X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Fstranal%2FDmdAnal.lhs;h=309cd2970516ae12dcf9e0954c45d47b600f6e6d;hb=6cac36cc16f7c4158eaf96c628bc5d64226c24e8;hp=6adda66ed5ae6ed5e053454ac29684e2778685b3;hpb=c94408e522e5af3b79a5beadc7e6d15cee553ee7;p=ghc-hetmet.git

diff --git a/compiler/stranal/DmdAnal.lhs b/compiler/stranal/DmdAnal.lhs
index 6adda66..309cd29 100644
--- a/compiler/stranal/DmdAnal.lhs
+++ b/compiler/stranal/DmdAnal.lhs
@@ -171,10 +171,9 @@ dmdAnal sigs dmd (Cast e co)
     (dmd_ty, e') = dmdAnal sigs dmd' e
     to_co        = snd (coercionKind co)
     dmd'
---      | Just (tc, args) <- splitTyConApp_maybe to_co
-      = evalDmd
---      , isRecursiveTyCon tc = evalDmd
---      | otherwise           = 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
@@ -475,7 +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.