backwardbranchmarker.java

ProGuard 是一个免费的 Java类文件的压缩

package proguard.optimize.info;

import proguard.classfile.util.SimplifiedVisitor;
import proguard.classfile.instruction.visitor.InstructionVisitor;
import proguard.classfile.instruction.*;
import proguard.classfile.constant.visitor.ConstantVisitor;
import proguard.classfile.constant.RefConstant;
import proguard.classfile.*;
import proguard.classfile.attribute.CodeAttribute;

/**
 * This InstructionVisitor marks all methods that branch backward in any of the
 * instructions that it visits.
 *
 * @author Eric Lafortune
 */
public class BackwardBranchMarker
extends      SimplifiedVisitor
implements   InstructionVisitor
{
    // Implementations for InstructionVisitor.

    public void visitAnyInstruction(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, Instruction instruction) {}


    public void visitBranchInstruction(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, BranchInstruction branchInstruction)
    {
        markBackwardBranch(method, branchInstruction.branchOffset);
    }


    public void visitTableSwitchInstruction(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, TableSwitchInstruction tableSwitchInstruction)
    {
        markBackwardBranch(method, tableSwitchInstruction.defaultOffset);

        for (int index = 0; index < tableSwitchInstruction.jumpOffsetCount; index++)
        {
            markBackwardBranch(method, tableSwitchInstruction.jumpOffsets[index]);
        }
    }


    public void visitLookUpSwitchInstruction(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, LookUpSwitchInstruction lookUpSwitchInstruction)
    {
        markBackwardBranch(method, lookUpSwitchInstruction.defaultOffset);

        for (int index = 0; index < lookUpSwitchInstruction.jumpOffsetCount; index++)
        {
            markBackwardBranch(method, lookUpSwitchInstruction.jumpOffsets[index]);
        }
    }


    // Small utility methods.

    /**
     * Marks the given method if the given branch offset is negative.
     */
    private void markBackwardBranch(Method method, int branchOffset)
    {
        if (branchOffset < 0)
        {
            setBranchesBackward(method);
        }
    }


    private static void setBranchesBackward(Method method)
    {
        MethodOptimizationInfo info = MethodOptimizationInfo.getMethodOptimizationInfo(method);
        if (info != null)
        {
            info.setBranchesBackward();
        }
    }


    public static boolean branchesBackward(Method method)
    {
        MethodOptimizationInfo info = MethodOptimizationInfo.getMethodOptimizationInfo(method);
        return info == null || info.branchesBackward();
    }
}