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diff --git a/compiler/coreSyn/CoreUtils.lhs b/compiler/coreSyn/CoreUtils.lhs new file mode 100644 index 0000000000..e358be4439 --- /dev/null +++ b/compiler/coreSyn/CoreUtils.lhs @@ -0,0 +1,1316 @@ +% +% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998 +% +\section[CoreUtils]{Utility functions on @Core@ syntax} + +\begin{code} +module CoreUtils ( + -- Construction + mkInlineMe, mkSCC, mkCoerce, mkCoerce2, + bindNonRec, needsCaseBinding, + mkIfThenElse, mkAltExpr, mkPiType, mkPiTypes, + + -- Taking expressions apart + findDefault, findAlt, isDefaultAlt, + + -- 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 + ) where + +#include "HsVersions.h" + + +import GLAEXTS -- For `xori` + +import CoreSyn +import CoreFVs ( exprFreeVars ) +import PprCore ( pprCoreExpr ) +import Var ( Var ) +import VarSet ( unionVarSet ) +import VarEnv +import Name ( hashName ) +import Packages ( HomeModules ) +#if mingw32_TARGET_OS +import Packages ( isDllName ) +#endif +import Literal ( hashLiteral, literalType, litIsDupable, + litIsTrivial, isZeroLit, Literal( MachLabel ) ) +import DataCon ( DataCon, dataConRepArity, dataConInstArgTys, + isVanillaDataCon, dataConTyCon ) +import PrimOp ( PrimOp(..), primOpOkForSpeculation, primOpIsCheap ) +import Id ( Id, idType, globalIdDetails, idNewStrictness, + mkWildId, idArity, idName, idUnfolding, idInfo, + isOneShotBndr, isStateHackType, isDataConWorkId_maybe, mkSysLocal, + isDataConWorkId, isBottomingId + ) +import IdInfo ( GlobalIdDetails(..), megaSeqIdInfo ) +import NewDemand ( appIsBottom ) +import Type ( Type, mkFunTy, mkForAllTy, splitFunTy_maybe, + splitFunTy, tcEqTypeX, + applyTys, isUnLiftedType, seqType, mkTyVarTy, + splitForAllTy_maybe, isForAllTy, splitRecNewType_maybe, + splitTyConApp_maybe, coreEqType, funResultTy, applyTy + ) +import TyCon ( tyConArity ) +import TysWiredIn ( boolTy, trueDataCon, falseDataCon ) +import CostCentre ( CostCentre ) +import BasicTypes ( Arity ) +import Unique ( Unique ) +import Outputable +import TysPrim ( alphaTy ) -- Debugging only +import Util ( equalLength, lengthAtLeast, foldl2 ) +\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 (Note (Coerce ty _) e) = ty -- **! should take usage from 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 (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) +\end{code} + + + +%************************************************************************ +%* * +\subsection{Attaching notes} +%* * +%************************************************************************ + +mkNote removes redundant coercions, and SCCs where possible + +\begin{code} +#ifdef UNUSED +mkNote :: Note -> CoreExpr -> CoreExpr +mkNote (Coerce to_ty from_ty) expr = mkCoerce2 to_ty from_ty expr +mkNote (SCC cc) expr = mkSCC cc expr +mkNote InlineMe expr = mkInlineMe expr +mkNote note expr = Note note expr +#endif + +-- 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. + +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 :: Type -> CoreExpr -> CoreExpr +mkCoerce to_ty expr = mkCoerce2 to_ty (exprType expr) expr + +mkCoerce2 :: Type -> Type -> CoreExpr -> CoreExpr +mkCoerce2 to_ty from_ty (Note (Coerce to_ty2 from_ty2) expr) + = ASSERT( from_ty `coreEqType` to_ty2 ) + mkCoerce2 to_ty from_ty2 expr + +mkCoerce2 to_ty from_ty expr + | to_ty `coreEqType` from_ty = expr + | otherwise = ASSERT( from_ty `coreEqType` 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 +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} + + +%************************************************************************ +%* * +\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 ++ map varToCoreExpr 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 +\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 (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 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 (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 + 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 + | 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 + +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 + | otherwise + = case globalIdDetails id of + DataConWorkId _ -> True + RecordSelId {} -> n_val_args == 1 -- I'm experimenting with making record selection + ClassOpId _ -> n_val_args == 1 -- 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) + + 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 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 +==> + 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 +exprOkForSpeculation (Var v) = isUnLiftedType (idType v) +exprOkForSpeculation (Note _ e) = 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 (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. True, but +this form is illegal (see the invariants in CoreSyn). 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 (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 + | isDataConWorkId fun -- Constructor apps are values + || idArity fun > valArgCount args -- Under-applied function + = check_args (idType fun) args +app_is_value (App f a) as = app_is_value f (a:as) +app_is_value other as = False + + -- 'check_args' checks that unlifted-type args + -- are in fact guaranteed non-divergent +check_args fun_ty [] = True +check_args fun_ty (Type _ : args) = case splitForAllTy_maybe fun_ty of + Just (_, ty) -> check_args ty args +check_args fun_ty (arg : args) + | isUnLiftedType arg_ty = exprOkForSpeculation arg + | otherwise = check_args res_ty args + where + (arg_ty, res_ty) = splitFunTy fun_ty +\end{code} + +\begin{code} +exprIsConApp_maybe :: CoreExpr -> Maybe (DataCon, [CoreExpr]) +exprIsConApp_maybe (Note (Coerce to_ty from_ty) expr) + = -- Maybe this is over the top, but here we try to turn + -- coerce (S,T) ( x, y ) + -- effectively into + -- ( coerce S x, coerce T y ) + -- This happens in anger in PrelArrExts which has a coerce + -- case coerce memcpy a b of + -- (# r, s #) -> ... + -- where the memcpy is in the IO monad, but the call is in + -- the (ST s) monad + case exprIsConApp_maybe expr of { + Nothing -> Nothing ; + Just (dc, args) -> + + case splitTyConApp_maybe to_ty of { + Nothing -> Nothing ; + Just (tc, tc_arg_tys) | tc /= dataConTyCon dc -> Nothing + | not (isVanillaDataCon dc) -> Nothing + | otherwise -> + -- Type constructor must match + -- We knock out existentials to keep matters simple(r) + let + arity = tyConArity tc + val_args = drop arity args + to_arg_tys = dataConInstArgTys dc tc_arg_tys + mk_coerce ty arg = mkCoerce ty arg + new_val_args = zipWith mk_coerce to_arg_tys val_args + in + ASSERT( all isTypeArg (take arity args) ) + ASSERT( equalLength val_args to_arg_tys ) + Just (dc, map Type tc_arg_tys ++ new_val_args) + }} + +exprIsConApp_maybe (Note _ expr) + = exprIsConApp_maybe expr + -- We ignore InlineMe notes in case we have + -- x = __inline_me__ (a,b) + -- All part of making sure that INLINE pragmas never hurt + -- Marcin tripped on this one when making dictionaries more inlinable + -- + -- In fact, we ignore all notes. For example, + -- case _scc_ "foo" (C a b) of + -- C a b -> e + -- should be optimised away, but it will be only if we look + -- through the SCC note. + +exprIsConApp_maybe expr = analyse (collectArgs expr) + where + analyse (Var fun, args) + | 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 :: 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 e = arityDepth (arityType e) + +-- A limited sort of function type +data ArityType = AFun Bool ArityType -- True <=> one-shot + | ATop -- Know nothing + | ABot -- Diverges + +arityDepth :: ArityType -> Arity +arityDepth (AFun _ ty) = 1 + arityDepth ty +arityDepth ty = 0 + +andArityType ABot at2 = at2 +andArityType ATop at2 = ATop +andArityType (AFun t1 at1) (AFun t2 at2) = AFun (t1 && t2) (andArityType at1 at2) +andArityType at1 at2 = andArityType at2 at1 + +arityType :: CoreExpr -> ArityType + -- (go1 e) = [b1,..,bn] + -- means expression can be rewritten \x_b1 -> ... \x_bn -> body + -- where bi is True <=> the lambda is one-shot + +arityType (Note n e) = arityType e +-- Not needed any more: etaExpand is cleverer +-- | ok_note n = arityType e +-- | otherwise = ATop + +arityType (Var v) + = mk (idArity v) (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 + | 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 (Lam x e) | isId x = AFun (isOneShotBndr x) (arityType e) + | otherwise = arityType e + + -- Applications; decrease arity +arityType (App f (Type _)) = arityType f +arityType (App f a) = case arityType f of + AFun one_shot xs | 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 (Case scrut _ _ alts) = case foldr1 andArityType [arityType rhs | (_,_,rhs) <- alts] of + xs@(AFun one_shot _) | one_shot -> xs + xs | exprIsCheap scrut -> xs + | otherwise -> ATop + +arityType (Let b e) = case arityType e of + xs@(AFun one_shot _) | one_shot -> xs + xs | all exprIsCheap (rhssOfBind b) -> xs + | otherwise -> ATop + +arityType other = ATop + +{- NOT NEEDED ANY MORE: etaExpand is cleverer +ok_note InlineMe = False +ok_note other = True + -- Notice that we do not look through __inline_me__ + -- This may seem surprising, but consider + -- f = _inline_me (\x -> e) + -- We DO NOT want to eta expand this to + -- f = \x -> (_inline_me (\x -> e)) x + -- because the _inline_me gets dropped now it is applied, + -- giving just + -- f = \x -> e + -- A Bad Idea +-} +\end{code} + + +\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 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 + = case splitForAllTy_maybe ty of { + Just (tv,ty') -> Lam tv (eta_expand n us (App expr (Type (mkTyVarTy tv))) ty') + + ; Nothing -> + + case splitFunTy_maybe ty of { + Just (arg_ty, res_ty) -> Lam arg1 (eta_expand (n-1) us2 (App expr (Var arg1)) res_ty) + where + arg1 = mkSysLocal 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) + -- Only try this for recursive newtypes; the non-recursive kind + -- are transparent anyway + + case splitRecNewType_maybe ty of { + Just ty' -> mkCoerce2 ty ty' (eta_expand n us (mkCoerce2 ty' ty expr) ty') ; + 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 (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 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 (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 (Coerce t1 f1) (Coerce t2 f2) = tcEqTypeX env t1 t2 && tcEqTypeX env f1 f2 +eq_note env InlineCall InlineCall = True +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 (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 (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 +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} + +%************************************************************************ +%* * +\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 :: HomeModules -> 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 hmods 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 (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 hmods (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 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} |