Implement auto-specialisation of imported Ids

This big-ish patch arranges that if an Id 'f' is 
  * Type-class overloaded 
       f :: Ord a => [a] -> [a]
  * Defined with an INLINABLE pragma
       {-# INLINABLE f #-}
  * Exported from its defining module 'D'

then in any module 'U' that imports D

1. Any call of 'f' at a fixed type will generate 
   (a) a specialised version of f in U
   (b) a RULE that rewrites unspecialised calls to the
       specialised on

  e.g. if the call is (f Int dOrdInt xs) then the 
  specialiser will generate
     $sfInt :: [Int] -> [Int]
     $sfInt = <code for f, imported from D, specialised>
     {-# RULE forall d.  f Int d = $sfInt #-}

2. In addition, you can give an explicit {-# SPECIALISE -#}
   pragma for the imported Id
     {-# SPECIALISE f :: [Bool] -> [Bool] #-}
   This too generates a local specialised definition, 
   and the corresponding RULE 

The new RULES are exported from module 'U', so that any module
importing U will see the specialised versions of 'f', and will
not re-specialise them.

There's a flag -fwarn-auto-orphan that warns you if the auto-generated
RULES are orphan rules. It's not in -Wall, mainly to avoid lots of
error messages with existing packages.

Main implementation changes

 - A new flag on a CoreRule to say if it was auto-generated.
   This is persisted across interface files, so there's a small
   change in interface file format.

 - Quite a bit of fiddling with plumbing, to get the 
   {-# SPECIALISE #-} pragmas for imported Ids.  In particular, a
   new field tgc_imp_specs in TcGblEnv, to keep the specialise
   pragmas for imported Ids between the typechecker and the desugarer.

 - Some new code (although surprisingly little) in Specialise,
   to deal with calls of imported Ids

1 files changed, 9 insertions, 9 deletions

diff --git a/compiler/hsSyn/HsBinds.lhs b/compiler/hsSyn/HsBinds.lhs
index 7b4c17cb67..da247c28ed 100644
--- a/compiler/hsSyn/HsBinds.lhs
+++ b/compiler/hsSyn/HsBinds.lhs
@@ -315,7 +315,7 @@ ppr_monobind (AbsBinds { abs_tvs = tyvars, abs_ev_vars = dictvars
   where
     ppr_exp (tvs, gbl, lcl, prags)
 	= vcat [ppr gbl <+> ptext (sLit "<=") <+> ppr tvs <+> ppr lcl,
-	  	nest 2 (pprTcSpecPrags gbl prags)]
+	  	nest 2 (pprTcSpecPrags prags)]
 \end{code}
 
 
@@ -636,11 +636,14 @@ data FixitySig name = FixitySig (Located name) Fixity
 data TcSpecPrags 
   = IsDefaultMethod	-- Super-specialised: a default method should 
     			-- be macro-expanded at every call site
-  | SpecPrags [Located TcSpecPrag]
+  | SpecPrags [LTcSpecPrag]
   deriving (Data, Typeable)
 
+type LTcSpecPrag = Located TcSpecPrag
+
 data TcSpecPrag 
   = SpecPrag   
+        Id		-- The Id to be specialised
 	HsWrapper	-- An wrapper, that specialises the polymorphic function
 	InlinePragma 	-- Inlining spec for the specialised function
   deriving (Data, Typeable)
@@ -776,14 +779,11 @@ pprSpec var pp_ty inl = ptext (sLit "SPECIALIZE") <+> pp_inl <+> pprVarSig var p
     pp_inl | isDefaultInlinePragma inl = empty
            | otherwise = ppr inl
 
-pprTcSpecPrags :: Outputable id => id -> TcSpecPrags -> SDoc
-pprTcSpecPrags _   IsDefaultMethod = ptext (sLit "<default method>")
-pprTcSpecPrags gbl (SpecPrags ps)  = vcat (map (pprSpecPrag gbl) ps)
-
-pprSpecPrag :: Outputable id => id -> Located TcSpecPrag -> SDoc
-pprSpecPrag var (L _ (SpecPrag _expr inl)) = pprSpec var (ptext (sLit "<type>")) inl
+pprTcSpecPrags :: TcSpecPrags -> SDoc
+pprTcSpecPrags IsDefaultMethod = ptext (sLit "<default method>")
+pprTcSpecPrags (SpecPrags ps)  = vcat (map (ppr . unLoc) ps)
 
 instance Outputable TcSpecPrag where
-  ppr (SpecPrag _ p) = ptext (sLit "SpecPrag") <+> ppr p
+  ppr (SpecPrag var _ inl) = pprSpec var (ptext (sLit "<type>")) inl
 \end{code}