[project @ 1998-04-30 19:44:49 by sof]

When floating in, we have to be careful not to float a specialisation
of a binder past a use of that binder that may later be simplified to
use the specialised version that just floated past (and out of scope.)

Kludgily fix this by including the idSpecVars of a Var in its free
variable set.

diff --git a/ghc/compiler/coreSyn/FreeVars.lhs b/ghc/compiler/coreSyn/FreeVars.lhs
index a475c3f..9619f49 100644 (file)
--- a/ghc/compiler/coreSyn/FreeVars.lhs
+++ b/ghc/compiler/coreSyn/FreeVars.lhs
@@ -21,8 +21,9 @@ module FreeVars (
 import AnnCoreSyn      -- output
 
 import CoreSyn
+import CoreUtils       ( idSpecVars )
 import Id              ( idType, getIdArity, isBottomingId,
-                         emptyIdSet, unitIdSet, mkIdSet,
+                         emptyIdSet, unitIdSet, mkIdSet, unionIdSets,
                          elementOfIdSet, minusIdSet, unionManyIdSets,
                          IdSet, Id
                        )
@@ -36,6 +37,7 @@ import TyVar          ( emptyTyVarSet, unitTyVarSet, minusTyVarSet,
 import BasicTypes      ( Unused )
 import UniqSet         ( unionUniqSets, addOneToUniqSet )
 import Util            ( panic, assertPanic )
+
 \end{code}
 
 %************************************************************************
@@ -111,6 +113,7 @@ Main public interface:
 freeVars :: CoreExpr -> CoreExprWithFVs
 
 freeVars expr = fvExpr noIdCands noTyVarCands expr
+
 \end{code}
 
 %************************************************************************
@@ -132,13 +135,18 @@ fvExpr :: IdCands     -- In-scope Ids
        -> CoreExprWithFVs
 
 fvExpr id_cands tyvar_cands (Var v)
-  = (FVInfo (if (v `is_among` id_cands)
-            then aFreeId v
-            else noFreeIds)
-           noFreeTyVars
-           leakiness,
-     AnnVar v)
+  = (FVInfo fvs noFreeTyVars leakiness, AnnVar v)
   where
+    {-
+     ToDo: insert motivating example for why we *need*
+     to include the idSpecVars in the FV list.
+    -}
+    fvs = fvs_v `unionIdSets` mkIdSet (idSpecVars v)
+
+    fvs_v
+     | v `is_among` id_cands = aFreeId v
+     | otherwise            = noFreeIds
+     
     leakiness
       | isBottomingId v = lEAK_FREE_BIG        -- Hack
       | otherwise       = case getIdArity v of
@@ -305,9 +313,11 @@ fvExpr id_cands tyvar_cands (Note other_note expr)
 -- free vars of the RHS the idSpecVars of the binder,
 -- since those are, in truth, free in the definition.
 fvRhs id_cands tyvar_cands (bndr,rhs)
-  = (FVInfo (fvs `unionIdSets` idSpecVars bndr) ftvs leak, rhs')
+  = (FVInfo fvs' ftvs leak, rhs')
   where
     (FVInfo fvs ftvs leak, rhs') = fvExpr id_cands tyvar_cands rhs
+    fvs' = fvs `unionIdSets` mkIdSet (idSpecVars bndr)
+
 \end{code}
 
 \begin{code}