WALA/com.ibm.wala.core.tests/src/com/ibm/wala/examples/analysis/dataflow/ContextInsensitiveReachingDefs.java

/*******************************************************************************
 * Copyright (c) 2008 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.examples.analysis.dataflow;

import java.util.ArrayList;
import java.util.Map;

import com.ibm.wala.classLoader.IField;
import com.ibm.wala.dataflow.graph.AbstractMeetOperator;
import com.ibm.wala.dataflow.graph.BitVectorFramework;
import com.ibm.wala.dataflow.graph.BitVectorIdentity;
import com.ibm.wala.dataflow.graph.BitVectorKillAll;
import com.ibm.wala.dataflow.graph.BitVectorKillGen;
import com.ibm.wala.dataflow.graph.BitVectorSolver;
import com.ibm.wala.dataflow.graph.BitVectorUnion;
import com.ibm.wala.dataflow.graph.ITransferFunctionProvider;
import com.ibm.wala.fixpoint.BitVectorVariable;
import com.ibm.wala.fixpoint.UnaryOperator;
import com.ibm.wala.ipa.callgraph.CGNode;
import com.ibm.wala.ipa.cfg.BasicBlockInContext;
import com.ibm.wala.ipa.cfg.ExplodedInterproceduralCFG;
import com.ibm.wala.ipa.cha.IClassHierarchy;
import com.ibm.wala.ssa.IR;
import com.ibm.wala.ssa.SSAAbstractInvokeInstruction;
import com.ibm.wala.ssa.SSAInstruction;
import com.ibm.wala.ssa.SSAPutInstruction;
import com.ibm.wala.ssa.analysis.IExplodedBasicBlock;
import com.ibm.wala.util.CancelException;
import com.ibm.wala.util.collections.HashMapFactory;
import com.ibm.wala.util.collections.ObjectArrayMapping;
import com.ibm.wala.util.collections.Pair;
import com.ibm.wala.util.intset.BitVector;
import com.ibm.wala.util.intset.OrdinalSetMapping;

/**
 * Computes interprocedural reaching definitions for static fields in a context-insensitive manner.
 */
public class ContextInsensitiveReachingDefs {

  /**
   * the exploded interprocedural control-flow graph on which to compute the analysis
   */
  private final ExplodedInterproceduralCFG icfg;

  /**
   * maps call graph node and instruction index of putstatic instructions to more compact numbering for bitvectors
   */
  private final OrdinalSetMapping<Pair<CGNode, Integer>> putInstrNumbering;

  /**
   * for resolving field references in putstatic instructions
   */
  private final IClassHierarchy cha;

  /**
   * maps each static field to the numbers of the statements (in {@link #putInstrNumbering}) that define it; used for kills in flow
   * functions
   */
  private final Map<IField, BitVector> staticField2DefStatements = HashMapFactory.make();

  private static final boolean VERBOSE = true;

  public ContextInsensitiveReachingDefs(ExplodedInterproceduralCFG icfg, IClassHierarchy cha) {
    this.icfg = icfg;
    this.cha = cha;
    this.putInstrNumbering = numberPutStatics();
  }

  /**
   * generate a numbering of the putstatic instructions
   */
  private OrdinalSetMapping<Pair<CGNode, Integer>> numberPutStatics() {
    ArrayList<Pair<CGNode, Integer>> putInstrs = new ArrayList<>();
    for (CGNode node : icfg.getCallGraph()) {
      IR ir = node.getIR();
      if (ir == null) {
        continue;
      }
      SSAInstruction[] instructions = ir.getInstructions();
      for (int i = 0; i < instructions.length; i++) {
        SSAInstruction instruction = instructions[i];
        if (instruction instanceof SSAPutInstruction && ((SSAPutInstruction) instruction).isStatic()) {
          SSAPutInstruction putInstr = (SSAPutInstruction) instruction;
          // instrNum is the number that will be assigned to this putstatic
          int instrNum = putInstrs.size();
          putInstrs.add(Pair.make(node, i));
          // also update the mapping of static fields to def'ing statements
          IField field = cha.resolveField(putInstr.getDeclaredField());
          assert field != null;
          BitVector bv = staticField2DefStatements.get(field);
          if (bv == null) {
            bv = new BitVector();
            staticField2DefStatements.put(field, bv);
          }
          bv.set(instrNum);
        }
      }
    }
    return new ObjectArrayMapping<>(putInstrs.toArray(new Pair[putInstrs.size()]));
  }

  private class TransferFunctions implements ITransferFunctionProvider<BasicBlockInContext<IExplodedBasicBlock>, BitVectorVariable> {

    /**
     * our meet operator is set union
     */
    @Override
    public AbstractMeetOperator<BitVectorVariable> getMeetOperator() {
      return BitVectorUnion.instance();
    }

    @Override
    public UnaryOperator<BitVectorVariable> getNodeTransferFunction(BasicBlockInContext<IExplodedBasicBlock> node) {
      IExplodedBasicBlock ebb = node.getDelegate();
      SSAInstruction instruction = ebb.getInstruction();
      int instructionIndex = ebb.getFirstInstructionIndex();
      CGNode cgNode = node.getNode();
      if (instruction instanceof SSAPutInstruction && ((SSAPutInstruction) instruction).isStatic()) {
        // kill all defs of the same static field, and gen this instruction
        final SSAPutInstruction putInstr = (SSAPutInstruction) instruction;
        final IField field = cha.resolveField(putInstr.getDeclaredField());
        assert field != null;
        BitVector kill = staticField2DefStatements.get(field);
        BitVector gen = new BitVector();
        gen.set(putInstrNumbering.getMappedIndex(Pair.make(cgNode, instructionIndex)));
        return new BitVectorKillGen(kill, gen);
      } else {
        // identity function for non-putstatic instructions
        return BitVectorIdentity.instance();
      }
    }

    /**
     * here we need an edge transfer function for call-to-return edges (see
     * {@link #getEdgeTransferFunction(BasicBlockInContext, BasicBlockInContext)})
     */
    @Override
    public boolean hasEdgeTransferFunctions() {
      return true;
    }

    @Override
    public boolean hasNodeTransferFunctions() {
      return true;
    }

    /**
     * for direct call-to-return edges at a call site, the edge transfer function will kill all facts, since we only want to
     * consider facts that arise from going through the callee
     */
    @Override
    public UnaryOperator<BitVectorVariable> getEdgeTransferFunction(BasicBlockInContext<IExplodedBasicBlock> src,
        BasicBlockInContext<IExplodedBasicBlock> dst) {
      if (isCallToReturnEdge(src, dst)) {
        return BitVectorKillAll.instance();
      } else {
        return BitVectorIdentity.instance();
      }
    }

    private boolean isCallToReturnEdge(BasicBlockInContext<IExplodedBasicBlock> src, BasicBlockInContext<IExplodedBasicBlock> dst) {
      SSAInstruction srcInst = src.getDelegate().getInstruction();
      return srcInst instanceof SSAAbstractInvokeInstruction && src.getNode().equals(dst.getNode());
    }

  }

  /**
   * run the analysis
   * 
   * @return the solver used for the analysis, which contains the analysis result
   */
  public BitVectorSolver<BasicBlockInContext<IExplodedBasicBlock>> analyze() {
    // the framework describes the dataflow problem, in particular the underlying graph and the transfer functions
    BitVectorFramework<BasicBlockInContext<IExplodedBasicBlock>, Pair<CGNode, Integer>> framework = new BitVectorFramework<>(
        icfg, new TransferFunctions(), putInstrNumbering);
    BitVectorSolver<BasicBlockInContext<IExplodedBasicBlock>> solver = new BitVectorSolver<>(
        framework);
    try {
      solver.solve(null);
    } catch (CancelException e) {
      // this shouldn't happen
      assert false;
    }
    if (VERBOSE) {
      for (BasicBlockInContext<IExplodedBasicBlock> ebb : icfg) {
        System.out.println(ebb);
        System.out.println(ebb.getDelegate().getInstruction());
        System.out.println(solver.getIn(ebb));
        System.out.println(solver.getOut(ebb));
      }
    }
    return solver;
  }

  /**
   * gets putstatic instruction corresponding to some fact number from a bitvector in the analysis result
   */
  public Pair<CGNode, Integer> getNodeAndInstrForNumber(int num) {
    return putInstrNumbering.getMappedObject(num);
  }
}