01: /***
02: * ASM Guide
03: * Copyright (c) 2007 Eric Bruneton
04: * All rights reserved.
05: *
06: * Redistribution and use in source and binary forms, with or without
07: * modification, are permitted provided that the following conditions
08: * are met:
09: * 1. Redistributions of source code must retain the above copyright
10: * notice, this list of conditions and the following disclaimer.
11: * 2. Redistributions in binary form must reproduce the above copyright
12: * notice, this list of conditions and the following disclaimer in the
13: * documentation and/or other materials provided with the distribution.
14: * 3. Neither the name of the copyright holders nor the names of its
15: * contributors may be used to endorse or promote products derived from
16: * this software without specific prior written permission.
17: *
18: * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
19: * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
20: * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
21: * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
22: * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
23: * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
24: * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
25: * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
26: * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
27: * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
28: * THE POSSIBILITY OF SUCH DAMAGE.
29: */package ch6.sec1;
30:
31: import static org.objectweb.asm.Opcodes.ATHROW;
32: import static org.objectweb.asm.Opcodes.GOTO;
33: import static org.objectweb.asm.Opcodes.IRETURN;
34: import static org.objectweb.asm.Opcodes.RETURN;
35:
36: import java.util.Iterator;
37:
38: import org.objectweb.asm.tree.AbstractInsnNode;
39: import org.objectweb.asm.tree.InsnList;
40: import org.objectweb.asm.tree.JumpInsnNode;
41: import org.objectweb.asm.tree.LabelNode;
42: import org.objectweb.asm.tree.MethodNode;
43:
44: /**
45: * ASM Guide example class.
46: *
47: * @author Eric Bruneton
48: */
49: public class OptimizeJumpTransformer extends MethodTransformer {
50:
51: public OptimizeJumpTransformer(MethodTransformer mt) {
52: super (mt);
53: }
54:
55: public void transform(MethodNode mn) {
56: InsnList insns = mn.instructions;
57: Iterator i = insns.iterator();
58: while (i.hasNext()) {
59: AbstractInsnNode in = (AbstractInsnNode) i.next();
60: if (in instanceof JumpInsnNode) {
61: LabelNode label = ((JumpInsnNode) in).label;
62: AbstractInsnNode target;
63: // while target == goto l, replace label with l
64: while (true) {
65: target = label;
66: while (target != null && target.getOpcode() < 0) {
67: target = target.getNext();
68: }
69: if (target != null && target.getOpcode() == GOTO) {
70: label = ((JumpInsnNode) target).label;
71: } else {
72: break;
73: }
74: }
75: // update target
76: ((JumpInsnNode) in).label = label;
77: // if possible, replace jump with target instruction
78: if (in.getOpcode() == GOTO && target != null) {
79: int op = target.getOpcode();
80: if ((op >= IRETURN && op <= RETURN) || op == ATHROW) {
81: // replace 'in' with clone of 'target'
82: insns.set(in, target.clone(null));
83: }
84: }
85: }
86: }
87: super.transform(mn);
88: }
89: }
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