bindNonRec, mkIfThenElse, mkAltExpr,
mkPiType,
+ -- Taking expressions apart
+ findDefault, findAlt, hasDefault,
+
-- Properties of expressions
exprType, coreAltsType,
exprIsBottom, exprIsDupable, exprIsTrivial, exprIsCheap,
exprIsValue,exprOkForSpeculation, exprIsBig,
exprIsConApp_maybe, exprIsAtom,
idAppIsBottom, idAppIsCheap,
- exprArity,
+ exprArity,
-- Expr transformation
etaReduce, etaExpand,
import Name ( hashName )
import Literal ( hashLiteral, literalType, litIsDupable )
import DataCon ( DataCon, dataConRepArity )
-import PrimOp ( primOpOkForSpeculation, primOpIsCheap,
- primOpIsDupable )
-import Id ( Id, idType, idFlavour, idStrictness, idLBVarInfo,
- mkWildId, idArity, idName, idUnfolding, idInfo,
- isDataConId_maybe, isPrimOpId_maybe, mkSysLocal, hasNoBinding
+import PrimOp ( primOpOkForSpeculation, primOpIsCheap )
+import Id ( Id, idType, globalIdDetails, idStrictness, idLBVarInfo,
+ mkWildId, idArity, idName, idUnfolding, idInfo, isOneShotLambda,
+ isDataConId_maybe, mkSysLocal, hasNoBinding
)
import IdInfo ( LBVarInfo(..),
- IdFlavour(..),
+ GlobalIdDetails(..),
megaSeqIdInfo )
import Demand ( appIsBottom )
import Type ( Type, mkFunTy, mkForAllTy, splitFunTy_maybe,
applyTys, isUnLiftedType, seqType, mkUTy, mkTyVarTy,
- splitForAllTy_maybe, splitNewType_maybe
+ splitForAllTy_maybe, isForAllTy, eqType
)
import TysWiredIn ( boolTy, trueDataCon, falseDataCon )
import CostCentre ( CostCentre )
import UniqSupply ( UniqSupply, splitUniqSupply, uniqFromSupply )
-import Maybes ( maybeToBool )
import Outputable
import TysPrim ( alphaTy ) -- Debugging only
\end{code}
mkCoerce :: Type -> Type -> CoreExpr -> CoreExpr
mkCoerce to_ty from_ty (Note (Coerce to_ty2 from_ty2) expr)
- = ASSERT( from_ty == to_ty2 )
+ = ASSERT( from_ty `eqType` to_ty2 )
mkCoerce to_ty from_ty2 expr
mkCoerce to_ty from_ty expr
- | to_ty == from_ty = expr
- | otherwise = ASSERT( from_ty == exprType expr )
- Note (Coerce to_ty from_ty) expr
+ | to_ty `eqType` from_ty = expr
+ | otherwise = ASSERT( from_ty `eqType` exprType expr )
+ Note (Coerce to_ty from_ty) expr
\end{code}
\begin{code}
mkSCC :: CostCentre -> Expr b -> Expr b
-- Note: Nested SCC's *are* preserved for the benefit of
- -- cost centre stack profiling (Durham)
-
-mkSCC cc (Lit lit) = Lit lit
-mkSCC cc (Lam x e) = Lam x (mkSCC cc e) -- Move _scc_ inside lambda
-mkSCC cc expr = Note (SCC cc) expr
+ -- cost centre stack profiling
+mkSCC cc (Lit lit) = Lit lit
+mkSCC cc (Lam x e) = Lam x (mkSCC cc e) -- Move _scc_ inside lambda
+mkSCC cc (Note (SCC cc') e) = Note (SCC cc) (Note (SCC cc') e)
+mkSCC cc (Note n e) = Note n (mkSCC cc e) -- Move _scc_ inside notes
+mkSCC cc expr = Note (SCC cc) expr
\end{code}
(DataAlt falseDataCon, [], else_expr) ]
\end{code}
+
+%************************************************************************
+%* *
+\subsection{Taking expressions apart}
+%* *
+%************************************************************************
+
+The default alternative must be first, if it exists at all.
+This makes it easy to find, though it makes matching marginally harder.
+
+\begin{code}
+hasDefault :: [CoreAlt] -> Bool
+hasDefault ((DEFAULT,_,_) : alts) = True
+hasDefault _ = False
+
+findDefault :: [CoreAlt] -> ([CoreAlt], Maybe CoreExpr)
+findDefault ((DEFAULT,args,rhs) : alts) = ASSERT( null args ) (alts, Just rhs)
+findDefault alts = (alts, Nothing)
+
+findAlt :: AltCon -> [CoreAlt] -> CoreAlt
+findAlt con alts
+ = case alts of
+ (deflt@(DEFAULT,_,_):alts) -> go alts deflt
+ other -> go alts panic_deflt
+
+ where
+ panic_deflt = pprPanic "Missing alternative" (ppr con $$ vcat (map ppr alts))
+
+ go [] deflt = deflt
+ go (alt@(con1,_,_) : alts) deflt | con == con1 = alt
+ | otherwise = ASSERT( not (con1 == DEFAULT) )
+ go alts deflt
+\end{code}
+
+
%************************************************************************
%* *
\subsection{Figuring out things about expressions}
| otherwise = True
exprIsTrivial (Type _) = True
exprIsTrivial (Lit lit) = True
-exprIsTrivial (App e arg) = isTypeArg arg && exprIsTrivial e
+exprIsTrivial (App e arg) = not (isRuntimeArg arg) && exprIsTrivial e
exprIsTrivial (Note _ e) = exprIsTrivial e
-exprIsTrivial (Lam b body) | isTyVar b = exprIsTrivial body
+exprIsTrivial (Lam b body) = not (isRuntimeVar b) && exprIsTrivial body
exprIsTrivial other = False
exprIsAtom :: CoreExpr -> Bool
exprIsAtom (Var v) = True -- primOpIsDupable?
exprIsAtom (Lit lit) = True
exprIsAtom (Type ty) = True
+exprIsAtom (Note (SCC _) e) = False
exprIsAtom (Note _ e) = exprIsAtom e
exprIsAtom other = False
\end{code}
\begin{code}
-exprIsDupable (Type _) = True
-exprIsDupable (Var v) = True
-exprIsDupable (Lit lit) = litIsDupable lit
-exprIsDupable (Note _ e) = exprIsDupable e
+exprIsDupable (Type _) = True
+exprIsDupable (Var v) = True
+exprIsDupable (Lit lit) = litIsDupable lit
+exprIsDupable (Note InlineMe e) = True
+exprIsDupable (Note _ e) = exprIsDupable e
exprIsDupable expr
= go expr 0
where
exprIsCheap (Lit lit) = True
exprIsCheap (Type _) = True
exprIsCheap (Var _) = True
+exprIsCheap (Note InlineMe e) = True
exprIsCheap (Note _ e) = exprIsCheap e
-exprIsCheap (Lam x e) = if isId x then True else exprIsCheap e
+exprIsCheap (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
-- because it certainly doesn't need to be shared!
go (App f a) n_args args_cheap
- | isTypeArg a = go f n_args args_cheap
- | otherwise = go f (n_args + 1) (exprIsCheap a && args_cheap)
+ | not (isRuntimeArg a) = go f n_args args_cheap
+ | otherwise = go f (n_args + 1) (exprIsCheap a && args_cheap)
go other n_args args_cheap = False
| n_val_args == 0 = True -- Just a type application of
-- a variable (f t1 t2 t3)
-- counts as WHNF
- | otherwise = case idFlavour id of
+ | otherwise = case globalIdDetails id of
DataConId _ -> True
RecordSelId _ -> True -- I'm experimenting with making record selection
-- look cheap, so we will substitute it inside a
= go other_expr 0 True
where
go (Var f) n_args args_ok
- = case idFlavour f of
+ = case globalIdDetails f of
DataConId _ -> True -- The strictness of the constructor has already
-- been expressed by its "wrapper", so we don't need
-- to take the arguments into account
other -> False
go (App f a) n_args args_ok
- | isTypeArg a = go f n_args args_ok
- | otherwise = go f (n_args + 1) (exprOkForSpeculation a && args_ok)
+ | not (isRuntimeArg a) = go f n_args args_ok
+ | otherwise = go f (n_args + 1) (exprOkForSpeculation a && args_ok)
go other n_args args_ok = False
\end{code}
\end{code}
@exprIsValue@ returns true for expressions that are certainly *already*
-evaluated to WHNF. This is used to decide wether it's ok to change
+evaluated to WHNF. This is used to decide whether it's ok to change
case x of _ -> e ===> e
and to decide whether it's safe to discard a `seq`
-So, it does *not* treat variables as evaluated, unless they say they are
+So, it does *not* treat variables as evaluated, unless they say they are.
+
+But it *does* treat partial applications and constructor applications
+as values, even if their arguments are non-trivial;
+ e.g. (:) (f x) (map f xs) is a value
+ map (...redex...) is a value
+Because `seq` on such things completes immediately
+
+A possible worry: constructors with unboxed args:
+ C (f x :: Int#)
+Suppose (f x) diverges; then C (f x) is not a value. True, but
+this form is illegal (see the invariants in CoreSyn). Args of unboxed
+type must be ok-for-speculation (or trivial).
\begin{code}
exprIsValue :: CoreExpr -> Bool -- True => Value-lambda, constructor, PAP
exprIsValue (Type ty) = True -- Types are honorary Values; we don't mind
-- copying them
exprIsValue (Lit l) = True
-exprIsValue (Lam b e) = isId b || exprIsValue e
+exprIsValue (Lam b e) = isRuntimeVar b || exprIsValue e
exprIsValue (Note _ e) = exprIsValue e
exprIsValue other_expr
= go other_expr 0
go (Var f) n_args = idAppIsValue f n_args
go (App f a) n_args
- | isTypeArg a = go f n_args
- | otherwise = go f (n_args + 1)
+ | not (isRuntimeArg a) = go f n_args
+ | otherwise = go f (n_args + 1)
go (Note _ f) n_args = go f n_args
idAppIsValue :: Id -> Int -> Bool
idAppIsValue id n_val_args
- = case idFlavour id of
+ = case globalIdDetails id of
DataConId _ -> True
PrimOpId _ -> n_val_args < idArity id
other | n_val_args == 0 -> isEvaldUnfolding (idUnfolding id)
\begin{code}
exprIsConApp_maybe :: CoreExpr -> Maybe (DataCon, [CoreExpr])
-exprIsConApp_maybe expr
- = analyse (collectArgs expr)
+exprIsConApp_maybe (Note InlineMe expr) = exprIsConApp_maybe expr
+ -- We ignore InlineMe notes in case we have
+ -- x = __inline_me__ (a,b)
+ -- All part of making sure that INLINE pragmas never hurt
+ -- Marcin tripped on this one when making dictionaries more inlinable
+
+exprIsConApp_maybe expr = analyse (collectArgs expr)
where
analyse (Var fun, args)
- | maybeToBool maybe_con_app = maybe_con_app
- where
- maybe_con_app = case isDataConId_maybe fun of
- Just con | length args >= dataConRepArity con
- -- Might be > because the arity excludes type args
- -> Just (con, args)
- other -> Nothing
+ | Just con <- isDataConId_maybe fun,
+ length args >= dataConRepArity con
+ -- Might be > because the arity excludes type args
+ = Just (con,args)
+ -- Look through unfoldings, but only cheap ones, because
+ -- we are effectively duplicating the unfolding
analyse (Var fun, [])
- = case maybeUnfoldingTemplate (idUnfolding fun) of
- Nothing -> Nothing
- Just unf -> exprIsConApp_maybe unf
+ | let unf = idUnfolding fun,
+ isCheapUnfolding unf
+ = exprIsConApp_maybe (unfoldingTemplate unf)
analyse other = Nothing
\end{code}
-The arity of an expression (in the code-generator sense, i.e. the
-number of lambdas at the beginning).
-
-\begin{code}
-exprArity :: CoreExpr -> Int
-exprArity (Lam x e)
- | isTyVar x = exprArity e
- | otherwise = 1 + exprArity e
-exprArity (Note _ e)
- -- Ignore coercions. Top level sccs are removed by the final
- -- profiling pass, so we ignore those too.
- = exprArity e
-exprArity _ = 0
-\end{code}
%************************************************************************
-- case x of p -> \s -> ...
-- because for I/O ish things we really want to get that \s to the top.
-- We are prepared to evaluate x each time round the loop in order to get that
--- Hence "generous" arity
+--
+-- Consider let x = expensive in \y z -> E
+-- We want this to have arity 2 if the \y-abstraction is a 1-shot lambda
+--
+-- Hence the list of Bools returned by go1
+-- NB: this is particularly important/useful for IO state
+-- transformers, where we often get
+-- let x = E in \ s -> ...
+-- and the \s is a real-world state token abstraction. Such
+-- abstractions are almost invariably 1-shot, so we want to
+-- pull the \s out, past the let x=E.
+-- The hack is in Id.isOneShotLambda
exprEtaExpandArity e
= go 0 e
where
+ go :: Int -> CoreExpr -> (Int,Bool)
go ar (Lam x e) | isId x = go (ar+1) e
| otherwise = go ar e
go ar (Note n e) | ok_note n = go ar e
go ar other = (ar + ar', ar' == 0)
where
- ar' = go1 other `max` 0
-
- go1 (Var v) = idArity v
- go1 (Lam x e) | isId x = go1 e + 1
- | otherwise = go1 e
- go1 (Note n e) | ok_note n = go1 e
- go1 (App f (Type _)) = go1 f
- go1 (App f a) | exprIsCheap a = go1 f - 1
- go1 (Case scrut _ alts)
- | exprIsCheap scrut = min_zero [go1 rhs | (_,_,rhs) <- alts]
- go1 (Let b e)
- | all exprIsCheap (rhssOfBind b) = go1 e
-
- go1 other = 0
+ ar' = length (go1 other)
+
+ go1 :: CoreExpr -> [Bool]
+ -- (go1 e) = [b1,..,bn]
+ -- means expression can be rewritten \x_b1 -> ... \x_bn -> body
+ -- where bi is True <=> the lambda is one-shot
+
+ go1 (Note n e) | ok_note n = go1 e
+ go1 (Var v) = replicate (idArity v) False -- When the type of the Id
+ -- encodes one-shot-ness, use
+ -- the idinfo here
+
+ -- Lambdas; increase arity
+ go1 (Lam x e) | isId x = isOneShotLambda x : go1 e
+ | otherwise = go1 e
+
+ -- Applications; decrease arity
+ go1 (App f (Type _)) = go1 f
+ go1 (App f a) = case go1 f of
+ (one_shot : xs) | one_shot || exprIsCheap a -> xs
+ other -> []
+
+ -- Case/Let; keep arity if either the expression is cheap
+ -- or it's a 1-shot lambda
+ go1 (Case scrut _ alts) = case foldr1 (zipWith (&&)) [go1 rhs | (_,_,rhs) <- alts] of
+ xs@(one_shot : _) | one_shot || exprIsCheap scrut -> xs
+ other -> []
+ go1 (Let b e) = case go1 e of
+ xs@(one_shot : _) | one_shot || all exprIsCheap (rhssOfBind b) -> xs
+ other -> []
+
+ go1 other = []
ok_note (Coerce _ _) = True
ok_note InlineCall = True
ok_note other = False
-- Notice that we do not look through __inline_me__
- -- This one is a bit more surprising, but consider
+ -- 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
-- giving just
-- f = \x -> e
-- A Bad Idea
-
-min_zero :: [Int] -> Int -- Find the minimum, but zero is the smallest
-min_zero (x:xs) = go x xs
- where
- go 0 xs = 0 -- Nothing beats zero
- go min [] = min
- go min (x:xs) | x < min = go x xs
- | otherwise = go min xs
-
\end{code}
-- would return
-- (/\b. coerce T (\y::A -> (coerce (A->B) (E b) y)
--- (case x of { I# x -> /\ a -> coerce T E)
-
etaExpand n us expr ty
- | n == 0 -- Saturated, so nothing to do
+ | n == 0 &&
+ -- The ILX code generator requires eta expansion for type arguments
+ -- too, but alas the 'n' doesn't tell us how many of them there
+ -- may be. So we eagerly eta expand any big lambdas, and just
+ -- cross our fingers about possible loss of sharing in the
+ -- ILX case.
+ -- The Right Thing is probably to make 'arity' include
+ -- type variables throughout the compiler. (ToDo.)
+ not (isForAllTy ty)
+ -- Saturated, so nothing to do
= expr
| otherwise -- An unsaturated constructor or primop; eta expand it
(us1, us2) = splitUniqSupply us
uniq = uniqFromSupply us1
- ; Nothing ->
-
- case splitNewType_maybe ty of {
- Just ty' -> mkCoerce ty ty' (etaExpand n us (mkCoerce ty' ty expr) ty') ;
-
- Nothing -> pprTrace "Bad eta expand" (ppr expr $$ ppr ty) expr
- }}}
+ ; Nothing -> pprTrace "Bad eta expand" (ppr expr $$ ppr ty) expr
+ }}
+\end{code}
+
+
+exprArity is a cheap-and-cheerful version of exprEtaExpandArity.
+It tells how many things the expression can be applied to before doing
+any work. It doesn't look inside cases, lets, etc. The idea is that
+exprEtaExpandArity will do the hard work, leaving something that's easy
+for exprArity to grapple with. In particular, Simplify uses exprArity to
+compute the ArityInfo for the Id.
+
+Originally I thought that it was enough just to look for top-level lambdas, but
+it isn't. I've seen this
+
+ foo = PrelBase.timesInt
+
+We want foo to get arity 2 even though the eta-expander will leave it
+unchanged, in the expectation that it'll be inlined. But occasionally it
+isn't, because foo is blacklisted (used in a rule).
+
+Similarly, see the ok_note check in exprEtaExpandArity. So
+ f = __inline_me (\x -> e)
+won't be eta-expanded.
+
+And in any case it seems more robust to have exprArity be a bit more intelligent.
+
+\begin{code}
+exprArity :: CoreExpr -> Int
+exprArity e = go e `max` 0
+ where
+ go (Lam x e) | isId x = go e + 1
+ | otherwise = go e
+ go (Note _ e) = go e
+ go (App e (Type t)) = go e
+ go (App f a) | exprIsCheap a = go f - 1
+ -- Important! f (fac x) does not have arity 2,
+ -- even if f does!
+ go (Var v) = idArity v
+ go _ = 0
\end{code}
cheapEqExpr (Var v1) (Var v2) = v1==v2
cheapEqExpr (Lit lit1) (Lit lit2) = lit1 == lit2
-cheapEqExpr (Type t1) (Type t2) = t1 == t2
+cheapEqExpr (Type t1) (Type t2) = t1 `eqType` t2
cheapEqExpr (App f1 a1) (App f2 a2)
= f1 `cheapEqExpr` f2 && a1 `cheapEqExpr` a2
\begin{code}
eqExpr :: CoreExpr -> CoreExpr -> Bool
-- Works ok at more general type, but only needed at CoreExpr
+ -- Used in rule matching, so when we find a type we use
+ -- eqTcType, which doesn't look through newtypes
+ -- [And it doesn't risk falling into a black hole either.]
eqExpr e1 e2
= eq emptyVarEnv e1 e2
where
env' = extendVarEnv env v1 v2
eq env (Note n1 e1) (Note n2 e2) = eq_note env n1 n2 && eq env e1 e2
- eq env (Type t1) (Type t2) = t1 == t2
+ eq env (Type t1) (Type t2) = t1 `eqType` t2
eq env e1 e2 = False
eq_list env [] [] = True
eq (extendVarEnvList env (vs1 `zip` vs2)) r1 r2
eq_note env (SCC cc1) (SCC cc2) = cc1 == cc2
- eq_note env (Coerce t1 f1) (Coerce t2 f2) = t1==t2 && f1==f2
+ eq_note env (Coerce t1 f1) (Coerce t2 f2) = t1 `eqType` t2 && f1 `eqType` f2
eq_note env InlineCall InlineCall = True
eq_note env other1 other2 = False
\end{code}