% % (c) The University of Glasgow 2006 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998 % Utility functions on @Core@ syntax \begin{code} module CoreUtils ( -- Construction mkInlineMe, mkSCC, mkCoerce, bindNonRec, needsCaseBinding, mkIfThenElse, mkAltExpr, mkPiType, mkPiTypes, -- Taking expressions apart findDefault, findAlt, isDefaultAlt, mergeAlts, trimConArgs, -- Properties of expressions exprType, coreAltType, exprIsDupable, exprIsTrivial, exprIsCheap, exprIsHNF,exprOkForSpeculation, exprIsBig, exprIsConApp_maybe, exprIsBottom, rhsIsStatic, -- Arity and eta expansion manifestArity, exprArity, exprEtaExpandArity, etaExpand, -- Size coreBindsSize, -- Hashing hashExpr, -- Equality cheapEqExpr, tcEqExpr, tcEqExprX, applyTypeToArgs, applyTypeToArg, dataConOrigInstPat, dataConRepInstPat, dataConRepFSInstPat ) where #include "HsVersions.h" import CoreSyn import CoreFVs import PprCore import Var import SrcLoc import VarSet import VarEnv import Name #if mingw32_TARGET_OS import Packages #endif import Literal import DataCon import PrimOp import Id import IdInfo import NewDemand import Type import Coercion import TyCon import TysWiredIn import CostCentre import BasicTypes import PackageConfig import Unique import Outputable import DynFlags import TysPrim import FastString import Maybes import Util import Data.Word import Data.Bits import GHC.Exts -- For `xori` \end{code} %************************************************************************ %* * \subsection{Find the type of a Core atom/expression} %* * %************************************************************************ \begin{code} exprType :: CoreExpr -> Type exprType (Var var) = idType var exprType (Lit lit) = literalType lit exprType (Let _ body) = exprType body exprType (Case _ _ ty alts) = ty exprType (Cast e co) = let (_, ty) = coercionKind co in ty 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 (exprType fun) args exprType other = pprTrace "exprType" (pprCoreExpr other) alphaTy coreAltType :: CoreAlt -> Type coreAltType (_,_,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 mkPiTypes :: [Var] -> Type -> Type -- doesn't work... mkPiTypes vs ty = foldr mkPiType ty vs mkPiType v ty | isId v = mkFunTy (idType v) ty | otherwise = mkForAllTy v ty \end{code} \begin{code} applyTypeToArg :: Type -> CoreExpr -> Type applyTypeToArg fun_ty (Type arg_ty) = applyTy fun_ty arg_ty applyTypeToArg fun_ty other_arg = funResultTy fun_ty applyTypeToArgs :: CoreExpr -> Type -> [CoreExpr] -> Type -- A more efficient version of applyTypeToArg -- when we have several args -- The first argument is just for debugging applyTypeToArgs e op_ty [] = op_ty applyTypeToArgs e op_ty (Type ty : args) = -- Accumulate type arguments so we can instantiate all at once go [ty] args where go rev_tys (Type ty : args) = go (ty:rev_tys) args go rev_tys rest_args = applyTypeToArgs e op_ty' rest_args where op_ty' = applyTys op_ty (reverse rev_tys) applyTypeToArgs e op_ty (other_arg : args) = case (splitFunTy_maybe op_ty) of Just (_, res_ty) -> applyTypeToArgs e res_ty args Nothing -> pprPanic "applyTypeToArgs" (pprCoreExpr e $$ ppr op_ty) \end{code} %************************************************************************ %* * \subsection{Attaching notes} %* * %************************************************************************ mkNote removes redundant coercions, and SCCs where possible \begin{code} #ifdef UNUSED mkNote :: Note -> CoreExpr -> CoreExpr mkNote (SCC cc) expr = mkSCC cc expr mkNote InlineMe expr = mkInlineMe expr mkNote note expr = Note note expr #endif \end{code} Drop trivial InlineMe's. This is somewhat important, because if we have an unfolding that looks like (Note InlineMe (Var v)), the InlineMe doesn't go away because it may not be *applied* to anything. We don't use exprIsTrivial here, though, because we sometimes generate worker/wrapper bindings like fw = ... f = inline_me (coerce t fw) As usual, the inline_me prevents the worker from getting inlined back into the wrapper. We want the split, so that the coerces can cancel at the call site. However, we can get left with tiresome type applications. Notably, consider f = /\ a -> let t = e in (t, w) Then lifting the let out of the big lambda gives t' = /\a -> e f = /\ a -> let t = inline_me (t' a) in (t, w) The inline_me is to stop the simplifier inlining t' right back into t's RHS. In the next phase we'll substitute for t (since its rhs is trivial) and *then* we could get rid of the inline_me. But it hardly seems worth it, so I don't bother. \begin{code} mkInlineMe (Var v) = Var v mkInlineMe e = Note InlineMe e \end{code} \begin{code} mkCoerce :: Coercion -> CoreExpr -> CoreExpr mkCoerce co (Cast expr co2) = ASSERT(let { (from_ty, _to_ty) = coercionKind co; (_from_ty2, to_ty2) = coercionKind co2} in from_ty `coreEqType` to_ty2 ) mkCoerce (mkTransCoercion co2 co) expr mkCoerce co expr = let (from_ty, to_ty) = coercionKind co in -- if to_ty `coreEqType` from_ty -- then expr -- else ASSERT2(from_ty `coreEqType` (exprType expr), text "Trying to coerce" <+> text "(" <> ppr expr $$ text "::" <+> ppr (exprType expr) <> text ")" $$ ppr co $$ ppr (coercionKindPredTy co)) (Cast expr co) \end{code} \begin{code} mkSCC :: CostCentre -> Expr b -> Expr b -- Note: Nested SCC's *are* preserved for the benefit of -- 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 (Cast e co) = Cast (mkSCC cc e) co -- Move _scc_ inside cast 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 | needsCaseBinding (idType bndr) rhs = Case rhs bndr (exprType body) [(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} 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 ++ varsToCoreExprs args) mkAltExpr (LitAlt lit) [] [] = Lit lit mkIfThenElse :: CoreExpr -> CoreExpr -> CoreExpr -> CoreExpr mkIfThenElse guard then_expr else_expr -- Not going to be refining, so okay to take the type of the "then" clause = Case guard (mkWildId boolTy) (exprType then_expr) [ (DataAlt falseDataCon, [], else_expr), -- Increasing order of tag! (DataAlt trueDataCon, [], then_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} 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 = case con `cmpAltCon` con1 of LT -> deflt -- Missed it already; the alts are in increasing order EQ -> alt GT -> ASSERT( not (con1 == DEFAULT) ) go alts deflt isDefaultAlt :: CoreAlt -> Bool isDefaultAlt (DEFAULT, _, _) = True isDefaultAlt other = False --------------------------------- mergeAlts :: [CoreAlt] -> [CoreAlt] -> [CoreAlt] -- Merge preserving order; alternatives in the first arg -- shadow ones in the second mergeAlts [] as2 = as2 mergeAlts as1 [] = as1 mergeAlts (a1:as1) (a2:as2) = case a1 `cmpAlt` a2 of LT -> a1 : mergeAlts as1 (a2:as2) EQ -> a1 : mergeAlts as1 as2 -- Discard a2 GT -> a2 : mergeAlts (a1:as1) as2 --------------------------------- trimConArgs :: AltCon -> [CoreArg] -> [CoreArg] -- Given case (C a b x y) of -- C b x y -> ... -- we want to drop the leading type argument of the scrutinee -- leaving the arguments to match agains the pattern trimConArgs DEFAULT args = ASSERT( null args ) [] trimConArgs (LitAlt lit) args = ASSERT( null args ) [] trimConArgs (DataAlt dc) args = dropList (dataConUnivTyVars dc) args \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 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. SCC notes. We do not treat (_scc_ "foo" x) as trivial, because a) it really generates code, (and a heap object when it's a function arg) to capture the cost centre b) see the note [SCC-and-exprIsTrivial] in Simplify.simplLazyBind \begin{code} exprIsTrivial (Var v) = True -- See notes above exprIsTrivial (Type _) = True exprIsTrivial (Lit lit) = litIsTrivial lit exprIsTrivial (App e arg) = not (isRuntimeArg arg) && exprIsTrivial e exprIsTrivial (Note (SCC _) e) = False -- See notes above exprIsTrivial (Note _ e) = exprIsTrivial e exprIsTrivial (Cast e co) = exprIsTrivial e exprIsTrivial (Lam b body) = not (isRuntimeVar b) && exprIsTrivial body exprIsTrivial other = False \end{code} @exprIsDupable@ is true of expressions that can be duplicated at a modest 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 (Var v) = True exprIsDupable (Lit lit) = litIsDupable lit exprIsDupable (Note InlineMe e) = True exprIsDupable (Note _ e) = exprIsDupable e exprIsDupable (Cast e co) = exprIsDupable e 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 \end{code} @exprIsCheap@ looks at a Core expression and returns \tr{True} if 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, 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) * let x = e in b (where e and b are cheap) * op x1 ... xn (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. \begin{code} exprIsCheap :: CoreExpr -> Bool exprIsCheap (Lit lit) = True exprIsCheap (Type _) = True exprIsCheap (Var _) = True exprIsCheap (Note InlineMe e) = True exprIsCheap (Note _ e) = exprIsCheap e exprIsCheap (Cast e co) = 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 -- (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 -- Applications and variables = go other_expr [] where -- Accumulate value arguments, then decide go (App f a) val_args | isRuntimeArg a = go f (a:val_args) | otherwise = go f val_args go (Var f) [] = True -- Just a type application of a variable -- (f t1 t2 t3) counts as WHNF go (Var f) args = case globalIdDetails f of RecordSelId {} -> go_sel args ClassOpId _ -> go_sel args PrimOpId op -> go_primop op args DataConWorkId _ -> go_pap args other | length args < idArity f -> go_pap args other -> isBottomingId f -- Application of a function which -- always gives bottom; we treat this as cheap -- because it certainly doesn't need to be shared! go other args = False -------------- go_pap args = all exprIsTrivial args -- For constructor applications and primops, check that all -- the args are trivial. We don't want to treat as cheap, say, -- (1:2:3:4:5:[]) -- We'll put up with one constructor application, but not dozens -------------- go_primop op args = primOpIsCheap op && all exprIsCheap args -- 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 -------------- go_sel [arg] = exprIsCheap arg -- I'm experimenting with making record selection go_sel other = False -- look cheap, so we will substitute it inside a -- lambda. Particularly for dictionary field selection. -- BUT: Take care with (sel d x)! The (sel d) might be cheap, but -- there's no guarantee that (sel d x) will be too. Hence (n_val_args == 1) \end{code} 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) NB: if exprIsHNF e, then exprOkForSpecuation e E.G. let x = case y# +# 1# of { r# -> I# r# } in E ==> case y# +# 1# of { r# -> let x = I# r# in E } We can only do this if the (y+1) is ok for speculation: it has no side effects, and can't diverge or raise an exception. \begin{code} exprOkForSpeculation :: CoreExpr -> Bool exprOkForSpeculation (Lit _) = True exprOkForSpeculation (Type _) = True -- Tick boxes are *not* suitable for speculation exprOkForSpeculation (Var v) = isUnLiftedType (idType v) && not (isTickBoxOp v) exprOkForSpeculation (Note _ e) = exprOkForSpeculation e exprOkForSpeculation (Cast e co) = exprOkForSpeculation e exprOkForSpeculation other_expr = case collectArgs other_expr of (Var f, args) -> spec_ok (globalIdDetails f) args other -> False where spec_ok (DataConWorkId _) 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 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} \begin{code} exprIsBottom :: CoreExpr -> Bool -- True => definitely bottom exprIsBottom e = go 0 e where -- n is the number of args go n (Note _ e) = go n e go n (Cast e co) = go n e go n (Let _ e) = go n 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 (Lit _) = False go n (Lam _ _) = False go n (Type _) = False idAppIsBottom :: Id -> Int -> Bool idAppIsBottom id n_val_args = appIsBottom (idNewStrictness id) n_val_args \end{code} @exprIsHNF@ returns true for expressions that are certainly *already* 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. 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. However this can't happen: see CoreSyn Note [CoreSyn let/app invariant]. Args of unboxed type must be ok-for-speculation (or trivial). \begin{code} exprIsHNF :: CoreExpr -> Bool -- True => Value-lambda, constructor, PAP exprIsHNF (Var v) -- NB: There are no value args at this point = isDataConWorkId v -- Catches nullary constructors, -- so that [] and () are values, for example || idArity v > 0 -- Catches (e.g.) primops that don't have unfoldings || isEvaldUnfolding (idUnfolding v) -- Check the thing's unfolding; it might be bound to a value -- A worry: what if an Id's unfolding is just itself: -- then we could get an infinite loop... exprIsHNF (Lit l) = True exprIsHNF (Type ty) = True -- Types are honorary Values; -- we don't mind copying them exprIsHNF (Lam b e) = isRuntimeVar b || exprIsHNF e exprIsHNF (Note _ e) = exprIsHNF e exprIsHNF (Cast e co) = exprIsHNF e exprIsHNF (App e (Type _)) = exprIsHNF e exprIsHNF (App e a) = app_is_value e [a] exprIsHNF other = False -- There is at least one value argument app_is_value (Var fun) args = idArity fun > valArgCount args -- Under-applied function || isDataConWorkId fun -- or data constructor app_is_value (Note n f) as = app_is_value f as app_is_value (Cast f _) as = app_is_value f as app_is_value (App f a) as = app_is_value f (a:as) app_is_value other as = False \end{code} \begin{code} -- These InstPat functions go here to avoid circularity between DataCon and Id dataConRepInstPat = dataConInstPat dataConRepArgTys (repeat (FSLIT("ipv"))) dataConRepFSInstPat = dataConInstPat dataConRepArgTys dataConOrigInstPat = dataConInstPat dc_arg_tys (repeat (FSLIT("ipv"))) where dc_arg_tys dc = map mkPredTy (dataConTheta dc) ++ dataConOrigArgTys dc -- Remember to include the existential dictionaries dataConInstPat :: (DataCon -> [Type]) -- function used to find arg tys -> [FastString] -- A long enough list of FSs to use for names -> [Unique] -- An equally long list of uniques, at least one for each binder -> DataCon -> [Type] -- Types to instantiate the universally quantified tyvars -> ([TyVar], [CoVar], [Id]) -- Return instantiated variables -- dataConInstPat arg_fun fss us con inst_tys returns a triple -- (ex_tvs, co_tvs, arg_ids), -- -- ex_tvs are intended to be used as binders for existential type args -- -- co_tvs are intended to be used as binders for coercion args and the kinds -- of these vars have been instantiated by the inst_tys and the ex_tys -- -- arg_ids are indended to be used as binders for value arguments, including -- dicts, and their types have been instantiated with inst_tys and ex_tys -- -- Example. -- The following constructor T1 -- -- data T a where -- T1 :: forall b. Int -> b -> T(a,b) -- ... -- -- has representation type -- forall a. forall a1. forall b. (a :=: (a1,b)) => -- Int -> b -> T a -- -- dataConInstPat fss us T1 (a1',b') will return -- -- ([a1'', b''], [c :: (a1', b'):=:(a1'', b'')], [x :: Int, y :: b'']) -- -- where the double-primed variables are created with the FastStrings and -- Uniques given as fss and us dataConInstPat arg_fun fss uniqs con inst_tys = (ex_bndrs, co_bndrs, id_bndrs) where univ_tvs = dataConUnivTyVars con ex_tvs = dataConExTyVars con arg_tys = arg_fun con eq_spec = dataConEqSpec con eq_preds = eqSpecPreds eq_spec n_ex = length ex_tvs n_co = length eq_spec -- split the Uniques and FastStrings (ex_uniqs, uniqs') = splitAt n_ex uniqs (co_uniqs, id_uniqs) = splitAt n_co uniqs' (ex_fss, fss') = splitAt n_ex fss (co_fss, id_fss) = splitAt n_co fss' -- Make existential type variables ex_bndrs = zipWith3 mk_ex_var ex_uniqs ex_fss ex_tvs mk_ex_var uniq fs var = mkTyVar new_name kind where new_name = mkSysTvName uniq fs kind = tyVarKind var -- Make the instantiating substitution subst = zipOpenTvSubst (univ_tvs ++ ex_tvs) (inst_tys ++ map mkTyVarTy ex_bndrs) -- Make new coercion vars, instantiating kind co_bndrs = zipWith3 mk_co_var co_uniqs co_fss eq_preds mk_co_var uniq fs eq_pred = mkCoVar new_name co_kind where new_name = mkSysTvName uniq fs co_kind = substTy subst (mkPredTy eq_pred) -- make value vars, instantiating types mk_id_var uniq fs ty = mkUserLocal (mkVarOccFS fs) uniq (substTy subst ty) noSrcLoc id_bndrs = zipWith3 mk_id_var id_uniqs id_fss arg_tys exprIsConApp_maybe :: CoreExpr -> Maybe (DataCon, [CoreExpr]) -- Returns (Just (dc, [x1..xn])) if the argument expression is -- a constructor application of the form (dc x1 .. xn) exprIsConApp_maybe (Cast expr co) = -- Here we do the PushC reduction rule as described in the FC paper case exprIsConApp_maybe expr of { Nothing -> Nothing ; Just (dc, dc_args) -> -- The transformation applies iff we have -- (C e1 ... en) `cast` co -- where co :: (T t1 .. tn) :=: (T s1 ..sn) -- That is, with a T at the top of both sides -- The left-hand one must be a T, because exprIsConApp returned True -- but the right-hand one might not be. (Though it usually will.) let (from_ty, to_ty) = coercionKind co (from_tc, from_tc_arg_tys) = splitTyConApp from_ty -- The inner one must be a TyConApp in case splitTyConApp_maybe to_ty of { Nothing -> Nothing ; Just (to_tc, to_tc_arg_tys) | from_tc /= to_tc -> Nothing -- These two Nothing cases are possible; we might see -- (C x y) `cast` (g :: T a ~ S [a]), -- where S is a type function. In fact, exprIsConApp -- will probably not be called in such circumstances, -- but there't nothing wrong with it | otherwise -> let tc_arity = tyConArity from_tc (univ_args, rest1) = splitAt tc_arity dc_args (ex_args, rest2) = splitAt n_ex_tvs rest1 (co_args, val_args) = splitAt n_cos rest2 arg_tys = dataConRepArgTys dc dc_univ_tyvars = dataConUnivTyVars dc dc_ex_tyvars = dataConExTyVars dc dc_eq_spec = dataConEqSpec dc dc_tyvars = dc_univ_tyvars ++ dc_ex_tyvars n_ex_tvs = length dc_ex_tyvars n_cos = length dc_eq_spec -- Make the "theta" from Fig 3 of the paper gammas = decomposeCo tc_arity co new_tys = gammas ++ map (\ (Type t) -> t) ex_args theta = zipOpenTvSubst dc_tyvars new_tys -- First we cast the existential coercion arguments cast_co (tv,ty) (Type co) = Type $ mkSymCoercion (substTyVar theta tv) `mkTransCoercion` co `mkTransCoercion` (substTy theta ty) new_co_args = zipWith cast_co dc_eq_spec co_args -- ...and now value arguments new_val_args = zipWith cast_arg arg_tys val_args cast_arg arg_ty arg = mkCoerce (substTy theta arg_ty) arg in ASSERT( length univ_args == tc_arity ) ASSERT( from_tc == dataConTyCon dc ) ASSERT( and (zipWith coreEqType [t | Type t <- univ_args] from_tc_arg_tys) ) ASSERT( all isTypeArg (univ_args ++ ex_args) ) ASSERT2( equalLength val_args arg_tys, ppr dc $$ ppr dc_tyvars $$ ppr dc_ex_tyvars $$ ppr arg_tys $$ ppr dc_args $$ ppr univ_args $$ ppr ex_args $$ ppr val_args $$ ppr arg_tys ) Just (dc, map Type to_tc_arg_tys ++ ex_args ++ new_co_args ++ new_val_args) }} {- -- We do not want to tell the world that we have a -- Cons, to *stop* Case of Known Cons, which removes -- the TickBox. exprIsConApp_maybe (Note (TickBox {}) expr) = Nothing exprIsConApp_maybe (Note (BinaryTickBox {}) expr) = Nothing -} 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) | Just con <- isDataConWorkId_maybe fun, args `lengthAtLeast` 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, []) | let unf = idUnfolding fun, isCheapUnfolding unf = exprIsConApp_maybe (unfoldingTemplate unf) analyse other = Nothing \end{code} %************************************************************************ %* * \subsection{Eta reduction and expansion} %* * %************************************************************************ \begin{code} exprEtaExpandArity :: DynFlags -> CoreExpr -> Arity {- The Arity returned is the number of value args the thing can be applied to without doing much work exprEtaExpandArity 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 It's all a bit more subtle than it looks: 1. One-shot lambdas 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 2. The state-transformer hack The one-shot lambda special cause 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, even if E is expensive. So we treat state-token lambdas as one-shot even if they aren't really. The hack is in Id.isOneShotBndr. 3. Dealing with bottom Consider also f = \x -> error "foo" Here, arity 1 is fine. But if it is f = \x -> case x of True -> error "foo" False -> \y -> x+y then we want to get arity 2. Tecnically, this isn't quite right, because (f True) `seq` 1 should diverge, but it'll converge if we eta-expand f. Nevertheless, we do so; it improves some programs significantly, and increasing convergence isn't a bad thing. Hence the ABot/ATop in ArityType. Actually, the situation is worse. Consider f = \x -> case x of True -> \y -> x+y False -> \y -> x-y Can we eta-expand here? At first the answer looks like "yes of course", but consider (f bot) `seq` 1 This should diverge! But if we eta-expand, it won't. Again, we ignore this "problem", because being scrupulous would lose an important transformation for many programs. 4. Newtypes Non-recursive newtypes are transparent, and should not get in the way. We do (currently) eta-expand recursive newtypes too. So if we have, say newtype T = MkT ([T] -> Int) Suppose we have e = coerce T f where f has arity 1. Then: etaExpandArity e = 1; that is, etaExpandArity looks through the coerce. When we eta-expand e to arity 1: eta_expand 1 e T we want to get: coerce T (\x::[T] -> (coerce ([T]->Int) e) x) HOWEVER, note that if you use coerce bogusly you can ge coerce Int negate And since negate has arity 2, you might try to eta expand. But you can't decopose Int to a function type. Hence the final case in eta_expand. -} exprEtaExpandArity dflags e = arityDepth (arityType dflags 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 :: DynFlags -> 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 dflags (Note n e) = arityType dflags e -- Not needed any more: etaExpand is cleverer -- | ok_note n = arityType dflags e -- | otherwise = ATop arityType dflags (Cast e co) = arityType dflags e arityType dflags (Var v) = mk (idArity v) (arg_tys (idType v)) where mk :: Arity -> [Type] -> ArityType -- The argument types are only to steer the "state hack" -- Consider case x of -- True -> foo -- False -> \(s:RealWorld) -> e -- where foo has arity 1. Then we want the state hack to -- apply to foo too, so we can eta expand the case. mk 0 tys | isBottomingId v = ABot | (ty:tys) <- tys, isStateHackType ty = AFun True ATop | otherwise = ATop mk n (ty:tys) = AFun (isStateHackType ty) (mk (n-1) tys) mk n [] = AFun False (mk (n-1) []) arg_tys :: Type -> [Type] -- Ignore for-alls arg_tys ty | Just (_, ty') <- splitForAllTy_maybe ty = arg_tys ty' | Just (arg,res) <- splitFunTy_maybe ty = arg : arg_tys res | otherwise = [] -- Lambdas; increase arity arityType dflags (Lam x e) | isId x = AFun (isOneShotBndr x) (arityType dflags e) | otherwise = arityType dflags e -- Applications; decrease arity arityType dflags (App f (Type _)) = arityType dflags f arityType dflags (App f a) = case arityType dflags f of AFun 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 -- The former is not really right for Haskell -- f x = case x of { (a,b) -> \y. e } -- ===> -- f x y = case x of { (a,b) -> e } -- The difference is observable using 'seq' arityType dflags (Case scrut _ _ alts) = case foldr1 andArityType [arityType dflags rhs | (_,_,rhs) <- alts] of xs | exprIsCheap scrut -> xs xs@(AFun one_shot _) | one_shot -> AFun True ATop other -> ATop arityType dflags (Let b e) = case arityType dflags e of xs | cheap_bind b -> xs xs@(AFun one_shot _) | one_shot -> AFun True ATop other -> ATop where cheap_bind (NonRec b e) = is_cheap (b,e) cheap_bind (Rec prs) = all is_cheap prs is_cheap (b,e) = (dopt Opt_DictsCheap dflags && isDictId b) || exprIsCheap e -- If the experimental -fdicts-cheap flag is on, we eta-expand through -- dictionary bindings. This improves arities. Thereby, it also -- means that full laziness is less prone to floating out the -- application of a function to its dictionary arguments, which -- can thereby lose opportunities for fusion. Example: -- foo :: Ord a => a -> ... -- foo = /\a \(d:Ord a). let d' = ...d... in \(x:a). .... -- -- So foo has arity 1 -- -- f = \x. foo dInt $ bar x -- -- The (foo DInt) is floated out, and makes ineffective a RULE -- foo (bar x) = ... -- -- One could go further and make exprIsCheap reply True to any -- dictionary-typed expression, but that's more work. arityType dflags 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} \begin{code} 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' -- -- Note that SCCs are not treated specially. If we have -- etaExpand 2 (\x -> scc "foo" e) -- = (\xy -> (scc "foo" e) y) -- So the costs of evaluating 'e' (not 'e y') are attributed to "foo" etaExpand n us expr ty | manifestArity expr >= n = expr -- The no-op case | otherwise = eta_expand n us expr ty where -- 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 (Cast 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 -- 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)) -- We used to have a special case that stepped inside Coerces here, -- thus: eta_expand n us (Note note@(Coerce _ ty) e) _ -- = Note note (eta_expand n us e ty) -- BUT this led to an infinite loop -- Example: newtype T = MkT (Int -> Int) -- eta_expand 1 (coerce (Int->Int) e) -- --> coerce (Int->Int) (eta_expand 1 T e) -- by the bogus eqn -- --> coerce (Int->Int) (coerce T -- (\x::Int -> eta_expand 1 (coerce (Int->Int) e))) -- by the splitNewType_maybe case below -- and round we go eta_expand n us expr ty = ASSERT2 (exprType expr `coreEqType` ty, ppr (exprType expr) $$ ppr ty) case splitForAllTy_maybe ty of { Just (tv,ty') -> Lam lam_tv (eta_expand n us2 (App expr (Type (mkTyVarTy lam_tv))) (substTyWith [tv] [mkTyVarTy lam_tv] ty')) where lam_tv = setVarName tv (mkSysTvName uniq FSLIT("etaT")) -- Using tv as a base retains its tyvar/covar-ness (uniq:us2) = us ; 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 FSLIT("eta") uniq arg_ty (uniq:us2) = us ; Nothing -> -- Given this: -- newtype T = MkT ([T] -> Int) -- Consider eta-expanding this -- eta_expand 1 e T -- We want to get -- coerce T (\x::[T] -> (coerce ([T]->Int) e) x) case splitNewTypeRepCo_maybe ty of { Just(ty1,co) -> mkCoerce (mkSymCoercion co) (eta_expand n us (mkCoerce co expr) ty1) ; Nothing -> -- We have an expression of arity > 0, but its type isn't a function -- This *can* legitmately happen: e.g. coerce Int (\x. x) -- Essentially the programmer is playing fast and loose with types -- (Happy does this a lot). So we simply decline to eta-expand. 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. 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 (Cast 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} %************************************************************************ %* * \subsection{Equality} %* * %************************************************************************ @cheapEqExpr@ is a cheap equality test which bales out fast! True => definitely equal False => may or may not be equal \begin{code} 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 `coreEqType` t2 cheapEqExpr (App f1 a1) (App f2 a2) = f1 `cheapEqExpr` f2 && a1 `cheapEqExpr` a2 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 (Cast e _) = exprIsBig e -- Hopefully coercions are not too big! exprIsBig other = True \end{code} \begin{code} tcEqExpr :: CoreExpr -> CoreExpr -> Bool -- Used in rule matching, so does *not* look through -- newtypes, predicate types; hence tcEqExpr tcEqExpr e1 e2 = tcEqExprX rn_env e1 e2 where rn_env = mkRnEnv2 (mkInScopeSet (exprFreeVars e1 `unionVarSet` exprFreeVars e2)) tcEqExprX :: RnEnv2 -> CoreExpr -> CoreExpr -> Bool tcEqExprX env (Var v1) (Var v2) = rnOccL env v1 == rnOccR env v2 tcEqExprX env (Lit lit1) (Lit lit2) = lit1 == lit2 tcEqExprX env (App f1 a1) (App f2 a2) = tcEqExprX env f1 f2 && tcEqExprX env a1 a2 tcEqExprX env (Lam v1 e1) (Lam v2 e2) = tcEqExprX (rnBndr2 env v1 v2) e1 e2 tcEqExprX env (Let (NonRec v1 r1) e1) (Let (NonRec v2 r2) e2) = tcEqExprX env r1 r2 && tcEqExprX (rnBndr2 env v1 v2) e1 e2 tcEqExprX env (Let (Rec ps1) e1) (Let (Rec ps2) e2) = equalLength ps1 ps2 && and (zipWith eq_rhs ps1 ps2) && tcEqExprX env' e1 e2 where env' = foldl2 rn_bndr2 env ps2 ps2 rn_bndr2 env (b1,_) (b2,_) = rnBndr2 env b1 b2 eq_rhs (_,r1) (_,r2) = tcEqExprX env' r1 r2 tcEqExprX env (Case e1 v1 t1 a1) (Case e2 v2 t2 a2) = tcEqExprX env e1 e2 && tcEqTypeX env t1 t2 && equalLength a1 a2 && and (zipWith (eq_alt env') a1 a2) where env' = rnBndr2 env v1 v2 tcEqExprX env (Note n1 e1) (Note n2 e2) = eq_note env n1 n2 && tcEqExprX env e1 e2 tcEqExprX env (Cast e1 co1) (Cast e2 co2) = tcEqTypeX env co1 co2 && tcEqExprX env e1 e2 tcEqExprX env (Type t1) (Type t2) = tcEqTypeX env t1 t2 tcEqExprX env e1 e2 = False eq_alt env (c1,vs1,r1) (c2,vs2,r2) = c1==c2 && tcEqExprX (rnBndrs2 env vs1 vs2) r1 r2 eq_note env (SCC cc1) (SCC cc2) = cc1 == cc2 eq_note env (CoreNote s1) (CoreNote s2) = s1 == s2 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) = v `seq` 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 t as) = seqType t `seq` exprSize e + varSize b + 1 + foldr ((+) . altSize) 0 as exprSize (Cast e co) = (seqType co `seq` 1) + exprSize e exprSize (Note n e) = noteSize n + exprSize e exprSize (Type t) = seqType t `seq` 1 noteSize (SCC cc) = cc `seq` 1 noteSize InlineMe = 1 noteSize (CoreNote s) = s `seq` 1 -- hdaume: core annotations 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 -- Two expressions that hash to the same Int may be equal (but may not be) -- Two expressions that hash to the different Ints are definitely unequal -- -- But "unequal" here means "not identical"; two alpha-equivalent -- expressions may hash to the different Ints -- -- The emphasis is on a crude, fast hash, rather than on high precision -- -- We must be careful that \x.x and \y.y map to the same hash code, -- (at least if we want the above invariant to be true) hashExpr e = fromIntegral (hash_expr (1,emptyVarEnv) e .&. 0x7fffffff) -- UniqFM doesn't like negative Ints type HashEnv = (Int, VarEnv Int) -- Hash code for bound variables hash_expr :: HashEnv -> CoreExpr -> Word32 -- Word32, because we're expecting overflows here, and overflowing -- signed types just isn't cool. In C it's even undefined. hash_expr env (Note _ e) = hash_expr env e hash_expr env (Cast e co) = hash_expr env e hash_expr env (Var v) = hashVar env v hash_expr env (Lit lit) = fromIntegral (hashLiteral lit) hash_expr env (App f e) = hash_expr env f * fast_hash_expr env e hash_expr env (Let (NonRec b r) e) = hash_expr (extend_env env b) e * fast_hash_expr env r hash_expr env (Let (Rec ((b,r):_)) e) = hash_expr (extend_env env b) e hash_expr env (Case e _ _ _) = hash_expr env e hash_expr env (Lam b e) = hash_expr (extend_env env b) e hash_expr env (Type t) = WARN(True, text "hash_expr: type") 1 -- Shouldn't happen. Better to use WARN than trace, because trace -- prevents the CPR optimisation kicking in for hash_expr. fast_hash_expr env (Var v) = hashVar env v fast_hash_expr env (Type t) = fast_hash_type env t fast_hash_expr env (Lit lit) = fromIntegral (hashLiteral lit) fast_hash_expr env (Cast e co) = fast_hash_expr env e fast_hash_expr env (Note n e) = fast_hash_expr env e fast_hash_expr env (App f a) = fast_hash_expr env a -- A bit idiosyncratic ('a' not 'f')! fast_hash_expr env other = 1 fast_hash_type :: HashEnv -> Type -> Word32 fast_hash_type env ty | Just tv <- getTyVar_maybe ty = hashVar env tv | Just (tc,_) <- splitTyConApp_maybe ty = fromIntegral (hashName (tyConName tc)) | otherwise = 1 extend_env :: HashEnv -> Var -> (Int, VarEnv Int) extend_env (n,env) b = (n+1, extendVarEnv env b n) hashVar :: HashEnv -> Var -> Word32 hashVar (_,env) v = fromIntegral (lookupVarEnv env v `orElse` hashName (idName v)) \end{code} %************************************************************************ %* * \subsection{Determining non-updatable right-hand-sides} %* * %************************************************************************ Top-level constructor applications can usually be allocated statically, but they can't if the constructor, or any of the arguments, come from another DLL (because we can't refer to static labels in other DLLs). If this happens we simply make the RHS into an updatable thunk, and 'exectute' it rather than allocating it statically. \begin{code} rhsIsStatic :: PackageId -> CoreExpr -> Bool -- This function is called only on *top-level* right-hand sides -- Returns True if the RHS can be allocated statically, with -- no thunks involved at all. -- -- It's called (i) in TidyPgm.hasCafRefs to decide if the rhs is, or -- refers to, CAFs; and (ii) in CoreToStg to decide whether to put an -- update flag on it. -- -- The basic idea is that rhsIsStatic returns True only if the RHS is -- (a) a value lambda -- (b) a saturated constructor application with static args -- -- BUT watch out for -- (i) Any cross-DLL references kill static-ness completely -- because they must be 'executed' not statically allocated -- ("DLL" here really only refers to Windows DLLs, on other platforms, -- this is not necessary) -- -- (ii) We treat partial applications as redexes, because in fact we -- make a thunk for them that runs and builds a PAP -- at run-time. The only appliations that are treated as -- static are *saturated* applications of constructors. -- We used to try to be clever with nested structures like this: -- ys = (:) w ((:) w []) -- on the grounds that CorePrep will flatten ANF-ise it later. -- But supporting this special case made the function much more -- complicated, because the special case only applies if there are no -- enclosing type lambdas: -- ys = /\ a -> Foo (Baz ([] a)) -- Here the nested (Baz []) won't float out to top level in CorePrep. -- -- But in fact, even without -O, nested structures at top level are -- flattened by the simplifier, so we don't need to be super-clever here. -- -- Examples -- -- f = \x::Int. x+7 TRUE -- p = (True,False) TRUE -- -- d = (fst p, False) FALSE because there's a redex inside -- (this particular one doesn't happen but...) -- -- h = D# (1.0## /## 2.0##) FALSE (redex again) -- n = /\a. Nil a TRUE -- -- t = /\a. (:) (case w a of ...) (Nil a) FALSE (redex) -- -- -- This is a bit like CoreUtils.exprIsHNF, with the following differences: -- a) scc "foo" (\x -> ...) is updatable (so we catch the right SCC) -- -- b) (C x xs), where C is a contructors is updatable if the application is -- dynamic -- -- c) don't look through unfolding of f in (f x). -- -- When opt_RuntimeTypes is on, we keep type lambdas and treat -- them as making the RHS re-entrant (non-updatable). rhsIsStatic this_pkg rhs = is_static False rhs where is_static :: Bool -- True <=> in a constructor argument; must be atomic -> CoreExpr -> Bool is_static False (Lam b e) = isRuntimeVar b || is_static False e is_static in_arg (Note (SCC _) e) = False is_static in_arg (Note _ e) = is_static in_arg e is_static in_arg (Cast e co) = is_static in_arg e is_static in_arg (Lit lit) = case lit of MachLabel _ _ -> False other -> True -- A MachLabel (foreign import "&foo") in an argument -- prevents a constructor application from being static. The -- reason is that it might give rise to unresolvable symbols -- in the object file: under Linux, references to "weak" -- symbols from the data segment give rise to "unresolvable -- relocation" errors at link time This might be due to a bug -- in the linker, but we'll work around it here anyway. -- SDM 24/2/2004 is_static in_arg other_expr = go other_expr 0 where go (Var f) n_val_args #if mingw32_TARGET_OS | not (isDllName this_pkg (idName f)) #endif = saturated_data_con f n_val_args || (in_arg && n_val_args == 0) -- A naked un-applied variable is *not* deemed a static RHS -- E.g. f = g -- Reason: better to update so that the indirection gets shorted -- out, and the true value will be seen -- NB: if you change this, you'll break the invariant that THUNK_STATICs -- are always updatable. If you do so, make sure that non-updatable -- ones have enough space for their static link field! go (App f a) n_val_args | isTypeArg a = go f n_val_args | not in_arg && is_static True a = go f (n_val_args + 1) -- The (not in_arg) checks that we aren't in a constructor argument; -- if we are, we don't allow (value) applications of any sort -- -- NB. In case you wonder, args are sometimes not atomic. eg. -- x = D# (1.0## /## 2.0##) -- can't float because /## can fail. go (Note (SCC _) f) n_val_args = False go (Note _ f) n_val_args = go f n_val_args go (Cast e co) n_val_args = go e n_val_args go other n_val_args = False saturated_data_con f n_val_args = case isDataConWorkId_maybe f of Just dc -> n_val_args == dataConRepArity dc Nothing -> False \end{code}