--- /dev/null	2017-01-22 10:16:57.869617664 -0800
+++ new/src/jdk.internal.vm.compiler/share/classes/org.graalvm.compiler.lir/src/org/graalvm/compiler/lir/dfa/UniqueWorkList.java	2017-02-15 17:05:47.175401854 -0800
@@ -0,0 +1,73 @@
+/*
+ * Copyright (c) 2014, 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
+ * 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.
+ */
+package org.graalvm.compiler.lir.dfa;
+
+import java.util.ArrayDeque;
+import java.util.BitSet;
+import java.util.Collection;
+
+import org.graalvm.compiler.core.common.cfg.AbstractBlockBase;
+
+/**
+ * Ensures that an element is only in the worklist once.
+ *
+ */
+class UniqueWorkList extends ArrayDeque<AbstractBlockBase<?>> {
+    private static final long serialVersionUID = 8009554570990975712L;
+    BitSet valid;
+
+    UniqueWorkList(int size) {
+        this.valid = new BitSet(size);
+    }
+
+    @Override
+    public AbstractBlockBase<?> poll() {
+        AbstractBlockBase<?> result = super.poll();
+        if (result != null) {
+            valid.set(result.getId(), false);
+        }
+        return result;
+    }
+
+    @Override
+    public boolean add(AbstractBlockBase<?> pred) {
+        if (!valid.get(pred.getId())) {
+            valid.set(pred.getId(), true);
+            return super.add(pred);
+        }
+        return false;
+    }
+
+    @Override
+    public boolean addAll(Collection<? extends AbstractBlockBase<?>> collection) {
+        boolean changed = false;
+        for (AbstractBlockBase<?> element : collection) {
+            if (!valid.get(element.getId())) {
+                valid.set(element.getId(), true);
+                super.add(element);
+                changed = true;
+            }
+        }
+        return changed;
+    }
+}