X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=ghc%2Fcompiler%2FcoreSyn%2FCoreUtils.lhs;h=24b1f35cf2a5fec6ce9a8cc9161417d743d7b19b;hb=fda5605a79bc7bc5f0ef5bbaf241f89d951b65ce;hp=049578e67fd486561aa0dc3340287115427e5d21;hpb=f922d7032692a14890391d0720751c38ce0f7546;p=ghc-hetmet.git diff --git a/ghc/compiler/coreSyn/CoreUtils.lhs b/ghc/compiler/coreSyn/CoreUtils.lhs index 049578e..24b1f35 100644 --- a/ghc/compiler/coreSyn/CoreUtils.lhs +++ b/ghc/compiler/coreSyn/CoreUtils.lhs @@ -5,41 +5,64 @@ \begin{code} module CoreUtils ( - coreExprType, coreAltsType, + -- Construction + mkNote, mkInlineMe, mkSCC, mkCoerce, + bindNonRec, mkIfThenElse, mkAltExpr, + mkPiType, - exprIsBottom, exprIsDupable, exprIsTrivial, exprIsWHNF, exprIsCheap, - exprOkForSpeculation, - FormSummary(..), mkFormSummary, whnfOrBottom, exprArity, + -- Properties of expressions + exprType, coreAltsType, + exprIsBottom, exprIsDupable, exprIsTrivial, exprIsCheap, + exprIsValue,exprOkForSpeculation, exprIsBig, + exprIsConApp_maybe, + idAppIsBottom, idAppIsCheap, + + -- Expr transformation + etaReduceExpr, exprEtaExpandArity, + + -- Size + coreBindsSize, + + -- Hashing + hashExpr, + + -- Equality cheapEqExpr, eqExpr, applyTypeToArgs ) where #include "HsVersions.h" +import GlaExts -- For `xori` + import CoreSyn +import CoreFVs ( exprFreeVars ) import PprCore ( pprCoreExpr ) -import Var ( IdOrTyVar, isId, isTyVar ) +import Var ( Var, isId, isTyVar ) import VarSet import VarEnv -import Name ( isLocallyDefined ) -import Const ( Con, isWHNFCon, conIsTrivial, conIsCheap, conIsDupable, - conType, conOkForSpeculation, conStrictness - ) -import Id ( Id, idType, setIdType, idUnique, idAppIsBottom, - getIdArity, - getIdSpecialisation, setIdSpecialisation, - getInlinePragma, setInlinePragma, - getIdUnfolding, setIdUnfolding, idInfo +import Name ( isLocallyDefined, hashName ) +import Literal ( 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 IdInfo ( arityLowerBound, InlinePragInfo(..), lbvarInfo, LBVarInfo(..) ) +import IdInfo ( arityLowerBound, InlinePragInfo(..), + LBVarInfo(..), + IdFlavour(..), + megaSeqIdInfo ) +import Demand ( appIsBottom ) import Type ( Type, mkFunTy, mkForAllTy, splitFunTy_maybe, tyVarsOfType, tyVarsOfTypes, isNotUsgTy, mkUsgTy, unUsgTy, UsageAnn(..), - tidyTyVar, applyTys, isUnLiftedType + applyTys, isUnLiftedType, seqType ) -import Demand ( isPrim, isLazy ) -import Unique ( buildIdKey, augmentIdKey ) -import Util ( zipWithEqual, mapAccumL ) +import TysWiredIn ( boolTy, stringTy, trueDataCon, falseDataCon ) +import CostCentre ( CostCentre ) +import Maybes ( maybeToBool ) import Outputable import TysPrim ( alphaTy ) -- Debugging only \end{code} @@ -52,31 +75,38 @@ import TysPrim ( alphaTy ) -- Debugging only %************************************************************************ \begin{code} -coreExprType :: CoreExpr -> Type - -coreExprType (Var var) = idType var -coreExprType (Let _ body) = coreExprType body -coreExprType (Case _ _ alts) = coreAltsType alts -coreExprType (Note (Coerce ty _) e) = ty -coreExprType (Note (TermUsg u) e) = mkUsgTy u (unUsgTy (coreExprType e)) -coreExprType (Note other_note e) = coreExprType e -coreExprType e@(Con con args) = applyTypeToArgs e (conType con) args - -coreExprType (Lam binder expr) - | isId binder = (case (lbvarInfo . idInfo) binder of - IsOneShotLambda -> mkUsgTy UsOnce - otherwise -> id) $ - idType binder `mkFunTy` coreExprType expr - | isTyVar binder = mkForAllTy binder (coreExprType expr) - -coreExprType e@(App _ _) +exprType :: CoreExpr -> Type + +exprType (Var var) = idType var +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) = mkPiType binder (exprType expr) +exprType e@(App _ _) = case collectArgs e of - (fun, args) -> applyTypeToArgs e (coreExprType fun) args + (fun, args) -> applyTypeToArgs e (exprType fun) args -coreExprType other = pprTrace "coreExprType" (pprCoreExpr other) alphaTy +exprType other = pprTrace "exprType" (pprCoreExpr other) alphaTy coreAltsType :: [CoreAlt] -> Type -coreAltsType ((_,_,rhs) : _) = coreExprType rhs +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 + IsOneShotLambda -> mkUsgTy UsOnce + otherwise -> id) $ + mkFunTy (idType v) ty + | isTyVar v = mkForAllTy v ty \end{code} \begin{code} @@ -86,7 +116,9 @@ 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 ) + 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 @@ -100,107 +132,153 @@ applyTypeToArgs e op_ty (other_arg : args) \end{code} + %************************************************************************ %* * -\subsection{Figuring out things about expressions} +\subsection{Attaching notes} %* * %************************************************************************ +mkNote removes redundant coercions, and SCCs where possible + +\begin{code} +mkNote :: Note -> CoreExpr -> CoreExpr +mkNote (Coerce to_ty from_ty) expr = mkCoerce to_ty from_ty expr +mkNote (SCC cc) expr = mkSCC cc expr +mkNote InlineMe expr = mkInlineMe expr +mkNote note expr = Note note expr + +-- Slide InlineCall in around the function +-- No longer necessary I think (SLPJ Apr 99) +-- mkNote InlineCall (App f a) = App (mkNote InlineCall f) a +-- mkNote InlineCall (Var v) = Note InlineCall (Var v) +-- mkNote InlineCall expr = expr +\end{code} + +Drop trivial InlineMe's. This is somewhat important, because if we have an unfolding +that looks like (Note InlineMe (Var v)), the InlineMe doesn't go away because it may +not be *applied* to anything. + \begin{code} -data FormSummary - = VarForm -- Expression is a variable (or scc var, etc) - - | ValueForm -- Expression is a value: i.e. a value-lambda,constructor, or literal - -- May 1999: I'm experimenting with allowing "cheap" non-values - -- here. - - | BottomForm -- Expression is guaranteed to be bottom. We're more gung - -- ho about inlining such things, because it can't waste work - | OtherForm -- Anything else - -instance Outputable FormSummary where - ppr VarForm = ptext SLIT("Var") - ppr ValueForm = ptext SLIT("Value") - ppr BottomForm = ptext SLIT("Bot") - ppr OtherForm = ptext SLIT("Other") - -whnfOrBottom :: FormSummary -> Bool -whnfOrBottom VarForm = True -whnfOrBottom ValueForm = True -whnfOrBottom BottomForm = True -whnfOrBottom OtherForm = False +mkInlineMe e | exprIsTrivial e = e + | otherwise = Note InlineMe e \end{code} + + \begin{code} -mkFormSummary :: CoreExpr -> FormSummary -mkFormSummary expr - = go (0::Int) expr -- The "n" is the number of *value* arguments so far - where - go n (Con con _) | isWHNFCon con = ValueForm - | otherwise = OtherForm - - go n (Note _ e) = go n e - - go n (Let (NonRec b r) e) | exprIsCheap r = go n e -- let f = f' alpha in (f,g) - -- should be treated as a value - go n (Let _ e) = OtherForm - - -- We want selectors to look like values - -- e.g. case x of { (a,b) -> a } - -- should give a ValueForm, so that it will be inlined - -- vigorously - go n expr@(Case _ _ _) | exprIsCheap expr = ValueForm - | otherwise = OtherForm - - go 0 (Lam x e) | isId x = ValueForm -- NB: \x.bottom /= bottom! - | otherwise = go 0 e - go n (Lam x e) | isId x = go (n-1) e -- Applied lambda - | otherwise = go n e - - go n (App fun (Type _)) = go n fun -- Ignore type args - go n (App fun arg) = go (n+1) fun - - go n (Var f) | idAppIsBottom f n = BottomForm - go 0 (Var f) = VarForm - go n (Var f) | n < arityLowerBound (getIdArity f) = ValueForm - | otherwise = OtherForm +mkCoerce :: Type -> Type -> CoreExpr -> CoreExpr + +mkCoerce to_ty from_ty (Note (Coerce to_ty2 from_ty2) expr) + = ASSERT( from_ty == 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 +\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 +\end{code} + + +%************************************************************************ +%* * +\subsection{Other expression construction} +%* * +%************************************************************************ + +\begin{code} +bindNonRec :: Id -> CoreExpr -> CoreExpr -> CoreExpr +-- (bindNonRec x r b) produces either +-- let x = r in b +-- or +-- case r of x { _DEFAULT_ -> b } +-- +-- depending on whether x is unlifted or not +-- It's used by the desugarer to avoid building bindings +-- 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 \end{code} -@exprIsTrivial@ is true of expressions we are unconditionally - happy to duplicate; simple variables and constants, - and type applications. +\begin{code} +mkAltExpr :: AltCon -> [CoreBndr] -> [Type] -> CoreExpr + -- This guy constructs the value that the scrutinee must have + -- when you are in one particular branch of a case +mkAltExpr (DataAlt con) args inst_tys + = mkConApp con (map Type inst_tys ++ map varToCoreExpr args) +mkAltExpr (LitAlt lit) [] [] + = Lit lit + +mkIfThenElse :: CoreExpr -> CoreExpr -> CoreExpr -> CoreExpr +mkIfThenElse guard then_expr else_expr + = Case guard (mkWildId boolTy) + [ (DataAlt trueDataCon, [], then_expr), + (DataAlt falseDataCon, [], else_expr) ] +\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. 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 (Var v) = True -exprIsTrivial (App e arg) = isTypeArg arg && exprIsTrivial e -exprIsTrivial (Note _ e) = exprIsTrivial e -exprIsTrivial (Con con args) = conIsTrivial con && all isTypeArg args -exprIsTrivial (Lam b body) | isTyVar b = exprIsTrivial body -exprIsTrivial other = False +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 \end{code} @exprIsDupable@ is true of expressions that can be duplicated at a modest - cost in space. This will only happen in different case + cost in code size. This will only happen in different case branches, so there's no issue about duplicating work. + + That is, exprIsDupable returns True of (f x) even if + f is very very expensive to call. + Its only purpose is to avoid fruitless let-binding and then inlining of case join points \begin{code} exprIsDupable (Type _) = True -exprIsDupable (Con con args) = conIsDupable con && - all exprIsDupable args && - valArgCount args <= dupAppSize - +exprIsDupable (Var v) = True +exprIsDupable (Lit lit) = litIsDupable lit exprIsDupable (Note _ e) = exprIsDupable e -exprIsDupable expr = case collectArgs expr of - (Var f, args) -> valArgCount args <= dupAppSize - other -> False +exprIsDupable expr + = go expr 0 + where + go (Var v) n_args = True + go (App f a) n_args = n_args < dupAppSize + && exprIsDupable a + && go f (n_args+1) + go other n_args = False dupAppSize :: Int dupAppSize = 4 -- Size of application we are prepared to duplicate @@ -210,64 +288,100 @@ dupAppSize = 4 -- Size of application we are prepared to duplicate it is obviously in weak head normal form, or is cheap to get to WHNF. [Note that that's not the same as exprIsDupable; an expression might be big, and hence not dupable, but still cheap.] -By ``cheap'' we mean a computation we're willing to push inside a lambda -in order to bring a couple of lambdas together. That might mean it gets -evaluated more than once, instead of being shared. The main examples of things -which aren't WHNF but are ``cheap'' are: + +By ``cheap'' we mean a computation we're willing to: + push inside a lambda, or + inline at more than one place +That might mean it gets evaluated more than once, instead of being +shared. The main examples of things which aren't WHNF but are +``cheap'' 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) -\begin{code} -exprIsCheap :: CoreExpr -> Bool -exprIsCheap (Type _) = True -exprIsCheap (Var _) = True -exprIsCheap (Con con args) = conIsCheap con && all exprIsCheap args -exprIsCheap (Note _ e) = exprIsCheap e -exprIsCheap (Lam x e) = if isId x then True else exprIsCheap e -exprIsCheap (Let bind body) = all exprIsCheap (rhssOfBind bind) && exprIsCheap body -exprIsCheap (Case scrut _ alts) = exprIsCheap scrut && - all (\(_,_,rhs) -> exprIsCheap rhs) alts - -exprIsCheap other_expr -- look for manifest partial application - = case collectArgs other_expr of - (f, args) -> isPap f (valArgCount args) && all exprIsCheap args -\end{code} +Notice that a variable is considered 'cheap': we can push it inside a lambda, +because sharing will make sure it is only evaluated once. \begin{code} -isPap :: CoreExpr -- Function - -> Int -- Number of value args - -> Bool -isPap (Var f) n_val_args - = idAppIsBottom f n_val_args - -- Application of a function which - -- always gives bottom; we treat this as - -- a WHNF, because it certainly doesn't - -- need to be shared! - - || n_val_args == 0 -- Just a type application of +exprIsCheap :: CoreExpr -> Bool +exprIsCheap (Lit lit) = True +exprIsCheap (Type _) = True +exprIsCheap (Var _) = True +exprIsCheap (Note _ e) = exprIsCheap e +exprIsCheap (Lam x e) = if isId x then True else 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 + go (Var f) n_args args_cheap + = (idAppIsCheap f n_args && args_cheap) + -- A constructor, cheap primop, or partial application + + || idAppIsBottom f n_args + -- Application of a function which + -- 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) + + go other n_args args_cheap = False + +idAppIsCheap :: Id -> Int -> Bool +idAppIsCheap id n_val_args + | n_val_args == 0 = True -- Just a type application of -- a variable (f t1 t2 t3) -- counts as WHNF - - || n_val_args < arityLowerBound (getIdArity f) - -isPap fun n_val_args = False + | otherwise = case idFlavour id of + DataConId _ -> True + RecordSelId _ -> True -- I'm experimenting with making record selection + -- look cheap, so we will substitute it inside a + -- lambda. Particularly for dictionary field selection + + PrimOpId op -> primOpIsCheap op -- In principle we should worry about primops + -- that return a type variable, since the result + -- might be applied to something, but I'm not going + -- to bother to check the number of args + other -> n_val_args < idArity id \end{code} -exprOkForSpeculation returns True of an UNLIFTED-TYPE expression that it is safe -to evaluate even if normal order eval might not evaluate the expression -at all. E.G. +exprOkForSpeculation returns True of an expression that it is + + * safe to evaluate even if normal order eval might not + evaluate the expression at all, or + + * safe *not* to evaluate even if normal order would do so + +It returns True iff + + the expression guarantees to terminate, + soon, + without raising an exception, + without causing a side effect (e.g. writing a mutable variable) + +E.G. let x = case y# +# 1# of { r# -> I# r# } in E ==> @@ -281,26 +395,29 @@ side effects, and can't diverge or raise an exception. \begin{code} exprOkForSpeculation :: CoreExpr -> Bool -exprOkForSpeculation (Var v) = True -- Unlifted type => already evaluated - -exprOkForSpeculation (Note _ e) = exprOkForSpeculation e -exprOkForSpeculation (Let (NonRec b r) e) = isUnLiftedType (idType b) && - exprOkForSpeculation r && - exprOkForSpeculation e -exprOkForSpeculation (Let (Rec _) _) = False -exprOkForSpeculation (Case _ _ _) = False -- Conservative -exprOkForSpeculation (App _ _) = False - -exprOkForSpeculation (Con con args) - = conOkForSpeculation con && - and (zipWith ok (filter isValArg args) (fst (conStrictness con))) +exprOkForSpeculation (Lit _) = True +exprOkForSpeculation (Var v) = isUnLiftedType (idType v) +exprOkForSpeculation (Note _ e) = exprOkForSpeculation e +exprOkForSpeculation other_expr + = go other_expr 0 True where - ok arg demand | isLazy demand = True - | isPrim demand = exprOkForSpeculation arg - | otherwise = False - -exprOkForSpeculation other = panic "exprOkForSpeculation" - -- Lam, Type + 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 + -- 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 \end{code} @@ -314,46 +431,164 @@ exprIsBottom e = go 0 e go n (Case e _ _) = go 0 e -- Just check the scrut go n (App e _) = go (n+1) e go n (Var v) = idAppIsBottom v n - go n (Con _ _) = False + go n (Lit _) = False go n (Lam _ _) = False + +idAppIsBottom :: Id -> Int -> Bool +idAppIsBottom id n_val_args = appIsBottom (idStrictness id) n_val_args \end{code} -exprIsWHNF reports True for head normal forms. Note that does not necessarily -mean *normal* forms; constructors might have non-trivial argument expressions, for -example. We use a let binding for WHNFs, rather than a case binding, even if it's -used strictly. We try to expose WHNFs by floating lets out of the RHS of lets. +@exprIsValue@ returns true for expressions that are certainly *already* +evaluated to WHNF. This is used to decide wether it's ok to change + case x of _ -> e ===> e + +and to decide whether it's safe to discard a `seq` -We treat applications of buildId and augmentId as honorary WHNFs, because we -want them to get exposed +So, it does *not* treat variables as evaluated, unless they say they are \begin{code} -exprIsWHNF :: CoreExpr -> Bool -- True => Variable, value-lambda, constructor, PAP -exprIsWHNF (Type ty) = True -- Types are honorary WHNFs; we don't mind +exprIsValue :: CoreExpr -> Bool -- True => Value-lambda, constructor, PAP +exprIsValue (Type ty) = True -- Types are honorary Values; we don't mind -- copying them -exprIsWHNF (Var v) = True -exprIsWHNF (Lam b e) = isId b || exprIsWHNF e -exprIsWHNF (Note _ e) = exprIsWHNF e -exprIsWHNF (Let _ e) = False -exprIsWHNF (Case _ _ _) = False -exprIsWHNF (Con con _) = isWHNFCon con -exprIsWHNF e@(App _ _) = case collectArgs e of - (Var v, args) -> n_val_args == 0 || - fun_arity > n_val_args || - v_uniq == buildIdKey || - v_uniq == augmentIdKey - where - n_val_args = valArgCount args - fun_arity = arityLowerBound (getIdArity v) - v_uniq = idUnique v - - _ -> False +exprIsValue (Lit l) = True +exprIsValue (Lam b e) = isId 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 + -- A worry: what if an Id's unfolding is just itself: + -- then we could get an infinite loop... +\end{code} + +\begin{code} +exprIsConApp_maybe :: CoreExpr -> Maybe (DataCon, [CoreExpr]) +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 + + analyse (Var fun, []) + = case maybeUnfoldingTemplate (idUnfolding fun) of + Nothing -> Nothing + Just unf -> exprIsConApp_maybe unf + + analyse other = Nothing +\end{code} + + +%************************************************************************ +%* * +\subsection{Eta reduction and expansion} +%* * +%************************************************************************ + +@etaReduceExpr@ trys an eta reduction at the top level of a Core Expr. + +e.g. \ x y -> f x y ===> f + +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 + +etaReduceExpr expr@(Lam bndr body) + = check (reverse binders) body + where + (binders, body) = collectBinders expr + + check [] body + | not (any (`elemVarSet` body_fvs) binders) + = body -- Success! + where + body_fvs = exprFreeVars body + + check (b : bs) (App fun arg) + | (varToCoreExpr b `cheapEqExpr` arg) + = check bs fun + + check _ _ = expr -- Bale out + +etaReduceExpr expr = expr -- The common case \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 other = 0 +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 + +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 + \end{code} @@ -370,17 +605,22 @@ exprArity other = 0 \begin{code} cheapEqExpr :: Expr b -> Expr b -> Bool -cheapEqExpr (Var v1) (Var v2) = v1==v2 -cheapEqExpr (Con con1 args1) (Con con2 args2) - = con1 == con2 && - and (zipWithEqual "cheapEqExpr" cheapEqExpr args1 args2) +cheapEqExpr (Var v1) (Var v2) = v1==v2 +cheapEqExpr (Lit lit1) (Lit lit2) = lit1 == lit2 +cheapEqExpr (Type t1) (Type t2) = t1 == t2 cheapEqExpr (App f1 a1) (App f2 a2) = f1 `cheapEqExpr` f2 && a1 `cheapEqExpr` a2 -cheapEqExpr (Type t1) (Type t2) = t1 == t2 - cheapEqExpr _ _ = False + +exprIsBig :: Expr b -> Bool +-- Returns True of expressions that are too big to be compared by cheapEqExpr +exprIsBig (Lit _) = False +exprIsBig (Var v) = False +exprIsBig (Type t) = False +exprIsBig (App f a) = exprIsBig f || exprIsBig a +exprIsBig other = True \end{code} @@ -397,7 +637,7 @@ eqExpr e1 e2 Just v1' -> v1' == v2 Nothing -> v1 == v2 - eq env (Con c1 es1) (Con c2 es2) = c1 == c2 && eq_list env es1 es2 + eq env (Lit lit1) (Lit lit2) = lit1 == lit2 eq env (App f1 a1) (App f2 a2) = eq env f1 f2 && eq env a1 a2 eq env (Lam v1 e1) (Lam v2 e2) = eq (extendVarEnv env v1 v2) e1 e2 eq env (Let (NonRec v1 r1) e1) @@ -428,8 +668,89 @@ eqExpr e1 e2 eq (extendVarEnvList env (vs1 `zip` vs2)) r1 r2 eq_note env (SCC cc1) (SCC cc2) = cc1 == cc2 - eq_note env (Coerce f1 t1) (Coerce f2 t2) = f1==f2 && t1==t2 + eq_note env (Coerce t1 f1) (Coerce t2 f2) = t1==t2 && f1==f2 eq_note env InlineCall InlineCall = True eq_note env other1 other2 = False \end{code} + +%************************************************************************ +%* * +\subsection{The size of an expression} +%* * +%************************************************************************ + +\begin{code} +coreBindsSize :: [CoreBind] -> Int +coreBindsSize bs = foldr ((+) . bindSize) 0 bs + +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) = 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) = noteSize n + exprSize e +exprSize (Type t) = seqType t `seq` 1 + +noteSize (SCC cc) = cc `seq` 1 +noteSize (Coerce t1 t2) = seqType t1 `seq` seqType t2 `seq` 1 +noteSize InlineCall = 1 +noteSize InlineMe = 1 +noteSize (TermUsg usg) = usg `seq` 1 + +exprsSize = foldr ((+) . exprSize) 0 + +varSize :: Var -> Int +varSize b | isTyVar b = 1 + | otherwise = seqType (idType b) `seq` + megaSeqIdInfo (idInfo b) `seq` + 1 + +varsSize = foldr ((+) . varSize) 0 + +bindSize (NonRec b e) = varSize b + exprSize e +bindSize (Rec prs) = foldr ((+) . pairSize) 0 prs + +pairSize (b,e) = varSize b + exprSize e + +altSize (c,bs,e) = c `seq` varsSize bs + exprSize e +\end{code} + + +%************************************************************************ +%* * +\subsection{Hashing} +%* * +%************************************************************************ + +\begin{code} +hashExpr :: CoreExpr -> Int +hashExpr e | hash < 0 = 77 -- Just in case we hit -maxInt + | otherwise = hash + where + hash = abs (hash_expr e) -- Negative numbers kill UniqFM + +hash_expr (Note _ e) = hash_expr e +hash_expr (Let (NonRec b r) e) = hashId b +hash_expr (Let (Rec ((b,r):_)) e) = hashId b +hash_expr (Case _ b _) = hashId b +hash_expr (App f e) = hash_expr f * fast_hash_expr e +hash_expr (Var v) = hashId v +hash_expr (Lit lit) = hashLiteral lit +hash_expr (Lam b _) = hashId b +hash_expr (Type t) = trace "hash_expr: type" 1 -- Shouldn't happen + +fast_hash_expr (Var v) = hashId v +fast_hash_expr (Lit lit) = hashLiteral lit +fast_hash_expr (App f (Type _)) = fast_hash_expr f +fast_hash_expr (App f a) = fast_hash_expr a +fast_hash_expr (Lam b _) = hashId b +fast_hash_expr other = 1 + +hashId :: Id -> Int +hashId id = hashName (idName id) +\end{code}