livenessanalyzer.java

ProGuard 是一个免费的 Java类文件的压缩

/*
 * ProGuard -- shrinking, optimization, obfuscation, and preverification
 *             of Java bytecode.
 *
 * Copyright (c) 2002-2007 Eric Lafortune ([e-mail])
 *
 * This library is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the Free
 * Software Foundation; either version 2 of the License, or (at your option)
 * any later version.
 *
 * This library 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 Lesser General Public License
 * for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this library; if not, write to the Free Software Foundation,
 * Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 */
package proguard.optimize.evaluation;

import proguard.classfile.*;
import proguard.classfile.attribute.*;
import proguard.classfile.attribute.visitor.*;
import proguard.classfile.instruction.*;
import proguard.classfile.instruction.visitor.InstructionVisitor;
import proguard.classfile.util.*;
import proguard.evaluation.value.*;

/**
 * This AttributeVisitor analyzes the liveness of the variables in the code
 * attributes that it visits, based on partial evaluation.
 *
 * @author Eric Lafortune
 */
public class LivenessAnalyzer
extends      SimplifiedVisitor
implements   AttributeVisitor,
             InstructionVisitor,
             ExceptionInfoVisitor
{
    //*
    private static final boolean DEBUG = false;
    /*/
    private static       boolean DEBUG = true;
    //*/

    private static final int MAX_VARIABLES_SIZE = 64;

    private PartialEvaluator partialEvaluator;

    private long[] isAliveBefore = new long[ClassConstants.TYPICAL_CODE_LENGTH];
    private long[] isAliveAfter  = new long[ClassConstants.TYPICAL_CODE_LENGTH];
    private long[] isCategory2   = new long[ClassConstants.TYPICAL_CODE_LENGTH];

    // A field acting as a global temporary variable.
    private long alive;


    /**
     * Creates a new LivenessAnalyzer.
     */
    public LivenessAnalyzer()
    {
        this(new PartialEvaluator());
    }


    /**
     * Creates a new LivenessAnalyzer that will use the given partial evaluator.
     * It will run this evaluator on every code attribute that it visits.
     */
    public LivenessAnalyzer(PartialEvaluator partialEvaluator)
    {
        this.partialEvaluator = partialEvaluator;
    }


    /**
     * Returns whether the specified variable is alive before the instruction
     * at the given offset.
     */
    public boolean isAliveBefore(int instructionOffset, int variableIndex)
    {
        return variableIndex >= MAX_VARIABLES_SIZE ||
               (isAliveBefore[instructionOffset] & (1L << variableIndex)) != 0;
    }


    /**
     * Sets whether the specified variable is alive before the instruction
     * at the given offset.
     */
    public void setAliveBefore(int instructionOffset, int variableIndex, boolean alive)
    {
        if (variableIndex < MAX_VARIABLES_SIZE)
        {
            if (alive)
            {
                isAliveBefore[instructionOffset] |= 1L << variableIndex;
            }
            else
            {
                isAliveBefore[instructionOffset] &= ~(1L << variableIndex);
            }
        }
    }


    /**
     * Returns whether the specified variable is alive after the instruction
     * at the given offset.
     */
    public boolean isAliveAfter(int instructionOffset, int variableIndex)
    {
        return variableIndex >= MAX_VARIABLES_SIZE ||
               (isAliveAfter[instructionOffset] & (1L << variableIndex)) != 0;
    }


    /**
     * Sets whether the specified variable is alive after the instruction
     * at the given offset.
     */
    public void setAliveAfter(int instructionOffset, int variableIndex, boolean alive)
    {
        if (variableIndex < MAX_VARIABLES_SIZE)
        {
            if (alive)
            {
                isAliveAfter[instructionOffset] |= 1L << variableIndex;
            }
            else
            {
                isAliveAfter[instructionOffset] &= ~(1L << variableIndex);
            }
        }
    }


    /**
     * Returns whether the specified variable takes up two entries after the
     * instruction at the given offset.
     */
    public boolean isCategory2(int instructionOffset, int variableIndex)
    {
        return variableIndex < MAX_VARIABLES_SIZE &&
               (isCategory2[instructionOffset] & (1L << variableIndex)) != 0;
    }


    /**
     * Sets whether the specified variable takes up two entries after the
     * instruction at the given offset.
     */
    public void setCategory2(int instructionOffset, int variableIndex, boolean category2)
    {
        if (variableIndex < MAX_VARIABLES_SIZE)
        {
            if (category2)
            {
                isCategory2[instructionOffset] |= 1L << variableIndex;
            }
            else
            {
                isCategory2[instructionOffset] &= ~(1L << variableIndex);
            }
        }
    }


    // Implementations for AttributeVisitor.

    public void visitAnyAttribute(Clazz clazz, Attribute attribute) {}


    public void visitCodeAttribute(Clazz clazz, Method method, CodeAttribute codeAttribute)
    {
//        DEBUG =
//            clazz.getName().equals("abc/Def") &&
//            method.getName(clazz).equals("abc");

        if (DEBUG)
        {
            System.out.println();
            System.out.println("Liveness analysis: "+clazz.getName()+"."+method.getName(clazz)+method.getDescriptor(clazz));
        }

        // Initialize the global arrays.
        initializeArrays(codeAttribute);

        // Evaluate the method.
        partialEvaluator.visitCodeAttribute(clazz, method, codeAttribute);

        int codeLength    = codeAttribute.u4codeLength;
        int variablesSize = codeAttribute.u2maxLocals;

        // We'll only really analyze the first 64 variables.
        if (variablesSize > MAX_VARIABLES_SIZE)
        {
            variablesSize = MAX_VARIABLES_SIZE;
        }

        // Mark liveness blocks, as many times as necessary.
        boolean checkAgain;
        do
        {
            checkAgain = false;

            alive = 0L;

            // Loop over all traced instructions, backward.
            for (int offset = codeLength - 1; offset >= 0; offset--)
            {
                if (partialEvaluator.isTraced(offset))
                {
                    // Update the liveness after the instruction.
                    isAliveAfter[offset] |= alive;

                    // Update the liveness based on the instruction.
                    codeAttribute.instructionAccept(clazz, method, offset, this);

                    // Update the liveness based on the branch targets.
                    InstructionOffsetValue branchTargets = partialEvaluator.branchTargets(offset);
                    if (branchTargets != null)
                    {
                        alive |= combinedLiveness(branchTargets);

                        // Mark the variables right after the switch instruction.
                        isAliveAfter[offset] = alive;
                    }

                    // Update the liveness before the instruction.
                    if ((~isAliveBefore[offset] & alive) != 0)
                    {
                        isAliveBefore[offset] |= alive;

                        // Do we have to check again after this loop?
                        if (!checkAgain)
                        {
                            checkAgain = offset < maxOffset(partialEvaluator.branchOrigins(offset));
                        }
                    }
                }
            }
        }
        while (checkAgain);

        // Check the liveness at the start of the exception handlers.
        codeAttribute.exceptionsAccept(clazz, method, this);

        // Loop over all instructions, to mark variables that take up two entries.