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