add UT

test/Optimizer/isarrbug.js

@@ -0,0 +1,13 @@
+//-------------------------------------------------------------------------------------------------------
+// Copyright (C) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE.txt file in the project root for full license information.
+//-------------------------------------------------------------------------------------------------------
+
+function foo(){
+    return Array.isArray(1);
+};
+
+let failed = foo();
+failed |= foo();
+failed |= foo();
+failed ? print("Fail") : print("Pass");

test/Optimizer/rlexe.xml

@@ -25,6 +25,11 @@
       <files>bug1868543.js</files>
     </default>
   </test>
+  <test>
+    <default>
+      <files>isarrbug.js</files>
+    </default>
+  </test>
   <test>
     <default>
       <files>bug469.js</files>