001: /***
002: * ASM Guide
003: * Copyright (c) 2007 Eric Bruneton
004: * All rights reserved.
005: *
006: * Redistribution and use in source and binary forms, with or without
007: * modification, are permitted provided that the following conditions
008: * are met:
009: * 1. Redistributions of source code must retain the above copyright
010: * notice, this list of conditions and the following disclaimer.
011: * 2. Redistributions in binary form must reproduce the above copyright
012: * notice, this list of conditions and the following disclaimer in the
013: * documentation and/or other materials provided with the distribution.
014: * 3. Neither the name of the copyright holders nor the names of its
015: * contributors may be used to endorse or promote products derived from
016: * this software without specific prior written permission.
017: *
018: * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
019: * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
020: * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
021: * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
022: * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
023: * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
024: * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
025: * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
026: * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
027: * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
028: * THE POSSIBILITY OF SUCH DAMAGE.
029: */package ch6.sec1;
030:
031: import static org.objectweb.asm.Opcodes.ALOAD;
032: import static org.objectweb.asm.Opcodes.GETFIELD;
033: import static org.objectweb.asm.Opcodes.PUTFIELD;
034:
035: import java.util.Iterator;
036:
037: import org.objectweb.asm.tree.AbstractInsnNode;
038: import org.objectweb.asm.tree.FieldInsnNode;
039: import org.objectweb.asm.tree.InsnList;
040: import org.objectweb.asm.tree.LineNumberNode;
041: import org.objectweb.asm.tree.MethodNode;
042: import org.objectweb.asm.tree.VarInsnNode;
043:
044: /**
045: * ASM Guide example class.
046: *
047: * @author Eric Bruneton
048: */
049: public class RemoveGetFieldPutFieldTransformer extends
050: MethodTransformer {
051:
052: public RemoveGetFieldPutFieldTransformer(MethodTransformer mt) {
053: super (mt);
054: }
055:
056: public void transform(MethodNode mn) {
057: InsnList insns = mn.instructions;
058: Iterator i = insns.iterator();
059: while (i.hasNext()) {
060: AbstractInsnNode i1 = (AbstractInsnNode) i.next();
061: if (isALOAD0(i1)) {
062: AbstractInsnNode i2 = getNext(i1);
063: if (i2 != null && isALOAD0(i2)) {
064: AbstractInsnNode i3 = getNext(i2);
065: if (i3 != null && i3.getOpcode() == GETFIELD) {
066: AbstractInsnNode i4 = getNext(i3);
067: if (i4 != null && i4.getOpcode() == PUTFIELD) {
068: if (sameField(i3, i4)) {
069: while (i.next() != i4) {
070: }
071: insns.remove(i1);
072: insns.remove(i2);
073: insns.remove(i3);
074: insns.remove(i4);
075: }
076: }
077: }
078: }
079: }
080: }
081: super .transform(mn);
082: }
083:
084: private static AbstractInsnNode getNext(AbstractInsnNode insn) {
085: do {
086: insn = insn.getNext();
087: if (insn != null && !(insn instanceof LineNumberNode)) {
088: break;
089: }
090: } while (insn != null);
091: return insn;
092: }
093:
094: private static boolean isALOAD0(AbstractInsnNode i) {
095: return i.getOpcode() == ALOAD && ((VarInsnNode) i).var == 0;
096: }
097:
098: private static boolean sameField(AbstractInsnNode i,
099: AbstractInsnNode j) {
100: return ((FieldInsnNode) i).name
101: .equals(((FieldInsnNode) j).name);
102: }
103: }
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