X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=ghc%2Fcompiler%2FcoreSyn%2FCoreUtils.lhs;h=2cd4249ca2c084e93d87def87fa7268ea61ef88d;hb=fcfe16433bd582d0e00404ea652806d13d14103c;hp=b5e7133705bf8e79b70846aa2f8b7453358149fb;hpb=bca9dd54c2b39638cb4638aaccf6015a104a1df5;p=ghc-hetmet.git diff --git a/ghc/compiler/coreSyn/CoreUtils.lhs b/ghc/compiler/coreSyn/CoreUtils.lhs index b5e7133..2cd4249 100644 --- a/ghc/compiler/coreSyn/CoreUtils.lhs +++ b/ghc/compiler/coreSyn/CoreUtils.lhs @@ -7,18 +7,23 @@ module CoreUtils ( -- Construction mkNote, mkInlineMe, mkSCC, mkCoerce, - bindNonRec, mkIfThenElse, mkAltExpr, - mkPiType, + bindNonRec, needsCaseBinding, + mkIfThenElse, mkAltExpr, mkPiType, + + -- Taking expressions apart + findDefault, findAlt, hasDefault, -- Properties of expressions exprType, coreAltsType, exprIsBottom, exprIsDupable, exprIsTrivial, exprIsCheap, exprIsValue,exprOkForSpeculation, exprIsBig, - exprIsConApp_maybe, + exprIsConApp_maybe, exprIsAtom, idAppIsBottom, idAppIsCheap, - -- Expr transformation - etaReduceExpr, exprEtaExpandArity, + + -- Arity and eta expansion + manifestArity, exprArity, + exprEtaExpandArity, etaExpand, -- Size coreBindsSize, @@ -36,32 +41,31 @@ module CoreUtils ( import GlaExts -- For `xori` import CoreSyn -import CoreFVs ( exprFreeVars ) import PprCore ( pprCoreExpr ) import Var ( Var, isId, isTyVar ) -import VarSet import VarEnv import Name ( hashName ) -import Literal ( hashLiteral, literalType, litIsDupable ) -import DataCon ( DataCon, dataConRepArity ) -import PrimOp ( primOpOkForSpeculation, primOpIsCheap, - primOpIsDupable ) -import Id ( Id, idType, idFlavour, idStrictness, idLBVarInfo, - mkWildId, idArity, idName, idUnfolding, idInfo, - isDataConId_maybe, isPrimOpId_maybe +import Literal ( hashLiteral, literalType, litIsDupable, isZeroLit ) +import DataCon ( DataCon, dataConRepArity, dataConArgTys, isExistentialDataCon, dataConTyCon ) +import PrimOp ( PrimOp(..), primOpOkForSpeculation, primOpIsCheap ) +import Id ( Id, idType, globalIdDetails, idNewStrictness, idLBVarInfo, + mkWildId, idArity, idName, idUnfolding, idInfo, isOneShotLambda, + isDataConId_maybe, mkSysLocal, isDataConId, isBottomingId ) import IdInfo ( LBVarInfo(..), - IdFlavour(..), + GlobalIdDetails(..), megaSeqIdInfo ) -import Demand ( appIsBottom ) -import Type ( Type, mkFunTy, mkForAllTy, - splitFunTy_maybe, tyVarsOfType, tyVarsOfTypes, - applyTys, isUnLiftedType, seqType, - mkUTy +import NewDemand ( appIsBottom ) +import Type ( Type, mkFunTy, mkForAllTy, splitFunTy_maybe, splitFunTy, + applyTys, isUnLiftedType, seqType, mkUTy, mkTyVarTy, + splitForAllTy_maybe, isForAllTy, splitNewType_maybe, + splitTyConApp_maybe, eqType, funResultTy, applyTy ) +import TyCon ( tyConArity ) import TysWiredIn ( boolTy, trueDataCon, falseDataCon ) import CostCentre ( CostCentre ) -import Maybes ( maybeToBool ) +import BasicTypes ( Arity ) +import Unique ( Unique ) import Outputable import TysPrim ( alphaTy ) -- Debugging only \end{code} @@ -154,9 +158,26 @@ Drop trivial InlineMe's. This is somewhat important, because if we have an unfo that looks like (Note InlineMe (Var v)), the InlineMe doesn't go away because it may not be *applied* to anything. +We don't use exprIsTrivial here, though, because we sometimes generate worker/wrapper +bindings like + fw = ... + f = inline_me (coerce t fw) +As usual, the inline_me prevents the worker from getting inlined back into the wrapper. +We want the split, so that the coerces can cancel at the call site. + +However, we can get left with tiresome type applications. Notably, consider + f = /\ a -> let t = e in (t, w) +Then lifting the let out of the big lambda gives + t' = /\a -> e + f = /\ a -> let t = inline_me (t' a) in (t, w) +The inline_me is to stop the simplifier inlining t' right back +into t's RHS. In the next phase we'll substitute for t (since +its rhs is trivial) and *then* we could get rid of the inline_me. +But it hardly seems worth it, so I don't bother. + \begin{code} -mkInlineMe e | exprIsTrivial e = e - | otherwise = Note InlineMe e +mkInlineMe (Var v) = Var v +mkInlineMe e = Note InlineMe e \end{code} @@ -165,23 +186,24 @@ mkInlineMe e | exprIsTrivial e = e mkCoerce :: Type -> Type -> CoreExpr -> CoreExpr mkCoerce to_ty from_ty (Note (Coerce to_ty2 from_ty2) expr) - = ASSERT( from_ty == to_ty2 ) + = ASSERT( from_ty `eqType` to_ty2 ) mkCoerce to_ty from_ty2 expr mkCoerce to_ty from_ty expr - | to_ty == from_ty = expr - | otherwise = ASSERT( from_ty == exprType expr ) - Note (Coerce to_ty from_ty) expr + | to_ty `eqType` from_ty = expr + | otherwise = ASSERT( from_ty `eqType` exprType expr ) + Note (Coerce to_ty from_ty) expr \end{code} \begin{code} mkSCC :: CostCentre -> Expr b -> Expr b -- Note: Nested SCC's *are* preserved for the benefit of - -- cost centre stack profiling (Durham) - -mkSCC cc (Lit lit) = Lit lit -mkSCC cc (Lam x e) = Lam x (mkSCC cc e) -- Move _scc_ inside lambda -mkSCC cc expr = Note (SCC cc) expr + -- cost centre stack profiling +mkSCC cc (Lit lit) = Lit lit +mkSCC cc (Lam x e) = Lam x (mkSCC cc e) -- Move _scc_ inside lambda +mkSCC cc (Note (SCC cc') e) = Note (SCC cc) (Note (SCC cc') e) +mkSCC cc (Note n e) = Note n (mkSCC cc e) -- Move _scc_ inside notes +mkSCC cc expr = Note (SCC cc) expr \end{code} @@ -203,8 +225,13 @@ bindNonRec :: Id -> CoreExpr -> CoreExpr -> CoreExpr -- that give Core Lint a heart attack. Actually the simplifier -- deals with them perfectly well. bindNonRec bndr rhs body - | isUnLiftedType (idType bndr) = Case rhs bndr [(DEFAULT,[],body)] - | otherwise = Let (NonRec bndr rhs) body + | needsCaseBinding (idType bndr) rhs = Case rhs bndr [(DEFAULT,[],body)] + | otherwise = Let (NonRec bndr rhs) body + +needsCaseBinding ty rhs = isUnLiftedType ty && not (exprOkForSpeculation rhs) + -- Make a case expression instead of a let + -- These can arise either from the desugarer, + -- or from beta reductions: (\x.e) (x +# y) \end{code} \begin{code} @@ -223,6 +250,41 @@ mkIfThenElse guard then_expr else_expr (DataAlt falseDataCon, [], else_expr) ] \end{code} + +%************************************************************************ +%* * +\subsection{Taking expressions apart} +%* * +%************************************************************************ + +The default alternative must be first, if it exists at all. +This makes it easy to find, though it makes matching marginally harder. + +\begin{code} +hasDefault :: [CoreAlt] -> Bool +hasDefault ((DEFAULT,_,_) : alts) = True +hasDefault _ = False + +findDefault :: [CoreAlt] -> ([CoreAlt], Maybe CoreExpr) +findDefault ((DEFAULT,args,rhs) : alts) = ASSERT( null args ) (alts, Just rhs) +findDefault alts = (alts, Nothing) + +findAlt :: AltCon -> [CoreAlt] -> CoreAlt +findAlt con alts + = case alts of + (deflt@(DEFAULT,_,_):alts) -> go alts deflt + other -> go alts panic_deflt + + where + panic_deflt = pprPanic "Missing alternative" (ppr con $$ vcat (map ppr alts)) + + go [] deflt = deflt + go (alt@(con1,_,_) : alts) deflt | con == con1 = alt + | otherwise = ASSERT( not (con1 == DEFAULT) ) + go alts deflt +\end{code} + + %************************************************************************ %* * \subsection{Figuring out things about expressions} @@ -237,16 +299,35 @@ mkIfThenElse guard then_expr else_expr @exprIsBottom@ is true of expressions that are guaranteed to diverge +There used to be a gruesome test for (hasNoBinding v) in the +Var case: + exprIsTrivial (Var v) | hasNoBinding v = idArity v == 0 +The idea here is that a constructor worker, like $wJust, is +really short for (\x -> $wJust x), becuase $wJust has no binding. +So it should be treated like a lambda. Ditto unsaturated primops. +But now constructor workers are not "have-no-binding" Ids. And +completely un-applied primops and foreign-call Ids are sufficiently +rare that I plan to allow them to be duplicated and put up with +saturating them. + \begin{code} -exprIsTrivial (Var v) - | Just op <- isPrimOpId_maybe v = primOpIsDupable op - | otherwise = True -exprIsTrivial (Type _) = True -exprIsTrivial (Lit lit) = True -exprIsTrivial (App e arg) = isTypeArg arg && exprIsTrivial e -exprIsTrivial (Note _ e) = exprIsTrivial e -exprIsTrivial (Lam b body) | isTyVar b = exprIsTrivial body -exprIsTrivial other = False +exprIsTrivial (Var v) = True -- See notes above +exprIsTrivial (Type _) = True +exprIsTrivial (Lit lit) = True +exprIsTrivial (App e arg) = not (isRuntimeArg arg) && exprIsTrivial e +exprIsTrivial (Note _ e) = exprIsTrivial e +exprIsTrivial (Lam b body) = not (isRuntimeVar b) && exprIsTrivial body +exprIsTrivial other = False + +exprIsAtom :: CoreExpr -> Bool +-- Used to decide whether to let-binding an STG argument +-- when compiling to ILX => type applications are not allowed +exprIsAtom (Var v) = True -- primOpIsDupable? +exprIsAtom (Lit lit) = True +exprIsAtom (Type ty) = True +exprIsAtom (Note (SCC _) e) = False +exprIsAtom (Note _ e) = exprIsAtom e +exprIsAtom other = False \end{code} @@ -262,10 +343,11 @@ exprIsTrivial other = False \begin{code} -exprIsDupable (Type _) = True -exprIsDupable (Var v) = True -exprIsDupable (Lit lit) = litIsDupable lit -exprIsDupable (Note _ e) = exprIsDupable e +exprIsDupable (Type _) = True +exprIsDupable (Var v) = True +exprIsDupable (Lit lit) = litIsDupable lit +exprIsDupable (Note InlineMe e) = True +exprIsDupable (Note _ e) = exprIsDupable e exprIsDupable expr = go expr 0 where @@ -312,8 +394,9 @@ exprIsCheap :: CoreExpr -> Bool exprIsCheap (Lit lit) = True exprIsCheap (Type _) = True exprIsCheap (Var _) = True +exprIsCheap (Note InlineMe e) = True exprIsCheap (Note _ e) = exprIsCheap e -exprIsCheap (Lam x e) = if isId x then True else exprIsCheap e +exprIsCheap (Lam x e) = isRuntimeVar x || exprIsCheap e exprIsCheap (Case e _ alts) = exprIsCheap e && and [exprIsCheap rhs | (_,_,rhs) <- alts] -- Experimentally, treat (case x of ...) as cheap @@ -339,8 +422,8 @@ exprIsCheap other_expr -- because it certainly doesn't need to be shared! go (App f a) n_args args_cheap - | isTypeArg a = go f n_args args_cheap - | otherwise = go f (n_args + 1) (exprIsCheap a && args_cheap) + | not (isRuntimeArg a) = go f n_args args_cheap + | otherwise = go f (n_args + 1) (exprIsCheap a && args_cheap) go other n_args args_cheap = False @@ -349,7 +432,7 @@ idAppIsCheap id n_val_args | n_val_args == 0 = True -- Just a type application of -- a variable (f t1 t2 t3) -- counts as WHNF - | otherwise = case idFlavour id of + | otherwise = case globalIdDetails id of DataConId _ -> True RecordSelId _ -> True -- I'm experimenting with making record selection -- look cheap, so we will substitute it inside a @@ -391,28 +474,50 @@ side effects, and can't diverge or raise an exception. \begin{code} exprOkForSpeculation :: CoreExpr -> Bool exprOkForSpeculation (Lit _) = True +exprOkForSpeculation (Type _) = True exprOkForSpeculation (Var v) = isUnLiftedType (idType v) exprOkForSpeculation (Note _ e) = exprOkForSpeculation e exprOkForSpeculation other_expr - = go other_expr 0 True + = case collectArgs other_expr of + (Var f, args) -> spec_ok (globalIdDetails f) args + other -> False + where - go (Var f) n_args args_ok - = case idFlavour f of - DataConId _ -> True -- The strictness of the constructor has already - -- been expressed by its "wrapper", so we don't need - -- to take the arguments into account - - PrimOpId op -> primOpOkForSpeculation op && args_ok + spec_ok (DataConId _) args + = True -- The strictness of the constructor has already + -- been expressed by its "wrapper", so we don't need + -- to take the arguments into account + + spec_ok (PrimOpId op) args + | isDivOp op, -- Special case for dividing operations that fail + [arg1, Lit lit] <- args -- only if the divisor is zero + = not (isZeroLit lit) && exprOkForSpeculation arg1 + -- Often there is a literal divisor, and this + -- can get rid of a thunk in an inner looop + + | otherwise + = primOpOkForSpeculation op && + all exprOkForSpeculation args -- A bit conservative: we don't really need -- to care about lazy arguments, but this is easy - other -> False - - go (App f a) n_args args_ok - | isTypeArg a = go f n_args args_ok - | otherwise = go f (n_args + 1) (exprOkForSpeculation a && args_ok) - - go other n_args args_ok = False + spec_ok other args = False + +isDivOp :: PrimOp -> Bool +-- True of dyadic operators that can fail +-- only if the second arg is zero +-- This function probably belongs in PrimOp, or even in +-- an automagically generated file.. but it's such a +-- special case I thought I'd leave it here for now. +isDivOp IntQuotOp = True +isDivOp IntRemOp = True +isDivOp WordQuotOp = True +isDivOp WordRemOp = True +isDivOp IntegerQuotRemOp = True +isDivOp IntegerDivModOp = True +isDivOp FloatDivOp = True +isDivOp DoubleDivOp = True +isDivOp other = False \end{code} @@ -430,69 +535,129 @@ exprIsBottom e = go 0 e go n (Lam _ _) = False idAppIsBottom :: Id -> Int -> Bool -idAppIsBottom id n_val_args = appIsBottom (idStrictness id) n_val_args +idAppIsBottom id n_val_args = appIsBottom (idNewStrictness id) n_val_args \end{code} @exprIsValue@ returns true for expressions that are certainly *already* -evaluated to WHNF. This is used to decide wether it's ok to change +evaluated to *head* normal form. This is used to decide whether it's ok +to change + case x of _ -> e ===> e and to decide whether it's safe to discard a `seq` -So, it does *not* treat variables as evaluated, unless they say they are +So, it does *not* treat variables as evaluated, unless they say they are. + +But it *does* treat partial applications and constructor applications +as values, even if their arguments are non-trivial, provided the argument +type is lifted; + e.g. (:) (f x) (map f xs) is a value + map (...redex...) is a value +Because `seq` on such things completes immediately + +For unlifted argument types, we have to be careful: + C (f x :: Int#) +Suppose (f x) diverges; then C (f x) is not a value. True, but +this form is illegal (see the invariants in CoreSyn). Args of unboxed +type must be ok-for-speculation (or trivial). \begin{code} exprIsValue :: CoreExpr -> Bool -- True => Value-lambda, constructor, PAP exprIsValue (Type ty) = True -- Types are honorary Values; we don't mind -- copying them exprIsValue (Lit l) = True -exprIsValue (Lam b e) = isId b || exprIsValue e +exprIsValue (Lam b e) = isRuntimeVar b || exprIsValue e exprIsValue (Note _ e) = exprIsValue e -exprIsValue other_expr - = go other_expr 0 - where - go (Var f) n_args = idAppIsValue f n_args - - go (App f a) n_args - | isTypeArg a = go f n_args - | otherwise = go f (n_args + 1) - - go (Note _ f) n_args = go f n_args - - go other n_args = False - -idAppIsValue :: Id -> Int -> Bool -idAppIsValue id n_val_args - = case idFlavour id of - DataConId _ -> True - PrimOpId _ -> n_val_args < idArity id - other | n_val_args == 0 -> isEvaldUnfolding (idUnfolding id) - | otherwise -> n_val_args < idArity id +exprIsValue (Var v) = idArity v > 0 || isEvaldUnfolding (idUnfolding v) + -- The idArity case catches data cons and primops that + -- don't have unfoldings -- A worry: what if an Id's unfolding is just itself: -- then we could get an infinite loop... +exprIsValue other_expr + | (Var fun, args) <- collectArgs other_expr, + isDataConId fun || valArgCount args < idArity fun + = check (idType fun) args + | otherwise + = False + where + -- 'check' checks that unlifted-type args are in + -- fact guaranteed non-divergent + check fun_ty [] = True + check fun_ty (Type _ : args) = case splitForAllTy_maybe fun_ty of + Just (_, ty) -> check ty args + check fun_ty (arg : args) + | isUnLiftedType arg_ty = exprOkForSpeculation arg + | otherwise = check res_ty args + where + (arg_ty, res_ty) = splitFunTy fun_ty \end{code} \begin{code} exprIsConApp_maybe :: CoreExpr -> Maybe (DataCon, [CoreExpr]) -exprIsConApp_maybe expr - = analyse (collectArgs expr) +exprIsConApp_maybe (Note (Coerce to_ty from_ty) expr) + = -- Maybe this is over the top, but here we try to turn + -- coerce (S,T) ( x, y ) + -- effectively into + -- ( coerce S x, coerce T y ) + -- This happens in anger in PrelArrExts which has a coerce + -- case coerce memcpy a b of + -- (# r, s #) -> ... + -- where the memcpy is in the IO monad, but the call is in + -- the (ST s) monad + case exprIsConApp_maybe expr of { + Nothing -> Nothing ; + Just (dc, args) -> + + case splitTyConApp_maybe to_ty of { + Nothing -> Nothing ; + Just (tc, tc_arg_tys) | tc /= dataConTyCon dc -> Nothing + | isExistentialDataCon dc -> Nothing + | otherwise -> + -- Type constructor must match + -- We knock out existentials to keep matters simple(r) + let + arity = tyConArity tc + val_args = drop arity args + to_arg_tys = dataConArgTys dc tc_arg_tys + mk_coerce ty arg = mkCoerce ty (exprType arg) arg + new_val_args = zipWith mk_coerce to_arg_tys val_args + in + ASSERT( all isTypeArg (take arity args) ) + ASSERT( length val_args == length to_arg_tys ) + Just (dc, map Type tc_arg_tys ++ new_val_args) + }} + +exprIsConApp_maybe (Note _ expr) + = exprIsConApp_maybe expr + -- We ignore InlineMe notes in case we have + -- x = __inline_me__ (a,b) + -- All part of making sure that INLINE pragmas never hurt + -- Marcin tripped on this one when making dictionaries more inlinable + -- + -- In fact, we ignore all notes. For example, + -- case _scc_ "foo" (C a b) of + -- C a b -> e + -- should be optimised away, but it will be only if we look + -- through the SCC note. + +exprIsConApp_maybe expr = analyse (collectArgs expr) where analyse (Var fun, args) - | maybeToBool maybe_con_app = maybe_con_app - where - maybe_con_app = case isDataConId_maybe fun of - Just con | length args >= dataConRepArity con - -- Might be > because the arity excludes type args - -> Just (con, args) - other -> Nothing + | Just con <- isDataConId_maybe fun, + length args >= dataConRepArity con + -- Might be > because the arity excludes type args + = Just (con,args) + -- Look through unfoldings, but only cheap ones, because + -- we are effectively duplicating the unfolding analyse (Var fun, []) - = case maybeUnfoldingTemplate (idUnfolding fun) of - Nothing -> Nothing - Just unf -> exprIsConApp_maybe unf + | let unf = idUnfolding fun, + isCheapUnfolding unf + = exprIsConApp_maybe (unfoldingTemplate unf) analyse other = Nothing -\end{code} +\end{code} + %************************************************************************ @@ -501,89 +666,244 @@ exprIsConApp_maybe expr %* * %************************************************************************ -@etaReduceExpr@ trys an eta reduction at the top level of a Core Expr. +\begin{code} +exprEtaExpandArity :: CoreExpr -> Arity +-- The Int is number of value args the thing can be +-- applied to without doing much work +-- +-- This is used when eta expanding +-- e ==> \xy -> e x y +-- +-- It returns 1 (or more) to: +-- case x of p -> \s -> ... +-- because for I/O ish things we really want to get that \s to the top. +-- We are prepared to evaluate x each time round the loop in order to get that -e.g. \ x y -> f x y ===> f +-- It's all a bit more subtle than it looks. Consider one-shot lambdas +-- let x = expensive in \y z -> E +-- We want this to have arity 2 if the \y-abstraction is a 1-shot lambda +-- Hence the ArityType returned by arityType + +-- NB: this is particularly important/useful for IO state +-- transformers, where we often get +-- let x = E in \ s -> ... +-- and the \s is a real-world state token abstraction. Such +-- abstractions are almost invariably 1-shot, so we want to +-- pull the \s out, past the let x=E. +-- The hack is in Id.isOneShotLambda +-- +-- Consider also +-- f = \x -> error "foo" +-- Here, arity 1 is fine. But if it is +-- f = \x -> case e of +-- True -> error "foo" +-- False -> \y -> x+y +-- then we want to get arity 2. +-- Hence the ABot/ATop in ArityType + + +exprEtaExpandArity e = arityDepth (arityType e) + +-- A limited sort of function type +data ArityType = AFun Bool ArityType -- True <=> one-shot + | ATop -- Know nothing + | ABot -- Diverges + +arityDepth :: ArityType -> Arity +arityDepth (AFun _ ty) = 1 + arityDepth ty +arityDepth ty = 0 + +andArityType ABot at2 = at2 +andArityType ATop at2 = ATop +andArityType (AFun t1 at1) (AFun t2 at2) = AFun (t1 && t2) (andArityType at1 at2) +andArityType at1 at2 = andArityType at2 at1 + +arityType :: CoreExpr -> ArityType + -- (go1 e) = [b1,..,bn] + -- means expression can be rewritten \x_b1 -> ... \x_bn -> body + -- where bi is True <=> the lambda is one-shot + +arityType (Note n e) = arityType e +-- Not needed any more: etaExpand is cleverer +-- | ok_note n = arityType e +-- | otherwise = ATop + +arityType (Var v) + = mk (idArity v) + where + mk :: Arity -> ArityType + mk 0 | isBottomingId v = ABot + | otherwise = ATop + mk n = AFun False (mk (n-1)) + + -- When the type of the Id encodes one-shot-ness, + -- use the idinfo here + + -- Lambdas; increase arity +arityType (Lam x e) | isId x = AFun (isOneShotLambda x) (arityType e) + | otherwise = arityType e + + -- Applications; decrease arity +arityType (App f (Type _)) = arityType f +arityType (App f a) = case arityType f of + AFun one_shot xs | one_shot -> xs + | exprIsCheap a -> xs + other -> ATop + + -- Case/Let; keep arity if either the expression is cheap + -- or it's a 1-shot lambda +arityType (Case scrut _ alts) = case foldr1 andArityType [arityType rhs | (_,_,rhs) <- alts] of + xs@(AFun one_shot _) | one_shot -> xs + xs | exprIsCheap scrut -> xs + | otherwise -> ATop + +arityType (Let b e) = case arityType e of + xs@(AFun one_shot _) | one_shot -> xs + xs | all exprIsCheap (rhssOfBind b) -> xs + | otherwise -> ATop + +arityType other = ATop + +{- NOT NEEDED ANY MORE: etaExpand is cleverer +ok_note InlineMe = False +ok_note other = True + -- Notice that we do not look through __inline_me__ + -- This may seem surprising, but consider + -- f = _inline_me (\x -> e) + -- We DO NOT want to eta expand this to + -- f = \x -> (_inline_me (\x -> e)) x + -- because the _inline_me gets dropped now it is applied, + -- giving just + -- f = \x -> e + -- A Bad Idea +-} +\end{code} -But we only do this if it gets rid of a whole lambda, not part. -The idea is that lambdas are often quite helpful: they indicate -head normal forms, so we don't want to chuck them away lightly. \begin{code} -etaReduceExpr :: CoreExpr -> CoreExpr - -- ToDo: we should really check that we don't turn a non-bottom - -- lambda into a bottom variable. Sigh +etaExpand :: Arity -- Result should have this number of value args + -> [Unique] + -> CoreExpr -> Type -- Expression and its type + -> CoreExpr +-- (etaExpand n us e ty) returns an expression with +-- the same meaning as 'e', but with arity 'n'. +-- +-- Given e' = etaExpand n us e ty +-- We should have +-- ty = exprType e = exprType e' -etaReduceExpr expr@(Lam bndr body) - = check (reverse binders) body +etaExpand n us expr ty + | manifestArity expr >= n = expr -- The no-op case + | otherwise = eta_expand n us expr ty where - (binders, body) = collectBinders expr - check [] body - | not (any (`elemVarSet` body_fvs) binders) - = body -- Success! - where - body_fvs = exprFreeVars body +-- manifestArity sees how many leading value lambdas there are +manifestArity :: CoreExpr -> Arity +manifestArity (Lam v e) | isId v = 1 + manifestArity e + | otherwise = manifestArity e +manifestArity (Note _ e) = manifestArity e +manifestArity e = 0 + +-- etaExpand deals with for-alls. For example: +-- etaExpand 1 E +-- where E :: forall a. a -> a +-- would return +-- (/\b. \y::a -> E b y) +-- +-- It deals with coerces too, though they are now rare +-- so perhaps the extra code isn't worth it + +eta_expand n us expr ty + | n == 0 && + -- The ILX code generator requires eta expansion for type arguments + -- too, but alas the 'n' doesn't tell us how many of them there + -- may be. So we eagerly eta expand any big lambdas, and just + -- cross our fingers about possible loss of sharing in the + -- ILX case. + -- The Right Thing is probably to make 'arity' include + -- type variables throughout the compiler. (ToDo.) + not (isForAllTy ty) + -- Saturated, so nothing to do + = expr + +eta_expand n us (Note note@(Coerce _ ty) e) _ + = Note note (eta_expand n us e ty) + + -- Use mkNote so that _scc_s get pushed inside any lambdas that + -- are generated as part of the eta expansion. We rely on this + -- behaviour in CorePrep, when we eta expand an already-prepped RHS. +eta_expand n us (Note note e) ty + = mkNote note (eta_expand n us e ty) + + -- Short cut for the case where there already + -- is a lambda; no point in gratuitously adding more +eta_expand n us (Lam v body) ty + | isTyVar v + = Lam v (eta_expand n us body (applyTy ty (mkTyVarTy v))) + + | otherwise + = Lam v (eta_expand (n-1) us body (funResultTy ty)) + +eta_expand n us expr ty + = case splitForAllTy_maybe ty of { + Just (tv,ty') -> Lam tv (eta_expand n us (App expr (Type (mkTyVarTy tv))) ty') + + ; Nothing -> + + case splitFunTy_maybe ty of { + Just (arg_ty, res_ty) -> Lam arg1 (eta_expand (n-1) us2 (App expr (Var arg1)) res_ty) + where + arg1 = mkSysLocal SLIT("eta") uniq arg_ty + (uniq:us2) = us + + ; Nothing -> + + case splitNewType_maybe ty of { + Just ty' -> mkCoerce ty ty' (eta_expand n us (mkCoerce ty' ty expr) ty') ; + Nothing -> pprTrace "Bad eta expand" (ppr expr $$ ppr ty) expr + }}} +\end{code} - check (b : bs) (App fun arg) - | (varToCoreExpr b `cheapEqExpr` arg) - = check bs fun +exprArity is a cheap-and-cheerful version of exprEtaExpandArity. +It tells how many things the expression can be applied to before doing +any work. It doesn't look inside cases, lets, etc. The idea is that +exprEtaExpandArity will do the hard work, leaving something that's easy +for exprArity to grapple with. In particular, Simplify uses exprArity to +compute the ArityInfo for the Id. - check _ _ = expr -- Bale out +Originally I thought that it was enough just to look for top-level lambdas, but +it isn't. I've seen this -etaReduceExpr expr = expr -- The common case -\end{code} - + foo = PrelBase.timesInt -\begin{code} -exprEtaExpandArity :: CoreExpr -> Int -- The number of args the thing can be applied to - -- without doing much work --- This is used when eta expanding --- e ==> \xy -> e x y --- --- It returns 1 (or more) to: --- case x of p -> \s -> ... --- because for I/O ish things we really want to get that \s to the top. --- We are prepared to evaluate x each time round the loop in order to get that --- Hence "generous" arity +We want foo to get arity 2 even though the eta-expander will leave it +unchanged, in the expectation that it'll be inlined. But occasionally it +isn't, because foo is blacklisted (used in a rule). -exprEtaExpandArity e - = go e `max` 0 -- Never go -ve! - where - go (Var v) = idArity v - go (App f (Type _)) = go f - go (App f a) | exprIsCheap a = go f - 1 - go (Lam x e) | isId x = go e + 1 - | otherwise = go e - go (Note n e) | ok_note n = go e - go (Case scrut _ alts) - | exprIsCheap scrut = min_zero [go rhs | (_,_,rhs) <- alts] - go (Let b e) - | all exprIsCheap (rhssOfBind b) = go e - - go other = 0 - - ok_note (Coerce _ _) = True - ok_note InlineCall = True - ok_note other = False - -- Notice that we do not look through __inline_me__ - -- This one is a bit more surprising, but consider - -- f = _inline_me (\x -> e) - -- We DO NOT want to eta expand this to - -- f = \x -> (_inline_me (\x -> e)) x - -- because the _inline_me gets dropped now it is applied, - -- giving just - -- f = \x -> e - -- A Bad Idea - -min_zero :: [Int] -> Int -- Find the minimum, but zero is the smallest -min_zero (x:xs) = go x xs - where - go 0 xs = 0 -- Nothing beats zero - go min [] = min - go min (x:xs) | x < min = go x xs - | otherwise = go min xs +Similarly, see the ok_note check in exprEtaExpandArity. So + f = __inline_me (\x -> e) +won't be eta-expanded. +And in any case it seems more robust to have exprArity be a bit more intelligent. +But note that (\x y z -> f x y z) +should have arity 3, regardless of f's arity. + +\begin{code} +exprArity :: CoreExpr -> Arity +exprArity e = go e + where + go (Var v) = idArity v + go (Lam x e) | isId x = go e + 1 + | otherwise = go e + go (Note n e) = go e + go (App e (Type t)) = go e + go (App f a) | exprIsCheap a = (go f - 1) `max` 0 + -- NB: exprIsCheap a! + -- f (fac x) does not have arity 2, + -- even if f has arity 3! + -- NB: `max 0`! (\x y -> f x) has arity 2, even if f is + -- unknown, hence arity 0 + go _ = 0 \end{code} @@ -602,7 +922,7 @@ cheapEqExpr :: Expr b -> Expr b -> Bool cheapEqExpr (Var v1) (Var v2) = v1==v2 cheapEqExpr (Lit lit1) (Lit lit2) = lit1 == lit2 -cheapEqExpr (Type t1) (Type t2) = t1 == t2 +cheapEqExpr (Type t1) (Type t2) = t1 `eqType` t2 cheapEqExpr (App f1 a1) (App f2 a2) = f1 `cheapEqExpr` f2 && a1 `cheapEqExpr` a2 @@ -622,6 +942,9 @@ exprIsBig other = True \begin{code} eqExpr :: CoreExpr -> CoreExpr -> Bool -- Works ok at more general type, but only needed at CoreExpr + -- Used in rule matching, so when we find a type we use + -- eqTcType, which doesn't look through newtypes + -- [And it doesn't risk falling into a black hole either.] eqExpr e1 e2 = eq emptyVarEnv e1 e2 where @@ -652,7 +975,7 @@ eqExpr e1 e2 env' = extendVarEnv env v1 v2 eq env (Note n1 e1) (Note n2 e2) = eq_note env n1 n2 && eq env e1 e2 - eq env (Type t1) (Type t2) = t1 == t2 + eq env (Type t1) (Type t2) = t1 `eqType` t2 eq env e1 e2 = False eq_list env [] [] = True @@ -663,7 +986,7 @@ eqExpr e1 e2 eq (extendVarEnvList env (vs1 `zip` vs2)) r1 r2 eq_note env (SCC cc1) (SCC cc2) = cc1 == cc2 - eq_note env (Coerce t1 f1) (Coerce t2 f2) = t1==t2 && f1==f2 + eq_note env (Coerce t1 f1) (Coerce t2 f2) = t1 `eqType` t2 && f1 `eqType` f2 eq_note env InlineCall InlineCall = True eq_note env other1 other2 = False \end{code}