[project @ 2002-11-21 14:59:51 by simonpj]

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

diff --git a/ghc/compiler/simplCore/SimplUtils.lhs b/ghc/compiler/simplCore/SimplUtils.lhs
index 1d9b987..f6e4b66 100644 (file)
--- a/ghc/compiler/simplCore/SimplUtils.lhs
+++ b/ghc/compiler/simplCore/SimplUtils.lhs
@@ -25,12 +25,13 @@ import CmdLineOpts  ( SimplifierSwitch(..),
                          opt_SimplCaseMerge, opt_UF_UpdateInPlace
                        )
 import CoreSyn
-import CoreUtils       ( cheapEqExpr, exprType, 
+import CoreFVs         ( exprFreeVars )
+import CoreUtils       ( cheapEqExpr, exprType, exprIsTrivial,
                          etaExpand, exprEtaExpandArity, bindNonRec, mkCoerce2,
                          findDefault, exprOkForSpeculation, exprIsValue
                        )
 import qualified Subst ( simplBndrs, simplBndr, simplLetId, simplLamBndr )
-import Id              ( Id, idType, idInfo, 
+import Id              ( Id, idType, idInfo, isDataConId,
                          mkSysLocal, isDeadBinder, idNewDemandInfo,
                          idUnfolding, idNewStrictness
                        )
@@ -44,6 +45,7 @@ import OccName                ( EncodedFS )
 import TyCon           ( tyConDataCons_maybe, isAlgTyCon, isNewTyCon )
 import DataCon         ( dataConRepArity, dataConExistentialTyVars, dataConArgTys )
 import Var             ( mkSysTyVar, tyVarKind )
+import VarSet
 import Util            ( lengthExceeds, mapAccumL )
 import Outputable
 \end{code}
@@ -273,6 +275,9 @@ interestingArg :: OutExpr -> Bool
 interestingArg (Var v)          = hasSomeUnfolding (idUnfolding v)
                                        -- Was: isValueUnfolding (idUnfolding v')
                                        -- But that seems over-pessimistic
+                                || isDataConId v
+                                       -- This accounts for an argument like
+                                       -- () or [], which is definitely interesting
 interestingArg (Type _)                 = False
 interestingArg (App fn (Type _)) = interestingArg fn
 interestingArg (Note _ a)       = interestingArg a
@@ -540,17 +545,17 @@ tryEtaReduce bndrs body
        -- efficient here:
        --  (a) we already have the binders
        --  (b) we can do the triviality test before computing the free vars
-       --      [in fact I take the simple path and look for just a variable]
   = go (reverse bndrs) body
   where
     go (b : bs) (App fun arg) | ok_arg b arg = go bs fun       -- Loop round
-    go []       (Var fun)     | ok_fun fun   = Just (Var fun)  -- Success!
+    go []       fun           | ok_fun fun   = Just fun                -- Success!
     go _        _                           = Nothing          -- Failure!
 
-    ok_fun fun = not (fun `elem` bndrs) && 
-                (isEvaldUnfolding (idUnfolding fun) || all ok_lam bndrs)
+    ok_fun fun =  exprIsTrivial fun
+              && not (any (`elemVarSet` (exprFreeVars fun)) bndrs)
+              && (exprIsValue fun || all ok_lam bndrs)
     ok_lam v = isTyVar v || isDictTy (idType v)
-       -- The isEvaldUnfolding is because eta reduction is not 
+       -- The exprIsValue is because eta reduction is not 
        -- valid in general:  \x. bot  /=  bot
        -- So we need to be sure that the "fun" is a value.
        --