From 0f41825723ff9c22962e19ff5c34d7ed1c00ad3e Mon Sep 17 00:00:00 2001
From: simonpj <unknown>
Date: Fri, 23 Mar 2001 14:52:30 +0000
Subject: [PATCH] [project @ 2001-03-23 14:52:30 by simonpj] Add comment

---
 ghc/compiler/simplCore/CSE.lhs |    2 ++
 1 file changed, 2 insertions(+)

diff --git a/ghc/compiler/simplCore/CSE.lhs b/ghc/compiler/simplCore/CSE.lhs
index 66038f3..041fdfb 100644
--- a/ghc/compiler/simplCore/CSE.lhs
+++ b/ghc/compiler/simplCore/CSE.lhs
@@ -220,6 +220,8 @@ lookup_list ((x,e):es) expr | cheapEqExpr e expr = Just x
 
 addCSEnvItem env id expr | exprIsBig expr = env
 			 | otherwise      = extendCSEnv env id expr
+   -- We don't try to CSE big expressions, because they are expensive to compare
+   -- (and are unlikely to be the same anyway)
 
 extendCSEnv (CS cs in_scope sub) id expr
   = CS (addToUFM_C combine cs hash [(id, expr)]) in_scope sub
-- 
1.7.10.4