EliminateLoopsHelper.java

/*
 * Copyright 2000-2016 JetBrains s.r.o.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.jetbrains.java.decompiler.modules.decompiler;

import org.jetbrains.java.decompiler.modules.decompiler.stats.DoStatement;
import org.jetbrains.java.decompiler.modules.decompiler.stats.Statement;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;


public class EliminateLoopsHelper {


  //	public static boolean eliminateLoops(Statement root) {
  //
  //		boolean ret = eliminateLoopsRec(root);
  //
  //		if(ret) {
  //			SequenceHelper.condenseSequences(root);
  //
  //			HashSet<Integer> setReorderedIfs = new HashSet<Integer>();
  //
  //			SimplifyExprentsHelper sehelper = new SimplifyExprentsHelper(false);
  //			while(sehelper.simplifyStackVarsStatement(root, setReorderedIfs, null)) {
  //				SequenceHelper.condenseSequences(root);
  //			}
  //		}
  //
  //		return ret;
  //	}

  private static boolean eliminateLoopsRec(Statement stat) {

    for (Statement st : stat.getStats()) {
      if (eliminateLoopsRec(st)) {
        return true;
      }
    }

    if (stat.type == Statement.TYPE_DO && isLoopRedundant((DoStatement)stat)) {
      return true;
    }

    return false;
  }

  private static boolean isLoopRedundant(DoStatement loop) {

    if (loop.getLooptype() != DoStatement.LOOP_DO) {
      return false;
    }

    // get parent loop if exists
    Statement parentloop = loop.getParent();
    while (parentloop != null && parentloop.type != Statement.TYPE_DO) {
      parentloop = parentloop.getParent();
    }

    if (parentloop == null || parentloop.getBasichead() != loop.getBasichead()) {
      return false;
    }

    // collect relevant break edges
    List<StatEdge> lstBreakEdges = new ArrayList<>();
    for (StatEdge edge : loop.getLabelEdges()) {
      if (edge.getType() == StatEdge.TYPE_BREAK) { // all break edges are explicit because of LOOP_DO type
        lstBreakEdges.add(edge);
      }
    }


    Statement loopcontent = loop.getFirst();

    boolean firstok = loopcontent.getAllSuccessorEdges().isEmpty();
    if (!firstok) {
      StatEdge edge = loopcontent.getAllSuccessorEdges().get(0);
      firstok = (edge.closure == loop && edge.getType() == StatEdge.TYPE_BREAK);
      if (firstok) {
        lstBreakEdges.remove(edge);
      }
    }


    if (!lstBreakEdges.isEmpty()) {
      if (firstok) {

        HashMap<Integer, Boolean> statLabeled = new HashMap<>();
        List<Statement> lstEdgeClosures = new ArrayList<>();

        for (StatEdge edge : lstBreakEdges) {
          Statement minclosure = LowBreakHelper.getMinClosure(loopcontent, edge.getSource());
          lstEdgeClosures.add(minclosure);
        }

        int precount = loop.isLabeled() ? 1 : 0;
        for (Statement st : lstEdgeClosures) {
          if (!statLabeled.containsKey(st.id)) {
            boolean btemp = st.isLabeled();
            precount += btemp ? 1 : 0;
            statLabeled.put(st.id, btemp);
          }
        }

        for (int i = 0; i < lstBreakEdges.size(); i++) {
          Statement st = lstEdgeClosures.get(i);
          statLabeled.put(st.id, LowBreakHelper.isBreakEdgeLabeled(lstBreakEdges.get(i).getSource(), st) | statLabeled.get(st.id));
        }

        for (int i = 0; i < lstBreakEdges.size(); i++) {
          lstEdgeClosures.set(i, getMaxBreakLift(lstEdgeClosures.get(i), lstBreakEdges.get(i), statLabeled, loop));
        }

        statLabeled.clear();
        for (Statement st : lstEdgeClosures) {
          statLabeled.put(st.id, st.isLabeled());
        }

        for (int i = 0; i < lstBreakEdges.size(); i++) {
          Statement st = lstEdgeClosures.get(i);
          statLabeled.put(st.id, LowBreakHelper.isBreakEdgeLabeled(lstBreakEdges.get(i).getSource(), st) | statLabeled.get(st.id));
        }

        long postcount = statLabeled.values().stream().filter(Boolean::booleanValue).count();

        if (precount <= postcount) {
          return false;
        }
        else {
          for (int i = 0; i < lstBreakEdges.size(); i++) {
            lstEdgeClosures.get(i).addLabeledEdge(lstBreakEdges.get(i));
          }
        }
      }
      else {
        return false;
      }
    }

    eliminateLoop(loop, parentloop);

    return true;
  }

  private static Statement getMaxBreakLift(Statement stat, StatEdge edge, HashMap<Integer, Boolean> statLabeled, Statement max) {

    Statement closure = stat;
    Statement newclosure = stat;

    while ((newclosure = getNextBreakLift(newclosure, edge, statLabeled, max)) != null) {
      closure = newclosure;
    }

    return closure;
  }

  private static Statement getNextBreakLift(Statement stat, StatEdge edge, HashMap<Integer, Boolean> statLabeled, Statement max) {

    Statement closure = stat.getParent();

    while (closure != null && closure != max && !closure.containsStatementStrict(edge.getDestination())) {

      boolean edge_labeled = LowBreakHelper.isBreakEdgeLabeled(edge.getSource(), closure);
      boolean stat_labeled = statLabeled.containsKey(closure.id) ? statLabeled.get(closure.id) : closure.isLabeled();

      if (stat_labeled || !edge_labeled) {
        return closure;
      }

      closure = closure.getParent();
    }

    return null;
  }

  private static void eliminateLoop(Statement loop, Statement parentloop) {

    // move continue edges to the parent loop
    List<StatEdge> lst = new ArrayList<>(loop.getLabelEdges());
    for (StatEdge edge : lst) {
      loop.removePredecessor(edge);
      edge.getSource().changeEdgeNode(Statement.DIRECTION_FORWARD, edge, parentloop);
      parentloop.addPredecessor(edge);

      parentloop.addLabeledEdge(edge);
    }

    // remove the last break edge, if exists
    Statement loopcontent = loop.getFirst();
    if (!loopcontent.getAllSuccessorEdges().isEmpty()) {
      loopcontent.removeSuccessor(loopcontent.getAllSuccessorEdges().get(0));
    }

    // replace loop with its content
    loop.getParent().replaceStatement(loop, loopcontent);
  }
}