\begin{code}
module SimplUtils (
simplBinder, simplBinders, simplIds,
- mkRhsTyLam,
+ transformRhs,
etaCoreExpr,
- etaExpandCount,
- mkCase, findAlt, findDefault
+ mkCase, findAlt, findDefault,
+ mkCoerce
) where
#include "HsVersions.h"
import BinderInfo
-import CmdLineOpts ( opt_DoEtaReduction, switchIsOn, SimplifierSwitch(..) )
+import CmdLineOpts ( opt_SimplDoLambdaEtaExpansion, opt_SimplCaseMerge )
import CoreSyn
-import CoreUtils ( exprIsCheap, exprIsTrivial, exprFreeVars, cheapEqExpr,
- FormSummary(..),
- substId, substIds
+import CoreFVs ( exprFreeVars )
+import CoreUtils ( exprIsCheap, exprIsTrivial, cheapEqExpr, coreExprType,
+ exprIsWHNF, FormSummary(..)
)
+import Subst ( substBndrs, substBndr, substIds )
import Id ( Id, idType, getIdArity, isId, idName,
getInlinePragma, setInlinePragma,
- getIdDemandInfo
+ getIdDemandInfo, mkId
)
-import IdInfo ( arityLowerBound, InlinePragInfo(..) )
-import Maybes ( maybeToBool )
+import IdInfo ( arityLowerBound, InlinePragInfo(..), setInlinePragInfo, vanillaIdInfo )
+import Maybes ( maybeToBool, catMaybes )
import Const ( Con(..) )
-import Name ( isLocalName )
+import Name ( isLocalName, setNameUnique )
import SimplMonad
import Type ( Type, tyVarsOfType, tyVarsOfTypes, mkForAllTys,
- splitTyConApp_maybe, substTyVar, mkTyVarTys
+ splitTyConApp_maybe, mkTyVarTys, applyTys, splitFunTys, mkFunTys
)
+import TysPrim ( statePrimTyCon )
import Var ( setVarUnique )
import VarSet
import UniqSupply ( splitUniqSupply, uniqFromSupply )
%* *
%************************************************************************
-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}
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' $
+ 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' $
+ 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'
+ setSubst subst' $
+ thing_inside bndrs'
+\end{code}
-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')
- | 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
+%************************************************************************
+%* *
+\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}
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,
-mkRhsTyLam other_expr -- No-op if not a type lambda
- = returnSmpl other_expr
+ 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
-mkRhsTyLam_help tyvars body
+ 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.
+
+
+\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)
+ | otherwise
= go (\x -> x) body
where
+ 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 = exprIsWHNF e
+
main_tyvar_set = mkVarSet tyvars
go fn (Let bind@(NonRec var rhs) body) | exprIsTrivial rhs
-- /\ 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)
go fn body = returnSmpl (mkLams tyvars (fn body))
mk_poly tyvars_here var
- = newId (mkForAllTys tyvars_here (idType var)) $ \ poly_id ->
+ = 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
+
-- 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.
--
- -- *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 E. 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 originaly
+ -- pinned on x.
+ poly_info = vanillaIdInfo `setInlinePragInfo` getInlinePragma var
+
+ poly_id = mkId poly_name poly_ty poly_info
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
+ mk_silly_bind var rhs = NonRec (setInlinePragma var IMustBeINLINEd) rhs
-- The addInlinePragma is really important! If we don't say
-- INLINE on these silly little bindings then look what happens!
-- Suppose we start with:
-- * 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
+ -- The silly binding for g* must be IMustBeINLINEs, so that
+ -- we simply substitute for g* throughout.
+\end{code}
+
+
+%************************************************************************
+%* *
+\subsection{Eta expansion}
+%* *
+%************************************************************************
+
+ 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
+
+where (in both cases) N is a NORMAL FORM (i.e. no redexes anywhere)
+wanting a suitable number of extra args.
+
+NB: the Ei may have unlifted type, but the simplifier (which is applied
+to the result) deals OK with this).
+
+There is no point in looking for a combination of the two,
+because that would leave use with some lets sandwiched between lambdas;
+but it's awkward to detect that case, so we don't bother.
+
+\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
+ = returnSmpl rhs
+
+ | otherwise -- Consider eta expansion
+ = newIds y_tys ( \ y_bndrs ->
+ tick (EtaExpansion (head y_bndrs)) `thenSmpl_`
+ mapAndUnzipSmpl bind_z_arg args `thenSmpl` (\ (z_binds, z_args) ->
+ returnSmpl (mkLams x_bndrs $
+ mkLets (catMaybes z_binds) $
+ mkLams y_bndrs $
+ mkApps (mkApps fun z_args) (map Var y_bndrs))))
+ where
+ (x_bndrs, body) = collectValBinders rhs
+ (fun, args) = collectArgs body
+ no_of_xs = length x_bndrs
+ fun_arity = case fun of
+ Var v -> arityLowerBound (getIdArity v)
+ other -> 0
+
+ bind_z_arg arg | exprIsTrivial arg = returnSmpl (Nothing, arg)
+ | otherwise = newId (coreExprType arg) $ \ z ->
+ returnSmpl (Just (NonRec z arg), Var z)
+
+ -- Note: I used to try to avoid the coreExprType 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, inner_ty) = splitFunTys (coreExprType body)
+
+ y_tys :: [InType]
+ y_tys = take no_extras_wanted potential_extra_arg_tys
+
+ no_extras_wanted :: Int
+ no_extras_wanted =
+
+ -- 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) `max`
+
+ -- 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}
e.g. \ x y -> f x y ===> f
It is used
- a) Before constructing an Unfolding, to
- try to make the unfolding smaller;
+-- OLD
+-- a) Before constructing an Unfolding, to
+-- try to make the unfolding smaller;
b) In tidyCoreExpr, which is done just before converting to STG.
But we only do this if
The idea is that lambdas are often quite helpful: they indicate
head normal forms, so we don't want to chuck them away lightly.
- ii) It exposes a simple variable or a type application; in short
- it exposes a "trivial" expression. (exprIsTrivial)
+-- OLD: in core2stg we want to do this even if the result isn't trivial
+-- ii) It exposes a simple variable or a type application; in short
+-- it exposes a "trivial" expression. (exprIsTrivial)
\begin{code}
etaCoreExpr :: CoreExpr -> CoreExpr
-- lambda into a bottom variable. Sigh
etaCoreExpr expr@(Lam bndr body)
- | opt_DoEtaReduction
= check (reverse binders) body
where
(binders, body) = collectBinders expr
check [] body
- | exprIsTrivial body && not (any (`elemVarSet` body_fvs) binders)
+ | not (any (`elemVarSet` body_fvs) binders)
= body -- Success!
where
body_fvs = exprFreeVars body
%************************************************************************
%* *
-\subsection{Eta expansion}
-%* *
-%************************************************************************
-
-@etaExpandCount@ takes an expression, E, and returns an integer n,
-such that
-
- E ===> (\x1::t1 x1::t2 ... xn::tn -> E x1 x2 ... xn)
-
-is a safe transformation. In particular, the transformation should
-not cause work to be duplicated, unless it is ``cheap'' (see
-@manifestlyCheap@ below).
-
-@etaExpandCount@ errs on the conservative side. It is always safe to
-return 0.
-
-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.
-
-\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
-\end{code}
-
-
-%************************************************************************
-%* *
\subsection{Case absorption and identity-case elimination}
%* *
%************************************************************************
\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
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}
matches (DEFAULT, _, _) = True
matches (con1, _, _) = con == con1
+
+
+mkCoerce to_ty (Note (Coerce _ from_ty) expr)
+ | to_ty == from_ty = expr
+ | otherwise = Note (Coerce to_ty from_ty) expr
+mkCoerce to_ty expr
+ = Note (Coerce to_ty (coreExprType expr)) expr
\end{code}
projects / ghc-hetmet.git / blobdiff