-- | Commonly useful utilites for manipulating the Core language module CoreUtils ( -- * Constructing expressions mkCast, mkTick, mkTickNoHNF, bindNonRec, needsCaseBinding, mkAltExpr, -- * Taking expressions apart findDefault, findAlt, isDefaultAlt, mergeAlts, trimConArgs, -- * Properties of expressions exprType, coreAltType, coreAltsType, exprIsDupable, exprIsTrivial, getIdFromTrivialExpr, exprIsBottom, exprIsCheap, exprIsExpandable, exprIsCheap', CheapAppFun, exprIsHNF, exprOkForSpeculation, exprOkForSideEffects, exprIsBig, exprIsConLike, rhsIsStatic, isCheapApp, isExpandableApp, -- * Expression and bindings size coreBindsSize, exprSize, CoreStats(..), coreBindsStats, -- * Hashing hashExpr, -- * Equality cheapEqExpr, eqExpr, eqExprX, -- * Eta reduction tryEtaReduce, -- * Manipulating data constructors and types applyTypeToArgs, applyTypeToArg, dataConRepInstPat, dataConRepFSInstPat ) where #include "HsVersions.h" import CoreSyn import PprCore import Var import SrcLoc import VarEnv import VarSet import Name import Literal import DataCon import PrimOp import Id import IdInfo import Type import Coercion import TyCon import Unique import Outputable import TysPrim import FastString import Maybes import Util import Pair import Data.Word import Data.Bits import Data.List ( mapAccumL )\end{code} %************************************************************************ %* * \subsection{Find the type of a Core atom/expression} %* * %************************************************************************ \begin{code}
exprType :: CoreExpr -> Type -- ^ Recover the type of a well-typed Core expression. Fails when -- applied to the actual 'CoreSyn.Type' expression as it cannot -- really be said to have a type exprType (Var var) = idType var exprType (Lit lit) = literalType lit exprType (Coercion co) = coercionType co exprType (Let _ body) = exprType body exprType (Case _ _ ty _) = ty exprType (Cast _ co) = pSnd (coercionKind co) exprType (Tick _ 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 -- ^ Returns the type of the alternatives right hand side coreAltType (_,bs,rhs) | any bad_binder bs = expandTypeSynonyms ty | otherwise = ty -- Note [Existential variables and silly type synonyms] where ty = exprType rhs free_tvs = tyVarsOfType ty bad_binder b = isTyVar b && b `elemVarSet` free_tvs coreAltsType :: [CoreAlt] -> Type -- ^ Returns the type of the first alternative, which should be the same as for all alternatives coreAltsType (alt:_) = coreAltType alt coreAltsType [] = panic "corAltsType"\end{code} Note [Existential variables and silly type synonyms] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Consider data T = forall a. T (Funny a) type Funny a = Bool f :: T -> Bool f (T x) = x Now, the type of 'x' is (Funny a), where 'a' is existentially quantified. That means that 'exprType' and 'coreAltsType' may give a result that *appears* to mention an out-of-scope type variable. See Trac #3409 for a more real-world example. Various possibilities suggest themselves: - Ignore the problem, and make Lint not complain about such variables - Expand all type synonyms (or at least all those that discard arguments) This is tricky, because at least for top-level things we want to retain the type the user originally specified. - Expand synonyms on the fly, when the problem arises. That is what we are doing here. It's not too expensive, I think. \begin{code}
applyTypeToArg :: Type -> CoreExpr -> Type -- ^ Determines the type resulting from applying an expression to a function with the given type applyTypeToArg fun_ty (Type arg_ty) = applyTy fun_ty arg_ty applyTypeToArg fun_ty _ = funResultTy fun_ty applyTypeToArgs :: CoreExpr -> Type -> [CoreExpr] -> Type -- ^ A more efficient version of 'applyTypeToArg' when we have several arguments. -- The first argument is just for debugging, and gives some context applyTypeToArgs _ 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' = applyTysD msg op_ty (reverse rev_tys) msg = ptext (sLit "applyTypeToArgs") <+> panic_msg e op_ty applyTypeToArgs e op_ty (_ : args) = case (splitFunTy_maybe op_ty) of Just (_, res_ty) -> applyTypeToArgs e res_ty args Nothing -> pprPanic "applyTypeToArgs" (panic_msg e op_ty) panic_msg :: CoreExpr -> Type -> SDoc panic_msg e op_ty = pprCoreExpr e $$ ppr op_ty\end{code} %************************************************************************ %* * \subsection{Attaching notes} %* * %************************************************************************ \begin{code}
-- | Wrap the given expression in the coercion safely, dropping -- identity coercions and coalescing nested coercions mkCast :: CoreExpr -> Coercion -> CoreExpr mkCast e co | isReflCo co = e mkCast (Coercion e_co) co = Coercion new_co where -- g :: (s1 ~# s2) ~# (t1 ~# t2) -- g1 :: s1 ~# t1 -- g2 :: s2 ~# t2 new_co = mkSymCo g1 `mkTransCo` e_co `mkTransCo` g2 [_reflk, g1, g2] = decomposeCo 3 co -- Remember, (~#) :: forall k. k -> k -> * -- so it takes *three* arguments, not two mkCast (Cast expr co2) co = ASSERT(let { Pair from_ty _to_ty = coercionKind co; Pair _from_ty2 to_ty2 = coercionKind co2} in from_ty `eqType` to_ty2 ) mkCast expr (mkTransCo co2 co) mkCast expr co = let Pair from_ty _to_ty = coercionKind co in -- if to_ty `eqType` from_ty -- then expr -- else WARN(not (from_ty `eqType` exprType expr), text "Trying to coerce" <+> text "(" <> ppr expr $$ text "::" <+> ppr (exprType expr) <> text ")" $$ ppr co $$ pprEqPred (coercionKind co)) (Cast expr co)\end{code} \begin{code}
-- | Wraps the given expression in the source annotation, dropping the -- annotation if possible. mkTick :: Tickish Id -> CoreExpr -> CoreExpr mkTick t (Var x) | isFunTy (idType x) = Tick t (Var x) | otherwise = if tickishCounts t then if tickishScoped t && tickishCanSplit t then Tick (mkNoScope t) (Var x) else Tick t (Var x) else Var x mkTick t (Cast e co) = Cast (mkTick t e) co -- Move tick inside cast mkTick _ (Coercion co) = Coercion co mkTick t (Lit l) | not (tickishCounts t) = Lit l mkTick t expr@(App f arg) | not (isRuntimeArg arg) = App (mkTick t f) arg | isSaturatedConApp expr = if not (tickishCounts t) then tickHNFArgs t expr else if tickishScoped t && tickishCanSplit t then Tick (mkNoScope t) (tickHNFArgs (mkNoTick t) expr) else Tick t expr mkTick t (Lam x e) -- if this is a type lambda, or the tick does not count entries, -- then we can push the tick inside: | not (isRuntimeVar x) || not (tickishCounts t) = Lam x (mkTick t e) -- if it is both counting and scoped, we split the tick into its -- two components, keep the counting tick on the outside of the lambda -- and push the scoped tick inside. The point of this is that the -- counting tick can probably be floated, and the lambda may then be -- in a position to be beta-reduced. | tickishScoped t && tickishCanSplit t = Tick (mkNoScope t) (Lam x (mkTick (mkNoTick t) e)) -- just a counting tick: leave it on the outside | otherwise = Tick t (Lam x e) mkTick t other = Tick t other isSaturatedConApp :: CoreExpr -> Bool isSaturatedConApp e = go e [] where go (App f a) as = go f (a:as) go (Var fun) args = isConLikeId fun && idArity fun == valArgCount args go (Cast f _) as = go f as go _ _ = False mkTickNoHNF :: Tickish Id -> CoreExpr -> CoreExpr mkTickNoHNF t e | exprIsHNF e = tickHNFArgs t e | otherwise = mkTick t e -- push a tick into the arguments of a HNF (call or constructor app) tickHNFArgs :: Tickish Id -> CoreExpr -> CoreExpr tickHNFArgs t e = push t e where push t (App f (Type u)) = App (push t f) (Type u) push t (App f arg) = App (push t f) (mkTick t arg) push _t e = e\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 we have to use a @case@ or @let@ -- binding for the expression (see 'needsCaseBinding'). -- It's used by the desugarer to avoid building bindings -- that give Core Lint a heart attack, although actually -- the simplifier deals with them perfectly well. See -- also 'MkCore.mkCoreLet' bindNonRec bndr rhs body | needsCaseBinding (idType bndr) rhs = Case rhs bndr (exprType body) [(DEFAULT, [], body)] | otherwise = Let (NonRec bndr rhs) body -- | Tests whether we have to use a @case@ rather than @let@ binding for this expression -- as per the invariants of 'CoreExpr': see "CoreSyn#let_app_invariant" needsCaseBinding :: Type -> CoreExpr -> Bool 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 -- ^ Case alternative constructor -> [CoreBndr] -- ^ Things bound by the pattern match -> [Type] -- ^ The type arguments to the case alternative -> CoreExpr -- ^ This guy constructs the value that the scrutinee must have -- given that 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 mkAltExpr (LitAlt _) _ _ = panic "mkAltExpr LitAlt" mkAltExpr DEFAULT _ _ = panic "mkAltExpr DEFAULT"\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}
-- | Extract the default case alternative findDefault :: [CoreAlt] -> ([CoreAlt], Maybe CoreExpr) findDefault ((DEFAULT,args,rhs) : alts) = ASSERT( null args ) (alts, Just rhs) findDefault alts = (alts, Nothing) isDefaultAlt :: CoreAlt -> Bool isDefaultAlt (DEFAULT, _, _) = True isDefaultAlt _ = False -- | Find the case alternative corresponding to a particular -- constructor: panics if no such constructor exists findAlt :: AltCon -> [CoreAlt] -> Maybe CoreAlt -- A "Nothing" result *is* legitmiate -- See Note [Unreachable code] findAlt con alts = case alts of (deflt@(DEFAULT,_,_):alts) -> go alts (Just deflt) _ -> go alts Nothing where 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 -> Just alt GT -> ASSERT( not (con1 == DEFAULT) ) go alts deflt --------------------------------- mergeAlts :: [CoreAlt] -> [CoreAlt] -> [CoreAlt] -- ^ Merge alternatives preserving order; alternatives in -- the first argument 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 _) args = ASSERT( null args ) [] trimConArgs (DataAlt dc) args = dropList (dataConUnivTyVars dc) args\end{code} Note [Unreachable code] ~~~~~~~~~~~~~~~~~~~~~~~ It is possible (although unusual) for GHC to find a case expression that cannot match. For example: data Col = Red | Green | Blue x = Red f v = case x of Red -> ... _ -> ...(case x of { Green -> e1; Blue -> e2 })... Suppose that for some silly reason, x isn't substituted in the case expression. (Perhaps there's a NOINLINE on it, or profiling SCC stuff gets in the way; cf Trac #3118.) Then the full-lazines pass might produce this x = Red lvl = case x of { Green -> e1; Blue -> e2 }) f v = case x of Red -> ... _ -> ...lvl... Now if x gets inlined, we won't be able to find a matching alternative for 'Red'. That's because 'lvl' is unreachable. So rather than crashing we generate (error "Inaccessible alternative"). Similar things can happen (augmented by GADTs) when the Simplifier filters down the matching alternatives in Simplify.rebuildCase. %************************************************************************ %* * exprIsTrivial %* * %************************************************************************ Note [exprIsTrivial] ~~~~~~~~~~~~~~~~~~~~ @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 Note [Variable are trivial] ~~~~~~~~~~~~~~~~~~~~~~~~~~~ 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. Note [Tick trivial] ~~~~~~~~~~~~~~~~~~~ Ticks are not trivial. If we treat "tick
exprIsTrivial :: CoreExpr -> Bool exprIsTrivial (Var _) = True -- See Note [Variables are trivial] exprIsTrivial (Type _) = True exprIsTrivial (Coercion _) = True exprIsTrivial (Lit lit) = litIsTrivial lit exprIsTrivial (App e arg) = not (isRuntimeArg arg) && exprIsTrivial e exprIsTrivial (Tick _ _) = False -- See Note [Tick trivial] exprIsTrivial (Cast e _) = exprIsTrivial e exprIsTrivial (Lam b body) = not (isRuntimeVar b) && exprIsTrivial body exprIsTrivial _ = False\end{code} When substituting in a breakpoint we need to strip away the type cruft from a trivial expression and get back to the Id. The invariant is that the expression we're substituting was originally trivial according to exprIsTrivial. \begin{code}
getIdFromTrivialExpr :: CoreExpr -> Id getIdFromTrivialExpr e = go e where go (Var v) = v go (App f t) | not (isRuntimeArg t) = go f go (Cast e _) = go e go (Lam b e) | not (isRuntimeVar b) = go e go e = pprPanic "getIdFromTrivialExpr" (ppr e)\end{code} exprIsBottom is a very cheap and cheerful function; it may return False for bottoming expressions, but it never costs much to ask. See also CoreArity.exprBotStrictness_maybe, but that's a bit more expensive. \begin{code}
exprIsBottom :: CoreExpr -> Bool exprIsBottom e = go 0 e where go n (Var v) = isBottomingId v && n >= idArity v go n (App e a) | isTypeArg a = go n e | otherwise = go (n+1) e go n (Tick _ e) = go n e go n (Cast e _) = go n e go n (Let _ e) = go n e go _ _ = False\end{code} %************************************************************************ %* * exprIsDupable %* * %************************************************************************ Note [exprIsDupable] ~~~~~~~~~~~~~~~~~~~~ @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 :: CoreExpr -> Bool exprIsDupable e = isJust (go dupAppSize e) where go :: Int -> CoreExpr -> Maybe Int go n (Type {}) = Just n go n (Coercion {}) = Just n go n (Var {}) = decrement n go n (Tick _ e) = go n e go n (Cast e _) = go n e go n (App f a) | Just n' <- go n a = go n' f go n (Lit lit) | litIsDupable lit = decrement n go _ _ = Nothing decrement :: Int -> Maybe Int decrement 0 = Nothing decrement n = Just (n-1) dupAppSize :: Int dupAppSize = 8 -- Size of term we are prepared to duplicate -- This is *just* big enough to make test MethSharing -- inline enough join points. Really it should be -- smaller, and could be if we fixed Trac #4960.\end{code} %************************************************************************ %* * exprIsCheap, exprIsExpandable %* * %************************************************************************ Note [exprIsCheap] See also Note [Interaction of exprIsCheap and lone variables] ~~~~~~~~~~~~~~~~~~ in CoreUnfold.lhs @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. Note [exprIsCheap and exprIsHNF] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Note that exprIsHNF does not imply exprIsCheap. Eg let x = fac 20 in Just x This responds True to exprIsHNF (you can discard a seq), but False to exprIsCheap. \begin{code}
exprIsCheap :: CoreExpr -> Bool exprIsCheap = exprIsCheap' isCheapApp exprIsExpandable :: CoreExpr -> Bool exprIsExpandable = exprIsCheap' isExpandableApp -- See Note [CONLIKE pragma] in BasicTypes type CheapAppFun = Id -> Int -> Bool exprIsCheap' :: CheapAppFun -> CoreExpr -> Bool exprIsCheap' _ (Lit _) = True exprIsCheap' _ (Type _) = True exprIsCheap' _ (Coercion _) = True exprIsCheap' _ (Var _) = True exprIsCheap' good_app (Cast e _) = exprIsCheap' good_app e exprIsCheap' good_app (Lam x e) = isRuntimeVar x || exprIsCheap' good_app e exprIsCheap' good_app (Case e _ _ alts) = exprIsCheap' good_app e && and [exprIsCheap' good_app 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' good_app (Tick t e) | tickishCounts t = False | otherwise = exprIsCheap' good_app e -- never duplicate ticks. If we get this wrong, then HPC's entry -- counts will be off (check test in libraries/hpc/tests/raytrace) exprIsCheap' good_app (Let (NonRec x _) e) | isUnLiftedType (idType x) = exprIsCheap' good_app e | otherwise = False -- Strict lets always have cheap right hand sides, -- and do no allocation, so just look at the body -- Non-strict lets do allocation so we don't treat them as cheap -- See also exprIsCheap' good_app other_expr -- Applications and variables = go other_expr [] where -- Accumulate value arguments, then decide go (Cast e _) val_args = go e val_args go (App f a) val_args | isRuntimeArg a = go f (a:val_args) | otherwise = go f val_args go (Var _) [] = True -- Just a type application of a variable -- (f t1 t2 t3) counts as WHNF go (Var f) args = case idDetails f of RecSelId {} -> go_sel args ClassOpId {} -> go_sel args PrimOpId op -> go_primop op args _ | good_app f (length args) -> go_pap args | isBottomingId f -> True | otherwise -> False -- Application of a function which -- always gives bottom; we treat this as cheap -- because it certainly doesn't need to be shared! go _ _ = False -------------- go_pap args = all (exprIsCheap' good_app) args -- Used to be "all exprIsTrivial args" due to concerns about -- duplicating nested constructor applications, but see #4978. -- The principle here is that -- let x = a +# b in c *# x -- should behave equivalently to -- c *# (a +# b) -- Since lets with cheap RHSs are accepted, -- so should paps with cheap arguments -------------- go_primop op args = primOpIsCheap op && all (exprIsCheap' good_app) 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' good_app arg -- I'm experimenting with making record selection go_sel _ = 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) isCheapApp :: CheapAppFun isCheapApp fn n_val_args = isDataConWorkId fn || n_val_args < idArity fn isExpandableApp :: CheapAppFun isExpandableApp fn n_val_args = isConLikeId fn || n_val_args < idArity fn || go n_val_args (idType fn) where -- See if all the arguments are PredTys (implicit params or classes) -- If so we'll regard it as expandable; see Note [Expandable overloadings] go 0 _ = True go n_val_args ty | Just (_, ty) <- splitForAllTy_maybe ty = go n_val_args ty | Just (arg, ty) <- splitFunTy_maybe ty , isPredTy arg = go (n_val_args-1) ty | otherwise = False\end{code} Note [Expandable overloadings] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Suppose the user wrote this {-# RULE forall x. foo (negate x) = h x #-} f x = ....(foo (negate x)).... He'd expect the rule to fire. But since negate is overloaded, we might get this: f = \d -> let n = negate d in \x -> ...foo (n x)... So we treat the application of a function (negate in this case) to a *dictionary* as expandable. In effect, every function is CONLIKE when it's applied only to dictionaries. %************************************************************************ %* * exprOkForSpeculation %* * %************************************************************************ \begin{code}
----------------------------- -- | 'exprOkForSpeculation' returns True of an expression that 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 is usually called on arguments of unlifted type, but not always -- In particular, Simplify.rebuildCase calls it on lifted types -- when a 'case' is a plain 'seq'. See the example in -- Note [exprOkForSpeculation: case expressions] below -- -- Precisely, 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) -- -- Note that if @exprIsHNF e@, then @exprOkForSpecuation e@. -- As an example of the considerations in this test, consider: -- -- > let x = case y# +# 1# of { r# -> I# r# } -- > in E -- -- being translated to: -- -- > 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. exprOkForSpeculation, exprOkForSideEffects :: Expr b -> Bool exprOkForSpeculation = expr_ok primOpOkForSpeculation exprOkForSideEffects = expr_ok primOpOkForSideEffects -- Polymorphic in binder type -- There is one call at a non-Id binder type, in SetLevels expr_ok :: (PrimOp -> Bool) -> Expr b -> Bool expr_ok _ (Lit _) = True expr_ok _ (Type _) = True expr_ok _ (Coercion _) = True expr_ok primop_ok (Var v) = app_ok primop_ok v [] expr_ok primop_ok (Cast e _) = expr_ok primop_ok e -- Tick annotations that *tick* cannot be speculated, because these -- are meant to identify whether or not (and how often) the particular -- source expression was evaluated at runtime. expr_ok primop_ok (Tick tickish e) | tickishCounts tickish = False | otherwise = expr_ok primop_ok e expr_ok primop_ok (Case e _ _ alts) = expr_ok primop_ok e -- Note [exprOkForSpeculation: case expressions] && all (\(_,_,rhs) -> expr_ok primop_ok rhs) alts && altsAreExhaustive alts -- Note [Exhaustive alts] expr_ok primop_ok other_expr = case collectArgs other_expr of (Var f, args) -> app_ok primop_ok f args _ -> False ----------------------------- app_ok :: (PrimOp -> Bool) -> Id -> [Expr b] -> Bool app_ok primop_ok fun args = case idDetails fun of DFunId new_type -> not new_type -- DFuns terminate, unless the dict is implemented -- with a newtype in which case they may not DataConWorkId {} -> True -- The strictness of the constructor has already -- been expressed by its "wrapper", so we don't need -- to take the arguments into account PrimOpId op | isDivOp op -- Special case for dividing operations that fail , [arg1, Lit lit] <- args -- only if the divisor is zero -> not (isZeroLit lit) && expr_ok primop_ok arg1 -- Often there is a literal divisor, and this -- can get rid of a thunk in an inner looop | DataToTagOp <- op -- See Note [dataToTag speculation] -> True | otherwise -> primop_ok op -- A bit conservative: we don't really need && all (expr_ok primop_ok) args -- to care about lazy arguments, but this is easy _other -> isUnLiftedType (idType fun) -- c.f. the Var case of exprIsHNF || idArity fun > n_val_args -- Partial apps || (n_val_args == 0 && isEvaldUnfolding (idUnfolding fun)) -- Let-bound values where n_val_args = valArgCount args ----------------------------- altsAreExhaustive :: [Alt b] -> Bool -- True <=> the case alterantives are definiely exhaustive -- False <=> they may or may not be altsAreExhaustive [] = False -- Should not happen altsAreExhaustive ((con1,_,_) : alts) = case con1 of DEFAULT -> True LitAlt {} -> False DataAlt c -> 1 + length alts == tyConFamilySize (dataConTyCon c) -- It is possible to have an exhaustive case that does not -- enumerate all constructors, notably in a GADT match, but -- we behave conservatively here -- I don't think it's important -- enough to deserve special treatment -- | True of dyadic operators that can fail only if the second arg is zero! isDivOp :: PrimOp -> Bool -- 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 FloatDivOp = True isDivOp DoubleDivOp = True isDivOp _ = False\end{code} Note [exprOkForSpeculation: case expressions] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ It's always sound for exprOkForSpeculation to return False, and we don't want it to take too long, so it bales out on complicated-looking terms. Notably lets, which can be stacked very deeply; and in any case the argument of exprOkForSpeculation is usually in a strict context, so any lets will have been floated away. However, we keep going on case-expressions. An example like this one showed up in DPH code (Trac #3717): foo :: Int -> Int foo 0 = 0 foo n = (if n < 5 then 1 else 2) `seq` foo (n-1) If exprOkForSpeculation doesn't look through case expressions, you get this: T.$wfoo = \ (ww :: GHC.Prim.Int#) -> case ww of ds { __DEFAULT -> case (case <# ds 5 of _ { GHC.Types.False -> lvl1; GHC.Types.True -> lvl}) of _ { __DEFAULT -> T.$wfoo (GHC.Prim.-# ds_XkE 1) }; 0 -> 0 } The inner case is redundant, and should be nuked. Note [Exhaustive alts] ~~~~~~~~~~~~~~~~~~~~~~ We might have something like case x of { A -> ... _ -> ...(case x of { B -> ...; C -> ... })... Here, the inner case is fine, because the A alternative can't happen, but it's not ok to float the inner case outside the outer one (even if we know x is evaluated outside), because then it would be non-exhaustive. See Trac #5453. Similarly, this is a valid program (albeit a slightly dodgy one) let v = case x of { B -> ...; C -> ... } in case x of A -> ... _ -> ...v...v.... But we don't want to speculate the v binding. One could try to be clever, but the easy fix is simpy to regard a non-exhaustive case as *not* okForSpeculation. Note [dataToTag speculation] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Is this OK? f x = let v::Int# = dataToTag# x in ... We say "yes", even though 'x' may not be evaluated. Reasons * dataToTag#'s strictness means that its argument often will be evaluated, but FloatOut makes that temporarily untrue case x of y -> let v = dataToTag# y in ... --> case x of y -> let v = dataToTag# x in ... Note that we look at 'x' instead of 'y' (this is to improve floating in FloatOut). So Lint complains. Moreover, it really *might* improve floating to let the v-binding float out * CorePrep makes sure dataToTag#'s argument is evaluated, just before code gen. Until then, it's not guaranteed %************************************************************************ %* * exprIsHNF, exprIsConLike %* * %************************************************************************ \begin{code}
-- Note [exprIsHNF] See also Note [exprIsCheap and exprIsHNF] -- ~~~~~~~~~~~~~~~~ -- | 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 -- -- into: -- -- > 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. -- However, it /does/ treat partial applications and constructor applications -- as values, even if their arguments are non-trivial, provided the argument -- type is lifted. For example, both of these are values: -- -- > (:) (f x) (map f xs) -- > map (...redex...) -- -- 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#let_app_invariant". This invariant states that arguments of -- unboxed type must be ok-for-speculation (or trivial). exprIsHNF :: CoreExpr -> Bool -- True => Value-lambda, constructor, PAP exprIsHNF = exprIsHNFlike isDataConWorkId isEvaldUnfolding\end{code} \begin{code}
-- | Similar to 'exprIsHNF' but includes CONLIKE functions as well as -- data constructors. Conlike arguments are considered interesting by the -- inliner. exprIsConLike :: CoreExpr -> Bool -- True => lambda, conlike, PAP exprIsConLike = exprIsHNFlike isConLikeId isConLikeUnfolding -- | Returns true for values or value-like expressions. These are lambdas, -- constructors / CONLIKE functions (as determined by the function argument) -- or PAPs. -- exprIsHNFlike :: (Var -> Bool) -> (Unfolding -> Bool) -> CoreExpr -> Bool exprIsHNFlike is_con is_con_unf = is_hnf_like where is_hnf_like (Var v) -- NB: There are no value args at this point = is_con v -- Catches nullary constructors, -- so that [] and () are values, for example || idArity v > 0 -- Catches (e.g.) primops that don't have unfoldings || is_con_unf (idUnfolding v) -- Check the thing's unfolding; it might be bound to a value -- We don't look through loop breakers here, which is a bit conservative -- but otherwise I worry that if an Id's unfolding is just itself, -- we could get an infinite loop is_hnf_like (Lit _) = True is_hnf_like (Type _) = True -- Types are honorary Values; -- we don't mind copying them is_hnf_like (Coercion _) = True -- Same for coercions is_hnf_like (Lam b e) = isRuntimeVar b || is_hnf_like e is_hnf_like (Tick tickish e) = not (tickishCounts tickish) && is_hnf_like e -- See Note [exprIsHNF Tick] is_hnf_like (Cast e _) = is_hnf_like e is_hnf_like (App e (Type _)) = is_hnf_like e is_hnf_like (App e (Coercion _)) = is_hnf_like e is_hnf_like (App e a) = app_is_value e [a] is_hnf_like (Let _ e) = is_hnf_like e -- Lazy let(rec)s don't affect us is_hnf_like _ = False -- There is at least one value argument app_is_value :: CoreExpr -> [CoreArg] -> Bool app_is_value (Var fun) args = idArity fun > valArgCount args -- Under-applied function || is_con fun -- or constructor-like app_is_value (Tick _ 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 _ _ = False {- Note [exprIsHNF Tick] We can discard source annotations on HNFs as long as they aren't tick-like: scc c (\x . e) => \x . e scc c (C x1..xn) => C x1..xn So we regard these as HNFs. Tick annotations that tick are not regarded as HNF if the expression they surround is HNF, because the tick is there to tell us that the expression was evaluated, so we don't want to discard a seq on it. -}\end{code} %************************************************************************ %* * Instantiating data constructors %* * %************************************************************************ These InstPat functions go here to avoid circularity between DataCon and Id \begin{code}
dataConRepInstPat :: [Unique] -> DataCon -> [Type] -> ([TyVar], [Id]) dataConRepFSInstPat :: [FastString] -> [Unique] -> DataCon -> [Type] -> ([TyVar], [Id]) dataConRepInstPat = dataConInstPat (repeat ((fsLit "ipv"))) dataConRepFSInstPat = dataConInstPat dataConInstPat :: [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], [Id]) -- Return instantiated variables -- dataConInstPat arg_fun fss us con inst_tys returns a triple -- (ex_tvs, arg_ids), -- -- ex_tvs are intended to be used as binders for existential type args -- -- arg_ids are indended to be used as binders for value arguments, -- and their types have been instantiated with inst_tys and ex_tys -- The arg_ids include both evidence and -- programmer-specified arguments (both after rep-ing) -- -- 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 fss uniqs con inst_tys = ASSERT( univ_tvs `equalLength` inst_tys ) (ex_bndrs, arg_ids) where univ_tvs = dataConUnivTyVars con ex_tvs = dataConExTyVars con arg_tys = dataConRepArgTys con n_ex = length ex_tvs -- split the Uniques and FastStrings (ex_uniqs, id_uniqs) = splitAt n_ex uniqs (ex_fss, id_fss) = splitAt n_ex fss -- Make the instantiating substitution for universals univ_subst = zipOpenTvSubst univ_tvs inst_tys -- Make existential type variables, applyingn and extending the substitution (full_subst, ex_bndrs) = mapAccumL mk_ex_var univ_subst (zip3 ex_tvs ex_fss ex_uniqs) mk_ex_var :: TvSubst -> (TyVar, FastString, Unique) -> (TvSubst, TyVar) mk_ex_var subst (tv, fs, uniq) = (Type.extendTvSubst subst tv (mkTyVarTy new_tv) , new_tv) where new_tv = mkTyVar new_name kind new_name = mkSysTvName uniq fs kind = Type.substTy subst (tyVarKind tv) -- Make value vars, instantiating types arg_ids = zipWith3 mk_id_var id_uniqs id_fss arg_tys mk_id_var uniq fs ty = mkUserLocal (mkVarOccFS fs) uniq (Type.substTy full_subst ty) noSrcSpan\end{code} %************************************************************************ %* * Equality %* * %************************************************************************ \begin{code}
-- | A cheap equality test which bales out fast! -- If it returns @True@ the arguments are definitely equal, -- otherwise, they may or may not be equal. -- -- See also 'exprIsBig' 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 `eqType` t2 cheapEqExpr (Coercion c1) (Coercion c2) = c1 `coreEqCoercion` c2 cheapEqExpr (App f1 a1) (App f2 a2) = f1 `cheapEqExpr` f2 && a1 `cheapEqExpr` a2 cheapEqExpr (Cast e1 t1) (Cast e2 t2) = e1 `cheapEqExpr` e2 && t1 `coreEqCoercion` t2 cheapEqExpr _ _ = False\end{code} \begin{code}
exprIsBig :: Expr b -> Bool -- ^ Returns @True@ of expressions that are too big to be compared by 'cheapEqExpr' exprIsBig (Lit _) = False exprIsBig (Var _) = False exprIsBig (Type _) = False exprIsBig (Coercion _) = False exprIsBig (Lam _ e) = exprIsBig e exprIsBig (App f a) = exprIsBig f || exprIsBig a exprIsBig (Cast e _) = exprIsBig e -- Hopefully coercions are not too big! exprIsBig _ = True\end{code} \begin{code}
eqExpr :: InScopeSet -> CoreExpr -> CoreExpr -> Bool -- Compares for equality, modulo alpha eqExpr in_scope e1 e2 = eqExprX id_unf (mkRnEnv2 in_scope) e1 e2 where id_unf _ = noUnfolding -- Don't expand\end{code} \begin{code}
eqExprX :: IdUnfoldingFun -> RnEnv2 -> CoreExpr -> CoreExpr -> Bool -- ^ Compares expressions for equality, modulo alpha. -- Does /not/ look through newtypes or predicate types -- Used in rule matching, and also CSE eqExprX id_unfolding_fun env e1 e2 = go env e1 e2 where go env (Var v1) (Var v2) | rnOccL env v1 == rnOccR env v2 = True -- The next two rules expand non-local variables -- C.f. Note [Expanding variables] in Rules.lhs -- and Note [Do not expand locally-bound variables] in Rules.lhs go env (Var v1) e2 | not (locallyBoundL env v1) , Just e1' <- expandUnfolding_maybe (id_unfolding_fun (lookupRnInScope env v1)) = go (nukeRnEnvL env) e1' e2 go env e1 (Var v2) | not (locallyBoundR env v2) , Just e2' <- expandUnfolding_maybe (id_unfolding_fun (lookupRnInScope env v2)) = go (nukeRnEnvR env) e1 e2' go _ (Lit lit1) (Lit lit2) = lit1 == lit2 go env (Type t1) (Type t2) = eqTypeX env t1 t2 go env (Coercion co1) (Coercion co2) = coreEqCoercion2 env co1 co2 go env (Cast e1 co1) (Cast e2 co2) = coreEqCoercion2 env co1 co2 && go env e1 e2 go env (App f1 a1) (App f2 a2) = go env f1 f2 && go env a1 a2 go env (Tick n1 e1) (Tick n2 e2) = go_tickish n1 n2 && go env e1 e2 go env (Lam b1 e1) (Lam b2 e2) = eqTypeX env (varType b1) (varType b2) -- False for Id/TyVar combination && go (rnBndr2 env b1 b2) e1 e2 go env (Let (NonRec v1 r1) e1) (Let (NonRec v2 r2) e2) = go env r1 r2 -- No need to check binder types, since RHSs match && go (rnBndr2 env v1 v2) e1 e2 go env (Let (Rec ps1) e1) (Let (Rec ps2) e2) = all2 (go env') rs1 rs2 && go env' e1 e2 where (bs1,rs1) = unzip ps1 (bs2,rs2) = unzip ps2 env' = rnBndrs2 env bs1 bs2 go env (Case e1 b1 _ a1) (Case e2 b2 _ a2) = go env e1 e2 && eqTypeX env (idType b1) (idType b2) && all2 (go_alt (rnBndr2 env b1 b2)) a1 a2 go _ _ _ = False ----------- go_alt env (c1, bs1, e1) (c2, bs2, e2) = c1 == c2 && go (rnBndrs2 env bs1 bs2) e1 e2 ----------- go_tickish (Breakpoint lid lids) (Breakpoint rid rids) = lid == rid && map (rnOccL env) lids == map (rnOccR env) rids go_tickish l r = l == r\end{code} Auxiliary functions \begin{code}
locallyBoundL, locallyBoundR :: RnEnv2 -> Var -> Bool locallyBoundL rn_env v = inRnEnvL rn_env v locallyBoundR rn_env v = inRnEnvR rn_env v\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, strictly greater than 0 -- It also forces the expression pretty drastically as a side effect -- Counts *leaves*, not internal nodes. Types and coercions are not counted. 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) = (seqCo co `seq` 1) + exprSize e exprSize (Tick n e) = tickSize n + exprSize e exprSize (Type t) = seqType t `seq` 1 exprSize (Coercion co) = seqCo co `seq` 1 tickSize :: Tickish Id -> Int tickSize (ProfNote cc _ _) = cc `seq` 1 tickSize _ = 1 -- the rest are strict varSize :: Var -> Int varSize b | isTyVar b = 1 | otherwise = seqType (idType b) `seq` megaSeqIdInfo (idInfo b) `seq` 1 varsSize :: [Var] -> Int varsSize = sum . map varSize bindSize :: CoreBind -> Int bindSize (NonRec b e) = varSize b + exprSize e bindSize (Rec prs) = foldr ((+) . pairSize) 0 prs pairSize :: (Var, CoreExpr) -> Int pairSize (b,e) = varSize b + exprSize e altSize :: CoreAlt -> Int altSize (c,bs,e) = c `seq` varsSize bs + exprSize e\end{code} \begin{code}
data CoreStats = CS { cs_tm, cs_ty, cs_co :: Int } instance Outputable CoreStats where ppr (CS { cs_tm = i1, cs_ty = i2, cs_co = i3 }) = text "size of" <+> vcat [ text "terms =" <+> int i1 , text "types =" <+> int i2 , text "coercions =" <+> int i3 ] plusCS :: CoreStats -> CoreStats -> CoreStats plusCS (CS { cs_tm = p1, cs_ty = q1, cs_co = r1 }) (CS { cs_tm = p2, cs_ty = q2, cs_co = r2 }) = CS { cs_tm = p1+p2, cs_ty = q1+q2, cs_co = r1+r2 } zeroCS, oneTM :: CoreStats zeroCS = CS { cs_tm = 0, cs_ty = 0, cs_co = 0 } oneTM = zeroCS { cs_tm = 1 } sumCS :: (a -> CoreStats) -> [a] -> CoreStats sumCS f = foldr (plusCS . f) zeroCS coreBindsStats :: [CoreBind] -> CoreStats coreBindsStats = sumCS bindStats bindStats :: CoreBind -> CoreStats bindStats (NonRec v r) = bindingStats v r bindStats (Rec prs) = sumCS (\(v,r) -> bindingStats v r) prs bindingStats :: Var -> CoreExpr -> CoreStats bindingStats v r = bndrStats v `plusCS` exprStats r bndrStats :: Var -> CoreStats bndrStats v = oneTM `plusCS` tyStats (varType v) exprStats :: CoreExpr -> CoreStats exprStats (Var {}) = oneTM exprStats (Lit {}) = oneTM exprStats (Type t) = tyStats t exprStats (Coercion c) = coStats c exprStats (App f a) = exprStats f `plusCS` exprStats a exprStats (Lam b e) = bndrStats b `plusCS` exprStats e exprStats (Let b e) = bindStats b `plusCS` exprStats e exprStats (Case e b _ as) = exprStats e `plusCS` bndrStats b `plusCS` sumCS altStats as exprStats (Cast e co) = coStats co `plusCS` exprStats e exprStats (Tick _ e) = exprStats e altStats :: CoreAlt -> CoreStats altStats (_, bs, r) = sumCS bndrStats bs `plusCS` exprStats r tyStats :: Type -> CoreStats tyStats ty = zeroCS { cs_ty = typeSize ty } coStats :: Coercion -> CoreStats coStats co = zeroCS { cs_co = coercionSize co }\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. -- -- The emphasis is on a crude, fast hash, rather than on high precision. -- -- But unequal here means \"not identical\"; two alpha-equivalent -- expressions may hash to the different Ints. -- -- 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 (Tick _ e) = hash_expr env e hash_expr env (Cast e _) = hash_expr env e hash_expr env (Var v) = hashVar env v hash_expr _ (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,_):_)) e) = hash_expr (extend_env env b) e hash_expr _ (Let (Rec []) _) = panic "hash_expr: Let (Rec []) _" 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 (Coercion co) = fast_hash_co env co hash_expr _ (Type _) = 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 :: HashEnv -> CoreExpr -> Word32 fast_hash_expr env (Var v) = hashVar env v fast_hash_expr env (Type t) = fast_hash_type env t fast_hash_expr env (Coercion co) = fast_hash_co env co fast_hash_expr _ (Lit lit) = fromIntegral (hashLiteral lit) fast_hash_expr env (Cast e _) = fast_hash_expr env e fast_hash_expr env (Tick _ e) = fast_hash_expr env e fast_hash_expr env (App _ a) = fast_hash_expr env a -- A bit idiosyncratic ('a' not 'f')! fast_hash_expr _ _ = 1 fast_hash_type :: HashEnv -> Type -> Word32 fast_hash_type env ty | Just tv <- getTyVar_maybe ty = hashVar env tv | Just (tc,tys) <- splitTyConApp_maybe ty = let hash_tc = fromIntegral (hashName (tyConName tc)) in foldr (\t n -> fast_hash_type env t + n) hash_tc tys | otherwise = 1 fast_hash_co :: HashEnv -> Coercion -> Word32 fast_hash_co env co | Just cv <- getCoVar_maybe co = hashVar env cv | Just (tc,cos) <- splitTyConAppCo_maybe co = let hash_tc = fromIntegral (hashName (tyConName tc)) in foldr (\c n -> fast_hash_co env c + n) hash_tc cos | 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} %************************************************************************ %* * Eta reduction %* * %************************************************************************ Note [Eta reduction conditions] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ We try for eta reduction here, but *only* if we get all the way to an trivial expression. We don't want to remove extra lambdas unless we are going to avoid allocating this thing altogether. There are some particularly delicate points here: * Eta reduction is not valid in general: \x. bot /= bot This matters, partly for old-fashioned correctness reasons but, worse, getting it wrong can yield a seg fault. Consider f = \x.f x h y = case (case y of { True -> f `seq` True; False -> False }) of True -> ...; False -> ... If we (unsoundly) eta-reduce f to get f=f, the strictness analyser says f=bottom, and replaces the (f `seq` True) with just (f `cast` unsafe-co). BUT, as thing stand, 'f' got arity 1, and it *keeps* arity 1 (perhaps also wrongly). So CorePrep eta-expands the definition again, so that it does not termninate after all. Result: seg-fault because the boolean case actually gets a function value. See Trac #1947. So it's important to to the right thing. * Note [Arity care]: we need to be careful if we just look at f's arity. Currently (Dec07), f's arity is visible in its own RHS (see Note [Arity robustness] in SimplEnv) so we must *not* trust the arity when checking that 'f' is a value. Otherwise we will eta-reduce f = \x. f x to f = f Which might change a terminiating program (think (f `seq` e)) to a non-terminating one. So we check for being a loop breaker first. However for GlobalIds we can look at the arity; and for primops we must, since they have no unfolding. * Regardless of whether 'f' is a value, we always want to reduce (/\a -> f a) to f This came up in a RULE: foldr (build (/\a -> g a)) did not match foldr (build (/\b -> ...something complex...)) The type checker can insert these eta-expanded versions, with both type and dictionary lambdas; hence the slightly ad-hoc isDictId * Never *reduce* arity. For example f = \xy. g x y Then if h has arity 1 we don't want to eta-reduce because then f's arity would decrease, and that is bad These delicacies are why we don't use exprIsTrivial and exprIsHNF here. Alas. Note [Eta reduction with casted arguments] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Consider (\(x:t3). f (x |> g)) :: t3 -> t2 where f :: t1 -> t2 g :: t3 ~ t1 This should be eta-reduced to f |> (sym g -> t2) So we need to accumulate a coercion, pushing it inward (past variable arguments only) thus: f (x |> co_arg) |> co --> (f |> (sym co_arg -> co)) x f (x:t) |> co --> (f |> (t -> co)) x f @ a |> co --> (f |> (forall a.co)) @ a f @ (g:t1~t2) |> co --> (f |> (t1~t2 => co)) @ (g:t1~t2) These are the equations for ok_arg. It's true that we could also hope to eta reduce these: (\xy. (f x |> g) y) (\xy. (f x y) |> g) But the simplifier pushes those casts outwards, so we don't need to address that here. \begin{code}
tryEtaReduce :: [Var] -> CoreExpr -> Maybe CoreExpr tryEtaReduce bndrs body = go (reverse bndrs) body (mkReflCo (exprType body)) where incoming_arity = count isId bndrs go :: [Var] -- Binders, innermost first, types [a3,a2,a1] -> CoreExpr -- Of type tr -> Coercion -- Of type tr ~ ts -> Maybe CoreExpr -- Of type a1 -> a2 -> a3 -> ts -- See Note [Eta reduction with casted arguments] -- for why we have an accumulating coercion go [] fun co | ok_fun fun = Just (mkCast fun co) go (b : bs) (App fun arg) co | Just co' <- ok_arg b arg co = go bs fun co' go _ _ _ = Nothing -- Failure! --------------- -- Note [Eta reduction conditions] ok_fun (App fun (Type ty)) | not (any (`elemVarSet` tyVarsOfType ty) bndrs) = ok_fun fun ok_fun (Var fun_id) = not (fun_id `elem` bndrs) && (ok_fun_id fun_id || all ok_lam bndrs) ok_fun _fun = False --------------- ok_fun_id fun = fun_arity fun >= incoming_arity --------------- fun_arity fun -- See Note [Arity care] | isLocalId fun && isStrongLoopBreaker (idOccInfo fun) = 0 | otherwise = idArity fun --------------- ok_lam v = isTyVar v || isEvVar v --------------- ok_arg :: Var -- Of type bndr_t -> CoreExpr -- Of type arg_t -> Coercion -- Of kind (t1~t2) -> Maybe Coercion -- Of type (arg_t -> t1 ~ bndr_t -> t2) -- (and similarly for tyvars, coercion args) -- See Note [Eta reduction with casted arguments] ok_arg bndr (Type ty) co | Just tv <- getTyVar_maybe ty , bndr == tv = Just (mkForAllCo tv co) ok_arg bndr (Var v) co | bndr == v = Just (mkFunCo (mkReflCo (idType bndr)) co) ok_arg bndr (Cast (Var v) co_arg) co | bndr == v = Just (mkFunCo (mkSymCo co_arg) co) -- The simplifier combines multiple casts into one, -- so we can have a simple-minded pattern match here ok_arg _ _ _ = Nothing\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 'execute' it rather than allocating it statically. \begin{code}
-- | This function is called only on *top-level* right-hand sides. -- Returns @True@ if the RHS can be allocated statically in the output, -- with no thunks involved at all. rhsIsStatic :: (Name -> Bool) -> CoreExpr -> Bool -- It's called (i) in TidyPgm.hasCafRefs to decide if the rhs is, or -- refers to, CAFs; (ii) in CoreToStg to decide whether to put an -- update flag on it and (iii) in DsExpr to decide how to expand -- list literals -- -- 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 contructor is updatable if the application is -- dynamic -- -- c) don't look through unfolding of f in (f x). rhsIsStatic _is_dynamic_name 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 (Tick n e) = not (tickishIsCode n) && is_static in_arg e is_static in_arg (Cast e _) = is_static in_arg e is_static _ (Coercion {}) = True -- Behaves just like a literal is_static _ (Lit (LitInteger {})) = False is_static _ (Lit (MachLabel {})) = False is_static _ (Lit _) = 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 (_is_dynamic_name (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 (Tick n f) n_val_args = not (tickishIsCode n) && go f n_val_args go (Cast e _) n_val_args = go e n_val_args go _ _ = False saturated_data_con f n_val_args = case isDataConWorkId_maybe f of Just dc -> n_val_args == dataConRepArity dc Nothing -> False\end{code}