soot.jimple.toolkits.annotation.nullcheck.NullCheckEliminator Maven / Gradle / Ivy

package soot.jimple.toolkits.annotation.nullcheck;

/*-
 * #%L
 * Soot - a J*va Optimization Framework
 * %%
 * Copyright (C) 2004 Ganesh Sittampalam
 * %%
 * 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.Map;

import soot.Body;
import soot.BodyTransformer;
import soot.Immediate;
import soot.Unit;
import soot.Value;
import soot.jimple.BinopExpr;
import soot.jimple.EqExpr;
import soot.jimple.IfStmt;
import soot.jimple.Jimple;
import soot.jimple.NeExpr;
import soot.jimple.NullConstant;
import soot.jimple.Stmt;
import soot.toolkits.graph.ExceptionalUnitGraph;
import soot.toolkits.graph.UnitGraph;
import soot.util.Chain;

public class NullCheckEliminator extends BodyTransformer {

  public static class AnalysisFactory {
    public NullnessAnalysis newAnalysis(UnitGraph g) {
      return new NullnessAnalysis(g);
    }
  }

  private AnalysisFactory analysisFactory;

  public NullCheckEliminator() {
    this(new AnalysisFactory());
  }

  public NullCheckEliminator(AnalysisFactory f) {
    this.analysisFactory = f;
  }

  public void internalTransform(Body body, String phaseName, Map options) {

    // really, the analysis should be able to use its own results to determine
    // that some branches are dead, but since it doesn't we just iterate.
    boolean changed;
    do {
      changed = false;

      NullnessAnalysis analysis = analysisFactory.newAnalysis(new ExceptionalUnitGraph(body));

      Chain units = body.getUnits();
      Stmt s;
      for (s = (Stmt) units.getFirst(); s != null; s = (Stmt) units.getSuccOf(s)) {
        if (!(s instanceof IfStmt)) {
          continue;
        }
        IfStmt is = (IfStmt) s;
        Value c = is.getCondition();
        if (!(c instanceof EqExpr || c instanceof NeExpr)) {
          continue;
        }
        BinopExpr e = (BinopExpr) c;
        Immediate i = null;
        if (e.getOp1() instanceof NullConstant) {
          i = (Immediate) e.getOp2();
        }
        if (e.getOp2() instanceof NullConstant) {
          i = (Immediate) e.getOp1();
        }
        if (i == null) {
          continue;
        }
        boolean alwaysNull = analysis.isAlwaysNullBefore(s, i);
        boolean alwaysNonNull = analysis.isAlwaysNonNullBefore(s, i);
        int elim = 0; // -1 => condition is false, 1 => condition is true
        if (alwaysNonNull) {
          elim = c instanceof EqExpr ? -1 : 1;
        }
        if (alwaysNull) {
          elim = c instanceof EqExpr ? 1 : -1;
        }
        Stmt newstmt = null;
        if (elim == -1) {
          newstmt = Jimple.v().newNopStmt();
        }
        if (elim == 1) {
          newstmt = Jimple.v().newGotoStmt(is.getTarget());
        }
        if (newstmt != null) {
          units.swapWith(s, newstmt);
          s = newstmt;
          changed = true;
        }
      }
    } while (changed);
  }

}