soot.jimple.toolkits.annotation.nullcheck.NullCheckEliminator Maven / Gradle / Ivy
/* Soot - a J*va Optimization Framework
* Copyright (C) 2004 Ganesh Sittampalam
*
* This library 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 library 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
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the
* Free Software Foundation, Inc., 59 Temple Place - Suite 330,
* Boston, MA 02111-1307, USA.
*/
package soot.jimple.toolkits.annotation.nullcheck;
import java.util.Map;
import soot.Body;
import soot.BodyTransformer;
import soot.Immediate;
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);
}
}