X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2FsimplCore%2FOccurAnal.lhs;h=7692b628abef16a25f7a4131a5b87dbdb039ee79;hb=7b0ff1792d699ff02a604163c9ccf4a98a1ca3eb;hp=0bc62966cade69cd37eb16bab90a8fc3d8705d49;hpb=16dd51fb989fa0fe10f04da19f9724ff31838470;p=ghc-hetmet.git

diff --git a/compiler/simplCore/OccurAnal.lhs b/compiler/simplCore/OccurAnal.lhs
index 0bc6296..7692b62 100644
--- a/compiler/simplCore/OccurAnal.lhs
+++ b/compiler/simplCore/OccurAnal.lhs
@@ -1146,7 +1146,7 @@ wrapProxy (bndr, rhs_var, co) (body_usg, body)
   where
     (body_usg', tagged_bndr) = tagBinder body_usg bndr
     rhs_usg = unitVarEnv rhs_var NoOccInfo	-- We don't need exact info
-    rhs = mkCoerceI co (Var rhs_var)
+    rhs = mkCoerceI co (Var (zapIdOccInfo rhs_var)) -- See Note [Zap case binders in proxy bindings]
 \end{code}
 
 
@@ -1352,9 +1352,11 @@ extendFvs env s
 %************************************************************************
 
 \begin{code}
-data ProxyEnv 
-   = PE (IdEnv (Id, [(Id,CoercionI)])) VarSet
-     	-- Main env, and its free variables (of both range and domain)
+data ProxyEnv	-- See Note [ProxyEnv]
+   = PE (IdEnv	-- Domain = scrutinee variables
+           (Id,                  -- The scrutinee variable again
+            [(Id,CoercionI)])) 	 -- The case binders that it maps to
+        VarSet	-- Free variables of both range and domain
 \end{code}
 
 Note [ProxyEnv]
@@ -1497,6 +1499,17 @@ From this we want to extract the bindings
 Notice that later bindings may mention earlier ones, and that
 we need to go "both ways".
 
+Note [Zap case binders in proxy bindings]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+From the original
+     case x of cb(dead) { p -> ...x... }
+we will get
+     case x of cb(live) { p -> let x = cb in ...x... }
+
+Core Lint never expects to find an *occurence* of an Id marked
+as Dead, so we must zap the OccInfo on cb before making the 
+binding x = cb.  See Trac #5028.
+
 Historical note [no-case-of-case]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 We *used* to suppress the binder-swap in case expressions when 
@@ -1580,10 +1593,11 @@ extendProxyEnv pe scrut co case_bndr
 	-- Localise the scrut_var before shadowing it; we're making a 
 	-- new binding for it, and it might have an External Name, or
 	-- even be a GlobalId; Note [Binder swap on GlobalId scrutinees]
-	-- Also we don't want any INLILNE or NOINLINE pragmas!
+	-- Also we don't want any INLINE or NOINLINE pragmas!
 
 -----------
 type ProxyBind = (Id, Id, CoercionI)
+     -- (scrut variable, case-binder variable, coercion)
 
 getProxies :: OccEnv -> Id -> Bag ProxyBind
 -- Return a bunch of bindings [...(xi,ei)...]