X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Fstranal%2FDmdAnal.lhs;h=84c189e56bb74e2c9d2d85860253eca99f9c7f31;hb=262c142b90c94ca1aa577c950a6ceae1f255e2d6;hp=c5cfb7b4bdedde682e5b88669b8305dfef7c07ab;hpb=0065d5ab628975892cea1ec7303f968c3338cbe1;p=ghc-hetmet.git

diff --git a/compiler/stranal/DmdAnal.lhs b/compiler/stranal/DmdAnal.lhs
index c5cfb7b..84c189e 100644
--- a/compiler/stranal/DmdAnal.lhs
+++ b/compiler/stranal/DmdAnal.lhs
@@ -40,13 +40,16 @@ import TysWiredIn	( unboxedPairDataCon )
 import TysPrim		( realWorldStatePrimTy )
 import UniqFM		( plusUFM_C, addToUFM_Directly, lookupUFM_Directly,
 			  keysUFM, minusUFM, ufmToList, filterUFM )
-import Type		( isUnLiftedType, coreEqType )
+import Type		( isUnLiftedType, coreEqType, splitTyConApp_maybe )
+import Coercion         ( coercionKind )
 import CoreLint		( showPass, endPass )
-import Util		( mapAndUnzip, mapAccumL, mapAccumR, lengthIs )
+import Util		( mapAndUnzip, lengthIs )
 import BasicTypes	( Arity, TopLevelFlag(..), isTopLevel, isNeverActive,
 			  RecFlag(..), isRec )
 import Maybes		( orElse, expectJust )
 import Outputable
+
+import Data.List
 \end{code}
 
 To think about
@@ -164,16 +167,25 @@ dmdAnal sigs dmd (Lit lit)
 dmdAnal sigs dmd (Var var)
   = (dmdTransform sigs var dmd, Var var)
 
+dmdAnal sigs dmd (Cast e co)
+  = (dmd_ty, Cast e' co)
+  where
+    (dmd_ty, e') = dmdAnal sigs dmd' e
+    to_co        = snd (coercionKind co)
+    dmd'
+      | Just (tc, args) <- splitTyConApp_maybe to_co
+      , isRecursiveTyCon tc = evalDmd
+      | otherwise           = dmd
+	-- This coerce usually arises from a recursive
+        -- newtype, and we don't want to look inside them
+	-- for exactly the same reason that we don't look
+	-- inside recursive products -- we might not reach
+	-- a fixpoint.  So revert to a vanilla Eval demand
+
 dmdAnal sigs dmd (Note n e)
   = (dmd_ty, Note n e')
   where
-    (dmd_ty, e') = dmdAnal sigs dmd' e	
-    dmd' = case n of
-	     Coerce _ _ -> evalDmd  -- This coerce usually arises from a recursive
-	     other	-> dmd 	    -- newtype, and we don't want to look inside them
-				    -- for exactly the same reason that we don't look
-				    -- inside recursive products -- we might not reach
-				    -- a fixpoint.  So revert to a vanilla Eval demand
+    (dmd_ty, e') = dmdAnal sigs dmd e	
 
 dmdAnal sigs dmd (App fun (Type ty))
   = (fun_ty, App fun' (Type ty))
@@ -252,8 +264,8 @@ dmdAnal sigs dmd (Case scrut case_bndr ty [alt@(DataAlt dc,bndrs,rhs)])
 	-- The insight is, of course, that a demand on y is a demand on the
 	-- scrutinee, so we need to `both` it with the scrut demand
 
-        scrut_dmd 	   = Eval (Prod [idNewDemandInfo b | b <- bndrs', isId b])
-				   `both`
+	alt_dmd 	   = Eval (Prod [idNewDemandInfo b | b <- bndrs', isId b])
+        scrut_dmd 	   = alt_dmd `both`
 			     idNewDemandInfo case_bndr'
 
 	(scrut_ty, scrut') = dmdAnal sigs scrut_dmd scrut
@@ -464,7 +476,27 @@ The thunk_cpr_ok stuff [CPR-AND-STRICTNESS]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 If the rhs is a thunk, we usually forget the CPR info, because
 it is presumably shared (else it would have been inlined, and 
-so we'd lose sharing if w/w'd it into a function.
+so we'd lose sharing if w/w'd it into a function).  E.g.
+
+	let r = case expensive of
+		  (a,b) -> (b,a)
+	in ...
+
+If we marked r as having the CPR property, then we'd w/w into
+
+	let $wr = \() -> case expensive of
+			    (a,b) -> (# b, a #)
+	    r = case $wr () of
+		  (# b,a #) -> (b,a)
+	in ...
+
+But now r is a thunk, which won't be inlined, so we are no further ahead.
+But consider
+
+	f x = let r = case expensive of (a,b) -> (b,a)
+	      in if foo r then r else (x,x)
+
+Does f have the CPR property?  Well, no.
 
 However, if the strictness analyser has figured out (in a previous 
 iteration) that it's strict, then we DON'T need to forget the CPR info.
@@ -530,34 +562,6 @@ by dmdAnalTopBind.
 
 \begin{code}
 mk_sig_ty never_inline thunk_cpr_ok rhs (DmdType fv dmds res) 
-  | never_inline && not (isBotRes res)
-	-- 			HACK ALERT
-	-- Don't strictness-analyse NOINLINE things.  Why not?  Because
-	-- the NOINLINE says "don't expose any of the inner workings at the call 
-	-- site" and the strictness is certainly an inner working.
-	--
-	-- More concretely, the demand analyser discovers the following strictness
-	-- for unsafePerformIO:  C(U(AV))
-	-- But then consider
-	--	unsafePerformIO (\s -> let r = f x in 
-	--			       case writeIORef v r s of (# s1, _ #) ->
-	--			       (# s1, r #)
-	-- The strictness analyser will find that the binding for r is strict,
-	-- (becuase of uPIO's strictness sig), and so it'll evaluate it before 
-	-- doing the writeIORef.  This actually makes tests/lib/should_run/memo002
-	-- get a deadlock!  
-	--
-	-- Solution: don't expose the strictness of unsafePerformIO.
-	--
-	-- But we do want to expose the strictness of error functions, 
-	-- which are also often marked NOINLINE
-	--	{-# NOINLINE foo #-}
-	--	foo x = error ("wubble buggle" ++ x)
-	-- So (hack, hack) we only drop the strictness for non-bottom things
-	-- This is all very unsatisfactory.
-  = (deferEnv fv, topSig)
-
-  | otherwise
   = (lazy_fv, mkStrictSig dmd_ty)
   where
     dmd_ty = DmdType strict_fv final_dmds res'
@@ -989,7 +993,7 @@ lub d1@(Eval _) d2	          = d2 `lub` d1	-- Bot,Abs,Top,Call,Defer
 lub (Box d1)   (Box d2) = box (d1 `lub` d2)
 lub d1@(Box _)  d2	= d2 `lub` d1
 
-lubs = zipWithDmds lub
+lubs ds1 ds2 = zipWithDmds lub ds1 ds2
 
 ---------------------
 -- box is the smart constructor for Box
@@ -1096,7 +1100,7 @@ both d1@(Eval ds1) d2	       = d2 `both` d1
 both (Defer ds1) (Defer ds2) = deferEval (ds1 `boths` ds2)
 both d1@(Defer ds1) d2	     = d2 `both` d1
  
-boths = zipWithDmds both
+boths ds1 ds2 = zipWithDmds both ds1 ds2
 \end{code}