X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=blobdiff_plain;f=compiler%2Fstranal%2FWwLib.lhs;h=391c07c0894595954e1b9f42112cae71a68e9765;hp=4254d35de8aab0f637148cc6bd2d68701791c905;hb=febf1ced754a3996ac1a5877dcded87828560d1c;hpb=30c122df62ec75f9ed7f392f24c2925675bf1d06 diff --git a/compiler/stranal/WwLib.lhs b/compiler/stranal/WwLib.lhs index 4254d35..391c07c 100644 --- a/compiler/stranal/WwLib.lhs +++ b/compiler/stranal/WwLib.lhs @@ -1,7 +1,7 @@ % % (c) The GRASP/AQUA Project, Glasgow University, 1993-1998 % -\section[WwLib]{A library for the ``worker/wrapper'' back-end to the strictness analyser} +\section[WwLib]{A library for the ``worker\/wrapper'' back-end to the strictness analyser} \begin{code} module WwLib ( mkWwBodies, mkWWstr, mkWorkerArgs ) where @@ -10,26 +10,27 @@ module WwLib ( mkWwBodies, mkWWstr, mkWorkerArgs ) where import CoreSyn import CoreUtils ( exprType ) -import Id ( Id, idType, mkSysLocal, idNewDemandInfo, setIdNewDemandInfo, +import Id ( Id, idType, mkSysLocal, idDemandInfo, setIdDemandInfo, isOneShotLambda, setOneShotLambda, setIdUnfolding, setIdInfo ) import IdInfo ( vanillaIdInfo ) import DataCon -import NewDemand ( Demand(..), DmdResult(..), Demands(..) ) -import MkId ( realWorldPrimId, voidArgId, mkRuntimeErrorApp, rUNTIME_ERROR_ID, +import Demand ( Demand(..), DmdResult(..), Demands(..) ) +import MkCore ( mkRuntimeErrorApp, aBSENT_ERROR_ID ) +import MkId ( realWorldPrimId, voidArgId, mkUnpackCase, mkProductBox ) +import TysPrim ( realWorldStatePrimTy ) import TysWiredIn ( tupleCon ) import Type -import Coercion ( mkSymCoercion, splitNewTypeRepCo_maybe ) +import Coercion ( mkSymCo, splitNewTypeRepCo_maybe ) import BasicTypes ( Boxity(..) ) -import Var ( Var, isId ) +import Literal ( absentLiteralOf ) import UniqSupply import Unique -import Util ( zipWithEqual, notNull ) +import Util ( zipWithEqual ) import Outputable import FastString -import List ( zipWith4 ) \end{code} @@ -44,7 +45,7 @@ Here's an example. The original function is: \begin{verbatim} g :: forall a . Int -> [a] -> a -g = /\ a -> \ x ys -> +g = \/\ a -> \ x ys -> case x of 0 -> head ys _ -> head (tail ys) @@ -55,7 +56,7 @@ From this, we want to produce: -- wrapper (an unfolding) g :: forall a . Int -> [a] -> a -g = /\ a -> \ x ys -> +g = \/\ a -> \ x ys -> case x of I# x# -> $wg a x# ys -- call the worker; don't forget the type args! @@ -63,7 +64,7 @@ g = /\ a -> \ x ys -> -- worker $wg :: forall a . Int# -> [a] -> a -$wg = /\ a -> \ x# ys -> +$wg = \/\ a -> \ x# ys -> let x = I# x# in @@ -98,7 +99,7 @@ the unusable strictness-info into the interfaces. %* * %************************************************************************ -@mkWwBodies@ is called when doing the worker/wrapper split inside a module. +@mkWwBodies@ is called when doing the worker\/wrapper split inside a module. \begin{code} mkWwBodies :: Type -- Type of original function @@ -120,21 +121,23 @@ mkWwBodies :: Type -- Type of original function -- let x = (a,b) in -- E -mkWwBodies fun_ty demands res_info one_shots = do - (wrap_args, wrap_fn_args, work_fn_args, res_ty) <- mkWWargs fun_ty demands one_shots' - (work_args, wrap_fn_str, work_fn_str) <- mkWWstr wrap_args - let (work_lam_args, work_call_args) = mkWorkerArgs work_args res_ty +mkWwBodies fun_ty demands res_info one_shots + = do { let arg_info = demands `zip` (one_shots ++ repeat False) + ; (wrap_args, wrap_fn_args, work_fn_args, res_ty) <- mkWWargs emptyTvSubst fun_ty arg_info + ; (work_args, wrap_fn_str, work_fn_str) <- mkWWstr wrap_args + -- Don't do CPR if the worker doesn't have any value arguments -- Then the worker is just a constant, so we don't want to unbox it. - (wrap_fn_cpr, work_fn_cpr, _cpr_res_ty) - <- if any isId work_args then - mkWWcpr res_ty res_info - else - return (id, id, res_ty) - - return ([idNewDemandInfo v | v <- work_call_args, isId v], - Note InlineMe . wrap_fn_args . wrap_fn_cpr . wrap_fn_str . applyToVars work_call_args . Var, - mkLams work_lam_args. work_fn_str . work_fn_cpr . work_fn_args) + ; (wrap_fn_cpr, work_fn_cpr, _cpr_res_ty) + <- if any isId work_args then + mkWWcpr res_ty res_info + else + return (id, id, res_ty) + + ; let (work_lam_args, work_call_args) = mkWorkerArgs work_args res_ty + ; return ([idDemandInfo v | v <- work_call_args, isId v], + wrap_fn_args . wrap_fn_cpr . wrap_fn_str . applyToVars work_call_args . Var, + mkLams work_lam_args. work_fn_str . work_fn_cpr . work_fn_args) } -- We use an INLINE unconditionally, even if the wrapper turns out to be -- something trivial like -- fw = ... @@ -142,8 +145,6 @@ mkWwBodies fun_ty demands res_info one_shots = do -- The point is to propagate the coerce to f's call sites, so even though -- f's RHS is now trivial (size 1) we still want the __inline__ to prevent -- fw from being inlined into f's RHS - where - one_shots' = one_shots ++ repeat False \end{code} @@ -183,7 +184,6 @@ mkWorkerArgs args res_ty %* * %************************************************************************ - We really want to "look through" coerces. Reason: I've seen this situation: @@ -210,20 +210,22 @@ Now we'll see that fw has arity 1, and will arity expand the \x to get what we want. \begin{code} --- mkWWargs is driven off the function type and arity. +-- mkWWargs just does eta expansion +-- is driven off the function type and arity. -- It chomps bites off foralls, arrows, newtypes -- and keeps repeating that until it's satisfied the supplied arity -mkWWargs :: Type - -> [Demand] - -> [Bool] -- True for a one-shot arg; ** may be infinite ** +mkWWargs :: TvSubst -- Freshening substitution to apply to the type + -- See Note [Freshen type variables] + -> Type -- The type of the function + -> [(Demand,Bool)] -- Demands and one-shot info for value arguments -> UniqSM ([Var], -- Wrapper args CoreExpr -> CoreExpr, -- Wrapper fn CoreExpr -> CoreExpr, -- Worker fn Type) -- Type of wrapper body -mkWWargs fun_ty demands one_shots - | Just (rep_ty, co) <- splitNewTypeRepCo_maybe fun_ty = do +mkWWargs subst fun_ty arg_info + | Just (rep_ty, co) <- splitNewTypeRepCo_maybe fun_ty -- The newtype case is for when the function has -- a recursive newtype after the arrow (rare) -- We check for arity >= 0 to avoid looping in the case @@ -234,57 +236,69 @@ mkWWargs fun_ty demands one_shots -- wrapped in a recursive newtype, at least if CPR analysis can look -- through such newtypes, which it probably can since they are -- simply coerces. - (wrap_args, wrap_fn_args, work_fn_args, res_ty) <- mkWWargs rep_ty demands one_shots - return (wrap_args, - \ e -> Cast (wrap_fn_args e) (mkSymCoercion co), - \ e -> work_fn_args (Cast e co), - res_ty) - | notNull demands = do - wrap_uniqs <- getUniquesM - let - (tyvars, tau) = splitForAllTys fun_ty - (arg_tys, body_ty) = splitFunTys tau - - n_demands = length demands - n_arg_tys = length arg_tys - n_args = n_demands `min` n_arg_tys - - new_fun_ty = mkFunTys (drop n_demands arg_tys) body_ty - new_demands = drop n_arg_tys demands - new_one_shots = drop n_args one_shots - - val_args = zipWith4 mk_wrap_arg wrap_uniqs arg_tys demands one_shots - wrap_args = tyvars ++ val_args -{- ASSERT( notNull tyvars || notNull arg_tys ) -} - if (null tyvars) && (null arg_tys) then - pprTrace "mkWWargs" (ppr fun_ty $$ ppr demands) - return ([], id, id, fun_ty) - else do - - (more_wrap_args, wrap_fn_args, work_fn_args, res_ty) <- - mkWWargs new_fun_ty new_demands new_one_shots - - return (wrap_args ++ more_wrap_args, - mkLams wrap_args . wrap_fn_args, - work_fn_args . applyToVars wrap_args, - res_ty) + -- + -- Note (Sept 08): This case applies even if demands is empty. + -- I'm not quite sure why; perhaps it makes it + -- easier for CPR + = do { (wrap_args, wrap_fn_args, work_fn_args, res_ty) + <- mkWWargs subst rep_ty arg_info + ; return (wrap_args, + \e -> Cast (wrap_fn_args e) (mkSymCo co), + \e -> work_fn_args (Cast e co), + res_ty) } + + | null arg_info + = return ([], id, id, substTy subst fun_ty) + + | Just (tv, fun_ty') <- splitForAllTy_maybe fun_ty + = do { let (subst', tv') = substTyVarBndr subst tv + -- This substTyVarBndr clones the type variable when necy + -- See Note [Freshen type variables] + ; (wrap_args, wrap_fn_args, work_fn_args, res_ty) + <- mkWWargs subst' fun_ty' arg_info + ; return (tv' : wrap_args, + Lam tv' . wrap_fn_args, + work_fn_args . (`App` Type (mkTyVarTy tv')), + res_ty) } + + | ((dmd,one_shot):arg_info') <- arg_info + , Just (arg_ty, fun_ty') <- splitFunTy_maybe fun_ty + = do { uniq <- getUniqueM + ; let arg_ty' = substTy subst arg_ty + id = mk_wrap_arg uniq arg_ty' dmd one_shot + ; (wrap_args, wrap_fn_args, work_fn_args, res_ty) + <- mkWWargs subst fun_ty' arg_info' + ; return (id : wrap_args, + Lam id . wrap_fn_args, + work_fn_args . (`App` varToCoreExpr id), + res_ty) } | otherwise - = return ([], id, id, fun_ty) - + = WARN( True, ppr fun_ty ) -- Should not happen: if there is a demand + return ([], id, id, substTy subst fun_ty) -- then there should be a function arrow applyToVars :: [Var] -> CoreExpr -> CoreExpr applyToVars vars fn = mkVarApps fn vars -mk_wrap_arg :: Unique -> Type -> NewDemand.Demand -> Bool -> Id +mk_wrap_arg :: Unique -> Type -> Demand -> Bool -> Id mk_wrap_arg uniq ty dmd one_shot - = set_one_shot one_shot (setIdNewDemandInfo (mkSysLocal FSLIT("w") uniq ty) dmd) + = set_one_shot one_shot (setIdDemandInfo (mkSysLocal (fsLit "w") uniq ty) dmd) where set_one_shot True id = setOneShotLambda id set_one_shot False id = id \end{code} - +Note [Freshen type variables] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Wen we do a worker/wrapper split, we must not use shadowed names, +else we'll get + f = /\ a /\a. fw a a +which is obviously wrong. Type variables can can in principle shadow, +within a type (e.g. forall a. a -> forall a. a->a). But type +variables *are* mentioned in , so we must substitute. + +That's why we carry the TvSubst through mkWWargs + %************************************************************************ %* * \subsection{Strictness stuff} @@ -322,13 +336,13 @@ mkWWstr_one arg = return ([arg], nop_fn, nop_fn) | otherwise - = case idNewDemandInfo arg of + = case idDemandInfo arg of - -- Absent case. We don't deal with absence for unlifted types, - -- though, because it's not so easy to manufacture a placeholder - -- We'll see if this turns out to be a problem - Abs | not (isUnLiftedType (idType arg)) -> - return ([], nop_fn, mk_absent_let arg) + -- Absent case. We can't always handle absence for arbitrary + -- unlifted types, so we need to choose just the cases we can + -- (that's what mk_absent_let does) + Abs | Just work_fn <- mk_absent_let arg + -> return ([], nop_fn, work_fn) -- Unpack case Eval (Prod cs) @@ -374,7 +388,7 @@ mkWWstr_one arg -- If the wrapper argument is a one-shot lambda, then -- so should (all) the corresponding worker arguments be -- This bites when we do w/w on a case join point - set_worker_arg_info worker_arg demand = set_one_shot (setIdNewDemandInfo worker_arg demand) + set_worker_arg_info worker_arg demand = set_one_shot (setIdDemandInfo worker_arg demand) set_one_shot | isOneShotLambda arg = setOneShotLambda | otherwise = \x -> x @@ -474,18 +488,45 @@ workerCase bndr e args con body = mkUnpackCase bndr e args con body %* * %************************************************************************ +Note [Absent errors] +~~~~~~~~~~~~~~~~~~~~ +We make a new binding for Ids that are marked absent, thus + let x = absentError "x :: Int" +The idea is that this binding will never be used; but if it +buggily is used we'll get a runtime error message. + +Coping with absence for *unlifted* types is important; see, for +example, Trac #4306. For these we find a suitable literal, +using Literal.absentLiteralOf. We don't have literals for +every primitive type, so the function is partial. + + [I did try the experiment of using an error thunk for unlifted + things too, relying on the simplifier to drop it as dead code, + by making absentError + (a) *not* be a bottoming Id, + (b) be "ok for speculation" + But that relies on the simplifier finding that it really + is dead code, which is fragile, and indeed failed when + profiling is on, which disables various optimisations. So + using a literal will do.] \begin{code} -mk_absent_let :: Id -> CoreExpr -> CoreExpr -mk_absent_let arg body +mk_absent_let :: Id -> Maybe (CoreExpr -> CoreExpr) +mk_absent_let arg | not (isUnLiftedType arg_ty) - = Let (NonRec arg abs_rhs) body + = Just (Let (NonRec arg abs_rhs)) + | Just (tc, _) <- splitTyConApp_maybe arg_ty + , Just lit <- absentLiteralOf tc + = Just (Let (NonRec arg (Lit lit))) + | arg_ty `eqType` realWorldStatePrimTy + = Just (Let (NonRec arg (Var realWorldPrimId))) | otherwise - = panic "WwLib: haven't done mk_absent_let for primitives yet" + = WARN( True, ptext (sLit "No absent value for") <+> ppr arg_ty ) + Nothing where - arg_ty = idType arg - abs_rhs = mkRuntimeErrorApp rUNTIME_ERROR_ID arg_ty msg - msg = "Oops! Entered absent arg " ++ showSDocDebug (ppr arg <+> ppr (idType arg)) + arg_ty = idType arg + abs_rhs = mkRuntimeErrorApp aBSENT_ERROR_ID arg_ty msg + msg = showSDocDebug (ppr arg <+> ppr (idType arg)) mk_seq_case :: Id -> CoreExpr -> CoreExpr mk_seq_case arg body = Case (Var arg) (sanitiseCaseBndr arg) (exprType body) [(DEFAULT, [], body)] @@ -502,5 +543,5 @@ sanitiseCaseBndr :: Id -> Id sanitiseCaseBndr id = id `setIdInfo` vanillaIdInfo mk_ww_local :: Unique -> Type -> Id -mk_ww_local uniq ty = mkSysLocal FSLIT("ww") uniq ty +mk_ww_local uniq ty = mkSysLocal (fsLit "ww") uniq ty \end{code}