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

diff --git a/compiler/stranal/DmdAnal.lhs b/compiler/stranal/DmdAnal.lhs
index 127fa78..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.