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/***
* ASM examples: examples showing how ASM can be used
* Copyright (c) 2000-2011 INRIA, France Telecom
* 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.
*/
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Set;
import org.objectweb.asm.ClassReader;
import org.objectweb.asm.MethodVisitor;
import org.objectweb.asm.Opcodes;
import org.objectweb.asm.tree.AbstractInsnNode;
import org.objectweb.asm.tree.ClassNode;
import org.objectweb.asm.tree.IincInsnNode;
import org.objectweb.asm.tree.MethodNode;
import org.objectweb.asm.tree.VarInsnNode;
import org.objectweb.asm.tree.analysis.Analyzer;
import org.objectweb.asm.tree.analysis.BasicValue;
import org.objectweb.asm.tree.analysis.BasicVerifier;
import org.objectweb.asm.tree.analysis.Frame;
import org.objectweb.asm.tree.analysis.SourceInterpreter;
import org.objectweb.asm.tree.analysis.SourceValue;
import org.objectweb.asm.util.TraceMethodVisitor;
import org.objectweb.asm.util.Textifier;
/**
* @author Eric Bruneton
*/
public class Analysis implements Opcodes {
public static void main(final String[] args) throws Exception {
ClassReader cr = new ClassReader("Analysis");
ClassNode cn = new ClassNode();
cr.accept(cn, ClassReader.SKIP_DEBUG);
List<MethodNode> methods = cn.methods;
for (int i = 0; i < methods.size(); ++i) {
MethodNode method = methods.get(i);
if (method.instructions.size() > 0) {
if (!analyze(cn, method)) {
Analyzer<?> a = new Analyzer<BasicValue>(
new BasicVerifier());
try {
a.analyze(cn.name, method);
} catch (Exception ignored) {
}
final Frame<?>[] frames = a.getFrames();
Textifier t = new Textifier() {
@Override
public void visitMaxs(final int maxStack,
final int maxLocals) {
for (int i = 0; i < text.size(); ++i) {
StringBuffer s = new StringBuffer(
frames[i] == null ? "null"
: frames[i].toString());
while (s.length() < Math.max(20, maxStack
+ maxLocals + 1)) {
s.append(' ');
}
System.err.print(Integer.toString(i + 1000)
.substring(1)
+ " "
+ s
+ " : "
+ text.get(i));
}
System.err.println();
}
};
MethodVisitor mv = new TraceMethodVisitor(t);
for (int j = 0; j < method.instructions.size(); ++j) {
Object insn = method.instructions.get(j);
((AbstractInsnNode) insn).accept(mv);
}
mv.visitMaxs(0, 0);
}
}
}
}
/*
* Detects unused xSTORE instructions, i.e. xSTORE instructions without at
* least one xLOAD corresponding instruction in their successor instructions
* (in the control flow graph).
*/
public static boolean analyze(final ClassNode c, final MethodNode m)
throws Exception {
Analyzer<SourceValue> a = new Analyzer<SourceValue>(
new SourceInterpreter());
Frame<SourceValue>[] frames = a.analyze(c.name, m);
// for each xLOAD instruction, we find the xSTORE instructions that can
// produce the value loaded by this instruction, and we put them in
// 'stores'
Set<AbstractInsnNode> stores = new HashSet<AbstractInsnNode>();
for (int i = 0; i < m.instructions.size(); ++i) {
AbstractInsnNode insn = m.instructions.get(i);
int opcode = insn.getOpcode();
if ((opcode >= ILOAD && opcode <= ALOAD) || opcode == IINC) {
int var = opcode == IINC ? ((IincInsnNode) insn).var
: ((VarInsnNode) insn).var;
Frame<SourceValue> f = frames[i];
if (f != null) {
Set<AbstractInsnNode> s = f.getLocal(var).insns;
Iterator<AbstractInsnNode> j = s.iterator();
while (j.hasNext()) {
insn = j.next();
if (insn instanceof VarInsnNode) {
stores.add(insn);
}
}
}
}
}
// we then find all the xSTORE instructions that are not in 'stores'
boolean ok = true;
for (int i = 0; i < m.instructions.size(); ++i) {
AbstractInsnNode insn = m.instructions.get(i);
int opcode = insn.getOpcode();
if (opcode >= ISTORE && opcode <= ASTORE) {
if (!stores.contains(insn)) {
ok = false;
System.err.println("method " + m.name + ", instruction "
+ i + ": useless store instruction");
}
}
}
return ok;
}
/*
* Test for the above method, with three useless xSTORE instructions.
*/
public int test(int i, int j) {
i = i + 1; // ok, because i can be read after this point
if (j == 0) {
j = 1; // useless
} else {
try {
j = j - 1; // ok, because j can be accessed in the catch
int k = 0;
if (i > 0) {
k = i - 1;
}
return k;
} catch (Exception e) { // useless ASTORE (e is never used)
j = j + 1; // useless
}
}
return 0;
}
}
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