Do not GVN HLocalGet. If the local is final, the GVN thinks it can loop hoist accesses to it (which…

tests/language/final_used_in_try_test.dart

Index: tests/language/final_used_in_try_test.dart
===================================================================
--- tests/language/final_used_in_try_test.dart	(revision 0)
+++ tests/language/final_used_in_try_test.dart	(revision 0)
@@ -0,0 +1,15 @@
+// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+main() {
+  while (true) {
+    final a = 'fff'.substring(1, 2);
+    try {
+      Expect.equals('f', a);
+    } catch (e) {
+      throw;
+    }
+    break;
+  }
+}