X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=ghc%2Fcompiler%2FsimplCore%2FSimplUtils.lhs;h=57c7274027e059697389d3c00f91d2139dc7c4fd;hb=711e4d7a4d65472a3a1fb35bcad8e1c9a109c728;hp=e53bc0420cee35a00c242cf4bbc0478a2f83e9fc;hpb=e55df039ad34fa0fef6c2a746643a43c9b0515cd;p=ghc-hetmet.git diff --git a/ghc/compiler/simplCore/SimplUtils.lhs b/ghc/compiler/simplCore/SimplUtils.lhs index e53bc04..57c7274 100644 --- a/ghc/compiler/simplCore/SimplUtils.lhs +++ b/ghc/compiler/simplCore/SimplUtils.lhs @@ -5,8 +5,8 @@ \begin{code} module SimplUtils ( - simplBinder, simplBinders, simplRecBndrs, simplLetBndr, - simplLamBndrs, simplTopBndrs, + simplBinder, simplBinders, simplRecBndrs, + simplLetBndr, simplLamBndrs, newId, mkLam, mkCase, -- The continuation type @@ -30,18 +30,18 @@ import CoreUtils ( cheapEqExpr, exprType, findDefault, exprOkForSpeculation, exprIsValue ) import qualified Subst ( simplBndrs, simplBndr, simplLetId, simplLamBndr ) -import Id ( Id, idType, idInfo, isLocalId, - 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, splitRepFunTys, isStrictType, + splitTyConApp_maybe, tyConAppArgs, mkTyVarTys ) +import TcType ( isDictTy ) import OccName ( UserFS ) -import TyCon ( tyConDataConsIfAvailable, isAlgTyCon, isNewTyCon ) +import TyCon ( tyConDataCons_maybe, isAlgTyCon, isNewTyCon ) import DataCon ( dataConRepArity, dataConSig, dataConArgTys ) import Var ( mkSysTyVar, tyVarKind ) import Util ( lengthExceeds, mapAccumL ) @@ -77,14 +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 @@ -98,7 +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 @@ -120,7 +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 @@ -131,7 +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 @@ -404,10 +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} @@ -447,26 +448,11 @@ simplLetBndr env id seqBndr id' `seq` returnSmpl (setSubst env subst', id') -simplTopBndrs, simplLamBndrs, simplRecBndrs +simplLamBndrs, simplRecBndrs :: SimplEnv -> [InBinder] -> SimplM (SimplEnv, [OutBinder]) -simplTopBndrs = simplBndrs simplTopBinder simplRecBndrs = simplBndrs Subst.simplLetId simplLamBndrs = simplBndrs Subst.simplLamBndr --- For top-level binders, don't use simplLetId for GlobalIds. --- There are some of these, notably consructor wrappers, and we don't --- want to clone them or fiddle with them at all. --- Rather tiresomely, the specialiser may float a use of a constructor --- wrapper to before its definition (which shouldn't really matter) --- because it doesn't see the constructor wrapper as free in the binding --- it is floating (because it's a GlobalId). --- Then the simplifier brings all top level Ids into scope at the --- beginning, and we don't want to lose the IdInfo on the constructor --- wrappers. It would also be Bad to clone it! -simplTopBinder subst bndr - | isLocalId bndr = Subst.simplLetId subst bndr - | otherwise = (subst, bndr) - simplBndrs simpl_bndr env bndrs = let (subst', bndrs') = mapAccumL simpl_bndr (getSubst env) bndrs @@ -561,9 +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} @@ -791,10 +788,10 @@ tryRhsTyLam env tyvars body -- Only does something if there's a let mkCase puts a case expression back together, trying various transformations first. \begin{code} -mkCase :: OutExpr -> OutId -> [OutAlt] -> SimplM OutExpr +mkCase :: OutExpr -> [AltCon] -> OutId -> [OutAlt] -> SimplM OutExpr -mkCase scrut case_bndr alts - = mkAlts scrut case_bndr alts `thenSmpl` \ better_alts -> +mkCase scrut handled_cons case_bndr alts + = mkAlts scrut handled_cons case_bndr alts `thenSmpl` \ better_alts -> mkCase1 scrut case_bndr better_alts \end{code} @@ -869,7 +866,7 @@ and similarly in cascade for all the join points! -------------------------------------------------- -- 1. Merge identical branches -------------------------------------------------- -mkAlts scrut case_bndr alts@((con1,bndrs1,rhs1) : con_alts) +mkAlts scrut handled_cons case_bndr alts@((con1,bndrs1,rhs1) : con_alts) | all isDeadBinder bndrs1, -- Remember the default length filtered_alts < length con_alts -- alternative comes first = tick (AltMerge case_bndr) `thenSmpl_` @@ -884,16 +881,21 @@ 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), - isAlgTyCon tycon, -- It's a data type, tuple, or unboxed tuples. - -- We aren't expecting any newtypes at this point. - (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! - = ASSERT( not (isNewTyCon tycon) ) - tick (FillInCaseDefault case_bndr) `thenSmpl_` +mkAlts scrut handled_cons case_bndr alts + | (alts_no_deflt, Just rhs) <- findDefault alts, + -- There is a DEFAULT case + + 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, + [missing_con] <- [con | con <- all_cons, not (con `elem` handled_data_cons)] + -- There is just one missing constructor! + + = tick (FillInCaseDefault case_bndr) `thenSmpl_` getUniquesSmpl `thenSmpl` \ tv_uniqs -> getUniquesSmpl `thenSmpl` \ id_uniqs -> let @@ -906,16 +908,13 @@ mkAlts scrut case_bndr alts 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) + handled_data_cons = [data_con | DataAlt data_con <- handled_cons] -------------------------------------------------- -- 3. Merge nested cases -------------------------------------------------- -mkAlts scrut outer_bndr outer_alts +mkAlts scrut handled_cons outer_bndr outer_alts | opt_SimplCaseMerge, (outer_alts_without_deflt, maybe_outer_deflt) <- findDefault outer_alts, Just (Case (Var scrut_var) inner_bndr inner_alts) <- maybe_outer_deflt, @@ -959,7 +958,7 @@ mkAlts scrut outer_bndr outer_alts -- Catch-all -------------------------------------------------- -mkAlts scrut case_bndr other_alts = returnSmpl other_alts +mkAlts scrut handled_cons case_bndr other_alts = returnSmpl other_alts \end{code} @@ -1055,6 +1054,45 @@ 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} -------------------------------------------------- @@ -1088,6 +1126,7 @@ 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)