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diff --git a/Source/JavaScriptCore/dfg/DFGStructureRegistrationPhase.h b/Source/JavaScriptCore/dfg/DFGStructureRegistrationPhase.h
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+/*
+ * Copyright (C) 2014 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 DFGStructureRegistrationPhase_h
+#define DFGStructureRegistrationPhase_h
+
+#if ENABLE(DFG_JIT)
+
+namespace JSC { namespace DFG {
+
+class Graph;
+
+// Registers any structures we know about as weak references, and sets watchpoints on any
+// such structures that we know of that are currently watchable. It's somewhat
+// counterintuitive, but this ends up being the cleanest and most effective way of reducing
+// structure checks on terminal structures:
+//
+// - We used to only set watchpoints on watchable structures if we knew that this would
+//   remove a structure check. Experiments show that switching from that, to blindly
+//   setting watchpoints on all watchable structures, was not a regression.
+//
+// - It makes abstract interpretation a whole lot easier. We just assume that watchable
+//   structures are unclobberable without having to do any other logic.
+
+bool performStructureRegistration(Graph&);
+
+} } // namespace JSC::DFG
+
+#endif // ENABLE(DFG_JIT)
+
+#endif // DFGStructureRegistrationPhase_h
+