\begin{code}
module CoreUtils (
- IdSubst, SubstCoreExpr(..),
+ -- Construction
+ mkNote, mkInlineMe, mkSCC, mkCoerce, mkCoerce2,
+ bindNonRec, needsCaseBinding,
+ mkIfThenElse, mkAltExpr, mkPiType, mkPiTypes,
- coreExprType, coreAltsType, exprFreeVars, exprSomeFreeVars,
+ -- Taking expressions apart
+ findDefault, findAlt, hasDefault,
- exprIsBottom, exprIsDupable, exprIsTrivial, exprIsWHNF, exprIsCheap,
- FormSummary(..), mkFormSummary, whnfOrBottom,
- cheapEqExpr,
+ -- Properties of expressions
+ exprType, coreAltsType,
+ exprIsBottom, exprIsDupable, exprIsTrivial, exprIsCheap,
+ exprIsValue,exprOkForSpeculation, exprIsBig,
+ exprIsConApp_maybe,
+ rhsIsStatic,
- substExpr, substId, substIds,
- idSpecVars, idFreeVars,
+ -- Arity and eta expansion
+ manifestArity, exprArity,
+ exprEtaExpandArity, etaExpand,
- squashableDictishCcExpr
+ -- Size
+ coreBindsSize,
+
+ -- Hashing
+ hashExpr,
+
+ -- Equality
+ cheapEqExpr, eqExpr, applyTypeToArgs, applyTypeToArg
) where
#include "HsVersions.h"
-import {-# SOURCE #-} CoreUnfold ( noUnfolding, hasUnfolding )
+
+import GLAEXTS -- For `xori`
import CoreSyn
-import PprCore () -- Instances only
-import Var ( IdOrTyVar, isId, isTyVar )
-import VarSet
+import PprCore ( pprCoreExpr )
+import Var ( Var, isId, isTyVar )
import VarEnv
-import Name ( isLocallyDefined )
-import Const ( Con(..), isWHNFCon, conIsTrivial, conIsCheap )
-import Id ( Id, idType, setIdType, idUnique, idAppIsBottom,
- getIdArity, idFreeTyVars,
- getIdSpecialisation, setIdSpecialisation,
- getInlinePragma, setInlinePragma,
- getIdUnfolding, setIdUnfolding
+import Name ( hashName, isDllName )
+import Literal ( hashLiteral, literalType, litIsDupable,
+ litIsTrivial, isZeroLit, isLitLitLit )
+import DataCon ( DataCon, dataConRepArity, dataConArgTys,
+ isExistentialDataCon, dataConTyCon, dataConName )
+import PrimOp ( PrimOp(..), primOpOkForSpeculation, primOpIsCheap )
+import Id ( Id, idType, globalIdDetails, idNewStrictness,
+ mkWildId, idArity, idName, idUnfolding, idInfo,
+ isOneShotLambda, isDataConWorkId_maybe, mkSysLocal,
+ isDataConWorkId, isBottomingId
)
-import IdInfo ( arityLowerBound, InlinePragInfo(..) )
-import SpecEnv ( emptySpecEnv, specEnvToList, isEmptySpecEnv )
-import CostCentre ( isDictCC, CostCentre )
-import Const ( Con, conType )
-import Type ( Type, TyVarSubst, mkFunTy, mkForAllTy,
- splitFunTy_maybe, applyTys, tyVarsOfType, tyVarsOfTypes,
- fullSubstTy, substTyVar )
-import Unique ( buildIdKey, augmentIdKey )
-import Util ( zipWithEqual, mapAccumL )
+import IdInfo ( GlobalIdDetails(..), megaSeqIdInfo )
+import NewDemand ( appIsBottom )
+import Type ( Type, mkFunTy, mkForAllTy, splitFunTy_maybe,
+ splitFunTy,
+ applyTys, isUnLiftedType, seqType, mkTyVarTy,
+ splitForAllTy_maybe, isForAllTy, splitNewType_maybe,
+ splitTyConApp_maybe, eqType, funResultTy, applyTy,
+ funResultTy, applyTy
+ )
+import TyCon ( tyConArity )
+import TysWiredIn ( boolTy, trueDataCon, falseDataCon )
+import CostCentre ( CostCentre )
+import BasicTypes ( Arity )
+import Unique ( Unique )
import Outputable
-import TysPrim ( alphaTy ) -- Debgging only
+import TysPrim ( alphaTy ) -- Debugging only
+import Util ( equalLength, lengthAtLeast )
+import TysPrim ( statePrimTyCon )
\end{code}
%************************************************************************
%* *
-\subsection{Substitutions}
+\subsection{Find the type of a Core atom/expression}
%* *
%************************************************************************
\begin{code}
-type IdSubst = IdEnv SubstCoreExpr -- Maps Ids to SubstCoreExpr
+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 (exprType fun) args
-data SubstCoreExpr
- = Done CoreExpr -- No more substitution needed
- | SubstMe CoreExpr TyVarSubst IdSubst -- A suspended substitution
+exprType other = pprTrace "exprType" (pprCoreExpr other) alphaTy
+
+coreAltsType :: [CoreAlt] -> Type
+coreAltsType ((_,_,rhs) : _) = exprType rhs
\end{code}
-%************************************************************************
-%* *
-\subsection{Find the type of a Core atom/expression}
-%* *
-%************************************************************************
+@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}
-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 other_note e) = coreExprType e
-coreExprType e@(Con con args) = applyTypeToArgs e (conType con) args
-
-coreExprType (Lam binder expr)
- | isId binder = idType binder `mkFunTy` coreExprType expr
- | isTyVar binder = mkForAllTy binder (coreExprType expr)
-
-coreExprType e@(App _ _)
- = case collectArgs e of
- (fun, args) -> applyTypeToArgs e (coreExprType fun) args
+mkPiType :: Var -> Type -> Type -- The more polymorphic version
+mkPiTypes :: [Var] -> Type -> Type -- doesn't work...
-coreExprType other = pprTrace "coreExprType" (ppr other) alphaTy
+mkPiTypes vs ty = foldr mkPiType ty vs
-coreAltsType :: [CoreAlt] -> Type
-coreAltsType ((_,_,rhs) : _) = coreExprType rhs
+mkPiType v ty
+ | isId v = mkFunTy (idType v) ty
+ | otherwise = mkForAllTy v ty
\end{code}
\begin{code}
--- The "e" argument is just for debugging
-
+applyTypeToArg :: Type -> CoreExpr -> Type
+applyTypeToArg fun_ty (Type arg_ty) = applyTy fun_ty arg_ty
+applyTypeToArg fun_ty other_arg = funResultTy fun_ty
+
+applyTypeToArgs :: CoreExpr -> Type -> [CoreExpr] -> Type
+-- A more efficient version of applyTypeToArg
+-- when we have several args
+-- The first argument is just for debugging
applyTypeToArgs e op_ty [] = op_ty
applyTypeToArgs e op_ty (Type ty : args)
= -- Accumulate type arguments so we can instantiate all at once
- applyTypeToArgs e (applyTys op_ty tys) rest_args
+ go [ty] args
where
- (tys, rest_args) = go [ty] args
- go tys (Type ty : args) = go (ty:tys) args
- go tys rest_args = (reverse tys, rest_args)
+ go rev_tys (Type ty : args) = go (ty:rev_tys) args
+ go rev_tys rest_args = applyTypeToArgs e op_ty' rest_args
+ where
+ op_ty' = applyTys op_ty (reverse rev_tys)
applyTypeToArgs e op_ty (other_arg : args)
= case (splitFunTy_maybe op_ty) of
Just (_, res_ty) -> applyTypeToArgs e res_ty args
- Nothing -> pprPanic "applyTypeToArgs" (ppr e)
+ Nothing -> pprPanic "applyTypeToArgs" (pprCoreExpr e)
\end{code}
+
%************************************************************************
%* *
-\subsection{Figuring out things about expressions}
+\subsection{Attaching notes}
%* *
%************************************************************************
+mkNote removes redundant coercions, and SCCs where possible
+
\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
- | 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
+mkNote :: Note -> CoreExpr -> CoreExpr
+mkNote (Coerce to_ty from_ty) expr = mkCoerce2 to_ty from_ty expr
+mkNote (SCC cc) expr = mkSCC cc expr
+mkNote InlineMe expr = mkInlineMe expr
+mkNote note expr = Note note expr
+
+-- 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}
-mkFormSummary :: CoreExpr -> FormSummary
-mkFormSummary expr
- = go (0::Int) expr -- The "n" is the number of *value* arguments so far
- where
- go n (Con con _) | isWHNFCon con = ValueForm
- | otherwise = OtherForm
+mkInlineMe (Var v) = Var v
+mkInlineMe e = Note InlineMe e
+\end{code}
- go n (Note _ e) = go n e
- go n (Let (NonRec b r) e) | exprIsTrivial r = go n e -- let f = f' alpha in (f,g)
- -- should be treated as a value
- go n (Let _ e) = OtherForm
- go n (Case _ _ _) = 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
+\begin{code}
+mkCoerce :: Type -> CoreExpr -> CoreExpr
+mkCoerce to_ty expr = mkCoerce2 to_ty (exprType expr) expr
+
+mkCoerce2 :: Type -> Type -> CoreExpr -> CoreExpr
+mkCoerce2 to_ty from_ty (Note (Coerce to_ty2 from_ty2) expr)
+ = ASSERT( from_ty `eqType` to_ty2 )
+ mkCoerce2 to_ty from_ty2 expr
+
+mkCoerce2 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
+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}
- 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
+%************************************************************************
+%* *
+\subsection{Other expression construction}
+%* *
+%************************************************************************
+
+\begin{code}
+bindNonRec :: Id -> CoreExpr -> CoreExpr -> CoreExpr
+-- (bindNonRec x r b) produces either
+-- let x = r in b
+-- or
+-- case r of x { _DEFAULT_ -> b }
+--
+-- depending on whether x is unlifted or not
+-- It's used by the desugarer to avoid building bindings
+-- that give Core Lint a heart attack. Actually the simplifier
+-- deals with them perfectly well.
+bindNonRec bndr rhs body
+ | needsCaseBinding (idType bndr) rhs = Case rhs bndr [(DEFAULT,[],body)]
+ | otherwise = Let (NonRec bndr rhs) body
+
+needsCaseBinding ty rhs = isUnLiftedType ty && not (exprOkForSpeculation rhs)
+ -- Make a case expression instead of a let
+ -- These can arise either from the desugarer,
+ -- or from beta reductions: (\x.e) (x +# y)
\end{code}
-@exprIsTrivial@ is true of expressions we are unconditionally
- happy to duplicate; simple variables and constants,
- and type applications.
+\begin{code}
+mkAltExpr :: AltCon -> [CoreBndr] -> [Type] -> CoreExpr
+ -- This guy constructs the value that the scrutinee must have
+ -- when you are in one particular branch of a case
+mkAltExpr (DataAlt con) args inst_tys
+ = mkConApp con (map Type inst_tys ++ map varToCoreExpr args)
+mkAltExpr (LitAlt lit) [] []
+ = Lit lit
+
+mkIfThenElse :: CoreExpr -> CoreExpr -> CoreExpr -> CoreExpr
+mkIfThenElse guard then_expr else_expr
+ = Case guard (mkWildId boolTy)
+ [ (DataAlt trueDataCon, [], then_expr),
+ (DataAlt falseDataCon, [], else_expr) ]
+\end{code}
-@exprIsDupable@ is true of expressions that can be duplicated at a modest
- cost in space, but without duplicating any work.
+%************************************************************************
+%* *
+\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}
+%* *
+%************************************************************************
+
+@exprIsTrivial@ is true of expressions we are unconditionally happy to
+ duplicate; simple variables and constants, and type
+ applications. Note that primop Ids aren't considered
+ trivial unless
@exprIsBottom@ is true of expressions that are guaranteed to diverge
+There used to be a gruesome test for (hasNoBinding v) in the
+Var case:
+ exprIsTrivial (Var v) | hasNoBinding v = idArity v == 0
+The idea here is that a constructor worker, like $wJust, is
+really short for (\x -> $wJust x), becuase $wJust has no binding.
+So it should be treated like a lambda. Ditto unsaturated primops.
+But now constructor workers are not "have-no-binding" Ids. And
+completely un-applied primops and foreign-call Ids are sufficiently
+rare that I plan to allow them to be duplicated and put up with
+saturating them.
+
\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) = True -- See notes above
+exprIsTrivial (Type _) = True
+exprIsTrivial (Lit lit) = litIsTrivial lit
+exprIsTrivial (App e arg) = not (isRuntimeArg arg) && exprIsTrivial e
+exprIsTrivial (Note _ e) = exprIsTrivial e
+exprIsTrivial (Lam b body) = not (isRuntimeVar b) && exprIsTrivial body
+exprIsTrivial other = False
\end{code}
+@exprIsDupable@ is true of expressions that can be duplicated at a modest
+ cost in code size. This will only happen in different case
+ branches, so there's no issue about duplicating work.
+
+ That is, exprIsDupable returns True of (f x) even if
+ f is very very expensive to call.
+
+ Its only purpose is to avoid fruitless let-binding
+ and then inlining of case join points
+
+
\begin{code}
-exprIsDupable (Type _) = True
-exprIsDupable (Con con args) = conIsCheap con &&
- all exprIsDupable args &&
- valArgCount args <= dupAppSize
-
-exprIsDupable (Note _ e) = exprIsDupable e
-exprIsDupable expr = case collectArgs expr of
- (Var v, args) -> n_val_args == 0 ||
- (n_val_args < fun_arity &&
- all exprIsDupable args &&
- n_val_args <= dupAppSize)
- where
- n_val_args = valArgCount args
- fun_arity = arityLowerBound (getIdArity v)
-
- _ -> 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)
+
+Notice that a variable is considered 'cheap': we can push it inside a lambda,
+because sharing will make sure it is only evaluated once.
\begin{code}
exprIsCheap :: CoreExpr -> Bool
-exprIsCheap (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
+exprIsCheap (Lit lit) = True
+exprIsCheap (Type _) = True
+exprIsCheap (Var _) = True
+exprIsCheap (Note InlineMe e) = True
+exprIsCheap (Note _ e) = exprIsCheap e
+exprIsCheap (Lam x e) = isRuntimeVar x || exprIsCheap e
+exprIsCheap (Case e _ alts) = exprIsCheap e &&
+ and [exprIsCheap rhs | (_,_,rhs) <- alts]
+ -- Experimentally, treat (case x of ...) as cheap
+ -- (and case __coerce x etc.)
+ -- This improves arities of overloaded functions where
+ -- there is only dictionary selection (no construction) involved
+exprIsCheap (Let (NonRec x _) e)
+ | isUnLiftedType (idType x) = exprIsCheap e
+ | otherwise = False
+ -- strict lets always have cheap right hand sides, and
+ -- do no allocation.
+
+exprIsCheap other_expr
+ = go other_expr 0 True
+ where
+ go (Var f) n_args args_cheap
+ = (idAppIsCheap f n_args && args_cheap)
+ -- A constructor, cheap primop, or partial application
+
+ || idAppIsBottom f n_args
+ -- Application of a function which
+ -- always gives bottom; we treat this as cheap
+ -- because it certainly doesn't need to be shared!
+
+ go (App f a) n_args args_cheap
+ | not (isRuntimeArg a) = go f n_args args_cheap
+ | otherwise = go f (n_args + 1) (exprIsCheap a && args_cheap)
+
+ go other n_args args_cheap = False
+
+idAppIsCheap :: Id -> Int -> Bool
+idAppIsCheap id n_val_args
+ | n_val_args == 0 = True -- Just a type application of
+ -- a variable (f t1 t2 t3)
+ -- counts as WHNF
+ | otherwise = case globalIdDetails id of
+ DataConWorkId _ -> True
+ RecordSelId _ -> True -- I'm experimenting with making record selection
+ ClassOpId _ -> True -- 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 expression that it is
- (Var f, args) | idAppIsBottom f (length args)
- -> True -- Application of a function which
- -- always gives bottom; we treat this as
- -- a WHNF, because it certainly doesn't
- -- need to be shared!
-
- (Var f, args) ->
- let
- num_val_args = valArgCount args
- in
- num_val_args == 0 || -- Just a type application of
- -- a variable (f t1 t2 t3)
- -- counts as WHNF
- num_val_args < arityLowerBound (getIdArity f)
-
- _ -> False
+ * safe to evaluate even if normal order eval might not
+ evaluate the expression at all, or
+
+ * safe *not* to evaluate even if normal order would do so
+
+It returns True iff
+
+ the expression guarantees to terminate,
+ soon,
+ without raising an exception,
+ without causing a side effect (e.g. writing a mutable variable)
+
+E.G.
+ let x = case y# +# 1# of { r# -> I# r# }
+ in E
+==>
+ case y# +# 1# of { r# ->
+ let x = I# r#
+ in E
+ }
+
+We can only do this if the (y+1) is ok for speculation: it has no
+side effects, and can't diverge or raise an exception.
+
+\begin{code}
+exprOkForSpeculation :: CoreExpr -> Bool
+exprOkForSpeculation (Lit _) = True
+exprOkForSpeculation (Type _) = True
+exprOkForSpeculation (Var v) = isUnLiftedType (idType v)
+exprOkForSpeculation (Note _ e) = exprOkForSpeculation e
+exprOkForSpeculation other_expr
+ = case collectArgs other_expr of
+ (Var f, args) -> spec_ok (globalIdDetails f) args
+ other -> False
+
+ where
+ spec_ok (DataConWorkId _) args
+ = True -- The strictness of the constructor has already
+ -- been expressed by its "wrapper", so we don't need
+ -- to take the arguments into account
+
+ spec_ok (PrimOpId op) args
+ | isDivOp op, -- Special case for dividing operations that fail
+ [arg1, Lit lit] <- args -- only if the divisor is zero
+ = not (isZeroLit lit) && exprOkForSpeculation arg1
+ -- Often there is a literal divisor, and this
+ -- can get rid of a thunk in an inner looop
+
+ | otherwise
+ = primOpOkForSpeculation op &&
+ all exprOkForSpeculation args
+ -- A bit conservative: we don't really need
+ -- to care about lazy arguments, but this is easy
+
+ spec_ok other args = False
+
+isDivOp :: PrimOp -> Bool
+-- True of dyadic operators that can fail
+-- only if the second arg is zero
+-- This function probably belongs in PrimOp, or even in
+-- an automagically generated file.. but it's such a
+-- special case I thought I'd leave it here for now.
+isDivOp IntQuotOp = True
+isDivOp IntRemOp = True
+isDivOp WordQuotOp = True
+isDivOp WordRemOp = True
+isDivOp IntegerQuotRemOp = True
+isDivOp IntegerDivModOp = True
+isDivOp FloatDivOp = True
+isDivOp DoubleDivOp = True
+isDivOp other = False
\end{code}
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 (idNewStrictness 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 *head* normal form. This is used to decide whether it's ok
+to change
-We treat applications of buildId and augmentId as honorary WHNFs, because we
-want them to get exposed
+ case x of _ -> e ===> e
-\begin{code}
-exprIsWHNF :: CoreExpr -> Bool -- True => Variable, value-lambda, constructor, PAP
-exprIsWHNF (Type ty) = True -- Types are honorary WHNFs; 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
-\end{code}
+and to decide whether it's safe to discard a `seq`
+
+So, it does *not* treat variables as evaluated, unless they say they are.
-I don't like this function but I'n not confidnt enough to change it.
+But it *does* treat partial applications and constructor applications
+as values, even if their arguments are non-trivial, provided the argument
+type is lifted;
+ e.g. (:) (f x) (map f xs) is a value
+ map (...redex...) is a value
+Because `seq` on such things completes immediately
+
+For unlifted argument types, we have to be careful:
+ C (f x :: Int#)
+Suppose (f x) diverges; then C (f x) is not a value. True, but
+this form is illegal (see the invariants in CoreSyn). Args of unboxed
+type must be ok-for-speculation (or trivial).
\begin{code}
-squashableDictishCcExpr :: CostCentre -> Expr b -> Bool
-squashableDictishCcExpr cc expr
- | isDictCC cc = False -- that was easy...
- | otherwise = squashable expr
+exprIsValue :: CoreExpr -> Bool -- True => Value-lambda, constructor, PAP
+exprIsValue (Var v) -- NB: There are no value args at this point
+ = isDataConWorkId v -- Catches nullary constructors,
+ -- so that [] and () are values, for example
+ || idArity v > 0 -- Catches (e.g.) primops that don't have unfoldings
+ || isEvaldUnfolding (idUnfolding v)
+ -- Check the thing's unfolding; it might be bound to a value
+ -- A worry: what if an Id's unfolding is just itself:
+ -- then we could get an infinite loop...
+
+exprIsValue (Lit l) = True
+exprIsValue (Type ty) = True -- Types are honorary Values;
+ -- we don't mind copying them
+exprIsValue (Lam b e) = isRuntimeVar b || exprIsValue e
+exprIsValue (Note _ e) = exprIsValue e
+exprIsValue (App e (Type _)) = exprIsValue e
+exprIsValue (App e a) = app_is_value e [a]
+exprIsValue other = False
+
+-- There is at least one value argument
+app_is_value (Var fun) args
+ | isDataConWorkId fun -- Constructor apps are values
+ || idArity fun > valArgCount args -- Under-applied function
+ = check_args (idType fun) args
+app_is_value (App f a) as = app_is_value f (a:as)
+app_is_value other as = False
+
+ -- 'check_args' checks that unlifted-type args
+ -- are in fact guaranteed non-divergent
+check_args fun_ty [] = True
+check_args fun_ty (Type _ : args) = case splitForAllTy_maybe fun_ty of
+ Just (_, ty) -> check_args ty args
+check_args fun_ty (arg : args)
+ | isUnLiftedType arg_ty = exprOkForSpeculation arg
+ | otherwise = check_args res_ty args
where
- squashable (Var _) = True
- squashable (Con _ _) = True -- I think so... WDP 94/09
- squashable (App f a)
- | isTypeArg a = squashable f
- squashable other = False
+ (arg_ty, res_ty) = splitFunTy fun_ty
\end{code}
-
-@cheapEqExpr@ is a cheap equality test which bales out fast!
- True => definitely equal
- False => may or may not be equal
-
\begin{code}
-cheapEqExpr :: Expr b -> Expr b -> Bool
-
-cheapEqExpr (Var v1) (Var v2) = v1==v2
-cheapEqExpr (Con con1 args1) (Con con2 args2)
- = con1 == con2 &&
- and (zipWithEqual "cheapEqExpr" cheapEqExpr args1 args2)
-
-cheapEqExpr (App f1 a1) (App f2 a2)
- = f1 `cheapEqExpr` f2 && a1 `cheapEqExpr` a2
-
-cheapEqExpr (Type t1) (Type t2) = t1 == t2
+exprIsConApp_maybe :: CoreExpr -> Maybe (DataCon, [CoreExpr])
+exprIsConApp_maybe (Note (Coerce to_ty from_ty) expr)
+ = -- Maybe this is over the top, but here we try to turn
+ -- coerce (S,T) ( x, y )
+ -- effectively into
+ -- ( coerce S x, coerce T y )
+ -- This happens in anger in PrelArrExts which has a coerce
+ -- case coerce memcpy a b of
+ -- (# r, s #) -> ...
+ -- where the memcpy is in the IO monad, but the call is in
+ -- the (ST s) monad
+ case exprIsConApp_maybe expr of {
+ Nothing -> Nothing ;
+ Just (dc, args) ->
+
+ case splitTyConApp_maybe to_ty of {
+ Nothing -> Nothing ;
+ Just (tc, tc_arg_tys) | tc /= dataConTyCon dc -> Nothing
+ | isExistentialDataCon dc -> Nothing
+ | otherwise ->
+ -- Type constructor must match
+ -- We knock out existentials to keep matters simple(r)
+ let
+ arity = tyConArity tc
+ val_args = drop arity args
+ to_arg_tys = dataConArgTys dc tc_arg_tys
+ mk_coerce ty arg = mkCoerce ty arg
+ new_val_args = zipWith mk_coerce to_arg_tys val_args
+ in
+ ASSERT( all isTypeArg (take arity args) )
+ ASSERT( equalLength val_args to_arg_tys )
+ Just (dc, map Type tc_arg_tys ++ new_val_args)
+ }}
-cheapEqExpr _ _ = False
+exprIsConApp_maybe (Note _ expr)
+ = exprIsConApp_maybe expr
+ -- We ignore InlineMe notes in case we have
+ -- x = __inline_me__ (a,b)
+ -- All part of making sure that INLINE pragmas never hurt
+ -- Marcin tripped on this one when making dictionaries more inlinable
+ --
+ -- In fact, we ignore all notes. For example,
+ -- case _scc_ "foo" (C a b) of
+ -- C a b -> e
+ -- should be optimised away, but it will be only if we look
+ -- through the SCC note.
+
+exprIsConApp_maybe expr = analyse (collectArgs expr)
+ where
+ analyse (Var fun, args)
+ | Just con <- isDataConWorkId_maybe fun,
+ args `lengthAtLeast` dataConRepArity con
+ -- Might be > because the arity excludes type args
+ = Just (con,args)
+
+ -- Look through unfoldings, but only cheap ones, because
+ -- we are effectively duplicating the unfolding
+ analyse (Var fun, [])
+ | let unf = idUnfolding fun,
+ isCheapUnfolding unf
+ = exprIsConApp_maybe (unfoldingTemplate unf)
+
+ analyse other = Nothing
\end{code}
+
%************************************************************************
%* *
-\section{Finding the free variables of an expression}
+\subsection{Eta reduction and expansion}
%* *
%************************************************************************
-This function simply finds the free variables of an expression.
-So far as type variables are concerned, it only finds tyvars that are
+\begin{code}
+exprEtaExpandArity :: CoreExpr -> Arity
+{- The Arity returned is the number of value args the
+ thing can be applied to without doing much work
+
+exprEtaExpandArity is used when eta expanding
+ e ==> \xy -> e x y
+
+It returns 1 (or more) to:
+ case x of p -> \s -> ...
+because for I/O ish things we really want to get that \s to the top.
+We are prepared to evaluate x each time round the loop in order to get that
+
+It's all a bit more subtle than it looks:
+
+1. One-shot lambdas
+
+Consider one-shot lambdas
+ let x = expensive in \y z -> E
+We want this to have arity 2 if the \y-abstraction is a 1-shot lambda
+Hence the ArityType returned by arityType
+
+2. The state-transformer hack
+
+The one-shot lambda special cause is particularly important/useful for
+IO state transformers, where we often get
+ let x = E in \ s -> ...
+
+and the \s is a real-world state token abstraction. Such abstractions
+are almost invariably 1-shot, so we want to pull the \s out, past the
+let x=E, even if E is expensive. So we treat state-token lambdas as
+one-shot even if they aren't really. The hack is in Id.isOneShotLambda.
+
+3. Dealing with bottom
+
+Consider also
+ f = \x -> error "foo"
+Here, arity 1 is fine. But if it is
+ f = \x -> case x of
+ True -> error "foo"
+ False -> \y -> x+y
+then we want to get arity 2. Tecnically, this isn't quite right, because
+ (f True) `seq` 1
+should diverge, but it'll converge if we eta-expand f. Nevertheless, we
+do so; it improves some programs significantly, and increasing convergence
+isn't a bad thing. Hence the ABot/ATop in ArityType.
+
+Actually, the situation is worse. Consider
+ f = \x -> case x of
+ True -> \y -> x+y
+ False -> \y -> x-y
+Can we eta-expand here? At first the answer looks like "yes of course", but
+consider
+ (f bot) `seq` 1
+This should diverge! But if we eta-expand, it won't. Again, we ignore this
+"problem", because being scrupulous would lose an important transformation for
+many programs.
+-}
+
- * free in type arguments,
- * free in the type of a binder,
+exprEtaExpandArity e = arityDepth (arityType e)
-but not those that are free in the type of variable occurrence.
+-- A limited sort of function type
+data ArityType = AFun Bool ArityType -- True <=> one-shot
+ | ATop -- Know nothing
+ | ABot -- Diverges
-\begin{code}
-exprFreeVars :: CoreExpr -> IdOrTyVarSet -- Find all locally-defined free Ids or tyvars
-exprFreeVars = exprSomeFreeVars isLocallyDefined
+arityDepth :: ArityType -> Arity
+arityDepth (AFun _ ty) = 1 + arityDepth ty
+arityDepth ty = 0
+
+andArityType ABot at2 = at2
+andArityType ATop at2 = ATop
+andArityType (AFun t1 at1) (AFun t2 at2) = AFun (t1 && t2) (andArityType at1 at2)
+andArityType at1 at2 = andArityType at2 at1
-exprSomeFreeVars :: InterestingVarFun -- Says which Vars are interesting
- -> CoreExpr
- -> IdOrTyVarSet
-exprSomeFreeVars fv_cand e = expr_fvs e fv_cand emptyVarSet
+arityType :: CoreExpr -> ArityType
+ -- (go1 e) = [b1,..,bn]
+ -- means expression can be rewritten \x_b1 -> ... \x_bn -> body
+ -- where bi is True <=> the lambda is one-shot
-type InterestingVarFun = IdOrTyVar -> Bool -- True <=> interesting
+arityType (Note n e) = arityType e
+-- Not needed any more: etaExpand is cleverer
+-- | ok_note n = arityType e
+-- | otherwise = ATop
+
+arityType (Var v)
+ = mk (idArity v)
+ where
+ mk :: Arity -> ArityType
+ mk 0 | isBottomingId v = ABot
+ | otherwise = ATop
+ mk n = AFun False (mk (n-1))
+
+ -- When the type of the Id encodes one-shot-ness,
+ -- use the idinfo here
+
+ -- Lambdas; increase arity
+arityType (Lam x e) | isId x = AFun (isOneShotLambda x || isStateHack x) (arityType e)
+ | otherwise = arityType e
+
+ -- Applications; decrease arity
+arityType (App f (Type _)) = arityType f
+arityType (App f a) = case arityType f of
+ AFun one_shot xs | exprIsCheap a -> xs
+ other -> ATop
+
+ -- Case/Let; keep arity if either the expression is cheap
+ -- or it's a 1-shot lambda
+arityType (Case scrut _ alts) = case foldr1 andArityType [arityType rhs | (_,_,rhs) <- alts] of
+ xs@(AFun one_shot _) | one_shot -> xs
+ xs | exprIsCheap scrut -> xs
+ | otherwise -> ATop
+
+arityType (Let b e) = case arityType e of
+ xs@(AFun one_shot _) | one_shot -> xs
+ xs | all exprIsCheap (rhssOfBind b) -> xs
+ | otherwise -> ATop
+
+arityType other = ATop
+
+isStateHack id = case splitTyConApp_maybe (idType id) of
+ Just (tycon,_) | tycon == statePrimTyCon -> True
+ other -> False
+
+ -- The last clause is a gross hack. It claims that
+ -- every function over realWorldStatePrimTy is a one-shot
+ -- function. This is pretty true in practice, and makes a big
+ -- difference. For example, consider
+ -- a `thenST` \ r -> ...E...
+ -- The early full laziness pass, if it doesn't know that r is one-shot
+ -- will pull out E (let's say it doesn't mention r) to give
+ -- let lvl = E in a `thenST` \ r -> ...lvl...
+ -- When `thenST` gets inlined, we end up with
+ -- let lvl = E in \s -> case a s of (r, s') -> ...lvl...
+ -- and we don't re-inline E.
+ --
+ -- It would be better to spot that r was one-shot to start with, but
+ -- I don't want to rely on that.
+ --
+ -- Another good example is in fill_in in PrelPack.lhs. We should be able to
+ -- spot that fill_in has arity 2 (and when Keith is done, we will) but we can't yet.
+
+{- NOT NEEDED ANY MORE: etaExpand is cleverer
+ok_note InlineMe = False
+ok_note other = True
+ -- Notice that we do not look through __inline_me__
+ -- This may seem surprising, but consider
+ -- f = _inline_me (\x -> e)
+ -- We DO NOT want to eta expand this to
+ -- f = \x -> (_inline_me (\x -> e)) x
+ -- because the _inline_me gets dropped now it is applied,
+ -- giving just
+ -- f = \x -> e
+ -- A Bad Idea
+-}
\end{code}
\begin{code}
-type FV = InterestingVarFun
- -> IdOrTyVarSet -- In scope
- -> IdOrTyVarSet -- Free vars
+etaExpand :: Arity -- Result should have this number of value args
+ -> [Unique]
+ -> CoreExpr -> Type -- Expression and its type
+ -> CoreExpr
+-- (etaExpand n us e ty) returns an expression with
+-- the same meaning as 'e', but with arity 'n'.
+--
+-- Given e' = etaExpand n us e ty
+-- We should have
+-- ty = exprType e = exprType e'
+--
+-- Note that SCCs are not treated specially. If we have
+-- etaExpand 2 (\x -> scc "foo" e)
+-- = (\xy -> (scc "foo" e) y)
+-- So the costs of evaluating 'e' (not 'e y') are attributed to "foo"
+
+etaExpand n us expr ty
+ | manifestArity expr >= n = expr -- The no-op case
+ | otherwise = eta_expand n us expr ty
+ where
-union :: FV -> FV -> FV
-union fv1 fv2 fv_cand in_scope = fv1 fv_cand in_scope `unionVarSet` fv2 fv_cand in_scope
+-- manifestArity sees how many leading value lambdas there are
+manifestArity :: CoreExpr -> Arity
+manifestArity (Lam v e) | isId v = 1 + manifestArity e
+ | otherwise = manifestArity e
+manifestArity (Note _ e) = manifestArity e
+manifestArity e = 0
+
+-- etaExpand deals with for-alls. For example:
+-- etaExpand 1 E
+-- where E :: forall a. a -> a
+-- would return
+-- (/\b. \y::a -> E b y)
+--
+-- It deals with coerces too, though they are now rare
+-- so perhaps the extra code isn't worth it
+
+eta_expand n us expr ty
+ | n == 0 &&
+ -- The ILX code generator requires eta expansion for type arguments
+ -- too, but alas the 'n' doesn't tell us how many of them there
+ -- may be. So we eagerly eta expand any big lambdas, and just
+ -- cross our fingers about possible loss of sharing in the ILX case.
+ -- The Right Thing is probably to make 'arity' include
+ -- type variables throughout the compiler. (ToDo.)
+ not (isForAllTy ty)
+ -- Saturated, so nothing to do
+ = expr
+
+ -- Short cut for the case where there already
+ -- is a lambda; no point in gratuitously adding more
+eta_expand n us (Lam v body) ty
+ | isTyVar v
+ = Lam v (eta_expand n us body (applyTy ty (mkTyVarTy v)))
-noVars :: FV
-noVars fv_cand in_scope = emptyVarSet
+ | otherwise
+ = Lam v (eta_expand (n-1) us body (funResultTy ty))
+
+-- We used to have a special case that stepped inside Coerces here,
+-- thus: eta_expand n us (Note note@(Coerce _ ty) e) _
+-- = Note note (eta_expand n us e ty)
+-- BUT this led to an infinite loop
+-- Example: newtype T = MkT (Int -> Int)
+-- eta_expand 1 (coerce (Int->Int) e)
+-- --> coerce (Int->Int) (eta_expand 1 T e)
+-- by the bogus eqn
+-- --> coerce (Int->Int) (coerce T
+-- (\x::Int -> eta_expand 1 (coerce (Int->Int) e)))
+-- by the splitNewType_maybe case below
+-- and round we go
+
+eta_expand n us expr ty
+ = case splitForAllTy_maybe ty of {
+ Just (tv,ty') -> Lam tv (eta_expand n us (App expr (Type (mkTyVarTy tv))) ty')
+
+ ; Nothing ->
+
+ case splitFunTy_maybe ty of {
+ Just (arg_ty, res_ty) -> Lam arg1 (eta_expand (n-1) us2 (App expr (Var arg1)) res_ty)
+ where
+ arg1 = mkSysLocal FSLIT("eta") uniq arg_ty
+ (uniq:us2) = us
+
+ ; Nothing ->
+
+ -- Given this:
+ -- newtype T = MkT (Int -> Int)
+ -- Consider eta-expanding this
+ -- eta_expand 1 e T
+ -- We want to get
+ -- coerce T (\x::Int -> (coerce (Int->Int) e) x)
+
+ case splitNewType_maybe ty of {
+ Just ty' -> mkCoerce2 ty ty' (eta_expand n us (mkCoerce2 ty' ty expr) ty') ;
+ Nothing -> pprTrace "Bad eta expand" (ppr expr $$ ppr ty) expr
+ }}}
+\end{code}
-oneVar :: IdOrTyVar -> FV
-oneVar var fv_cand in_scope
- | keep_it fv_cand in_scope var = unitVarSet var
- | otherwise = emptyVarSet
+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.
-someVars :: IdOrTyVarSet -> FV
-someVars vars fv_cand in_scope
- = filterVarSet (keep_it fv_cand in_scope) vars
+Originally I thought that it was enough just to look for top-level lambdas, but
+it isn't. I've seen this
-keep_it fv_cand in_scope var
- | var `elemVarSet` in_scope = False
- | fv_cand var = True
- | otherwise = False
+ 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).
-addBndr :: CoreBndr -> FV -> FV
-addBndr bndr fv fv_cand in_scope
- | isId bndr = inside_fvs `unionVarSet` someVars (idFreeVars bndr) fv_cand in_scope
- | otherwise = inside_fvs
- where
- inside_fvs = fv fv_cand (in_scope `extendVarSet` bndr)
+Similarly, see the ok_note check in exprEtaExpandArity. So
+ f = __inline_me (\x -> e)
+won't be eta-expanded.
+
+And in any case it seems more robust to have exprArity be a bit more intelligent.
+But note that (\x y z -> f x y z)
+should have arity 3, regardless of f's arity.
-addBndrs :: [CoreBndr] -> FV -> FV
-addBndrs bndrs fv = foldr addBndr fv bndrs
+\begin{code}
+exprArity :: CoreExpr -> Arity
+exprArity e = go e
+ where
+ go (Var v) = idArity v
+ go (Lam x e) | isId x = go e + 1
+ | otherwise = go e
+ go (Note n e) = go e
+ go (App e (Type t)) = go e
+ go (App f a) | exprIsCheap a = (go f - 1) `max` 0
+ -- NB: exprIsCheap a!
+ -- f (fac x) does not have arity 2,
+ -- even if f has arity 3!
+ -- NB: `max 0`! (\x y -> f x) has arity 2, even if f is
+ -- unknown, hence arity 0
+ go _ = 0
\end{code}
+%************************************************************************
+%* *
+\subsection{Equality}
+%* *
+%************************************************************************
+
+@cheapEqExpr@ is a cheap equality test which bales out fast!
+ True => definitely equal
+ False => may or may not be equal
\begin{code}
-expr_fvs :: CoreExpr -> FV
+cheapEqExpr :: Expr b -> Expr b -> Bool
-expr_fvs (Type ty) = someVars (tyVarsOfType ty)
-expr_fvs (Var var) = oneVar var
-expr_fvs (Con con args) = foldr (union . expr_fvs) noVars args
-expr_fvs (Note _ expr) = expr_fvs expr
-expr_fvs (App fun arg) = expr_fvs fun `union` expr_fvs arg
-expr_fvs (Lam bndr body) = addBndr bndr (expr_fvs body)
+cheapEqExpr (Var v1) (Var v2) = v1==v2
+cheapEqExpr (Lit lit1) (Lit lit2) = lit1 == lit2
+cheapEqExpr (Type t1) (Type t2) = t1 `eqType` t2
-expr_fvs (Case scrut bndr alts)
- = expr_fvs scrut `union` addBndr bndr (foldr (union. alt_fvs) noVars alts)
- where
- alt_fvs (con, bndrs, rhs) = addBndrs bndrs (expr_fvs rhs)
+cheapEqExpr (App f1 a1) (App f2 a2)
+ = f1 `cheapEqExpr` f2 && a1 `cheapEqExpr` a2
-expr_fvs (Let (NonRec bndr rhs) body)
- = expr_fvs rhs `union` addBndr bndr (expr_fvs body)
+cheapEqExpr _ _ = False
-expr_fvs (Let (Rec pairs) body)
- = addBndrs bndrs (foldr (union . expr_fvs) (expr_fvs body) rhss)
- where
- (bndrs,rhss) = unzip pairs
+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}
-Given an Id, idSpecVars returns all its specialisations.
-We extract these from its SpecEnv.
-This is used by the occurrence analyser and free-var finder;
-we regard an Id's specialisations as free in the Id's definition.
-
\begin{code}
-idSpecVars :: Id -> IdOrTyVarSet
-idSpecVars id
- = foldr (unionVarSet . spec_item_fvs)
- emptyVarSet
- (specEnvToList (getIdSpecialisation id))
+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
- spec_item_fvs (tyvars, tys, rhs) = foldl delVarSet
- (tyVarsOfTypes tys `unionVarSet` exprFreeVars rhs)
- tyvars
-
-idFreeVars :: Id -> IdOrTyVarSet
-idFreeVars id = idSpecVars id `unionVarSet` idFreeTyVars id
+ -- The "env" maps variables in e1 to variables in ty2
+ -- So when comparing lambdas etc,
+ -- we in effect substitute v2 for v1 in e1 before continuing
+ eq env (Var v1) (Var v2) = case lookupVarEnv env v1 of
+ Just v1' -> v1' == v2
+ Nothing -> v1 == v2
+
+ 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)
+ (Let (NonRec v2 r2) e2) = eq env r1 r2 && eq (extendVarEnv env v1 v2) e1 e2
+ eq env (Let (Rec ps1) e1)
+ (Let (Rec ps2) e2) = equalLength ps1 ps2 &&
+ and (zipWith eq_rhs ps1 ps2) &&
+ eq env' e1 e2
+ where
+ env' = extendVarEnvList env [(v1,v2) | ((v1,_),(v2,_)) <- zip ps1 ps2]
+ eq_rhs (_,r1) (_,r2) = eq env' r1 r2
+ eq env (Case e1 v1 a1)
+ (Case e2 v2 a2) = eq env e1 e2 &&
+ equalLength a1 a2 &&
+ and (zipWith (eq_alt env') a1 a2)
+ 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 `eqType` t2
+ eq env e1 e2 = False
+
+ eq_list env [] [] = True
+ eq_list env (e1:es1) (e2:es2) = eq env e1 e2 && eq_list env es1 es2
+ eq_list env es1 es2 = False
+
+ eq_alt env (c1,vs1,r1) (c2,vs2,r2) = c1==c2 &&
+ 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 `eqType` t2 && f1 `eqType` f2
+ eq_note env InlineCall InlineCall = True
+ eq_note env (CoreNote s1) (CoreNote s2) = s1 == s2
+ eq_note env other1 other2 = False
\end{code}
%************************************************************************
%* *
-\section{Substitution}
+\subsection{The size of an expression}
%* *
%************************************************************************
-This expression substituter deals correctly with name capture, much
-like Type.substTy.
-
-BUT NOTE that substExpr silently discards the
- unfolding, and
- spec env
-IdInfo attached to any binders in the expression. It's quite
-tricky to do them 'right' in the case of mutually recursive bindings,
-and so far has proved unnecessary.
-
\begin{code}
-substExpr :: TyVarSubst -> IdSubst -- Substitution
- -> IdOrTyVarSet -- Superset of in-scope
- -> CoreExpr
- -> CoreExpr
-
-substExpr te ve in_scope expr = subst_expr (te, ve, in_scope) expr
-
-subst_expr env@(te, ve, in_scope) expr
- = go expr
- where
- go (Var v) = case lookupVarEnv ve v of
- Just (Done e')
- -> e'
-
- Just (SubstMe e' te' ve')
- -> subst_expr (te', ve', in_scope) e'
-
- Nothing -> case lookupVarSet in_scope v of
- Just v' -> Var v'
- Nothing -> Var v
- -- NB: we look up in the in_scope set because the variable
- -- there may have more info. In particular, when substExpr
- -- is called from the simplifier, the type inside the *occurrences*
- -- of a variable may not be right; we should replace it with the
- -- binder, from the in_scope set.
-
- go (Type ty) = Type (go_ty ty)
- go (Con con args) = Con con (map go args)
- go (App fun arg) = App (go fun) (go arg)
- go (Note note e) = Note (go_note note) (go e)
-
- go (Lam bndr body) = Lam bndr' (subst_expr env' body)
- where
- (env', bndr') = go_bndr env bndr
-
- go (Let (NonRec bndr rhs) body) = Let (NonRec bndr' (go rhs)) (subst_expr env' body)
- where
- (env', bndr') = go_bndr env bndr
-
- go (Let (Rec pairs) body) = Let (Rec pairs') (subst_expr env' body)
- where
- (ve', in_scope', _, bndrs')
- = substIds clone_fn te ve in_scope undefined (map fst pairs)
- env' = (te, ve', in_scope')
- pairs' = bndrs' `zip` rhss'
- rhss' = map (subst_expr env' . snd) pairs
-
- go (Case scrut bndr alts) = Case (go scrut) bndr' (map (go_alt env') alts)
- where
- (env', bndr') = go_bndr env bndr
-
- go_alt env (con, bndrs, rhs) = (con, bndrs', subst_expr env' rhs)
- where
- (env', bndrs') = mapAccumL go_bndr env bndrs
-
- go_note (Coerce ty1 ty2) = Coerce (go_ty ty1) (go_ty ty2)
- go_note note = note
-
- go_ty ty = fullSubstTy te in_scope ty
-
- go_bndr (te, ve, in_scope) bndr
- | isTyVar bndr
- = case substTyVar te in_scope bndr of
- (te', in_scope', bndr') -> ((te', ve, in_scope'), bndr')
-
- | otherwise
- = case substId clone_fn te ve in_scope undefined bndr of
- (ve', in_scope', _, bndr') -> ((te, ve', in_scope'), bndr')
-
-
- clone_fn in_scope _ bndr
- | bndr `elemVarSet` in_scope = Just (uniqAway in_scope bndr, undefined)
- | otherwise = Nothing
-
+coreBindsSize :: [CoreBind] -> Int
+coreBindsSize bs = foldr ((+) . bindSize) 0 bs
+
+exprSize :: CoreExpr -> Int
+ -- A measure of the size of the expressions
+ -- It also forces the expression pretty drastically as a side effect
+exprSize (Var v) = v `seq` 1
+exprSize (Lit lit) = lit `seq` 1
+exprSize (App f a) = exprSize f + exprSize a
+exprSize (Lam b e) = varSize b + exprSize e
+exprSize (Let b e) = bindSize b + exprSize e
+exprSize (Case e b 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
+noteSize (CoreNote s) = s `seq` 1 -- hdaume: core annotations
+
+varSize :: Var -> Int
+varSize b | isTyVar b = 1
+ | otherwise = seqType (idType b) `seq`
+ megaSeqIdInfo (idInfo b) `seq`
+ 1
+
+varsSize = foldr ((+) . varSize) 0
+
+bindSize (NonRec b e) = varSize b + exprSize e
+bindSize (Rec prs) = foldr ((+) . pairSize) 0 prs
+
+pairSize (b,e) = varSize b + exprSize e
+
+altSize (c,bs,e) = c `seq` varsSize bs + exprSize e
\end{code}
-Substituting in binders is a rather tricky part of the whole compiler.
-
-\begin{code}
-substIds :: (IdOrTyVarSet -> us -> Id -> Maybe (us, Id)) -- Cloner
- -> TyVarSubst -> IdSubst -> IdOrTyVarSet -- Usual stuff
- -> us -- Unique supply
- -> [Id]
- -> (IdSubst, IdOrTyVarSet, -- New id_subst, in_scope
- us, -- New unique supply
- [Id])
-
-substIds clone_fn ty_subst id_subst in_scope us []
- = (id_subst, in_scope, us, [])
-
-substIds clone_fn ty_subst id_subst in_scope us (id:ids)
- = case (substId clone_fn ty_subst id_subst in_scope us id) of {
- (id_subst', in_scope', us', id') ->
- case (substIds clone_fn ty_subst id_subst' in_scope' us' ids) of {
- (id_subst'', in_scope'', us'', ids') ->
-
- (id_subst'', in_scope'', us'', id':ids')
- }}
+%************************************************************************
+%* *
+\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}
-substId :: (IdOrTyVarSet -> us -> Id -> Maybe (us, Id)) -- Cloner
- -> TyVarSubst -> IdSubst -> IdOrTyVarSet -- Usual stuff
- -> us -- Unique supply
- -> Id
- -> (IdSubst, IdOrTyVarSet, -- New id_subst, in_scope
- us, -- New unique supply
- Id)
+%************************************************************************
+%* *
+\subsection{Determining non-updatable right-hand-sides}
+%* *
+%************************************************************************
--- Returns an Id with empty unfolding and spec-env.
--- It's up to the caller to sort these out.
+Top-level constructor applications can usually be allocated
+statically, but they can't if
+ a) the constructor, or any of the arguments, come from another DLL
+ b) any of the arguments are LitLits
+(because we can't refer to static labels in other DLLs).
-substId clone_fn
- ty_subst id_subst in_scope
- us id
- | old_id_will_do
- -- No need to clone, but we *must* zap any current substitution
- -- for the variable. For example:
- -- (\x.e) with id_subst = [x |-> e']
- -- Here we must simply zap the substitution for x
- = (delVarEnv id_subst id, extendVarSet in_scope id, us, id)
+If this happens we simply make the RHS into an updatable thunk,
+and 'exectute' it rather than allocating it statically.
- | otherwise
- = (extendVarEnv id_subst id (Done (Var new_id)),
- extendVarSet in_scope new_id,
- new_us,
- new_id)
+\begin{code}
+rhsIsStatic :: CoreExpr -> Bool
+-- This function is called only on *top-level* right-hand sides
+-- Returns True if the RHS can be allocated statically, with
+-- no thunks involved at all.
+--
+-- It's called (i) in TidyPgm.hasCafRefs to decide if the rhs is, or
+-- refers to, CAFs; and (ii) in CoreToStg to decide whether to put an
+-- update flag on it.
+--
+-- The basic idea is that rhsIsStatic returns True only if the RHS is
+-- (a) a value lambda
+-- (b) a saturated constructor application with static args
+--
+-- BUT watch out for
+-- (i) Any cross-DLL references kill static-ness completely
+-- because they must be 'executed' not statically allocated
+--
+-- (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.exprIsValue, with the following differences:
+-- a) scc "foo" (\x -> ...) is updatable (so we catch the right SCC)
+--
+-- b) (C x xs), where C is a contructors is updatable if the application is
+-- dynamic
+--
+-- c) don't look through unfolding of f in (f x).
+--
+-- When opt_RuntimeTypes is on, we keep type lambdas and treat
+-- them as making the RHS re-entrant (non-updatable).
+
+rhsIsStatic rhs = is_static False rhs
+
+is_static :: Bool -- True <=> in a constructor argument; must be atomic
+ -> CoreExpr -> Bool
+
+is_static False (Lam b e) = isRuntimeVar b || is_static False e
+
+is_static in_arg (Note (SCC _) e) = False
+is_static in_arg (Note _ e) = is_static in_arg e
+
+is_static in_arg (Lit lit) = not (isLitLitLit lit)
+ -- lit-lit arguments cannot be used in static constructors either.
+ -- (litlits are deprecated, so I'm not going to bother cleaning up this infelicity --SDM).
+
+is_static in_arg other_expr = go other_expr 0
where
- id_ty = idType id
- old_id_will_do = old1 && old2 && old3 && {-old4 && -}not cloned
-
- -- id1 has its type zapped
- (id1,old1) | isEmptyVarEnv ty_subst
- || isEmptyVarSet (tyVarsOfType id_ty) = (id, True)
- | otherwise = (setIdType id ty', False)
-
- ty' = fullSubstTy ty_subst in_scope id_ty
-
- -- id2 has its SpecEnv zapped
- -- It's filled in later by
- (id2,old2) | isEmptySpecEnv spec_env = (id1, True)
- | otherwise = (setIdSpecialisation id1 emptySpecEnv, False)
- spec_env = getIdSpecialisation id
-
- -- id3 has its Unfolding zapped
- -- This is very important; occasionally a let-bound binder is used
- -- as a binder in some lambda, in which case its unfolding is utterly
- -- bogus. Also the unfolding uses old binders so if we left it we'd
- -- have to substitute it. Much better simply to give the Id a new
- -- unfolding each time, which is what the simplifier does.
- (id3,old3) | hasUnfolding (getIdUnfolding id) = (id2 `setIdUnfolding` noUnfolding, False)
- | otherwise = (id2, True)
-
- -- new_id is cloned if necessary
- (new_us, new_id, cloned) = case clone_fn in_scope us id3 of
- Nothing -> (us, id3, False)
- Just (us', id') -> (us', id', True)
-
- -- new_id_bndr has its Inline info neutered. We must forget about whether it
- -- was marked safe-to-inline, because that isn't necessarily true in
- -- the simplified expression. We do this for the *binder* which will
- -- be used at the binding site, but we *dont* do it for new_id, which
- -- is put into the in_scope env. Why not? Because the in_scope env
- -- carries down the occurrence information to usage sites!
- --
- -- Net result: post-simplification, occurrences may have over-optimistic
- -- occurrence info, but binders won't.
-{- (new_id_bndr, old4)
- = case getInlinePragma id of
- ICanSafelyBeINLINEd _ _ -> (setInlinePragma new_id NoInlinePragInfo, False)
- other -> (new_id, True)
--}
+ go (Var f) n_val_args
+ | not (isDllName (idName f))
+ = saturated_data_con f n_val_args
+ || (in_arg && n_val_args == 0)
+ -- A naked un-applied variable is *not* deemed a static RHS
+ -- E.g. f = g
+ -- Reason: better to update so that the indirection gets shorted
+ -- out, and the true value will be seen
+ -- NB: if you change this, you'll break the invariant that THUNK_STATICs
+ -- are always updatable. If you do so, make sure that non-updatable
+ -- ones have enough space for their static link field!
+
+ go (App f a) n_val_args
+ | isTypeArg a = go f n_val_args
+ | not in_arg && is_static True a = go f (n_val_args + 1)
+ -- The (not in_arg) checks that we aren't in a constructor argument;
+ -- if we are, we don't allow (value) applications of any sort
+ --
+ -- NB. In case you wonder, args are sometimes not atomic. eg.
+ -- x = D# (1.0## /## 2.0##)
+ -- can't float because /## can fail.
+
+ go (Note (SCC _) f) n_val_args = False
+ go (Note _ f) n_val_args = go f n_val_args
+
+ go other n_val_args = False
+
+ saturated_data_con f n_val_args
+ = case isDataConWorkId_maybe f of
+ Just dc -> n_val_args == dataConRepArity dc
+ Nothing -> False
\end{code}
-
-
-
-
-
projects / ghc-hetmet.git / blobdiff