\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,
- countValArgs, countArgs,
+ countValArgs, countArgs, mkRhsStop, mkStop,
getContArgs, interestingCallContext, interestingArg, isStrictType, discardInline
) where
#include "HsVersions.h"
import CmdLineOpts ( switchIsOn, SimplifierSwitch(..),
- opt_SimplDoLambdaEtaExpansion, opt_SimplCaseMerge, opt_DictsStrict
+ opt_SimplDoLambdaEtaExpansion, opt_SimplCaseMerge, opt_DictsStrict,
+ opt_UF_UpdateInPlace
)
import CoreSyn
-import CoreUnfold ( isValueUnfolding )
-import CoreUtils ( exprIsTrivial, cheapEqExpr, exprType, exprIsCheap, exprEtaExpandArity, bindNonRec )
-import Subst ( InScopeSet, mkSubst, substBndrs, substBndr, substIds, lookupIdSubst )
-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(..), arityLowerBound, setOccInfo, vanillaIdInfo )
+import Subst ( InScopeSet, mkSubst, substExpr )
+import qualified Subst ( simplBndrs, simplBndr, simplLetId )
+import Id ( idType, idName,
+ idUnfolding, idStrictness,
+ mkLocalId, idInfo
+ )
+import IdInfo ( StrictnessInfo(..) )
import Maybes ( maybeToBool, catMaybes )
-import Name ( isLocalName, setNameUnique )
-import Demand ( Demand, isStrict, wwLazy, wwLazy )
+import Name ( setNameUnique )
+import Demand ( isStrict )
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, repType,
+ splitTyConApp_maybe, tyConAppArgs, mkTyVarTys,
+ isDictTy, isDataType, isUnLiftedType,
splitRepFunTys
)
import TyCon ( tyConDataConsIfAvailable )
import DataCon ( dataConRepArity )
-import VarSet
-import VarEnv ( SubstEnv, SubstResult(..) )
-import Util ( lengthExceeds )
+import VarEnv ( SubstEnv )
+import Util ( lengthExceeds, mapAccumL )
import Outputable
\end{code}
\begin{code}
data SimplCont -- Strict contexts
- = Stop OutType -- Type of the result
+ = 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
-- The result expression in the OutExprStuff has type cont_ty
instance Outputable SimplCont where
- ppr (Stop _) = ptext SLIT("Stop")
+ ppr (Stop _ _) = ptext SLIT("Stop")
ppr (ApplyTo dup arg se cont) = (ptext SLIT("ApplyTo") <+> ppr dup <+> ppr arg) $$ ppr cont
ppr (ArgOf dup _ _) = ptext SLIT("ArgOf...") <+> ppr dup
ppr (Select dup bndr alts se cont) = (ptext SLIT("Select") <+> ppr dup <+> ppr bndr) $$
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 (Stop _ _) = True
contIsDupable (ApplyTo OkToDup _ _ _) = True
contIsDupable (ArgOf OkToDup _ _) = True
contIsDupable (Select OkToDup _ _ _ _) = True
-------------------
discardableCont :: SimplCont -> Bool
-discardableCont (Stop _) = False
+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 (Stop to_ty) = Stop to_ty
-discardCont cont = CoerceIt to_ty (Stop to_ty)
- where
- to_ty = contResultType cont
+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 (Stop to_ty _) = to_ty
contResultType (ArgOf _ to_ty _) = to_ty
contResultType (ApplyTo _ _ _ cont) = contResultType cont
contResultType (CoerceIt _ cont) = contResultType cont
-- (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 arg
+ = 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)
- = case lookupIdSubst (mkSubst in_scope subst) v of
- DoneId v' _ -> hasSomeUnfolding (idUnfolding v')
- -- was: isValueUnfolding (idUnfolding v')
- -- But that seems over-pessimistic
-
- other -> True -- was: False
- -- But that is *definitely* too pessimistic.
- -- E.g. let x = 3 in f
- -- Here, x will be unconditionally substituted, via
- -- the substitution!
+ 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
-- 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).
- -- Why not? At least in the case-scrutinee situation, turning
- -- case x of y -> ...
+ -- 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 y = (a,b) in ...
+ -- 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
-- 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 isn't a lone variable. Consider
+ -- 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 as
- -- "lone". The motivating example was
+ -- 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
interestingCallContext some_args some_val_args cont
= interesting cont
where
- interesting (InlinePlease _) = True
- interesting (ApplyTo _ _ _ _) = some_args -- Can happen if we have (coerce t (f x)) y
- interesting (Select _ _ _ _ _) = some_args
- interesting (ArgOf _ _ _) = some_val_args
- interesting (Stop ty) = some_val_args && canUpdateInPlace ty
- interesting (CoerceIt _ cont) = interesting cont
+ interesting (InlinePlease _) = True
+ interesting (Select _ _ _ _ _) = some_args
+ 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
-- 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.
-- Note the repType: we want to look through newtypes for this purpose
-canUpdateInPlace ty = case splitTyConApp_maybe (repType ty) of {
+canUpdateInPlace ty
+ | not opt_UF_UpdateInPlace = False
+ | otherwise
+ = case splitTyConApp_maybe (repType ty) of {
Nothing -> False ;
Just (tycon, _) ->
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 :: InExpr -> SimplM InExpr
-transformRhs rhs
- = tryEtaExpansion body `thenSmpl` \ body' ->
- mkRhsTyLam tyvars body'
- where
- (tyvars, body) = collectTyBinders rhs
-\end{code}
-
-
-%************************************************************************
-%* *
\subsection{Local tyvar-lifting}
%* *
%************************************************************************
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
\begin{code}
-mkRhsTyLam tyvars body -- Only does something if there's a let
- | null tyvars || not (worth_it body) -- inside a type lambda, and a WHNF inside that
- = returnSmpl (mkLams tyvars body)
+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
+ = go (\x -> x) body `thenSmpl` \ (binds, body') ->
+ returnSmpl (binds, mkLams tyvars body')
+
where
- worth_it (Let _ e) = whnf_in_middle e
- worth_it other = False
+ (tyvars, body) = collectTyBinders rhs
+
+ 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) | exprIsTrivial rhs
+ go fn (Let bind@(NonRec var rhs) body)
+ | exprIsTrivial rhs
= go (fn . Let bind) body
- go fn (Let bind@(NonRec var rhs) body)
+ 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` \ body' ->
- returnSmpl (Let (NonRec var' (mkLams tyvars_here (fn rhs))) body')
+ 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
-- main_tyvar_set = mkVarSet tyvars
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
- go gn body `thenSmpl` \ body' ->
- returnSmpl (Let (Rec (vars' `zip` [mkLams tyvars_here (gn rhs) | rhs <- rhss])) body')
+ 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 = returnSmpl (mkLams tyvars (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 = mkLocalId poly_name poly_ty
- -- It's crucial to copy the occInfo 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.
+ -- 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
--
-- It's even right to retain single-occurrence or dead-var info:
-- Suppose we started with /\a -> let x = E 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.
- poly_info = vanillaIdInfo `setOccInfo` idOccInfo var
-
- poly_id = mkId poly_name poly_ty poly_info
in
returnSmpl (poly_id, mkTyApps (Var poly_id) (mkTyVarTys tyvars_here))
- mk_silly_bind var rhs = NonRec var rhs
- -- We need to be careful about inlining.
+ 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, and there's
- -- a danger of making the simplifier loop here.
+ -- 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}
Try eta expansion for RHSs
We go for:
- \x1..xn -> N ==> \x1..xn y1..ym -> N y1..ym
- AND
- N E1..En ==> let z1=E1 .. zn=En in \y1..ym -> N z1..zn y1..ym
+ 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
+
+where (in both cases)
+
+ * The xi can include type variables
-where (in both cases) N is a NORMAL FORM (i.e. no redexes anywhere)
-wanting a suitable number of extra args.
+ * The yi are all value variables
-NB: the Ei may have unlifted type, but the simplifier (which is applied
-to the result) deals OK with this.
+ * N is a NORMAL FORM (i.e. no redexes anywhere)
+ wanting a suitable number of extra args.
-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.
+ * the Ei must not have unlifted type
+
+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.
+
+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.
\begin{code}
-tryEtaExpansion :: InExpr -> SimplM InExpr
-tryEtaExpansion rhs
- | not opt_SimplDoLambdaEtaExpansion
- || exprIsTrivial rhs -- Don't eta-expand a trival RHS
- || null y_tys -- No useful expansion
- || not (null x_bndrs || and trivial_args) -- Not (no x-binders or no z-binds)
- = returnSmpl rhs
-
- | otherwise -- Consider eta expansion
- = newIds SLIT("y") y_tys $ ( \ y_bndrs ->
- tick (EtaExpansion (head y_bndrs)) `thenSmpl_`
- mapAndUnzipSmpl bind_z_arg (args `zip` trivial_args) `thenSmpl` (\ (maybe_z_binds, z_args) ->
- returnSmpl (mkLams x_bndrs $
- mkLets (catMaybes maybe_z_binds) $
- mkLams y_bndrs $
- mkApps (mkApps fun z_args) (map Var y_bndrs))))
- where
- (x_bndrs, body) = collectValBinders rhs
- (fun, args) = collectArgs body
- trivial_args = map exprIsTrivial args
- fun_arity = exprEtaExpandArity fun
+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)
- bind_z_arg (arg, trivial_arg)
+ | 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") (exprType arg) $ \ z ->
+ | otherwise = newId SLIT("z") arg_ty $ \ z ->
returnSmpl (Just (NonRec z arg), Var z)
-
- -- Note: I used to try to avoid the exprType call by using
- -- the type of the binder. But this type doesn't necessarily
- -- belong to the same substitution environment as this rhs;
- -- and we are going to make extra term binders (y_bndrs) from the type
- -- which will be processed with the rhs substitution environment.
- -- This only went wrong in a mind bendingly complicated case.
- (potential_extra_arg_tys, _) = splitFunTys (exprType body)
-
- y_tys :: [InType]
- y_tys = take no_extras_wanted potential_extra_arg_tys
-
- no_extras_wanted :: Int
- no_extras_wanted = 0 `max`
-
- -- 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`
-
- -- See if the body could obviously do with more args
- (fun_arity - valArgCount args)
-
--- This case is now deal with by exprEtaExpandArity
- -- Finally, see if it's a state transformer, and xs is non-null
- -- (so it's also a function not a thunk) in which
- -- case we eta-expand on principle! This can waste work,
- -- but usually doesn't.
- -- I originally checked for a singleton type [ty] in this case
- -- but then I found a situation in which I had
- -- \ x -> let {..} in \ s -> f (...) s
- -- AND f RETURNED A FUNCTION. That is, 's' wasn't the only
- -- potential extra arg.
--- case (x_bndrs, potential_extra_arg_tys) of
--- (_:_, ty:_) -> case splitTyConApp_maybe ty of
--- Just (tycon,_) | tycon == statePrimTyCon -> 1
--- other -> 0
--- other -> 0
\end{code}
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
\end{code}
-\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
-
- matches (DEFAULT, _, _) = True
- matches (con1, _, _) = con == con1
-\end{code}
projects / ghc-hetmet.git / blobdiff