[project @ 2001-12-14 17:24:03 by simonpj]

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

diff --git a/ghc/compiler/simplCore/CSE.lhs b/ghc/compiler/simplCore/CSE.lhs
index 66038f3..4eb977d 100644 (file)
--- a/ghc/compiler/simplCore/CSE.lhs
+++ b/ghc/compiler/simplCore/CSE.lhs
@@ -10,7 +10,7 @@ module CSE (
 
 #include "HsVersions.h"
 
-import CmdLineOpts     ( DynFlag(..), DynFlags, dopt )
+import CmdLineOpts     ( DynFlag(..), DynFlags )
 import Id              ( Id, idType )
 import CoreUtils       ( hashExpr, cheapEqExpr, exprIsBig, mkAltExpr )
 import DataCon         ( isUnboxedTupleCon )
@@ -21,7 +21,7 @@ import CoreSyn
 import VarEnv  
 import CoreLint                ( showPass, endPass )
 import Outputable
-import Util            ( mapAccumL )
+import Util            ( mapAccumL, lengthExceeds )
 import UniqFM
 \end{code}
 
@@ -220,12 +220,14 @@ 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
   where
     hash   = hashExpr expr
-    combine old new = WARN( length result > 4, text "extendCSEnv: long list:" <+> ppr result )
+    combine old new = WARN( result `lengthExceeds` 4, text "extendCSEnv: long list:" <+> ppr result )
                      result
                    where
                      result = new ++ old