floatExposesHNF,
- etaCoreExpr,
+ etaCoreExpr, mkRhsTyLam,
etaExpandCount,
simplIdWantsToBeINLINEd,
- type_ok_for_let_to_case
+ singleConstructorType, typeOkForCase
) where
IMP_Ubiq(){-uitous-}
import BinderInfo
import CmdLineOpts ( opt_DoEtaReduction, SimplifierSwitch(..) )
import CoreSyn
-import CoreUnfold ( SimpleUnfolding, mkFormSummary, FormSummary(..) )
-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 ( ArityInfo(..) )
+import IdInfo ( ArityInfo(..), DemandInfo )
import Maybes ( maybeToBool )
import PrelVals ( augmentId, buildId )
import PrimOp ( primOpIsCheap )
import SimplEnv
import SimplMonad
-import Type ( tyVarsOfType, isPrimType, maybeAppDataTyConExpandingDicts )
+import Type ( tyVarsOfType, mkForAllTys, mkTyVarTys, isPrimType,
+ maybeAppDataTyConExpandingDicts, SYN_IE(Type)
+ )
import TysWiredIn ( realWorldStateTy )
import TyVar ( elementOfTyVarSet,
GenTyVar{-instance Eq-} )
try_deflt (BindDefault _ rhs) = try rhs
\end{code}
+
+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.
\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
+mkIdentityAlts rhs_ty demand_info
= case (maybeAppDataTyConExpandingDicts rhs_ty) of
Just (tycon, ty_args, [data_con]) -> -- algebraic type suitable for unpacking
let
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
+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 / commitdiff