Make TcUnify warning-free

[ghc-hetmet.git] / compiler / basicTypes / Id.lhs

diff --git a/compiler/basicTypes/Id.lhs b/compiler/basicTypes/Id.lhs
index d8ae31d..070526e 100644 (file)
--- a/compiler/basicTypes/Id.lhs
+++ b/compiler/basicTypes/Id.lhs
@@ -22,7 +22,7 @@ module Id (
        -- Modifying an Id
        setIdName, setIdUnique, Id.setIdType, setIdExported, setIdNotExported, 
        setIdInfo, lazySetIdInfo, modifyIdInfo, maybeModifyIdInfo,
-       zapLamIdInfo, zapDemandIdInfo, zapFragileIdInfo,
+       zapLamIdInfo, zapDemandIdInfo, zapFragileIdInfo, transferPolyIdInfo,
 
        -- Predicates
        isImplicitId, isDeadBinder, isDictId, isStrictId,
@@ -136,15 +136,27 @@ Absolutely all Ids are made by mkId.  It is just like Var.mkId,
 but in addition it pins free-tyvar-info onto the Id's type, 
 where it can easily be found.
 
+Note [Free type variables]
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+At one time we cached the free type variables of the type of an Id
+at the root of the type in a TyNote.  The idea was to avoid repeating
+the free-type-variable calculation.  But it turned out to slow down
+the compiler overall. I don't quite know why; perhaps finding free
+type variables of an Id isn't all that common whereas applying a 
+substitution (which changes the free type variables) is more common.
+Anyway, we removed it in March 2008.
+
 \begin{code}
 mkLocalIdWithInfo :: Name -> Type -> IdInfo -> Id
-mkLocalIdWithInfo name ty info = Var.mkLocalId name (addFreeTyVars ty) info
+mkLocalIdWithInfo name ty info = Var.mkLocalId name ty info
+       -- Note [Free type variables]
 
 mkExportedLocalId :: Name -> Type -> Id
-mkExportedLocalId name ty = Var.mkExportedLocalId name (addFreeTyVars ty) vanillaIdInfo
+mkExportedLocalId name ty = Var.mkExportedLocalId name ty vanillaIdInfo
+       -- Note [Free type variables]
 
 mkGlobalId :: GlobalIdDetails -> Name -> Type -> IdInfo -> Id
-mkGlobalId details name ty info = Var.mkGlobalId details name (addFreeTyVars ty) info
+mkGlobalId details name ty info = Var.mkGlobalId details name ty info
 \end{code}
 
 \begin{code}
@@ -171,7 +183,7 @@ instantiated before use.
 \begin{code}
 -- "Wild Id" typically used when you need a binder that you don't expect to use
 mkWildId :: Type -> Id
-mkWildId ty = mkSysLocal FSLIT("wild") (mkBuiltinUnique 1) ty
+mkWildId ty = mkSysLocal (fsLit "wild") (mkBuiltinUnique 1) ty
 
 mkWorkerId :: Unique -> Id -> Type -> Id
 -- A worker gets a local name.  CoreTidy will externalise it if necessary.
@@ -189,7 +201,7 @@ mkTemplateLocalsNum :: Int -> [Type] -> [Id]
 mkTemplateLocalsNum n tys = zipWith mkTemplateLocal [n..] tys
 
 mkTemplateLocal :: Int -> Type -> Id
-mkTemplateLocal i ty = mkSysLocal FSLIT("tpl") (mkBuiltinUnique i) ty
+mkTemplateLocal i ty = mkSysLocal (fsLit "tpl") (mkBuiltinUnique i) ty
 \end{code}
 
 
@@ -202,7 +214,7 @@ mkTemplateLocal i ty = mkSysLocal FSLIT("tpl") (mkBuiltinUnique i) ty
 \begin{code}
 setIdType :: Id -> Type -> Id
        -- Add free tyvar info to the type
-setIdType id ty = seqType ty `seq` Var.setIdType id (addFreeTyVars ty)
+setIdType id ty = seqType ty `seq` Var.setIdType id ty
 
 idPrimRep :: Id -> PrimRep
 idPrimRep id = typePrimRep (idType id)
@@ -585,3 +597,35 @@ zapFragileIdInfo :: Id -> Id
 zapFragileIdInfo = zapInfo zapFragileInfo 
 \end{code}
 
+Note [transferPolyIdInfo]
+~~~~~~~~~~~~~~~~~~~~~~~~~
+Suppose we have
+
+   f = /\a. let g = rhs in ...
+
+where g has interesting strictness information.  Then if we float thus
+
+   g' = /\a. rhs
+   f = /\a. ...[g' a/g]
+
+we *do not* want to lose the strictness information on g.  Nor arity.
+
+It's simple to retain strictness and arity, but not so simple to retain
+       worker info
+       rules
+so we simply discard those.  Sooner or later this may bite us.
+
+This transfer is used in two places: 
+       FloatOut (long-distance let-floating)
+       SimplUtils.abstractFloats (short-distance let-floating)
+
+\begin{code}
+transferPolyIdInfo :: Id -> Id -> Id
+transferPolyIdInfo old_id new_id
+  = modifyIdInfo transfer new_id
+  where
+    old_info = idInfo old_id
+    transfer new_info = new_info `setNewStrictnessInfo` (newStrictnessInfo old_info)
+                                `setArityInfo` (arityInfo old_info)
+\end{code}
+