{- (c) The University of Glasgow 2006 (c) The GRASP/AQUA Project, Glasgow University, 1992-1998 \section[Demand]{@Demand@: A decoupled implementation of a demand domain} -} {-# LANGUAGE CPP, FlexibleInstances, TypeSynonymInstances, RecordWildCards #-} module Demand ( StrDmd, UseDmd(..), Count, Demand, CleanDemand, getStrDmd, getUseDmd, mkProdDmd, mkOnceUsedDmd, mkManyUsedDmd, mkHeadStrict, oneifyDmd, toCleanDmd, absDmd, topDmd, botDmd, seqDmd, lubDmd, bothDmd, lazyApply1Dmd, lazyApply2Dmd, strictApply1Dmd, catchArgDmd, isTopDmd, isAbsDmd, isSeqDmd, peelUseCall, cleanUseDmd_maybe, strictenDmd, bothCleanDmd, addCaseBndrDmd, DmdType(..), dmdTypeDepth, lubDmdType, bothDmdType, nopDmdType, botDmdType, mkDmdType, addDemand, removeDmdTyArgs, BothDmdArg, mkBothDmdArg, toBothDmdArg, DmdEnv, emptyDmdEnv, peelFV, findIdDemand, DmdResult, CPRResult, isBotRes, isTopRes, topRes, botRes, exnRes, cprProdRes, vanillaCprProdRes, cprSumRes, appIsBottom, isBottomingSig, pprIfaceStrictSig, trimCPRInfo, returnsCPR_maybe, StrictSig(..), mkStrictSig, mkClosedStrictSig, nopSig, botSig, exnSig, cprProdSig, isTopSig, hasDemandEnvSig, splitStrictSig, strictSigDmdEnv, increaseStrictSigArity, etaExpandStrictSig, seqDemand, seqDemandList, seqDmdType, seqStrictSig, evalDmd, cleanEvalDmd, cleanEvalProdDmd, isStrictDmd, splitDmdTy, splitFVs, deferAfterIO, postProcessUnsat, postProcessDmdType, splitProdDmd_maybe, peelCallDmd, mkCallDmd, mkWorkerDemand, dmdTransformSig, dmdTransformDataConSig, dmdTransformDictSelSig, argOneShots, argsOneShots, saturatedByOneShots, trimToType, TypeShape(..), useCount, isUsedOnce, reuseEnv, killUsageDemand, killUsageSig, zapUsageDemand, zapUsageEnvSig, zapUsedOnceDemand, zapUsedOnceSig, strictifyDictDmd ) where #include "HsVersions.h" import GhcPrelude import DynFlags import Outputable import Var ( Var ) import VarEnv import UniqFM import Util import BasicTypes import Binary import Maybes ( orElse ) import Type ( Type, isUnliftedType ) import TyCon ( isNewTyCon, isClassTyCon ) import DataCon ( splitDataProductType_maybe ) {- ************************************************************************ * * Joint domain for Strictness and Absence * * ************************************************************************ -} data JointDmd s u = JD { sd :: s, ud :: u } deriving ( Eq, Show ) getStrDmd :: JointDmd s u -> s getStrDmd = sd getUseDmd :: JointDmd s u -> u getUseDmd = ud -- Pretty-printing instance (Outputable s, Outputable u) => Outputable (JointDmd s u) where ppr (JD {sd = s, ud = u}) = angleBrackets (ppr s <> char ',' <> ppr u) -- Well-formedness preserving constructors for the joint domain mkJointDmd :: s -> u -> JointDmd s u mkJointDmd s u = JD { sd = s, ud = u } mkJointDmds :: [s] -> [u] -> [JointDmd s u] mkJointDmds ss as = zipWithEqual "mkJointDmds" mkJointDmd ss as {- ************************************************************************ * * Strictness domain * * ************************************************************************ Lazy | ExnStr x - | HeadStr / \ SCall SProd \ / HyperStr Note [Exceptions and strictness] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Exceptions need rather careful treatment, especially because of 'catch' ('catch#'), 'catchSTM' ('catchSTM#'), and 'orElse' ('catchRetry#'). See Trac #11555, #10712 and #13330, and for some more background, #11222. There are three main pieces. * The Termination type includes ThrowsExn, meaning "under the given demand this expression either diverges or throws an exception". This is relatively uncontroversial. The primops raise# and raiseIO# both return ThrowsExn; nothing else does. * An ArgStr has an ExnStr flag to say how to process the Termination result of the argument. If the ExnStr flag is ExnStr, we squash ThrowsExn to topRes. (This is done in postProcessDmdResult.) Here is the key example catchRetry# (\s -> retry# s) blah We analyse the argument (\s -> retry# s) with demand Str ExnStr (SCall HeadStr) i.e. with the ExnStr flag set. - First we analyse the argument with the "clean-demand" (SCall HeadStr), getting a DmdResult of ThrowsExn from the saturated application of retry#. - Then we apply the post-processing for the shell, squashing the ThrowsExn to topRes. This also applies uniformly to free variables. Consider let r = \st -> retry# st in catchRetry# (\s -> ...(r s')..) handler st If we give the first argument of catch a strict signature, we'll get a demand 'C(S)' for 'r'; that is, 'r' is definitely called with one argument, which indeed it is. But when we post-process the free-var demands on catchRetry#'s argument (in postProcessDmdEnv), we'll give 'r' a demand of (Str ExnStr (SCall HeadStr)); and if we feed that into r's RHS (which would be reasonable) we'll squash the retry just as if we'd inlined 'r'. * We don't try to get clever about 'catch#' and 'catchSTM#' at the moment. We previously (#11222) tried to take advantage of the fact that 'catch#' calls its first argument eagerly. See especially commit 9915b6564403a6d17651e9969e9ea5d7d7e78e7f. We analyzed that first argument with a strict demand, and then performed a post-processing step at the end to change ThrowsExn to TopRes. The trouble, I believe, is that to use this approach correctly, we'd need somewhat different information about that argument. Diverges, ThrowsExn (i.e., diverges or throws an exception), and Dunno are the wrong split here. In order to evaluate part of the argument speculatively, we'd need to know that it *does not throw an exception*. That is, that it either diverges or succeeds. But we don't currently have a way to talk about that. Abstractly and approximately, catch# m f s = case ORACLE m s of DivergesOrSucceeds -> m s Fails exc -> f exc s where the magical ORACLE determines whether or not (m s) throws an exception when run, and if so which one. If we want, we can safely consider (catch# m f s) strict in anything that both branches are strict in (by performing demand analysis for 'catch#' in the same way we do for case). We could also safely consider it strict in anything demanded by (m s) that is guaranteed not to throw an exception under that demand, but I don't know if we have the means to express that. My mind keeps turning to this model (not as an actual change to the type, but as a way to think about what's going on in the analysis): newtype IO a = IO {unIO :: State# s -> (# s, (# SomeException | a #) #)} instance Monad IO where return a = IO $ \s -> (# s, (# | a #) #) IO m >>= f = IO $ \s -> case m s of (# s', (# e | #) #) -> (# s', e #) (# s', (# | a #) #) -> unIO (f a) s raiseIO# e s = (# s, (# e | #) #) catch# m f s = case m s of (# s', (# e | #) #) -> f e s' res -> res Thinking about it this way seems likely to be productive for analyzing IO exception behavior, but imprecise exceptions and asynchronous exceptions remain quite slippery beasts. Can we incorporate them? I think we can. We can imagine applying 'seq#' to evaluate @m s@, determining whether it throws an imprecise or asynchronous exception or whether it succeeds or throws an IO exception. This confines the peculiarities to 'seq#', which is indeed rather essentially peculiar. -} -- | Vanilla strictness domain data StrDmd = HyperStr -- ^ Hyper-strict (bottom of the lattice). -- See Note [HyperStr and Use demands] | SCall StrDmd -- ^ Call demand -- Used only for values of function type | SProd [ArgStr] -- ^ Product -- Used only for values of product type -- Invariant: not all components are HyperStr (use HyperStr) -- not all components are Lazy (use HeadStr) | HeadStr -- ^ Head-Strict -- A polymorphic demand: used for values of all types, -- including a type variable deriving ( Eq, Show ) -- | Strictness of a function argument. type ArgStr = Str StrDmd -- | Strictness demand. data Str s = Lazy -- ^ Lazy (top of the lattice) | Str ExnStr s -- ^ Strict deriving ( Eq, Show ) -- | How are exceptions handled for strict demands? data ExnStr -- See Note [Exceptions and strictness] = VanStr -- ^ "Vanilla" case, ordinary strictness | ExnStr -- ^ @Str ExnStr d@ means be strict like @d@ but then degrade -- the 'Termination' info 'ThrowsExn' to 'Dunno'. -- e.g. the first argument of @catch@ has this strictness. deriving( Eq, Show ) -- Well-formedness preserving constructors for the Strictness domain strBot, strTop :: ArgStr strBot = Str VanStr HyperStr strTop = Lazy mkSCall :: StrDmd -> StrDmd mkSCall HyperStr = HyperStr mkSCall s = SCall s mkSProd :: [ArgStr] -> StrDmd mkSProd sx | any isHyperStr sx = HyperStr | all isLazy sx = HeadStr | otherwise = SProd sx isLazy :: ArgStr -> Bool isLazy Lazy = True isLazy (Str {}) = False isHyperStr :: ArgStr -> Bool isHyperStr (Str _ HyperStr) = True isHyperStr _ = False -- Pretty-printing instance Outputable StrDmd where ppr HyperStr = char 'B' ppr (SCall s) = char 'C' <> parens (ppr s) ppr HeadStr = char 'S' ppr (SProd sx) = char 'S' <> parens (hcat (map ppr sx)) instance Outputable ArgStr where ppr (Str x s) = (case x of VanStr -> empty; ExnStr -> char 'x') <> ppr s ppr Lazy = char 'L' lubArgStr :: ArgStr -> ArgStr -> ArgStr lubArgStr Lazy _ = Lazy lubArgStr _ Lazy = Lazy lubArgStr (Str x1 s1) (Str x2 s2) = Str (x1 `lubExnStr` x2) (s1 `lubStr` s2) lubExnStr :: ExnStr -> ExnStr -> ExnStr lubExnStr VanStr VanStr = VanStr lubExnStr _ _ = ExnStr -- ExnStr is lazier lubStr :: StrDmd -> StrDmd -> StrDmd lubStr HyperStr s = s lubStr (SCall s1) HyperStr = SCall s1 lubStr (SCall _) HeadStr = HeadStr lubStr (SCall s1) (SCall s2) = SCall (s1 `lubStr` s2) lubStr (SCall _) (SProd _) = HeadStr lubStr (SProd sx) HyperStr = SProd sx lubStr (SProd _) HeadStr = HeadStr lubStr (SProd s1) (SProd s2) | s1 `equalLength` s2 = mkSProd (zipWith lubArgStr s1 s2) | otherwise = HeadStr lubStr (SProd _) (SCall _) = HeadStr lubStr HeadStr _ = HeadStr bothArgStr :: ArgStr -> ArgStr -> ArgStr bothArgStr Lazy s = s bothArgStr s Lazy = s bothArgStr (Str x1 s1) (Str x2 s2) = Str (x1 `bothExnStr` x2) (s1 `bothStr` s2) bothExnStr :: ExnStr -> ExnStr -> ExnStr bothExnStr ExnStr ExnStr = ExnStr bothExnStr _ _ = VanStr bothStr :: StrDmd -> StrDmd -> StrDmd bothStr HyperStr _ = HyperStr bothStr HeadStr s = s bothStr (SCall _) HyperStr = HyperStr bothStr (SCall s1) HeadStr = SCall s1 bothStr (SCall s1) (SCall s2) = SCall (s1 `bothStr` s2) bothStr (SCall _) (SProd _) = HyperStr -- Weird bothStr (SProd _) HyperStr = HyperStr bothStr (SProd s1) HeadStr = SProd s1 bothStr (SProd s1) (SProd s2) | s1 `equalLength` s2 = mkSProd (zipWith bothArgStr s1 s2) | otherwise = HyperStr -- Weird bothStr (SProd _) (SCall _) = HyperStr -- utility functions to deal with memory leaks seqStrDmd :: StrDmd -> () seqStrDmd (SProd ds) = seqStrDmdList ds seqStrDmd (SCall s) = seqStrDmd s seqStrDmd _ = () seqStrDmdList :: [ArgStr] -> () seqStrDmdList [] = () seqStrDmdList (d:ds) = seqArgStr d `seq` seqStrDmdList ds seqArgStr :: ArgStr -> () seqArgStr Lazy = () seqArgStr (Str x s) = x `seq` seqStrDmd s -- Splitting polymorphic demands splitArgStrProdDmd :: Int -> ArgStr -> Maybe [ArgStr] splitArgStrProdDmd n Lazy = Just (replicate n Lazy) splitArgStrProdDmd n (Str _ s) = splitStrProdDmd n s splitStrProdDmd :: Int -> StrDmd -> Maybe [ArgStr] splitStrProdDmd n HyperStr = Just (replicate n strBot) splitStrProdDmd n HeadStr = Just (replicate n strTop) splitStrProdDmd n (SProd ds) = WARN( not (ds `lengthIs` n), text "splitStrProdDmd" $$ ppr n $$ ppr ds ) Just ds splitStrProdDmd _ (SCall {}) = Nothing -- This can happen when the programmer uses unsafeCoerce, -- and we don't then want to crash the compiler (Trac #9208) {- ************************************************************************ * * Absence domain * * ************************************************************************ Used / \ UCall UProd \ / UHead | Count x - | Abs -} -- | Domain for genuine usage data UseDmd = UCall Count UseDmd -- ^ Call demand for absence. -- Used only for values of function type | UProd [ArgUse] -- ^ Product. -- Used only for values of product type -- See Note [Don't optimise UProd(Used) to Used] -- -- Invariant: Not all components are Abs -- (in that case, use UHead) | UHead -- ^ May be used but its sub-components are -- definitely *not* used. Roughly U(AAA) -- e.g. the usage of @x@ in @x `seq` e@ -- A polymorphic demand: used for values of all types, -- including a type variable -- Since (UCall _ Abs) is ill-typed, UHead doesn't -- make sense for lambdas | Used -- ^ May be used and its sub-components may be used. -- (top of the lattice) deriving ( Eq, Show ) -- Extended usage demand for absence and counting type ArgUse = Use UseDmd data Use u = Abs -- Definitely unused -- Bottom of the lattice | Use Count u -- May be used with some cardinality deriving ( Eq, Show ) -- | Abstract counting of usages data Count = One | Many deriving ( Eq, Show ) -- Pretty-printing instance Outputable ArgUse where ppr Abs = char 'A' ppr (Use Many a) = ppr a ppr (Use One a) = char '1' <> char '*' <> ppr a instance Outputable UseDmd where ppr Used = char 'U' ppr (UCall c a) = char 'C' <> ppr c <> parens (ppr a) ppr UHead = char 'H' ppr (UProd as) = char 'U' <> parens (hcat (punctuate (char ',') (map ppr as))) instance Outputable Count where ppr One = char '1' ppr Many = text "" useBot, useTop :: ArgUse useBot = Abs useTop = Use Many Used mkUCall :: Count -> UseDmd -> UseDmd --mkUCall c Used = Used c mkUCall c a = UCall c a mkUProd :: [ArgUse] -> UseDmd mkUProd ux | all (== Abs) ux = UHead | otherwise = UProd ux lubCount :: Count -> Count -> Count lubCount _ Many = Many lubCount Many _ = Many lubCount x _ = x lubArgUse :: ArgUse -> ArgUse -> ArgUse lubArgUse Abs x = x lubArgUse x Abs = x lubArgUse (Use c1 a1) (Use c2 a2) = Use (lubCount c1 c2) (lubUse a1 a2) lubUse :: UseDmd -> UseDmd -> UseDmd lubUse UHead u = u lubUse (UCall c u) UHead = UCall c u lubUse (UCall c1 u1) (UCall c2 u2) = UCall (lubCount c1 c2) (lubUse u1 u2) lubUse (UCall _ _) _ = Used lubUse (UProd ux) UHead = UProd ux lubUse (UProd ux1) (UProd ux2) | ux1 `equalLength` ux2 = UProd $ zipWith lubArgUse ux1 ux2 | otherwise = Used lubUse (UProd {}) (UCall {}) = Used -- lubUse (UProd {}) Used = Used lubUse (UProd ux) Used = UProd (map (`lubArgUse` useTop) ux) lubUse Used (UProd ux) = UProd (map (`lubArgUse` useTop) ux) lubUse Used _ = Used -- Note [Used should win] -- `both` is different from `lub` in its treatment of counting; if -- `both` is computed for two used, the result always has -- cardinality `Many` (except for the inner demands of UCall demand -- [TODO] explain). -- Also, x `bothUse` x /= x (for anything but Abs). bothArgUse :: ArgUse -> ArgUse -> ArgUse bothArgUse Abs x = x bothArgUse x Abs = x bothArgUse (Use _ a1) (Use _ a2) = Use Many (bothUse a1 a2) bothUse :: UseDmd -> UseDmd -> UseDmd bothUse UHead u = u bothUse (UCall c u) UHead = UCall c u -- Exciting special treatment of inner demand for call demands: -- use `lubUse` instead of `bothUse`! bothUse (UCall _ u1) (UCall _ u2) = UCall Many (u1 `lubUse` u2) bothUse (UCall {}) _ = Used bothUse (UProd ux) UHead = UProd ux bothUse (UProd ux1) (UProd ux2) | ux1 `equalLength` ux2 = UProd $ zipWith bothArgUse ux1 ux2 | otherwise = Used bothUse (UProd {}) (UCall {}) = Used -- bothUse (UProd {}) Used = Used -- Note [Used should win] bothUse Used (UProd ux) = UProd (map (`bothArgUse` useTop) ux) bothUse (UProd ux) Used = UProd (map (`bothArgUse` useTop) ux) bothUse Used _ = Used -- Note [Used should win] peelUseCall :: UseDmd -> Maybe (Count, UseDmd) peelUseCall (UCall c u) = Just (c,u) peelUseCall _ = Nothing addCaseBndrDmd :: Demand -- On the case binder -> [Demand] -- On the components of the constructor -> [Demand] -- Final demands for the components of the constructor -- See Note [Demand on case-alternative binders] addCaseBndrDmd (JD { sd = ms, ud = mu }) alt_dmds = case mu of Abs -> alt_dmds Use _ u -> zipWith bothDmd alt_dmds (mkJointDmds ss us) where Just ss = splitArgStrProdDmd arity ms -- Guaranteed not to be a call Just us = splitUseProdDmd arity u -- Ditto where arity = length alt_dmds {- Note [Demand on case-alternative binders] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The demand on a binder in a case alternative comes (a) From the demand on the binder itself (b) From the demand on the case binder Forgetting (b) led directly to Trac #10148. Example. Source code: f x@(p,_) = if p then foo x else True foo (p,True) = True foo (p,q) = foo (q,p) After strictness analysis: f = \ (x_an1 [Dmd=<S(SL),1*U(U,1*U)>] :: (Bool, Bool)) -> case x_an1 of wild_X7 [Dmd=<L,1*U(1*U,1*U)>] { (p_an2 [Dmd=<S,1*U>], ds_dnz [Dmd=<L,A>]) -> case p_an2 of _ { False -> GHC.Types.True; True -> foo wild_X7 } It's true that ds_dnz is *itself* absent, but the use of wild_X7 means that it is very much alive and demanded. See Trac #10148 for how the consequences play out. This is needed even for non-product types, in case the case-binder is used but the components of the case alternative are not. Note [Don't optimise UProd(Used) to Used] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ These two UseDmds: UProd [Used, Used] and Used are semantically equivalent, but we do not turn the former into the latter, for a regrettable-subtle reason. Suppose we did. then f (x,y) = (y,x) would get StrDmd = Str = SProd [Lazy, Lazy] UseDmd = Used = UProd [Used, Used] But with the joint demand of <Str, Used> doesn't convey any clue that there is a product involved, and so the worthSplittingFun will not fire. (We'd need to use the type as well to make it fire.) Moreover, consider g h p@(_,_) = h p This too would get <Str, Used>, but this time there really isn't any point in w/w since the components of the pair are not used at all. So the solution is: don't aggressively collapse UProd [Used,Used] to Used; intead leave it as-is. In effect we are using the UseDmd to do a little bit of boxity analysis. Not very nice. Note [Used should win] ~~~~~~~~~~~~~~~~~~~~~~ Both in lubUse and bothUse we want (Used `both` UProd us) to be Used. Why? Because Used carries the implication the whole thing is used, box and all, so we don't want to w/w it. If we use it both boxed and unboxed, then we are definitely using the box, and so we are quite likely to pay a reboxing cost. So we make Used win here. Example is in the Buffer argument of GHC.IO.Handle.Internals.writeCharBuffer Baseline: (A) Not making Used win (UProd wins) Compare with: (B) making Used win for lub and both Min -0.3% -5.6% -10.7% -11.0% -33.3% Max +0.3% +45.6% +11.5% +11.5% +6.9% Geometric Mean -0.0% +0.5% +0.3% +0.2% -0.8% Baseline: (B) Making Used win for both lub and both Compare with: (C) making Used win for both, but UProd win for lub Min -0.1% -0.3% -7.9% -8.0% -6.5% Max +0.1% +1.0% +21.0% +21.0% +0.5% Geometric Mean +0.0% +0.0% -0.0% -0.1% -0.1% -} -- If a demand is used multiple times (i.e. reused), than any use-once -- mentioned there, that is not protected by a UCall, can happen many times. markReusedDmd :: ArgUse -> ArgUse markReusedDmd Abs = Abs markReusedDmd (Use _ a) = Use Many (markReused a) markReused :: UseDmd -> UseDmd markReused (UCall _ u) = UCall Many u -- No need to recurse here markReused (UProd ux) = UProd (map markReusedDmd ux) markReused u = u isUsedMU :: ArgUse -> Bool -- True <=> markReusedDmd d = d isUsedMU Abs = True isUsedMU (Use One _) = False isUsedMU (Use Many u) = isUsedU u isUsedU :: UseDmd -> Bool -- True <=> markReused d = d isUsedU Used = True isUsedU UHead = True isUsedU (UProd us) = all isUsedMU us isUsedU (UCall One _) = False isUsedU (UCall Many _) = True -- No need to recurse -- Squashing usage demand demands seqUseDmd :: UseDmd -> () seqUseDmd (UProd ds) = seqArgUseList ds seqUseDmd (UCall c d) = c `seq` seqUseDmd d seqUseDmd _ = () seqArgUseList :: [ArgUse] -> () seqArgUseList [] = () seqArgUseList (d:ds) = seqArgUse d `seq` seqArgUseList ds seqArgUse :: ArgUse -> () seqArgUse (Use c u) = c `seq` seqUseDmd u seqArgUse _ = () -- Splitting polymorphic Maybe-Used demands splitUseProdDmd :: Int -> UseDmd -> Maybe [ArgUse] splitUseProdDmd n Used = Just (replicate n useTop) splitUseProdDmd n UHead = Just (replicate n Abs) splitUseProdDmd n (UProd ds) = WARN( not (ds `lengthIs` n), text "splitUseProdDmd" $$ ppr n $$ ppr ds ) Just ds splitUseProdDmd _ (UCall _ _) = Nothing -- This can happen when the programmer uses unsafeCoerce, -- and we don't then want to crash the compiler (Trac #9208) useCount :: Use u -> Count useCount Abs = One useCount (Use One _) = One useCount _ = Many {- ************************************************************************ * * Clean demand for Strictness and Usage * * ************************************************************************ This domain differst from JointDemand in the sence that pure absence is taken away, i.e., we deal *only* with non-absent demands. Note [Strict demands] ~~~~~~~~~~~~~~~~~~~~~ isStrictDmd returns true only of demands that are both strict and used In particular, it is False for <HyperStr, Abs>, which can and does arise in, say (Trac #7319) f x = raise# <some exception> Then 'x' is not used, so f gets strictness <HyperStr,Abs> -> . Now the w/w generates fx = let x <HyperStr,Abs> = absentError "unused" in raise <some exception> At this point we really don't want to convert to fx = case absentError "unused" of x -> raise <some exception> Since the program is going to diverge, this swaps one error for another, but it's really a bad idea to *ever* evaluate an absent argument. In Trac #7319 we get T7319.exe: Oops! Entered absent arg w_s1Hd{v} [lid] [base:GHC.Base.String{tc 36u}] Note [Dealing with call demands] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Call demands are constructed and deconstructed coherently for strictness and absence. For instance, the strictness signature for the following function f :: (Int -> (Int, Int)) -> (Int, Bool) f g = (snd (g 3), True) should be: <L,C(U(AU))>m -} type CleanDemand = JointDmd StrDmd UseDmd -- A demand that is at least head-strict bothCleanDmd :: CleanDemand -> CleanDemand -> CleanDemand bothCleanDmd (JD { sd = s1, ud = a1}) (JD { sd = s2, ud = a2}) = JD { sd = s1 `bothStr` s2, ud = a1 `bothUse` a2 } mkHeadStrict :: CleanDemand -> CleanDemand mkHeadStrict cd = cd { sd = HeadStr } mkOnceUsedDmd, mkManyUsedDmd :: CleanDemand -> Demand mkOnceUsedDmd (JD {sd = s,ud = a}) = JD { sd = Str VanStr s, ud = Use One a } mkManyUsedDmd (JD {sd = s,ud = a}) = JD { sd = Str VanStr s, ud = Use Many a } evalDmd :: Demand -- Evaluated strictly, and used arbitrarily deeply evalDmd = JD { sd = Str VanStr HeadStr, ud = useTop } mkProdDmd :: [Demand] -> CleanDemand mkProdDmd dx = JD { sd = mkSProd $ map getStrDmd dx , ud = mkUProd $ map getUseDmd dx } mkCallDmd :: CleanDemand -> CleanDemand mkCallDmd (JD {sd = d, ud = u}) = JD { sd = mkSCall d, ud = mkUCall One u } -- See Note [Demand on the worker] in WorkWrap mkWorkerDemand :: Int -> Demand mkWorkerDemand n = JD { sd = Lazy, ud = Use One (go n) } where go 0 = Used go n = mkUCall One $ go (n-1) cleanEvalDmd :: CleanDemand cleanEvalDmd = JD { sd = HeadStr, ud = Used } cleanEvalProdDmd :: Arity -> CleanDemand cleanEvalProdDmd n = JD { sd = HeadStr, ud = UProd (replicate n useTop) } {- ************************************************************************ * * Demand: combining stricness and usage * * ************************************************************************ -} type Demand = JointDmd ArgStr ArgUse lubDmd :: Demand -> Demand -> Demand lubDmd (JD {sd = s1, ud = a1}) (JD {sd = s2, ud = a2}) = JD { sd = s1 `lubArgStr` s2 , ud = a1 `lubArgUse` a2 } bothDmd :: Demand -> Demand -> Demand bothDmd (JD {sd = s1, ud = a1}) (JD {sd = s2, ud = a2}) = JD { sd = s1 `bothArgStr` s2 , ud = a1 `bothArgUse` a2 } lazyApply1Dmd, lazyApply2Dmd, strictApply1Dmd, catchArgDmd :: Demand strictApply1Dmd = JD { sd = Str VanStr (SCall HeadStr) , ud = Use Many (UCall One Used) } -- First argument of catchRetry# and catchSTM#: -- uses its arg once, applies it once -- and catches exceptions (the ExnStr) part catchArgDmd = JD { sd = Str ExnStr (SCall HeadStr) , ud = Use One (UCall One Used) } lazyApply1Dmd = JD { sd = Lazy , ud = Use One (UCall One Used) } -- Second argument of catch#: -- uses its arg at most once, applies it once -- but is lazy (might not be called at all) lazyApply2Dmd = JD { sd = Lazy , ud = Use One (UCall One (UCall One Used)) } absDmd :: Demand absDmd = JD { sd = Lazy, ud = Abs } topDmd :: Demand topDmd = JD { sd = Lazy, ud = useTop } botDmd :: Demand botDmd = JD { sd = strBot, ud = useBot } seqDmd :: Demand seqDmd = JD { sd = Str VanStr HeadStr, ud = Use One UHead } oneifyDmd :: Demand -> Demand oneifyDmd (JD { sd = s, ud = Use _ a }) = JD { sd = s, ud = Use One a } oneifyDmd jd = jd isTopDmd :: Demand -> Bool -- Used to suppress pretty-printing of an uninformative demand isTopDmd (JD {sd = Lazy, ud = Use Many Used}) = True isTopDmd _ = False isAbsDmd :: Demand -> Bool isAbsDmd (JD {ud = Abs}) = True -- The strictness part can be HyperStr isAbsDmd _ = False -- for a bottom demand isSeqDmd :: Demand -> Bool isSeqDmd (JD {sd = Str VanStr HeadStr, ud = Use _ UHead}) = True isSeqDmd _ = False isUsedOnce :: Demand -> Bool isUsedOnce (JD { ud = a }) = case useCount a of One -> True Many -> False -- More utility functions for strictness seqDemand :: Demand -> () seqDemand (JD {sd = s, ud = u}) = seqArgStr s `seq` seqArgUse u seqDemandList :: [Demand] -> () seqDemandList [] = () seqDemandList (d:ds) = seqDemand d `seq` seqDemandList ds isStrictDmd :: Demand -> Bool -- See Note [Strict demands] isStrictDmd (JD {ud = Abs}) = False isStrictDmd (JD {sd = Lazy}) = False isStrictDmd _ = True isWeakDmd :: Demand -> Bool isWeakDmd (JD {sd = s, ud = a}) = isLazy s && isUsedMU a cleanUseDmd_maybe :: Demand -> Maybe UseDmd cleanUseDmd_maybe (JD { ud = Use _ u }) = Just u cleanUseDmd_maybe _ = Nothing splitFVs :: Bool -- Thunk -> DmdEnv -> (DmdEnv, DmdEnv) splitFVs is_thunk rhs_fvs | is_thunk = nonDetFoldUFM_Directly add (emptyVarEnv, emptyVarEnv) rhs_fvs -- It's OK to use nonDetFoldUFM_Directly because we -- immediately forget the ordering by putting the elements -- in the envs again | otherwise = partitionVarEnv isWeakDmd rhs_fvs where add uniq dmd@(JD { sd = s, ud = u }) (lazy_fv, sig_fv) | Lazy <- s = (addToUFM_Directly lazy_fv uniq dmd, sig_fv) | otherwise = ( addToUFM_Directly lazy_fv uniq (JD { sd = Lazy, ud = u }) , addToUFM_Directly sig_fv uniq (JD { sd = s, ud = Abs }) ) data TypeShape = TsFun TypeShape | TsProd [TypeShape] | TsUnk instance Outputable TypeShape where ppr TsUnk = text "TsUnk" ppr (TsFun ts) = text "TsFun" <> parens (ppr ts) ppr (TsProd tss) = parens (hsep $ punctuate comma $ map ppr tss) trimToType :: Demand -> TypeShape -> Demand -- See Note [Trimming a demand to a type] trimToType (JD { sd = ms, ud = mu }) ts = JD (go_ms ms ts) (go_mu mu ts) where go_ms :: ArgStr -> TypeShape -> ArgStr go_ms Lazy _ = Lazy go_ms (Str x s) ts = Str x (go_s s ts) go_s :: StrDmd -> TypeShape -> StrDmd go_s HyperStr _ = HyperStr go_s (SCall s) (TsFun ts) = SCall (go_s s ts) go_s (SProd mss) (TsProd tss) | equalLength mss tss = SProd (zipWith go_ms mss tss) go_s _ _ = HeadStr go_mu :: ArgUse -> TypeShape -> ArgUse go_mu Abs _ = Abs go_mu (Use c u) ts = Use c (go_u u ts) go_u :: UseDmd -> TypeShape -> UseDmd go_u UHead _ = UHead go_u (UCall c u) (TsFun ts) = UCall c (go_u u ts) go_u (UProd mus) (TsProd tss) | equalLength mus tss = UProd (zipWith go_mu mus tss) go_u _ _ = Used {- Note [Trimming a demand to a type] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Consider this: f :: a -> Bool f x = case ... of A g1 -> case (x |> g1) of (p,q) -> ... B -> error "urk" where A,B are the constructors of a GADT. We'll get a U(U,U) demand on x from the A branch, but that's a stupid demand for x itself, which has type 'a'. Indeed we get ASSERTs going off (notably in splitUseProdDmd, Trac #8569). Bottom line: we really don't want to have a binder whose demand is more deeply-nested than its type. There are various ways to tackle this. When processing (x |> g1), we could "trim" the incoming demand U(U,U) to match x's type. But I'm currently doing so just at the moment when we pin a demand on a binder, in DmdAnal.findBndrDmd. Note [Threshold demands] ~~~~~~~~~~~~~~~~~~~~~~~~ Threshold usage demand is generated to figure out if cardinality-instrumented demands of a binding's free variables should be unleashed. See also [Aggregated demand for cardinality]. Note [Replicating polymorphic demands] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Some demands can be considered as polymorphic. Generally, it is applicable to such beasts as tops, bottoms as well as Head-Used and Head-stricts demands. For instance, S ~ S(L, ..., L) Also, when top or bottom is occurred as a result demand, it in fact can be expanded to saturate a callee's arity. -} splitProdDmd_maybe :: Demand -> Maybe [Demand] -- Split a product into its components, iff there is any -- useful information to be extracted thereby -- The demand is not necessarily strict! splitProdDmd_maybe (JD { sd = s, ud = u }) = case (s,u) of (Str _ (SProd sx), Use _ u) | Just ux <- splitUseProdDmd (length sx) u -> Just (mkJointDmds sx ux) (Str _ s, Use _ (UProd ux)) | Just sx <- splitStrProdDmd (length ux) s -> Just (mkJointDmds sx ux) (Lazy, Use _ (UProd ux)) -> Just (mkJointDmds (replicate (length ux) Lazy) ux) _ -> Nothing {- ************************************************************************ * * Demand results * * ************************************************************************ DmdResult: Dunno CPRResult / ThrowsExn / Diverges CPRResult: NoCPR / \ RetProd RetSum ConTag Product constructors return (Dunno (RetProd rs)) In a fixpoint iteration, start from Diverges We have lubs, but not glbs; but that is ok. -} ------------------------------------------------------------------------ -- Constructed Product Result ------------------------------------------------------------------------ data Termination r = Diverges -- Definitely diverges | ThrowsExn -- Definitely throws an exception or diverges | Dunno r -- Might diverge or converge deriving( Eq, Show ) type DmdResult = Termination CPRResult data CPRResult = NoCPR -- Top of the lattice | RetProd -- Returns a constructor from a product type | RetSum ConTag -- Returns a constructor from a data type deriving( Eq, Show ) lubCPR :: CPRResult -> CPRResult -> CPRResult lubCPR (RetSum t1) (RetSum t2) | t1 == t2 = RetSum t1 lubCPR RetProd RetProd = RetProd lubCPR _ _ = NoCPR lubDmdResult :: DmdResult -> DmdResult -> DmdResult lubDmdResult Diverges r = r lubDmdResult ThrowsExn Diverges = ThrowsExn lubDmdResult ThrowsExn r = r lubDmdResult (Dunno c1) Diverges = Dunno c1 lubDmdResult (Dunno c1) ThrowsExn = Dunno c1 lubDmdResult (Dunno c1) (Dunno c2) = Dunno (c1 `lubCPR` c2) -- This needs to commute with defaultDmd, i.e. -- defaultDmd (r1 `lubDmdResult` r2) = defaultDmd r1 `lubDmd` defaultDmd r2 -- (See Note [Default demand on free variables] for why) bothDmdResult :: DmdResult -> Termination () -> DmdResult -- See Note [Asymmetry of 'both' for DmdType and DmdResult] bothDmdResult _ Diverges = Diverges bothDmdResult r ThrowsExn = case r of { Diverges -> r; _ -> ThrowsExn } bothDmdResult r (Dunno {}) = r -- This needs to commute with defaultDmd, i.e. -- defaultDmd (r1 `bothDmdResult` r2) = defaultDmd r1 `bothDmd` defaultDmd r2 -- (See Note [Default demand on free variables] for why) instance Outputable r => Outputable (Termination r) where ppr Diverges = char 'b' ppr ThrowsExn = char 'x' ppr (Dunno c) = ppr c instance Outputable CPRResult where ppr NoCPR = empty ppr (RetSum n) = char 'm' <> int n ppr RetProd = char 'm' seqDmdResult :: DmdResult -> () seqDmdResult Diverges = () seqDmdResult ThrowsExn = () seqDmdResult (Dunno c) = seqCPRResult c seqCPRResult :: CPRResult -> () seqCPRResult NoCPR = () seqCPRResult (RetSum n) = n `seq` () seqCPRResult RetProd = () ------------------------------------------------------------------------ -- Combined demand result -- ------------------------------------------------------------------------ -- [cprRes] lets us switch off CPR analysis -- by making sure that everything uses TopRes topRes, exnRes, botRes :: DmdResult topRes = Dunno NoCPR exnRes = ThrowsExn botRes = Diverges cprSumRes :: ConTag -> DmdResult cprSumRes tag = Dunno $ RetSum tag cprProdRes :: [DmdType] -> DmdResult cprProdRes _arg_tys = Dunno $ RetProd vanillaCprProdRes :: Arity -> DmdResult vanillaCprProdRes _arity = Dunno $ RetProd isTopRes :: DmdResult -> Bool isTopRes (Dunno NoCPR) = True isTopRes _ = False isBotRes :: DmdResult -> Bool -- True if the result diverges or throws an exception isBotRes Diverges = True isBotRes ThrowsExn = True isBotRes (Dunno {}) = False trimCPRInfo :: Bool -> Bool -> DmdResult -> DmdResult trimCPRInfo trim_all trim_sums res = trimR res where trimR (Dunno c) = Dunno (trimC c) trimR res = res trimC (RetSum n) | trim_all || trim_sums = NoCPR | otherwise = RetSum n trimC RetProd | trim_all = NoCPR | otherwise = RetProd trimC NoCPR = NoCPR returnsCPR_maybe :: DmdResult -> Maybe ConTag returnsCPR_maybe (Dunno c) = retCPR_maybe c returnsCPR_maybe _ = Nothing retCPR_maybe :: CPRResult -> Maybe ConTag retCPR_maybe (RetSum t) = Just t retCPR_maybe RetProd = Just fIRST_TAG retCPR_maybe NoCPR = Nothing -- See Notes [Default demand on free variables] -- and [defaultDmd vs. resTypeArgDmd] defaultDmd :: Termination r -> Demand defaultDmd (Dunno {}) = absDmd defaultDmd _ = botDmd -- Diverges or ThrowsExn resTypeArgDmd :: Termination r -> Demand -- TopRes and BotRes are polymorphic, so that -- BotRes === (Bot -> BotRes) === ... -- TopRes === (Top -> TopRes) === ... -- This function makes that concrete -- Also see Note [defaultDmd vs. resTypeArgDmd] resTypeArgDmd (Dunno _) = topDmd resTypeArgDmd _ = botDmd -- Diverges or ThrowsExn {- Note [defaultDmd and resTypeArgDmd] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ These functions are similar: They express the demand on something not explicitly mentioned in the environment resp. the argument list. Yet they are different: * Variables not mentioned in the free variables environment are definitely unused, so we can use absDmd there. * Further arguments *can* be used, of course. Hence topDmd is used. Note [Worthy functions for Worker-Wrapper split] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ For non-bottoming functions a worker-wrapper transformation takes into account several possibilities to decide if the function is worthy for splitting: 1. The result is of product type and the function is strict in some (or even all) of its arguments. The check that the argument is used is more of sanity nature, since strictness implies usage. Example: f :: (Int, Int) -> Int f p = (case p of (a,b) -> a) + 1 should be splitted to f :: (Int, Int) -> Int f p = case p of (a,b) -> $wf a $wf :: Int -> Int $wf a = a + 1 2. Sometimes it also makes sense to perform a WW split if the strictness analysis cannot say for sure if the function is strict in components of its argument. Then we reason according to the inferred usage information: if the function uses its product argument's components, the WW split can be beneficial. Example: g :: Bool -> (Int, Int) -> Int g c p = case p of (a,b) -> if c then a else b The function g is strict in is argument p and lazy in its components. However, both components are used in the RHS. The idea is since some of the components (both in this case) are used in the right-hand side, the product must presumable be taken apart. Therefore, the WW transform splits the function g to g :: Bool -> (Int, Int) -> Int g c p = case p of (a,b) -> $wg c a b $wg :: Bool -> Int -> Int -> Int $wg c a b = if c then a else b 3. If an argument is absent, it would be silly to pass it to a function, hence the worker with reduced arity is generated. Note [Worker-wrapper for bottoming functions] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ We used not to split if the result is bottom. [Justification: there's no efficiency to be gained.] But it's sometimes bad not to make a wrapper. Consider fw = \x# -> let x = I# x# in case e of p1 -> error_fn x p2 -> error_fn x p3 -> the real stuff The re-boxing code won't go away unless error_fn gets a wrapper too. [We don't do reboxing now, but in general it's better to pass an unboxed thing to f, and have it reboxed in the error cases....] However we *don't* want to do this when the argument is not actually taken apart in the function at all. Otherwise we risk decomposing a massive tuple which is barely used. Example: f :: ((Int,Int) -> String) -> (Int,Int) -> a f g pr = error (g pr) main = print (f fst (1, error "no")) Here, f does not take 'pr' apart, and it's stupid to do so. Imagine that it had millions of fields. This actually happened in GHC itself where the tuple was DynFlags ************************************************************************ * * Demand environments and types * * ************************************************************************ -} type DmdEnv = VarEnv Demand -- See Note [Default demand on free variables] data DmdType = DmdType DmdEnv -- Demand on explicitly-mentioned -- free variables [Demand] -- Demand on arguments DmdResult -- See [Nature of result demand] {- Note [Nature of result demand] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ A DmdResult contains information about termination (currently distinguishing definite divergence and no information; it is possible to include definite convergence here), and CPR information about the result. The semantics of this depends on whether we are looking at a DmdType, i.e. the demand put on by an expression _under a specific incoming demand_ on its environment, or at a StrictSig describing a demand transformer. For a * DmdType, the termination information is true given the demand it was generated with, while for * a StrictSig it holds after applying enough arguments. The CPR information, though, is valid after the number of arguments mentioned in the type is given. Therefore, when forgetting the demand on arguments, as in dmdAnalRhs, this needs to be considere (via removeDmdTyArgs). Consider b2 x y = x `seq` y `seq` error (show x) this has a strictness signature of <S><S>b meaning that "b2 `seq` ()" and "b2 1 `seq` ()" might well terminate, but for "b2 1 2 `seq` ()" we get definite divergence. For comparison, b1 x = x `seq` error (show x) has a strictness signature of <S>b and "b1 1 `seq` ()" is known to terminate. Now consider a function h with signature "<C(S)>", and the expression e1 = h b1 now h puts a demand of <C(S)> onto its argument, and the demand transformer turns it into <S>b Now the DmdResult "b" does apply to us, even though "b1 `seq` ()" does not diverge, and we do not anything being passed to b. Note [Asymmetry of 'both' for DmdType and DmdResult] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 'both' for DmdTypes is *asymmetrical*, because there is only one result! For example, given (e1 e2), we get a DmdType dt1 for e1, use its arg demand to analyse e2 giving dt2, and then do (dt1 `bothType` dt2). Similarly with case e of { p -> rhs } we get dt_scrut from the scrutinee and dt_rhs from the RHS, and then compute (dt_rhs `bothType` dt_scrut). We 1. combine the information on the free variables, 2. take the demand on arguments from the first argument 3. combine the termination results, but 4. take CPR info from the first argument. 3 and 4 are implementd in bothDmdResult. -} -- Equality needed for fixpoints in DmdAnal instance Eq DmdType where (==) (DmdType fv1 ds1 res1) (DmdType fv2 ds2 res2) = nonDetUFMToList fv1 == nonDetUFMToList fv2 -- It's OK to use nonDetUFMToList here because we're testing for -- equality and even though the lists will be in some arbitrary -- Unique order, it is the same order for both && ds1 == ds2 && res1 == res2 lubDmdType :: DmdType -> DmdType -> DmdType lubDmdType d1 d2 = DmdType lub_fv lub_ds lub_res where n = max (dmdTypeDepth d1) (dmdTypeDepth d2) (DmdType fv1 ds1 r1) = ensureArgs n d1 (DmdType fv2 ds2 r2) = ensureArgs n d2 lub_fv = plusVarEnv_CD lubDmd fv1 (defaultDmd r1) fv2 (defaultDmd r2) lub_ds = zipWithEqual "lubDmdType" lubDmd ds1 ds2 lub_res = lubDmdResult r1 r2 {- Note [The need for BothDmdArg] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Previously, the right argument to bothDmdType, as well as the return value of dmdAnalStar via postProcessDmdType, was a DmdType. But bothDmdType only needs to know about the free variables and termination information, but nothing about the demand put on arguments, nor cpr information. So we make that explicit by only passing the relevant information. -} type BothDmdArg = (DmdEnv, Termination ()) mkBothDmdArg :: DmdEnv -> BothDmdArg mkBothDmdArg env = (env, Dunno ()) toBothDmdArg :: DmdType -> BothDmdArg toBothDmdArg (DmdType fv _ r) = (fv, go r) where go (Dunno {}) = Dunno () go ThrowsExn = ThrowsExn go Diverges = Diverges bothDmdType :: DmdType -> BothDmdArg -> DmdType bothDmdType (DmdType fv1 ds1 r1) (fv2, t2) -- See Note [Asymmetry of 'both' for DmdType and DmdResult] -- 'both' takes the argument/result info from its *first* arg, -- using its second arg just for its free-var info. = DmdType (plusVarEnv_CD bothDmd fv1 (defaultDmd r1) fv2 (defaultDmd t2)) ds1 (r1 `bothDmdResult` t2) instance Outputable DmdType where ppr (DmdType fv ds res) = hsep [hcat (map ppr ds) <> ppr res, if null fv_elts then empty else braces (fsep (map pp_elt fv_elts))] where pp_elt (uniq, dmd) = ppr uniq <> text "->" <> ppr dmd fv_elts = nonDetUFMToList fv -- It's OK to use nonDetUFMToList here because we only do it for -- pretty printing emptyDmdEnv :: VarEnv Demand emptyDmdEnv = emptyVarEnv -- nopDmdType is the demand of doing nothing -- (lazy, absent, no CPR information, no termination information). -- Note that it is ''not'' the top of the lattice (which would be "may use everything"), -- so it is (no longer) called topDmd nopDmdType, botDmdType, exnDmdType :: DmdType nopDmdType = DmdType emptyDmdEnv [] topRes botDmdType = DmdType emptyDmdEnv [] botRes exnDmdType = DmdType emptyDmdEnv [] exnRes cprProdDmdType :: Arity -> DmdType cprProdDmdType arity = DmdType emptyDmdEnv [] (vanillaCprProdRes arity) isTopDmdType :: DmdType -> Bool isTopDmdType (DmdType env [] res) | isTopRes res && isEmptyVarEnv env = True isTopDmdType _ = False mkDmdType :: DmdEnv -> [Demand] -> DmdResult -> DmdType mkDmdType fv ds res = DmdType fv ds res dmdTypeDepth :: DmdType -> Arity dmdTypeDepth (DmdType _ ds _) = length ds -- Remove any demand on arguments. This is used in dmdAnalRhs on the body removeDmdTyArgs :: DmdType -> DmdType removeDmdTyArgs = ensureArgs 0 -- This makes sure we can use the demand type with n arguments, -- It extends the argument list with the correct resTypeArgDmd -- It also adjusts the DmdResult: Divergence survives additional arguments, -- CPR information does not (and definite converge also would not). ensureArgs :: Arity -> DmdType -> DmdType ensureArgs n d | n == depth = d | otherwise = DmdType fv ds' r' where depth = dmdTypeDepth d DmdType fv ds r = d ds' = take n (ds ++ repeat (resTypeArgDmd r)) r' = case r of -- See [Nature of result demand] Dunno _ -> topRes _ -> r seqDmdType :: DmdType -> () seqDmdType (DmdType env ds res) = seqDmdEnv env `seq` seqDemandList ds `seq` seqDmdResult res `seq` () seqDmdEnv :: DmdEnv -> () seqDmdEnv env = seqEltsUFM seqDemandList env splitDmdTy :: DmdType -> (Demand, DmdType) -- Split off one function argument -- We already have a suitable demand on all -- free vars, so no need to add more! splitDmdTy (DmdType fv (dmd:dmds) res_ty) = (dmd, DmdType fv dmds res_ty) splitDmdTy ty@(DmdType _ [] res_ty) = (resTypeArgDmd res_ty, ty) -- When e is evaluated after executing an IO action, and d is e's demand, then -- what of this demand should we consider, given that the IO action can cleanly -- exit? -- * We have to kill all strictness demands (i.e. lub with a lazy demand) -- * We can keep usage information (i.e. lub with an absent demand) -- * We have to kill definite divergence -- * We can keep CPR information. -- See Note [IO hack in the demand analyser] in DmdAnal deferAfterIO :: DmdType -> DmdType deferAfterIO d@(DmdType _ _ res) = case d `lubDmdType` nopDmdType of DmdType fv ds _ -> DmdType fv ds (defer_res res) where defer_res r@(Dunno {}) = r defer_res _ = topRes -- Diverges and ThrowsExn strictenDmd :: Demand -> CleanDemand strictenDmd (JD { sd = s, ud = u}) = JD { sd = poke_s s, ud = poke_u u } where poke_s Lazy = HeadStr poke_s (Str _ s) = s poke_u Abs = UHead poke_u (Use _ u) = u -- Deferring and peeling type DmdShell -- Describes the "outer shell" -- of a Demand = JointDmd (Str ()) (Use ()) toCleanDmd :: Demand -> Type -> (DmdShell, CleanDemand) -- Splits a Demand into its "shell" and the inner "clean demand" toCleanDmd (JD { sd = s, ud = u }) expr_ty = (JD { sd = ss, ud = us }, JD { sd = s', ud = u' }) -- See Note [Analyzing with lazy demand and lambdas] where (ss, s') = case s of Str x s' -> (Str x (), s') Lazy | is_unlifted -> (Str VanStr (), HeadStr) | otherwise -> (Lazy, HeadStr) (us, u') = case u of Use c u' -> (Use c (), u') Abs | is_unlifted -> (Use One (), Used) | otherwise -> (Abs, Used) is_unlifted = isUnliftedType expr_ty -- See Note [Analysing with absent demand] -- This is used in dmdAnalStar when post-processing -- a function's argument demand. So we only care about what -- does to free variables, and whether it terminates. -- see Note [The need for BothDmdArg] postProcessDmdType :: DmdShell -> DmdType -> BothDmdArg postProcessDmdType du@(JD { sd = ss }) (DmdType fv _ res_ty) = (postProcessDmdEnv du fv, term_info) where term_info = case postProcessDmdResult ss res_ty of Dunno _ -> Dunno () ThrowsExn -> ThrowsExn Diverges -> Diverges postProcessDmdResult :: Str () -> DmdResult -> DmdResult postProcessDmdResult Lazy _ = topRes postProcessDmdResult (Str ExnStr _) ThrowsExn = topRes -- Key point! -- Note that only ThrowsExn results can be caught, not Diverges postProcessDmdResult _ res = res postProcessDmdEnv :: DmdShell -> DmdEnv -> DmdEnv postProcessDmdEnv ds@(JD { sd = ss, ud = us }) env | Abs <- us = emptyDmdEnv -- In this case (postProcessDmd ds) == id; avoid a redundant rebuild -- of the environment. Be careful, bad things will happen if this doesn't -- match postProcessDmd (see #13977). | Str VanStr _ <- ss , Use One _ <- us = env | otherwise = mapVarEnv (postProcessDmd ds) env -- For the Absent case just discard all usage information -- We only processed the thing at all to analyse the body -- See Note [Always analyse in virgin pass] reuseEnv :: DmdEnv -> DmdEnv reuseEnv = mapVarEnv (postProcessDmd (JD { sd = Str VanStr (), ud = Use Many () })) postProcessUnsat :: DmdShell -> DmdType -> DmdType postProcessUnsat ds@(JD { sd = ss }) (DmdType fv args res_ty) = DmdType (postProcessDmdEnv ds fv) (map (postProcessDmd ds) args) (postProcessDmdResult ss res_ty) postProcessDmd :: DmdShell -> Demand -> Demand postProcessDmd (JD { sd = ss, ud = us }) (JD { sd = s, ud = a}) = JD { sd = s', ud = a' } where s' = case ss of Lazy -> Lazy Str ExnStr _ -> markExnStr s Str VanStr _ -> s a' = case us of Abs -> Abs Use Many _ -> markReusedDmd a Use One _ -> a markExnStr :: ArgStr -> ArgStr markExnStr (Str VanStr s) = Str ExnStr s markExnStr s = s -- Peels one call level from the demand, and also returns -- whether it was unsaturated (separately for strictness and usage) peelCallDmd :: CleanDemand -> (CleanDemand, DmdShell) -- Exploiting the fact that -- on the strictness side C(B) = B -- and on the usage side C(U) = U peelCallDmd (JD {sd = s, ud = u}) = (JD { sd = s', ud = u' }, JD { sd = ss, ud = us }) where (s', ss) = case s of SCall s' -> (s', Str VanStr ()) HyperStr -> (HyperStr, Str VanStr ()) _ -> (HeadStr, Lazy) (u', us) = case u of UCall c u' -> (u', Use c ()) _ -> (Used, Use Many ()) -- The _ cases for usage includes UHead which seems a bit wrong -- because the body isn't used at all! -- c.f. the Abs case in toCleanDmd -- Peels that multiple nestings of calls clean demand and also returns -- whether it was unsaturated (separately for strictness and usage -- see Note [Demands from unsaturated function calls] peelManyCalls :: Int -> CleanDemand -> DmdShell peelManyCalls n (JD { sd = str, ud = abs }) = JD { sd = go_str n str, ud = go_abs n abs } where go_str :: Int -> StrDmd -> Str () -- True <=> unsaturated, defer go_str 0 _ = Str VanStr () go_str _ HyperStr = Str VanStr () -- == go_str (n-1) HyperStr, as HyperStr = Call(HyperStr) go_str n (SCall d') = go_str (n-1) d' go_str _ _ = Lazy go_abs :: Int -> UseDmd -> Use () -- Many <=> unsaturated, or at least go_abs 0 _ = Use One () -- one UCall Many in the demand go_abs n (UCall One d') = go_abs (n-1) d' go_abs _ _ = Use Many () {- Note [Demands from unsaturated function calls] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Consider a demand transformer d1 -> d2 -> r for f. If a sufficiently detailed demand is fed into this transformer, e.g <C(C(S)), C1(C1(S))> arising from "f x1 x2" in a strict, use-once context, then d1 and d2 is precisely the demand unleashed onto x1 and x2 (similar for the free variable environment) and furthermore the result information r is the one we want to use. An anonymous lambda is also an unsaturated function all (needs one argument, none given), so this applies to that case as well. But the demand fed into f might be less than <C(C(S)), C1(C1(S))>. There are a few cases: * Not enough demand on the strictness side: - In that case, we need to zap all strictness in the demand on arguments and free variables. - Furthermore, we remove CPR information. It could be left, but given the incoming demand is not enough to evaluate so far we just do not bother. - And finally termination information: If r says that f diverges for sure, then this holds when the demand guarantees that two arguments are going to be passed. If the demand is lower, we may just as well converge. If we were tracking definite convegence, than that would still hold under a weaker demand than expected by the demand transformer. * Not enough demand from the usage side: The missing usage can be expanded using UCall Many, therefore this is subsumed by the third case: * At least one of the uses has a cardinality of Many. - Even if f puts a One demand on any of its argument or free variables, if we call f multiple times, we may evaluate this argument or free variable multiple times. So forget about any occurrence of "One" in the demand. In dmdTransformSig, we call peelManyCalls to find out if we are in any of these cases, and then call postProcessUnsat to reduce the demand appropriately. Similarly, dmdTransformDictSelSig and dmdAnal, when analyzing a Lambda, use peelCallDmd, which peels only one level, but also returns the demand put on the body of the function. -} peelFV :: DmdType -> Var -> (DmdType, Demand) peelFV (DmdType fv ds res) id = -- pprTrace "rfv" (ppr id <+> ppr dmd $$ ppr fv) (DmdType fv' ds res, dmd) where fv' = fv `delVarEnv` id -- See Note [Default demand on free variables] dmd = lookupVarEnv fv id `orElse` defaultDmd res addDemand :: Demand -> DmdType -> DmdType addDemand dmd (DmdType fv ds res) = DmdType fv (dmd:ds) res findIdDemand :: DmdType -> Var -> Demand findIdDemand (DmdType fv _ res) id = lookupVarEnv fv id `orElse` defaultDmd res {- Note [Default demand on free variables] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ If the variable is not mentioned in the environment of a demand type, its demand is taken to be a result demand of the type. For the stricness component, if the result demand is a Diverges, then we use HyperStr else we use Lazy For the usage component, we use Absent. So we use either absDmd or botDmd. Also note the equations for lubDmdResult (resp. bothDmdResult) noted there. Note [Always analyse in virgin pass] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Tricky point: make sure that we analyse in the 'virgin' pass. Consider rec { f acc x True = f (...rec { g y = ...g... }...) f acc x False = acc } In the virgin pass for 'f' we'll give 'f' a very strict (bottom) type. That might mean that we analyse the sub-expression containing the E = "...rec g..." stuff in a bottom demand. Suppose we *didn't analyse* E, but just returned botType. Then in the *next* (non-virgin) iteration for 'f', we might analyse E in a weaker demand, and that will trigger doing a fixpoint iteration for g. But *because it's not the virgin pass* we won't start g's iteration at bottom. Disaster. (This happened in $sfibToList' of nofib/spectral/fibheaps.) So in the virgin pass we make sure that we do analyse the expression at least once, to initialise its signatures. Note [Analyzing with lazy demand and lambdas] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The insight for analyzing lambdas follows from the fact that for strictness S = C(L). This polymorphic expansion is critical for cardinality analysis of the following example: {-# NOINLINE build #-} build g = (g (:) [], g (:) []) h c z = build (\x -> let z1 = z ++ z in if c then \y -> x (y ++ z1) else \y -> x (z1 ++ y)) One can see that `build` assigns to `g` demand <L,C(C1(U))>. Therefore, when analyzing the lambda `(\x -> ...)`, we expect each lambda \y -> ... to be annotated as "one-shot" one. Therefore (\x -> \y -> x (y ++ z)) should be analyzed with a demand <C(C(..), C(C1(U))>. This is achieved by, first, converting the lazy demand L into the strict S by the second clause of the analysis. Note [Analysing with absent demand] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Suppose we analyse an expression with demand <L,A>. The "A" means "absent", so this expression will never be needed. What should happen? There are several wrinkles: * We *do* want to analyse the expression regardless. Reason: Note [Always analyse in virgin pass] But we can post-process the results to ignore all the usage demands coming back. This is done by postProcessDmdType. * But in the case of an *unlifted type* we must be extra careful, because unlifted values are evaluated even if they are not used. Example (see Trac #9254): f :: (() -> (# Int#, () #)) -> () -- Strictness signature is -- <C(S(LS)), 1*C1(U(A,1*U()))> -- I.e. calls k, but discards first component of result f k = case k () of (# _, r #) -> r g :: Int -> () g y = f (\n -> (# case y of I# y2 -> y2, n #)) Here f's strictness signature says (correctly) that it calls its argument function and ignores the first component of its result. This is correct in the sense that it'd be fine to (say) modify the function so that always returned 0# in the first component. But in function g, we *will* evaluate the 'case y of ...', because it has type Int#. So 'y' will be evaluated. So we must record this usage of 'y', else 'g' will say 'y' is absent, and will w/w so that 'y' is bound to an aBSENT_ERROR thunk. An alternative would be to replace the 'case y of ...' with (say) 0#, but I have not tried that. It's not a common situation, but it is not theoretical: unsafePerformIO's implementation is very very like 'f' above. ************************************************************************ * * Demand signatures * * ************************************************************************ In a let-bound Id we record its strictness info. In principle, this strictness info is a demand transformer, mapping a demand on the Id into a DmdType, which gives a) the free vars of the Id's value b) the Id's arguments c) an indication of the result of applying the Id to its arguments However, in fact we store in the Id an extremely emascuated demand transfomer, namely a single DmdType (Nevertheless we dignify StrictSig as a distinct type.) This DmdType gives the demands unleashed by the Id when it is applied to as many arguments as are given in by the arg demands in the DmdType. Also see Note [Nature of result demand] for the meaning of a DmdResult in a strictness signature. If an Id is applied to less arguments than its arity, it means that the demand on the function at a call site is weaker than the vanilla call demand, used for signature inference. Therefore we place a top demand on all arguments. Otherwise, the demand is specified by Id's signature. For example, the demand transformer described by the demand signature StrictSig (DmdType {x -> <S,1*U>} <L,A><L,U(U,U)>m) says that when the function is applied to two arguments, it unleashes demand <S,1*U> on the free var x, <L,A> on the first arg, and <L,U(U,U)> on the second, then returning a constructor. If this same function is applied to one arg, all we can say is that it uses x with <L,U>, and its arg with demand <L,U>. -} newtype StrictSig = StrictSig DmdType deriving( Eq ) instance Outputable StrictSig where ppr (StrictSig ty) = ppr ty -- Used for printing top-level strictness pragmas in interface files pprIfaceStrictSig :: StrictSig -> SDoc pprIfaceStrictSig (StrictSig (DmdType _ dmds res)) = hcat (map ppr dmds) <> ppr res mkStrictSig :: DmdType -> StrictSig mkStrictSig dmd_ty = StrictSig dmd_ty mkClosedStrictSig :: [Demand] -> DmdResult -> StrictSig mkClosedStrictSig ds res = mkStrictSig (DmdType emptyDmdEnv ds res) splitStrictSig :: StrictSig -> ([Demand], DmdResult) splitStrictSig (StrictSig (DmdType _ dmds res)) = (dmds, res) increaseStrictSigArity :: Int -> StrictSig -> StrictSig -- Add extra arguments to a strictness signature increaseStrictSigArity arity_increase sig@(StrictSig dmd_ty@(DmdType env dmds res)) | isTopDmdType dmd_ty = sig | arity_increase <= 0 = sig | otherwise = StrictSig (DmdType env dmds' res) where dmds' = replicate arity_increase topDmd ++ dmds etaExpandStrictSig :: Arity -> StrictSig -> StrictSig -- We are expanding (\x y. e) to (\x y z. e z) -- Add exta demands to the /end/ of the arg demands if necessary etaExpandStrictSig arity sig@(StrictSig dmd_ty@(DmdType env dmds res)) | isTopDmdType dmd_ty = sig | arity_increase <= 0 = sig | otherwise = StrictSig (DmdType env dmds' res) where arity_increase = arity - length dmds dmds' = dmds ++ replicate arity_increase topDmd isTopSig :: StrictSig -> Bool isTopSig (StrictSig ty) = isTopDmdType ty hasDemandEnvSig :: StrictSig -> Bool hasDemandEnvSig (StrictSig (DmdType env _ _)) = not (isEmptyVarEnv env) strictSigDmdEnv :: StrictSig -> DmdEnv strictSigDmdEnv (StrictSig (DmdType env _ _)) = env isBottomingSig :: StrictSig -> Bool -- True if the signature diverges or throws an exception isBottomingSig (StrictSig (DmdType _ _ res)) = isBotRes res nopSig, botSig, exnSig :: StrictSig nopSig = StrictSig nopDmdType botSig = StrictSig botDmdType exnSig = StrictSig exnDmdType cprProdSig :: Arity -> StrictSig cprProdSig arity = StrictSig (cprProdDmdType arity) seqStrictSig :: StrictSig -> () seqStrictSig (StrictSig ty) = seqDmdType ty dmdTransformSig :: StrictSig -> CleanDemand -> DmdType -- (dmdTransformSig fun_sig dmd) considers a call to a function whose -- signature is fun_sig, with demand dmd. We return the demand -- that the function places on its context (eg its args) dmdTransformSig (StrictSig dmd_ty@(DmdType _ arg_ds _)) cd = postProcessUnsat (peelManyCalls (length arg_ds) cd) dmd_ty -- see Note [Demands from unsaturated function calls] dmdTransformDataConSig :: Arity -> StrictSig -> CleanDemand -> DmdType -- Same as dmdTransformSig but for a data constructor (worker), -- which has a special kind of demand transformer. -- If the constructor is saturated, we feed the demand on -- the result into the constructor arguments. dmdTransformDataConSig arity (StrictSig (DmdType _ _ con_res)) (JD { sd = str, ud = abs }) | Just str_dmds <- go_str arity str , Just abs_dmds <- go_abs arity abs = DmdType emptyDmdEnv (mkJointDmds str_dmds abs_dmds) con_res -- Must remember whether it's a product, hence con_res, not TopRes | otherwise -- Not saturated = nopDmdType where go_str 0 dmd = splitStrProdDmd arity dmd go_str n (SCall s') = go_str (n-1) s' go_str n HyperStr = go_str (n-1) HyperStr go_str _ _ = Nothing go_abs 0 dmd = splitUseProdDmd arity dmd go_abs n (UCall One u') = go_abs (n-1) u' go_abs _ _ = Nothing dmdTransformDictSelSig :: StrictSig -> CleanDemand -> DmdType -- Like dmdTransformDataConSig, we have a special demand transformer -- for dictionary selectors. If the selector is saturated (ie has one -- argument: the dictionary), we feed the demand on the result into -- the indicated dictionary component. dmdTransformDictSelSig (StrictSig (DmdType _ [dict_dmd] _)) cd | (cd',defer_use) <- peelCallDmd cd , Just jds <- splitProdDmd_maybe dict_dmd = postProcessUnsat defer_use $ DmdType emptyDmdEnv [mkOnceUsedDmd $ mkProdDmd $ map (enhance cd') jds] topRes | otherwise = nopDmdType -- See Note [Demand transformer for a dictionary selector] where enhance cd old | isAbsDmd old = old | otherwise = mkOnceUsedDmd cd -- This is the one! dmdTransformDictSelSig _ _ = panic "dmdTransformDictSelSig: no args" {- Note [Demand transformer for a dictionary selector] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ If we evaluate (op dict-expr) under demand 'd', then we can push the demand 'd' into the appropriate field of the dictionary. What *is* the appropriate field? We just look at the strictness signature of the class op, which will be something like: U(AAASAAAAA). Then replace the 'S' by the demand 'd'. For single-method classes, which are represented by newtypes the signature of 'op' won't look like U(...), so the splitProdDmd_maybe will fail. That's fine: if we are doing strictness analysis we are also doing inlining, so we'll have inlined 'op' into a cast. So we can bale out in a conservative way, returning nopDmdType. It is (just.. Trac #8329) possible to be running strictness analysis *without* having inlined class ops from single-method classes. Suppose you are using ghc --make; and the first module has a local -O0 flag. So you may load a class without interface pragmas, ie (currently) without an unfolding for the class ops. Now if a subsequent module in the --make sweep has a local -O flag you might do strictness analysis, but there is no inlining for the class op. This is weird, so I'm not worried about whether this optimises brilliantly; but it should not fall over. -} argsOneShots :: StrictSig -> Arity -> [[OneShotInfo]] -- See Note [Computing one-shot info] argsOneShots (StrictSig (DmdType _ arg_ds _)) n_val_args | unsaturated_call = [] | otherwise = go arg_ds where unsaturated_call = arg_ds `lengthExceeds` n_val_args go [] = [] go (arg_d : arg_ds) = argOneShots arg_d `cons` go arg_ds -- Avoid list tail like [ [], [], [] ] cons [] [] = [] cons a as = a:as -- saturatedByOneShots n C1(C1(...)) = True, -- <=> -- there are at least n nested C1(..) calls -- See Note [Demand on the worker] in WorkWrap saturatedByOneShots :: Int -> Demand -> Bool saturatedByOneShots n (JD { ud = usg }) = case usg of Use _ arg_usg -> go n arg_usg _ -> False where go 0 _ = True go n (UCall One u) = go (n-1) u go _ _ = False argOneShots :: Demand -- depending on saturation -> [OneShotInfo] argOneShots (JD { ud = usg }) = case usg of Use _ arg_usg -> go arg_usg _ -> [] where go (UCall One u) = OneShotLam : go u go (UCall Many u) = NoOneShotInfo : go u go _ = [] {- Note [Computing one-shot info] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Consider a call f (\pqr. e1) (\xyz. e2) e3 where f has usage signature C1(C(C1(U))) C1(U) U Then argsOneShots returns a [[OneShotInfo]] of [[OneShot,NoOneShotInfo,OneShot], [OneShot]] The occurrence analyser propagates this one-shot infor to the binders \pqr and \xyz; see Note [Use one-shot information] in OccurAnal. -} -- appIsBottom returns true if an application to n args -- would diverge or throw an exception -- See Note [Unsaturated applications] appIsBottom :: StrictSig -> Int -> Bool appIsBottom (StrictSig (DmdType _ ds res)) n | isBotRes res = not $ lengthExceeds ds n appIsBottom _ _ = False {- Note [Unsaturated applications] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ If a function having bottom as its demand result is applied to a less number of arguments than its syntactic arity, we cannot say for sure that it is going to diverge. This is the reason why we use the function appIsBottom, which, given a strictness signature and a number of arguments, says conservatively if the function is going to diverge or not. Zap absence or one-shot information, under control of flags Note [Killing usage information] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The flags -fkill-one-shot and -fkill-absence let you switch off the generation of absence or one-shot information altogether. This is only used for performance tests, to see how important they are. -} zapUsageEnvSig :: StrictSig -> StrictSig -- Remove the usage environment from the demand zapUsageEnvSig (StrictSig (DmdType _ ds r)) = mkClosedStrictSig ds r zapUsageDemand :: Demand -> Demand -- Remove the usage info, but not the strictness info, from the demand zapUsageDemand = kill_usage $ KillFlags { kf_abs = True , kf_used_once = True , kf_called_once = True } -- | Remove all 1* information (but not C1 information) from the demand zapUsedOnceDemand :: Demand -> Demand zapUsedOnceDemand = kill_usage $ KillFlags { kf_abs = False , kf_used_once = True , kf_called_once = False } -- | Remove all 1* information (but not C1 information) from the strictness -- signature zapUsedOnceSig :: StrictSig -> StrictSig zapUsedOnceSig (StrictSig (DmdType env ds r)) = StrictSig (DmdType env (map zapUsedOnceDemand ds) r) killUsageDemand :: DynFlags -> Demand -> Demand -- See Note [Killing usage information] killUsageDemand dflags dmd | Just kfs <- killFlags dflags = kill_usage kfs dmd | otherwise = dmd killUsageSig :: DynFlags -> StrictSig -> StrictSig -- See Note [Killing usage information] killUsageSig dflags sig@(StrictSig (DmdType env ds r)) | Just kfs <- killFlags dflags = StrictSig (DmdType env (map (kill_usage kfs) ds) r) | otherwise = sig data KillFlags = KillFlags { kf_abs :: Bool , kf_used_once :: Bool , kf_called_once :: Bool } killFlags :: DynFlags -> Maybe KillFlags -- See Note [Killing usage information] killFlags dflags | not kf_abs && not kf_used_once = Nothing | otherwise = Just (KillFlags {..}) where kf_abs = gopt Opt_KillAbsence dflags kf_used_once = gopt Opt_KillOneShot dflags kf_called_once = kf_used_once kill_usage :: KillFlags -> Demand -> Demand kill_usage kfs (JD {sd = s, ud = u}) = JD {sd = s, ud = zap_musg kfs u} zap_musg :: KillFlags -> ArgUse -> ArgUse zap_musg kfs Abs | kf_abs kfs = useTop | otherwise = Abs zap_musg kfs (Use c u) | kf_used_once kfs = Use Many (zap_usg kfs u) | otherwise = Use c (zap_usg kfs u) zap_usg :: KillFlags -> UseDmd -> UseDmd zap_usg kfs (UCall c u) | kf_called_once kfs = UCall Many (zap_usg kfs u) | otherwise = UCall c (zap_usg kfs u) zap_usg kfs (UProd us) = UProd (map (zap_musg kfs) us) zap_usg _ u = u -- If the argument is a used non-newtype dictionary, give it strict -- demand. Also split the product type & demand and recur in order to -- similarly strictify the argument's contained used non-newtype -- superclass dictionaries. We use the demand as our recursive measure -- to guarantee termination. strictifyDictDmd :: Type -> Demand -> Demand strictifyDictDmd ty dmd = case getUseDmd dmd of Use n _ | Just (tycon, _arg_tys, _data_con, inst_con_arg_tys) <- splitDataProductType_maybe ty, not (isNewTyCon tycon), isClassTyCon tycon -- is a non-newtype dictionary -> seqDmd `bothDmd` -- main idea: ensure it's strict case splitProdDmd_maybe dmd of -- superclass cycles should not be a problem, since the demand we are -- consuming would also have to be infinite in order for us to diverge Nothing -> dmd -- no components have interesting demand, so stop -- looking for superclass dicts Just dmds | all (not . isAbsDmd) dmds -> evalDmd -- abstract to strict w/ arbitrary component use, since this -- smells like reboxing; results in CBV boxed -- -- TODO revisit this if we ever do boxity analysis | otherwise -> case mkProdDmd $ zipWith strictifyDictDmd inst_con_arg_tys dmds of JD {sd = s,ud = a} -> JD (Str VanStr s) (Use n a) -- TODO could optimize with an aborting variant of zipWith since -- the superclass dicts are always a prefix _ -> dmd -- unused or not a dictionary {- Note [HyperStr and Use demands] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The information "HyperStr" needs to be in the strictness signature, and not in the demand signature, because we still want to know about the demand on things. Consider f (x,y) True = error (show x) f (x,y) False = x+1 The signature of f should be <S(SL),1*U(1*U(U),A)><S,1*U>m. If we were not distinguishing the uses on x and y in the True case, we could either not figure out how deeply we can unpack x, or that we do not have to pass y. ************************************************************************ * * Serialisation * * ************************************************************************ -} instance Binary StrDmd where put_ bh HyperStr = do putByte bh 0 put_ bh HeadStr = do putByte bh 1 put_ bh (SCall s) = do putByte bh 2 put_ bh s put_ bh (SProd sx) = do putByte bh 3 put_ bh sx get bh = do h <- getByte bh case h of 0 -> do return HyperStr 1 -> do return HeadStr 2 -> do s <- get bh return (SCall s) _ -> do sx <- get bh return (SProd sx) instance Binary ExnStr where put_ bh VanStr = putByte bh 0 put_ bh ExnStr = putByte bh 1 get bh = do h <- getByte bh return (case h of 0 -> VanStr _ -> ExnStr) instance Binary ArgStr where put_ bh Lazy = do putByte bh 0 put_ bh (Str x s) = do putByte bh 1 put_ bh x put_ bh s get bh = do h <- getByte bh case h of 0 -> return Lazy _ -> do x <- get bh s <- get bh return $ Str x s instance Binary Count where put_ bh One = do putByte bh 0 put_ bh Many = do putByte bh 1 get bh = do h <- getByte bh case h of 0 -> return One _ -> return Many instance Binary ArgUse where put_ bh Abs = do putByte bh 0 put_ bh (Use c u) = do putByte bh 1 put_ bh c put_ bh u get bh = do h <- getByte bh case h of 0 -> return Abs _ -> do c <- get bh u <- get bh return $ Use c u instance Binary UseDmd where put_ bh Used = do putByte bh 0 put_ bh UHead = do putByte bh 1 put_ bh (UCall c u) = do putByte bh 2 put_ bh c put_ bh u put_ bh (UProd ux) = do putByte bh 3 put_ bh ux get bh = do h <- getByte bh case h of 0 -> return $ Used 1 -> return $ UHead 2 -> do c <- get bh u <- get bh return (UCall c u) _ -> do ux <- get bh return (UProd ux) instance (Binary s, Binary u) => Binary (JointDmd s u) where put_ bh (JD { sd = x, ud = y }) = do put_ bh x; put_ bh y get bh = do x <- get bh y <- get bh return $ JD { sd = x, ud = y } instance Binary StrictSig where put_ bh (StrictSig aa) = do put_ bh aa get bh = do aa <- get bh return (StrictSig aa) instance Binary DmdType where -- Ignore DmdEnv when spitting out the DmdType put_ bh (DmdType _ ds dr) = do put_ bh ds put_ bh dr get bh = do ds <- get bh dr <- get bh return (DmdType emptyDmdEnv ds dr) instance Binary DmdResult where put_ bh (Dunno c) = do { putByte bh 0; put_ bh c } put_ bh ThrowsExn = putByte bh 1 put_ bh Diverges = putByte bh 2 get bh = do { h <- getByte bh ; case h of 0 -> do { c <- get bh; return (Dunno c) } 1 -> return ThrowsExn _ -> return Diverges } instance Binary CPRResult where put_ bh (RetSum n) = do { putByte bh 0; put_ bh n } put_ bh RetProd = putByte bh 1 put_ bh NoCPR = putByte bh 2 get bh = do h <- getByte bh case h of 0 -> do { n <- get bh; return (RetSum n) } 1 -> return RetProd _ -> return NoCPR