examples/analysis/src/Analysis.java

/***
 * ASM examples: examples showing how ASM can be used
 * Copyright (c) 2000,2002,2003 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.Constants;
import org.objectweb.asm.Label;
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.TreeClassAdapter;
import org.objectweb.asm.tree.VarInsnNode;
import org.objectweb.asm.tree.analysis.Analyzer;
import org.objectweb.asm.tree.analysis.DataflowInterpreter;
import org.objectweb.asm.tree.analysis.DataflowValue;
import org.objectweb.asm.tree.analysis.Frame;
import org.objectweb.asm.util.TraceCodeVisitor;

/**
 * @author Eric Bruneton
 */

public class Analysis implements Constants {
  
  public static void main (String[] args) throws Exception {
    ClassReader cr = new ClassReader("Analysis");
    TreeClassAdapter ca = new TreeClassAdapter(null);
    cr.accept(ca, true);
    
    List methods = ca.classNode.methods;
    for (int i = 0; i < methods.size(); ++i) {
      MethodNode method = (MethodNode)methods.get(i);
      if (method.instructions.size() > 0) {
        if (!analyze(ca.classNode, method)) {
          TraceCodeVisitor cv = new TraceCodeVisitor(null) {
            public void visitMaxs (int maxStack, int maxLocals) {
              for (int i = 0; i < text.size(); ++i) {
                System.err.print(
                  Integer.toString(i + 1000).substring(1) + ":" + text.get(i));
              }
              System.err.println();
            }
          };
          for (int j = 0; j < method.instructions.size(); ++j) {
            Object insn = method.instructions.get(j);
            if (insn instanceof AbstractInsnNode) {
              ((AbstractInsnNode)insn).accept(cv);
            } else {
              cv.visitLabel((Label)insn);
            }
          }
          cv.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 (ClassNode c, MethodNode m) {
    Analyzer a = new Analyzer(new DataflowInterpreter());
    Frame[] frames = a.analyze(c, 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 stores = new HashSet();
    for (int i = 0; i < m.instructions.size(); ++i) {
      Object insn = m.instructions.get(i);
      if (insn instanceof AbstractInsnNode) {
        int opcode = ((AbstractInsnNode)insn).getOpcode();
        if ((opcode >= ILOAD && opcode <= ALOAD) || opcode == IINC) {
          int var = (opcode == IINC ? ((IincInsnNode)insn).var : ((VarInsnNode)insn).var);
          Frame f = frames[i];
          if (f != null) {
            Set s = ((DataflowValue)f.getLocal(var)).insns;
            Iterator 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) {
      Object insn = m.instructions.get(i);
      if (insn instanceof AbstractInsnNode) {
        int opcode = ((AbstractInsnNode)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 exception handler
        int k = 0;
        if (i > 0) {
          k = i - 1;
        }
        return k;
      } catch (Exception e) { // useless ASTORE instruction (e is never used)
        j = j + 1; // useless
      }
    }
    
    return 0;
  }
}