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Diffstat (limited to 'compiler/stranal/DmdAnal.lhs')
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diff --git a/compiler/stranal/DmdAnal.lhs b/compiler/stranal/DmdAnal.lhs new file mode 100644 index 0000000000..c5cfb7b4bd --- /dev/null +++ b/compiler/stranal/DmdAnal.lhs @@ -0,0 +1,1185 @@ +% +% (c) The GRASP/AQUA Project, Glasgow University, 1993-1998 +% + + ----------------- + A demand analysis + ----------------- + +\begin{code} +module DmdAnal ( dmdAnalPgm, dmdAnalTopRhs, + both {- needed by WwLib -} + ) where + +#include "HsVersions.h" + +import DynFlags ( DynFlags, DynFlag(..) ) +import StaticFlags ( opt_MaxWorkerArgs ) +import NewDemand -- All of it +import CoreSyn +import PprCore +import CoreUtils ( exprIsHNF, exprIsTrivial, exprArity ) +import DataCon ( dataConTyCon ) +import TyCon ( isProductTyCon, isRecursiveTyCon ) +import Id ( Id, idType, idInlinePragma, + isDataConWorkId, isGlobalId, idArity, +#ifdef OLD_STRICTNESS + idDemandInfo, idStrictness, idCprInfo, idName, +#endif + idNewStrictness, idNewStrictness_maybe, + setIdNewStrictness, idNewDemandInfo, + idNewDemandInfo_maybe, + setIdNewDemandInfo + ) +#ifdef OLD_STRICTNESS +import IdInfo ( newStrictnessFromOld, newDemand ) +#endif +import Var ( Var ) +import VarEnv +import TysWiredIn ( unboxedPairDataCon ) +import TysPrim ( realWorldStatePrimTy ) +import UniqFM ( plusUFM_C, addToUFM_Directly, lookupUFM_Directly, + keysUFM, minusUFM, ufmToList, filterUFM ) +import Type ( isUnLiftedType, coreEqType ) +import CoreLint ( showPass, endPass ) +import Util ( mapAndUnzip, mapAccumL, mapAccumR, lengthIs ) +import BasicTypes ( Arity, TopLevelFlag(..), isTopLevel, isNeverActive, + RecFlag(..), isRec ) +import Maybes ( orElse, expectJust ) +import Outputable +\end{code} + +To think about + +* set a noinline pragma on bottoming Ids + +* Consider f x = x+1 `fatbar` error (show x) + We'd like to unbox x, even if that means reboxing it in the error case. + + +%************************************************************************ +%* * +\subsection{Top level stuff} +%* * +%************************************************************************ + +\begin{code} +dmdAnalPgm :: DynFlags -> [CoreBind] -> IO [CoreBind] +dmdAnalPgm dflags binds + = do { + showPass dflags "Demand analysis" ; + let { binds_plus_dmds = do_prog binds } ; + + endPass dflags "Demand analysis" + Opt_D_dump_stranal binds_plus_dmds ; +#ifdef OLD_STRICTNESS + -- Only if OLD_STRICTNESS is on, because only then is the old + -- strictness analyser run + let { dmd_changes = get_changes binds_plus_dmds } ; + printDump (text "Changes in demands" $$ dmd_changes) ; +#endif + return binds_plus_dmds + } + where + do_prog :: [CoreBind] -> [CoreBind] + do_prog binds = snd $ mapAccumL dmdAnalTopBind emptySigEnv binds + +dmdAnalTopBind :: SigEnv + -> CoreBind + -> (SigEnv, CoreBind) +dmdAnalTopBind sigs (NonRec id rhs) + = let + ( _, _, (_, rhs1)) = dmdAnalRhs TopLevel NonRecursive sigs (id, rhs) + (sigs2, _, (id2, rhs2)) = dmdAnalRhs TopLevel NonRecursive sigs (id, rhs1) + -- Do two passes to improve CPR information + -- See comments with ignore_cpr_info in mk_sig_ty + -- and with extendSigsWithLam + in + (sigs2, NonRec id2 rhs2) + +dmdAnalTopBind sigs (Rec pairs) + = let + (sigs', _, pairs') = dmdFix TopLevel sigs pairs + -- We get two iterations automatically + -- c.f. the NonRec case above + in + (sigs', Rec pairs') +\end{code} + +\begin{code} +dmdAnalTopRhs :: CoreExpr -> (StrictSig, CoreExpr) +-- Analyse the RHS and return +-- a) appropriate strictness info +-- b) the unfolding (decorated with stricntess info) +dmdAnalTopRhs rhs + = (sig, rhs2) + where + call_dmd = vanillaCall (exprArity rhs) + (_, rhs1) = dmdAnal emptySigEnv call_dmd rhs + (rhs_ty, rhs2) = dmdAnal emptySigEnv call_dmd rhs1 + sig = mkTopSigTy rhs rhs_ty + -- Do two passes; see notes with extendSigsWithLam + -- Otherwise we get bogus CPR info for constructors like + -- newtype T a = MkT a + -- The constructor looks like (\x::T a -> x), modulo the coerce + -- extendSigsWithLam will optimistically give x a CPR tag the + -- first time, which is wrong in the end. +\end{code} + +%************************************************************************ +%* * +\subsection{The analyser itself} +%* * +%************************************************************************ + +\begin{code} +dmdAnal :: SigEnv -> Demand -> CoreExpr -> (DmdType, CoreExpr) + +dmdAnal sigs Abs e = (topDmdType, e) + +dmdAnal sigs dmd e + | not (isStrictDmd dmd) + = let + (res_ty, e') = dmdAnal sigs evalDmd e + in + (deferType res_ty, e') + -- It's important not to analyse e with a lazy demand because + -- a) When we encounter case s of (a,b) -> + -- we demand s with U(d1d2)... but if the overall demand is lazy + -- that is wrong, and we'd need to reduce the demand on s, + -- which is inconvenient + -- b) More important, consider + -- f (let x = R in x+x), where f is lazy + -- We still want to mark x as demanded, because it will be when we + -- enter the let. If we analyse f's arg with a Lazy demand, we'll + -- just mark x as Lazy + -- c) The application rule wouldn't be right either + -- Evaluating (f x) in a L demand does *not* cause + -- evaluation of f in a C(L) demand! + + +dmdAnal sigs dmd (Lit lit) + = (topDmdType, Lit lit) + +dmdAnal sigs dmd (Var var) + = (dmdTransform sigs var dmd, Var var) + +dmdAnal sigs dmd (Note n e) + = (dmd_ty, Note n e') + where + (dmd_ty, e') = dmdAnal sigs dmd' e + dmd' = case n of + Coerce _ _ -> evalDmd -- This coerce usually arises from a recursive + other -> dmd -- newtype, and we don't want to look inside them + -- for exactly the same reason that we don't look + -- inside recursive products -- we might not reach + -- a fixpoint. So revert to a vanilla Eval demand + +dmdAnal sigs dmd (App fun (Type ty)) + = (fun_ty, App fun' (Type ty)) + where + (fun_ty, fun') = dmdAnal sigs dmd fun + +-- Lots of the other code is there to make this +-- beautiful, compositional, application rule :-) +dmdAnal sigs dmd e@(App fun arg) -- Non-type arguments + = let -- [Type arg handled above] + (fun_ty, fun') = dmdAnal sigs (Call dmd) fun + (arg_ty, arg') = dmdAnal sigs arg_dmd arg + (arg_dmd, res_ty) = splitDmdTy fun_ty + in + (res_ty `bothType` arg_ty, App fun' arg') + +dmdAnal sigs dmd (Lam var body) + | isTyVar var + = let + (body_ty, body') = dmdAnal sigs dmd body + in + (body_ty, Lam var body') + + | Call body_dmd <- dmd -- A call demand: good! + = let + sigs' = extendSigsWithLam sigs var + (body_ty, body') = dmdAnal sigs' body_dmd body + (lam_ty, var') = annotateLamIdBndr body_ty var + in + (lam_ty, Lam var' body') + + | otherwise -- Not enough demand on the lambda; but do the body + = let -- anyway to annotate it and gather free var info + (body_ty, body') = dmdAnal sigs evalDmd body + (lam_ty, var') = annotateLamIdBndr body_ty var + in + (deferType lam_ty, Lam var' body') + +dmdAnal sigs dmd (Case scrut case_bndr ty [alt@(DataAlt dc,bndrs,rhs)]) + | let tycon = dataConTyCon dc, + isProductTyCon tycon, + not (isRecursiveTyCon tycon) + = let + sigs_alt = extendSigEnv NotTopLevel sigs case_bndr case_bndr_sig + (alt_ty, alt') = dmdAnalAlt sigs_alt dmd alt + (alt_ty1, case_bndr') = annotateBndr alt_ty case_bndr + (_, bndrs', _) = alt' + case_bndr_sig = cprSig + -- Inside the alternative, the case binder has the CPR property. + -- Meaning that a case on it will successfully cancel. + -- Example: + -- f True x = case x of y { I# x' -> if x' ==# 3 then y else I# 8 } + -- f False x = I# 3 + -- + -- We want f to have the CPR property: + -- f b x = case fw b x of { r -> I# r } + -- fw True x = case x of y { I# x' -> if x' ==# 3 then x' else 8 } + -- fw False x = 3 + + -- Figure out whether the demand on the case binder is used, and use + -- that to set the scrut_dmd. This is utterly essential. + -- Consider f x = case x of y { (a,b) -> k y a } + -- If we just take scrut_demand = U(L,A), then we won't pass x to the + -- worker, so the worker will rebuild + -- x = (a, absent-error) + -- and that'll crash. + -- So at one stage I had: + -- dead_case_bndr = isAbsentDmd (idNewDemandInfo case_bndr') + -- keepity | dead_case_bndr = Drop + -- | otherwise = Keep + -- + -- But then consider + -- case x of y { (a,b) -> h y + a } + -- where h : U(LL) -> T + -- The above code would compute a Keep for x, since y is not Abs, which is silly + -- The insight is, of course, that a demand on y is a demand on the + -- scrutinee, so we need to `both` it with the scrut demand + + scrut_dmd = Eval (Prod [idNewDemandInfo b | b <- bndrs', isId b]) + `both` + idNewDemandInfo case_bndr' + + (scrut_ty, scrut') = dmdAnal sigs scrut_dmd scrut + in + (alt_ty1 `bothType` scrut_ty, Case scrut' case_bndr' ty [alt']) + +dmdAnal sigs dmd (Case scrut case_bndr ty alts) + = let + (alt_tys, alts') = mapAndUnzip (dmdAnalAlt sigs dmd) alts + (scrut_ty, scrut') = dmdAnal sigs evalDmd scrut + (alt_ty, case_bndr') = annotateBndr (foldr1 lubType alt_tys) case_bndr + in +-- pprTrace "dmdAnal:Case" (ppr alts $$ ppr alt_tys) + (alt_ty `bothType` scrut_ty, Case scrut' case_bndr' ty alts') + +dmdAnal sigs dmd (Let (NonRec id rhs) body) + = let + (sigs', lazy_fv, (id1, rhs')) = dmdAnalRhs NotTopLevel NonRecursive sigs (id, rhs) + (body_ty, body') = dmdAnal sigs' dmd body + (body_ty1, id2) = annotateBndr body_ty id1 + body_ty2 = addLazyFVs body_ty1 lazy_fv + in + -- If the actual demand is better than the vanilla call + -- demand, you might think that we might do better to re-analyse + -- the RHS with the stronger demand. + -- But (a) That seldom happens, because it means that *every* path in + -- the body of the let has to use that stronger demand + -- (b) It often happens temporarily in when fixpointing, because + -- the recursive function at first seems to place a massive demand. + -- But we don't want to go to extra work when the function will + -- probably iterate to something less demanding. + -- In practice, all the times the actual demand on id2 is more than + -- the vanilla call demand seem to be due to (b). So we don't + -- bother to re-analyse the RHS. + (body_ty2, Let (NonRec id2 rhs') body') + +dmdAnal sigs dmd (Let (Rec pairs) body) + = let + bndrs = map fst pairs + (sigs', lazy_fv, pairs') = dmdFix NotTopLevel sigs pairs + (body_ty, body') = dmdAnal sigs' dmd body + body_ty1 = addLazyFVs body_ty lazy_fv + in + sigs' `seq` body_ty `seq` + let + (body_ty2, _) = annotateBndrs body_ty1 bndrs + -- Don't bother to add demand info to recursive + -- binders as annotateBndr does; + -- being recursive, we can't treat them strictly. + -- But we do need to remove the binders from the result demand env + in + (body_ty2, Let (Rec pairs') body') + + +dmdAnalAlt sigs dmd (con,bndrs,rhs) + = let + (rhs_ty, rhs') = dmdAnal sigs dmd rhs + (alt_ty, bndrs') = annotateBndrs rhs_ty bndrs + final_alt_ty | io_hack_reqd = alt_ty `lubType` topDmdType + | otherwise = alt_ty + + -- There's a hack here for I/O operations. Consider + -- case foo x s of { (# s, r #) -> y } + -- Is this strict in 'y'. Normally yes, but what if 'foo' is an I/O + -- operation that simply terminates the program (not in an erroneous way)? + -- In that case we should not evaluate y before the call to 'foo'. + -- Hackish solution: spot the IO-like situation and add a virtual branch, + -- as if we had + -- case foo x s of + -- (# s, r #) -> y + -- other -> return () + -- So the 'y' isn't necessarily going to be evaluated + -- + -- A more complete example where this shows up is: + -- do { let len = <expensive> ; + -- ; when (...) (exitWith ExitSuccess) + -- ; print len } + + io_hack_reqd = con == DataAlt unboxedPairDataCon && + idType (head bndrs) `coreEqType` realWorldStatePrimTy + in + (final_alt_ty, (con, bndrs', rhs')) +\end{code} + +%************************************************************************ +%* * +\subsection{Bindings} +%* * +%************************************************************************ + +\begin{code} +dmdFix :: TopLevelFlag + -> SigEnv -- Does not include bindings for this binding + -> [(Id,CoreExpr)] + -> (SigEnv, DmdEnv, + [(Id,CoreExpr)]) -- Binders annotated with stricness info + +dmdFix top_lvl sigs orig_pairs + = loop 1 initial_sigs orig_pairs + where + bndrs = map fst orig_pairs + initial_sigs = extendSigEnvList sigs [(id, (initialSig id, top_lvl)) | id <- bndrs] + + loop :: Int + -> SigEnv -- Already contains the current sigs + -> [(Id,CoreExpr)] + -> (SigEnv, DmdEnv, [(Id,CoreExpr)]) + loop n sigs pairs + | found_fixpoint + = (sigs', lazy_fv, pairs') + -- Note: use pairs', not pairs. pairs' is the result of + -- processing the RHSs with sigs (= sigs'), whereas pairs + -- is the result of processing the RHSs with the *previous* + -- iteration of sigs. + + | n >= 10 = pprTrace "dmdFix loop" (ppr n <+> (vcat + [ text "Sigs:" <+> ppr [(id,lookup sigs id, lookup sigs' id) | (id,_) <- pairs], + text "env:" <+> ppr (ufmToList sigs), + text "binds:" <+> pprCoreBinding (Rec pairs)])) + (emptySigEnv, lazy_fv, orig_pairs) -- Safe output + -- The lazy_fv part is really important! orig_pairs has no strictness + -- info, including nothing about free vars. But if we have + -- letrec f = ....y..... in ...f... + -- where 'y' is free in f, we must record that y is mentioned, + -- otherwise y will get recorded as absent altogether + + | otherwise = loop (n+1) sigs' pairs' + where + found_fixpoint = all (same_sig sigs sigs') bndrs + -- Use the new signature to do the next pair + -- The occurrence analyser has arranged them in a good order + -- so this can significantly reduce the number of iterations needed + ((sigs',lazy_fv), pairs') = mapAccumL (my_downRhs top_lvl) (sigs, emptyDmdEnv) pairs + + my_downRhs top_lvl (sigs,lazy_fv) (id,rhs) + = -- pprTrace "downRhs {" (ppr id <+> (ppr old_sig)) + -- (new_sig `seq` + -- pprTrace "downRhsEnd" (ppr id <+> ppr new_sig <+> char '}' ) + ((sigs', lazy_fv'), pair') + -- ) + where + (sigs', lazy_fv1, pair') = dmdAnalRhs top_lvl Recursive sigs (id,rhs) + lazy_fv' = plusUFM_C both lazy_fv lazy_fv1 + -- old_sig = lookup sigs id + -- new_sig = lookup sigs' id + + same_sig sigs sigs' var = lookup sigs var == lookup sigs' var + lookup sigs var = case lookupVarEnv sigs var of + Just (sig,_) -> sig + + -- Get an initial strictness signature from the Id + -- itself. That way we make use of earlier iterations + -- of the fixpoint algorithm. (Cunning plan.) + -- Note that the cunning plan extends to the DmdEnv too, + -- since it is part of the strictness signature +initialSig id = idNewStrictness_maybe id `orElse` botSig + +dmdAnalRhs :: TopLevelFlag -> RecFlag + -> SigEnv -> (Id, CoreExpr) + -> (SigEnv, DmdEnv, (Id, CoreExpr)) +-- Process the RHS of the binding, add the strictness signature +-- to the Id, and augment the environment with the signature as well. + +dmdAnalRhs top_lvl rec_flag sigs (id, rhs) + = (sigs', lazy_fv, (id', rhs')) + where + arity = idArity id -- The idArity should be up to date + -- The simplifier was run just beforehand + (rhs_dmd_ty, rhs') = dmdAnal sigs (vanillaCall arity) rhs + (lazy_fv, sig_ty) = WARN( arity /= dmdTypeDepth rhs_dmd_ty && not (exprIsTrivial rhs), ppr id ) + -- The RHS can be eta-reduced to just a variable, + -- in which case we should not complain. + mkSigTy top_lvl rec_flag id rhs rhs_dmd_ty + id' = id `setIdNewStrictness` sig_ty + sigs' = extendSigEnv top_lvl sigs id sig_ty +\end{code} + +%************************************************************************ +%* * +\subsection{Strictness signatures and types} +%* * +%************************************************************************ + +\begin{code} +mkTopSigTy :: CoreExpr -> DmdType -> StrictSig + -- Take a DmdType and turn it into a StrictSig + -- NB: not used for never-inline things; hence False +mkTopSigTy rhs dmd_ty = snd (mk_sig_ty False False rhs dmd_ty) + +mkSigTy :: TopLevelFlag -> RecFlag -> Id -> CoreExpr -> DmdType -> (DmdEnv, StrictSig) +mkSigTy top_lvl rec_flag id rhs dmd_ty + = mk_sig_ty never_inline thunk_cpr_ok rhs dmd_ty + where + never_inline = isNeverActive (idInlinePragma id) + maybe_id_dmd = idNewDemandInfo_maybe id + -- Is Nothing the first time round + + thunk_cpr_ok + | isTopLevel top_lvl = False -- Top level things don't get + -- their demandInfo set at all + | isRec rec_flag = False -- Ditto recursive things + | Just dmd <- maybe_id_dmd = isStrictDmd dmd + | otherwise = True -- Optimistic, first time round + -- See notes below +\end{code} + +The thunk_cpr_ok stuff [CPR-AND-STRICTNESS] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +If the rhs is a thunk, we usually forget the CPR info, because +it is presumably shared (else it would have been inlined, and +so we'd lose sharing if w/w'd it into a function. + +However, if the strictness analyser has figured out (in a previous +iteration) that it's strict, then we DON'T need to forget the CPR info. +Instead we can retain the CPR info and do the thunk-splitting transform +(see WorkWrap.splitThunk). + +This made a big difference to PrelBase.modInt, which had something like + modInt = \ x -> let r = ... -> I# v in + ...body strict in r... +r's RHS isn't a value yet; but modInt returns r in various branches, so +if r doesn't have the CPR property then neither does modInt +Another case I found in practice (in Complex.magnitude), looks like this: + let k = if ... then I# a else I# b + in ... body strict in k .... +(For this example, it doesn't matter whether k is returned as part of +the overall result; but it does matter that k's RHS has the CPR property.) +Left to itself, the simplifier will make a join point thus: + let $j k = ...body strict in k... + if ... then $j (I# a) else $j (I# b) +With thunk-splitting, we get instead + let $j x = let k = I#x in ...body strict in k... + in if ... then $j a else $j b +This is much better; there's a good chance the I# won't get allocated. + +The difficulty with this is that we need the strictness type to +look at the body... but we now need the body to calculate the demand +on the variable, so we can decide whether its strictness type should +have a CPR in it or not. Simple solution: + a) use strictness info from the previous iteration + b) make sure we do at least 2 iterations, by doing a second + round for top-level non-recs. Top level recs will get at + least 2 iterations except for totally-bottom functions + which aren't very interesting anyway. + +NB: strictly_demanded is never true of a top-level Id, or of a recursive Id. + +The Nothing case in thunk_cpr_ok [CPR-AND-STRICTNESS] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Demand info now has a 'Nothing' state, just like strictness info. +The analysis works from 'dangerous' towards a 'safe' state; so we +start with botSig for 'Nothing' strictness infos, and we start with +"yes, it's demanded" for 'Nothing' in the demand info. The +fixpoint iteration will sort it all out. + +We can't start with 'not-demanded' because then consider + f x = let + t = ... I# x + in + if ... then t else I# y else f x' + +In the first iteration we'd have no demand info for x, so assume +not-demanded; then we'd get TopRes for f's CPR info. Next iteration +we'd see that t was demanded, and so give it the CPR property, but by +now f has TopRes, so it will stay TopRes. Instead, with the Nothing +setting the first time round, we say 'yes t is demanded' the first +time. + +However, this does mean that for non-recursive bindings we must +iterate twice to be sure of not getting over-optimistic CPR info, +in the case where t turns out to be not-demanded. This is handled +by dmdAnalTopBind. + + +\begin{code} +mk_sig_ty never_inline thunk_cpr_ok rhs (DmdType fv dmds res) + | never_inline && not (isBotRes res) + -- HACK ALERT + -- Don't strictness-analyse NOINLINE things. Why not? Because + -- the NOINLINE says "don't expose any of the inner workings at the call + -- site" and the strictness is certainly an inner working. + -- + -- More concretely, the demand analyser discovers the following strictness + -- for unsafePerformIO: C(U(AV)) + -- But then consider + -- unsafePerformIO (\s -> let r = f x in + -- case writeIORef v r s of (# s1, _ #) -> + -- (# s1, r #) + -- The strictness analyser will find that the binding for r is strict, + -- (becuase of uPIO's strictness sig), and so it'll evaluate it before + -- doing the writeIORef. This actually makes tests/lib/should_run/memo002 + -- get a deadlock! + -- + -- Solution: don't expose the strictness of unsafePerformIO. + -- + -- But we do want to expose the strictness of error functions, + -- which are also often marked NOINLINE + -- {-# NOINLINE foo #-} + -- foo x = error ("wubble buggle" ++ x) + -- So (hack, hack) we only drop the strictness for non-bottom things + -- This is all very unsatisfactory. + = (deferEnv fv, topSig) + + | otherwise + = (lazy_fv, mkStrictSig dmd_ty) + where + dmd_ty = DmdType strict_fv final_dmds res' + + lazy_fv = filterUFM (not . isStrictDmd) fv + strict_fv = filterUFM isStrictDmd fv + -- We put the strict FVs in the DmdType of the Id, so + -- that at its call sites we unleash demands on its strict fvs. + -- An example is 'roll' in imaginary/wheel-sieve2 + -- Something like this: + -- roll x = letrec + -- go y = if ... then roll (x-1) else x+1 + -- in + -- go ms + -- We want to see that roll is strict in x, which is because + -- go is called. So we put the DmdEnv for x in go's DmdType. + -- + -- Another example: + -- f :: Int -> Int -> Int + -- f x y = let t = x+1 + -- h z = if z==0 then t else + -- if z==1 then x+1 else + -- x + h (z-1) + -- in + -- h y + -- Calling h does indeed evaluate x, but we can only see + -- that if we unleash a demand on x at the call site for t. + -- + -- Incidentally, here's a place where lambda-lifting h would + -- lose the cigar --- we couldn't see the joint strictness in t/x + -- + -- ON THE OTHER HAND + -- We don't want to put *all* the fv's from the RHS into the + -- DmdType, because that makes fixpointing very slow --- the + -- DmdType gets full of lazy demands that are slow to converge. + + final_dmds = setUnpackStrategy dmds + -- Set the unpacking strategy + + res' = case res of + RetCPR | ignore_cpr_info -> TopRes + other -> res + ignore_cpr_info = not (exprIsHNF rhs || thunk_cpr_ok) +\end{code} + +The unpack strategy determines whether we'll *really* unpack the argument, +or whether we'll just remember its strictness. If unpacking would give +rise to a *lot* of worker args, we may decide not to unpack after all. + +\begin{code} +setUnpackStrategy :: [Demand] -> [Demand] +setUnpackStrategy ds + = snd (go (opt_MaxWorkerArgs - nonAbsentArgs ds) ds) + where + go :: Int -- Max number of args available for sub-components of [Demand] + -> [Demand] + -> (Int, [Demand]) -- Args remaining after subcomponents of [Demand] are unpacked + + go n (Eval (Prod cs) : ds) + | n' >= 0 = Eval (Prod cs') `cons` go n'' ds + | otherwise = Box (Eval (Prod cs)) `cons` go n ds + where + (n'',cs') = go n' cs + n' = n + 1 - non_abs_args + -- Add one to the budget 'cos we drop the top-level arg + non_abs_args = nonAbsentArgs cs + -- Delete # of non-absent args to which we'll now be committed + + go n (d:ds) = d `cons` go n ds + go n [] = (n,[]) + + cons d (n,ds) = (n, d:ds) + +nonAbsentArgs :: [Demand] -> Int +nonAbsentArgs [] = 0 +nonAbsentArgs (Abs : ds) = nonAbsentArgs ds +nonAbsentArgs (d : ds) = 1 + nonAbsentArgs ds +\end{code} + + +%************************************************************************ +%* * +\subsection{Strictness signatures and types} +%* * +%************************************************************************ + +\begin{code} +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 fv [] res_ty) = (resTypeArgDmd res_ty, ty) +\end{code} + +\begin{code} +unitVarDmd var dmd = DmdType (unitVarEnv var dmd) [] TopRes + +addVarDmd top_lvl dmd_ty@(DmdType fv ds res) var dmd + | isTopLevel top_lvl = dmd_ty -- Don't record top level things + | otherwise = DmdType (extendVarEnv fv var dmd) ds res + +addLazyFVs (DmdType fv ds res) lazy_fvs + = DmdType both_fv1 ds res + where + both_fv = (plusUFM_C both fv lazy_fvs) + both_fv1 = modifyEnv (isBotRes res) (`both` Bot) lazy_fvs fv both_fv + -- This modifyEnv is vital. Consider + -- let f = \x -> (x,y) + -- in error (f 3) + -- Here, y is treated as a lazy-fv of f, but we must `both` that L + -- demand with the bottom coming up from 'error' + -- + -- I got a loop in the fixpointer without this, due to an interaction + -- with the lazy_fv filtering in mkSigTy. Roughly, it was + -- letrec f n x + -- = letrec g y = x `fatbar` + -- letrec h z = z + ...g... + -- in h (f (n-1) x) + -- in ... + -- In the initial iteration for f, f=Bot + -- Suppose h is found to be strict in z, but the occurrence of g in its RHS + -- is lazy. Now consider the fixpoint iteration for g, esp the demands it + -- places on its free variables. Suppose it places none. Then the + -- x `fatbar` ...call to h... + -- will give a x->V demand for x. That turns into a L demand for x, + -- which floats out of the defn for h. Without the modifyEnv, that + -- L demand doesn't get both'd with the Bot coming up from the inner + -- call to f. So we just get an L demand for x for g. + -- + -- A better way to say this is that the lazy-fv filtering should give the + -- same answer as putting the lazy fv demands in the function's type. + +annotateBndr :: DmdType -> Var -> (DmdType, Var) +-- The returned env has the var deleted +-- The returned var is annotated with demand info +-- No effect on the argument demands +annotateBndr dmd_ty@(DmdType fv ds res) var + | isTyVar var = (dmd_ty, var) + | otherwise = (DmdType fv' ds res, setIdNewDemandInfo var dmd) + where + (fv', dmd) = removeFV fv var res + +annotateBndrs = mapAccumR annotateBndr + +annotateLamIdBndr dmd_ty@(DmdType fv ds res) id +-- For lambdas we add the demand to the argument demands +-- Only called for Ids + = ASSERT( isId id ) + (DmdType fv' (hacked_dmd:ds) res, setIdNewDemandInfo id hacked_dmd) + where + (fv', dmd) = removeFV fv id res + hacked_dmd = argDemand dmd + -- This call to argDemand is vital, because otherwise we label + -- a lambda binder with demand 'B'. But in terms of calling + -- conventions that's Abs, because we don't pass it. But + -- when we do a w/w split we get + -- fw x = (\x y:B -> ...) x (error "oops") + -- And then the simplifier things the 'B' is a strict demand + -- and evaluates the (error "oops"). Sigh + +removeFV fv id res = (fv', zapUnlifted id dmd) + where + fv' = fv `delVarEnv` id + dmd = lookupVarEnv fv id `orElse` deflt + deflt | isBotRes res = Bot + | otherwise = Abs + +-- For unlifted-type variables, we are only +-- interested in Bot/Abs/Box Abs +zapUnlifted is Bot = Bot +zapUnlifted id Abs = Abs +zapUnlifted id dmd | isUnLiftedType (idType id) = lazyDmd + | otherwise = dmd +\end{code} + +%************************************************************************ +%* * +\subsection{Strictness signatures} +%* * +%************************************************************************ + +\begin{code} +type SigEnv = VarEnv (StrictSig, TopLevelFlag) + -- We use the SigEnv to tell us whether to + -- record info about a variable in the DmdEnv + -- We do so if it's a LocalId, but not top-level + -- + -- The DmdEnv gives the demand on the free vars of the function + -- when it is given enough args to satisfy the strictness signature + +emptySigEnv = emptyVarEnv + +extendSigEnv :: TopLevelFlag -> SigEnv -> Id -> StrictSig -> SigEnv +extendSigEnv top_lvl env var sig = extendVarEnv env var (sig, top_lvl) + +extendSigEnvList = extendVarEnvList + +extendSigsWithLam :: SigEnv -> Id -> SigEnv +-- Extend the SigEnv when we meet a lambda binder +-- If the binder is marked demanded with a product demand, then give it a CPR +-- signature, because in the likely event that this is a lambda on a fn defn +-- [we only use this when the lambda is being consumed with a call demand], +-- it'll be w/w'd and so it will be CPR-ish. E.g. +-- f = \x::(Int,Int). if ...strict in x... then +-- x +-- else +-- (a,b) +-- We want f to have the CPR property because x does, by the time f has been w/w'd +-- +-- Also note that we only want to do this for something that +-- definitely has product type, else we may get over-optimistic +-- CPR results (e.g. from \x -> x!). + +extendSigsWithLam sigs id + = case idNewDemandInfo_maybe id of + Nothing -> extendVarEnv sigs id (cprSig, NotTopLevel) + -- Optimistic in the Nothing case; + -- See notes [CPR-AND-STRICTNESS] + Just (Eval (Prod ds)) -> extendVarEnv sigs id (cprSig, NotTopLevel) + other -> sigs + + +dmdTransform :: SigEnv -- The strictness environment + -> Id -- The function + -> Demand -- The demand on the function + -> DmdType -- The demand type of the function in this context + -- Returned DmdEnv includes the demand on + -- this function plus demand on its free variables + +dmdTransform sigs var dmd + +------ DATA CONSTRUCTOR + | isDataConWorkId var -- Data constructor + = let + StrictSig dmd_ty = idNewStrictness var -- It must have a strictness sig + DmdType _ _ con_res = dmd_ty + arity = idArity var + in + if arity == call_depth then -- Saturated, so unleash the demand + let + -- Important! If we Keep the constructor application, then + -- we need the demands the constructor places (always lazy) + -- If not, we don't need to. For example: + -- f p@(x,y) = (p,y) -- S(AL) + -- g a b = f (a,b) + -- It's vital that we don't calculate Absent for a! + dmd_ds = case res_dmd of + Box (Eval ds) -> mapDmds box ds + Eval ds -> ds + other -> Poly Top + + -- ds can be empty, when we are just seq'ing the thing + -- If so we must make up a suitable bunch of demands + arg_ds = case dmd_ds of + Poly d -> replicate arity d + Prod ds -> ASSERT( ds `lengthIs` arity ) ds + + in + mkDmdType emptyDmdEnv arg_ds con_res + -- Must remember whether it's a product, hence con_res, not TopRes + else + topDmdType + +------ IMPORTED FUNCTION + | isGlobalId var, -- Imported function + let StrictSig dmd_ty = idNewStrictness var + = if dmdTypeDepth dmd_ty <= call_depth then -- Saturated, so unleash the demand + dmd_ty + else + topDmdType + +------ LOCAL LET/REC BOUND THING + | Just (StrictSig dmd_ty, top_lvl) <- lookupVarEnv sigs var + = let + fn_ty | dmdTypeDepth dmd_ty <= call_depth = dmd_ty + | otherwise = deferType dmd_ty + -- NB: it's important to use deferType, and not just return topDmdType + -- Consider let { f x y = p + x } in f 1 + -- The application isn't saturated, but we must nevertheless propagate + -- a lazy demand for p! + in + addVarDmd top_lvl fn_ty var dmd + +------ LOCAL NON-LET/REC BOUND THING + | otherwise -- Default case + = unitVarDmd var dmd + + where + (call_depth, res_dmd) = splitCallDmd dmd +\end{code} + + +%************************************************************************ +%* * +\subsection{Demands} +%* * +%************************************************************************ + +\begin{code} +splitCallDmd :: Demand -> (Int, Demand) +splitCallDmd (Call d) = case splitCallDmd d of + (n, r) -> (n+1, r) +splitCallDmd d = (0, d) + +vanillaCall :: Arity -> Demand +vanillaCall 0 = evalDmd +vanillaCall n = Call (vanillaCall (n-1)) + +deferType :: DmdType -> DmdType +deferType (DmdType fv _ _) = DmdType (deferEnv fv) [] TopRes + -- Notice that we throw away info about both arguments and results + -- For example, f = let ... in \x -> x + -- We don't want to get a stricness type V->T for f. + -- Peter?? + +deferEnv :: DmdEnv -> DmdEnv +deferEnv fv = mapVarEnv defer fv + + +---------------- +argDemand :: Demand -> Demand +-- The 'Defer' demands are just Lazy at function boundaries +-- Ugly! Ask John how to improve it. +argDemand Top = lazyDmd +argDemand (Defer d) = lazyDmd +argDemand (Eval ds) = Eval (mapDmds argDemand ds) +argDemand (Box Bot) = evalDmd +argDemand (Box d) = box (argDemand d) +argDemand Bot = Abs -- Don't pass args that are consumed (only) by bottom +argDemand d = d +\end{code} + +\begin{code} +------------------------- +-- Consider (if x then y else []) with demand V +-- Then the first branch gives {y->V} and the second +-- *implicitly* has {y->A}. So we must put {y->(V `lub` A)} +-- in the result env. +lubType (DmdType fv1 ds1 r1) (DmdType fv2 ds2 r2) + = DmdType lub_fv2 (lub_ds ds1 ds2) (r1 `lubRes` r2) + where + lub_fv = plusUFM_C lub fv1 fv2 + lub_fv1 = modifyEnv (not (isBotRes r1)) absLub fv2 fv1 lub_fv + lub_fv2 = modifyEnv (not (isBotRes r2)) absLub fv1 fv2 lub_fv1 + -- lub is the identity for Bot + + -- Extend the shorter argument list to match the longer + lub_ds (d1:ds1) (d2:ds2) = lub d1 d2 : lub_ds ds1 ds2 + lub_ds [] [] = [] + lub_ds ds1 [] = map (`lub` resTypeArgDmd r2) ds1 + lub_ds [] ds2 = map (resTypeArgDmd r1 `lub`) ds2 + +----------------------------------- +-- (t1 `bothType` t2) takes the argument/result info from t1, +-- using t2 just for its free-var info +-- NB: Don't forget about r2! It might be BotRes, which is +-- a bottom demand on all the in-scope variables. +-- Peter: can this be done more neatly? +bothType (DmdType fv1 ds1 r1) (DmdType fv2 ds2 r2) + = DmdType both_fv2 ds1 (r1 `bothRes` r2) + where + both_fv = plusUFM_C both fv1 fv2 + both_fv1 = modifyEnv (isBotRes r1) (`both` Bot) fv2 fv1 both_fv + both_fv2 = modifyEnv (isBotRes r2) (`both` Bot) fv1 fv2 both_fv1 + -- both is the identity for Abs +\end{code} + + +\begin{code} +lubRes BotRes r = r +lubRes r BotRes = r +lubRes RetCPR RetCPR = RetCPR +lubRes r1 r2 = TopRes + +-- If either diverges, the whole thing does +-- Otherwise take CPR info from the first +bothRes r1 BotRes = BotRes +bothRes r1 r2 = r1 +\end{code} + +\begin{code} +modifyEnv :: Bool -- No-op if False + -> (Demand -> Demand) -- The zapper + -> DmdEnv -> DmdEnv -- Env1 and Env2 + -> DmdEnv -> DmdEnv -- Transform this env + -- Zap anything in Env1 but not in Env2 + -- Assume: dom(env) includes dom(Env1) and dom(Env2) + +modifyEnv need_to_modify zapper env1 env2 env + | need_to_modify = foldr zap env (keysUFM (env1 `minusUFM` env2)) + | otherwise = env + where + zap uniq env = addToUFM_Directly env uniq (zapper current_val) + where + current_val = expectJust "modifyEnv" (lookupUFM_Directly env uniq) +\end{code} + + +%************************************************************************ +%* * +\subsection{LUB and BOTH} +%* * +%************************************************************************ + +\begin{code} +lub :: Demand -> Demand -> Demand + +lub Bot d2 = d2 +lub Abs d2 = absLub d2 +lub Top d2 = Top +lub (Defer ds1) d2 = defer (Eval ds1 `lub` d2) + +lub (Call d1) (Call d2) = Call (d1 `lub` d2) +lub d1@(Call _) (Box d2) = d1 `lub` d2 -- Just strip the box +lub d1@(Call _) d2@(Eval _) = d2 -- Presumably seq or vanilla eval +lub d1@(Call _) d2 = d2 `lub` d1 -- Bot, Abs, Top + +-- For the Eval case, we use these approximation rules +-- Box Bot <= Eval (Box Bot ...) +-- Box Top <= Defer (Box Bot ...) +-- Box (Eval ds) <= Eval (map Box ds) +lub (Eval ds1) (Eval ds2) = Eval (ds1 `lubs` ds2) +lub (Eval ds1) (Box Bot) = Eval (mapDmds (`lub` Box Bot) ds1) +lub (Eval ds1) (Box (Eval ds2)) = Eval (ds1 `lubs` mapDmds box ds2) +lub (Eval ds1) (Box Abs) = deferEval (mapDmds (`lub` Box Bot) ds1) +lub d1@(Eval _) d2 = d2 `lub` d1 -- Bot,Abs,Top,Call,Defer + +lub (Box d1) (Box d2) = box (d1 `lub` d2) +lub d1@(Box _) d2 = d2 `lub` d1 + +lubs = zipWithDmds lub + +--------------------- +-- box is the smart constructor for Box +-- It computes <B,bot> & d +-- INVARIANT: (Box d) => d = Bot, Abs, Eval +-- Seems to be no point in allowing (Box (Call d)) +box (Call d) = Call d -- The odd man out. Why? +box (Box d) = Box d +box (Defer _) = lazyDmd +box Top = lazyDmd -- Box Abs and Box Top +box Abs = lazyDmd -- are the same <B,L> +box d = Box d -- Bot, Eval + +--------------- +defer :: Demand -> Demand + +-- defer is the smart constructor for Defer +-- The idea is that (Defer ds) = <U(ds), L> +-- +-- It specifies what happens at a lazy function argument +-- or a lambda; the L* operator +-- Set the strictness part to L, but leave +-- the boxity side unaffected +-- It also ensures that Defer (Eval [LLLL]) = L + +defer Bot = Abs +defer Abs = Abs +defer Top = Top +defer (Call _) = lazyDmd -- Approximation here? +defer (Box _) = lazyDmd +defer (Defer ds) = Defer ds +defer (Eval ds) = deferEval ds + +-- deferEval ds = defer (Eval ds) +deferEval ds | allTop ds = Top + | otherwise = Defer ds + +--------------------- +absLub :: Demand -> Demand +-- Computes (Abs `lub` d) +-- For the Bot case consider +-- f x y = if ... then x else error x +-- Then for y we get Abs `lub` Bot, and we really +-- want Abs overall +absLub Bot = Abs +absLub Abs = Abs +absLub Top = Top +absLub (Call _) = Top +absLub (Box _) = Top +absLub (Eval ds) = Defer (absLubs ds) -- Or (Defer ds)? +absLub (Defer ds) = Defer (absLubs ds) -- Or (Defer ds)? + +absLubs = mapDmds absLub + +--------------- +both :: Demand -> Demand -> Demand + +both Abs d2 = d2 + +both Bot Bot = Bot +both Bot Abs = Bot +both Bot (Eval ds) = Eval (mapDmds (`both` Bot) ds) + -- Consider + -- f x = error x + -- From 'error' itself we get demand Bot on x + -- From the arg demand on x we get + -- x :-> evalDmd = Box (Eval (Poly Abs)) + -- So we get Bot `both` Box (Eval (Poly Abs)) + -- = Seq Keep (Poly Bot) + -- + -- Consider also + -- f x = if ... then error (fst x) else fst x + -- Then we get (Eval (Box Bot, Bot) `lub` Eval (SA)) + -- = Eval (SA) + -- which is what we want. +both Bot d = errDmd + +both Top Bot = errDmd +both Top Abs = Top +both Top Top = Top +both Top (Box d) = Box d +both Top (Call d) = Call d +both Top (Eval ds) = Eval (mapDmds (`both` Top) ds) +both Top (Defer ds) -- = defer (Top `both` Eval ds) + -- = defer (Eval (mapDmds (`both` Top) ds)) + = deferEval (mapDmds (`both` Top) ds) + + +both (Box d1) (Box d2) = box (d1 `both` d2) +both (Box d1) d2@(Call _) = box (d1 `both` d2) +both (Box d1) d2@(Eval _) = box (d1 `both` d2) +both (Box d1) (Defer d2) = Box d1 +both d1@(Box _) d2 = d2 `both` d1 + +both (Call d1) (Call d2) = Call (d1 `both` d2) +both (Call d1) (Eval ds2) = Call d1 -- Could do better for (Poly Bot)? +both (Call d1) (Defer ds2) = Call d1 -- Ditto +both d1@(Call _) d2 = d1 `both` d1 + +both (Eval ds1) (Eval ds2) = Eval (ds1 `boths` ds2) +both (Eval ds1) (Defer ds2) = Eval (ds1 `boths` mapDmds defer ds2) +both d1@(Eval ds1) d2 = d2 `both` d1 + +both (Defer ds1) (Defer ds2) = deferEval (ds1 `boths` ds2) +both d1@(Defer ds1) d2 = d2 `both` d1 + +boths = zipWithDmds both +\end{code} + + + +%************************************************************************ +%* * +\subsection{Miscellaneous +%* * +%************************************************************************ + + +\begin{code} +#ifdef OLD_STRICTNESS +get_changes binds = vcat (map get_changes_bind binds) + +get_changes_bind (Rec pairs) = vcat (map get_changes_pr pairs) +get_changes_bind (NonRec id rhs) = get_changes_pr (id,rhs) + +get_changes_pr (id,rhs) + = get_changes_var id $$ get_changes_expr rhs + +get_changes_var var + | isId var = get_changes_str var $$ get_changes_dmd var + | otherwise = empty + +get_changes_expr (Type t) = empty +get_changes_expr (Var v) = empty +get_changes_expr (Lit l) = empty +get_changes_expr (Note n e) = get_changes_expr e +get_changes_expr (App e1 e2) = get_changes_expr e1 $$ get_changes_expr e2 +get_changes_expr (Lam b e) = {- get_changes_var b $$ -} get_changes_expr e +get_changes_expr (Let b e) = get_changes_bind b $$ get_changes_expr e +get_changes_expr (Case e b a) = get_changes_expr e $$ {- get_changes_var b $$ -} vcat (map get_changes_alt a) + +get_changes_alt (con,bs,rhs) = {- vcat (map get_changes_var bs) $$ -} get_changes_expr rhs + +get_changes_str id + | new_better && old_better = empty + | new_better = message "BETTER" + | old_better = message "WORSE" + | otherwise = message "INCOMPARABLE" + where + message word = text word <+> text "strictness for" <+> ppr id <+> info + info = (text "Old" <+> ppr old) $$ (text "New" <+> ppr new) + new = squashSig (idNewStrictness id) -- Don't report spurious diffs that the old + -- strictness analyser can't track + old = newStrictnessFromOld (idName id) (idArity id) (idStrictness id) (idCprInfo id) + old_better = old `betterStrictness` new + new_better = new `betterStrictness` old + +get_changes_dmd id + | isUnLiftedType (idType id) = empty -- Not useful + | new_better && old_better = empty + | new_better = message "BETTER" + | old_better = message "WORSE" + | otherwise = message "INCOMPARABLE" + where + message word = text word <+> text "demand for" <+> ppr id <+> info + info = (text "Old" <+> ppr old) $$ (text "New" <+> ppr new) + new = squashDmd (argDemand (idNewDemandInfo id)) -- To avoid spurious improvements + -- A bit of a hack + old = newDemand (idDemandInfo id) + new_better = new `betterDemand` old + old_better = old `betterDemand` new + +betterStrictness :: StrictSig -> StrictSig -> Bool +betterStrictness (StrictSig t1) (StrictSig t2) = betterDmdType t1 t2 + +betterDmdType t1 t2 = (t1 `lubType` t2) == t2 + +betterDemand :: Demand -> Demand -> Bool +-- If d1 `better` d2, and d2 `better` d2, then d1==d2 +betterDemand d1 d2 = (d1 `lub` d2) == d2 + +squashSig (StrictSig (DmdType fv ds res)) + = StrictSig (DmdType emptyDmdEnv (map squashDmd ds) res) + where + -- squash just gets rid of call demands + -- which the old analyser doesn't track +squashDmd (Call d) = evalDmd +squashDmd (Box d) = Box (squashDmd d) +squashDmd (Eval ds) = Eval (mapDmds squashDmd ds) +squashDmd (Defer ds) = Defer (mapDmds squashDmd ds) +squashDmd d = d +#endif +\end{code} |