X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=ghc%2Fcompiler%2FcoreSyn%2FCoreUtils.lhs;h=447768c31b79eb21008cb20dad7b6a5827cac5d6;hb=fce821cae79c1a4749880100148f5bdd2bf29412;hp=131bd4706170fe08ae79466edc9d34decb43e5d7;hpb=a127213c1890584702075d732d7bb9887113e4ff;p=ghc-hetmet.git diff --git a/ghc/compiler/coreSyn/CoreUtils.lhs b/ghc/compiler/coreSyn/CoreUtils.lhs index 131bd47..447768c 100644 --- a/ghc/compiler/coreSyn/CoreUtils.lhs +++ b/ghc/compiler/coreSyn/CoreUtils.lhs @@ -5,19 +5,25 @@ \begin{code} module CoreUtils ( - exprType, coreAltsType, - -- Construction mkNote, mkInlineMe, mkSCC, mkCoerce, bindNonRec, mkIfThenElse, mkAltExpr, + mkPiType, + + -- Taking expressions apart + findDefault, findAlt, hasDefault, + -- Properties of expressions + exprType, coreAltsType, exprIsBottom, exprIsDupable, exprIsTrivial, exprIsCheap, exprIsValue,exprOkForSpeculation, exprIsBig, - exprArity, exprIsConApp_maybe, - + exprIsConApp_maybe, exprIsAtom, idAppIsBottom, idAppIsCheap, + exprArity, - etaReduceExpr, exprEtaExpandArity, + -- Expr transformation + etaReduce, etaExpand, + exprArity, exprEtaExpandArity, -- Size coreBindsSize, @@ -40,29 +46,25 @@ import PprCore ( pprCoreExpr ) import Var ( Var, isId, isTyVar ) import VarSet import VarEnv -import Name ( isLocallyDefined, hashName ) -import Literal ( Literal, hashLiteral, literalType ) +import Name ( hashName ) +import Literal ( hashLiteral, literalType, litIsDupable ) import DataCon ( DataCon, dataConRepArity ) import PrimOp ( primOpOkForSpeculation, primOpIsCheap ) -import Id ( Id, idType, idFlavour, idStrictness, idLBVarInfo, mkWildId, - idArity, idName, idUnfolding, idInfo, isDataConId_maybe - +import Id ( Id, idType, globalIdDetails, idNewStrictness, idLBVarInfo, + mkWildId, idArity, idName, idUnfolding, idInfo, isOneShotLambda, + isDataConId_maybe, mkSysLocal, hasNoBinding ) -import IdInfo ( arityLowerBound, InlinePragInfo(..), - LBVarInfo(..), - IdFlavour(..), +import IdInfo ( LBVarInfo(..), + GlobalIdDetails(..), megaSeqIdInfo ) -import Demand ( appIsBottom ) -import Type ( Type, mkFunTy, mkForAllTy, - splitFunTy_maybe, tyVarsOfType, tyVarsOfTypes, - isNotUsgTy, mkUsgTy, unUsgTy, UsageAnn(..), - applyTys, isUnLiftedType, seqType +import NewDemand ( appIsBottom ) +import Type ( Type, mkFunTy, mkForAllTy, splitFunTy_maybe, + applyTys, isUnLiftedType, seqType, mkUTy, mkTyVarTy, + splitForAllTy_maybe, isForAllTy, splitNewType_maybe, eqType ) -import TysWiredIn ( boolTy, stringTy, trueDataCon, falseDataCon ) +import TysWiredIn ( boolTy, trueDataCon, falseDataCon ) import CostCentre ( CostCentre ) -import Unique ( buildIdKey, augmentIdKey ) -import Util ( zipWithEqual, mapAccumL ) -import Maybes ( maybeToBool ) +import UniqSupply ( UniqSupply, splitUniqSupply, uniqFromSupply ) import Outputable import TysPrim ( alphaTy ) -- Debugging only \end{code} @@ -82,15 +84,8 @@ exprType (Lit lit) = literalType lit exprType (Let _ body) = exprType body exprType (Case _ _ alts) = coreAltsType alts exprType (Note (Coerce ty _) e) = ty -- **! should take usage from e -exprType (Note (TermUsg u) e) = mkUsgTy u (unUsgTy (exprType e)) exprType (Note other_note e) = exprType e -exprType (Lam binder expr) - | isId binder = (case idLBVarInfo binder of - IsOneShotLambda -> mkUsgTy UsOnce - otherwise -> id) $ - idType binder `mkFunTy` exprType expr - | isTyVar binder = mkForAllTy binder (exprType expr) - +exprType (Lam binder expr) = mkPiType binder (exprType expr) exprType e@(App _ _) = case collectArgs e of (fun, args) -> applyTypeToArgs e (exprType fun) args @@ -101,6 +96,20 @@ coreAltsType :: [CoreAlt] -> Type coreAltsType ((_,_,rhs) : _) = exprType rhs \end{code} +@mkPiType@ makes a (->) type or a forall type, depending on whether +it is given a type variable or a term variable. We cleverly use the +lbvarinfo field to figure out the right annotation for the arrove in +case of a term variable. + +\begin{code} +mkPiType :: Var -> Type -> Type -- The more polymorphic version doesn't work... +mkPiType v ty | isId v = (case idLBVarInfo v of + LBVarInfo u -> mkUTy u + otherwise -> id) $ + mkFunTy (idType v) ty + | isTyVar v = mkForAllTy v ty +\end{code} + \begin{code} -- The first argument is just for debugging applyTypeToArgs :: CoreExpr -> Type -> [CoreExpr] -> Type @@ -108,9 +117,6 @@ applyTypeToArgs e op_ty [] = op_ty applyTypeToArgs e op_ty (Type ty : args) = -- Accumulate type arguments so we can instantiate all at once - ASSERT2( all isNotUsgTy tys, - ppr e <+> text "of" <+> ppr op_ty <+> text "to" <+> - ppr (Type ty : args) <+> text "i.e." <+> ppr tys ) applyTypeToArgs e (applyTys op_ty tys) rest_args where (tys, rest_args) = go [ty] args @@ -151,35 +157,52 @@ 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} \begin{code} -mkCoerce :: Type -> Type -> Expr b -> Expr b --- In (mkCoerce to_ty from_ty e), we require that from_ty = exprType e --- But exprType is defined in CoreUtils, so we don't check the assertion +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 = 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} @@ -221,27 +244,85 @@ 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} %* * %************************************************************************ -@exprIsTrivial@ is true of expressions we are unconditionally - happy to duplicate; simple variables and constants, - and type applications. +@exprIsTrivial@ is true of expressions we are unconditionally happy to + duplicate; simple variables and constants, and type + applications. Note that primop Ids aren't considered + trivial unless @exprIsBottom@ is true of expressions that are guaranteed to diverge \begin{code} -exprIsTrivial (Type _) = True -exprIsTrivial (Lit lit) = True -exprIsTrivial (Var v) = 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) + | hasNoBinding v = idArity v == 0 + -- WAS: | Just op <- isPrimOpId_maybe v = primOpIsDupable op + -- 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. + -- This came up when dealing with eta expansion/reduction for + -- x = $wJust + -- Here we want to eta-expand. This looks like an optimisation, + -- but it's important (albeit tiresome) that CoreSat doesn't increase + -- anything's arity + | otherwise = True +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} @@ -257,10 +338,11 @@ exprIsTrivial other = False \begin{code} -exprIsDupable (Type _) = True -exprIsDupable (Var v) = True -exprIsDupable (Lit lit) = True -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 @@ -288,19 +370,16 @@ shared. The main examples of things which aren't WHNF but are * case e of pi -> ei + (where e, and all the ei are cheap) - where e, and all the ei are cheap; and - - * let x = e - in b - - where e and b are cheap; and + * let x = e in b + (where e and b are cheap) * op x1 ... xn - - where op is a cheap primitive operator + (where op is a cheap primitive operator) * error "foo" + (because we are happy to substitute it inside a lambda) Notice that a variable is considered 'cheap': we can push it inside a lambda, because sharing will make sure it is only evaluated once. @@ -310,12 +389,21 @@ 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 (Case (Var v) _ alts) = and [exprIsCheap rhs | (_,_,rhs) <- alts] +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 + -- (and case __coerce x etc.) -- This improves arities of overloaded functions where -- there is only dictionary selection (no construction) involved +exprIsCheap (Let (NonRec x _) e) + | isUnLiftedType (idType x) = exprIsCheap e + | otherwise = False + -- strict lets always have cheap right hand sides, and + -- do no allocation. + exprIsCheap other_expr = go other_expr 0 True where @@ -325,13 +413,12 @@ exprIsCheap other_expr || idAppIsBottom f n_args -- Application of a function which - -- always gives bottom; we treat this as - -- a WHNF, because it certainly doesn't - -- need to be shared! + -- always gives bottom; we treat this as cheap + -- 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 @@ -340,7 +427,7 @@ 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 @@ -388,7 +475,7 @@ exprOkForSpeculation other_expr = go other_expr 0 True where go (Var f) n_args args_ok - = case idFlavour f of + = case globalIdDetails 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 @@ -400,8 +487,8 @@ exprOkForSpeculation other_expr 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) + | not (isRuntimeArg a) = go f n_args args_ok + | otherwise = go f (n_args + 1) (exprOkForSpeculation a && args_ok) go other n_args args_ok = False \end{code} @@ -421,23 +508,35 @@ 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 WHNF. 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; + e.g. (:) (f x) (map f xs) is a value + map (...redex...) is a value +Because `seq` on such things completes immediately + +A possible worry: constructors with unboxed args: + 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 @@ -445,8 +544,8 @@ exprIsValue other_expr 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) + | not (isRuntimeArg a) = go f n_args + | otherwise = go f (n_args + 1) go (Note _ f) n_args = go f n_args @@ -454,7 +553,7 @@ exprIsValue other_expr idAppIsValue :: Id -> Int -> Bool idAppIsValue id n_val_args - = case idFlavour id of + = case globalIdDetails id of DataConId _ -> True PrimOpId _ -> n_val_args < idArity id other | n_val_args == 0 -> isEvaldUnfolding (idUnfolding id) @@ -464,45 +563,31 @@ idAppIsValue id n_val_args \end{code} \begin{code} -exprArity :: CoreExpr -> Int -- How many value lambdas are at the top -exprArity (Lam b e) | isTyVar b = exprArity e - | otherwise = 1 + exprArity e - -exprArity (Note note e) | ok_note note = exprArity e - where - ok_note (Coerce _ _) = True - -- We *do* look through coerces when getting arities. - -- Reason: arities are to do with *representation* and - -- work duplication. - ok_note InlineMe = True - ok_note InlineCall = True - ok_note other = False - -- SCC and TermUsg might be over-conservative? - -exprArity other = 0 -\end{code} - -\begin{code} exprIsConApp_maybe :: CoreExpr -> Maybe (DataCon, [CoreExpr]) -exprIsConApp_maybe expr - = analyse (collectArgs expr) +exprIsConApp_maybe (Note InlineMe 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 + +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} + %************************************************************************ @@ -511,7 +596,7 @@ exprIsConApp_maybe expr %* * %************************************************************************ -@etaReduceExpr@ trys an eta reduction at the top level of a Core Expr. +@etaReduce@ trys an eta reduction at the top level of a Core Expr. e.g. \ x y -> f x y ===> f @@ -520,11 +605,11 @@ 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 +etaReduce :: CoreExpr -> CoreExpr -- ToDo: we should really check that we don't turn a non-bottom -- lambda into a bottom variable. Sigh -etaReduceExpr expr@(Lam bndr body) +etaReduce expr@(Lam bndr body) = check (reverse binders) body where (binders, body) = collectBinders expr @@ -541,13 +626,18 @@ etaReduceExpr expr@(Lam bndr body) check _ _ = expr -- Bale out -etaReduceExpr expr = expr -- The common case +etaReduce expr = expr -- The common case \end{code} \begin{code} -exprEtaExpandArity :: CoreExpr -> Int -- The number of args the thing can be applied to - -- without doing much work +exprEtaExpandArity :: CoreExpr -> (Int, Bool) +-- The Int is number of value args the thing can be +-- applied to without doing much work +-- The Bool is True iff there are enough explicit value lambdas +-- at the top to make this arity apparent +-- (but ignore it when arity==0) + -- This is used when eta expanding -- e ==> \xy -> e x y -- @@ -555,29 +645,65 @@ exprEtaExpandArity :: CoreExpr -> Int -- The number of args the thing can be ap -- 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 +-- +-- Consider 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 list of Bools returned by go1 +-- 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 exprEtaExpandArity e - = go e + = go 0 e where - go (Var v) = idArity v - go (App f (Type _)) = go f - go (App f a) | exprIsCheap a = (go f - 1) `max` 0 -- Never go -ve! - 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 :: Int -> CoreExpr -> (Int,Bool) + go ar (Lam x e) | isId x = go (ar+1) e + | otherwise = go ar e + go ar (Note n e) | ok_note n = go ar e + go ar other = (ar + ar', ar' == 0) + where + ar' = length (go1 other) + + go1 :: CoreExpr -> [Bool] + -- (go1 e) = [b1,..,bn] + -- means expression can be rewritten \x_b1 -> ... \x_bn -> body + -- where bi is True <=> the lambda is one-shot + + go1 (Note n e) | ok_note n = go1 e + go1 (Var v) = replicate (idArity v) False -- When the type of the Id + -- encodes one-shot-ness, use + -- the idinfo here + + -- Lambdas; increase arity + go1 (Lam x e) | isId x = isOneShotLambda x : go1 e + | otherwise = go1 e + + -- Applications; decrease arity + go1 (App f (Type _)) = go1 f + go1 (App f a) = case go1 f of + (one_shot : xs) | one_shot || exprIsCheap a -> xs + other -> [] + + -- Case/Let; keep arity if either the expression is cheap + -- or it's a 1-shot lambda + go1 (Case scrut _ alts) = case foldr1 (zipWith (&&)) [go1 rhs | (_,_,rhs) <- alts] of + xs@(one_shot : _) | one_shot || exprIsCheap scrut -> xs + other -> [] + go1 (Let b e) = case go1 e of + xs@(one_shot : _) | one_shot || all exprIsCheap (rhssOfBind b) -> xs + other -> [] + + go1 other = [] - go other = 0 - - ok_note (Coerce _ _) = True - ok_note InlineCall = True - ok_note other = False + ok_note InlineMe = False + ok_note other = True -- Notice that we do not look through __inline_me__ - -- This one is a bit more surprising, but consider + -- 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 @@ -585,15 +711,103 @@ exprEtaExpandArity e -- giving just -- f = \x -> e -- A Bad Idea +\end{code} -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 +\begin{code} +etaExpand :: Int -- Add this number of value args + -> UniqSupply + -> 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' +-- +-- 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 + +etaExpand 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 + + | otherwise -- An unsaturated constructor or primop; eta expand it + = case splitForAllTy_maybe ty of { + Just (tv,ty') -> Lam tv (etaExpand n us (App expr (Type (mkTyVarTy tv))) ty') + + ; Nothing -> + + case splitFunTy_maybe ty of { + Just (arg_ty, res_ty) -> Lam arg1 (etaExpand (n-1) us2 (App expr (Var arg1)) res_ty) + where + arg1 = mkSysLocal SLIT("eta") uniq arg_ty + (us1, us2) = splitUniqSupply us + uniq = uniqFromSupply us1 + + ; Nothing -> + + case splitNewType_maybe ty of { + Just ty' -> mkCoerce ty ty' (etaExpand n us (mkCoerce ty' ty expr) ty') ; + Nothing -> pprTrace "Bad eta expand" (ppr expr $$ ppr ty) expr + }}} +\end{code} + + +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. + +Originally I thought that it was enough just to look for top-level lambdas, but +it isn't. I've seen this + + foo = PrelBase.timesInt + +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). + +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. + +\begin{code} +exprArity :: CoreExpr -> Int +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} @@ -612,7 +826,7 @@ 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 @@ -632,6 +846,9 @@ 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 @@ -662,7 +879,7 @@ 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 @@ -673,7 +890,7 @@ 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} @@ -693,22 +910,24 @@ exprSize :: CoreExpr -> Int -- A measure of the size of the expressions -- It also forces the expression pretty drastically as a side effect exprSize (Var v) = varSize v -exprSize (Lit lit) = 1 +exprSize (Lit lit) = lit `seq` 1 exprSize (App f a) = exprSize f + exprSize a exprSize (Lam b e) = varSize b + exprSize e exprSize (Let b e) = bindSize b + exprSize e -exprSize (Case e b as) = exprSize e + varSize b + foldr ((+) . altSize) 0 as -exprSize (Note n e) = exprSize e -exprSize (Type t) = seqType t `seq` - 1 +exprSize (Case e b as) = exprSize e + varSize b + foldr ((+) . altSize) 0 as +exprSize (Note n e) = noteSize n + exprSize e +exprSize (Type t) = seqType t `seq` 1 -exprsSize = foldr ((+) . exprSize) 0 +noteSize (SCC cc) = cc `seq` 1 +noteSize (Coerce t1 t2) = seqType t1 `seq` seqType t2 `seq` 1 +noteSize InlineCall = 1 +noteSize InlineMe = 1 varSize :: Var -> Int -varSize b | isTyVar b = 1 - | otherwise = seqType (idType b) `seq` - megaSeqIdInfo (idInfo b) `seq` - 1 +varSize b | isTyVar b = 1 + | otherwise = seqType (idType b) `seq` + megaSeqIdInfo (idInfo b) `seq` + 1 varsSize = foldr ((+) . varSize) 0