\begin{code}
module SimplUtils (
simplBinder, simplBinders, simplIds,
- mkRhsTyLam,
- etaCoreExpr,
- etaExpandCount,
- mkCase, findAlt, findDefault
+ transformRhs,
+ mkCase, findAlt, findDefault,
+
+ -- The continuation type
+ SimplCont(..), DupFlag(..), contIsDupable, contResultType,
+ countValArgs, countArgs, mkRhsStop, mkStop,
+ getContArgs, interestingCallContext, interestingArg, isStrictType, discardInline
+
) where
#include "HsVersions.h"
-import BinderInfo
-import CmdLineOpts ( opt_DoEtaReduction, switchIsOn, SimplifierSwitch(..) )
-import CoreSyn
-import CoreUtils ( exprIsCheap, exprIsTrivial, exprFreeVars, cheapEqExpr,
- FormSummary(..),
- substId, substIds
+import CmdLineOpts ( switchIsOn, SimplifierSwitch(..),
+ opt_SimplDoLambdaEtaExpansion, opt_SimplCaseMerge, opt_DictsStrict,
+ opt_UF_UpdateInPlace
)
-import Id ( Id, idType, getIdArity, isId, idName,
- getInlinePragma, setInlinePragma,
- getIdDemandInfo
+import CoreSyn
+import CoreUtils ( exprIsTrivial, cheapEqExpr, exprType, exprIsCheap, exprEtaExpandArity, bindNonRec )
+import Subst ( InScopeSet, mkSubst, substBndrs, substBndr, substIds, substExpr )
+import Id ( idType, idName,
+ idUnfolding, idStrictness,
+ mkVanillaId, idInfo
)
-import IdInfo ( arityLowerBound, InlinePragInfo(..) )
-import Maybes ( maybeToBool )
-import Const ( Con(..) )
-import Name ( isLocalName )
+import IdInfo ( StrictnessInfo(..), ArityInfo, atLeastArity, vanillaIdInfo )
+import Maybes ( maybeToBool, catMaybes )
+import Name ( setNameUnique )
+import Demand ( isStrict )
import SimplMonad
-import Type ( Type, tyVarsOfType, tyVarsOfTypes, mkForAllTys, mkTyVarTys,
- splitTyConApp_maybe, mkTyVarTy, substTyVar
+import Type ( Type, mkForAllTys, seqType, repType,
+ splitTyConApp_maybe, mkTyVarTys, splitFunTys,
+ isDictTy, isDataType, isUnLiftedType,
+ splitRepFunTys
)
-import Var ( setVarUnique )
-import VarSet
-import UniqSupply ( splitUniqSupply, uniqFromSupply )
-import Util ( zipWithEqual, mapAccumL )
+import TyCon ( tyConDataConsIfAvailable )
+import DataCon ( dataConRepArity )
+import VarEnv ( SubstEnv )
+import Util ( lengthExceeds )
import Outputable
\end{code}
%************************************************************************
%* *
-\section{Dealing with a single binder}
+\subsection{The continuation data type}
%* *
%************************************************************************
-When we hit a binder we may need to
- (a) apply the the type envt (if non-empty) to its type
- (b) apply the type envt and id envt to its SpecEnv (if it has one)
- (c) give it a new unique to avoid name clashes
+\begin{code}
+data SimplCont -- Strict contexts
+ = Stop OutType -- Type of the result
+ Bool -- True => This is the RHS of a thunk whose type suggests
+ -- that update-in-place would be possible
+ -- (This makes the inliner a little keener.)
+
+ | CoerceIt OutType -- The To-type, simplified
+ SimplCont
+
+ | InlinePlease -- This continuation makes a function very
+ SimplCont -- keen to inline itelf
+
+ | ApplyTo DupFlag
+ InExpr SubstEnv -- The argument, as yet unsimplified,
+ SimplCont -- and its subst-env
+
+ | Select DupFlag
+ InId [InAlt] SubstEnv -- The case binder, alts, and subst-env
+ SimplCont
+
+ | ArgOf DupFlag -- An arbitrary strict context: the argument
+ -- of a strict function, or a primitive-arg fn
+ -- or a PrimOp
+ OutType -- cont_ty: the type of the expression being sought by the context
+ -- f (error "foo") ==> coerce t (error "foo")
+ -- when f is strict
+ -- We need to know the type t, to which to coerce.
+ (OutExpr -> SimplM OutExprStuff) -- What to do with the result
+ -- The result expression in the OutExprStuff has type cont_ty
+
+instance Outputable SimplCont where
+ ppr (Stop _ _) = ptext SLIT("Stop")
+ ppr (ApplyTo dup arg se cont) = (ptext SLIT("ApplyTo") <+> ppr dup <+> ppr arg) $$ ppr cont
+ ppr (ArgOf dup _ _) = ptext SLIT("ArgOf...") <+> ppr dup
+ ppr (Select dup bndr alts se cont) = (ptext SLIT("Select") <+> ppr dup <+> ppr bndr) $$
+ (nest 4 (ppr alts)) $$ ppr cont
+ ppr (CoerceIt ty cont) = (ptext SLIT("CoerceIt") <+> ppr ty) $$ ppr cont
+ ppr (InlinePlease cont) = ptext SLIT("InlinePlease") $$ ppr cont
+
+data DupFlag = OkToDup | NoDup
+
+instance Outputable DupFlag where
+ ppr OkToDup = ptext SLIT("ok")
+ ppr NoDup = ptext SLIT("nodup")
+
+
+-------------------
+mkRhsStop, mkStop :: OutType -> SimplCont
+mkStop ty = Stop ty False
+mkRhsStop ty = Stop ty (canUpdateInPlace ty)
+
+
+-------------------
+contIsDupable :: SimplCont -> Bool
+contIsDupable (Stop _ _) = True
+contIsDupable (ApplyTo OkToDup _ _ _) = True
+contIsDupable (ArgOf OkToDup _ _) = True
+contIsDupable (Select OkToDup _ _ _ _) = True
+contIsDupable (CoerceIt _ cont) = contIsDupable cont
+contIsDupable (InlinePlease cont) = contIsDupable cont
+contIsDupable other = False
+
+-------------------
+discardInline :: SimplCont -> SimplCont
+discardInline (InlinePlease cont) = cont
+discardInline (ApplyTo d e s cont) = ApplyTo d e s (discardInline cont)
+discardInline cont = cont
+
+-------------------
+discardableCont :: SimplCont -> Bool
+discardableCont (Stop _ _) = False
+discardableCont (CoerceIt _ cont) = discardableCont cont
+discardableCont (InlinePlease cont) = discardableCont cont
+discardableCont other = True
+
+discardCont :: SimplCont -- A continuation, expecting
+ -> SimplCont -- Replace the continuation with a suitable coerce
+discardCont cont = case cont of
+ Stop to_ty _ -> cont
+ other -> CoerceIt to_ty (mkStop to_ty)
+ where
+ to_ty = contResultType cont
+
+-------------------
+contResultType :: SimplCont -> OutType
+contResultType (Stop to_ty _) = to_ty
+contResultType (ArgOf _ to_ty _) = to_ty
+contResultType (ApplyTo _ _ _ cont) = contResultType cont
+contResultType (CoerceIt _ cont) = contResultType cont
+contResultType (InlinePlease cont) = contResultType cont
+contResultType (Select _ _ _ _ cont) = contResultType cont
+
+-------------------
+countValArgs :: SimplCont -> Int
+countValArgs (ApplyTo _ (Type ty) se cont) = countValArgs cont
+countValArgs (ApplyTo _ val_arg se cont) = 1 + countValArgs cont
+countValArgs other = 0
+
+countArgs :: SimplCont -> Int
+countArgs (ApplyTo _ arg se cont) = 1 + countArgs cont
+countArgs other = 0
+\end{code}
+
+
+\begin{code}
+getContArgs :: OutId -> SimplCont
+ -> SimplM ([(InExpr, SubstEnv, Bool)], -- Arguments; the Bool is true for strict args
+ SimplCont, -- Remaining continuation
+ Bool) -- Whether we came across an InlineCall
+-- getContArgs id k = (args, k', inl)
+-- args are the leading ApplyTo items in k
+-- (i.e. outermost comes first)
+-- augmented with demand info from the functionn
+getContArgs fun orig_cont
+ = getSwitchChecker `thenSmpl` \ chkr ->
+ let
+ -- Ignore strictness info if the no-case-of-case
+ -- flag is on. Strictness changes evaluation order
+ -- and that can change full laziness
+ stricts | switchIsOn chkr NoCaseOfCase = vanilla_stricts
+ | otherwise = computed_stricts
+ in
+ go [] stricts False orig_cont
+ where
+ ----------------------------
+
+ -- Type argument
+ go acc ss inl (ApplyTo _ arg@(Type _) se cont)
+ = go ((arg,se,False) : acc) ss inl cont
+ -- NB: don't bother to instantiate the function type
+
+ -- Value argument
+ go acc (s:ss) inl (ApplyTo _ arg se cont)
+ = go ((arg,se,s) : acc) ss inl cont
+
+ -- An Inline continuation
+ go acc ss inl (InlinePlease cont)
+ = go acc ss True cont
+
+ -- We're run out of arguments, or else we've run out of demands
+ -- The latter only happens if the result is guaranteed bottom
+ -- This is the case for
+ -- * case (error "hello") of { ... }
+ -- * (error "Hello") arg
+ -- * f (error "Hello") where f is strict
+ -- etc
+ go acc ss inl cont
+ | null ss && discardableCont cont = tick BottomFound `thenSmpl_`
+ returnSmpl (reverse acc, discardCont cont, inl)
+ | otherwise = returnSmpl (reverse acc, cont, inl)
+
+ ----------------------------
+ vanilla_stricts, computed_stricts :: [Bool]
+ vanilla_stricts = repeat False
+ computed_stricts = zipWith (||) fun_stricts arg_stricts
+
+ ----------------------------
+ (val_arg_tys, _) = splitRepFunTys (idType fun)
+ arg_stricts = map isStrictType val_arg_tys ++ repeat False
+ -- These argument types are used as a cheap and cheerful way to find
+ -- unboxed arguments, which must be strict. But it's an InType
+ -- and so there might be a type variable where we expect a function
+ -- type (the substitution hasn't happened yet). And we don't bother
+ -- doing the type applications for a polymorphic function.
+ -- Hence the split*Rep*FunTys
+
+ ----------------------------
+ -- If fun_stricts is finite, it means the function returns bottom
+ -- after that number of value args have been consumed
+ -- Otherwise it's infinite, extended with False
+ fun_stricts
+ = case idStrictness fun of
+ StrictnessInfo demands result_bot
+ | not (demands `lengthExceeds` countValArgs orig_cont)
+ -> -- Enough args, use the strictness given.
+ -- For bottoming functions we used to pretend that the arg
+ -- is lazy, so that we don't treat the arg as an
+ -- interesting context. This avoids substituting
+ -- top-level bindings for (say) strings into
+ -- calls to error. But now we are more careful about
+ -- inlining lone variables, so its ok (see SimplUtils.analyseCont)
+ if result_bot then
+ map isStrict demands -- Finite => result is bottom
+ else
+ map isStrict demands ++ vanilla_stricts
+
+ other -> vanilla_stricts -- Not enough args, or no strictness
+
+
+-------------------
+isStrictType :: Type -> Bool
+ -- isStrictType computes whether an argument (or let RHS) should
+ -- be computed strictly or lazily, based only on its type
+isStrictType ty
+ | isUnLiftedType ty = True
+ | opt_DictsStrict && isDictTy ty && isDataType ty = True
+ | otherwise = False
+ -- Return true only for dictionary types where the dictionary
+ -- has more than one component (else we risk poking on the component
+ -- of a newtype dictionary)
+
+-------------------
+interestingArg :: InScopeSet -> InExpr -> SubstEnv -> Bool
+ -- An argument is interesting if it has *some* structure
+ -- We are here trying to avoid unfolding a function that
+ -- is applied only to variables that have no unfolding
+ -- (i.e. they are probably lambda bound): f x y z
+ -- There is little point in inlining f here.
+interestingArg in_scope arg subst
+ = analyse (substExpr (mkSubst in_scope subst) arg)
+ -- 'analyse' only looks at the top part of the result
+ -- and substExpr is lazy, so this isn't nearly as brutal
+ -- as it looks.
+ where
+ analyse (Var v) = hasSomeUnfolding (idUnfolding v)
+ -- Was: isValueUnfolding (idUnfolding v')
+ -- But that seems over-pessimistic
+ analyse (Type _) = False
+ analyse (App fn (Type _)) = analyse fn
+ analyse (Note _ a) = analyse a
+ analyse other = True
+ -- Consider let x = 3 in f x
+ -- The substitution will contain (x -> ContEx 3), and we want to
+ -- to say that x is an interesting argument.
+ -- But consider also (\x. f x y) y
+ -- The substitution will contain (x -> ContEx y), and we want to say
+ -- that x is not interesting (assuming y has no unfolding)
+\end{code}
+
+Comment about interestingCallContext
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+We want to avoid inlining an expression where there can't possibly be
+any gain, such as in an argument position. Hence, if the continuation
+is interesting (eg. a case scrutinee, application etc.) then we
+inline, otherwise we don't.
+
+Previously some_benefit used to return True only if the variable was
+applied to some value arguments. This didn't work:
+
+ let x = _coerce_ (T Int) Int (I# 3) in
+ case _coerce_ Int (T Int) x of
+ I# y -> ....
+
+we want to inline x, but can't see that it's a constructor in a case
+scrutinee position, and some_benefit is False.
+
+Another example:
+
+dMonadST = _/\_ t -> :Monad (g1 _@_ t, g2 _@_ t, g3 _@_ t)
+
+.... case dMonadST _@_ x0 of (a,b,c) -> ....
+
+we'd really like to inline dMonadST here, but we *don't* want to
+inline if the case expression is just
+
+ case x of y { DEFAULT -> ... }
+
+since we can just eliminate this case instead (x is in WHNF). Similar
+applies when x is bound to a lambda expression. Hence
+contIsInteresting looks for case expressions with just a single
+default case.
+
+\begin{code}
+interestingCallContext :: Bool -- False <=> no args at all
+ -> Bool -- False <=> no value args
+ -> SimplCont -> Bool
+ -- The "lone-variable" case is important. I spent ages
+ -- messing about with unsatisfactory varaints, but this is nice.
+ -- The idea is that if a variable appear all alone
+ -- as an arg of lazy fn, or rhs Stop
+ -- as scrutinee of a case Select
+ -- as arg of a strict fn ArgOf
+ -- then we should not inline it (unless there is some other reason,
+ -- e.g. is is the sole occurrence). We achieve this by making
+ -- interestingCallContext return False for a lone variable.
+ --
+ -- Why? At least in the case-scrutinee situation, turning
+ -- let x = (a,b) in case x of y -> ...
+ -- into
+ -- let x = (a,b) in case (a,b) of y -> ...
+ -- and thence to
+ -- let x = (a,b) in let y = (a,b) in ...
+ -- is bad if the binding for x will remain.
+ --
+ -- Another example: I discovered that strings
+ -- were getting inlined straight back into applications of 'error'
+ -- because the latter is strict.
+ -- s = "foo"
+ -- f = \x -> ...(error s)...
+
+ -- Fundamentally such contexts should not ecourage inlining becuase
+ -- the context can ``see'' the unfolding of the variable (e.g. case or a RULE)
+ -- so there's no gain.
+ --
+ -- However, even a type application or coercion isn't a lone variable.
+ -- Consider
+ -- case $fMonadST @ RealWorld of { :DMonad a b c -> c }
+ -- We had better inline that sucker! The case won't see through it.
+ --
+ -- For now, I'm treating treating a variable applied to types
+ -- in a *lazy* context "lone". The motivating example was
+ -- f = /\a. \x. BIG
+ -- g = /\a. \y. h (f a)
+ -- There's no advantage in inlining f here, and perhaps
+ -- a significant disadvantage. Hence some_val_args in the Stop case
+
+interestingCallContext some_args some_val_args cont
+ = interesting cont
+ where
+ interesting (InlinePlease _) = True
+ interesting (Select _ _ _ _ _) = some_args
+ interesting (ApplyTo _ _ _ _) = some_args -- Can happen if we have (coerce t (f x)) y
+ interesting (ArgOf _ _ _) = some_val_args
+ interesting (Stop ty upd_in_place) = some_val_args && upd_in_place
+ interesting (CoerceIt _ cont) = interesting cont
+ -- If this call is the arg of a strict function, the context
+ -- is a bit interesting. If we inline here, we may get useful
+ -- evaluation information to avoid repeated evals: e.g.
+ -- x + (y * z)
+ -- Here the contIsInteresting makes the '*' keener to inline,
+ -- which in turn exposes a constructor which makes the '+' inline.
+ -- Assuming that +,* aren't small enough to inline regardless.
+ --
+ -- It's also very important to inline in a strict context for things
+ -- like
+ -- foldr k z (f x)
+ -- Here, the context of (f x) is strict, and if f's unfolding is
+ -- a build it's *great* to inline it here. So we must ensure that
+ -- the context for (f x) is not totally uninteresting.
+
+
+-------------------
+canUpdateInPlace :: Type -> Bool
+-- Consider let x = <wurble> in ...
+-- If <wurble> returns an explicit constructor, we might be able
+-- to do update in place. So we treat even a thunk RHS context
+-- as interesting if update in place is possible. We approximate
+-- this by seeing if the type has a single constructor with a
+-- small arity. But arity zero isn't good -- we share the single copy
+-- for that case, so no point in sharing.
+
+-- Note the repType: we want to look through newtypes for this purpose
+
+canUpdateInPlace ty
+ | not opt_UF_UpdateInPlace = False
+ | otherwise
+ = case splitTyConApp_maybe (repType ty) of {
+ Nothing -> False ;
+ Just (tycon, _) ->
+
+ case tyConDataConsIfAvailable tycon of
+ [dc] -> arity == 1 || arity == 2
+ where
+ arity = dataConRepArity dc
+ other -> False
+ }
+\end{code}
+
+
+
+%************************************************************************
+%* *
+\section{Dealing with a single binder}
+%* *
+%************************************************************************
\begin{code}
simplBinders :: [InBinder] -> ([OutBinder] -> SimplM a) -> SimplM a
simplBinders bndrs thing_inside
- = getSwitchChecker `thenSmpl` \ sw_chkr ->
- getSimplBinderStuff `thenSmpl` \ stuff ->
+ = getSubst `thenSmpl` \ subst ->
let
- must_clone = switchIsOn sw_chkr SimplPleaseClone
- (stuff', bndrs') = mapAccumL (subst_binder must_clone) stuff bndrs
+ (subst', bndrs') = substBndrs subst bndrs
in
- setSimplBinderStuff stuff' $
- thing_inside bndrs'
+ seqBndrs bndrs' `seq`
+ setSubst subst' (thing_inside bndrs')
simplBinder :: InBinder -> (OutBinder -> SimplM a) -> SimplM a
simplBinder bndr thing_inside
- = getSwitchChecker `thenSmpl` \ sw_chkr ->
- getSimplBinderStuff `thenSmpl` \ stuff ->
+ = getSubst `thenSmpl` \ subst ->
let
- must_clone = switchIsOn sw_chkr SimplPleaseClone
- (stuff', bndr') = subst_binder must_clone stuff bndr
+ (subst', bndr') = substBndr subst bndr
in
- setSimplBinderStuff stuff' $
- thing_inside bndr'
+ seqBndr bndr' `seq`
+ setSubst subst' (thing_inside bndr')
+
-- Same semantics as simplBinders, but a little less
-- plumbing and hence a little more efficient.
-- Maybe not worth the candle?
simplIds :: [InBinder] -> ([OutBinder] -> SimplM a) -> SimplM a
simplIds ids thing_inside
- = getSwitchChecker `thenSmpl` \ sw_chkr ->
- getSimplBinderStuff `thenSmpl` \ (ty_subst, id_subst, in_scope, us) ->
+ = getSubst `thenSmpl` \ subst ->
let
- must_clone = switchIsOn sw_chkr SimplPleaseClone
- (id_subst', in_scope', us', ids') = substIds (simpl_clone_fn must_clone)
- ty_subst id_subst in_scope us ids
+ (subst', bndrs') = substIds subst ids
in
- setSimplBinderStuff (ty_subst, id_subst', in_scope', us') $
- thing_inside ids'
+ seqBndrs bndrs' `seq`
+ setSubst subst' (thing_inside bndrs')
-subst_binder must_clone (ty_subst, id_subst, in_scope, us) bndr
- | isTyVar bndr
- = case substTyVar ty_subst in_scope bndr of
- (ty_subst', in_scope', bndr') -> ((ty_subst', id_subst, in_scope', us), bndr')
+seqBndrs [] = ()
+seqBndrs (b:bs) = seqBndr b `seq` seqBndrs bs
- | otherwise
- = case substId (simpl_clone_fn must_clone) ty_subst id_subst in_scope us bndr of
- (id_subst', in_scope', us', bndr')
- -> ((ty_subst, id_subst', in_scope', us'), bndr')
-
-simpl_clone_fn must_clone in_scope us id
- | (must_clone && isLocalName (idName id))
- || id `elemVarSet` in_scope
- = case splitUniqSupply us of
- (us1, us2) -> Just (us1, setVarUnique id (uniqFromSupply us2))
-
- | otherwise
- = Nothing
+seqBndr b | isTyVar b = b `seq` ()
+ | otherwise = seqType (idType b) `seq`
+ idInfo b `seq`
+ ()
+\end{code}
+
+
+%************************************************************************
+%* *
+\subsection{Transform a RHS}
+%* *
+%************************************************************************
+
+Try (a) eta expansion
+ (b) type-lambda swizzling
+
+\begin{code}
+transformRhs :: OutExpr
+ -> (ArityInfo -> OutExpr -> SimplM (OutStuff a))
+ -> SimplM (OutStuff a)
+
+transformRhs rhs thing_inside
+ = tryRhsTyLam rhs $ \ rhs1 ->
+ tryEtaExpansion rhs1 thing_inside
\end{code}
This optimisation is CRUCIAL in eliminating the junk introduced by
desugaring mutually recursive definitions. Don't eliminate it lightly!
-So far as the implemtation is concerned:
+So far as the implementation is concerned:
Invariant: go F e = /\tvs -> F e
where
G = F . Let {xi = xi' tvs}
-\begin{code}
-mkRhsTyLam (Lam b e)
- | isTyVar b = case collectTyBinders e of
- (bs,body) -> mkRhsTyLam_help (b:bs) body
+[May 1999] If we do this transformation *regardless* then we can
+end up with some pretty silly stuff. For example,
+
+ let
+ st = /\ s -> let { x1=r1 ; x2=r2 } in ...
+ in ..
+becomes
+ let y1 = /\s -> r1
+ y2 = /\s -> r2
+ st = /\s -> ...[y1 s/x1, y2 s/x2]
+ in ..
+
+Unless the "..." is a WHNF there is really no point in doing this.
+Indeed it can make things worse. Suppose x1 is used strictly,
+and is of the form
+
+ x1* = case f y of { (a,b) -> e }
+
+If we abstract this wrt the tyvar we then can't do the case inline
+as we would normally do.
-mkRhsTyLam other_expr -- No-op if not a type lambda
- = returnSmpl other_expr
+\begin{code}
+tryRhsTyLam rhs thing_inside -- Only does something if there's a let
+ | null tyvars || not (worth_it body) -- inside a type lambda, and a WHNF inside that
+ = thing_inside rhs
+ | otherwise
+ = go (\x -> x) body $ \ body' ->
+ thing_inside (mkLams tyvars body')
-mkRhsTyLam_help tyvars body
- = go (\x -> x) body
where
- main_tyvar_set = mkVarSet tyvars
+ (tyvars, body) = collectTyBinders rhs
+
+ worth_it (Let _ e) = whnf_in_middle e
+ worth_it other = False
+ whnf_in_middle (Let _ e) = whnf_in_middle e
+ whnf_in_middle e = exprIsCheap e
+
+
+ go fn (Let bind@(NonRec var rhs) body) thing_inside
+ | exprIsTrivial rhs
+ = go (fn . Let bind) body thing_inside
- go fn (Let bind@(NonRec var rhs) body) | exprIsTrivial rhs
- = go (fn . Let bind) body
+ go fn (Let bind@(NonRec var rhs) body) thing_inside
+ = mk_poly tyvars_here var `thenSmpl` \ (var', rhs') ->
+ addAuxiliaryBind (NonRec var' (mkLams tyvars_here (fn rhs))) $
+ go (fn . Let (mk_silly_bind var rhs')) body thing_inside
- go fn (Let bind@(NonRec var rhs) body)
- = mk_poly tyvars_here var `thenSmpl` \ (var', rhs') ->
- go (fn . Let (mk_silly_bind var rhs')) body `thenSmpl` \ body' ->
- returnSmpl (Let (NonRec var' (mkLams tyvars_here (fn rhs))) body')
where
tyvars_here = tyvars
+ -- main_tyvar_set = mkVarSet tyvars
+ -- var_ty = idType var
-- varSetElems (main_tyvar_set `intersectVarSet` tyVarsOfType var_ty)
-- tyvars_here was an attempt to reduce the number of tyvars
-- wrt which the new binding is abstracted. But the naive
-- /\ a b -> let t :: (a,b) = (e1, e2)
-- x :: a = fst t
-- in ...
- -- Here, b isn't free in a's type, but we must nevertheless
+ -- Here, b isn't free in x's type, but we must nevertheless
-- abstract wrt b as well, because t's type mentions b.
-- Since t is floated too, we'd end up with the bogus:
-- poly_t = /\ a b -> (e1, e2)
-- abstracting wrt *all* the tyvars. We'll see if that
-- gives rise to problems. SLPJ June 98
- var_ty = idType var
-
- go fn (Let (Rec prs) body)
+ go fn (Let (Rec prs) body) thing_inside
= mapAndUnzipSmpl (mk_poly tyvars_here) vars `thenSmpl` \ (vars', rhss') ->
let
- gn body = fn $ foldr Let body (zipWith mk_silly_bind vars rhss')
+ gn body = fn (foldr Let body (zipWith mk_silly_bind vars rhss'))
in
- go gn body `thenSmpl` \ body' ->
- returnSmpl (Let (Rec (vars' `zip` [mkLams tyvars_here (gn rhs) | rhs <- rhss])) body')
+ addAuxiliaryBind (Rec (vars' `zip` [mkLams tyvars_here (gn rhs) | rhs <- rhss])) $
+ go gn body thing_inside
where
(vars,rhss) = unzip prs
tyvars_here = tyvars
-- varSetElems (main_tyvar_set `intersectVarSet` tyVarsOfTypes var_tys)
+ -- var_tys = map idType vars
-- See notes with tyvars_here above
- var_tys = map idType vars
- go fn body = returnSmpl (mkLams tyvars (fn body))
+ go fn body thing_inside = thing_inside (fn body)
mk_poly tyvars_here var
- = newId (mkForAllTys tyvars_here (idType var)) $ \ poly_id ->
+ = getUniqueSmpl `thenSmpl` \ uniq ->
let
- -- It's crucial to copy the inline-prag of the original var, because
- -- we're looking at occurrence-analysed but as yet unsimplified code!
- -- In particular, we mustn't lose the loop breakers.
+ poly_name = setNameUnique (idName var) uniq -- Keep same name
+ poly_ty = mkForAllTys tyvars_here (idType var) -- But new type of course
+ poly_id = mkVanillaId poly_name poly_ty
+
+ -- In the olden days, it was crucial to copy the occInfo of the original var,
+ -- because we were looking at occurrence-analysed but as yet unsimplified code!
+ -- In particular, we mustn't lose the loop breakers. BUT NOW we are looking
+ -- at already simplified code, so it doesn't matter
--
- -- *However* we don't want to retain a single-occurrence or dead-var info
- -- because we're adding a load of "silly bindings" of the form
- -- var _U_ = poly_var t1 t2
- -- with a must-inline pragma on the silly binding to prevent the
- -- poly-var from being inlined right back in. Since poly_var now
- -- occurs inside an INLINE binding, it should be given a ManyOcc,
- -- else it may get inlined unconditionally
- poly_inline_prag = case getInlinePragma var of
- ICanSafelyBeINLINEd _ _ -> NoInlinePragInfo
- IAmDead -> NoInlinePragInfo
- var_inline_prag -> var_inline_prag
-
- poly_id' = setInlinePragma poly_id poly_inline_prag
+ -- It's even right to retain single-occurrence or dead-var info:
+ -- Suppose we started with /\a -> let x = E in B
+ -- where x occurs once in B. Then we transform to:
+ -- let x' = /\a -> E in /\a -> let x* = x' a in B
+ -- where x* has an INLINE prag on it. Now, once x* is inlined,
+ -- the occurrences of x' will be just the occurrences originally
+ -- pinned on x.
in
- returnSmpl (poly_id', mkTyApps (Var poly_id') (mkTyVarTys tyvars_here))
+ returnSmpl (poly_id, mkTyApps (Var poly_id) (mkTyVarTys tyvars_here))
- mk_silly_bind var rhs = NonRec (setInlinePragma var IWantToBeINLINEd) rhs
- -- The addInlinePragma is really important! If we don't say
- -- INLINE on these silly little bindings then look what happens!
+ mk_silly_bind var rhs = NonRec var (Note InlineMe rhs)
-- Suppose we start with:
--
- -- x = let g = /\a -> \x -> f x x
- -- in
- -- /\ b -> let g* = g b in E
+ -- x = /\ a -> let g = G in E
+ --
+ -- Then we'll float to get
+ --
+ -- x = let poly_g = /\ a -> G
+ -- in /\ a -> let g = poly_g a in E
--
- -- Then: * the binding for g gets floated out
- -- * but then it gets inlined into the rhs of g*
- -- * then the binding for g* is floated out of the /\b
- -- * so we're back to square one
- -- The silly binding for g* must be INLINE, so that no inlining
- -- will happen in its RHS.
- -- PS: Jun 98: actually this isn't important any more;
- -- inlineUnconditionally will catch the type applicn
- -- and inline it unconditionally, without ever trying
- -- to simplify the RHS
+ -- But now the occurrence analyser will see just one occurrence
+ -- of poly_g, not inside a lambda, so the simplifier will
+ -- PreInlineUnconditionally poly_g back into g! Badk to square 1!
+ -- (I used to think that the "don't inline lone occurrences" stuff
+ -- would stop this happening, but since it's the *only* occurrence,
+ -- PreInlineUnconditionally kicks in first!)
+ --
+ -- Solution: put an INLINE note on g's RHS, so that poly_g seems
+ -- to appear many times. (NB: mkInlineMe eliminates
+ -- such notes on trivial RHSs, so do it manually.)
\end{code}
%************************************************************************
%* *
-\subsection{Eta reduction}
+\subsection{Eta expansion}
%* *
%************************************************************************
-@etaCoreExpr@ trys an eta reduction at the top level of a Core Expr.
+ Try eta expansion for RHSs
-e.g. \ x y -> f x y ===> f
+We go for:
+ Case 1 f = \x1..xn -> N ==> f = \x1..xn y1..ym -> N y1..ym
+ (n >= 0)
+ OR
+ Case 2 f = N E1..En ==> z1=E1
+ (n > 0) ..
+ zn=En
+ f = \y1..ym -> N z1..zn y1..ym
-It is used
- a) Before constructing an Unfolding, to
- try to make the unfolding smaller;
- b) In tidyCoreExpr, which is done just before converting to STG.
+where (in both cases)
-But we only do this if
- i) 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.
+ * The xi can include type variables
- ii) It exposes a simple variable or a type application; in short
- it exposes a "trivial" expression. (exprIsTrivial)
+ * The yi are all value variables
-\begin{code}
-etaCoreExpr :: CoreExpr -> CoreExpr
- -- ToDo: we should really check that we don't turn a non-bottom
- -- lambda into a bottom variable. Sigh
-
-etaCoreExpr expr@(Lam bndr body)
- | opt_DoEtaReduction
- = check (reverse binders) body
- where
- (binders, body) = collectBinders expr
+ * N is a NORMAL FORM (i.e. no redexes anywhere)
+ wanting a suitable number of extra args.
- check [] body
- | exprIsTrivial body && not (any (`elemVarSet` body_fvs) binders)
- = body -- Success!
- where
- body_fvs = exprFreeVars body
+ * the Ei must not have unlifted type
- check (b : bs) (App fun arg)
- | (varToCoreExpr b `cheapEqExpr` arg)
- = check bs fun
+There is no point in looking for a combination of the two, because
+that would leave use with some lets sandwiched between lambdas; that's
+what the final test in the first equation is for.
- check _ _ = expr -- Bale out
+\begin{code}
+tryEtaExpansion :: OutExpr
+ -> (ArityInfo -> OutExpr -> SimplM (OutStuff a))
+ -> SimplM (OutStuff a)
+tryEtaExpansion rhs thing_inside
+ | not opt_SimplDoLambdaEtaExpansion
+ || null y_tys -- No useful expansion
+ || not (is_case1 || is_case2) -- Neither case matches
+ = thing_inside final_arity rhs -- So, no eta expansion, but
+ -- return a good arity
+
+ | is_case1
+ = make_y_bndrs $ \ y_bndrs ->
+ thing_inside final_arity
+ (mkLams x_bndrs $ mkLams y_bndrs $
+ mkApps body (map Var y_bndrs))
+
+ | otherwise -- Must be case 2
+ = mapAndUnzipSmpl bind_z_arg arg_infos `thenSmpl` \ (maybe_z_binds, z_args) ->
+ addAuxiliaryBinds (catMaybes maybe_z_binds) $
+ make_y_bndrs $ \ y_bndrs ->
+ thing_inside final_arity
+ (mkLams y_bndrs $
+ mkApps (mkApps fun z_args) (map Var y_bndrs))
+ where
+ all_trivial_args = all is_trivial arg_infos
+ is_case1 = all_trivial_args
+ is_case2 = null x_bndrs && not (any unlifted_non_trivial arg_infos)
-etaCoreExpr expr = expr -- The common case
-\end{code}
-
+ (x_bndrs, body) = collectBinders rhs -- NB: x_bndrs can include type variables
+ x_arity = valBndrCount x_bndrs
-%************************************************************************
-%* *
-\subsection{Eta expansion}
-%* *
-%************************************************************************
+ (fun, args) = collectArgs body
+ arg_infos = [(arg, exprType arg, exprIsTrivial arg) | arg <- args]
-@etaExpandCount@ takes an expression, E, and returns an integer n,
-such that
+ is_trivial (_, _, triv) = triv
+ unlifted_non_trivial (_, ty, triv) = not triv && isUnLiftedType ty
- E ===> (\x1::t1 x1::t2 ... xn::tn -> E x1 x2 ... xn)
+ fun_arity = exprEtaExpandArity fun
-is a safe transformation. In particular, the transformation should
-not cause work to be duplicated, unless it is ``cheap'' (see
-@manifestlyCheap@ below).
+ final_arity | all_trivial_args = atLeastArity (x_arity + extra_args_wanted)
+ | otherwise = atLeastArity x_arity
+ -- Arity can be more than the number of lambdas
+ -- because of coerces. E.g. \x -> coerce t (\y -> e)
+ -- will have arity at least 2
+ -- The worker/wrapper pass will bring the coerce out to the top
-@etaExpandCount@ errs on the conservative side. It is always safe to
-return 0.
+ bind_z_arg (arg, arg_ty, trivial_arg)
+ | trivial_arg = returnSmpl (Nothing, arg)
+ | otherwise = newId SLIT("z") arg_ty $ \ z ->
+ returnSmpl (Just (NonRec z arg), Var z)
-An application of @error@ is special, because it can absorb as many
-arguments as you care to give it. For this special case we return
-100, to represent "infinity", which is a bit of a hack.
+ make_y_bndrs thing_inside
+ = ASSERT( not (exprIsTrivial rhs) )
+ newIds SLIT("y") y_tys $ \ y_bndrs ->
+ tick (EtaExpansion (head y_bndrs)) `thenSmpl_`
+ thing_inside y_bndrs
-\begin{code}
-etaExpandCount :: CoreExpr
- -> Int -- Number of extra args you can safely abstract
-
-etaExpandCount (Lam b body)
- | isId b
- = 1 + etaExpandCount body
-
-etaExpandCount (Let bind body)
- | all exprIsCheap (rhssOfBind bind)
- = etaExpandCount body
-
-etaExpandCount (Case scrut _ alts)
- | exprIsCheap scrut
- = minimum [etaExpandCount rhs | (_,_,rhs) <- alts]
-
-etaExpandCount fun@(Var _) = eta_fun fun
-
-etaExpandCount (App fun (Type ty))
- = eta_fun fun
-etaExpandCount (App fun arg)
- | exprIsCheap arg = case etaExpandCount fun of
- 0 -> 0
- n -> n-1 -- Knock off one
-
-etaExpandCount other = 0 -- Give up
- -- Lit, Con, Prim,
- -- non-val Lam,
- -- Scc (pessimistic; ToDo),
- -- Let with non-whnf rhs(s),
- -- Case with non-whnf scrutinee
-
------------------------------
-eta_fun :: CoreExpr -- The function
- -> Int -- How many args it can safely be applied to
-
-eta_fun (App fun (Type ty)) = eta_fun fun
-eta_fun (Var v) = arityLowerBound (getIdArity v)
-eta_fun other = 0 -- Give up
+ (potential_extra_arg_tys, _) = splitFunTys (exprType body)
+
+ y_tys :: [InType]
+ y_tys = take extra_args_wanted potential_extra_arg_tys
+
+ extra_args_wanted :: Int -- Number of extra args we want
+ extra_args_wanted = 0 `max` (fun_arity - valArgCount args)
+
+ -- We used to expand the arity to the previous arity fo the
+ -- function; but this is pretty dangerous. Consdier
+ -- f = \xy -> e
+ -- so that f has arity 2. Now float something into f's RHS:
+ -- f = let z = BIG in \xy -> e
+ -- The last thing we want to do now is to put some lambdas
+ -- outside, to get
+ -- f = \xy -> let z = BIG in e
+ --
+ -- (bndr_arity - no_of_xs) `max`
\end{code}
%************************************************************************
\begin{code}
-mkCase :: SwitchChecker -> OutExpr -> OutId -> [OutAlt] -> SimplM OutExpr
+mkCase :: OutExpr -> OutId -> [OutAlt] -> SimplM OutExpr
\end{code}
@mkCase@ tries the following transformation (if possible):
variable is scrutinised multiple times.
\begin{code}
-mkCase sw_chkr scrut outer_bndr outer_alts
- | switchIsOn sw_chkr SimplCaseMerge
+mkCase scrut outer_bndr outer_alts
+ | opt_SimplCaseMerge
&& maybeToBool maybe_case_in_default
- = tick CaseMerge `thenSmpl_`
+ = tick (CaseMerge outer_bndr) `thenSmpl_`
returnSmpl (Case scrut outer_bndr new_alts)
-- Warning: don't call mkCase recursively!
-- Firstly, there's no point, because inner alts have already had
and similar friends.
\begin{code}
-mkCase sw_chkr scrut case_bndr alts
+mkCase scrut case_bndr alts
| all identity_alt alts
- = tick CaseIdentity `thenSmpl_`
+ = tick (CaseIdentity case_bndr) `thenSmpl_`
returnSmpl scrut
where
- identity_alt (DEFAULT, [], Var v) = v == case_bndr
- identity_alt (con, args, Con con' args') = con == con' &&
- and (zipWithEqual "mkCase"
- cheapEqExpr
- (map Type arg_tys ++ map varToCoreExpr args)
- args')
- identity_alt other = False
+ identity_alt (DEFAULT, [], Var v) = v == case_bndr
+ identity_alt (DataAlt con, args, rhs) = cheapEqExpr rhs
+ (mkConApp con (map Type arg_tys ++ map varToCoreExpr args))
+ identity_alt other = False
arg_tys = case splitTyConApp_maybe (idType case_bndr) of
Just (tycon, arg_tys) -> arg_tys
The catch-all case
\begin{code}
-mkCase sw_chkr other_scrut case_bndr other_alts
+mkCase other_scrut case_bndr other_alts
= returnSmpl (Case other_scrut case_bndr other_alts)
\end{code}
findDefault (alt : alts) = case findDefault alts of
(alts', deflt) -> (alt : alts', deflt)
-findAlt :: Con -> [CoreAlt] -> CoreAlt
+findAlt :: AltCon -> [CoreAlt] -> CoreAlt
findAlt con alts
= go alts
where
projects / ghc-hetmet.git / blobdiff