X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Fspecialise%2FSpecialise.lhs;h=9750bd042c8283c6243e84b98b6bcfd1f5cf117a;hb=35c5bf8991bd3954bc9dd3fe584da03791223a57;hp=fa9d2536215aa4709924276af4466987facace42;hpb=07f3c0c8ebbcc5298167b5b705a1660519b395c4;p=ghc-hetmet.git

diff --git a/compiler/specialise/Specialise.lhs b/compiler/specialise/Specialise.lhs
index fa9d253..9750bd0 100644
--- a/compiler/specialise/Specialise.lhs
+++ b/compiler/specialise/Specialise.lhs
@@ -4,6 +4,13 @@
 \section[Specialise]{Stamping out overloading, and (optionally) polymorphism}
 
 \begin{code}
+{-# OPTIONS -w #-}
+-- The above warning supression flag is a temporary kludge.
+-- While working on this module you are encouraged to remove it and fix
+-- any warnings in the module. See
+--     http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
+-- for details
+
 module Specialise ( specProgram ) where
 
 #include "HsVersions.h"
@@ -23,7 +30,7 @@ import VarSet
 import VarEnv
 import CoreSyn
 import CoreUtils	( applyTypeToArgs, mkPiTypes )
-import CoreFVs		( exprFreeVars, exprsFreeVars, idRuleVars )
+import CoreFVs		( exprFreeVars, exprsFreeVars, idFreeVars )
 import CoreTidy		( tidyRules )
 import CoreLint		( showPass, endPass )
 import Rules		( addIdSpecialisations, mkLocalRule, lookupRule, emptyRuleBase, rulesOfBinds )
@@ -32,7 +39,7 @@ import UniqSupply	( UniqSupply,
 			  UniqSM, initUs_, thenUs, returnUs, getUniqueUs, 
 			  getUs, mapUs
 			)
-import Name		( nameOccName, mkSpecOcc, getSrcLoc )
+import Name
 import MkId		( voidArgId, realWorldPrimId )
 import FiniteMap
 import Maybes		( catMaybes, maybeToBool )
@@ -783,8 +790,8 @@ specDefn :: Subst			-- Subst to use for RHS
 
 specDefn subst calls (fn, rhs)
 	-- The first case is the interesting one
-  |  rhs_tyvars `lengthIs` n_tyvars 	-- Rhs of fn's defn has right number of big lambdas
-  && rhs_bndrs  `lengthAtLeast` n_dicts	-- and enough dict args
+  |  rhs_tyvars `lengthIs`     n_tyvars -- Rhs of fn's defn has right number of big lambdas
+  && rhs_ids    `lengthAtLeast` n_dicts	-- and enough dict args
   && notNull calls_for_me		-- And there are some calls to specialise
 
 --   && not (certainlyWillInline (idUnfolding fn))	-- And it's not small
@@ -806,7 +813,9 @@ specDefn subst calls (fn, rhs)
 	      rhs_uds `plusUDs` plusUDList spec_uds)
 
   | otherwise	-- No calls or RHS doesn't fit our preconceptions
-  = specExpr subst rhs			`thenSM` \ (rhs', rhs_uds) ->
+  = WARN( notNull calls_for_me, ptext SLIT("Missed specialisation opportunity for") <+> ppr fn )
+	  -- Note [Specialisation shape]
+    specExpr subst rhs			`thenSM` \ (rhs', rhs_uds) ->
     returnSM ((fn, rhs'), [], rhs_uds)
   
   where
@@ -883,7 +892,8 @@ specDefn subst calls (fn, rhs)
 		-- The rule to put in the function's specialisation is:
 		--	forall b,d, d1',d2'.  f t1 b t3 d d1' d2' = f1 b d  
            spec_env_rule = mkLocalRule (mkFastString ("SPEC " ++ showSDoc (ppr fn)))
-				AlwaysActive (idName fn)
+				inline_prag 	-- Note [Auto-specialisation and RULES]
+			 	(idName fn)
 			        (poly_tyvars ++ rhs_dicts')
 				inst_args 
 				(mkVarApps (Var spec_f) app_args)
@@ -898,10 +908,69 @@ specDefn subst calls (fn, rhs)
 
       where
 	my_zipEqual doc xs ys 
-	 | not (equalLength xs ys) = pprPanic "my_zipEqual" (ppr xs $$ ppr ys $$ (ppr fn <+> ppr call_ts) $$ ppr rhs)
+#ifdef DEBUG
+	 | not (equalLength xs ys) = pprPanic "my_zipEqual" (vcat 
+						[ ppr xs, ppr ys
+						, ppr fn <+> ppr call_ts
+						, ppr (idType fn), ppr theta
+						, ppr n_dicts, ppr rhs_dicts 
+						, ppr rhs])
+#endif
 	 | otherwise		   = zipEqual doc xs ys
 \end{code}
 
+Note [Auto-specialisation and RULES]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Consider:
+   g :: Num a => a -> a
+   g = ...
+
+   f :: (Int -> Int) -> Int
+   f w = ...
+   {-# RULE f g = 0 #-}
+
+Suppose that auto-specialisation makes a specialised version of
+g::Int->Int That version won't appear in the LHS of the RULE for f.
+So if the specialisation rule fires too early, the rule for f may
+never fire. 
+
+It might be possible to add new rules, to "complete" the rewrite system.
+Thus when adding
+	RULE forall d. g Int d = g_spec
+also add
+	RULE f g_spec = 0
+
+But that's a bit complicated.  For now we ask the programmer's help,
+by *copying the INLINE activation pragma* to the auto-specialised rule.
+So if g says {-# NOINLINE[2] g #-}, then the auto-spec rule will also
+not be active until phase 2.  
+
+
+Note [Specialisation shape]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+We only specialise a function if it has visible top-level lambdas
+corresponding to its overloading.  E.g. if
+	f :: forall a. Eq a => ....
+then its body must look like
+	f = /\a. \d. ...
+
+Reason: when specialising the body for a call (f ty dexp), we want to
+substitute dexp for d, and pick up specialised calls in the body of f.
+
+This doesn't always work.  One example I came across was htis:
+	newtype Gen a = MkGen{ unGen :: Int -> a }
+
+	choose :: Eq a => a -> Gen a
+	choose n = MkGen (\r -> n)
+
+	oneof = choose (1::Int)
+
+It's a silly exapmle, but we get
+	choose = /\a. g `cast` co
+where choose doesn't have any dict arguments.  Thus far I have not
+tried to fix this (wait till there's a real example).
+
+
 Note [Inline specialisations]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 We transfer to the specialised function any INLINE stuff from the
@@ -1072,10 +1141,12 @@ bind_fvs (Rec prs)	   = foldl delVarSet rhs_fvs bndrs
 			     bndrs = map fst prs
 			     rhs_fvs = unionVarSets (map pair_fvs prs)
 
-pair_fvs (bndr, rhs) = exprFreeVars rhs `unionVarSet` idRuleVars bndr
+pair_fvs (bndr, rhs) = exprFreeVars rhs `unionVarSet` idFreeVars bndr
 	-- Don't forget variables mentioned in the
 	-- rules of the bndr.  C.f. OccAnal.addRuleUsage
-
+	-- Also tyvars mentioned in its type; they may not appear in the RHS
+	--	type T a = Int
+	--	x :: T a = 3
 
 addDictBind (dict,rhs) uds = uds { dict_binds = mkDB (NonRec dict rhs) `consBag` dict_binds uds }
 
@@ -1182,7 +1253,7 @@ newIdSM old_id new_ty
     let 
 	-- Give the new Id a similar occurrence name to the old one
 	name   = idName old_id
-	new_id = mkUserLocal (mkSpecOcc (nameOccName name)) uniq new_ty (getSrcLoc name)
+	new_id = mkUserLocal (mkSpecOcc (nameOccName name)) uniq new_ty (getSrcSpan name)
     in
     returnSM new_id
 \end{code}