diff -r 000000000000 -r 6474c204b198 js/src/tests/js1_5/Regress/regress-383674.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/tests/js1_5/Regress/regress-383674.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,58 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//-----------------------------------------------------------------------------
+var BUGNUMBER = 383674;
+var summary = 'Statement that implicitly calls toString should not be optimized away as a "useless expression"';
+var actual = '';
+var expect = '';
+
+
+//-----------------------------------------------------------------------------
+test();
+//-----------------------------------------------------------------------------
+
+function test()
+{
+  enterFunc ('test');
+  printBugNumber(BUGNUMBER);
+  printStatus (summary);
+    
+  options("strict");
+  options("werror");
+
+  expect = 'toString called';
+  actual = 'toString not called';
+  try
+  {
+    var x = {toString: function() { 
+        actual = 'toString called'; 
+        print(actual); 
+      } 
+    }; 
+    var f = function() { var j = x; j + ""; }
+    f();
+    reportCompare(expect, actual, summary + ': 1');
+  }
+  catch(ex)
+  {
+    reportCompare("No Error", ex + "", summary + ': 1');
+  }
+
+  actual = 'toString not called';
+  try
+  {
+    (function() { const a = 
+         ({toString: function(){
+             actual = 'toString called'; print(actual)} }); a += ""; })();
+    reportCompare(expect, actual, summary + ': 2');
+  }
+  catch(ex)
+  {
+    reportCompare("No Error", ex + "", summary + ': 2');
+  }
+
+  exitFunc ('test');
+}