From 43ff61950ef701fc7d6e8308fa7c5256f82f8dc5 Mon Sep 17 00:00:00 2001
From: simonmar <unknown>
Date: Wed, 17 Oct 2001 14:17:11 +0000
Subject: [PATCH] [project @ 2001-10-17 14:17:11 by simonmar] Fix a small
 performance bug.  In mkAlts, when calculating the
 impossible constructors, we were looking at the unfolding
 for the case binder instead of the scrutinee, with the
 result that we sometimes didn't notice that a DEFAULT case
 could be resolved into a specific pattern.

---
 ghc/compiler/simplCore/SimplUtils.lhs |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/ghc/compiler/simplCore/SimplUtils.lhs b/ghc/compiler/simplCore/SimplUtils.lhs
index 1dd3ea1..906568b 100644
--- a/ghc/compiler/simplCore/SimplUtils.lhs
+++ b/ghc/compiler/simplCore/SimplUtils.lhs
@@ -910,7 +910,9 @@ mkAlts scrut case_bndr alts
     in
     returnSmpl better_alts
   where
-    impossible_cons   = otherCons (idUnfolding case_bndr)
+    impossible_cons   = case scrut of
+			    Var v -> otherCons (idUnfolding v)
+			    other -> []
     handled_data_cons = [data_con | DataAlt data_con         <- impossible_cons] ++
 			[data_con | (DataAlt data_con, _, _) <- alts]
     is_missing con    = not (con `elem` handled_data_cons)
-- 
1.7.10.4