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diff --git a/Source/JavaScriptCore/dfg/DFGFiltrationResult.h b/Source/JavaScriptCore/dfg/DFGFiltrationResult.h
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+/*
+ * Copyright (C) 2013, 2015 Apple Inc. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+ * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+ * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
+ * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 
+ */
+
+#ifndef DFGFiltrationResult_h
+#define DFGFiltrationResult_h
+
+#if ENABLE(DFG_JIT)
+
+namespace JSC { namespace DFG {
+
+// Tells you if an operation that filters type (i.e. does a type check/speculation) will always
+// exit. Formally, this means that the proven type of a value prior to the filter was not
+// bottom (i.e. not "clear" or "SpecEmpty") but becomes bottom as a result of executing the
+// filter.
+//
+// Note that per this definition, a filter will not return Contradiction if the node's proven
+// type was already bottom. This is necessary because we have this yucky convention of using
+// a proven type of bottom for nodes that don't hold JS values, like Phi nodes in ThreadedCPS
+// and storage nodes.
+enum FiltrationResult {
+    // Means that this operation may not always exit.
+    FiltrationOK,
+    
+    // Means taht this operation will always exit.
+    Contradiction
+};
+
+} } // namespace JSC::DFG
+
+#endif // ENABLE(DFG_JIT)
+
+#endif // DFGFiltrationResult_h
+