Robustify the treatement of DFunUnfolding

[ghc-hetmet.git] / compiler / simplCore / Simplify.lhs

diff --git a/compiler/simplCore/Simplify.lhs b/compiler/simplCore/Simplify.lhs
index eec4521..ec7e190 100644 (file)
--- a/compiler/simplCore/Simplify.lhs
+++ b/compiler/simplCore/Simplify.lhs
@@ -562,7 +562,7 @@ makeTrivialWithInfo top_lvl env info expr
     expr_ty = exprType expr
 
 bindingOk :: TopLevelFlag -> CoreExpr -> Type -> Bool
--- True iff we can have a binding of this expression at this leve
+-- True iff we can have a binding of this expression at this level
 -- Precondition: the type is the type of the expression
 bindingOk top_lvl _ expr_ty
   | isTopLevel top_lvl = not (isUnLiftedType expr_ty) 
@@ -705,8 +705,8 @@ simplUnfolding :: SimplEnv-> TopLevelFlag
               -> OccInfo -> OutExpr
               -> Unfolding -> SimplM Unfolding
 -- Note [Setting the new unfolding]
-simplUnfolding env _ _ _ _ (DFunUnfolding con ops)
-  = return (DFunUnfolding con ops')
+simplUnfolding env _ _ _ _ (DFunUnfolding ar con ops)
+  = return (DFunUnfolding ar con ops')
   where
     ops' = map (substExpr (text "simplUnfolding") env) ops
 
@@ -2082,12 +2082,22 @@ An alternative plan is this:
 but that is bad if 'c' is *not* later scrutinised.  
 
 So instead we do both: we pass 'c' and 'c#' , and record in c's inlining
-that it's really I# c#, thus
+(an InlineRule) that it's really I# c#, thus
    
    $j = \c# -> \c[=I# c#] -> ...c....
 
 Absence analysis may later discard 'c'.
 
+NB: take great care when doing strictness analysis; 
+    see Note [Lamba-bound unfoldings] in DmdAnal.
+
+Also note that we can still end up passing stuff that isn't used.  Before
+strictness analysis we have
+   let $j x y c{=(x,y)} = (h c, ...)
+   in ...
+After strictness analysis we see that h is strict, we end up with
+   let $j x y c{=(x,y)} = ($wh x y, ...)
+and c is unused.
    
 Note [Duplicated env]
 ~~~~~~~~~~~~~~~~~~~~~