X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=ghc%2Fcompiler%2Fstranal%2FDmdAnal.lhs;h=c5cfb7b4bdedde682e5b88669b8305dfef7c07ab;hb=876b4ef2093cb9c104db33c7db1200b941b6d079;hp=a36ebbccd075ddccaf8d576fe27208813d2d487f;hpb=a32726a14f95b236413410bc6605f9e3cb6adae2;p=ghc-hetmet.git diff --git a/ghc/compiler/stranal/DmdAnal.lhs b/ghc/compiler/stranal/DmdAnal.lhs index a36ebbc..c5cfb7b 100644 --- a/ghc/compiler/stranal/DmdAnal.lhs +++ b/ghc/compiler/stranal/DmdAnal.lhs @@ -13,31 +13,34 @@ module DmdAnal ( dmdAnalPgm, dmdAnalTopRhs, #include "HsVersions.h" -import CmdLineOpts ( DynFlags, DynFlag(..), opt_MaxWorkerArgs ) +import DynFlags ( DynFlags, DynFlag(..) ) +import StaticFlags ( opt_MaxWorkerArgs ) import NewDemand -- All of it import CoreSyn import PprCore -import CoreUtils ( exprIsValue, exprArity ) +import CoreUtils ( exprIsHNF, exprIsTrivial, exprArity ) import DataCon ( dataConTyCon ) import TyCon ( isProductTyCon, isRecursiveTyCon ) import Id ( Id, idType, idInlinePragma, - isDataConId, isGlobalId, idArity, + isDataConWorkId, isGlobalId, idArity, #ifdef OLD_STRICTNESS - idDemandInfo, idStrictness, idCprInfo, + idDemandInfo, idStrictness, idCprInfo, idName, #endif idNewStrictness, idNewStrictness_maybe, setIdNewStrictness, idNewDemandInfo, idNewDemandInfo_maybe, - setIdNewDemandInfo, idName + 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 ) +import Type ( isUnLiftedType, coreEqType ) import CoreLint ( showPass, endPass ) import Util ( mapAndUnzip, mapAccumL, mapAccumR, lengthIs ) import BasicTypes ( Arity, TopLevelFlag(..), isTopLevel, isNeverActive, @@ -53,10 +56,6 @@ To think about * 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} %************************************************************************ %* * @@ -113,11 +112,18 @@ dmdAnalTopRhs :: CoreExpr -> (StrictSig, CoreExpr) -- a) appropriate strictness info -- b) the unfolding (decorated with stricntess info) dmdAnalTopRhs rhs - = (sig, rhs') + = (sig, rhs2) where - arity = exprArity rhs - (rhs_ty, rhs') = dmdAnal emptySigEnv (vanillaCall arity) rhs + 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} %************************************************************************ @@ -206,7 +212,7 @@ dmdAnal sigs dmd (Lam var body) in (deferType lam_ty, Lam var' body') -dmdAnal sigs dmd (Case scrut case_bndr [alt@(DataAlt dc,bndrs,rhs)]) +dmdAnal sigs dmd (Case scrut case_bndr ty [alt@(DataAlt dc,bndrs,rhs)]) | let tycon = dataConTyCon dc, isProductTyCon tycon, not (isRecursiveTyCon tycon) @@ -252,16 +258,16 @@ dmdAnal sigs dmd (Case scrut case_bndr [alt@(DataAlt dc,bndrs,rhs)]) (scrut_ty, scrut') = dmdAnal sigs scrut_dmd scrut in - (alt_ty1 `bothType` scrut_ty, Case scrut' case_bndr' [alt']) + (alt_ty1 `bothType` scrut_ty, Case scrut' case_bndr' ty [alt']) -dmdAnal sigs dmd (Case scrut case_bndr alts) +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' alts') + (alt_ty `bothType` scrut_ty, Case scrut' case_bndr' ty alts') dmdAnal sigs dmd (Let (NonRec id rhs) body) = let @@ -270,18 +276,18 @@ dmdAnal sigs dmd (Let (NonRec id rhs) body) (body_ty1, id2) = annotateBndr body_ty id1 body_ty2 = addLazyFVs body_ty1 lazy_fv in -#ifdef DEBUG - -- If the actual demand is better than the vanilla - -- demand, we might do better to re-analyse with the - -- stronger demand. - (let vanilla_dmd = vanillaCall (idArity id) - actual_dmd = idNewDemandInfo id2 - in - if actual_dmd `betterDemand` vanilla_dmd && actual_dmd /= vanilla_dmd then - pprTrace "dmdLet: better demand" (ppr id <+> vcat [text "vanilla" <+> ppr vanilla_dmd, - text "actual" <+> ppr actual_dmd]) - else \x -> x) -#endif + -- 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) @@ -306,8 +312,30 @@ dmdAnalAlt sigs dmd (con,bndrs,rhs) = let (rhs_ty, rhs') = dmdAnal sigs dmd rhs (alt_ty, bndrs') = annotateBndrs rhs_ty bndrs - in - (alt_ty, (con, bndrs', rhs')) + 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 = ; + -- ; 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} %************************************************************************ @@ -334,19 +362,27 @@ dmdFix top_lvl sigs orig_pairs -> [(Id,CoreExpr)] -> (SigEnv, DmdEnv, [(Id,CoreExpr)]) loop n sigs pairs - | all (same_sig sigs sigs') bndrs + | 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 + + | 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, emptyDmdEnv, orig_pairs) -- Safe output + (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 @@ -387,7 +423,9 @@ dmdAnalRhs top_lvl rec_flag sigs (id, rhs) 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 ) + (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 @@ -479,11 +517,10 @@ We can't start with 'not-demanded' because then consider 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. -ever_in -Instead, with the Nothing setting the first time round, we say -'yes t is demanded' the first time. +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, @@ -563,7 +600,7 @@ mk_sig_ty never_inline thunk_cpr_ok rhs (DmdType fv dmds res) res' = case res of RetCPR | ignore_cpr_info -> TopRes other -> res - ignore_cpr_info = not (exprIsValue rhs || thunk_cpr_ok) + ignore_cpr_info = not (exprIsHNF rhs || thunk_cpr_ok) \end{code} The unpack strategy determines whether we'll *really* unpack the argument, @@ -721,12 +758,15 @@ 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 +-- 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. --- --- NOTE: see notes [CPR-AND-STRICTNESS] +-- 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 @@ -735,12 +775,11 @@ extendSigsWithLam :: SigEnv -> Id -> SigEnv 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 -cprSig :: StrictSig -cprSig = StrictSig (mkDmdType emptyVarEnv [] RetCPR) - dmdTransform :: SigEnv -- The strictness environment -> Id -- The function @@ -752,7 +791,7 @@ dmdTransform :: SigEnv -- The strictness environment dmdTransform sigs var dmd ------ DATA CONSTRUCTOR - | isDataConId var -- Data constructor + | isDataConWorkId var -- Data constructor = let StrictSig dmd_ty = idNewStrictness var -- It must have a strictness sig DmdType _ _ con_res = dmd_ty @@ -848,26 +887,15 @@ 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 by bottom/err +argDemand Bot = Abs -- Don't pass args that are consumed (only) by bottom argDemand d = d \end{code} \begin{code} -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 -\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)} +-- *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) @@ -1133,7 +1161,15 @@ get_changes_dmd id old = newDemand (idDemandInfo id) new_better = new `betterDemand` old old_better = old `betterDemand` new -#endif + +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) @@ -1145,4 +1181,5 @@ 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}