parameterusagemarker.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 program 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 program 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 General Public License for
 * more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 */
package proguard.optimize.info;

import proguard.classfile.*;
import proguard.classfile.util.*;
import proguard.classfile.visitor.*;
import proguard.optimize.info.MethodOptimizationInfo;
import proguard.optimize.MethodDescriptorShrinker;

/**
 * This MemberVisitor counts the parameters and marks the used parameters
 * of the methods that it visits. It also marks the 'this' parameters of
 * methods that have a hierarchy.
 *
 * @author Eric Lafortune
 */
public class ParameterUsageMarker
extends      SimplifiedVisitor
implements   MemberVisitor
{
    private VariableUsageMarker variableUsageMarker = new VariableUsageMarker();


    // Implementations for MemberVisitor.

    public void visitProgramMethod(ProgramClass programClass, ProgramMethod programMethod)
    {
        int parameterSize = parameterSize(programClass, programMethod);
        if (parameterSize > 0)
        {
            long usedParameters = 0L;

            if ((programMethod.getAccessFlags() & ClassConstants.INTERNAL_ACC_ABSTRACT) == 0)
            {
                // Figure out the local variables that are used by the code.
                programMethod.attributesAccept(programClass, variableUsageMarker);

                // Mark the parameters that are used by the code.
                for (int index = 0; index < parameterSize; index++)
                {
                    if (variableUsageMarker.isVariableUsed(index))
                    {
                        usedParameters |= 1L << index;
                    }
                }
            }

            // Mark the 'this' parameter if the method can have other implementations.
            if (programClass.mayHaveImplementations(programMethod))
            {
                // All implementations must at least keep the 'this' parameter too.
                usedParameters |= 1L;
            }

            // Is it an <init> method?
            else if (programMethod.getName(programClass).equals(ClassConstants.INTERNAL_METHOD_NAME_INIT))
            {
                // Instance initializers always require the 'this' parameter.
                usedParameters |= 1L;

                // Mark the parameters preliminarily.
                markUsedParameters(programMethod, usedParameters);

                // Is there a name clash with some existing <init> method?
                if (programClass.findMethod(ClassConstants.INTERNAL_METHOD_NAME_INIT,
                                            MethodDescriptorShrinker.shrinkDescriptor(programClass,
                                                                                                        programMethod)) != null)
                {
                    // Cancel the shrinking. Mark all parameters.
                    usedParameters |= parameterMask(parameterSize);
                }
            }

            // Mark the parameters.
            markUsedParameters(programMethod, usedParameters);
        }

        // Set the parameter size.
        setParameterSize(programMethod, parameterSize);
    }


    public void visitLibraryMethod(LibraryClass libraryClass, LibraryMethod libraryMethod)
    {
        // Can the method have other implementations?
        if (libraryClass.mayHaveImplementations(libraryMethod))
        {
            // All implementations must keep all parameters of this method,
            // including the 'this' parameter.
            long usedParameters = parameterMask(parameterSize(libraryClass, libraryMethod));

            // Mark it.
            markUsedParameters(libraryMethod, usedParameters);
        }
    }


    // Small utility methods.

    /**
     * Sets the total size of the parameters.
     */
    private static void setParameterSize(Method method, int parameterSize)
    {
        MethodOptimizationInfo info = MethodOptimizationInfo.getMethodOptimizationInfo(method);
        if (info != null)
        {
            info.setParameterSize(parameterSize);
        }
    }


    /**
     * Returns the total size of the parameters.
     */
    public static int getParameterSize(Method method)
    {
        MethodOptimizationInfo info = MethodOptimizationInfo.getMethodOptimizationInfo(method);
        return info != null ? info.getParameterSize() : 0;
    }


    /**
     * Marks the given parameter as being used.
     */
    private static void markParameterUsed(Method method, int variableIndex)
    {
        MethodOptimizationInfo info = MethodOptimizationInfo.getMethodOptimizationInfo(method);
        if (info != null)
        {
            info.setParameterUsed(variableIndex);
        }
    }


    /**
     * Marks the given parameters as being used.
     */
    private void markUsedParameters(Method method, long usedParameters)
    {
        MethodOptimizationInfo info = MethodOptimizationInfo.getMethodOptimizationInfo(method);
        if (info != null)
        {
            info.setUsedParameters(info.getUsedParameters() | usedParameters);
        }
    }


    /**
     * Returns whether the given parameter is being used.
     */
    public static boolean isParameterUsed(Method method, int variableIndex)
    {
        MethodOptimizationInfo info = MethodOptimizationInfo.getMethodOptimizationInfo(method);
        return info == null ||
               info.isParameterUsed(variableIndex);
    }


    /**
     * Returns which parameters are being used.
     */
    public static long getUsedParameters(Method method)
    {
        MethodOptimizationInfo info = MethodOptimizationInfo.getMethodOptimizationInfo(method);
        return info != null ? info.getUsedParameters() : -1L;
    }


    /**
     * Returns a bit mask of 1-bits of the given size.
     */
    private int parameterMask(int parameterSize)
    {
        return (1 << parameterSize) - 1;
    }


    /**
     * Returns the parameter size of the given method, including the 'this'
     * parameter, if any.
     */
    private int parameterSize(Clazz clazz, Method method)
    {
        int parameterSize = ClassUtil.internalMethodParameterSize(method.getDescriptor(clazz));
        if ((method.getAccessFlags() & ClassConstants.INTERNAL_ACC_STATIC) == 0)
        {
            parameterSize++;
        }

        return parameterSize;
    }
}