--- a/nashorn/src/jdk.scripting.nashorn/share/classes/jdk/nashorn/internal/codegen/CodeGenerator.java	Mon Aug 25 20:26:53 2014 +0530
+++ b/nashorn/src/jdk.scripting.nashorn/share/classes/jdk/nashorn/internal/codegen/CodeGenerator.java	Mon Aug 25 22:36:05 2014 +0200
@@ -4316,7 +4316,11 @@
                         }
                     } else {
                         final Type storeType = assignNode.getType();
-                        method.convert(storeType);
+                        if (symbol.hasSlotFor(storeType)) {
+                            // Only emit a convert for a store known to be live; converts for dead stores can
+                            // give us an unnecessary ClassCastException.
+                            method.convert(storeType);
+                        }
                         storeIdentWithCatchConversion(node, storeType);
                     }
                     return false;

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/nashorn/test/script/basic/JDK-8055870.js	Mon Aug 25 22:36:05 2014 +0200
@@ -0,0 +1,41 @@
+/*
+ * Copyright (c) 2010, 2014, 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
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ * 
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ * 
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ * 
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/**
+ * JDK-8055870: iteration fails if index var is not used
+ *
+ * @test
+ * @run
+ */
+
+function isEmpty2(v) {
+ for (var k in v) {
+   return false;
+ }
+ return true;
+}
+
+x = {test: 'test'}
+
+print(isEmpty2(x))
+

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/nashorn/test/script/basic/JDK-8055870.js.EXPECTED	Mon Aug 25 22:36:05 2014 +0200
@@ -0,0 +1,1 @@
+false