instructionfinder.java

该开源工具主要用于class文件的操作

package org.apache.bcel.util;

/* ====================================================================
 * The Apache Software License, Version 1.1
 *
 * Copyright (c) 2001 The Apache Software Foundation.  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.
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 *    distribution.
 *
 * 3. The end-user documentation included with the redistribution,
 *    if any, must include the following acknowledgment:
 *       "This product includes software developed by the
 *        Apache Software Foundation (http://www.apache.org/)."
 *    Alternately, this acknowledgment may appear in the software itself,
 *    if and wherever such third-party acknowledgments normally appear.
 *
 * 4. The names "Apache" and "Apache Software Foundation" and
 *    "Apache BCEL" must not be used to endorse or promote products
 *    derived from this software without prior written permission. For
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 *
 * 5. Products derived from this software may not be called "Apache",
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 *
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 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 */

import java.util.*;
import org.apache.bcel.Constants;
import org.apache.bcel.generic.*;
import org.apache.regexp.*;

/** 
 * InstructionFinder is a tool to search for given instructions patterns,
 * i.e., match sequences of instructions in an instruction list via
 * regular expressions. This can be used, e.g., in order to implement
 * a peep hole optimizer that looks for code patterns and replaces
 * them with faster equivalents.
 *
 * <p>This class internally uses the <a href="http://jakarta.apache.org/regexp/">
 * Regexp</a> package to search for regular expressions.
 *
 * A typical application would look like this:
<pre>
    InstructionFinder f   = new InstructionFinder(il);
    String            pat = "IfInstruction ICONST_0 GOTO ICONST_1 NOP (IFEQ|IFNE)";
    
    for(Iterator i = f.search(pat, constraint); i.hasNext(); ) {
      InstructionHandle[] match = (InstructionHandle[])i.next();
      ...
      il.delete(match[1], match[5]);
      ...
    }
</pre>
 * @version $Id: InstructionFinder.java,v 1.1.1.1 2001/10/29 20:00:30 jvanzyl Exp $
 * @author  <A HREF="http://www.berlin.de/~markus.dahm/">M. Dahm</A>
 * @see Instruction
 * @see InstructionList
 */
public class InstructionFinder {
  private static final int OFFSET     = 32767; // char + OFFSET is outside of LATIN-1
  private static final int NO_OPCODES = 256;   // Potential number, some are not used

  private static final HashMap map = new HashMap(); // Map<String,Pattern>

  private InstructionList     il;
  private String              il_string;    // instruction list as string
  private InstructionHandle[] handles;      // map instruction list to array

  /**
   * @param il instruction list to search for given patterns
   */
  public InstructionFinder(InstructionList il) {
    this.il = il;
    reread();
  }

  /**
   * Reread the instruction list, e.g., after you've altered the list upon a match.
   */
  public final void reread() {
    int    size  = il.getLength();
    char[] buf   = new char[size]; // Create a string with length equal to il length
    handles      = il.getInstructionHandles();

    // Map opcodes to characters
    for(int i=0; i < size; i++)
      buf[i] = makeChar(handles[i].getInstruction().getOpcode());

    il_string = new String(buf);
  }

  /**
   * Map symbolic instruction names like "getfield" to a single character.
   *
   * @param pattern instruction pattern in lower case
   * @return encoded string for a pattern such as "BranchInstruction".
   */
  private static final String mapName(String pattern) {
    String result = (String)map.get(pattern);

    if(result != null)
      return result;

    for(short i=0; i < NO_OPCODES; i++)
      if(pattern.equals(Constants.OPCODE_NAMES[i]))
	return "" + makeChar(i);

    throw new RuntimeException("Instruction unknown: " + pattern);
  }

  /**
   * Replace symbolic names of instructions with the appropiate character and remove
   * all white space from string. Meta characters such as +, * are ignored.
   *
   * @param pattern The pattern to compile
   * @return translated regular expression string
   */
  private static final String compilePattern(String pattern) {
    String       lower      = pattern.toLowerCase();
    StringBuffer buf        = new StringBuffer();
    int          size       = pattern.length();

    for(int i=0; i < size; i++) {
      char ch = lower.charAt(i);
      
      if(Character.isLetterOrDigit(ch)) {
	StringBuffer name = new StringBuffer();
	
	while((Character.isLetterOrDigit(ch) || ch == '_') && i < size) {
	  name.append(ch);

	  if(++i < size)
	    ch = lower.charAt(i);
	  else
	    break;
	}
	
	i--;

	buf.append(mapName(name.toString()));
      } else if(!Character.isWhitespace(ch))
	buf.append(ch);
    }

    return buf.toString();
  }

  /**
   * @return the matched piece of code as an array of instruction (handles)
   */
  private InstructionHandle[] getMatch(int matched_from, int match_length) {
    InstructionHandle[] match = new InstructionHandle[match_length];
    System.arraycopy(handles, matched_from, match, 0, match_length);

    return match;
  }

  /**
   * Search for the given pattern in the instruction list. You can search for any valid
   * opcode via its symbolic name, e.g. "istore". You can also use a super class or
   * an interface name to match a whole set of instructions, e.g. "BranchInstruction" or
   * "LoadInstruction". "istore" is also an alias for all "istore_x" instructions. Additional
   * aliases are "if" for "ifxx", "if_icmp" for "if_icmpxx", "if_acmp" for "if_acmpxx".
   *
   * Consecutive instruction names must be separated by white space which will be removed
   * during the compilation of the pattern.
   *
   * For the rest the usual pattern matching rules for regular expressions apply.<P>
   * Example pattern:
   * <pre>
     search("BranchInstruction NOP ((IfInstruction|GOTO)+ ISTORE Instruction)*");
   * </pre>
   *
   * <p>If you alter the instruction list upon a match such that other
   * matching areas are affected, you should call reread() to update
   * the finder and call search() again, because the matches are cached.
   *
   * @param pattern the instruction pattern to search for, where case is ignored
   * @param from where to start the search in the instruction list
   * @param constraint optional CodeConstraint to check the found code pattern for
   * user-defined constraints
   * @return iterator of matches where e.nextElement() returns an array of instruction handles
   * describing the matched area 
   */
  public final Iterator search(String pattern, InstructionHandle from,
			       CodeConstraint constraint)
  {
    String search = compilePattern(pattern);
    int  start    = -1;

    for(int i=0; i < handles.length; i++) {