/*******************************************************************************
* Copyright (c) 2007 IBM Corporation.
* All rights reserved. This program and the accompanying materials
* are made available under the terms of the Eclipse Public License v1.0
* which accompanies this distribution, and is available at
* http://www.eclipse.org/legal/epl-v10.html
*
* Contributors:
* IBM Corporation - initial API and implementation
*******************************************************************************/
package com.ibm.wala.ssa;
import com.ibm.wala.util.collections.Pair;
/**
* A pi node policy with the following rule:
*
* If we have the following code: <verbatim> S1: if (c op null) { ... } </verbatim>
*
* replace it with: <verbatim> S1: if (c op null) { v2 = PI(c, S1) .... } </verbatim>
*
* This renaming allows SSA-based analysis to reason about the nullness of v2 depending on the outcome of the branch.
*/
public class NullTestPiPolicy implements SSAPiNodePolicy {
private final static NullTestPiPolicy singleton = new NullTestPiPolicy();
public static NullTestPiPolicy createNullTestPiPolicy() {
return singleton;
}
private NullTestPiPolicy() {}
/*
* @see com.ibm.wala.ssa.SSAPiNodePolicy#getPi(com.ibm.wala.ssa.SSAConditionalBranchInstruction,
* com.ibm.wala.ssa.SSAInstruction, com.ibm.wala.ssa.SSAInstruction, com.ibm.wala.ssa.SymbolTable)
*/
@Override
public Pair<Integer, SSAInstruction> getPi(SSAConditionalBranchInstruction cond, SSAInstruction def1, SSAInstruction def2,
SymbolTable symbolTable) {
if (symbolTable == null) {
throw new IllegalArgumentException("null symbolTable");
}
if (cond == null) {
throw new IllegalArgumentException("null cond");
}
if (symbolTable.isNullConstant(cond.getUse(1))) {
return Pair.<Integer,SSAInstruction>make(cond.getUse(0), cond);
}
if (symbolTable.isNullConstant(cond.getUse(0))) {
return Pair.<Integer,SSAInstruction>make(cond.getUse(1), cond);
}
return null;
}
@Override
public Pair<Integer, SSAInstruction> getPi(SSAAbstractInvokeInstruction call, SymbolTable symbolTable) {
return null;
}
}