--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/hotspot/share/prims/methodComparator.hpp	Tue Sep 12 19:03:39 2017 +0200
@@ -0,0 +1,55 @@
+/*
+ * Copyright (c) 2000, 2016, 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.
+ *
+ */
+
+#ifndef SHARE_VM_PRIMS_METHODCOMPARATOR_HPP
+#define SHARE_VM_PRIMS_METHODCOMPARATOR_HPP
+
+#include "interpreter/bytecodeStream.hpp"
+#include "oops/constantPool.hpp"
+#include "oops/method.hpp"
+
+// methodComparator provides an interface for determining if methods of
+// different versions of classes are equivalent or switchable
+
+class MethodComparator {
+ private:
+  static BytecodeStream *_s_old, *_s_new;
+  static ConstantPool* _old_cp;
+  static ConstantPool* _new_cp;
+
+  static bool args_same(Bytecodes::Code c_old, Bytecodes::Code c_new);
+  static bool pool_constants_same(int cpi_old, int cpi_new);
+  static int check_stack_and_locals_size(Method* old_method, Method* new_method);
+
+ public:
+  // Check if the new method is equivalent to the old one modulo constant pool (EMCP).
+  // Intuitive definition: two versions of the same method are EMCP, if they don't differ
+  // on the source code level. Practically, we check whether the only difference between
+  // method versions is some constantpool indices embedded into the bytecodes, and whether
+  // these indices eventually point to the same constants for both method versions.
+  static bool methods_EMCP(Method* old_method, Method* new_method);
+
+};
+
+#endif // SHARE_VM_PRIMS_METHODCOMPARATOR_HPP