001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 *  Unless required by applicable law or agreed to in writing, software
012 *  distributed under the License is distributed on an "AS IS" BASIS,
013 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 *  See the License for the specific language governing permissions and
015 *  limitations under the License.
016 */
017package org.apache.bcel.verifier.structurals;
018
019import java.util.ArrayList;
020
021import org.apache.bcel.generic.InstructionHandle;
022
023/**
024 * An InstructionContext offers convenient access to information like control flow successors and such.
025 */
026public interface InstructionContext {
027
028    /**
029     * This method symbolically executes the Instruction held in the InstructionContext. It "merges in" the incoming
030     * execution frame situation (see The Java Virtual Machine Specification, 2nd edition, page 146). By so doing, the
031     * outgoing execution frame situation is calculated.
032     *
033     * This method is JustIce-specific and is usually of no sense for users of the ControlFlowGraph class. They should use
034     * getInstruction().accept(Visitor), possibly in conjunction with the ExecutionVisitor.
035     *
036     *
037     * @see ControlFlowGraph
038     * @see ExecutionVisitor
039     * @see #getOutFrame(ArrayList)
040     * @return true - if and only if the "outgoing" frame situation changed from the one before execute()ing.
041     */
042    boolean execute(Frame inFrame, ArrayList<InstructionContext> executionPredecessors, InstConstraintVisitor icv, ExecutionVisitor ev);
043
044    /**
045     * Returns the exception handlers that protect this instruction. They are special control flow successors.
046     */
047    ExceptionHandler[] getExceptionHandlers();
048
049    Frame getInFrame();
050
051    /**
052     * Returns the InstructionHandle this InstructionContext is wrapped around.
053     *
054     * @return The InstructionHandle this InstructionContext is wrapped around.
055     */
056    InstructionHandle getInstruction();
057
058    /**
059     * This method returns the outgoing execution frame situation; therefore <B>it has to be calculated by execute(Frame,
060     * ArrayList) first.</B>
061     *
062     * @see #execute(Frame, ArrayList, InstConstraintVisitor, ExecutionVisitor)
063     */
064    Frame getOutFrame(ArrayList<InstructionContext> executionPredecessors);
065
066    /**
067     * Returns the usual control flow successors.
068     *
069     * @see #getExceptionHandlers()
070     */
071    InstructionContext[] getSuccessors();
072
073    /**
074     * The getTag and setTag methods may be used for temporary flagging, such as graph coloring. Nothing in the
075     * InstructionContext object depends on the value of the tag. JustIce does not use it.
076     *
077     * @see #setTag(int tag)
078     */
079    int getTag();
080
081    /**
082     * The getTag and setTag methods may be used for temporary flagging, such as graph coloring. Nothing in the
083     * InstructionContext object depends on the value of the tag. JustIce does not use it.
084     *
085     * @see #getTag()
086     */
087    void setTag(int tag);
088}