/***
* ASM Guide
* Copyright (c) 2007 Eric Bruneton
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. Neither the name of the copyright holders nor the names of its
* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
* THE POSSIBILITY OF SUCH DAMAGE.
*/
package ch6.sec1;
import static org.objectweb.asm.Opcodes.ATHROW;
import static org.objectweb.asm.Opcodes.GOTO;
import static org.objectweb.asm.Opcodes.IRETURN;
import static org.objectweb.asm.Opcodes.RETURN;
import java.util.Iterator;
import org.objectweb.asm.tree.AbstractInsnNode;
import org.objectweb.asm.tree.InsnList;
import org.objectweb.asm.tree.JumpInsnNode;
import org.objectweb.asm.tree.LabelNode;
import org.objectweb.asm.tree.MethodNode;
/**
* ASM Guide example class.
*
* @author Eric Bruneton
*/
public class OptimizeJumpTransformer extends MethodTransformer {
public OptimizeJumpTransformer(MethodTransformer mt) {
super(mt);
}
public void transform(MethodNode mn) {
InsnList insns = mn.instructions;
Iterator i = insns.iterator();
while (i.hasNext()) {
AbstractInsnNode in = (AbstractInsnNode) i.next();
if (in instanceof JumpInsnNode) {
LabelNode label = ((JumpInsnNode) in).label;
AbstractInsnNode target;
// while target == goto l, replace label with l
while (true) {
target = label;
while (target != null && target.getOpcode() < 0) {
target = target.getNext();
}
if (target != null && target.getOpcode() == GOTO) {
label = ((JumpInsnNode) target).label;
} else {
break;
}
}
// update target
((JumpInsnNode) in).label = label;
// if possible, replace jump with target instruction
if (in.getOpcode() == GOTO && target != null) {
int op = target.getOpcode();
if ((op >= IRETURN && op <= RETURN) || op == ATHROW) {
// replace 'in' with clone of 'target'
insns.set(in, target.clone(null));
}
}
}
}
super.transform(mn);
}
}