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, 3 insertions, 3 deletions

diff --git a/compiler/rename/RnExpr.lhs b/compiler/rename/RnExpr.lhs
index 5598cc0580..4e8219555e 100644
--- a/compiler/rename/RnExpr.lhs
+++ b/compiler/rename/RnExpr.lhs
@@ -21,7 +21,7 @@ import {-# SOURCE #-} TcSplice( runQuasiQuoteExpr )
 #endif 	/* GHCI */
 
 import RnSource  ( rnSrcDecls, findSplice )
-import RnBinds   ( rnLocalBindsAndThen, rnValBindsLHS, rnValBindsRHS,
+import RnBinds   ( rnLocalBindsAndThen, rnLocalValBindsLHS, rnLocalValBindsRHS,
                    rnMatchGroup, makeMiniFixityEnv) 
 import HsSyn
 import TcRnMonad
@@ -931,7 +931,7 @@ rn_rec_stmt_lhs _ (L _ (LetStmt binds@(HsIPBinds _)))
   = failWith (badIpBinds (ptext (sLit "an mdo expression")) binds)
 
 rn_rec_stmt_lhs fix_env (L loc (LetStmt (HsValBinds binds))) 
-    = do (_bound_names, binds') <- rnValBindsLHS fix_env binds
+    = do (_bound_names, binds') <- rnLocalValBindsLHS fix_env binds
          return [(L loc (LetStmt (HsValBinds binds')),
                  -- Warning: this is bogus; see function invariant
                  emptyFVs
@@ -995,7 +995,7 @@ rn_rec_stmt _ (L _ (LetStmt binds@(HsIPBinds _))) _
 rn_rec_stmt all_bndrs (L loc (LetStmt (HsValBinds binds'))) _ = do 
   (binds', du_binds) <- 
       -- fixities and unused are handled above in rn_rec_stmts_and_then
-      rnValBindsRHS (mkNameSet all_bndrs) binds'
+      rnLocalValBindsRHS (mkNameSet all_bndrs) binds'
   return [(duDefs du_binds, allUses du_binds, 
 	   emptyNameSet, L loc (LetStmt (HsValBinds binds')))]