X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=ghc%2Fcompiler%2Fstranal%2FDmdAnal.lhs;h=e02bf5e1ad87f991ad0fa38685784fc781004799;hb=0bffc410964e1688ad80d277d53400659e697ab5;hp=31ebc7b141079e644c85838dd26b5324c06c2740;hpb=fdc830018cb48210e2ca441942de8eae8e6aedd2;p=ghc-hetmet.git diff --git a/ghc/compiler/stranal/DmdAnal.lhs b/ghc/compiler/stranal/DmdAnal.lhs index 31ebc7b..e02bf5e 100644 --- a/ghc/compiler/stranal/DmdAnal.lhs +++ b/ghc/compiler/stranal/DmdAnal.lhs @@ -7,33 +7,56 @@ ----------------- \begin{code} -module DmdAnal ( dmdAnalPgm ) where +module DmdAnal ( dmdAnalPgm, dmdAnalTopRhs, + both {- needed by WwLib -} + ) where #include "HsVersions.h" -import CmdLineOpts ( DynFlags, DynFlag(..) ) +import CmdLineOpts ( DynFlags, DynFlag(..), opt_MaxWorkerArgs ) import NewDemand -- All of it import CoreSyn +import PprCore +import CoreUtils ( exprIsValue, exprArity ) import DataCon ( dataConTyCon ) import TyCon ( isProductTyCon, isRecursiveTyCon ) -import Id ( Id, idInfo, idArity, idStrictness, idCprInfo, idDemandInfo, - modifyIdInfo, isDataConId, isImplicitId ) -import IdInfo ( newStrictnessInfo, setNewStrictnessInfo, mkNewStrictnessInfo, - newDemandInfo, setNewDemandInfo, newDemand +import Id ( Id, idType, idInlinePragma, + isDataConId, 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 UniqFM ( plusUFM_C, addToUFM_Directly, keysUFM, minusUFM ) +import UniqFM ( plusUFM_C, addToUFM_Directly, lookupUFM_Directly, + keysUFM, minusUFM, ufmToList, filterUFM ) +import Type ( isUnLiftedType ) import CoreLint ( showPass, endPass ) -import ErrUtils ( dumpIfSet_dyn ) -import Util ( mapAccumL, mapAccumR, zipWithEqual ) -import BasicTypes ( Arity ) -import Maybes ( orElse ) +import Util ( mapAndUnzip, mapAccumL, mapAccumR, lengthIs ) +import BasicTypes ( Arity, TopLevelFlag(..), isTopLevel, isNeverActive, + RecFlag(..), isRec ) +import Maybes ( orElse, expectJust ) import Outputable -import FastTypes \end{code} -ToDo: set a noinline pragma on bottoming Ids +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. + +\begin{code} +instance Outputable TopLevelFlag where + ppr flag = empty +\end{code} %************************************************************************ %* * @@ -43,20 +66,19 @@ ToDo: set a noinline pragma on bottoming Ids \begin{code} dmdAnalPgm :: DynFlags -> [CoreBind] -> IO [CoreBind] -#ifndef DEBUG - -dmdAnalPgm dflags binds = return binds - -#else - dmdAnalPgm dflags binds = do { showPass dflags "Demand analysis" ; - let { binds_plus_dmds = do_prog binds ; - dmd_changes = get_changes binds_plus_dmds } ; + 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 @@ -67,22 +89,36 @@ dmdAnalTopBind :: SigEnv -> CoreBind -> (SigEnv, CoreBind) dmdAnalTopBind sigs (NonRec id rhs) - | isImplicitId id -- Don't touch the info on constructors, selectors etc - = (sigs, NonRec id rhs) -- It's pre-computed in MkId.lhs - | otherwise = let - (sig, rhs_env, (id', rhs')) = downRhs sigs (id, rhs) - sigs' = extendSigEnv sigs id sig + ( _, _, (_, 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 - (sigs', NonRec id' rhs') + (sigs2, NonRec id2 rhs2) dmdAnalTopBind sigs (Rec pairs) = let - (sigs', _, pairs') = dmdFix sigs pairs + (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, rhs') + where + arity = exprArity rhs + (rhs_ty, rhs') = dmdAnal emptySigEnv (vanillaCall arity) rhs + sig = mkTopSigTy rhs rhs_ty +\end{code} %************************************************************************ %* * @@ -91,153 +127,187 @@ dmdAnalTopBind sigs (Rec pairs) %************************************************************************ \begin{code} -dmdAnal :: SigEnv -> Demand -> CoreExpr -> (DmdType, DmdEnv, CoreExpr) +dmdAnal :: SigEnv -> Demand -> CoreExpr -> (DmdType, CoreExpr) -dmdAnal sigs Abs e = (DmdRes TopRes, emptyDmdEnv, e) +dmdAnal sigs Abs e = (topDmdType, e) -dmdAnal sigs Lazy e = let - (res_ty, dmd_env, e') = dmdAnal sigs Eval e - in - (res_ty, lazify dmd_env, 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 (inconvenient) + -- 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 (Var var) - = (res_ty, - blackHoleEnv res_ty (unitDmdEnv var dmd), - Var var) - where - res_ty = dmdTransform sigs var dmd - dmdAnal sigs dmd (Lit lit) - = (topDmdType, emptyDmdEnv, Lit lit) + = (topDmdType, Lit lit) + +dmdAnal sigs dmd (Var var) + = (dmdTransform sigs var dmd, Var var) dmdAnal sigs dmd (Note n e) - = (dmd_ty, dmd_env, Note n e') + = (dmd_ty, Note n e') where - (dmd_ty, dmd_env, e') = dmdAnal sigs dmd e + (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, fun_env, App fun' (Type ty)) + = (fun_ty, App fun' (Type ty)) where - (fun_ty, fun_env, fun') = dmdAnal sigs dmd fun + (fun_ty, fun') = dmdAnal sigs dmd fun -dmdAnal sigs dmd (App fun arg) -- Non-type arguments +-- 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_env, fun') = dmdAnal sigs (Call dmd) fun - (arg_ty, arg_env, arg') = dmdAnal sigs arg_dmd arg - (arg_dmd, res_ty) = splitDmdTy fun_ty + (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, - blackHoleEnv res_ty (fun_env `bothEnv` arg_env), - App fun' arg') + (res_ty `bothType` arg_ty, App fun' arg') dmdAnal sigs dmd (Lam var body) | isTyVar var = let - (body_ty, body_env, body') = dmdAnal sigs dmd body + (body_ty, body') = dmdAnal sigs dmd body in - (body_ty, body_env, Lam var body') + (body_ty, Lam var body') - | otherwise - = let - body_dmd = case dmd of - Call dmd -> dmd - other -> Lazy -- Conservative + | 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') - (body_ty, body_env, body') = dmdAnal sigs body_dmd body - (lam_env, var') = annotateBndr body_env var + | 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 - (DmdFun (idNewDemandInfo var') body_ty, - body_env `delDmdEnv` var, - Lam var' body') + (deferType lam_ty, Lam var' body') dmdAnal sigs dmd (Case scrut case_bndr [alt@(DataAlt dc,bndrs,rhs)]) | let tycon = dataConTyCon dc, isProductTyCon tycon, not (isRecursiveTyCon tycon) = let - bndr_ids = filter isId bndrs - (alt_ty, alt_env, alt') = dmdAnalAlt sigs dmd alt - (_, scrut_env, scrut') = dmdAnal sigs scrut_dmd scrut - (alt_env2, case_bndr') = annotateBndr alt_env case_bndr - (_, bndrs', _) = alt' - scrut_dmd = Seq Drop [idNewDemandInfo b | b <- bndrs', isId b] + 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_ty, - alt_env2 `bothEnv` scrut_env, - Case scrut' case_bndr' [alt']) + (alt_ty1 `bothType` scrut_ty, Case scrut' case_bndr' [alt']) dmdAnal sigs dmd (Case scrut case_bndr alts) = let - (alt_tys, alt_envs, alts') = unzip3 (map (dmdAnalAlt sigs dmd) alts) - (scrut_ty, scrut_env, scrut') = dmdAnal sigs Eval scrut - (alt_env2, case_bndr') = annotateBndr (foldr1 lubEnv alt_envs) case_bndr + (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 - (foldr1 lubDmdTy alt_tys, - alt_env2 `bothEnv` scrut_env, - Case scrut' case_bndr' alts') +-- pprTrace "dmdAnal:Case" (ppr alts $$ ppr alt_tys) + (alt_ty `bothType` scrut_ty, Case scrut' case_bndr' alts') dmdAnal sigs dmd (Let (NonRec id rhs) body) - | idArity id == 0 -- A thunk; analyse the body first, then the thunk = let - (body_ty, body_env, body') = dmdAnal sigs dmd body - (rhs_ty, rhs_env, rhs') = dmdAnal sigs (lookupDmd body_env id) rhs - (body_env1, id1) = annotateBndr body_env id + (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 - (body_ty, body_env1 `bothEnv` rhs_env, Let (NonRec id1 rhs') body') - - | otherwise -- A function; analyse the function first, then the body - = let - (sig, rhs_env, (id1, rhs')) = downRhs sigs (id, rhs) - sigs' = extendSigEnv sigs id sig - (body_ty, body_env, body') = dmdAnal sigs' dmd body - rhs_env1 = weaken body_env id rhs_env - (body_env1, id2) = annotateBndr body_env id1 - in - (body_ty, body_env1 `bothEnv` rhs_env1, Let (NonRec id2 rhs') body') + -- 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', rhs_envs, pairs') = dmdFix sigs pairs - (body_ty, body_env, body') = dmdAnal sigs' dmd body - - weakened_rhs_envs = zipWithEqual "dmdAnal:Let" (weaken body_env) bndrs rhs_envs - -- I saw occasions where it was really worth using the - -- call demands on the Ids to propagate demand info - -- on the free variables. 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 this is strict in x. - - rhs_env1 = foldr1 bothEnv weakened_rhs_envs - - result_env = delDmdEnvList (body_env `bothEnv` rhs_env1) bndrs + 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_ty, result_env, Let (Rec pairs') body') -\end{code} + (body_ty2, Let (Rec pairs') body') + -\begin{code} dmdAnalAlt sigs dmd (con,bndrs,rhs) = let - (rhs_ty, rhs_env, rhs') = dmdAnal sigs dmd rhs - (alt_env, bndrs') = annotateBndrs rhs_env bndrs + (rhs_ty, rhs') = dmdAnal sigs dmd rhs + (alt_ty, bndrs') = annotateBndrs rhs_ty bndrs in - (rhs_ty, alt_env, (con, bndrs', rhs')) + (alt_ty, (con, bndrs', rhs')) \end{code} %************************************************************************ @@ -247,46 +317,90 @@ dmdAnalAlt sigs dmd (con,bndrs,rhs) %************************************************************************ \begin{code} -dmdFix :: SigEnv -- Does not include bindings for this binding +dmdFix :: TopLevelFlag + -> SigEnv -- Does not include bindings for this binding -> [(Id,CoreExpr)] - -> (SigEnv, - [DmdEnv], -- Demands from RHSs + -> (SigEnv, DmdEnv, [(Id,CoreExpr)]) -- Binders annotated with stricness info -dmdFix sigs pairs - = loop (map initial_sig pairs) pairs +dmdFix top_lvl sigs orig_pairs + = loop 1 initial_sigs orig_pairs where - loop id_sigs pairs - | id_sigs == id_sigs' = (sigs', rhs_envs, pairs') - | otherwise = loop id_sigs' pairs' + 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 - extra_sigs = [(id,sig) | ((id,_),sig) <- pairs `zip` id_sigs] - sigs' = extendSigEnvList sigs extra_sigs - (id_sigs', rhs_envs, pairs') = unzip3 (map (downRhs sigs') pairs) + 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.) - initial_sig (id,_) = idNewStrictness_maybe id `orElse` botSig - - -downRhs :: SigEnv -> (Id, CoreExpr) - -> (StrictSig, DmdEnv, (Id, CoreExpr)) --- On the way down, compute a strictness signature --- for the function. Keep its annotated RHS and dmd env --- for use on the way up --- The demand-env is that computed for a vanilla call. - -downRhs sigs (id, rhs) - = (sig, rhs_env, (id', rhs')) + -- 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 - (rhs_ty, rhs_env, rhs') = dmdAnal sigs (vanillaCall arity) rhs - sig = mkStrictSig arity rhs_ty - id' = id `setIdNewStrictness` sig + 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, ppr id ) + 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} @@ -294,122 +408,301 @@ downRhs sigs (id, rhs) %************************************************************************ \begin{code} -data DmdEnv - = DmdEnv (VarEnv Demand) -- All the explicitly mentioned variables - Bool -- True <=> all the others are Bot - -- False <=> all the others are Abs - -emptyDmdEnv = DmdEnv emptyVarEnv False -unitDmdEnv var dmd = DmdEnv (unitVarEnv var dmd) False - -lookupDmd :: DmdEnv -> Var -> Demand -lookupDmd (DmdEnv env bh) var = lookupVarEnv env var `orElse` deflt - where - deflt | bh = Bot - | otherwise = Abs - -delDmdEnv :: DmdEnv -> Var -> DmdEnv -delDmdEnv (DmdEnv env b) var = DmdEnv (env `delVarEnv` var) b - -delDmdEnvList :: DmdEnv -> [Var] -> DmdEnv -delDmdEnvList (DmdEnv env b) vars = DmdEnv (env `delVarEnvList` vars) b - +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} -blackHoleEnv :: DmdType -> DmdEnv -> DmdEnv -blackHoleEnv (DmdRes BotRes) (DmdEnv env _) = DmdEnv env True -blackHoleEnv other env = env +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. -bothEnv (DmdEnv env1 b1) (DmdEnv env2 b2) - = DmdEnv both_env2 (b1 || b2) - where - both_env = plusUFM_C both env1 env2 - both_env1 = modifyEnv b1 Bot env2 env1 both_env - both_env2 = modifyEnv b2 Bot env1 env2 both_env1 -lubEnv (DmdEnv env1 b1) (DmdEnv env2 b2) - = DmdEnv lub_env2 (b1 && b2) - where - lub_env = plusUFM_C lub env1 env2 - lub_env1 = modifyEnv (not b1) Lazy env2 env1 lub_env - lub_env2 = modifyEnv (not b2) Lazy env1 env2 lub_env1 - -modifyEnv :: Bool -- No-op if False - -> Demand -- The zap value - -> VarEnv Demand -> VarEnv Demand -- Env1 and Env2 - -> VarEnv Demand -> VarEnv Demand -- Transform this env - -- Zap anything in Env1 but not in Env2 - -- Assume: dom(env) includes dom(Env1) and dom(Env2) +\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) -modifyEnv need_to_modify zap_value env1 env2 env - | need_to_modify = foldr zap env (keysUFM (env1 `minusUFM` env2)) - | otherwise = env + | otherwise + = (lazy_fv, mkStrictSig dmd_ty) where - zap uniq env = addToUFM_Directly env uniq zap_value + 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 (exprIsValue rhs || thunk_cpr_ok) +\end{code} -annotateBndr :: DmdEnv -> Var -> (DmdEnv, Var) --- The returned env has the var deleted --- The returned var is annotated with demand info -annotateBndr dmd_env var - | isTyVar var = (dmd_env, var) - | otherwise = (dmd_env `delDmdEnv` var, setIdNewDemandInfo var (lookupDmd dmd_env var)) +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. -annotateBndrs = mapAccumR annotateBndr - -weaken :: DmdEnv -- How the Id is used in its scope - -> Id - -> DmdEnv -- The RHS env for the Id, assuming a vanilla call demand - -> DmdEnv -- The RHS env given the actual demand --- Consider let f = \x -> R in B --- The vanilla call demand is C(V), and that's what we use to --- compute f's strictness signature. If the *actual* demand on --- f from B is less than this, we must weaken, or lazify, the --- demands in R to match this - -weaken body_env id rhs_env - | depth >= idArity id -- Enough demand - = rhs_env - | otherwise -- Not enough demand - = lazify rhs_env +\begin{code} +setUnpackStrategy :: [Demand] -> [Demand] +setUnpackStrategy ds + = snd (go (opt_MaxWorkerArgs - nonAbsentArgs ds) ds) where - (depth,_) = splitCallDmd (lookupDmd body_env id) - -lazify (DmdEnv env _) = DmdEnv (mapVarEnv (\_ -> Lazy) env) False + 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{Demand types} +\subsection{Strictness signatures and types} %* * %************************************************************************ \begin{code} splitDmdTy :: DmdType -> (Demand, DmdType) -- Split off one function argument -splitDmdTy (DmdFun dmd res_ty) = (dmd, res_ty) -splitDmdTy (DmdRes TopRes) = (topDmd, topDmdType) -splitDmdTy (DmdRes BotRes) = (Abs, DmdRes BotRes) - -- We already have a suitable demand on all - -- free vars, so no need to add more! -splitDmdTy (DmdRes RetCPR) = panic "splitDmdTy" +-- 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} -------------------------- -dmdTypeRes :: DmdType -> Result -dmdTypeRes (DmdFun dmd res_ty) = dmdTypeRes res_ty -dmdTypeRes (DmdRes res) = res +\begin{code} +unitVarDmd var dmd = DmdType (unitVarEnv var dmd) [] TopRes -------------------------- -lubDmdTy :: DmdType -> DmdType -> DmdType -lubDmdTy (DmdFun d1 t1) (DmdFun d2 t2) = DmdFun (d1 `lub` d2) (t1 `lubDmdTy` t2) -lubDmdTy (DmdRes r1) (DmdRes r2) = DmdRes (r1 `lubRes` r2) -lubDmdTy t1 t2 = topDmdType +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 -------------------------- -lubRes BotRes r = r -lubRes r BotRes = r -lubRes RetCPR RetCPR = RetCPR -lubRes r1 r2 = TopRes -\end{code} +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} %************************************************************************ %* * @@ -418,43 +711,113 @@ lubRes r1 r2 = TopRes %************************************************************************ \begin{code} -type SigEnv = VarEnv StrictSig +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 = extendVarEnv + +extendSigEnv :: TopLevelFlag -> SigEnv -> Id -> StrictSig -> SigEnv +extendSigEnv top_lvl env var sig = extendVarEnv env var (sig, top_lvl) + extendSigEnvList = extendVarEnvList -lookupSig sigs v = case lookupVarEnv sigs v of - Just sig -> Just sig - Nothing -> idNewStrictness_maybe v + +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 +-- +-- NOTE: see notes [CPR-AND-STRICTNESS] +-- +-- 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) + 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 - | isDataConId var, -- Data constructor - Seq k ds <- res_dmd, -- and the demand looks inside its fields - StrictSig arity dmd_ty <- idNewStrictness var, -- It must have a strictness sig - length ds == arity -- It's saturated - = mkDmdFun ds (dmdTypeRes dmd_ty) - -- Need to extract whether it's a product - - | Just (StrictSig arity dmd_ty) <- lookupSig sigs var, - arity <= depth -- Saturated function; - = dmd_ty -- Unleash the demand! +------ DATA CONSTRUCTOR + | isDataConId 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 - = topDmdType + = unitVarDmd var dmd where - (depth, res_dmd) = splitCallDmd dmd - -betterStrict :: StrictSig -> StrictSig -> Bool -betterStrict (StrictSig ar1 t1) (StrictSig ar2 t2) - = (ar1 >= ar2) && (t1 `betterDmdType` t2) - -betterDmdType t1 t2 = (t1 `lubDmdTy` t2) == t2 + (call_depth, res_dmd) = splitCallDmd dmd \end{code} @@ -471,81 +834,254 @@ splitCallDmd (Call d) = case splitCallDmd d of splitCallDmd d = (0, d) vanillaCall :: Arity -> Demand -vanillaCall 0 = Eval +vanillaCall 0 = evalDmd vanillaCall n = Call (vanillaCall (n-1)) ------------------------------------ -lub :: Demand -> Demand -> Demand - -lub Bot d = d - -lub Lazy d = Lazy - -lub Err Bot = Err -lub Err d = d +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} -lub Abs Bot = Abs -lub Abs Err = Abs -lub Abs Abs = Abs -lub Abs d = d +\begin{code} +betterStrictness :: StrictSig -> StrictSig -> Bool +betterStrictness (StrictSig t1) (StrictSig t2) = betterDmdType t1 t2 -lub Eval Abs = Lazy -lub Eval Lazy = Lazy -lub Eval (Seq k ds) = Seq Keep ds -lub Eval d = Eval +betterDmdType t1 t2 = (t1 `lubType` t2) == t2 -lub (Call d1) (Call d2) = Call (lub d1 d2) +betterDemand :: Demand -> Demand -> Bool +-- If d1 `better` d2, and d2 `better` d2, then d1==d2 +betterDemand d1 d2 = (d1 `lub` d2) == d2 +\end{code} -lub (Seq k1 ds1) (Seq k2 ds2) = Seq (k1 `vee` k2) - (zipWithEqual "lub" lub ds1 ds2) +\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 --- The last clauses deal with the remaining cases for Call and Seq -lub d1@(Call _) d2@(Seq _ _) = pprPanic "lub" (ppr d1 $$ ppr d2) -lub d1 d2 = lub d2 d1 + -- 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 ----------------------------------- -vee :: Keepity -> Keepity -> Keepity -vee Drop Drop = Drop -vee k1 k2 = Keep +-- (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} ------------------------------------ -both :: Demand -> Demand -> Demand -both Bot d = Bot +\begin{code} +lubRes BotRes r = r +lubRes r BotRes = r +lubRes RetCPR RetCPR = RetCPR +lubRes r1 r2 = TopRes -both Abs Bot = Bot -both Abs d = d +-- If either diverges, the whole thing does +-- Otherwise take CPR info from the first +bothRes r1 BotRes = BotRes +bothRes r1 r2 = r1 +\end{code} -both Err Bot = Bot -both Err Abs = Err -both Err d = d +\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) -both Lazy Bot = Bot -both Lazy Abs = Lazy -both Lazy Err = Lazy -both Lazy (Seq k ds) = Seq Keep ds -both Lazy d = d +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} -both Eval Bot = Bot -both Eval (Seq k ds) = Seq Keep ds -both Eval (Call d) = Call d -both Eval d = Eval -both (Seq k1 ds1) (Seq k2 ds2) = Seq (k1 `vee` k2) - (zipWithEqual "both" both ds1 ds2) +%************************************************************************ +%* * +\subsection{LUB and BOTH} +%* * +%************************************************************************ -both (Call d1) (Call d2) = Call (d1 `both` d2) +\begin{code} +lub :: Demand -> Demand -> Demand --- The last clauses deal with the remaining cases for Call and Seq -both d1@(Call _) d2@(Seq _ _) = pprPanic "both" (ppr d1 $$ ppr d2) -both d1 d2 = both d2 d1 +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 & 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 +box d = Box d -- Bot, Eval + +--------------- +defer :: Demand -> Demand + +-- defer is the smart constructor for Defer +-- The idea is that (Defer ds) = +-- +-- 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 -betterDemand :: Demand -> Demand -> Bool --- If d1 `better` d2, and d2 `better` d2, then d1==d2 -betterDemand d1 d2 = (d1 `lub` d2) == d2 +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 @@ -554,30 +1090,14 @@ betterDemand d1 d2 = (d1 `lub` d2) == d2 \begin{code} --- Move these to Id.lhs -idNewStrictness_maybe :: Id -> Maybe StrictSig -idNewStrictness :: Id -> StrictSig - -idNewStrictness_maybe id = newStrictnessInfo (idInfo id) -idNewStrictness id = idNewStrictness_maybe id `orElse` topSig - -setIdNewStrictness :: Id -> StrictSig -> Id -setIdNewStrictness id sig = modifyIdInfo (`setNewStrictnessInfo` sig) id - -idNewDemandInfo :: Id -> Demand -idNewDemandInfo id = newDemandInfo (idInfo id) - -setIdNewDemandInfo :: Id -> Demand -> Id -setIdNewDemandInfo id dmd = modifyIdInfo (`setNewDemandInfo` dmd) id -\end{code} - -\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 $$ get_changes_expr rhs +get_changes_pr (id,rhs) + = get_changes_var id $$ get_changes_expr rhs get_changes_var var | isId var = get_changes_str var $$ get_changes_dmd var @@ -588,11 +1108,11 @@ get_changes_expr (Var v) = empty get_changes_expr (Lit l) = empty get_changes_expr (Note n e) = get_changes_expr e get_changes_expr (App e1 e2) = get_changes_expr e1 $$ get_changes_expr e2 -get_changes_expr (Lam b e) = get_changes_var b $$ get_changes_expr e +get_changes_expr (Lam b e) = {- get_changes_var b $$ -} 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 $$ vcat (map get_changes_alt a) +get_changes_expr (Case e b a) = get_changes_expr e $$ {- 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_alt (con,bs,rhs) = {- vcat (map get_changes_var bs) $$ -} get_changes_expr rhs get_changes_str id | new_better && old_better = empty @@ -602,12 +1122,14 @@ get_changes_str id where message word = text word <+> text "strictness for" <+> ppr id <+> info info = (text "Old" <+> ppr old) $$ (text "New" <+> ppr new) - new = idNewStrictness id - old = mkNewStrictnessInfo (idArity id) (idStrictness id) (idCprInfo id) - old_better = old `betterStrict` new - new_better = new `betterStrict` old + 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" @@ -615,10 +1137,21 @@ get_changes_dmd id where message word = text word <+> text "demand for" <+> ppr id <+> info info = (text "Old" <+> ppr old) $$ (text "New" <+> ppr new) - new = idNewDemandInfo id + 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 -#endif /* DEBUG */ -\end{code} +#endif +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 +\end{code}