\begin{code}
module SimplUtils (
- simplBinder, simplBinders, simplIds,
- transformRhs,
- mkCase, findAlt, findDefault,
+ simplBinder, simplBinders, simplRecIds, simplLetId,
+ tryRhsTyLam, tryEtaExpansion,
+ mkCase,
-- The continuation type
SimplCont(..), DupFlag(..), contIsDupable, contResultType,
#include "HsVersions.h"
import CmdLineOpts ( switchIsOn, SimplifierSwitch(..),
- opt_SimplDoLambdaEtaExpansion, opt_SimplCaseMerge, opt_DictsStrict,
+ opt_SimplDoLambdaEtaExpansion, opt_SimplCaseMerge,
opt_UF_UpdateInPlace
)
import CoreSyn
-import CoreUnfold ( isValueUnfolding )
-import CoreUtils ( exprIsTrivial, cheapEqExpr, exprType, exprIsCheap, exprEtaExpandArity, bindNonRec )
-import Subst ( InScopeSet, mkSubst, substBndrs, substBndr, substIds, substExpr )
-import Id ( Id, idType, isId, idName,
- idOccInfo, idUnfolding, idStrictness,
- mkId, idInfo
+import CoreUtils ( exprIsTrivial, cheapEqExpr, exprType, exprIsCheap,
+ etaExpand, exprEtaExpandArity, bindNonRec, mkCoerce,
+ findDefault
)
-import IdInfo ( StrictnessInfo(..), ArityInfo, atLeastArity, setOccInfo, vanillaIdInfo )
+import Subst ( InScopeSet, mkSubst, substExpr )
+import qualified Subst ( simplBndrs, simplBndr, simplLetId )
+import Id ( idType, idName,
+ idUnfolding, idNewStrictness,
+ mkLocalId, idInfo
+ )
+import IdInfo ( StrictnessInfo(..) )
import Maybes ( maybeToBool, catMaybes )
-import Name ( isLocalName, setNameUnique )
-import Demand ( Demand, isStrict, wwLazy, wwLazy )
+import Name ( setNameUnique )
+import NewDemand ( isStrictDmd, isBotRes, splitStrictSig )
import SimplMonad
-import Type ( Type, tyVarsOfType, tyVarsOfTypes, mkForAllTys, seqType, repType,
- splitTyConApp_maybe, mkTyVarTys, applyTys, splitFunTys, mkFunTys,
- isDictTy, isDataType, applyTy, splitFunTy, isUnLiftedType,
+import Type ( Type, mkForAllTys, seqType,
+ splitTyConApp_maybe, tyConAppArgs, mkTyVarTys,
+ isUnLiftedType,
splitRepFunTys
)
+import TcType ( isStrictType )
import TyCon ( tyConDataConsIfAvailable )
import DataCon ( dataConRepArity )
-import VarSet
-import VarEnv ( SubstEnv, SubstResult(..) )
-import Util ( lengthExceeds )
-import BasicTypes ( Arity )
+import VarEnv ( SubstEnv )
+import Util ( lengthExceeds, mapAccumL )
import Outputable
\end{code}
-- 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
+ = case splitStrictSig (idNewStrictness fun) of
+ (demands, result_info)
| not (demands `lengthExceeds` countValArgs orig_cont)
-> -- Enough args, use the strictness given.
-- For bottoming functions we used to pretend that the arg
-- 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
+ if isBotRes result_info then
+ map isStrictDmd demands -- Finite => result is bottom
else
- map isStrict demands ++ vanilla_stricts
+ map isStrictDmd 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
where
interesting (InlinePlease _) = True
interesting (Select _ _ _ _ _) = some_args
- interesting (ApplyTo _ _ _ _) = some_args -- Can happen if we have (coerce t (f x)) y
+ interesting (ApplyTo _ _ _ _) = True -- Can happen if we have (coerce t (f x)) y
+ -- Perhaps True is a bit over-keen, but I've
+ -- seen (coerce f) x, where f has an INLINE prag,
+ -- So we have to give some motivaiton for inlining it
interesting (ArgOf _ _ _) = some_val_args
interesting (Stop ty upd_in_place) = some_val_args && upd_in_place
interesting (CoerceIt _ cont) = interesting cont
-- 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
- }
+ = case splitTyConApp_maybe ty of
+ Nothing -> False
+ Just (tycon, _) -> case tyConDataConsIfAvailable tycon of
+ [dc] -> arity == 1 || arity == 2
+ where
+ arity = dataConRepArity dc
+ other -> False
\end{code}
simplBinders bndrs thing_inside
= getSubst `thenSmpl` \ subst ->
let
- (subst', bndrs') = substBndrs subst bndrs
+ (subst', bndrs') = Subst.simplBndrs subst bndrs
in
seqBndrs bndrs' `seq`
setSubst subst' (thing_inside bndrs')
simplBinder bndr thing_inside
= getSubst `thenSmpl` \ subst ->
let
- (subst', bndr') = substBndr subst bndr
+ (subst', bndr') = Subst.simplBndr subst bndr
in
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
+simplRecIds :: [InBinder] -> ([OutBinder] -> SimplM a) -> SimplM a
+simplRecIds ids thing_inside
= getSubst `thenSmpl` \ subst ->
let
- (subst', bndrs') = substIds subst ids
+ (subst', ids') = mapAccumL Subst.simplLetId subst ids
in
- seqBndrs bndrs' `seq`
- setSubst subst' (thing_inside bndrs')
+ seqBndrs ids' `seq`
+ setSubst subst' (thing_inside ids')
+
+simplLetId :: InBinder -> (OutBinder -> SimplM a) -> SimplM a
+simplLetId id thing_inside
+ = getSubst `thenSmpl` \ subst ->
+ let
+ (subst', id') = Subst.simplLetId subst id
+ in
+ seqBndr id' `seq`
+ setSubst subst' (thing_inside id')
seqBndrs [] = ()
seqBndrs (b:bs) = seqBndr b `seq` seqBndrs bs
%************************************************************************
%* *
-\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}
-
-
-%************************************************************************
-%* *
\subsection{Local tyvar-lifting}
%* *
%************************************************************************
\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
+tryRhsTyLam :: OutExpr -> SimplM ([OutBind], OutExpr)
+
+tryRhsTyLam rhs -- Only does something if there's a let
+ | null tyvars || not (worth_it body) -- inside a type lambda,
+ = returnSmpl ([], rhs) -- and a WHNF inside that
+
| otherwise
- = go (\x -> x) body $ \ body' ->
- thing_inside (mkLams tyvars body')
+ = go (\x -> x) body `thenSmpl` \ (binds, body') ->
+ returnSmpl (binds, mkLams tyvars body')
where
(tyvars, body) = collectTyBinders rhs
- worth_it (Let _ e) = whnf_in_middle e
- worth_it other = False
+ worth_it e@(Let _ _) = whnf_in_middle e
+ worth_it e = False
+
+ whnf_in_middle (Let (NonRec x rhs) e) | isUnLiftedType (idType x) = 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
+ go fn (Let bind@(NonRec var rhs) body)
| exprIsTrivial rhs
- = go (fn . Let bind) body thing_inside
+ = 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 (NonRec var rhs) body)
+ = mk_poly tyvars_here var `thenSmpl` \ (var', rhs') ->
+ go (fn . Let (mk_silly_bind var rhs')) body `thenSmpl` \ (binds, body') ->
+ returnSmpl (NonRec var' (mkLams tyvars_here (fn rhs)) : binds, body')
where
tyvars_here = tyvars
-- abstracting wrt *all* the tyvars. We'll see if that
-- gives rise to problems. SLPJ June 98
- go fn (Let (Rec prs) body) thing_inside
+ go fn (Let (Rec prs) body)
= 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'))
+ new_bind = Rec (vars' `zip` [mkLams tyvars_here (gn rhs) | rhs <- rhss])
in
- addAuxiliaryBind (Rec (vars' `zip` [mkLams tyvars_here (gn rhs) | rhs <- rhss])) $
- go gn body thing_inside
+ go gn body `thenSmpl` \ (binds, body') ->
+ returnSmpl (new_bind : binds, body')
where
(vars,rhss) = unzip prs
tyvars_here = tyvars
-- var_tys = map idType vars
-- See notes with tyvars_here above
-
- go fn body thing_inside = thing_inside (fn body)
+ go fn body = returnSmpl ([], fn body)
mk_poly tyvars_here var
= getUniqueSmpl `thenSmpl` \ uniq ->
let
poly_name = setNameUnique (idName var) uniq -- Keep same name
poly_ty = mkForAllTys tyvars_here (idType var) -- But new type of course
- poly_id = mkId poly_name poly_ty vanillaIdInfo
+ poly_id = mkLocalId 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!
-- 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.
- -- poly_info = vanillaIdInfo `setOccInfo` idOccInfo var
in
returnSmpl (poly_id, mkTyApps (Var poly_id) (mkTyVarTys tyvars_here))
- mk_silly_bind var rhs = NonRec var rhs
+ 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 MIGHT get inlined into the rhs of g*
- -- * then the binding for g* is floated out of the /\b
- -- * so we're back to square one
- -- We rely on the simplifier not to inline g into the RHS of g*,
- -- because it's a "lone" occurrence, and there is no benefit in
- -- inlining. But it's a slightly delicate property; hence this comment
+ -- 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}
that would leave use with some lets sandwiched between lambdas; that's
what the final test in the first equation is for.
-\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)
-
- (x_bndrs, body) = collectBinders rhs -- NB: x_bndrs can include type variables
- x_arity = valBndrCount x_bndrs
+In Case 1, we may have to sandwich some coerces between the lambdas
+to make the types work. exprEtaExpandArity looks through coerces
+when computing arity; and etaExpand adds the coerces as necessary when
+actually computing the expansion.
- (fun, args) = collectArgs body
- arg_infos = [(arg, exprType arg, exprIsTrivial arg) | arg <- args]
-
- is_trivial (_, _, triv) = triv
- unlifted_non_trivial (_, ty, triv) = not triv && isUnLiftedType ty
-
- fun_arity = exprEtaExpandArity fun
+\begin{code}
+tryEtaExpansion :: OutExpr -> OutType -> SimplM ([OutBind], OutExpr)
+tryEtaExpansion rhs rhs_ty
+ | not opt_SimplDoLambdaEtaExpansion -- Not if switched off
+ || exprIsTrivial rhs -- Not if RHS is trivial
+ || final_arity == 0 -- Not if arity is zero
+ = returnSmpl ([], rhs)
+
+ | n_val_args == 0 && not arity_is_manifest
+ = -- Some lambdas but not enough: case 1
+ getUniqSupplySmpl `thenSmpl` \ us ->
+ returnSmpl ([], etaExpand final_arity us rhs rhs_ty)
+
+ | n_val_args > 0 && not (any cant_bind arg_infos)
+ = -- Partial application: case 2
+ mapAndUnzipSmpl bind_z_arg arg_infos `thenSmpl` \ (maybe_z_binds, z_args) ->
+ getUniqSupplySmpl `thenSmpl` \ us ->
+ returnSmpl (catMaybes maybe_z_binds,
+ etaExpand final_arity us (mkApps fun z_args) rhs_ty)
- 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
+ | otherwise
+ = returnSmpl ([], rhs)
+ where
+ (fun, args) = collectArgs rhs
+ n_val_args = valArgCount args
+ (fun_arity, arity_is_manifest) = exprEtaExpandArity fun
+ final_arity = 0 `max` (fun_arity - n_val_args)
+ arg_infos = [(arg, exprType arg, exprIsTrivial arg) | arg <- args]
+ cant_bind (_, ty, triv) = not triv && isUnLiftedType ty
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)
-
- 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
-
- (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}
-- Secondly, if you do, you get an infinite loop, because the bindNonRec
-- in munge_rhs puts a case into the DEFAULT branch!
where
- new_alts = outer_alts_without_deflt ++ munged_inner_alts
+ new_alts = add_default maybe_inner_default
+ (outer_alts_without_deflt ++ inner_con_alts)
+
maybe_case_in_default = case findDefault outer_alts of
(outer_alts_without_default,
Just (Case (Var scrut_var) inner_bndr inner_alts))
-
| outer_bndr == scrut_var
-> Just (outer_alts_without_default, inner_bndr, inner_alts)
other -> Nothing
not (con `elem` outer_cons) -- Eliminate shadowed inner alts
]
munge_rhs rhs = bindNonRec inner_bndr (Var outer_bndr) rhs
+
+ (inner_con_alts, maybe_inner_default) = findDefault munged_inner_alts
+
+ add_default (Just rhs) alts = (DEFAULT,[],rhs) : alts
+ add_default Nothing alts = alts
\end{code}
Now the identity-case transformation:
case e of ===> e
- True -> True;
+ True -> True;
False -> False
and similar friends.
mkCase scrut case_bndr alts
| all identity_alt alts
= tick (CaseIdentity case_bndr) `thenSmpl_`
- returnSmpl scrut
+ returnSmpl (re_note scrut)
where
- 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
+ identity_alt (con, args, rhs) = de_note rhs `cheapEqExpr` identity_rhs con args
+
+ identity_rhs (DataAlt con) args = mkConApp con (arg_tys ++ map varToCoreExpr args)
+ identity_rhs (LitAlt lit) _ = Lit lit
+ identity_rhs DEFAULT _ = Var case_bndr
+
+ arg_tys = map Type (tyConAppArgs (idType case_bndr))
+
+ -- We've seen this:
+ -- case coerce T e of x { _ -> coerce T' x }
+ -- And we definitely want to eliminate this case!
+ -- So we throw away notes from the RHS, and reconstruct
+ -- (at least an approximation) at the other end
+ de_note (Note _ e) = de_note e
+ de_note e = e
+
+ -- re_note wraps a coerce if it might be necessary
+ re_note scrut = case head alts of
+ (_,_,rhs1@(Note _ _)) -> mkCoerce (exprType rhs1) (idType case_bndr) scrut
+ other -> scrut
\end{code}
-The catch-all case
+The catch-all case. We do a final transformation that I've
+occasionally seen making a big difference:
-\begin{code}
-mkCase other_scrut case_bndr other_alts
- = returnSmpl (Case other_scrut case_bndr other_alts)
-\end{code}
+ case e of =====> case e of
+ C _ -> f x D v -> ....v....
+ D v -> ....v.... DEFAULT -> f x
+ DEFAULT -> f x
+The point is that we merge common RHSs, at least for the DEFAULT case.
+[One could do something more elaborate but I've never seen it needed.]
+The case where this came up was like this (lib/std/PrelCError.lhs):
-\begin{code}
-findDefault :: [CoreAlt] -> ([CoreAlt], Maybe CoreExpr)
-findDefault [] = ([], Nothing)
-findDefault ((DEFAULT,args,rhs) : alts) = ASSERT( null alts && null args )
- ([], Just rhs)
-findDefault (alt : alts) = case findDefault alts of
- (alts', deflt) -> (alt : alts', deflt)
-
-findAlt :: AltCon -> [CoreAlt] -> CoreAlt
-findAlt con alts
- = go alts
- where
- go [] = pprPanic "Missing alternative" (ppr con $$ vcat (map ppr alts))
- go (alt : alts) | matches alt = alt
- | otherwise = go alts
+ x | p `is` 1 -> e1
+ | p `is` 2 -> e2
+ ...etc...
+
+where @is@ was something like
+
+ p `is` n = p /= (-1) && p == n
+
+This gave rise to a horrible sequence of cases
- matches (DEFAULT, _, _) = True
- matches (con1, _, _) = con == con1
+ case p of
+ (-1) -> $j p
+ 1 -> e1
+ DEFAULT -> $j p
+
+and similarly in cascade for all the join points!
+
+\begin{code}
+mkCase other_scrut case_bndr other_alts
+ = returnSmpl (Case other_scrut case_bndr (mergeDefault other_alts))
+
+mergeDefault (deflt_alt@(DEFAULT,_,deflt_rhs) : con_alts)
+ = deflt_alt : [alt | alt@(con,_,rhs) <- con_alts, not (rhs `cheapEqExpr` deflt_rhs)]
+ -- NB: we can neglect the binders because we won't get equality if the
+ -- binders are mentioned in rhs (no shadowing)
+mergeDefault other_alts
+ = other_alts
\end{code}
projects / ghc-hetmet.git / blobdiff