From: Matthijs Kooijman <m.kooijman@student.utwente.nl>
Date: Tue, 14 Jul 2009 13:31:56 +0000 (+0200)
Subject: Don't create selector cases for unused binders.
X-Git-Url: https://git.stderr.nl/gitweb?p=matthijs%2Fmaster-project%2Fc%CE%BBash.git;a=commitdiff_plain;h=43c13fec6c7ce3eccb509b7b136789704ae2f952

Don't create selector cases for unused binders.

Previously, no selector cases were created for wild binders, using the
hacky is_wild predicate. Now, this checks the free variables of the case
value instead.
---

diff --git a/Normalize.hs b/Normalize.hs
index 16d7969..3f9389a 100644
--- a/Normalize.hs
+++ b/Normalize.hs
@@ -220,14 +220,16 @@ casewild expr@(Case scrut b ty alts) = do
     where
       -- Make all binders wild
       wildbndrs = map (\bndr -> Id.mkWildId (Id.idType bndr)) bndrs
+      -- A set of all the binders that are used by the expression
+      free_vars = CoreFVs.exprSomeFreeVars (`elem` bndrs) expr
       -- Creates a case statement to retrieve the ith element from the scrutinee
       -- and binds that to b.
       mkextracts :: CoreBndr -> Int -> TransformMonad (Maybe (CoreBndr, CoreExpr))
       mkextracts b i =
-        -- TODO: Use free variables instead of is_wild. is_wild is a hack.
-        if is_wild b || Type.isFunTy (Id.idType b) 
-          -- Don't create extra bindings for binders that are already wild, or
-          -- for binders that bind function types (to prevent loops with
+        if not (VarSet.elemVarSet b free_vars) || Type.isFunTy (Id.idType b) 
+          -- Don't create extra bindings for binders that are already wild
+          -- (e.g. not in the free variables of expr, so unused), or for
+          -- binders that bind function types (to prevent loops with
           -- inlinefun).
           then return Nothing
           else do