--- ghc-6.8.2-normal/compiler/codeGen/CgUtils.hs	2007-12-10 19:11:32.000000000 +0100
+++ ghc-6.8.2-fast2case/compiler/codeGen/CgUtils.hs	2008-02-22 14:06:14.000000000 +0100
@@ -696,6 +696,15 @@
 -- the branches is the tag 0, because comparing '== 0' is likely to be
 -- more efficient than other kinds of comparison.
 
+-- optimize 2 constructor datatype case
+mk_switch (CmmMachOp (MO_And rep) [arg, CmmLit (CmmInt tAG_MASK' rep')]) [(1, stmts1), (2, stmts2)] Nothing _ _ via_C
+    | tAG_MASK' == fromIntegral tAG_MASK = do
+    id <- forkCgStmts stmts2
+    return $ CmmComment (mkFastString "Fast2Case") `consCgStmt` (CmmCondBranch cond id `consCgStmt` stmts1)
+    where
+        tag_expr'   = CmmMachOp (MO_And rep) [arg, CmmLit (CmmInt 2 rep')]
+        cond        = cmmNeWord tag_expr' (CmmLit (mkIntCLit 0))
+
 -- DENSE TAG RANGE: use a switch statment.
 --
 -- We also use a switch uncoditionally when compiling via C, because