floatExposesHNF,
- mkTyLamTryingEta, mkValLamTryingEta,
+ etaCoreExpr, mkRhsTyLam,
etaExpandCount,
simplIdWantsToBeINLINEd,
- type_ok_for_let_to_case
+ singleConstructorType, typeOkForCase
) where
-import Ubiq{-uitous-}
+IMP_Ubiq(){-uitous-}
+IMPORT_DELOOPER(SmplLoop) -- paranoia checking
import BinderInfo
-import CmdLineOpts ( SimplifierSwitch(..) )
+import CmdLineOpts ( opt_DoEtaReduction, SimplifierSwitch(..) )
import CoreSyn
-import CoreUtils ( manifestlyWHNF )
-import Id ( idType, isBottomingId, idWantsToBeINLINEd, dataConArgTys,
+import CoreUnfold ( SimpleUnfolding, mkFormSummary, exprIsTrivial, FormSummary(..) )
+import Id ( idType, isBottomingId, addInlinePragma, addIdDemandInfo,
+ idWantsToBeINLINEd, dataConArgTys, SYN_IE(Id),
getIdArity, GenId{-instance Eq-}
)
-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, maybeAppDataTyCon, getTyVar_maybe )
-import TyVar ( GenTyVar{-instance Eq-} )
+import Type ( tyVarsOfType, mkForAllTys, mkTyVarTys, isPrimType,
+ maybeAppDataTyConExpandingDicts, SYN_IE(Type)
+ )
+import TysWiredIn ( realWorldStateTy )
+import TyVar ( elementOfTyVarSet,
+ GenTyVar{-instance Eq-} )
import Util ( isIn, panic )
\end{code}
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
+
+mkRhsTyLam tyvars body
+ = go (\x -> x) body
+ where
+ tyvar_tys = mkTyVarTys 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 var `thenSmpl` \ (var', rhs') ->
+ go (fn . Let (mk_silly_bind var rhs')) body `thenSmpl` \ body' ->
+ returnSmpl (Let (NonRec var' (mkTyLam tyvars (fn rhs))) body')
+
+ go fn (Let (Rec prs) body)
+ = mapAndUnzipSmpl mk_poly vars `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 (gn rhs) | rhs <- rhss])) body')
+ where
+ (vars,rhss) = unzip prs
+
+ go fn body = returnSmpl (mkTyLam tyvars (fn body))
+
+ mk_poly var
+ = newId (mkForAllTys tyvars (idType var)) `thenSmpl` \ poly_id ->
+ returnSmpl (poly_id, mkTyApp (Var poly_id) tyvar_tys)
+
+ 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
- \ 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:
- reduce_it [] residual
- | residual_ok residual = residual
- | otherwise = bale_out
+ f ab d = let d1 = ...d... in
+ letrec f' b x = ...d...(f' b)... in
+ f' b
+specialise ==>
- 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 b = letrec f' b x = ...dInt...(f' b)... in
+ f' b
- reduce_it ids other = bale_out
+float ==>
- is_elem = isIn "mkValLamTryingEta"
+ 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:
+
+ /\ 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) = tv `elementOfTyVarSet` tyVarsOfType ty
+ 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
+ residual_ok (Var v)
+ = not (eta_match bndr (VarArg v))
residual_ok (App fun arg)
- | notValArg arg = residual_ok fun
- residual_ok other = False
+ | eta_match bndr arg = False
+ | otherwise = residual_ok fun
+ residual_ok (Coerce coercion ty body)
+ | eta_match bndr (TyArg ty) = 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
~~~~~~~~~~~~~
| 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}
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:
-
- /\ 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)
-
- check_fun (Var f) = True -- Claim: tyvars not mentioned by type of f
- check_fun other = False
\end{code}
+
Let to case
~~~~~~~~~~~
\begin{code}
mkIdentityAlts
- :: Type -- type of RHS
+ :: Type -- type of RHS
+ -> DemandInfo -- Appropriate demand info
-> 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 (maybeAppDataTyCon rhs_ty) of
+mkIdentityAlts rhs_ty demand_info
+ = 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
NoDefault
)
- _ -> -- Multi-constructor or abstract algebraic type
- newId rhs_ty `thenSmpl` \ binder ->
- returnSmpl (AlgAlts [] (BindDefault (binder,bad_occ_info) (Var binder)))
+ _ -> panic "mkIdentityAlts" -- Should never happen; only called for single-constructor types
where
bad_occ_info = ManyOcc 0 -- Non-committal!
+
+
+{- SHOULD NEVER HAPPEN
+ | isPrimType rhs_ty
+ = newId rhs_ty `thenSmpl` \ binder ->
+ let
+ binder_w_info = binder `addIdDemandInfo` demand_info
+ -- It's occasionally really worth adding the right demand info. Consider
+ -- let x = E in B
+ -- where x is sure to be demanded in B
+ -- We will transform to:
+ -- case E of x -> B
+ -- Now suppose that E simplifies to just y; we get
+ -- case y of x -> B
+ -- Because x is sure to be demanded, we can eliminate the case
+ -- even if pedantic-bottoms is on; but we need to have the right
+ -- demand-info on the default branch of the case. That's what
+ -- we are doing here.
+ in
+ returnSmpl (PrimAlts [] (BindDefault (binder, bad_occ_info) (Var binder)))
+-}
\end{code}
\begin{code}
simplIdWantsToBeINLINEd :: Id -> SimplEnv -> Bool
simplIdWantsToBeINLINEd id env
- = if switchIsSet env IgnoreINLINEPragma
+ = {- 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
+ else
+ -}
+
+ idWantsToBeINLINEd id
+
+idMinArity id = case getIdArity id of
+ UnknownArity -> 0
+ ArityAtLeast n -> n
+ ArityExactly n -> n
-type_ok_for_let_to_case :: Type -> Bool
+singleConstructorType :: Type -> Bool
+singleConstructorType ty
+ = case (maybeAppDataTyConExpandingDicts ty) of
+ Just (tycon, ty_args, [con]) -> True
+ other -> False
-type_ok_for_let_to_case ty
- = case (maybeAppDataTyCon ty) of
+typeOkForCase :: Type -> Bool
+typeOkForCase 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
+ -- 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}
projects / ghc-hetmet.git / blobdiff