add TruffleBoundary in exists

com.oracle.truffle.r.nodes.builtin/src/com/oracle/truffle/r/nodes/builtin/base/Exists.java

 /*
- * Copyright (c) 2013, 2014, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2013, 2015, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -24,6 +24,7 @@ package com.oracle.truffle.r.nodes.builtin.base;
 
 import static com.oracle.truffle.r.runtime.RBuiltinKind.*;
 
+import com.oracle.truffle.api.CompilerDirectives.TruffleBoundary;
 import com.oracle.truffle.api.dsl.*;
 import com.oracle.truffle.r.nodes.*;
 import com.oracle.truffle.r.nodes.access.*;
@@ -44,9 +45,10 @@ public abstract class Exists extends RBuiltinNode {
     }
 
     @Specialization
+    @TruffleBoundary
     @SuppressWarnings("unused")
     protected byte existsStringEnv(RAbstractStringVector nameVec, REnvironment env, String mode, byte inherits) {
-        final String name = nameVec.getDataAt(0);
+        String name = nameVec.getDataAt(0);
         controlVisibility();
         if (inherits == RRuntime.LOGICAL_FALSE) {
             return RRuntime.asLogical(env.get(name) != null);
@@ -58,5 +60,4 @@ public abstract class Exists extends RBuiltinNode {
         }
         return RRuntime.LOGICAL_FALSE;
     }
-
 }