StateModelChecker.checkExpressionDD: cleanup

Previously, this method used the implicit knowledge that only
the stored JDDNode is cleared when clear() is called on a StateValuesMTBDD.
Now, it performs a copy() on the JDDNode and calls clear() on the StateValues object.



git-svn-id: https://www.prismmodelchecker.org/svn/prism/prism/trunk@12043 bbc10eb1-c90d-0410-af57-cb519fbb1720

prism/src/prism/StateModelChecker.java

@@ -310,7 +310,10 @@ public class StateModelChecker extends PrismComponent implements ModelChecker
 	@Override
 	public JDDNode checkExpressionDD(Expression expr, JDDNode statesOfInterest) throws PrismException
 	{
-		return checkExpression(expr, statesOfInterest).convertToStateValuesMTBDD().getJDDNode();
+		StateValuesMTBDD sv = checkExpression(expr, statesOfInterest).convertToStateValuesMTBDD();
+		JDDNode result = sv.getJDDNode().copy();
+		sv.clear();
+		return result;
 	}
 
 	// -----------------------------------------------------------------------------------