[project @ 2005-02-23 12:44:17 by simonmar]

[ghc-hetmet.git] / ghc / compiler / prelude / PrelRules.lhs

diff --git a/ghc/compiler/prelude/PrelRules.lhs b/ghc/compiler/prelude/PrelRules.lhs
index 4fdec53..3a3c02c 100644 (file)
--- a/ghc/compiler/prelude/PrelRules.lhs
+++ b/ghc/compiler/prelude/PrelRules.lhs
@@ -20,7 +20,7 @@ module PrelRules ( primOpRules, builtinRules ) where
 #include "HsVersions.h"
 
 import CoreSyn
-import Id              ( mkWildId )
+import Id              ( mkWildId, isPrimOpId_maybe )
 import Literal         ( Literal(..), mkMachInt, mkMachWord
                        , literalType
                        , word2IntLit, int2WordLit
@@ -289,7 +289,6 @@ litEq is_eq [expr, Lit lit] = do_lit_eq is_eq lit expr
 litEq is_eq other          = Nothing
 
 do_lit_eq is_eq lit expr
--- gaw 2004
   = Just (Case expr (mkWildId (literalType lit)) boolTy
                [(DEFAULT,    [], val_if_neq),
                 (LitAlt lit, [], val_if_eq)])
@@ -382,12 +381,15 @@ For dataToTag#, we can reduce if either
        (b) the argument is a variable whose unfolding is a known constructor
 
 \begin{code}
-dataToTagRule [_, val_arg]
-  = case exprIsConApp_maybe val_arg of
-       Just (dc,_) -> ASSERT( not (isNewTyCon (dataConTyCon dc)) )
-                      Just (mkIntVal (toInteger (dataConTag dc - fIRST_TAG)))
+dataToTagRule [Type ty1, Var tag_to_enum `App` Type ty2 `App` tag]
+  | Just TagToEnumOp <- isPrimOpId_maybe tag_to_enum
+  , ty1 `coreEqType` ty2
+  = Just tag   -- dataToTag (tagToEnum x)   ==>   x
 
-       other       -> Nothing
+dataToTagRule [_, val_arg]
+  | Just (dc,_) <- exprIsConApp_maybe val_arg
+  = ASSERT( not (isNewTyCon (dataConTyCon dc)) )
+    Just (mkIntVal (toInteger (dataConTag dc - fIRST_TAG)))
 
 dataToTagRule other = Nothing
 \end{code}