\begin{code}
module CoreUtils (
- coreExprType, coreAltsType,
+ -- Construction
+ mkNote, mkInlineMe, mkSCC, mkCoerce,
+ bindNonRec, mkIfThenElse, mkAltExpr,
+ mkPiType,
- exprIsBottom, exprIsDupable, exprIsTrivial, exprIsWHNF, exprIsCheap,
- exprOkForSpeculation,
- FormSummary(..), mkFormSummary, whnfOrBottom, exprArity,
+ -- Taking expressions apart
+ findDefault, findAlt,
+
+ -- Properties of expressions
+ exprType, coreAltsType,
+ exprIsBottom, exprIsDupable, exprIsTrivial, exprIsCheap,
+ exprIsValue,exprOkForSpeculation, exprIsBig,
+ exprIsConApp_maybe, exprIsAtom,
+ idAppIsBottom, idAppIsCheap,
+ exprArity,
+
+ -- Expr transformation
+ etaReduce, etaExpand,
+ exprArity, exprEtaExpandArity,
+
+ -- Size
+ coreBindsSize,
+
+ -- Hashing
+ hashExpr,
+
+ -- Equality
cheapEqExpr, eqExpr, applyTypeToArgs
) where
#include "HsVersions.h"
+import GlaExts -- For `xori`
+
import CoreSyn
+import CoreFVs ( exprFreeVars )
import PprCore ( pprCoreExpr )
-import Var ( IdOrTyVar, isId, isTyVar )
+import Var ( Var, isId, isTyVar )
import VarSet
import VarEnv
-import Name ( isLocallyDefined )
-import Const ( Con, isWHNFCon, conIsTrivial, conIsCheap, conIsDupable,
- conType, conOkForSpeculation, conStrictness
- )
-import Id ( Id, idType, setIdType, idUnique, idAppIsBottom,
- getIdArity,
- getIdSpecialisation, setIdSpecialisation,
- getInlinePragma, setInlinePragma,
- getIdUnfolding, setIdUnfolding, idInfo
+import Name ( hashName )
+import Literal ( hashLiteral, literalType, litIsDupable )
+import DataCon ( DataCon, dataConRepArity )
+import PrimOp ( primOpOkForSpeculation, primOpIsCheap,
+ primOpIsDupable )
+import Id ( Id, idType, globalIdDetails, idStrictness, idLBVarInfo,
+ mkWildId, idArity, idName, idUnfolding, idInfo, isOneShotLambda,
+ isDataConId_maybe, isPrimOpId_maybe, mkSysLocal, hasNoBinding
)
-import IdInfo ( arityLowerBound, InlinePragInfo(..), lbvarInfo, LBVarInfo(..) )
-import Type ( Type, mkFunTy, mkForAllTy,
- splitFunTy_maybe, tyVarsOfType, tyVarsOfTypes,
- isNotUsgTy, mkUsgTy, unUsgTy, UsageAnn(..),
- tidyTyVar, applyTys, isUnLiftedType
+import IdInfo ( LBVarInfo(..),
+ GlobalIdDetails(..),
+ megaSeqIdInfo )
+import Demand ( appIsBottom )
+import Type ( Type, mkFunTy, mkForAllTy, splitFunTy_maybe,
+ applyTys, isUnLiftedType, seqType, mkUTy, mkTyVarTy,
+ splitForAllTy_maybe, splitNewType_maybe
)
-import Demand ( isPrim, isLazy )
-import Unique ( buildIdKey, augmentIdKey )
-import Util ( zipWithEqual, mapAccumL )
+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}
%************************************************************************
\begin{code}
-coreExprType :: CoreExpr -> Type
-
-coreExprType (Var var) = idType var
-coreExprType (Let _ body) = coreExprType body
-coreExprType (Case _ _ alts) = coreAltsType alts
-coreExprType (Note (Coerce ty _) e) = ty
-coreExprType (Note (TermUsg u) e) = mkUsgTy u (unUsgTy (coreExprType e))
-coreExprType (Note other_note e) = coreExprType e
-coreExprType e@(Con con args) = applyTypeToArgs e (conType con) args
-
-coreExprType (Lam binder expr)
- | isId binder = (case (lbvarInfo . idInfo) binder of
- IsOneShotLambda -> mkUsgTy UsOnce
- otherwise -> id) $
- idType binder `mkFunTy` coreExprType expr
- | isTyVar binder = mkForAllTy binder (coreExprType expr)
-
-coreExprType e@(App _ _)
+exprType :: CoreExpr -> Type
+
+exprType (Var var) = idType var
+exprType (Lit lit) = literalType lit
+exprType (Let _ body) = exprType body
+exprType (Case _ _ alts) = coreAltsType alts
+exprType (Note (Coerce ty _) e) = ty -- **! should take usage from e
+exprType (Note other_note e) = exprType e
+exprType (Lam binder expr) = mkPiType binder (exprType expr)
+exprType e@(App _ _)
= case collectArgs e of
- (fun, args) -> applyTypeToArgs e (coreExprType fun) args
+ (fun, args) -> applyTypeToArgs e (exprType fun) args
-coreExprType other = pprTrace "coreExprType" (pprCoreExpr other) alphaTy
+exprType other = pprTrace "exprType" (pprCoreExpr other) alphaTy
coreAltsType :: [CoreAlt] -> Type
-coreAltsType ((_,_,rhs) : _) = coreExprType rhs
+coreAltsType ((_,_,rhs) : _) = exprType rhs
+\end{code}
+
+@mkPiType@ makes a (->) type or a forall type, depending on whether
+it is given a type variable or a term variable. We cleverly use the
+lbvarinfo field to figure out the right annotation for the arrove in
+case of a term variable.
+
+\begin{code}
+mkPiType :: Var -> Type -> Type -- The more polymorphic version doesn't work...
+mkPiType v ty | isId v = (case idLBVarInfo v of
+ LBVarInfo u -> mkUTy u
+ otherwise -> id) $
+ mkFunTy (idType v) ty
+ | isTyVar v = mkForAllTy v ty
\end{code}
\begin{code}
applyTypeToArgs e op_ty (Type ty : args)
= -- Accumulate type arguments so we can instantiate all at once
- ASSERT2( all isNotUsgTy tys, ppr e <+> text "of" <+> ppr op_ty <+> text "to" <+> ppr (Type ty : args) <+> text "i.e." <+> ppr tys )
applyTypeToArgs e (applyTys op_ty tys) rest_args
where
(tys, rest_args) = go [ty] args
\end{code}
+
%************************************************************************
%* *
-\subsection{Figuring out things about expressions}
+\subsection{Attaching notes}
+%* *
+%************************************************************************
+
+mkNote removes redundant coercions, and SCCs where possible
+
+\begin{code}
+mkNote :: Note -> CoreExpr -> CoreExpr
+mkNote (Coerce to_ty from_ty) expr = mkCoerce to_ty from_ty expr
+mkNote (SCC cc) expr = mkSCC cc expr
+mkNote InlineMe expr = mkInlineMe expr
+mkNote note expr = Note note expr
+
+-- Slide InlineCall in around the function
+-- No longer necessary I think (SLPJ Apr 99)
+-- mkNote InlineCall (App f a) = App (mkNote InlineCall f) a
+-- mkNote InlineCall (Var v) = Note InlineCall (Var v)
+-- mkNote InlineCall expr = expr
+\end{code}
+
+Drop trivial InlineMe's. This is somewhat important, because if we have an unfolding
+that looks like (Note InlineMe (Var v)), the InlineMe doesn't go away because it may
+not be *applied* to anything.
+
+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 -> Type -> CoreExpr -> CoreExpr
+
+mkCoerce to_ty from_ty (Note (Coerce to_ty2 from_ty2) expr)
+ = ASSERT( from_ty == to_ty2 )
+ mkCoerce to_ty from_ty2 expr
+
+mkCoerce to_ty from_ty expr
+ | to_ty == from_ty = expr
+ | otherwise = ASSERT( from_ty == exprType expr )
+ Note (Coerce to_ty from_ty) expr
+\end{code}
+
+\begin{code}
+mkSCC :: CostCentre -> Expr b -> Expr b
+ -- Note: Nested SCC's *are* preserved for the benefit of
+ -- cost centre stack profiling (Durham)
+
+mkSCC cc (Lit lit) = Lit lit
+mkSCC cc (Lam x e) = Lam x (mkSCC cc e) -- Move _scc_ inside lambda
+mkSCC cc expr = Note (SCC cc) expr
+\end{code}
+
+
+%************************************************************************
+%* *
+\subsection{Other expression construction}
%* *
%************************************************************************
\begin{code}
-data FormSummary
- = VarForm -- Expression is a variable (or scc var, etc)
-
- | ValueForm -- Expression is a value: i.e. a value-lambda,constructor, or literal
- -- May 1999: I'm experimenting with allowing "cheap" non-values
- -- here.
-
- | BottomForm -- Expression is guaranteed to be bottom. We're more gung
- -- ho about inlining such things, because it can't waste work
- | OtherForm -- Anything else
-
-instance Outputable FormSummary where
- ppr VarForm = ptext SLIT("Var")
- ppr ValueForm = ptext SLIT("Value")
- ppr BottomForm = ptext SLIT("Bot")
- ppr OtherForm = ptext SLIT("Other")
-
-whnfOrBottom :: FormSummary -> Bool
-whnfOrBottom VarForm = True
-whnfOrBottom ValueForm = True
-whnfOrBottom BottomForm = True
-whnfOrBottom OtherForm = False
+bindNonRec :: Id -> CoreExpr -> CoreExpr -> CoreExpr
+-- (bindNonRec x r b) produces either
+-- let x = r in b
+-- or
+-- case r of x { _DEFAULT_ -> b }
+--
+-- depending on whether x is unlifted or not
+-- It's used by the desugarer to avoid building bindings
+-- that give Core Lint a heart attack. Actually the simplifier
+-- deals with them perfectly well.
+bindNonRec bndr rhs body
+ | isUnLiftedType (idType bndr) = Case rhs bndr [(DEFAULT,[],body)]
+ | otherwise = Let (NonRec bndr rhs) body
\end{code}
\begin{code}
-mkFormSummary :: CoreExpr -> FormSummary
-mkFormSummary expr
- = go (0::Int) expr -- The "n" is the number of *value* arguments so far
+mkAltExpr :: AltCon -> [CoreBndr] -> [Type] -> CoreExpr
+ -- This guy constructs the value that the scrutinee must have
+ -- when you are in one particular branch of a case
+mkAltExpr (DataAlt con) args inst_tys
+ = mkConApp con (map Type inst_tys ++ map varToCoreExpr args)
+mkAltExpr (LitAlt lit) [] []
+ = Lit lit
+
+mkIfThenElse :: CoreExpr -> CoreExpr -> CoreExpr -> CoreExpr
+mkIfThenElse guard then_expr else_expr
+ = Case guard (mkWildId boolTy)
+ [ (DataAlt trueDataCon, [], then_expr),
+ (DataAlt falseDataCon, [], else_expr) ]
+\end{code}
+
+
+%************************************************************************
+%* *
+\subsection{Taking expressions apart}
+%* *
+%************************************************************************
+
+
+\begin{code}
+findDefault :: [CoreAlt] -> ([CoreAlt], Maybe CoreExpr)
+findDefault [] = ([], Nothing)
+findDefault ((DEFAULT,args,rhs) : alts) = ASSERT( null alts && null args )
+ ([], Just rhs)
+findDefault (alt : alts) = case findDefault alts of
+ (alts', deflt) -> (alt : alts', deflt)
+
+findAlt :: AltCon -> [CoreAlt] -> CoreAlt
+findAlt con alts
+ = go alts
where
- go n (Con con _) | isWHNFCon con = ValueForm
- | otherwise = OtherForm
-
- go n (Note _ e) = go n e
-
- go n (Let (NonRec b r) e) | exprIsCheap r = go n e -- let f = f' alpha in (f,g)
- -- should be treated as a value
- go n (Let _ e) = OtherForm
-
- -- We want selectors to look like values
- -- e.g. case x of { (a,b) -> a }
- -- should give a ValueForm, so that it will be inlined
- -- vigorously
- go n expr@(Case _ _ _) | exprIsCheap expr = ValueForm
- | otherwise = OtherForm
-
- go 0 (Lam x e) | isId x = ValueForm -- NB: \x.bottom /= bottom!
- | otherwise = go 0 e
- go n (Lam x e) | isId x = go (n-1) e -- Applied lambda
- | otherwise = go n e
-
- go n (App fun (Type _)) = go n fun -- Ignore type args
- go n (App fun arg) = go (n+1) fun
-
- go n (Var f) | idAppIsBottom f n = BottomForm
- go 0 (Var f) = VarForm
- go n (Var f) | n < arityLowerBound (getIdArity f) = ValueForm
- | otherwise = OtherForm
+ go [] = pprPanic "Missing alternative" (ppr con $$ vcat (map ppr alts))
+ go (alt : alts) | matches alt = alt
+ | otherwise = go alts
+
+ matches (DEFAULT, _, _) = True
+ matches (con1, _, _) = con == con1
\end{code}
-@exprIsTrivial@ is true of expressions we are unconditionally
- happy to duplicate; simple variables and constants,
- and type applications.
+
+%************************************************************************
+%* *
+\subsection{Figuring out things about expressions}
+%* *
+%************************************************************************
+
+@exprIsTrivial@ is true of expressions we are unconditionally happy to
+ duplicate; simple variables and constants, and type
+ applications. Note that primop Ids aren't considered
+ trivial unless
@exprIsBottom@ is true of expressions that are guaranteed to diverge
\begin{code}
-exprIsTrivial (Type _) = True
-exprIsTrivial (Var v) = True
-exprIsTrivial (App e arg) = isTypeArg arg && exprIsTrivial e
-exprIsTrivial (Note _ e) = exprIsTrivial e
-exprIsTrivial (Con con args) = conIsTrivial con && all isTypeArg args
-exprIsTrivial (Lam b body) | isTyVar b = exprIsTrivial body
-exprIsTrivial other = False
+exprIsTrivial (Var v)
+ | hasNoBinding v = idArity v == 0
+ -- WAS: | Just op <- isPrimOpId_maybe v = primOpIsDupable op
+ -- 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.
+ -- This came up when dealing with eta expansion/reduction for
+ -- x = $wJust
+ -- Here we want to eta-expand. This looks like an optimisation,
+ -- but it's important (albeit tiresome) that CoreSat doesn't increase
+ -- anything's arity
+ | otherwise = True
+exprIsTrivial (Type _) = True
+exprIsTrivial (Lit lit) = True
+exprIsTrivial (App e arg) = isTypeArg arg && exprIsTrivial e
+exprIsTrivial (Note _ e) = exprIsTrivial e
+exprIsTrivial (Lam b body) | isTyVar b = exprIsTrivial body
+exprIsTrivial other = False
+
+exprIsAtom :: CoreExpr -> Bool
+-- Used to decide whether to let-binding an STG argument
+-- when compiling to ILX => type applications are not allowed
+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}
@exprIsDupable@ is true of expressions that can be duplicated at a modest
- cost in space. This will only happen in different case
+ cost in code size. This will only happen in different case
branches, so there's no issue about duplicating work.
+
+ That is, exprIsDupable returns True of (f x) even if
+ f is very very expensive to call.
+
Its only purpose is to avoid fruitless let-binding
and then inlining of case join points
\begin{code}
-exprIsDupable (Type _) = True
-exprIsDupable (Con con args) = conIsDupable con &&
- all exprIsDupable args &&
- valArgCount args <= dupAppSize
-
-exprIsDupable (Note _ e) = exprIsDupable e
-exprIsDupable expr = case collectArgs expr of
- (Var f, args) -> valArgCount args <= dupAppSize
- other -> False
+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
it is obviously in weak head normal form, or is cheap to get to WHNF.
[Note that that's not the same as exprIsDupable; an expression might be
big, and hence not dupable, but still cheap.]
-By ``cheap'' we mean a computation we're willing to push inside a lambda
-in order to bring a couple of lambdas together. That might mean it gets
-evaluated more than once, instead of being shared. The main examples of things
-which aren't WHNF but are ``cheap'' are:
+
+By ``cheap'' we mean a computation we're willing to:
+ push inside a lambda, or
+ inline at more than one place
+That might mean it gets evaluated more than once, instead of being
+shared. The main examples of things which aren't WHNF but are
+``cheap'' are:
* case e of
pi -> ei
+ (where e, and all the ei are cheap)
- where e, and all the ei are cheap; and
-
- * let x = e
- in b
-
- where e and b are cheap; and
+ * let x = e in b
+ (where e and b are cheap)
* op x1 ... xn
+ (where op is a cheap primitive operator)
- where op is a cheap primitive operator
+ * error "foo"
+ (because we are happy to substitute it inside a lambda)
-\begin{code}
-exprIsCheap :: CoreExpr -> Bool
-exprIsCheap (Type _) = True
-exprIsCheap (Var _) = True
-exprIsCheap (Con con args) = conIsCheap con && all exprIsCheap args
-exprIsCheap (Note _ e) = exprIsCheap e
-exprIsCheap (Lam x e) = if isId x then True else exprIsCheap e
-exprIsCheap (Let bind body) = all exprIsCheap (rhssOfBind bind) && exprIsCheap body
-exprIsCheap (Case scrut _ alts) = exprIsCheap scrut &&
- all (\(_,_,rhs) -> exprIsCheap rhs) alts
-
-exprIsCheap other_expr -- look for manifest partial application
- = case collectArgs other_expr of
- (f, args) -> isPap f (valArgCount args) && all exprIsCheap args
-\end{code}
+Notice that a variable is considered 'cheap': we can push it inside a lambda,
+because sharing will make sure it is only evaluated once.
\begin{code}
-isPap :: CoreExpr -- Function
- -> Int -- Number of value args
- -> Bool
-isPap (Var f) n_val_args
- = idAppIsBottom f n_val_args
- -- Application of a function which
- -- always gives bottom; we treat this as
- -- a WHNF, because it certainly doesn't
- -- need to be shared!
-
- || n_val_args == 0 -- Just a type application of
+exprIsCheap :: CoreExpr -> Bool
+exprIsCheap (Lit lit) = True
+exprIsCheap (Type _) = True
+exprIsCheap (Var _) = True
+exprIsCheap (Note InlineMe e) = True
+exprIsCheap (Note _ e) = exprIsCheap e
+exprIsCheap (Lam x e) = if isId x then True else exprIsCheap e
+exprIsCheap (Case e _ alts) = exprIsCheap e &&
+ and [exprIsCheap rhs | (_,_,rhs) <- alts]
+ -- Experimentally, treat (case x of ...) as cheap
+ -- (and case __coerce x etc.)
+ -- This improves arities of overloaded functions where
+ -- there is only dictionary selection (no construction) involved
+exprIsCheap (Let (NonRec x _) e)
+ | isUnLiftedType (idType x) = exprIsCheap e
+ | otherwise = False
+ -- strict lets always have cheap right hand sides, and
+ -- do no allocation.
+
+exprIsCheap other_expr
+ = go other_expr 0 True
+ where
+ go (Var f) n_args args_cheap
+ = (idAppIsCheap f n_args && args_cheap)
+ -- A constructor, cheap primop, or partial application
+
+ || idAppIsBottom f n_args
+ -- Application of a function which
+ -- always gives bottom; we treat this as cheap
+ -- because it certainly doesn't need to be shared!
+
+ go (App f a) n_args args_cheap
+ | isTypeArg a = go f n_args args_cheap
+ | otherwise = go f (n_args + 1) (exprIsCheap a && args_cheap)
+
+ go other n_args args_cheap = False
+
+idAppIsCheap :: Id -> Int -> Bool
+idAppIsCheap id n_val_args
+ | n_val_args == 0 = True -- Just a type application of
-- a variable (f t1 t2 t3)
-- counts as WHNF
-
- || n_val_args < arityLowerBound (getIdArity f)
-
-isPap fun n_val_args = False
+ | otherwise = case globalIdDetails id of
+ DataConId _ -> True
+ RecordSelId _ -> True -- I'm experimenting with making record selection
+ -- look cheap, so we will substitute it inside a
+ -- lambda. Particularly for dictionary field selection
+
+ PrimOpId op -> primOpIsCheap op -- In principle we should worry about primops
+ -- that return a type variable, since the result
+ -- might be applied to something, but I'm not going
+ -- to bother to check the number of args
+ other -> n_val_args < idArity id
\end{code}
-exprOkForSpeculation returns True of an UNLIFTED-TYPE expression that it is safe
-to evaluate even if normal order eval might not evaluate the expression
-at all. E.G.
+exprOkForSpeculation returns True of an expression that it is
+
+ * safe to evaluate even if normal order eval might not
+ evaluate the expression at all, or
+
+ * safe *not* to evaluate even if normal order would do so
+
+It returns True iff
+
+ the expression guarantees to terminate,
+ soon,
+ without raising an exception,
+ without causing a side effect (e.g. writing a mutable variable)
+
+E.G.
let x = case y# +# 1# of { r# -> I# r# }
in E
==>
\begin{code}
exprOkForSpeculation :: CoreExpr -> Bool
-exprOkForSpeculation (Var v) = True -- Unlifted type => already evaluated
-
-exprOkForSpeculation (Note _ e) = exprOkForSpeculation e
-exprOkForSpeculation (Let (NonRec b r) e) = isUnLiftedType (idType b) &&
- exprOkForSpeculation r &&
- exprOkForSpeculation e
-exprOkForSpeculation (Let (Rec _) _) = False
-exprOkForSpeculation (Case _ _ _) = False -- Conservative
-exprOkForSpeculation (App _ _) = False
-
-exprOkForSpeculation (Con con args)
- = conOkForSpeculation con &&
- and (zipWith ok (filter isValArg args) (fst (conStrictness con)))
+exprOkForSpeculation (Lit _) = True
+exprOkForSpeculation (Var v) = isUnLiftedType (idType v)
+exprOkForSpeculation (Note _ e) = exprOkForSpeculation e
+exprOkForSpeculation other_expr
+ = go other_expr 0 True
where
- ok arg demand | isLazy demand = True
- | isPrim demand = exprOkForSpeculation arg
- | otherwise = False
-
-exprOkForSpeculation other = panic "exprOkForSpeculation"
- -- Lam, Type
+ go (Var f) n_args args_ok
+ = case 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
+
+ PrimOpId op -> primOpOkForSpeculation op && args_ok
+ -- A bit conservative: we don't really need
+ -- to care about lazy arguments, but this is easy
+
+ other -> False
+
+ go (App f a) n_args args_ok
+ | isTypeArg a = go f n_args args_ok
+ | otherwise = go f (n_args + 1) (exprOkForSpeculation a && args_ok)
+
+ go other n_args args_ok = False
\end{code}
go n (Case e _ _) = go 0 e -- Just check the scrut
go n (App e _) = go (n+1) e
go n (Var v) = idAppIsBottom v n
- go n (Con _ _) = False
+ go n (Lit _) = False
go n (Lam _ _) = False
+
+idAppIsBottom :: Id -> Int -> Bool
+idAppIsBottom id n_val_args = appIsBottom (idStrictness id) n_val_args
\end{code}
-exprIsWHNF reports True for head normal forms. Note that does not necessarily
-mean *normal* forms; constructors might have non-trivial argument expressions, for
-example. We use a let binding for WHNFs, rather than a case binding, even if it's
-used strictly. We try to expose WHNFs by floating lets out of the RHS of lets.
+@exprIsValue@ returns true for expressions that are certainly *already*
+evaluated to WHNF. This is used to decide wether it's ok to change
+ case x of _ -> e ===> e
+
+and to decide whether it's safe to discard a `seq`
+
+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
-We treat applications of buildId and augmentId as honorary WHNFs, because we
-want them to get exposed
+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}
-exprIsWHNF :: CoreExpr -> Bool -- True => Variable, value-lambda, constructor, PAP
-exprIsWHNF (Type ty) = True -- Types are honorary WHNFs; we don't mind
+exprIsValue :: CoreExpr -> Bool -- True => Value-lambda, constructor, PAP
+exprIsValue (Type ty) = True -- Types are honorary Values; we don't mind
-- copying them
-exprIsWHNF (Var v) = True
-exprIsWHNF (Lam b e) = isId b || exprIsWHNF e
-exprIsWHNF (Note _ e) = exprIsWHNF e
-exprIsWHNF (Let _ e) = False
-exprIsWHNF (Case _ _ _) = False
-exprIsWHNF (Con con _) = isWHNFCon con
-exprIsWHNF e@(App _ _) = case collectArgs e of
- (Var v, args) -> n_val_args == 0 ||
- fun_arity > n_val_args ||
- v_uniq == buildIdKey ||
- v_uniq == augmentIdKey
- where
- n_val_args = valArgCount args
- fun_arity = arityLowerBound (getIdArity v)
- v_uniq = idUnique v
-
- _ -> False
+exprIsValue (Lit l) = True
+exprIsValue (Lam b e) = isId b || exprIsValue e
+exprIsValue (Note _ e) = exprIsValue e
+exprIsValue other_expr
+ = go other_expr 0
+ where
+ go (Var f) n_args = idAppIsValue f n_args
+
+ go (App f a) n_args
+ | isTypeArg a = go f n_args
+ | otherwise = go f (n_args + 1)
+
+ go (Note _ f) n_args = go f n_args
+
+ go other n_args = False
+
+idAppIsValue :: Id -> Int -> Bool
+idAppIsValue id n_val_args
+ = case globalIdDetails id of
+ DataConId _ -> True
+ PrimOpId _ -> n_val_args < idArity id
+ other | n_val_args == 0 -> isEvaldUnfolding (idUnfolding id)
+ | otherwise -> n_val_args < idArity id
+ -- A worry: what if an Id's unfolding is just itself:
+ -- then we could get an infinite loop...
+\end{code}
+
+\begin{code}
+exprIsConApp_maybe :: CoreExpr -> Maybe (DataCon, [CoreExpr])
+exprIsConApp_maybe expr
+ = analyse (collectArgs expr)
+ where
+ analyse (Var fun, args)
+ | 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, [])
+ | 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}
+
+
+%************************************************************************
+%* *
+\subsection{Eta reduction and expansion}
+%* *
+%************************************************************************
+
+@etaReduce@ trys an eta reduction at the top level of a Core Expr.
+
+e.g. \ x y -> f x y ===> f
+
+But we only do this if it gets rid of a whole lambda, not part.
+The idea is that lambdas are often quite helpful: they indicate
+head normal forms, so we don't want to chuck them away lightly.
+
+\begin{code}
+etaReduce :: CoreExpr -> CoreExpr
+ -- ToDo: we should really check that we don't turn a non-bottom
+ -- lambda into a bottom variable. Sigh
+
+etaReduce expr@(Lam bndr body)
+ = check (reverse binders) body
+ where
+ (binders, body) = collectBinders expr
+
+ check [] body
+ | not (any (`elemVarSet` body_fvs) binders)
+ = body -- Success!
+ where
+ body_fvs = exprFreeVars body
+
+ check (b : bs) (App fun arg)
+ | (varToCoreExpr b `cheapEqExpr` arg)
+ = check bs fun
+
+ check _ _ = expr -- Bale out
+
+etaReduce expr = expr -- The common case
\end{code}
+
\begin{code}
-exprArity :: CoreExpr -> Int -- How many value lambdas are at the top
-exprArity (Lam b e) | isTyVar b = exprArity e
- | otherwise = 1 + exprArity e
-exprArity other = 0
+exprEtaExpandArity :: CoreExpr -> (Int, Bool)
+-- The Int is number of value args the thing can be
+-- applied to without doing much work
+-- The Bool is True iff there are enough explicit value lambdas
+-- at the top to make this arity apparent
+-- (but ignore it when arity==0)
+
+-- This is used when eta expanding
+-- e ==> \xy -> e x y
+--
+-- It returns 1 (or more) to:
+-- case x of p -> \s -> ...
+-- because for I/O ish things we really want to get that \s to the top.
+-- We are prepared to evaluate x each time round the loop in order to get that
+--
+-- 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 extra Bool 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' = 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
+ -- th iinfo 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
+ -- f = _inline_me (\x -> e)
+ -- We DO NOT want to eta expand this to
+ -- f = \x -> (_inline_me (\x -> e)) x
+ -- because the _inline_me gets dropped now it is applied,
+ -- giving just
+ -- f = \x -> e
+ -- A Bad Idea
+
+min_zero :: [Int] -> Int -- Find the minimum, but zero is the smallest
+min_zero (x:xs) = go x xs
+ where
+ go 0 xs = 0 -- Nothing beats zero
+ go min [] = min
+ go min (x:xs) | x < min = go x xs
+ | otherwise = go min xs
+
+\end{code}
+
+
+\begin{code}
+etaExpand :: Int -- Add this number of value args
+ -> UniqSupply
+ -> 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'
+--
+-- etaExpand deals with for-alls and coerces. For example:
+-- etaExpand 1 E
+-- where E :: forall a. T
+-- newtype T = MkT (A -> B)
+--
+-- 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
+ = expr
+
+ | otherwise -- An unsaturated constructor or primop; eta expand it
+ = case splitForAllTy_maybe ty of {
+ Just (tv,ty') -> Lam tv (etaExpand n us (App expr (Type (mkTyVarTy tv))) ty')
+
+ ; Nothing ->
+
+ case splitFunTy_maybe ty of {
+ Just (arg_ty, res_ty) -> Lam arg1 (etaExpand (n-1) us2 (App expr (Var arg1)) res_ty)
+ where
+ arg1 = mkSysLocal SLIT("eta") uniq arg_ty
+ (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
+ }}}
\end{code}
\begin{code}
cheapEqExpr :: Expr b -> Expr b -> Bool
-cheapEqExpr (Var v1) (Var v2) = v1==v2
-cheapEqExpr (Con con1 args1) (Con con2 args2)
- = con1 == con2 &&
- and (zipWithEqual "cheapEqExpr" cheapEqExpr args1 args2)
+cheapEqExpr (Var v1) (Var v2) = v1==v2
+cheapEqExpr (Lit lit1) (Lit lit2) = lit1 == lit2
+cheapEqExpr (Type t1) (Type t2) = t1 == t2
cheapEqExpr (App f1 a1) (App f2 a2)
= f1 `cheapEqExpr` f2 && a1 `cheapEqExpr` a2
-cheapEqExpr (Type t1) (Type t2) = t1 == t2
-
cheapEqExpr _ _ = False
+
+exprIsBig :: Expr b -> Bool
+-- Returns True of expressions that are too big to be compared by cheapEqExpr
+exprIsBig (Lit _) = False
+exprIsBig (Var v) = False
+exprIsBig (Type t) = False
+exprIsBig (App f a) = exprIsBig f || exprIsBig a
+exprIsBig other = True
\end{code}
Just v1' -> v1' == v2
Nothing -> v1 == v2
- eq env (Con c1 es1) (Con c2 es2) = c1 == c2 && eq_list env es1 es2
+ eq env (Lit lit1) (Lit lit2) = lit1 == lit2
eq env (App f1 a1) (App f2 a2) = eq env f1 f2 && eq env a1 a2
eq env (Lam v1 e1) (Lam v2 e2) = eq (extendVarEnv env v1 v2) e1 e2
eq env (Let (NonRec v1 r1) e1)
eq (extendVarEnvList env (vs1 `zip` vs2)) r1 r2
eq_note env (SCC cc1) (SCC cc2) = cc1 == cc2
- eq_note env (Coerce f1 t1) (Coerce f2 t2) = f1==f2 && t1==t2
+ eq_note env (Coerce t1 f1) (Coerce t2 f2) = t1==t2 && f1==f2
eq_note env InlineCall InlineCall = True
eq_note env other1 other2 = False
\end{code}
+
+%************************************************************************
+%* *
+\subsection{The size of an expression}
+%* *
+%************************************************************************
+
+\begin{code}
+coreBindsSize :: [CoreBind] -> Int
+coreBindsSize bs = foldr ((+) . bindSize) 0 bs
+
+exprSize :: CoreExpr -> Int
+ -- A measure of the size of the expressions
+ -- It also forces the expression pretty drastically as a side effect
+exprSize (Var v) = varSize v
+exprSize (Lit lit) = lit `seq` 1
+exprSize (App f a) = exprSize f + exprSize a
+exprSize (Lam b e) = varSize b + exprSize e
+exprSize (Let b e) = bindSize b + exprSize e
+exprSize (Case e b as) = exprSize e + varSize b + foldr ((+) . altSize) 0 as
+exprSize (Note n e) = noteSize n + exprSize e
+exprSize (Type t) = seqType t `seq` 1
+
+noteSize (SCC cc) = cc `seq` 1
+noteSize (Coerce t1 t2) = seqType t1 `seq` seqType t2 `seq` 1
+noteSize InlineCall = 1
+noteSize InlineMe = 1
+
+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}
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