asmlib.extra.RemoveUnusedTryCatchBlockMethodVisitor.java Source code

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Here is the source code for asmlib.extra.RemoveUnusedTryCatchBlockMethodVisitor.java

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/*
 * asmlib: a toolkit based on ASM for working with java bytecode
 * Copyright (C) 2015 Ivo Anjo <ivo.anjo@ist.utl.pt>
 *
 * This file is part of asmlib.
 *
 * asmlib 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 3 of the License, or
 * (at your option) any later version.
 *
 * asmlib 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 asmlib.  If not, see <http://www.gnu.org/licenses/>.
 */

package asmlib.extra;

import java.util.ArrayList;

import org.objectweb.asm.*;

/** MethodVisitor that removes unused TryCatchBlocks.
  * Currently it only considers as unused a TryCatchBlock with the same start and end as an earlier
  * (and thus higher priority) block, and having the same type.
  *
  * Correction issues due to incompleteness are not an issue here, because either the JVM will
  * accurately remove other TryCatchBlocks when the class is loaded, or it will signal an error.
  *
  * (To obtain a ClassVisitor, combine it with a GenericMethodVisitorAdapter)
  **/
public class RemoveUnusedTryCatchBlockMethodVisitor extends MethodVisitor {

    private static class TryCatchBlock {
        final Label _start;
        final Label _end;
        final String _type;

        TryCatchBlock(Label start, Label end, String type) {
            _start = start;
            _end = end;
            _type = (type != null) ? type : "java/lang/Throwable";
        }

        @Override
        public boolean equals(Object other) {
            if (!(other instanceof TryCatchBlock))
                throw new IllegalArgumentException();
            TryCatchBlock o = (TryCatchBlock) other;
            return (_start == o._start) && (_end == o._end) && (_type.equals(o._type));
        }
    }

    private final ArrayList<TryCatchBlock> _tryCatchBlockList = new ArrayList<TryCatchBlock>();

    public RemoveUnusedTryCatchBlockMethodVisitor(int access, String name, String desc, String signature,
            String[] exceptions, ClassVisitor cv) {
        super(Opcodes.ASM4, cv.visitMethod(access, name, desc, signature, exceptions));
    }

    @Override
    public void visitTryCatchBlock(Label start, Label end, Label handler, String type) {
        TryCatchBlock currentBlock = new TryCatchBlock(start, end, type);

        for (TryCatchBlock tcb : _tryCatchBlockList)
            if (tcb.equals(currentBlock))
                return;

        _tryCatchBlockList.add(currentBlock);
        super.visitTryCatchBlock(start, end, handler, type);
    }

}