X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=ghc%2Fcompiler%2FsimplCore%2FSimplUtils.lhs;h=1d9b9875ec53e942be019564b7d8e881040e9e56;hb=0534decda4b6b70236798075801e5f478bcc0aae;hp=21ebaa6c65505496dfe6e4b82d6a6395956ef45c;hpb=f659cb97f97051c2a5fa443e2baaa13fb5db87b9;p=ghc-hetmet.git diff --git a/ghc/compiler/simplCore/SimplUtils.lhs b/ghc/compiler/simplCore/SimplUtils.lhs index 21ebaa6..1d9b987 100644 --- a/ghc/compiler/simplCore/SimplUtils.lhs +++ b/ghc/compiler/simplCore/SimplUtils.lhs @@ -5,8 +5,9 @@ \begin{code} module SimplUtils ( - simplBinder, simplBinders, simplRecIds, simplLetId, simplLamBinders, - newId, mkLam, mkCase, + simplBinder, simplBinders, simplRecBndrs, + simplLetBndr, simplLamBndrs, + newId, mkLam, prepareAlts, mkCase, -- The continuation type SimplCont(..), DupFlag(..), LetRhsFlag(..), @@ -25,23 +26,23 @@ import CmdLineOpts ( SimplifierSwitch(..), ) import CoreSyn import CoreUtils ( cheapEqExpr, exprType, - etaExpand, exprEtaExpandArity, bindNonRec, mkCoerce, + etaExpand, exprEtaExpandArity, bindNonRec, mkCoerce2, findDefault, exprOkForSpeculation, exprIsValue ) import qualified Subst ( simplBndrs, simplBndr, simplLetId, simplLamBndr ) -import Id ( Id, idType, idInfo, - mkSysLocal, hasNoBinding, isDeadBinder, idNewDemandInfo, +import Id ( Id, idType, idInfo, + mkSysLocal, isDeadBinder, idNewDemandInfo, idUnfolding, idNewStrictness ) import NewDemand ( isStrictDmd, isBotRes, splitStrictSig ) import SimplMonad -import Type ( Type, seqType, - splitTyConApp_maybe, tyConAppArgs, mkTyVarTys, - splitRepFunTys, isStrictType +import Type ( Type, seqType, splitFunTys, dropForAlls, isStrictType, + splitTyConApp_maybe, tyConAppArgs, mkTyVarTys ) -import OccName ( UserFS ) -import TyCon ( tyConDataConsIfAvailable, isDataTyCon ) -import DataCon ( dataConRepArity, dataConSig, dataConArgTys ) +import TcType ( isDictTy ) +import OccName ( EncodedFS ) +import TyCon ( tyConDataCons_maybe, isAlgTyCon, isNewTyCon ) +import DataCon ( dataConRepArity, dataConExistentialTyVars, dataConArgTys ) import Var ( mkSysTyVar, tyVarKind ) import Util ( lengthExceeds, mapAccumL ) import Outputable @@ -76,14 +77,16 @@ data SimplCont -- Strict contexts InId [InAlt] SimplEnv -- The case binder, alts, and subst-env SimplCont - | ArgOf DupFlag -- An arbitrary strict context: the argument + | ArgOf LetRhsFlag -- An arbitrary strict context: the argument -- of a strict function, or a primitive-arg fn -- or a PrimOp - LetRhsFlag + -- No DupFlag because we never duplicate it + OutType -- arg_ty: type of the argument itself OutType -- cont_ty: the type of the expression being sought by the context -- f (error "foo") ==> coerce t (error "foo") -- when f is strict -- We need to know the type t, to which to coerce. + (SimplEnv -> OutExpr -> SimplM FloatsWithExpr) -- What to do with the result -- The result expression in the OutExprStuff has type cont_ty @@ -97,7 +100,7 @@ instance Outputable LetRhsFlag where instance Outputable SimplCont where ppr (Stop _ is_rhs _) = ptext SLIT("Stop") <> brackets (ppr is_rhs) ppr (ApplyTo dup arg se cont) = (ptext SLIT("ApplyTo") <+> ppr dup <+> ppr arg) $$ ppr cont - ppr (ArgOf dup _ _ _) = ptext SLIT("ArgOf...") <+> ppr dup + ppr (ArgOf _ _ _ _) = ptext SLIT("ArgOf...") ppr (Select dup bndr alts se cont) = (ptext SLIT("Select") <+> ppr dup <+> ppr bndr) $$ (nest 4 (ppr alts)) $$ ppr cont ppr (CoerceIt ty cont) = (ptext SLIT("CoerceIt") <+> ppr ty) $$ ppr cont @@ -119,7 +122,7 @@ mkStop ty is_rhs = Stop ty is_rhs (canUpdateInPlace ty) contIsRhs :: SimplCont -> Bool contIsRhs (Stop _ AnRhs _) = True -contIsRhs (ArgOf _ AnRhs _ _) = True +contIsRhs (ArgOf AnRhs _ _ _) = True contIsRhs other = False contIsRhsOrArg (Stop _ _ _) = True @@ -130,7 +133,6 @@ contIsRhsOrArg other = False contIsDupable :: SimplCont -> Bool contIsDupable (Stop _ _ _) = True contIsDupable (ApplyTo OkToDup _ _ _) = True -contIsDupable (ArgOf OkToDup _ _ _) = True contIsDupable (Select OkToDup _ _ _ _) = True contIsDupable (CoerceIt _ cont) = contIsDupable cont contIsDupable (InlinePlease cont) = contIsDupable cont @@ -230,14 +232,14 @@ getContArgs chkr fun orig_cont computed_stricts = zipWith (||) fun_stricts arg_stricts ---------------------------- - (val_arg_tys, _) = splitRepFunTys (idType fun) + (val_arg_tys, _) = splitFunTys (dropForAlls (idType fun)) arg_stricts = map isStrictType val_arg_tys ++ repeat False -- These argument types are used as a cheap and cheerful way to find -- unboxed arguments, which must be strict. But it's an InType -- and so there might be a type variable where we expect a function -- type (the substitution hasn't happened yet). And we don't bother -- doing the type applications for a polymorphic function. - -- Hence the split*Rep*FunTys + -- Hence the splitFunTys*IgnoringForAlls* ---------------------------- -- If fun_stricts is finite, it means the function returns bottom @@ -403,10 +405,10 @@ canUpdateInPlace ty | otherwise = case splitTyConApp_maybe ty of Nothing -> False - Just (tycon, _) -> case tyConDataConsIfAvailable tycon of - [dc] -> arity == 1 || arity == 2 - where - arity = dataConRepArity dc + Just (tycon, _) -> case tyConDataCons_maybe tycon of + Just [dc] -> arity == 1 || arity == 2 + where + arity = dataConRepArity dc other -> False \end{code} @@ -438,29 +440,25 @@ simplBinder env bndr returnSmpl (setSubst env subst', bndr') -simplLamBinders :: SimplEnv -> [InBinder] -> SimplM (SimplEnv, [OutBinder]) -simplLamBinders env bndrs +simplLetBndr :: SimplEnv -> InBinder -> SimplM (SimplEnv, OutBinder) +simplLetBndr env id = let - (subst', bndrs') = mapAccumL Subst.simplLamBndr (getSubst env) bndrs + (subst', id') = Subst.simplLetId (getSubst env) id in - seqBndrs bndrs' `seq` - returnSmpl (setSubst env subst', bndrs') + seqBndr id' `seq` + returnSmpl (setSubst env subst', id') -simplRecIds :: SimplEnv -> [InBinder] -> SimplM (SimplEnv, [OutBinder]) -simplRecIds env ids - = let - (subst', ids') = mapAccumL Subst.simplLetId (getSubst env) ids - in - seqBndrs ids' `seq` - returnSmpl (setSubst env subst', ids') +simplLamBndrs, simplRecBndrs + :: SimplEnv -> [InBinder] -> SimplM (SimplEnv, [OutBinder]) +simplRecBndrs = simplBndrs Subst.simplLetId +simplLamBndrs = simplBndrs Subst.simplLamBndr -simplLetId :: SimplEnv -> InBinder -> SimplM (SimplEnv, OutBinder) -simplLetId env id +simplBndrs simpl_bndr env bndrs = let - (subst', id') = Subst.simplLetId (getSubst env) id + (subst', bndrs') = mapAccumL simpl_bndr (getSubst env) bndrs in - seqBndr id' `seq` - returnSmpl (setSubst env subst', id') + seqBndrs bndrs' `seq` + returnSmpl (setSubst env subst', bndrs') seqBndrs [] = () seqBndrs (b:bs) = seqBndr b `seq` seqBndrs bs @@ -473,7 +471,7 @@ seqBndr b | isTyVar b = b `seq` () \begin{code} -newId :: UserFS -> Type -> SimplM Id +newId :: EncodedFS -> Type -> SimplM Id newId fs ty = getUniqueSmpl `thenSmpl` \ uniq -> returnSmpl (mkSysLocal fs uniq ty) \end{code} @@ -549,9 +547,20 @@ tryEtaReduce bndrs body go [] (Var fun) | ok_fun fun = Just (Var fun) -- Success! go _ _ = Nothing -- Failure! - ok_fun fun = not (fun `elem` bndrs) && not (hasNoBinding fun) - -- Note the awkward "hasNoBinding" test - -- Details with exprIsTrivial + ok_fun fun = not (fun `elem` bndrs) && + (isEvaldUnfolding (idUnfolding fun) || all ok_lam bndrs) + ok_lam v = isTyVar v || isDictTy (idType v) + -- The isEvaldUnfolding is because eta reduction is not + -- valid in general: \x. bot /= bot + -- So we need to be sure that the "fun" is a value. + -- + -- However, we always want to reduce (/\a -> f a) to f + -- This came up in a RULE: foldr (build (/\a -> g a)) + -- did not match foldr (build (/\b -> ...something complex...)) + -- The type checker can insert these eta-expanded versions, + -- with both type and dictionary lambdas; hence the slightly + -- ad-hoc isDictTy + ok_arg b arg = varToCoreExpr b `cheapEqExpr` arg \end{code} @@ -769,6 +778,132 @@ tryRhsTyLam env tyvars body -- Only does something if there's a let -} \end{code} +%************************************************************************ +%* * +\subsection{Case alternative filtering +%* * +%************************************************************************ + +prepareAlts does two things: + +1. Eliminate alternatives that cannot match, including the + DEFAULT alternative. + +2. If the DEFAULT alternative can match only one possible constructor, + then make that constructor explicit. + e.g. + case e of x { DEFAULT -> rhs } + ===> + case e of x { (a,b) -> rhs } + where the type is a single constructor type. This gives better code + when rhs also scrutinises x or e. + +It's a good idea do do this stuff before simplifying the alternatives, to +avoid simplifying alternatives we know can't happen, and to come up with +the list of constructors that are handled, to put into the IdInfo of the +case binder, for use when simplifying the alternatives. + +Eliminating the default alternative in (1) isn't so obvious, but it can +happen: + +data Colour = Red | Green | Blue + +f x = case x of + Red -> .. + Green -> .. + DEFAULT -> h x + +h y = case y of + Blue -> .. + DEFAULT -> [ case y of ... ] + +If we inline h into f, the default case of the inlined h can't happen. +If we don't notice this, we may end up filtering out *all* the cases +of the inner case y, which give us nowhere to go! + + +\begin{code} +prepareAlts :: OutExpr -- Scrutinee + -> InId -- Case binder + -> [InAlt] + -> SimplM ([InAlt], -- Better alternatives + [AltCon]) -- These cases are handled + +prepareAlts scrut case_bndr alts + = let + (alts_wo_default, maybe_deflt) = findDefault alts + + impossible_cons = case scrut of + Var v -> otherCons (idUnfolding v) + other -> [] + + -- Filter out alternatives that can't possibly match + better_alts | null impossible_cons = alts_wo_default + | otherwise = [alt | alt@(con,_,_) <- alts_wo_default, + not (con `elem` impossible_cons)] + + -- "handled_cons" are handled either by the context, + -- or by a branch in this case expression + -- (Don't add DEFAULT to the handled_cons!!) + handled_cons = impossible_cons ++ [con | (con,_,_) <- better_alts] + in + -- Filter out the default, if it can't happen, + -- or replace it with "proper" alternative if there + -- is only one constructor left + prepareDefault case_bndr handled_cons maybe_deflt `thenSmpl` \ deflt_alt -> + + returnSmpl (deflt_alt ++ better_alts, handled_cons) + +prepareDefault case_bndr handled_cons (Just rhs) + | Just (tycon, inst_tys) <- splitTyConApp_maybe (idType case_bndr), + isAlgTyCon tycon, -- It's a data type, tuple, or unboxed tuples. + not (isNewTyCon tycon), -- We can have a newtype, if we are just doing an eval: + -- case x of { DEFAULT -> e } + -- and we don't want to fill in a default for them! + Just all_cons <- tyConDataCons_maybe tycon, + not (null all_cons), -- This is a tricky corner case. If the data type has no constructors, + -- which GHC allows, then the case expression will have at most a default + -- alternative. We don't want to eliminate that alternative, because the + -- invariant is that there's always one alternative. It's more convenient + -- to leave + -- case x of { DEFAULT -> e } + -- as it is, rather than transform it to + -- error "case cant match" + -- which would be quite legitmate. But it's a really obscure corner, and + -- not worth wasting code on. + let handled_data_cons = [data_con | DataAlt data_con <- handled_cons], + let missing_cons = [con | con <- all_cons, + not (con `elem` handled_data_cons)] + = case missing_cons of + [] -> returnSmpl [] -- Eliminate the default alternative + -- if it can't match + + [con] -> -- It matches exactly one constructor, so fill it in + tick (FillInCaseDefault case_bndr) `thenSmpl_` + mk_args con inst_tys `thenSmpl` \ args -> + returnSmpl [(DataAlt con, args, rhs)] + + two_or_more -> returnSmpl [(DEFAULT, [], rhs)] + + | otherwise + = returnSmpl [(DEFAULT, [], rhs)] + +prepareDefault case_bndr handled_cons Nothing + = returnSmpl [] + +mk_args missing_con inst_tys + = getUniquesSmpl `thenSmpl` \ tv_uniqs -> + getUniquesSmpl `thenSmpl` \ id_uniqs -> + let + ex_tyvars = dataConExistentialTyVars missing_con + ex_tyvars' = zipWith mk tv_uniqs ex_tyvars + mk uniq tv = mkSysTyVar uniq (tyVarKind tv) + arg_tys = dataConArgTys missing_con (inst_tys ++ mkTyVarTys ex_tyvars') + arg_ids = zipWith (mkSysLocal FSLIT("a")) id_uniqs arg_tys + in + returnSmpl (ex_tyvars' ++ arg_ids) +\end{code} + %************************************************************************ %* * @@ -805,16 +940,7 @@ mkAlts tries these things: a) all branches equal b) some branches equal to the DEFAULT (which occurs first) -2. If the DEFAULT alternative can match only one possible constructor, - then make that constructor explicit. - e.g. - case e of x { DEFAULT -> rhs } - ===> - case e of x { (a,b) -> rhs } - where the type is a single constructor type. This gives better code - when rhs also scrutinises x or e. - -3. Case merging: +2. Case merging: case e of b { ==> case e of b { p1 -> rhs1 p1 -> rhs1 ... ... @@ -869,36 +995,7 @@ mkAlts scrut case_bndr alts@((con1,bndrs1,rhs1) : con_alts) -------------------------------------------------- --- 2. Fill in missing constructor --------------------------------------------------- - -mkAlts scrut case_bndr alts - | Just (tycon, inst_tys) <- splitTyConApp_maybe (idType case_bndr), - isDataTyCon tycon, -- It's a data type - (alts_no_deflt, Just rhs) <- findDefault alts, - -- There is a DEFAULT case - [missing_con] <- filter is_missing (tyConDataConsIfAvailable tycon) - -- There is just one missing constructor! - = tick (FillInCaseDefault case_bndr) `thenSmpl_` - getUniquesSmpl `thenSmpl` \ tv_uniqs -> - getUniquesSmpl `thenSmpl` \ id_uniqs -> - let - (_,_,ex_tyvars,_,_,_) = dataConSig missing_con - ex_tyvars' = zipWith mk tv_uniqs ex_tyvars - mk uniq tv = mkSysTyVar uniq (tyVarKind tv) - arg_ids = zipWith (mkSysLocal SLIT("a")) id_uniqs arg_tys - arg_tys = dataConArgTys missing_con (inst_tys ++ mkTyVarTys ex_tyvars') - better_alts = (DataAlt missing_con, ex_tyvars' ++ arg_ids, rhs) : alts_no_deflt - in - returnSmpl better_alts - where - impossible_cons = otherCons (idUnfolding case_bndr) - handled_data_cons = [data_con | DataAlt data_con <- impossible_cons] ++ - [data_con | (DataAlt data_con, _, _) <- alts] - is_missing con = not (con `elem` handled_data_cons) - --------------------------------------------------- --- 3. Merge nested cases +-- 2. Merge nested cases -------------------------------------------------- mkAlts scrut outer_bndr outer_alts @@ -1041,9 +1138,58 @@ So the case-elimination algorithm is: If so, then we can replace the case with one of the rhss. +Further notes about case elimination +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Consider: test :: Integer -> IO () + test = print + +Turns out that this compiles to: + Print.test + = \ eta :: Integer + eta1 :: State# RealWorld -> + case PrelNum.< eta PrelNum.zeroInteger of wild { __DEFAULT -> + case hPutStr stdout + (PrelNum.jtos eta ($w[] @ Char)) + eta1 + of wild1 { (# new_s, a4 #) -> PrelIO.lvl23 new_s }} + +Notice the strange '<' which has no effect at all. This is a funny one. +It started like this: + +f x y = if x < 0 then jtos x + else if y==0 then "" else jtos x + +At a particular call site we have (f v 1). So we inline to get + + if v < 0 then jtos x + else if 1==0 then "" else jtos x + +Now simplify the 1==0 conditional: + + if v<0 then jtos v else jtos v + +Now common-up the two branches of the case: + + case (v<0) of DEFAULT -> jtos v + +Why don't we drop the case? Because it's strict in v. It's technically +wrong to drop even unnecessary evaluations, and in practice they +may be a result of 'seq' so we *definitely* don't want to drop those. +I don't really know how to improve this situation. + \begin{code} -------------------------------------------------- +-- 0. Check for empty alternatives +-------------------------------------------------- + +#ifdef DEBUG +mkCase1 scrut case_bndr [] + = pprTrace "mkCase1: null alts" (ppr case_bndr <+> ppr scrut) $ + returnSmpl scrut +#endif + +-------------------------------------------------- -- 1. Eliminate the case altogether if poss -------------------------------------------------- @@ -1074,6 +1220,7 @@ mkCase1 scrut case_bndr [(con,bndrs,rhs)] -- Here we must *not* discard the case, because dataToTag# just fetches the tag from -- the info pointer. So we'll be pedantic all the time, and see if that gives any -- other problems +-- Also we don't want to discard 'seq's = tick (CaseElim case_bndr) `thenSmpl_` returnSmpl (bindCaseBndr case_bndr scrut rhs) @@ -1111,7 +1258,7 @@ mkCase1 scrut case_bndr alts -- Identity case -- re_note wraps a coerce if it might be necessary re_note scrut = case head alts of - (_,_,rhs1@(Note _ _)) -> mkCoerce (exprType rhs1) (idType case_bndr) scrut + (_,_,rhs1@(Note _ _)) -> mkCoerce2 (exprType rhs1) (idType case_bndr) scrut other -> scrut