only once). - -- Substituting a redex for this occurrence is - -- dangerous because it might duplicate work. +seqWorker :: WorkerInfo -> () +seqWorker (HasWorker id a) = id `seq` a `seq` () +seqWorker NoWorker = () -instance Outputable OccInfo where - ppr StrictOcc = text "s" - ppr LazyOcc = empty - ppr InsideLam = text "l" +ppWorkerInfo NoWorker = empty +ppWorkerInfo (HasWorker wk_id _) = ptext SLIT("__P") <+> ppr wk_id +workerExists :: WorkerInfo -> Bool +workerExists NoWorker = False +workerExists (HasWorker _ _) = True -notInsideLambda :: OccInfo -> Bool -notInsideLambda StrictOcc = True -notInsideLambda LazyOcc = True -notInsideLambda InsideLam = False +workerId :: WorkerInfo -> Id +workerId (HasWorker id _) = id + +wrapperArity :: WorkerInfo -> Arity +wrapperArity (HasWorker _ a) = a \end{code} + %************************************************************************ %* * -\subsection[specialisation-IdInfo]{Specialisation info about an @Id@} +\subsection[CG-IdInfo]{Code generator-related information} %* * %************************************************************************ -A @IdSpecEnv@ holds details of an @Id@'s specialisations. - \begin{code} -type IdSpecEnv = SpecEnv CoreExpr -\end{code} - -For example, if \tr{f}'s @SpecEnv@ contains the mapping: -\begin{verbatim} - [List a, b] ===> (\d -> f' a b) -\end{verbatim} -then when we find an application of f to matching types, we simply replace -it by the matching RHS: -\begin{verbatim} - f (List Int) Bool ===> (\d -> f' Int Bool) -\end{verbatim} -All the stuff about how many dictionaries to discard, and what types -to apply the specialised function to, are handled by the fact that the -SpecEnv contains a template for the result of the specialisation. +-- CafInfo is used to build Static Reference Tables (see simplStg/SRT.lhs). -There is one more exciting case, which is dealt with in exactly the same -way. If the specialised value is unboxed then it is lifted at its -definition site and unlifted at its uses. For example: +data CafInfo + = MayHaveCafRefs -- either: + -- (1) A function or static constructor + -- that refers to one or more CAFs, + -- (2) A real live CAF - pi :: forall a. Num a => a + | NoCafRefs -- A function or static constructor + -- that refers to no CAFs. -might have a specialisation +vanillaCafInfo = MayHaveCafRefs -- Definitely safe - [Int#] ===> (case pi' of Lift pi# -> pi#) +mayHaveCafRefs MayHaveCafRefs = True +mayHaveCafRefs _ = False -where pi' :: Lift Int# is the specialised version of pi. +seqCaf c = c `seq` () +ppCafInfo NoCafRefs = ptext SLIT("NoCafRefs") +ppCafInfo MayHaveCafRefs = empty +\end{code} %************************************************************************ %* * -\subsection[strictness-IdInfo]{Strictness info about an @Id@} +\subsection[cpr-IdInfo]{Constructed Product Result info about an @Id@} %* * %************************************************************************ -We specify the strictness of a function by giving information about -each of the ``wrapper's'' arguments (see the description about -worker/wrapper-style transformations in the PJ/Launchbury paper on -unboxed types). +If the @Id@ is a function then it may have CPR info. A CPR analysis +phase detects whether: -The list of @Demands@ specifies: (a)~the strictness properties -of a function's arguments; (b)~the {\em existence} of a ``worker'' -version of the function; and (c)~the type signature of that worker (if -it exists); i.e. its calling convention. +\begin{enumerate} +\item +The function's return value has a product type, i.e. an algebraic type +with a single constructor. Examples of such types are tuples and boxed +primitive values. +\item +The function always 'constructs' the value that it is returning. It +must do this on every path through, and it's OK if it calls another +function which constructs the result. +\end{enumerate} -\begin{code} -data StrictnessInfo - = NoStrictnessInfo - - | StrictnessInfo [Demand] - Bool -- True <=> the function diverges regardless of its arguments - -- Useful for "error" and other disguised variants thereof. - -- BUT NB: f = \x y. error "urk" - -- will have info SI [SS] True - -- but still (f) and (f 2) are not bot; only (f 3 2) is bot - - Bool -- True <=> there is a worker. There might not be, even for a - -- strict function, because: - -- (a) the function might be small enough to inline, - -- so no need for w/w split - -- (b) the strictness info might be "SSS" or something, so no w/w split. -\end{code} +If this is the case then we store a template which tells us the +function has the CPR property and which components of the result are +also CPRs. \begin{code} -mkStrictnessInfo :: ([Demand], Bool) -> Bool -> StrictnessInfo - -mkStrictnessInfo (xs, is_bot) has_wrkr - | all isLazy xs && not is_bot = NoStrictnessInfo -- Uninteresting - | otherwise = StrictnessInfo xs is_bot has_wrkr +#ifdef OLD_STRICTNESS +data CprInfo + = NoCPRInfo + | ReturnsCPR -- Yes, this function returns a constructed product + -- Implicitly, this means "after the function has been applied + -- to all its arguments", so the worker/wrapper builder in + -- WwLib.mkWWcpr checks that that it is indeed saturated before + -- making use of the CPR info -noStrictnessInfo = NoStrictnessInfo + -- We used to keep nested info about sub-components, but + -- we never used it so I threw it away -isBottomingStrictness (StrictnessInfo _ bot _) = bot -isBottomingStrictness NoStrictnessInfo = False +seqCpr :: CprInfo -> () +seqCpr ReturnsCPR = () +seqCpr NoCPRInfo = () --- appIsBottom returns true if an application to n args would diverge -appIsBottom (StrictnessInfo ds bot _) n = bot && (n >= length ds) -appIsBottom NoStrictnessInfo n = False +noCprInfo = NoCPRInfo -ppStrictnessInfo NoStrictnessInfo = empty -ppStrictnessInfo (StrictnessInfo wrapper_args bot wrkr_maybe) - = hsep [ptext SLIT("__S"), pprDemands wrapper_args bot] -\end{code} +ppCprInfo NoCPRInfo = empty +ppCprInfo ReturnsCPR = ptext SLIT("__M") +instance Outputable CprInfo where + ppr = ppCprInfo -\begin{code} -workerExists :: StrictnessInfo -> Bool -workerExists (StrictnessInfo _ _ worker_exists) = worker_exists -workerExists other = False +instance Show CprInfo where + showsPrec p c = showsPrecSDoc p (ppr c) +#endif \end{code} %************************************************************************ %* * -\subsection[update-IdInfo]{Update-analysis info about an @Id@} +\subsection[lbvar-IdInfo]{Lambda-bound var info about an @Id@} %* * %************************************************************************ +If the @Id@ is a lambda-bound variable then it may have lambda-bound +var info. Sometimes we know whether the lambda binding this var is a +``one-shot'' lambda; that is, whether it is applied at most once. + +This information may be useful in optimisation, as computations may +safely be floated inside such a lambda without risk of duplicating +work. + \begin{code} -data UpdateInfo - = NoUpdateInfo - | SomeUpdateInfo UpdateSpec - deriving (Eq, Ord) - -- we need Eq/Ord to cross-chk update infos in interfaces - --- the form in which we pass update-analysis info between modules: -type UpdateSpec = [Int] +data LBVarInfo = NoLBVarInfo + | IsOneShotLambda -- The lambda is applied at most once). + +seqLBVar l = l `seq` () \end{code} \begin{code} -mkUpdateInfo = SomeUpdateInfo +hasNoLBVarInfo NoLBVarInfo = True +hasNoLBVarInfo IsOneShotLambda = False -updateInfoMaybe NoUpdateInfo = Nothing -updateInfoMaybe (SomeUpdateInfo []) = Nothing -updateInfoMaybe (SomeUpdateInfo u) = Just u -\end{code} +noLBVarInfo = NoLBVarInfo -Text instance so that the update annotations can be read in. +pprLBVarInfo NoLBVarInfo = empty +pprLBVarInfo IsOneShotLambda = ptext SLIT("OneShot") -\begin{code} -ppUpdateInfo NoUpdateInfo = empty -ppUpdateInfo (SomeUpdateInfo []) = empty -ppUpdateInfo (SomeUpdateInfo spec) = (<>) (ptext SLIT("__U ")) (hcat (map int spec)) +instance Outputable LBVarInfo where + ppr = pprLBVarInfo + +instance Show LBVarInfo where + showsPrec p c = showsPrecSDoc p (ppr c) \end{code} + %************************************************************************ %* * -\subsection[CAF-IdInfo]{CAF-related information} +\subsection{Bulk operations on IdInfo} %* * %************************************************************************ -This information is used to build Static Reference Tables (see -simplStg/ComputeSRT.lhs). +@zapLamInfo@ is used for lambda binders that turn out to to be +part of an unsaturated lambda \begin{code} -data CafInfo - = MayHaveCafRefs -- either: - -- (1) A function or static constructor - -- that refers to one or more CAFs, - -- (2) A real live CAF +zapLamInfo :: IdInfo -> Maybe IdInfo +zapLamInfo info@(IdInfo {occInfo = occ, newDemandInfo = demand}) + | is_safe_occ occ && is_safe_dmd demand + = Nothing + | otherwise + = Just (info {occInfo = safe_occ, newDemandInfo = Nothing}) + where + -- The "unsafe" occ info is the ones that say I'm not in a lambda + -- because that might not be true for an unsaturated lambda + is_safe_occ (OneOcc in_lam once) = in_lam + is_safe_occ other = True + + safe_occ = case occ of + OneOcc _ once -> OneOcc insideLam once + other -> occ + + is_safe_dmd Nothing = True + is_safe_dmd (Just dmd) = not (isStrictDmd dmd) +\end{code} - | NoCafRefs -- A function or static constructor - -- that refers to no CAFs. +\begin{code} +zapDemandInfo :: IdInfo -> Maybe IdInfo +zapDemandInfo info@(IdInfo {newDemandInfo = dmd}) + | isJust dmd = Just (info {newDemandInfo = Nothing}) + | otherwise = Nothing +\end{code} --- LATER: not sure how easy this is... --- | OneCafRef Id +copyIdInfo is used when shorting out a top-level binding + f_local = BIG + f = f_local +where f is exported. We are going to swizzle it around to + f = BIG + f_local = f + +BUT (a) we must be careful about messing up rules + (b) we must ensure f's IdInfo ends up right + +(a) Messing up the rules +~~~~~~~~~~~~~~~~~~~~ +The example that went bad on me was this one: + + iterate :: (a -> a) -> a -> [a] + iterate = iterateList + + iterateFB c f x = x `c` iterateFB c f (f x) + iterateList f x = x : iterateList f (f x) + + {-# RULES + "iterate" forall f x. iterate f x = build (\c _n -> iterateFB c f x) + "iterateFB" iterateFB (:) = iterateList + #-} + +This got shorted out to: + + iterateList :: (a -> a) -> a -> [a] + iterateList = iterate + + iterateFB c f x = x `c` iterateFB c f (f x) + iterate f x = x : iterate f (f x) + + {-# RULES + "iterate" forall f x. iterate f x = build (\c _n -> iterateFB c f x) + "iterateFB" iterateFB (:) = iterate + #-} + +And now we get an infinite loop in the rule system + iterate f x -> build (\cn -> iterateFB c f x) + -> iterateFB (:) f x + -> iterate f x + +Tiresome solution: don't do shorting out if f has rewrite rules. +Hence shortableIdInfo. + +(b) Keeping the IdInfo right +~~~~~~~~~~~~~~~~~~~~~~~~ +We want to move strictness/worker info from f_local to f, but keep the rest. +Hence copyIdInfo. -ppCafInfo NoCafRefs = ptext SLIT("__C") -ppCafInfo MayHaveCafRefs = empty +\begin{code} +shortableIdInfo :: IdInfo -> Bool +shortableIdInfo info = isEmptyCoreRules (specInfo info) + +copyIdInfo :: IdInfo -- f_local + -> IdInfo -- f (the exported one) + -> IdInfo -- New info for f +copyIdInfo f_local f = f { newStrictnessInfo = newStrictnessInfo f_local, +#ifdef OLD_STRICTNESS + strictnessInfo = strictnessInfo f_local, + cprInfo = cprInfo f_local, +#endif + workerInfo = workerInfo f_local + } \end{code}