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/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
*/
import java.util.Iterator;
import org.apache.bcel.Repository;
import org.apache.bcel.classfile.JavaClass;
import org.apache.bcel.classfile.Method;
import org.apache.bcel.generic.ConstantPoolGen;
import org.apache.bcel.generic.InstructionHandle;
import org.apache.bcel.generic.InstructionList;
import org.apache.bcel.generic.InstructionTargeter;
import org.apache.bcel.generic.MethodGen;
import org.apache.bcel.generic.TargetLostException;
import org.apache.bcel.util.InstructionFinder;
/**
* Remove NOPs from given class
*
* @version $Id$
* @author <A HREF="mailto:m.dahm@gmx.de">M. Dahm</A>
*/
public class Peephole {
public static void main(String[] argv) {
try {
/* Load the class from CLASSPATH.
*/
JavaClass clazz = Repository.lookupClass(argv[0]);
Method[] methods = clazz.getMethods();
ConstantPoolGen cp = new ConstantPoolGen(clazz.getConstantPool());
for(int i=0; i < methods.length; i++) {
if(!(methods[i].isAbstract() || methods[i].isNative())) {
MethodGen mg = new MethodGen(methods[i],
clazz.getClassName(), cp);
Method stripped = removeNOPs(mg);
if(stripped != null) {
methods[i] = stripped; // Overwrite with stripped method
}
}
}
/* Dump the class to <class name>_.class
*/
clazz.setConstantPool(cp.getFinalConstantPool());
clazz.dump(clazz.getClassName() + "_.class");
} catch(Exception e) { e.printStackTrace(); }
}
private static final Method removeNOPs(MethodGen mg) {
InstructionList il = mg.getInstructionList();
InstructionFinder f = new InstructionFinder(il);
String pat = "NOP+"; // Find at least one NOP
InstructionHandle next = null;
int count = 0;
for(Iterator<InstructionHandle[]> e = f.search(pat); e.hasNext(); ) {
InstructionHandle[] match = e.next();
InstructionHandle first = match[0];
InstructionHandle last = match[match.length - 1];
/* Some nasty Java compilers may add NOP at end of method.
*/
if((next = last.getNext()) == null) {
break;
}
count += match.length;
/* Delete NOPs and redirect any references to them to the following
* (non-nop) instruction.
*/
try {
il.delete(first, last);
} catch(TargetLostException e2) {
InstructionHandle[] targets = e2.getTargets();
for(int i=0; i < targets.length; i++) {
InstructionTargeter[] targeters = targets[i].getTargeters();
for(int j=0; j < targeters.length; j++) {
targeters[j].updateTarget(targets[i], next);
}
}
}
}
Method m = null;
if(count > 0) {
System.out.println("Removed " + count + " NOP instructions from method " +
mg.getName());
m = mg.getMethod();
}
il.dispose(); // Reuse instruction handles
return m;
}
}
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