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 *
017 */
018package org.apache.bcel.verifier.structurals;
019
020
021import java.util.ArrayList;
022
023import org.apache.bcel.generic.InstructionHandle;
024
025/**
026 * An InstructionContext offers convenient access
027 * to information like control flow successors and
028 * such.
029 *
030 */
031public interface InstructionContext{
032
033    /**
034     * The getTag and setTag methods may be used for
035     * temporary flagging, such as graph colouring.
036     * Nothing in the InstructionContext object depends
037     * on the value of the tag. JustIce does not use it.
038     *
039     * @see #setTag(int tag)
040     */
041    int getTag();
042
043    /**
044     * The getTag and setTag methods may be used for
045     * temporary flagging, such as graph colouring.
046     * Nothing in the InstructionContext object depends
047     * on the value of the tag. JustIce does not use it.
048     *
049     * @see #getTag()
050     */
051    void setTag(int tag);
052
053    /**
054     * This method symbolically executes the Instruction
055     * held in the InstructionContext.
056     * It "merges in" the incoming execution frame situation
057     * (see The Java Virtual Machine Specification, 2nd
058     * edition, page 146).
059     * By so doing, the outgoing execution frame situation
060     * is calculated.
061     *
062     * This method is JustIce-specific and is usually of
063     * no sense for users of the ControlFlowGraph class.
064     * They should use getInstruction().accept(Visitor),
065     * possibly in conjunction with the ExecutionVisitor.
066     *
067     *
068     * @see ControlFlowGraph
069     * @see ExecutionVisitor
070     * @see #getOutFrame(ArrayList)
071     * @return true -  if and only if the "outgoing" frame situation
072     * changed from the one before execute()ing.
073     */
074    boolean execute(Frame inFrame, ArrayList<InstructionContext> executionPredecessors,
075            InstConstraintVisitor icv, ExecutionVisitor ev);
076
077    Frame getInFrame();
078
079    /**
080     * This method returns the outgoing execution frame situation;
081     * therefore <B>it has to be calculated by execute(Frame, ArrayList)
082     * first.</B>
083     *
084     * @see #execute(Frame, ArrayList, InstConstraintVisitor, ExecutionVisitor)
085     */
086    Frame getOutFrame(ArrayList<InstructionContext> executionPredecessors);
087
088    /**
089     * Returns the InstructionHandle this InstructionContext is wrapped around.
090     *
091     * @return The InstructionHandle this InstructionContext is wrapped around.
092     */
093    InstructionHandle getInstruction();
094
095    /**
096     * Returns the usual control flow successors.
097     * @see #getExceptionHandlers()
098     */
099    InstructionContext[] getSuccessors();
100
101    /**
102     * Returns the exception handlers that protect this instruction.
103     * They are special control flow successors.
104     */
105    ExceptionHandler[] getExceptionHandlers();
106}