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Java example source code file (methodComparator.hpp)

This example Java source code file (methodComparator.hpp) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

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Java - Java tags/keywords

bcimap, bytecodes\:\:code, bytecodestream, constantpool, growablearray, method, share_vm_prims_methodcomparator_hpp

The methodComparator.hpp Java example source code

/*
 * Copyright (c) 2000, 2012, 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"

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 ConstantPool* _old_cp;
  static ConstantPool* _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 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);

  static bool methods_switchable(Method* old_method, Method* 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;
  }
};

#endif // SHARE_VM_PRIMS_METHODCOMPARATOR_HPP

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