\section[SimplUtils]{The simplifier utilities}
\begin{code}
-#include "HsVersions.h"
-
module SimplUtils (
+ newId, newIds,
+
floatExposesHNF,
- mkTyLamTryingEta, mkValLamTryingEta,
+ etaCoreExpr, mkRhsTyLam,
etaExpandCount,
- mkIdentityAlts,
-
simplIdWantsToBeINLINEd,
- type_ok_for_let_to_case
+ singleConstructorType, typeOkForCase,
+
+ substSpecEnvRhs
) where
-import Ubiq{-uitous-}
+#include "HsVersions.h"
import BinderInfo
-import CmdLineOpts ( SimplifierSwitch(..) )
+import CmdLineOpts ( opt_DoEtaReduction, SimplifierSwitch(..) )
import CoreSyn
-import CoreUtils ( manifestlyWHNF )
-import Id ( idType, isBottomingId, idWantsToBeINLINEd, dataConArgTys,
- getIdArity, GenId{-instance Eq-}
+import CoreUnfold ( mkFormSummary, exprIsTrivial, FormSummary(..) )
+import MkId ( mkSysLocal )
+import Id ( idType, isBottomingId, getIdArity,
+ addInlinePragma, addIdDemandInfo,
+ idWantsToBeINLINEd, dataConArgTys, Id,
+ lookupIdEnv, delOneFromIdEnv
)
-import IdInfo ( arityMaybe )
+import IdInfo ( ArityInfo(..), DemandInfo )
import Maybes ( maybeToBool )
-import PrelInfo ( augmentId, buildId, realWorldStateTy )
+import PrelVals ( augmentId, buildId )
import PrimOp ( primOpIsCheap )
import SimplEnv
import SimplMonad
-import Type ( eqTy, isPrimType, maybeAppDataTyConExpandingDicts, getTyVar_maybe )
-import TyVar ( GenTyVar{-instance Eq-} )
-import Util ( isIn, panic )
+import Type ( tyVarsOfType, tyVarsOfTypes, mkForAllTys, mkTyVarTys, getTyVar_maybe,
+ splitAlgTyConApp_maybe, instantiateTy, Type
+ )
+import TyCon ( isDataTyCon )
+import TyVar ( mkTyVarSet, intersectTyVarSets, elementOfTyVarSet, tyVarSetToList,
+ delFromTyVarEnv
+ )
+import SrcLoc ( noSrcLoc )
+import Util ( isIn, zipWithEqual, panic, assertPanic )
+
+\end{code}
+
+%************************************************************************
+%* *
+\subsection{New ids}
+%* *
+%************************************************************************
+
+\begin{code}
+newId :: Type -> SmplM Id
+newId ty
+ = getUniqueSmpl `thenSmpl` \ uniq ->
+ returnSmpl (mkSysLocal SLIT("s") uniq ty noSrcLoc)
+
+newIds :: [Type] -> SmplM [Id]
+newIds tys
+ = getUniquesSmpl (length tys) `thenSmpl` \ uniqs ->
+ returnSmpl (zipWithEqual "newIds" mk_id tys uniqs)
+ where
+ mk_id ty uniq = mkSysLocal SLIT("s") uniq ty noSrcLoc
\end{code}
-Floating
-~~~~~~~~
+%************************************************************************
+%* *
+\subsection{Floating}
+%* *
+%************************************************************************
+
The function @floatExposesHNF@ tells whether let/case floating will
expose a head normal form. It is passed booleans indicating the
desired strategy.
floatExposesHNF
:: Bool -- Float let(rec)s out of rhs
-> Bool -- Float cheap primops out of rhs
- -> Bool -- OK to duplicate code
- -> GenCoreExpr bdr Id tyvar uvar
+ -> GenCoreExpr bdr Id flexi
-> Bool
-floatExposesHNF float_lets float_primops ok_to_dup rhs
+floatExposesHNF float_lets float_primops rhs
= try rhs
where
try (Case (Prim _ _) (PrimAlts alts deflt) )
- | float_primops && (null alts || ok_to_dup)
+ | float_primops && null alts
= or (try_deflt deflt : map try_alt alts)
try (Let bind body) | float_lets = try body
try (App (App (Var bld) _) _) | bld == buildId = True
try (App (App (App (Var aug) _) _) _) | aug == augmentId = True
- try other = manifestlyWHNF other
- {- but *not* necessarily "manifestlyBottom other"...
+ try other = case mkFormSummary other of
+ VarForm -> True
+ ValueForm -> True
+ other -> False
+ {- but *not* necessarily "BottomForm"...
We may want to float a let out of a let to expose WHNFs,
but to do that to expose a "bottom" is a Bad Idea:
\end{code}
-Eta reduction on ordinary lambdas
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-We have a go at doing
+Local tyvar-lifting
+~~~~~~~~~~~~~~~~~~~
+mkRhsTyLam tries this transformation, when the big lambda appears as
+the RHS of a let(rec) binding:
+
+ /\abc -> let(rec) x = e in b
+ ==>
+ let(rec) x' = /\abc -> let x = x' a b c in e
+ in
+ /\abc -> let x = x' a b c in b
+
+This is good because it can turn things like:
+
+ let f = /\a -> letrec g = ... g ... in g
+into
+ letrec g' = /\a -> ... g' a ...
+ in
+ let f = /\ a -> f a
+
+which is better. In effect, it means that big lambdas don't impede
+let-floating.
+
+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:
+
+ Invariant: go F e = /\tvs -> F e
+
+ Equalities:
+ go F (Let x=e in b)
+ = Let x' = /\tvs -> F e
+ in
+ go G b
+ where
+ G = F . Let x = x' tvs
+
+ go F (Letrec xi=ei in b)
+ = Letrec {xi' = /\tvs -> G ei}
+ in
+ go G b
+ where
+ G = F . Let {xi = xi' tvs}
+
+\begin{code}
+mkRhsTyLam [] body = returnSmpl body
- \ x y -> f x y ===> f
+mkRhsTyLam tyvars body
+ = go (\x -> x) body
+ where
+ main_tyvar_set = mkTyVarSet tyvars
+
+ go fn (Let bind@(NonRec var rhs) body) | exprIsTrivial rhs
+ = go (fn . Let bind) body
+
+ go fn (Let bind@(NonRec var rhs) body)
+ = mk_poly tyvars_here var_ty `thenSmpl` \ (var', rhs') ->
+ go (fn . Let (mk_silly_bind var rhs')) body `thenSmpl` \ body' ->
+ returnSmpl (Let (NonRec var' (mkTyLam tyvars_here (fn rhs))) body')
+ where
+ tyvars_here = tyVarSetToList (main_tyvar_set `intersectTyVarSets` tyVarsOfType var_ty)
+ var_ty = idType var
+
+ go fn (Let (Rec prs) body)
+ = mapAndUnzipSmpl (mk_poly tyvars_here) var_tys `thenSmpl` \ (vars', rhss') ->
+ let
+ gn body = fn $ foldr Let body (zipWith mk_silly_bind vars rhss')
+ in
+ go gn body `thenSmpl` \ body' ->
+ returnSmpl (Let (Rec (vars' `zip` [mkTyLam tyvars_here (gn rhs) | rhs <- rhss])) body')
+ where
+ (vars,rhss) = unzip prs
+ tyvars_here = tyVarSetToList (main_tyvar_set `intersectTyVarSets` tyVarsOfTypes var_tys)
+ var_tys = map idType vars
+
+ go fn body = returnSmpl (mkTyLam tyvars (fn body))
+
+ mk_poly tyvars_here var_ty
+ = newId (mkForAllTys tyvars_here var_ty) `thenSmpl` \ poly_id ->
+ returnSmpl (poly_id, mkTyApp (Var poly_id) (mkTyVarTys tyvars_here))
+
+ mk_silly_bind var rhs = NonRec (addInlinePragma var) 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:
+ --
+ -- x = let g = /\a -> \x -> f x x
+ -- in
+ -- /\ b -> let g* = g b 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.
+\end{code}
+
+Eta reduction
+~~~~~~~~~~~~~
+@etaCoreExpr@ trys an eta reduction at the top level of a Core Expr.
+
+e.g. \ x y -> f x y ===> f
+
+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.
But we only do this if it gets rid of a whole lambda, not part.
The idea is that lambdas are often quite helpful: they indicate
gives rise to a recursive function for the list comprehension, and
f turns out to be just a single call to this recursive function.
-\begin{code}
-mkValLamTryingEta :: [Id] -- Args to the lambda
- -> CoreExpr -- Lambda body
- -> CoreExpr
+Doing eta on type lambdas is useful too:
-mkValLamTryingEta [] body = body
+ /\a -> <expr> a ===> <expr>
-mkValLamTryingEta orig_ids body
- = reduce_it (reverse orig_ids) body
- where
- bale_out = mkValLam orig_ids body
+where <expr> doesn't mention a.
+This is sometimes quite useful, because we can get the sequence:
+
+ f ab d = let d1 = ...d... in
+ letrec f' b x = ...d...(f' b)... in
+ f' b
+specialise ==>
+
+ f.Int b = letrec f' b x = ...dInt...(f' b)... in
+ f' b
+
+float ==>
+
+ f' b x = ...dInt...(f' b)...
+ f.Int b = f' b
- reduce_it [] residual
- | residual_ok residual = residual
- | otherwise = bale_out
+Now we really want to simplify to
- reduce_it (id:ids) (App fun (VarArg arg))
- | id == arg
- && not (idType id `eqTy` realWorldStateTy)
- -- *never* eta-reduce away a PrimIO state token! (WDP 94/11)
- = reduce_it ids fun
+ f.Int = f'
- reduce_it ids other = bale_out
+and then replace all the f's with f.Ints.
+
+N.B. We are careful not to partially eta-reduce a sequence of type
+applications since this breaks the specialiser:
- is_elem = isIn "mkValLamTryingEta"
+ /\ a -> f Char# a =NO=> f Char#
+
+\begin{code}
+etaCoreExpr :: CoreExpr -> CoreExpr
+
+
+etaCoreExpr expr@(Lam bndr body)
+ | opt_DoEtaReduction
+ = case etaCoreExpr body of
+ App fun arg | eta_match bndr arg &&
+ residual_ok fun
+ -> fun -- Eta
+ other -> expr -- Can't eliminate it, so do nothing at all
+ where
+ eta_match (ValBinder v) (VarArg v') = v == v'
+ eta_match (TyBinder tv) (TyArg ty) = case getTyVar_maybe ty of
+ Nothing -> False
+ Just tv' -> tv == tv'
+ eta_match bndr arg = False
- -----------
residual_ok :: CoreExpr -> Bool -- Checks for type application
-- and function not one of the
-- bound vars
- residual_ok (Var v) = not (v `is_elem` orig_ids)
- -- Fun mustn't be one of the bound ids
+ (VarArg v) `mentions` (ValBinder v') = v == v'
+ (TyArg ty) `mentions` (TyBinder tv) = tv `elementOfTyVarSet` tyVarsOfType ty
+ bndr `mentions` arg = False
+
+ residual_ok (Var v)
+ = not (VarArg v `mentions` bndr)
residual_ok (App fun arg)
- | notValArg arg = residual_ok fun
- residual_ok other = False
+ | arg `mentions` bndr = False
+ | otherwise = residual_ok fun
+ residual_ok (Note (Coerce to_ty from_ty) body)
+ | TyArg to_ty `mentions` bndr
+ || TyArg from_ty `mentions` bndr = False
+ | otherwise = residual_ok body
+
+ residual_ok other = False -- Safe answer
+ -- This last clause may seem conservative, but consider:
+ -- primops, constructors, and literals, are impossible here
+ -- let and case are unlikely (the argument would have been floated inside)
+ -- SCCs we probably want to be conservative about (not sure, but it's safe to be)
+
+etaCoreExpr expr = expr -- The common case
\end{code}
+
Eta expansion
~~~~~~~~~~~~~
100, to represent "infinity", which is a bit of a hack.
\begin{code}
-etaExpandCount :: GenCoreExpr bdr Id tyvar uvar
+etaExpandCount :: GenCoreExpr bdr Id flexi
-> Int -- Number of extra args you can safely abstract
etaExpandCount (Lam (ValBinder _) body)
-- Case with non-whnf scrutinee
-----------------------------
-eta_fun :: GenCoreExpr bdr Id tv uv -- The function
+eta_fun :: GenCoreExpr bdr Id flexi -- The function
-> Int -- How many args it can safely be applied to
eta_fun (App fun arg) | notValArg arg = eta_fun fun
| isBottomingId v -- Bottoming ids have "infinite arity"
= 10000 -- Blargh. Infinite enough!
-eta_fun expr@(Var v)
- | maybeToBool arity_maybe -- We know the arity
- = arity
- where
- arity_maybe = arityMaybe (getIdArity v)
- arity = case arity_maybe of { Just arity -> arity }
+eta_fun expr@(Var v) = idMinArity v
eta_fun other = 0 -- Give up
\end{code}
where op is a cheap primitive operator
\begin{code}
-manifestlyCheap :: GenCoreExpr bndr Id tv uv -> Bool
+manifestlyCheap :: GenCoreExpr bndr Id flexi -> Bool
-manifestlyCheap (Var _) = True
-manifestlyCheap (Lit _) = True
-manifestlyCheap (Con _ _) = True
-manifestlyCheap (SCC _ e) = manifestlyCheap e
-manifestlyCheap (Coerce _ _ e) = manifestlyCheap e
-manifestlyCheap (Lam x e) = if isValBinder x then True else manifestlyCheap e
-manifestlyCheap (Prim op _) = primOpIsCheap op
+manifestlyCheap (Var _) = True
+manifestlyCheap (Lit _) = True
+manifestlyCheap (Con _ _) = True
+manifestlyCheap (Note _ e) = manifestlyCheap e
+manifestlyCheap (Lam x e) = if isValBinder x then True else manifestlyCheap e
+manifestlyCheap (Prim op _) = primOpIsCheap op
manifestlyCheap (Let bind body)
= manifestlyCheap body && all manifestlyCheap (rhssOfBind bind)
= manifestlyCheap scrut && all manifestlyCheap (rhssOfAlts alts)
manifestlyCheap other_expr -- look for manifest partial application
- = case (collectArgs other_expr) of { (fun, _, _, vargs) ->
+ = case (collectArgs other_expr) of { (fun, _, vargs) ->
case fun of
Var f | isBottomingId f -> True -- Application of a function which
num_val_args == 0 || -- Just a type application of
-- a variable (f t1 t2 t3)
-- counts as WHNF
- case (arityMaybe (getIdArity f)) of
- Nothing -> False
- Just arity -> num_val_args < arity
+ num_val_args < idMinArity f
_ -> False
}
-\end{code}
-
-Eta reduction on type lambdas
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-We have a go at doing
-
- /\a -> <expr> a ===> <expr>
-
-where <expr> doesn't mention a.
-This is sometimes quite useful, because we can get the sequence:
-
- f ab d = let d1 = ...d... in
- letrec f' b x = ...d...(f' b)... in
- f' b
-specialise ==>
-
- f.Int b = letrec f' b x = ...dInt...(f' b)... in
- f' b
-
-float ==>
-
- f' b x = ...dInt...(f' b)...
- f.Int b = f' b
-
-Now we really want to simplify to
-
- f.Int = f'
-and then replace all the f's with f.Ints.
-
-N.B. We are careful not to partially eta-reduce a sequence of type
-applications since this breaks the specialiser:
+\end{code}
- /\ a -> f Char# a =NO=> f Char#
\begin{code}
-mkTyLamTryingEta :: [TyVar] -> CoreExpr -> CoreExpr
-
-mkTyLamTryingEta tyvars tylam_body
- = if
- tyvars == tyvar_args && -- Same args in same order
- check_fun fun -- Function left is ok
- then
- -- Eta reduction worked
- fun
- else
- -- The vastly common case
- mkTyLam tyvars tylam_body
- where
- (tyvar_args, fun) = strip_tyvar_args [] tylam_body
-
- strip_tyvar_args args_so_far tyapp@(App fun (TyArg ty))
- = case getTyVar_maybe ty of
- Just tyvar_arg -> strip_tyvar_args (tyvar_arg:args_so_far) fun
- Nothing -> (args_so_far, tyapp)
-
- strip_tyvar_args args_so_far (App _ (UsageArg _))
- = panic "SimplUtils.mkTyLamTryingEta: strip_tyvar_args UsageArg"
-
- strip_tyvar_args args_so_far fun
- = (args_so_far, fun)
+simplIdWantsToBeINLINEd :: Id -> SimplEnv -> Bool
- check_fun (Var f) = True -- Claim: tyvars not mentioned by type of f
- check_fun other = False
+simplIdWantsToBeINLINEd id env
+ = {- We used to arrange that in the final simplification pass we'd switch
+ off all INLINE pragmas, so that we'd inline workers back into the
+ body of their wrapper if the wrapper hadn't itself been inlined by then.
+ This occurred especially for methods in dictionaries.
+
+ We no longer do this:
+ a) there's a good chance that the exported wrapper will get
+ inlined in some importing scope, in which case we don't
+ want to lose the w/w idea.
+
+ b) The occurrence analyser must agree about what has an
+ INLINE pragma. Not hard, but delicate.
+
+ c) if the worker gets inlined we have to tell the wrapepr
+ that it's no longer a wrapper, else the interface file stuff
+ asks for a worker that no longer exists.
+
+ if switchIsSet env IgnoreINLINEPragma
+ then False
+ else
+ -}
+
+ idWantsToBeINLINEd id
+
+idMinArity id = case getIdArity id of
+ UnknownArity -> 0
+ ArityAtLeast n -> n
+ ArityExactly n -> n
+
+singleConstructorType :: Type -> Bool
+singleConstructorType ty
+ = case (splitAlgTyConApp_maybe ty) of
+ Just (tycon, ty_args, [con]) | isDataTyCon tycon -> True
+ other -> False
+
+typeOkForCase :: Type -> Bool
+typeOkForCase ty
+ = case (splitAlgTyConApp_maybe ty) of
+ Just (tycon, ty_args, []) -> False
+ Just (tycon, ty_args, non_null_data_cons) | isDataTyCon tycon -> True
+ other -> False
+ -- Null data cons => type is abstract, which code gen can't
+ -- currently handle. (ToDo: when return-in-heap is universal we
+ -- don't need to worry about this.)
\end{code}
-Let to case
-~~~~~~~~~~~
-Given a type generate the case alternatives
-
- C a b -> C a b
-
-if there's one constructor, or
-
- x -> x
-
-if there's many, or if it's a primitive type.
+substSpecEnvRhs applies a substitution to the RHS's of a SpecEnv
+It exploits the known structure of a SpecEnv's RHS to have fewer
+equations.
\begin{code}
-mkIdentityAlts
- :: Type -- type of RHS
- -> SmplM InAlts -- result
-
-mkIdentityAlts rhs_ty
- | isPrimType rhs_ty
- = newId rhs_ty `thenSmpl` \ binder ->
- returnSmpl (PrimAlts [] (BindDefault (binder, bad_occ_info) (Var binder)))
-
- | otherwise
- = case (maybeAppDataTyConExpandingDicts rhs_ty) of
- Just (tycon, ty_args, [data_con]) -> -- algebraic type suitable for unpacking
- let
- inst_con_arg_tys = dataConArgTys data_con ty_args
- in
- newIds inst_con_arg_tys `thenSmpl` \ new_bindees ->
- let
- new_binders = [ (b, bad_occ_info) | b <- new_bindees ]
- in
- returnSmpl (
- AlgAlts
- [(data_con, new_binders, mkCon data_con [] ty_args (map VarArg new_bindees))]
- NoDefault
- )
-
- _ -> -- Multi-constructor or abstract algebraic type
- newId rhs_ty `thenSmpl` \ binder ->
- returnSmpl (AlgAlts [] (BindDefault (binder,bad_occ_info) (Var binder)))
+substSpecEnvRhs te ve rhs
+ = go te ve rhs
where
- bad_occ_info = ManyOcc 0 -- Non-committal!
-\end{code}
-
-\begin{code}
-simplIdWantsToBeINLINEd :: Id -> SimplEnv -> Bool
-
-simplIdWantsToBeINLINEd id env
- = if switchIsSet env IgnoreINLINEPragma
- then False
- else idWantsToBeINLINEd id
-
-type_ok_for_let_to_case :: Type -> Bool
-
-type_ok_for_let_to_case ty
- = case (maybeAppDataTyConExpandingDicts ty) of
- Nothing -> False
- Just (tycon, ty_args, []) -> False
- Just (tycon, ty_args, non_null_data_cons) -> True
- -- Null data cons => type is abstract
+ go te ve (App f (TyArg ty)) = App (go te ve f) (TyArg (instantiateTy te ty))
+ go te ve (App f (VarArg v)) = App (go te ve f) (case lookupIdEnv ve v of
+ Just (SubstVar v') -> VarArg v'
+ Just (SubstLit l) -> LitArg l
+ Nothing -> VarArg v)
+ go te ve (Var v) = case lookupIdEnv ve v of
+ Just (SubstVar v') -> Var v'
+ Just (SubstLit l) -> Lit l
+ Nothing -> Var v
+
+ -- These equations are a bit half baked, because
+ -- they don't deal properly wih capture.
+ -- But I'm sure it'll never matter... sigh.
+ go te ve (Lam b@(TyBinder tyvar) e) = Lam b (go te' ve e)
+ where
+ te' = delFromTyVarEnv te tyvar
+
+ go te ve (Lam b@(ValBinder v) e) = Lam b (go te ve' e)
+ where
+ ve' = delOneFromIdEnv ve v
\end{code}
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