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A Java Optimization Framework
There is a newer version: 4.6.0
package soot.toolkits.scalar;

/*-
 * #%L
 * Soot - a J*va Optimization Framework
 * %%
 * Copyright (C) 1997 - 1999 Raja Vallee-Rai
 * %%
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as
 * published by the Free Software Foundation, either version 2.1 of the
 * License, or (at your option) any later version.
 * 
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Lesser Public License for more details.
 * 
 * You should have received a copy of the GNU General Lesser Public
 * License along with this program.  If not, see
 * .
 * #L%
 */

import java.util.ArrayDeque;
import java.util.BitSet;
import java.util.Deque;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import soot.Body;
import soot.BodyTransformer;
import soot.G;
import soot.Local;
import soot.Scene;
import soot.Singletons;
import soot.Timers;
import soot.Unit;
import soot.Value;
import soot.ValueBox;
import soot.options.Options;
import soot.toolkits.exceptions.ThrowAnalysis;
import soot.toolkits.graph.ExceptionalUnitGraph;
import soot.util.LocalBitSetPacker;

/**
 * A BodyTransformer that attemps to indentify and separate uses of a local variable that are independent of each other.
 * Conceptually the inverse transform with respect to the LocalPacker transform.
 *
 *
 * For example the code:
 *
 * for(int i; i < k; i++); for(int i; i < k; i++);
 *
 * would be transformed into: for(int i; i < k; i++); for(int j; j < k; j++);
 *
 *
 *
 * @see BodyTransformer
 * @see LocalPacker
 * @see Body
 */
public class LocalSplitter extends BodyTransformer {
  private static final Logger logger = LoggerFactory.getLogger(LocalSplitter.class);

  protected ThrowAnalysis throwAnalysis;
  protected boolean omitExceptingUnitEdges;

  public LocalSplitter(Singletons.Global g) {
  }

  public LocalSplitter(ThrowAnalysis ta) {
    this(ta, false);
  }

  public LocalSplitter(ThrowAnalysis ta, boolean omitExceptingUnitEdges) {
    this.throwAnalysis = ta;
    this.omitExceptingUnitEdges = omitExceptingUnitEdges;
  }

  public static LocalSplitter v() {
    return G.v().soot_toolkits_scalar_LocalSplitter();
  }

  @Override
  protected void internalTransform(Body body, String phaseName, Map options) {
    if (Options.v().verbose()) {
      logger.debug("[" + body.getMethod().getName() + "] Splitting locals...");
    }

    if (Options.v().time()) {
      Timers.v().splitTimer.start();
    }

    if (Options.v().time()) {
      Timers.v().splitPhase1Timer.start();
    }

    if (throwAnalysis == null) {
      throwAnalysis = Scene.v().getDefaultThrowAnalysis();
    }

    if (omitExceptingUnitEdges == false) {
      omitExceptingUnitEdges = Options.v().omit_excepting_unit_edges();
    }

    // Pack the locals for efficiency
    final LocalBitSetPacker localPacker = new LocalBitSetPacker(body);
    localPacker.pack();

    // Go through the definitions, building the webs
    ExceptionalUnitGraph graph = new ExceptionalUnitGraph(body, throwAnalysis, omitExceptingUnitEdges);

    // run in panic mode on first split (maybe change this depending on the input
    // source)
    final LocalDefs defs = LocalDefs.Factory.newLocalDefs(graph, true);
    final LocalUses uses = LocalUses.Factory.newLocalUses(graph, defs);

    if (Options.v().time()) {
      Timers.v().splitPhase1Timer.end();
    }
    if (Options.v().time()) {
      Timers.v().splitPhase2Timer.start();
    }

    Set visited = new HashSet();

    // Collect the set of locals that we need to split^
    BitSet localsToSplit = new BitSet(localPacker.getLocalCount());
    {
      BitSet localsVisited = new BitSet(localPacker.getLocalCount());
      for (Unit s : body.getUnits()) {
        if (s.getDefBoxes().isEmpty()) {
          continue;
        }
        if (!(s.getDefBoxes().get(0).getValue() instanceof Local)) {
          continue;
        }

        // If we see a local the second time, we know that we must split it
        Local l = (Local) s.getDefBoxes().get(0).getValue();
        if (localsVisited.get(l.getNumber())) {
          localsToSplit.set(l.getNumber());
        }
        localsVisited.set(l.getNumber());
      }
    }

    int w = 0;
    for (Unit s : body.getUnits()) {
      if (s.getDefBoxes().isEmpty()) {
        continue;
      }

      if (s.getDefBoxes().size() > 1) {
        throw new RuntimeException("stmt with more than 1 defbox!");
      }

      if (!(s.getDefBoxes().get(0).getValue() instanceof Local)) {
        continue;
      }

      // we don't want to visit a node twice
      if (visited.remove(s)) {
        continue;
      }

      // always reassign locals to avoid "use before definition" bugs!
      // unfortunately this creates a lot of new locals, so it's important
      // to remove them afterwards
      Local oldLocal = (Local) s.getDefBoxes().get(0).getValue();
      if (!localsToSplit.get(oldLocal.getNumber())) {
        continue;
      }
      Local newLocal = (Local) oldLocal.clone();

      newLocal.setName(newLocal.getName() + '#' + ++w); // renaming should not be done here
      body.getLocals().add(newLocal);

      Deque queue = new ArrayDeque();
      queue.addFirst(s);
      do {
        final Unit head = queue.removeFirst();
        if (visited.add(head)) {
          for (UnitValueBoxPair use : uses.getUsesOf(head)) {
            ValueBox vb = use.valueBox;
            Value v = vb.getValue();

            if (v == newLocal) {
              continue;
            }

            // should always be true - but who knows ...
            if (v instanceof Local) {
              Local l = (Local) v;
              queue.addAll(defs.getDefsOfAt(l, use.unit));
              vb.setValue(newLocal);
            }
          }

          for (ValueBox vb : head.getDefBoxes()) {
            Value v = vb.getValue();
            if (v instanceof Local) {
              vb.setValue(newLocal);
            }
          }
        }
      } while (!queue.isEmpty());

      // keep the set small
      visited.remove(s);
    }

    // Restore the original local numbering
    localPacker.unpack();

    if (Options.v().time()) {
      Timers.v().splitPhase2Timer.end();
    }

    if (Options.v().time()) {
      Timers.v().splitTimer.end();
    }
  }
}