001/*
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 *   https://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing,
013 * software distributed under the License is distributed on an
014 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
015 * KIND, either express or implied.  See the License for the
016 * specific language governing permissions and limitations
017 * under the License.
018 */
019package org.apache.bcel.generic;
020
021/**
022 * Equality of instructions isn't clearly to be defined. You might wish, for example, to compare whether instructions
023 * have the same meaning. E.g., whether two INVOKEVIRTUALs describe the same call.
024 * <p>
025 * The DEFAULT comparator however, considers two instructions to be equal if they have same opcode and point to the same
026 * indexes (if any) in the constant pool or the same local variable index. Branch instructions must have the same
027 * target.
028 * </p>
029 *
030 * @see Instruction
031 */
032public interface InstructionComparator {
033
034    /**
035     * Default instruction comparator.
036     */
037    InstructionComparator DEFAULT = (i1, i2) -> {
038        if (i1.getOpcode() == i2.getOpcode()) {
039            if (i1 instanceof BranchInstruction) {
040                // BIs are never equal to make targeters work correctly (BCEL-195)
041                return false;
042//                } else if (i1 == i2) { TODO consider adding this shortcut
043//                    return true; // this must be AFTER the BI test
044            }
045            if (i1 instanceof ConstantPushInstruction) {
046                return ((ConstantPushInstruction) i1).getValue().equals(((ConstantPushInstruction) i2).getValue());
047            }
048            if (i1 instanceof IndexedInstruction) {
049                return ((IndexedInstruction) i1).getIndex() == ((IndexedInstruction) i2).getIndex();
050            }
051            if (i1 instanceof NEWARRAY) {
052                return ((NEWARRAY) i1).getTypecode() == ((NEWARRAY) i2).getTypecode();
053            }
054            return true;
055        }
056        return false;
057    };
058
059    /**
060     * Compares two instructions for equality.
061     *
062     * @param i1 the first instruction.
063     * @param i2 the second instruction.
064     * @return true if the instructions are equal, false otherwise.
065     */
066    boolean equals(Instruction i1, Instruction i2);
067}