diff -r fd16c54261b3 -r 489c9b5090e2 hotspot/src/share/vm/prims/methodComparator.hpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/hotspot/src/share/vm/prims/methodComparator.hpp	Sat Dec 01 00:00:00 2007 +0000
@@ -0,0 +1,122 @@
+/*
+ * Copyright 2000-2005 Sun Microsystems, Inc.  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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
+ * CA 95054 USA or visit www.sun.com if you need additional information or
+ * have any questions.
+ *
+ */
+
+class BciMap;
+
+// 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 constantPoolOop _old_cp, _new_cp;
+  static BciMap *_bci_map;
+  static bool _switchable_test;
+  static GrowableArray<int> *_fwd_jmps;
+
+  static bool args_same(Bytecodes::Code c_old, Bytecodes::Code c_new);
+  static int check_stack_and_locals_size(methodOop old_method, methodOop 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(methodOop old_method, methodOop new_method);
+
+  static bool methods_switchable(methodOop old_method, methodOop new_method, BciMap &bci_map);
+};
+
+
+// ByteCode Index Map. For two versions of the same method, where the new version may contain
+// fragments not found in the old version, provides a mapping from an index of a bytecode in
+// the old method to the index of the same bytecode in the new method.
+
+class BciMap {
+ private:
+  int *_old_bci, *_new_st_bci, *_new_end_bci;
+  int _cur_size, _cur_pos;
+  int _pos;
+
+ public:
+  BciMap() {
+    _cur_size = 50;
+    _old_bci = (int*) malloc(sizeof(int) * _cur_size);
+    _new_st_bci = (int*) malloc(sizeof(int) * _cur_size);
+    _new_end_bci = (int*) malloc(sizeof(int) * _cur_size);
+    _cur_pos = 0;
+  }
+
+  ~BciMap() {
+    free(_old_bci);
+    free(_new_st_bci);
+    free(_new_end_bci);
+  }
+
+  // Store the position of an added fragment, e.g.
+  //
+  //                              |<- old_bci
+  // -----------------------------------------
+  // Old method   |invokevirtual 5|aload 1|...
+  // -----------------------------------------
+  //
+  //                                 |<- new_st_bci          |<- new_end_bci
+  // --------------------------------------------------------------------
+  // New method       |invokevirual 5|aload 2|invokevirtual 6|aload 1|...
+  // --------------------------------------------------------------------
+  //                                 ^^^^^^^^^^^^^^^^^^^^^^^^
+  //                                    Added fragment
+
+  void store_fragment_location(int old_bci, int new_st_bci, int new_end_bci) {
+    if (_cur_pos == _cur_size) {
+      _cur_size += 10;
+      _old_bci = (int*) realloc(_old_bci, sizeof(int) * _cur_size);
+      _new_st_bci = (int*) realloc(_new_st_bci, sizeof(int) * _cur_size);
+      _new_end_bci = (int*) realloc(_new_end_bci, sizeof(int) * _cur_size);
+    }
+    _old_bci[_cur_pos] = old_bci;
+    _new_st_bci[_cur_pos] = new_st_bci;
+    _new_end_bci[_cur_pos] = new_end_bci;
+    _cur_pos++;
+  }
+
+  int new_bci_for_old(int old_bci) {
+    if (_cur_pos == 0 || old_bci < _old_bci[0]) return old_bci;
+    _pos = 1;
+    while (_pos < _cur_pos && old_bci >= _old_bci[_pos])
+      _pos++;
+    return _new_end_bci[_pos-1] + (old_bci - _old_bci[_pos-1]);
+  }
+
+  // Test if two indexes - one in the old method and another in the new one - correspond
+  // to the same bytecode
+  bool old_and_new_locations_same(int old_dest_bci, int new_dest_bci) {
+    if (new_bci_for_old(old_dest_bci) == new_dest_bci)
+      return true;
+    else if (_old_bci[_pos-1] == old_dest_bci)
+      return (new_dest_bci == _new_st_bci[_pos-1]);
+    else return false;
+  }
+};