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[ghc-hetmet.git] / compiler / stranal / DmdAnal.lhs

diff --git a/compiler/stranal/DmdAnal.lhs b/compiler/stranal/DmdAnal.lhs
index c5cfb7b..309cd29 100644 (file)
--- a/compiler/stranal/DmdAnal.lhs
+++ b/compiler/stranal/DmdAnal.lhs
@@ -40,7 +40,8 @@ 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 BasicTypes      ( Arity, TopLevelFlag(..), isTopLevel, isNeverActive,
@@ -164,16 +165,25 @@ 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))
@@ -464,7 +474,22 @@ 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.
+
 
 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 +555,6 @@ 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'