improving debugging of call site contributions to initial contexts

[IRC.git] / Robust / src / Analysis / Disjoint / DisjointAnalysis.java

package Analysis.Disjoint;

import Analysis.CallGraph.*;
import Analysis.Liveness;
import Analysis.ArrayReferencees;
import IR.*;
import IR.Flat.*;
import IR.Tree.Modifiers;
import java.util.*;
import java.io.*;


public class DisjointAnalysis {
        
          ///////////////////////////////////////////
          //
          //  Public interface to discover possible
          //  aliases in the program under analysis
          //
          ///////////////////////////////////////////
        
          public HashSet<AllocSite>
          getFlaggedAllocationSitesReachableFromTask(TaskDescriptor td) {
            checkAnalysisComplete();
            return getFlaggedAllocationSitesReachableFromTaskPRIVATE(td);
          }
          
          public AllocSite getAllocationSiteFromFlatNew(FlatNew fn) {
                    checkAnalysisComplete();
                    return getAllocSiteFromFlatNewPRIVATE(fn);
           }      
          
          public AllocSite getAllocationSiteFromHeapRegionNodeID(Integer id) {
                    checkAnalysisComplete();
                    return mapHrnIdToAllocSite.get(id);
          }
          
          public Set<HeapRegionNode> hasPotentialSharing(Descriptor taskOrMethod,
              int paramIndex1,
              int paramIndex2) {
                  checkAnalysisComplete();
                  ReachGraph rg=mapDescriptorToCompleteReachGraph.get(taskOrMethod);
                  FlatMethod fm=state.getMethodFlat(taskOrMethod);
                  assert(rg != null);
                  return rg.mayReachSharedObjects(fm, paramIndex1, paramIndex2);
          }
          
        public Set<HeapRegionNode> hasPotentialSharing(Descriptor taskOrMethod,
                        int paramIndex, AllocSite alloc) {
                checkAnalysisComplete();
                ReachGraph rg = mapDescriptorToCompleteReachGraph.get(taskOrMethod);
            FlatMethod fm=state.getMethodFlat(taskOrMethod);
                assert (rg != null);
                return rg.mayReachSharedObjects(fm, paramIndex, alloc);
        }

        public Set<HeapRegionNode> hasPotentialSharing(Descriptor taskOrMethod,
                        AllocSite alloc, int paramIndex) {
                checkAnalysisComplete();
                ReachGraph rg  = mapDescriptorToCompleteReachGraph.get(taskOrMethod);
                FlatMethod fm=state.getMethodFlat(taskOrMethod);
                assert (rg != null);
                return rg.mayReachSharedObjects(fm, paramIndex, alloc);
        }

        public Set<HeapRegionNode> hasPotentialSharing(Descriptor taskOrMethod,
                        AllocSite alloc1, AllocSite alloc2) {
                checkAnalysisComplete();
                ReachGraph rg  = mapDescriptorToCompleteReachGraph.get(taskOrMethod);
                assert (rg != null);
                return rg.mayReachSharedObjects(alloc1, alloc2);
        }
        
        public String prettyPrintNodeSet(Set<HeapRegionNode> s) {
                checkAnalysisComplete();

                String out = "{\n";

                Iterator<HeapRegionNode> i = s.iterator();
                while (i.hasNext()) {
                        HeapRegionNode n = i.next();

                        AllocSite as = n.getAllocSite();
                        if (as == null) {
                                out += "  " + n.toString() + ",\n";
                        } else {
                                out += "  " + n.toString() + ": " + as.toStringVerbose()
                                                + ",\n";
                        }
                }

                out += "}\n";
                return out;
        }
        
  // use the methods given above to check every possible sharing class
  // between task parameters and flagged allocation sites reachable
  // from the task
  public void writeAllSharing(String outputFile, 
                              String timeReport,
                              String justTime,
                              boolean tabularOutput,
                              int numLines
                              )
    throws java.io.IOException {
    checkAnalysisComplete();

    BufferedWriter bw = new BufferedWriter(new FileWriter(outputFile));

    if (!tabularOutput) {
      bw.write("Conducting ownership analysis with allocation depth = "
               + allocationDepth + "\n");
      bw.write(timeReport + "\n");
    }

    int numSharing = 0;

    // look through every task for potential sharing
    Iterator taskItr = state.getTaskSymbolTable().getDescriptorsIterator();
    while (taskItr.hasNext()) {
      TaskDescriptor td = (TaskDescriptor) taskItr.next();

      if (!tabularOutput) {
        bw.write("\n---------" + td + "--------\n");
      }

      HashSet<AllocSite> allocSites = getFlaggedAllocationSitesReachableFromTask(td);

      Set<HeapRegionNode> common;

      // for each task parameter, check for sharing classes with
      // other task parameters and every allocation site
      // reachable from this task
      boolean foundSomeSharing = false;

      FlatMethod fm = state.getMethodFlat(td);
      for (int i = 0; i < fm.numParameters(); ++i) {

        // skip parameters with types that cannot reference
        // into the heap
        if( !shouldAnalysisTrack( fm.getParameter( i ).getType() ) ) {
          continue;
        }
                          
        // for the ith parameter check for sharing classes to all
        // higher numbered parameters
        for (int j = i + 1; j < fm.numParameters(); ++j) {

          // skip parameters with types that cannot reference
          // into the heap
          if( !shouldAnalysisTrack( fm.getParameter( j ).getType() ) ) {
            continue;
          }


          common = hasPotentialSharing(td, i, j);
          if (!common.isEmpty()) {
            foundSomeSharing = true;
            ++numSharing;
            if (!tabularOutput) {
              bw.write("Potential sharing between parameters " + i
                       + " and " + j + ".\n");
              bw.write(prettyPrintNodeSet(common) + "\n");
            }
          }
        }

        // for the ith parameter, check for sharing classes against
        // the set of allocation sites reachable from this
        // task context
        Iterator allocItr = allocSites.iterator();
        while (allocItr.hasNext()) {
          AllocSite as = (AllocSite) allocItr.next();
          common = hasPotentialSharing(td, i, as);
          if (!common.isEmpty()) {
            foundSomeSharing = true;
            ++numSharing;
            if (!tabularOutput) {
              bw.write("Potential sharing between parameter " + i
                       + " and " + as.getFlatNew() + ".\n");
              bw.write(prettyPrintNodeSet(common) + "\n");
            }
          }
        }
      }

      // for each allocation site check for sharing classes with
      // other allocation sites in the context of execution
      // of this task
      HashSet<AllocSite> outerChecked = new HashSet<AllocSite>();
      Iterator allocItr1 = allocSites.iterator();
      while (allocItr1.hasNext()) {
        AllocSite as1 = (AllocSite) allocItr1.next();

        Iterator allocItr2 = allocSites.iterator();
        while (allocItr2.hasNext()) {
          AllocSite as2 = (AllocSite) allocItr2.next();

          if (!outerChecked.contains(as2)) {
            common = hasPotentialSharing(td, as1, as2);

            if (!common.isEmpty()) {
              foundSomeSharing = true;
              ++numSharing;
              if (!tabularOutput) {
                bw.write("Potential sharing between "
                         + as1.getFlatNew() + " and "
                         + as2.getFlatNew() + ".\n");
                bw.write(prettyPrintNodeSet(common) + "\n");
              }
            }
          }
        }

        outerChecked.add(as1);
      }

      if (!foundSomeSharing) {
        if (!tabularOutput) {
          bw.write("No sharing between flagged objects in Task " + td
                   + ".\n");
        }
      }
    }

                
    if (tabularOutput) {
      bw.write(" & " + numSharing + " & " + justTime + " & " + numLines
               + " & " + numMethodsAnalyzed() + " \\\\\n");
    } else {
      bw.write("\nNumber sharing classes: "+numSharing);
    }

    bw.close();
  }
        
  // this version of writeAllSharing is for Java programs that have no tasks
  public void writeAllSharingJava(String outputFile, 
                                  String timeReport,
                                  String justTime,
                                  boolean tabularOutput,
                                  int numLines
                                  )
    throws java.io.IOException {
    checkAnalysisComplete();

    assert !state.TASK;

    int numSharing = 0;

    BufferedWriter bw = new BufferedWriter(new FileWriter(outputFile));
    
    bw.write("Conducting disjoint reachability analysis with allocation depth = "
             + allocationDepth + "\n");
    bw.write(timeReport + "\n\n");

    boolean foundSomeSharing = false;

    Descriptor d = typeUtil.getMain();
    HashSet<AllocSite> allocSites = getFlaggedAllocationSites(d);

    // for each allocation site check for sharing classes with
    // other allocation sites in the context of execution
    // of this task
    HashSet<AllocSite> outerChecked = new HashSet<AllocSite>();
    Iterator allocItr1 = allocSites.iterator();
    while (allocItr1.hasNext()) {
      AllocSite as1 = (AllocSite) allocItr1.next();

      Iterator allocItr2 = allocSites.iterator();
      while (allocItr2.hasNext()) {
        AllocSite as2 = (AllocSite) allocItr2.next();

        if (!outerChecked.contains(as2)) {
          Set<HeapRegionNode> common = hasPotentialSharing(d,
                                                           as1, as2);

          if (!common.isEmpty()) {
            foundSomeSharing = true;
            bw.write("Potential sharing between "
                     + as1.getDisjointAnalysisId() + " and "
                     + as2.getDisjointAnalysisId() + ".\n");
            bw.write(prettyPrintNodeSet(common) + "\n");
            ++numSharing;
          }
        }
      }

      outerChecked.add(as1);
    }

    if (!foundSomeSharing) {
      bw.write("No sharing classes between flagged objects found.\n");
    } else {
      bw.write("\nNumber sharing classes: "+numSharing);
    }

    bw.write("Number of methods analyzed: "+numMethodsAnalyzed()+"\n");

    bw.close();
  }
          
  ///////////////////////////////////////////
  //
  // end public interface
  //
  ///////////////////////////////////////////

  protected void checkAnalysisComplete() {
    if( !analysisComplete ) {
      throw new Error("Warning: public interface method called while analysis is running.");
    }
  } 


  // run in faster mode, only when bugs wrung out!
  public static boolean releaseMode;

  // use command line option to set this, analysis
  // should attempt to be deterministic
  public static boolean determinismDesired;

  // when we want to enforce determinism in the 
  // analysis we need to sort descriptors rather
  // than toss them in efficient sets, use this
  public static DescriptorComparator dComp =
    new DescriptorComparator();


  // data from the compiler
  public State            state;
  public CallGraph        callGraph;
  public Liveness         liveness;
  public ArrayReferencees arrayReferencees;
  public TypeUtil         typeUtil;
  public int              allocationDepth;
  
  // data structure for public interface
  private Hashtable< Descriptor, HashSet<AllocSite> > 
    mapDescriptorToAllocSiteSet;

  
  // for public interface methods to warn that they
  // are grabbing results during analysis
  private boolean analysisComplete;


  // used to identify HeapRegionNode objects
  // A unique ID equates an object in one
  // ownership graph with an object in another
  // graph that logically represents the same
  // heap region
  // start at 10 and increment to reserve some
  // IDs for special purposes
  static protected int uniqueIDcount = 10;


  // An out-of-scope method created by the
  // analysis that has no parameters, and
  // appears to allocate the command line
  // arguments, then invoke the source code's
  // main method.  The purpose of this is to
  // provide the analysis with an explicit
  // top-level context with no parameters
  protected MethodDescriptor mdAnalysisEntry;
  protected FlatMethod       fmAnalysisEntry;

  // main method defined by source program
  protected MethodDescriptor mdSourceEntry;

  // the set of task and/or method descriptors
  // reachable in call graph
  protected Set<Descriptor> 
    descriptorsToAnalyze;

  // current descriptors to visit in fixed-point
  // interprocedural analysis, prioritized by
  // dependency in the call graph
  protected Stack<Descriptor>
    descriptorsToVisitStack;
  protected PriorityQueue<DescriptorQWrapper> 
    descriptorsToVisitQ;
  
  // a duplication of the above structure, but
  // for efficient testing of inclusion
  protected HashSet<Descriptor> 
    descriptorsToVisitSet;

  // storage for priorities (doesn't make sense)
  // to add it to the Descriptor class, just in
  // this analysis
  protected Hashtable<Descriptor, Integer> 
    mapDescriptorToPriority;

  // when analyzing a method and scheduling more:
  // remember set of callee's enqueued for analysis
  // so they can be put on top of the callers in
  // the stack-visit mode
  protected Set<Descriptor>
    calleesToEnqueue;

  // maps a descriptor to its current partial result
  // from the intraprocedural fixed-point analysis--
  // then the interprocedural analysis settles, this
  // mapping will have the final results for each
  // method descriptor
  protected Hashtable<Descriptor, ReachGraph> 
    mapDescriptorToCompleteReachGraph;

  // maps a descriptor to its known dependents: namely
  // methods or tasks that call the descriptor's method
  // AND are part of this analysis (reachable from main)
  protected Hashtable< Descriptor, Set<Descriptor> >
    mapDescriptorToSetDependents;

  // maps each flat new to one analysis abstraction
  // allocate site object, these exist outside reach graphs
  protected Hashtable<FlatNew, AllocSite>
    mapFlatNewToAllocSite;

  // maps intergraph heap region IDs to intergraph
  // allocation sites that created them, a redundant
  // structure for efficiency in some operations
  protected Hashtable<Integer, AllocSite>
    mapHrnIdToAllocSite;

  // maps a method to its initial heap model (IHM) that
  // is the set of reachability graphs from every caller
  // site, all merged together.  The reason that we keep
  // them separate is that any one call site's contribution
  // to the IHM may changed along the path to the fixed point
  protected Hashtable< Descriptor, Hashtable< FlatCall, ReachGraph > >
    mapDescriptorToIHMcontributions;

  // additionally, keep a mapping from descriptors to the
  // merged in-coming initial context, because we want this
  // initial context to be STRICTLY MONOTONIC
  protected Hashtable<Descriptor, ReachGraph>
    mapDescriptorToInitialContext;

  // make the result for back edges analysis-wide STRICTLY
  // MONOTONIC as well, but notice we use FlatNode as the
  // key for this map: in case we want to consider other
  // nodes as back edge's in future implementations
  protected Hashtable<FlatNode, ReachGraph>
    mapBackEdgeToMonotone;


  public static final String arrayElementFieldName = "___element_";
  static protected Hashtable<TypeDescriptor, FieldDescriptor>
    mapTypeToArrayField;

  // for controlling DOT file output
  protected boolean writeFinalDOTs;
  protected boolean writeAllIncrementalDOTs;

  // supporting DOT output--when we want to write every
  // partial method result, keep a tally for generating
  // unique filenames
  protected Hashtable<Descriptor, Integer>
    mapDescriptorToNumUpdates;
  
  //map task descriptor to initial task parameter 
  protected Hashtable<Descriptor, ReachGraph>
    mapDescriptorToReachGraph;

  protected PointerMethod pm;

  static protected Hashtable<FlatNode, ReachGraph> fn2rg =
    new Hashtable<FlatNode, ReachGraph>();

  private Hashtable<FlatCall, Descriptor> fc2enclosing;
  


  // allocate various structures that are not local
  // to a single class method--should be done once
  protected void allocateStructures() {
    
    if( determinismDesired ) {
      // use an ordered set
      descriptorsToAnalyze = new TreeSet<Descriptor>( dComp );      
    } else {
      // otherwise use a speedy hashset
      descriptorsToAnalyze = new HashSet<Descriptor>();
    }

    mapDescriptorToCompleteReachGraph =
      new Hashtable<Descriptor, ReachGraph>();

    mapDescriptorToNumUpdates =
      new Hashtable<Descriptor, Integer>();

    mapDescriptorToSetDependents =
      new Hashtable< Descriptor, Set<Descriptor> >();

    mapFlatNewToAllocSite = 
      new Hashtable<FlatNew, AllocSite>();

    mapDescriptorToIHMcontributions =
      new Hashtable< Descriptor, Hashtable< FlatCall, ReachGraph > >();

    mapDescriptorToInitialContext =
      new Hashtable<Descriptor, ReachGraph>();    

    mapBackEdgeToMonotone =
      new Hashtable<FlatNode, ReachGraph>();

    mapHrnIdToAllocSite =
      new Hashtable<Integer, AllocSite>();

    mapTypeToArrayField = 
      new Hashtable <TypeDescriptor, FieldDescriptor>();

    if( state.DISJOINTDVISITSTACK ||
        state.DISJOINTDVISITSTACKEESONTOP 
        ) {
      descriptorsToVisitStack =
        new Stack<Descriptor>();
    }

    if( state.DISJOINTDVISITPQUE ) {
      descriptorsToVisitQ =
        new PriorityQueue<DescriptorQWrapper>();
    }

    descriptorsToVisitSet =
      new HashSet<Descriptor>();

    mapDescriptorToPriority =
      new Hashtable<Descriptor, Integer>();
    
    calleesToEnqueue = 
      new HashSet<Descriptor>();    

    mapDescriptorToAllocSiteSet =
        new Hashtable<Descriptor,    HashSet<AllocSite> >();
    
    mapDescriptorToReachGraph = 
        new Hashtable<Descriptor, ReachGraph>();

    pm = new PointerMethod();

    fc2enclosing = new Hashtable<FlatCall, Descriptor>();
  }



  // this analysis generates a disjoint reachability
  // graph for every reachable method in the program
  public DisjointAnalysis( State            s,
                           TypeUtil         tu,
                           CallGraph        cg,
                           Liveness         l,
                           ArrayReferencees ar
                           ) throws java.io.IOException {
    init( s, tu, cg, l, ar );
  }
  
  protected void init( State            state,
                       TypeUtil         typeUtil,
                       CallGraph        callGraph,
                       Liveness         liveness,
                       ArrayReferencees arrayReferencees
                       ) throws java.io.IOException {
          
    analysisComplete = false;
    
    this.state                   = state;
    this.typeUtil                = typeUtil;
    this.callGraph               = callGraph;
    this.liveness                = liveness;
    this.arrayReferencees        = arrayReferencees;
    this.allocationDepth         = state.DISJOINTALLOCDEPTH;
    this.releaseMode             = state.DISJOINTRELEASEMODE;
    this.determinismDesired      = state.DISJOINTDETERMINISM;

    this.writeFinalDOTs          = state.DISJOINTWRITEDOTS && !state.DISJOINTWRITEALL;
    this.writeAllIncrementalDOTs = state.DISJOINTWRITEDOTS &&  state.DISJOINTWRITEALL;

    this.takeDebugSnapshots      = state.DISJOINTSNAPSYMBOL != null;
    this.descSymbolDebug         = state.DISJOINTSNAPSYMBOL;
    this.visitStartCapture       = state.DISJOINTSNAPVISITTOSTART;
    this.numVisitsToCapture      = state.DISJOINTSNAPNUMVISITS;
    this.stopAfterCapture        = state.DISJOINTSNAPSTOPAFTER;
    this.snapVisitCounter        = 1; // count visits from 1 (user will write 1, means 1st visit)
    this.snapNodeCounter         = 0; // count nodes from 0

    assert
      state.DISJOINTDVISITSTACK ||
      state.DISJOINTDVISITPQUE  ||
      state.DISJOINTDVISITSTACKEESONTOP;
    assert !(state.DISJOINTDVISITSTACK && state.DISJOINTDVISITPQUE);
    assert !(state.DISJOINTDVISITSTACK && state.DISJOINTDVISITSTACKEESONTOP);
    assert !(state.DISJOINTDVISITPQUE  && state.DISJOINTDVISITSTACKEESONTOP);
            
    // set some static configuration for ReachGraphs
    ReachGraph.allocationDepth = allocationDepth;
    ReachGraph.typeUtil        = typeUtil;

    ReachGraph.debugCallSiteVisitStartCapture
      = state.DISJOINTDEBUGCALLVISITTOSTART;

    ReachGraph.debugCallSiteNumVisitsToCapture
      = state.DISJOINTDEBUGCALLNUMVISITS;

    ReachGraph.debugCallSiteStopAfter
      = state.DISJOINTDEBUGCALLSTOPAFTER;

    ReachGraph.debugCallSiteVisitCounter 
      = 0; // count visits from 1, is incremented before first visit
    
    

    allocateStructures();

    double timeStartAnalysis = (double) System.nanoTime();

    // start interprocedural fixed-point computation
    analyzeMethods();
    analysisComplete=true;

    double timeEndAnalysis = (double) System.nanoTime();
    double dt = (timeEndAnalysis - timeStartAnalysis)/(Math.pow( 10.0, 9.0 ) );
    String treport = String.format( "The reachability analysis took %.3f sec.", dt );
    String justtime = String.format( "%.2f", dt );
    System.out.println( treport );

    if( writeFinalDOTs && !writeAllIncrementalDOTs ) {
      writeFinalGraphs();      
    }

    if( state.DISJOINTWRITEIHMS ) {
      writeFinalIHMs();
    }

    if( state.DISJOINTWRITEINITCONTEXTS ) {
      writeInitialContexts();
    }

    if( state.DISJOINTALIASFILE != null ) {
      if( state.TASK ) {
        writeAllSharing(state.DISJOINTALIASFILE, treport, justtime, state.DISJOINTALIASTAB, state.lines);
      } else {
        writeAllSharingJava(state.DISJOINTALIASFILE, 
                            treport, 
                            justtime, 
                            state.DISJOINTALIASTAB, 
                            state.lines
                            );
      }
    }
  }


  protected boolean moreDescriptorsToVisit() {
    if( state.DISJOINTDVISITSTACK ||
        state.DISJOINTDVISITSTACKEESONTOP
        ) {
      return !descriptorsToVisitStack.isEmpty();

    } else if( state.DISJOINTDVISITPQUE ) {
      return !descriptorsToVisitQ.isEmpty();
    }

    throw new Error( "Neither descriptor visiting mode set" );
  }


  // fixed-point computation over the call graph--when a
  // method's callees are updated, it must be reanalyzed
  protected void analyzeMethods() throws java.io.IOException {  

    // task or non-task (java) mode determines what the roots
    // of the call chain are, and establishes the set of methods
    // reachable from the roots that will be analyzed
    
    if( state.TASK ) {
      System.out.println( "Bamboo mode..." );
      
      Iterator taskItr = state.getTaskSymbolTable().getDescriptorsIterator();      
      while( taskItr.hasNext() ) {
        TaskDescriptor td = (TaskDescriptor) taskItr.next();
        if( !descriptorsToAnalyze.contains( td ) ) {
          // add all methods transitively reachable from the
          // tasks as well
          descriptorsToAnalyze.add( td );
          descriptorsToAnalyze.addAll( callGraph.getAllMethods( td ) );
        }         
      }
      
    } else {
      System.out.println( "Java mode..." );

      // add all methods transitively reachable from the
      // source's main to set for analysis
      mdSourceEntry = typeUtil.getMain();
      descriptorsToAnalyze.add( mdSourceEntry );
      descriptorsToAnalyze.addAll( callGraph.getAllMethods( mdSourceEntry ) );
      
      // fabricate an empty calling context that will call
      // the source's main, but call graph doesn't know
      // about it, so explicitly add it
      makeAnalysisEntryMethod( mdSourceEntry );
      descriptorsToAnalyze.add( mdAnalysisEntry );
    }


    // now, depending on the interprocedural mode for visiting 
    // methods, set up the needed data structures

    if( state.DISJOINTDVISITPQUE ) {
    
      // topologically sort according to the call graph so 
      // leaf calls are last, helps build contexts up first
      LinkedList<Descriptor> sortedDescriptors = 
        topologicalSort( descriptorsToAnalyze );

      // add sorted descriptors to priority queue, and duplicate
      // the queue as a set for efficiently testing whether some
      // method is marked for analysis
      int p = 0;
      Iterator<Descriptor> dItr;

      // for the priority queue, give items at the head
      // of the sorted list a low number (highest priority)
      while( !sortedDescriptors.isEmpty() ) {
        Descriptor d = sortedDescriptors.removeFirst();
        mapDescriptorToPriority.put( d, new Integer( p ) );
        descriptorsToVisitQ.add( new DescriptorQWrapper( p, d ) );
        descriptorsToVisitSet.add( d );
        ++p;
      }

    } else if( state.DISJOINTDVISITSTACK ||
               state.DISJOINTDVISITSTACKEESONTOP 
               ) {
      // if we're doing the stack scheme, just throw the root
      // method or tasks on the stack
      if( state.TASK ) {
        Iterator taskItr = state.getTaskSymbolTable().getDescriptorsIterator();      
        while( taskItr.hasNext() ) {
          TaskDescriptor td = (TaskDescriptor) taskItr.next();
          descriptorsToVisitStack.add( td );
          descriptorsToVisitSet.add( td );
        }
        
      } else {
        descriptorsToVisitStack.add( mdAnalysisEntry );
        descriptorsToVisitSet.add( mdAnalysisEntry );
      }

    } else {
      throw new Error( "Unknown method scheduling mode" );
    }


    // analyze scheduled methods until there are no more to visit
    while( moreDescriptorsToVisit() ) {
      Descriptor d = null;

      if( state.DISJOINTDVISITSTACK ||
          state.DISJOINTDVISITSTACKEESONTOP
          ) {
        d = descriptorsToVisitStack.pop();

      } else if( state.DISJOINTDVISITPQUE ) {
        d = descriptorsToVisitQ.poll().getDescriptor();
      }

      assert descriptorsToVisitSet.contains( d );
      descriptorsToVisitSet.remove( d );

      // because the task or method descriptor just extracted
      // was in the "to visit" set it either hasn't been analyzed
      // yet, or some method that it depends on has been
      // updated.  Recompute a complete reachability graph for
      // this task/method and compare it to any previous result.
      // If there is a change detected, add any methods/tasks
      // that depend on this one to the "to visit" set.

      System.out.println( "Analyzing " + d );

      if( state.DISJOINTDVISITSTACKEESONTOP ) {
        assert calleesToEnqueue.isEmpty();
      }

      ReachGraph rg     = analyzeMethod( d );
      ReachGraph rgPrev = getPartial( d );
      
      if( !rg.equals( rgPrev ) ) {
        setPartial( d, rg );
        
        if( state.DISJOINTDEBUGSCHEDULING ) {
          System.out.println( "  complete graph changed, scheduling callers for analysis:" );
        }

        // results for d changed, so enqueue dependents
        // of d for further analysis
        Iterator<Descriptor> depsItr = getDependents( d ).iterator();
        while( depsItr.hasNext() ) {
          Descriptor dNext = depsItr.next();
          enqueue( dNext );

          if( state.DISJOINTDEBUGSCHEDULING ) {
            System.out.println( "    "+dNext );
          }
        }
      }

      // whether or not the method under analysis changed,
      // we may have some callees that are scheduled for 
      // more analysis, and they should go on the top of
      // the stack now (in other method-visiting modes they
      // are already enqueued at this point
      if( state.DISJOINTDVISITSTACKEESONTOP ) {
        Iterator<Descriptor> depsItr = calleesToEnqueue.iterator();
        while( depsItr.hasNext() ) {
          Descriptor dNext = depsItr.next();
          enqueue( dNext );
        }
        calleesToEnqueue.clear();
      }     

    }   
  }

  protected ReachGraph analyzeMethod( Descriptor d ) 
    throws java.io.IOException {

    // get the flat code for this descriptor
    FlatMethod fm;
    if( d == mdAnalysisEntry ) {
      fm = fmAnalysisEntry;
    } else {
      fm = state.getMethodFlat( d );
    }
    pm.analyzeMethod( fm );

    // intraprocedural work set
    Set<FlatNode> flatNodesToVisit = new HashSet<FlatNode>();
    flatNodesToVisit.add( fm );

    // if determinism is desired by client, shadow the
    // set with a queue to make visit order deterministic
    Queue<FlatNode> flatNodesToVisitQ = null;
    if( determinismDesired ) {
      flatNodesToVisitQ = new LinkedList<FlatNode>();
      flatNodesToVisitQ.add( fm );
    }
    
    // mapping of current partial results
    Hashtable<FlatNode, ReachGraph> mapFlatNodeToReachGraph =
      new Hashtable<FlatNode, ReachGraph>();

    // the set of return nodes partial results that will be combined as
    // the final, conservative approximation of the entire method
    HashSet<FlatReturnNode> setReturns = new HashSet<FlatReturnNode>();

    while( !flatNodesToVisit.isEmpty() ) {

      FlatNode fn;      
      if( determinismDesired ) {
        assert !flatNodesToVisitQ.isEmpty();
        fn = flatNodesToVisitQ.remove();
      } else {
        fn = flatNodesToVisit.iterator().next();
      }
      flatNodesToVisit.remove( fn );

      // effect transfer function defined by this node,
      // then compare it to the old graph at this node
      // to see if anything was updated.

      ReachGraph rg = new ReachGraph();
      TaskDescriptor taskDesc;
      if(fn instanceof FlatMethod && (taskDesc=((FlatMethod)fn).getTask())!=null){
          if(mapDescriptorToReachGraph.containsKey(taskDesc)){
                  // retrieve existing reach graph if it is not first time
                  rg=mapDescriptorToReachGraph.get(taskDesc);
          }else{
                  // create initial reach graph for a task
                  rg=createInitialTaskReachGraph((FlatMethod)fn);
                  rg.globalSweep();
                  mapDescriptorToReachGraph.put(taskDesc, rg);
          }
      }

      // start by merging all node's parents' graphs
      for( int i = 0; i < pm.numPrev(fn); ++i ) {
        FlatNode pn = pm.getPrev(fn,i);
        if( mapFlatNodeToReachGraph.containsKey( pn ) ) {
          ReachGraph rgParent = mapFlatNodeToReachGraph.get( pn );
          rg.merge( rgParent );
        }
      }


      if( takeDebugSnapshots && 
          d.getSymbol().equals( descSymbolDebug ) 
          ) {
        debugSnapshot( rg, fn, true );
      }


      // modify rg with appropriate transfer function
      rg = analyzeFlatNode( d, fm, fn, setReturns, rg );


      if( takeDebugSnapshots && 
          d.getSymbol().equals( descSymbolDebug ) 
          ) {
        debugSnapshot( rg, fn, false );
        ++snapNodeCounter;
      }
          

      // if the results of the new graph are different from
      // the current graph at this node, replace the graph
      // with the update and enqueue the children
      ReachGraph rgPrev = mapFlatNodeToReachGraph.get( fn );
      if( !rg.equals( rgPrev ) ) {
        mapFlatNodeToReachGraph.put( fn, rg );

        for( int i = 0; i < pm.numNext( fn ); i++ ) {
          FlatNode nn = pm.getNext( fn, i );

          flatNodesToVisit.add( nn );
          if( determinismDesired ) {
            flatNodesToVisitQ.add( nn );
          }
        }
      }
    }


    // end by merging all return nodes into a complete
    // reach graph that represents all possible heap
    // states after the flat method returns
    ReachGraph completeGraph = new ReachGraph();

    assert !setReturns.isEmpty();
    Iterator retItr = setReturns.iterator();
    while( retItr.hasNext() ) {
      FlatReturnNode frn = (FlatReturnNode) retItr.next();

      assert mapFlatNodeToReachGraph.containsKey( frn );
      ReachGraph rgRet = mapFlatNodeToReachGraph.get( frn );

      completeGraph.merge( rgRet );
    }


    if( takeDebugSnapshots && 
        d.getSymbol().equals( descSymbolDebug ) 
        ) {
      // increment that we've visited the debug snap
      // method, and reset the node counter
      System.out.println( "    @@@ debug snap at visit "+snapVisitCounter );
      ++snapVisitCounter;
      snapNodeCounter = 0;

      if( snapVisitCounter == visitStartCapture + numVisitsToCapture && 
          stopAfterCapture 
          ) {
        System.out.println( "!!! Stopping analysis after debug snap captures. !!!" );
        System.exit( 0 );
      }
    }


    return completeGraph;
  }

  
  protected ReachGraph
    analyzeFlatNode( Descriptor              d,
                     FlatMethod              fmContaining,
                     FlatNode                fn,
                     HashSet<FlatReturnNode> setRetNodes,
                     ReachGraph              rg
                     ) throws java.io.IOException {

    
    // any variables that are no longer live should be
    // nullified in the graph to reduce edges
    //rg.nullifyDeadVars( liveness.getLiveInTemps( fmContaining, fn ) );

          
    TempDescriptor  lhs;
    TempDescriptor  rhs;
    FieldDescriptor fld;

    // use node type to decide what transfer function
    // to apply to the reachability graph
    switch( fn.kind() ) {

    case FKind.FlatMethod: {
      // construct this method's initial heap model (IHM)
      // since we're working on the FlatMethod, we know
      // the incoming ReachGraph 'rg' is empty

      Hashtable<FlatCall, ReachGraph> heapsFromCallers = 
        getIHMcontributions( d );

      Set entrySet = heapsFromCallers.entrySet();
      Iterator itr = entrySet.iterator();
      while( itr.hasNext() ) {
        Map.Entry  me        = (Map.Entry)  itr.next();
        FlatCall   fc        = (FlatCall)   me.getKey();
        ReachGraph rgContrib = (ReachGraph) me.getValue();

        assert fc.getMethod().equals( d );

        rg.merge( rgContrib );
      }

      // additionally, we are enforcing STRICT MONOTONICITY for the
      // method's initial context, so grow the context by whatever
      // the previously computed context was, and put the most
      // up-to-date context back in the map
      ReachGraph rgPrevContext = mapDescriptorToInitialContext.get( d );
      rg.merge( rgPrevContext );      
      mapDescriptorToInitialContext.put( d, rg );

    } break;
      
    case FKind.FlatOpNode:
      FlatOpNode fon = (FlatOpNode) fn;
      if( fon.getOp().getOp() == Operation.ASSIGN ) {
        lhs = fon.getDest();
        rhs = fon.getLeft();
        rg.assignTempXEqualToTempY( lhs, rhs );
      }
      break;

    case FKind.FlatCastNode:
      FlatCastNode fcn = (FlatCastNode) fn;
      lhs = fcn.getDst();
      rhs = fcn.getSrc();

      TypeDescriptor td = fcn.getType();
      assert td != null;
      
      rg.assignTempXEqualToCastedTempY( lhs, rhs, td );
      break;

    case FKind.FlatFieldNode:
      FlatFieldNode ffn = (FlatFieldNode) fn;
      lhs = ffn.getDst();
      rhs = ffn.getSrc();
      fld = ffn.getField();
      if( shouldAnalysisTrack( fld.getType() ) ) {
        rg.assignTempXEqualToTempYFieldF( lhs, rhs, fld );
      }          
      break;

    case FKind.FlatSetFieldNode:
      FlatSetFieldNode fsfn = (FlatSetFieldNode) fn;
      lhs = fsfn.getDst();
      fld = fsfn.getField();
      rhs = fsfn.getSrc();
      if( shouldAnalysisTrack( fld.getType() ) ) {
        rg.assignTempXFieldFEqualToTempY( lhs, fld, rhs );
      }           
      break;

    case FKind.FlatElementNode:
      FlatElementNode fen = (FlatElementNode) fn;
      lhs = fen.getDst();
      rhs = fen.getSrc();
      if( shouldAnalysisTrack( lhs.getType() ) ) {

        assert rhs.getType() != null;
        assert rhs.getType().isArray();
        
        TypeDescriptor  tdElement = rhs.getType().dereference();
        FieldDescriptor fdElement = getArrayField( tdElement );
  
        rg.assignTempXEqualToTempYFieldF( lhs, rhs, fdElement );
      }
      break;

    case FKind.FlatSetElementNode:
      FlatSetElementNode fsen = (FlatSetElementNode) fn;

      if( arrayReferencees.doesNotCreateNewReaching( fsen ) ) {
        // skip this node if it cannot create new reachability paths
        break;
      }

      lhs = fsen.getDst();
      rhs = fsen.getSrc();
      if( shouldAnalysisTrack( rhs.getType() ) ) {

        assert lhs.getType() != null;
        assert lhs.getType().isArray();
        
        TypeDescriptor  tdElement = lhs.getType().dereference();
        FieldDescriptor fdElement = getArrayField( tdElement );

        rg.assignTempXFieldFEqualToTempY( lhs, fdElement, rhs );
      }
      break;
      
    case FKind.FlatNew:
      FlatNew fnn = (FlatNew) fn;
      lhs = fnn.getDst();
      if( shouldAnalysisTrack( lhs.getType() ) ) {
        AllocSite as = getAllocSiteFromFlatNewPRIVATE( fnn );   
        rg.assignTempEqualToNewAlloc( lhs, as );
      }
      break;

    case FKind.FlatCall: {
      Descriptor mdCaller;
      if( fmContaining.getMethod() != null ){
        mdCaller = fmContaining.getMethod();
      } else {
        mdCaller = fmContaining.getTask();
      }      
      FlatCall         fc       = (FlatCall) fn;
      MethodDescriptor mdCallee = fc.getMethod();
      FlatMethod       fmCallee = state.getMethodFlat( mdCallee );


      boolean debugCallSite =
        mdCaller.getSymbol().equals( state.DISJOINTDEBUGCALLER ) &&
        mdCallee.getSymbol().equals( state.DISJOINTDEBUGCALLEE );

      boolean writeDebugDOTs = false;
      boolean stopAfter      = false;
      if( debugCallSite ) {
        ++ReachGraph.debugCallSiteVisitCounter;
        System.out.println( "    $$$ Debug call site visit "+
                            ReachGraph.debugCallSiteVisitCounter+
                            " $$$"
                            );
        if( 
           (ReachGraph.debugCallSiteVisitCounter >= 
            ReachGraph.debugCallSiteVisitStartCapture)  &&
           
           (ReachGraph.debugCallSiteVisitCounter < 
            ReachGraph.debugCallSiteVisitStartCapture + 
            ReachGraph.debugCallSiteNumVisitsToCapture)
            ) {
          writeDebugDOTs = true;
          System.out.println( "      $$$ Capturing this call site visit $$$" );
          if( ReachGraph.debugCallSiteStopAfter &&
              (ReachGraph.debugCallSiteVisitCounter == 
               ReachGraph.debugCallSiteVisitStartCapture + 
               ReachGraph.debugCallSiteNumVisitsToCapture - 1)
              ) {
            stopAfter = true;
          }
        }
      }


      // calculate the heap this call site can reach--note this is
      // not used for the current call site transform, we are
      // grabbing this heap model for future analysis of the callees,
      // so if different results emerge we will return to this site
      ReachGraph heapForThisCall_old = 
        getIHMcontribution( mdCallee, fc );

      // the computation of the callee-reachable heap
      // is useful for making the callee starting point
      // and for applying the call site transfer function
      Set<Integer> callerNodeIDsCopiedToCallee = 
        new HashSet<Integer>();

      ReachGraph heapForThisCall_cur = 
        rg.makeCalleeView( fc, 
                           fmCallee,
                           callerNodeIDsCopiedToCallee,
                           writeDebugDOTs
                           );

      if( !heapForThisCall_cur.equals( heapForThisCall_old ) ) {        
        // if heap at call site changed, update the contribution,
        // and reschedule the callee for analysis
        addIHMcontribution( mdCallee, fc, heapForThisCall_cur );        

        // map a FlatCall to its enclosing method/task descriptor 
        // so we can write that info out later
        fc2enclosing.put( fc, mdCaller );

        if( state.DISJOINTDEBUGSCHEDULING ) {
          System.out.println( "  context changed, scheduling callee: "+mdCallee );
        }

        if( state.DISJOINTDVISITSTACKEESONTOP ) {
          calleesToEnqueue.add( mdCallee );
        } else {
          enqueue( mdCallee );
        }

      }


      // the transformation for a call site should update the
      // current heap abstraction with any effects from the callee,
      // or if the method is virtual, the effects from any possible
      // callees, so find the set of callees...
      Set<MethodDescriptor> setPossibleCallees;
      if( determinismDesired ) {
        // use an ordered set
        setPossibleCallees = new TreeSet<MethodDescriptor>( dComp );        
      } else {
        // otherwise use a speedy hashset
        setPossibleCallees = new HashSet<MethodDescriptor>();
      }

      if( mdCallee.isStatic() ) {        
        setPossibleCallees.add( mdCallee );
      } else {
        TypeDescriptor typeDesc = fc.getThis().getType();
        setPossibleCallees.addAll( callGraph.getMethods( mdCallee, 
                                                         typeDesc )
                                   );
      }

      ReachGraph rgMergeOfEffects = new ReachGraph();

      Iterator<MethodDescriptor> mdItr = setPossibleCallees.iterator();
      while( mdItr.hasNext() ) {
        MethodDescriptor mdPossible = mdItr.next();
        FlatMethod       fmPossible = state.getMethodFlat( mdPossible );

        addDependent( mdPossible, // callee
                      d );        // caller

        // don't alter the working graph (rg) until we compute a 
        // result for every possible callee, merge them all together,
        // then set rg to that
        ReachGraph rgCopy = new ReachGraph();
        rgCopy.merge( rg );             
                
        ReachGraph rgEffect = getPartial( mdPossible );

        if( rgEffect == null ) {
          // if this method has never been analyzed just schedule it 
          // for analysis and skip over this call site for now
          if( state.DISJOINTDVISITSTACKEESONTOP ) {
            calleesToEnqueue.add( mdPossible );
          } else {
            enqueue( mdPossible );
          }
          
          if( state.DISJOINTDEBUGSCHEDULING ) {
            System.out.println( "  callee hasn't been analyzed, scheduling: "+mdPossible );
          }


        } else {
          rgCopy.resolveMethodCall( fc, 
                                    fmPossible, 
                                    rgEffect,
                                    callerNodeIDsCopiedToCallee,
                                    writeDebugDOTs
                                    );
        }
        
        rgMergeOfEffects.merge( rgCopy );
      }


      if( stopAfter ) {
        System.out.println( "$$$ Exiting after requested captures of call site. $$$" );
        System.exit( 0 );
      }


      // now that we've taken care of building heap models for
      // callee analysis, finish this transformation
      rg = rgMergeOfEffects;
    } break;
      

    case FKind.FlatReturnNode:
      FlatReturnNode frn = (FlatReturnNode) fn;
      rhs = frn.getReturnTemp();
      if( rhs != null && shouldAnalysisTrack( rhs.getType() ) ) {
        rg.assignReturnEqualToTemp( rhs );
      }
      setRetNodes.add( frn );
      break;

    } // end switch

    
    // dead variables were removed before the above transfer function
    // was applied, so eliminate heap regions and edges that are no
    // longer part of the abstractly-live heap graph, and sweep up
    // and reachability effects that are altered by the reduction
    //rg.abstractGarbageCollect();
    //rg.globalSweep();


    // back edges are strictly monotonic
    if( pm.isBackEdge( fn ) ) {
      ReachGraph rgPrevResult = mapBackEdgeToMonotone.get( fn );
      rg.merge( rgPrevResult );
      mapBackEdgeToMonotone.put( fn, rg );
    }
    
    // at this point rg should be the correct update
    // by an above transfer function, or untouched if
    // the flat node type doesn't affect the heap
    return rg;
  }


  
  // this method should generate integers strictly greater than zero!
  // special "shadow" regions are made from a heap region by negating
  // the ID
  static public Integer generateUniqueHeapRegionNodeID() {
    ++uniqueIDcount;
    return new Integer( uniqueIDcount );
  }


  
  static public FieldDescriptor getArrayField( TypeDescriptor tdElement ) {
    FieldDescriptor fdElement = mapTypeToArrayField.get( tdElement );
    if( fdElement == null ) {
      fdElement = new FieldDescriptor( new Modifiers( Modifiers.PUBLIC ),
                                       tdElement,
                                       arrayElementFieldName,
                                       null,
                                       false );
      mapTypeToArrayField.put( tdElement, fdElement );
    }
    return fdElement;
  }

  
  
  private void writeFinalGraphs() {
    Set entrySet = mapDescriptorToCompleteReachGraph.entrySet();
    Iterator itr = entrySet.iterator();
    while( itr.hasNext() ) {
      Map.Entry  me = (Map.Entry)  itr.next();
      Descriptor  d = (Descriptor) me.getKey();
      ReachGraph rg = (ReachGraph) me.getValue();

      rg.writeGraph( "COMPLETE"+d,
                     true,   // write labels (variables)                
                     true,   // selectively hide intermediate temp vars 
                     true,   // prune unreachable heap regions          
                     true,  // hide subset reachability states         
                     true ); // hide edge taints                        
    }
  }

  private void writeFinalIHMs() {
    Iterator d2IHMsItr = mapDescriptorToIHMcontributions.entrySet().iterator();
    while( d2IHMsItr.hasNext() ) {
      Map.Entry                        me1 = (Map.Entry)                       d2IHMsItr.next();
      Descriptor                         d = (Descriptor)                      me1.getKey();
      Hashtable<FlatCall, ReachGraph> IHMs = (Hashtable<FlatCall, ReachGraph>) me1.getValue();

      Iterator fc2rgItr = IHMs.entrySet().iterator();
      while( fc2rgItr.hasNext() ) {
        Map.Entry  me2 = (Map.Entry)  fc2rgItr.next();
        FlatCall   fc  = (FlatCall)   me2.getKey();
        ReachGraph rg  = (ReachGraph) me2.getValue();
                
        rg.writeGraph( "IHMPARTFOR"+d+"FROM"+fc2enclosing.get( fc )+fc,
                       true,   // write labels (variables)
                       true,   // selectively hide intermediate temp vars
                       true,   // prune unreachable heap regions
                       true,  // hide subset reachability states
                       true ); // hide edge taints
      }
    }
  }

  private void writeInitialContexts() {
    Set entrySet = mapDescriptorToInitialContext.entrySet();
    Iterator itr = entrySet.iterator();
    while( itr.hasNext() ) {
      Map.Entry  me = (Map.Entry)  itr.next();
      Descriptor  d = (Descriptor) me.getKey();
      ReachGraph rg = (ReachGraph) me.getValue();

      rg.writeGraph( "INITIAL"+d,
                     true,   // write labels (variables)                
                     true,   // selectively hide intermediate temp vars 
                     true,   // prune unreachable heap regions          
                     true,  // hide subset reachability states         
                     true ); // hide edge taints                        
    }
  }
   

  protected ReachGraph getPartial( Descriptor d ) {
    return mapDescriptorToCompleteReachGraph.get( d );
  }

  protected void setPartial( Descriptor d, ReachGraph rg ) {
    mapDescriptorToCompleteReachGraph.put( d, rg );

    // when the flag for writing out every partial
    // result is set, we should spit out the graph,
    // but in order to give it a unique name we need
    // to track how many partial results for this
    // descriptor we've already written out
    if( writeAllIncrementalDOTs ) {
      if( !mapDescriptorToNumUpdates.containsKey( d ) ) {
        mapDescriptorToNumUpdates.put( d, new Integer( 0 ) );
      }
      Integer n = mapDescriptorToNumUpdates.get( d );
      
      rg.writeGraph( d+"COMPLETE"+String.format( "%05d", n ),
                     true,   // write labels (variables)
                     true,   // selectively hide intermediate temp vars
                     true,   // prune unreachable heap regions
                     true,  // hide subset reachability states
                     true ); // hide edge taints
      
      mapDescriptorToNumUpdates.put( d, n + 1 );
    }
  }



  // return just the allocation site associated with one FlatNew node
  protected AllocSite getAllocSiteFromFlatNewPRIVATE( FlatNew fnew ) {

    if( !mapFlatNewToAllocSite.containsKey( fnew ) ) {
      AllocSite as = AllocSite.factory( allocationDepth, 
                                        fnew, 
                                        fnew.getDisjointId() 
                                        );

      // the newest nodes are single objects
      for( int i = 0; i < allocationDepth; ++i ) {
        Integer id = generateUniqueHeapRegionNodeID();
        as.setIthOldest( i, id );
        mapHrnIdToAllocSite.put( id, as );
      }

      // the oldest node is a summary node
      as.setSummary( generateUniqueHeapRegionNodeID() );

      mapFlatNewToAllocSite.put( fnew, as );
    }

    return mapFlatNewToAllocSite.get( fnew );
  }


  public static boolean shouldAnalysisTrack( TypeDescriptor type ) {
    // don't track primitive types, but an array
    // of primitives is heap memory
    if( type.isImmutable() ) {
      return type.isArray();
    }

    // everything else is an object
    return true;
  }

  protected int numMethodsAnalyzed() {    
    return descriptorsToAnalyze.size();
  }
  

  
  
  
  // Take in source entry which is the program's compiled entry and
  // create a new analysis entry, a method that takes no parameters
  // and appears to allocate the command line arguments and call the
  // source entry with them.  The purpose of this analysis entry is
  // to provide a top-level method context with no parameters left.
  protected void makeAnalysisEntryMethod( MethodDescriptor mdSourceEntry ) {

    Modifiers mods = new Modifiers();
    mods.addModifier( Modifiers.PUBLIC );
    mods.addModifier( Modifiers.STATIC );

    TypeDescriptor returnType = 
      new TypeDescriptor( TypeDescriptor.VOID );

    this.mdAnalysisEntry = 
      new MethodDescriptor( mods,
                            returnType,
                            "analysisEntryMethod"
                            );

    TempDescriptor cmdLineArgs = 
      new TempDescriptor( "args",
                          mdSourceEntry.getParamType( 0 )
                          );

    FlatNew fn = 
      new FlatNew( mdSourceEntry.getParamType( 0 ),
                   cmdLineArgs,
                   false // is global 
                   );
    
    TempDescriptor[] sourceEntryArgs = new TempDescriptor[1];
    sourceEntryArgs[0] = cmdLineArgs;
    
    FlatCall fc = 
      new FlatCall( mdSourceEntry,
                    null, // dst temp
                    null, // this temp
                    sourceEntryArgs
                    );

    FlatReturnNode frn = new FlatReturnNode( null );

    FlatExit fe = new FlatExit();

    this.fmAnalysisEntry = 
      new FlatMethod( mdAnalysisEntry, 
                      fe
                      );

    this.fmAnalysisEntry.addNext( fn );
    fn.addNext( fc );
    fc.addNext( frn );
    frn.addNext( fe );
  }


  protected LinkedList<Descriptor> topologicalSort( Set<Descriptor> toSort ) {

    Set<Descriptor> discovered;

    if( determinismDesired ) {
      // use an ordered set
      discovered = new TreeSet<Descriptor>( dComp );      
    } else {
      // otherwise use a speedy hashset
      discovered = new HashSet<Descriptor>();
    }

    LinkedList<Descriptor> sorted = new LinkedList<Descriptor>();
  
    Iterator<Descriptor> itr = toSort.iterator();
    while( itr.hasNext() ) {
      Descriptor d = itr.next();
          
      if( !discovered.contains( d ) ) {
        dfsVisit( d, toSort, sorted, discovered );
      }
    }
    
    return sorted;
  }
  
  // While we're doing DFS on call graph, remember
  // dependencies for efficient queuing of methods
  // during interprocedural analysis:
  //
  // a dependent of a method decriptor d for this analysis is:
  //  1) a method or task that invokes d
  //  2) in the descriptorsToAnalyze set
  protected void dfsVisit( Descriptor             d,
                           Set       <Descriptor> toSort,                        
                           LinkedList<Descriptor> sorted,
                           Set       <Descriptor> discovered ) {
    discovered.add( d );
    
    // only methods have callers, tasks never do
    if( d instanceof MethodDescriptor ) {

      MethodDescriptor md = (MethodDescriptor) d;

      // the call graph is not aware that we have a fabricated
      // analysis entry that calls the program source's entry
      if( md == mdSourceEntry ) {
        if( !discovered.contains( mdAnalysisEntry ) ) {
          addDependent( mdSourceEntry,  // callee
                        mdAnalysisEntry // caller
                        );
          dfsVisit( mdAnalysisEntry, toSort, sorted, discovered );
        }
      }

      // otherwise call graph guides DFS
      Iterator itr = callGraph.getCallerSet( md ).iterator();
      while( itr.hasNext() ) {
        Descriptor dCaller = (Descriptor) itr.next();
        
        // only consider callers in the original set to analyze
        if( !toSort.contains( dCaller ) ) {
          continue;
        }
          
        if( !discovered.contains( dCaller ) ) {
          addDependent( md,     // callee
                        dCaller // caller
                        );

          dfsVisit( dCaller, toSort, sorted, discovered );
        }
      }
    }
    
    // for leaf-nodes last now!
    sorted.addLast( d );
  }


  protected void enqueue( Descriptor d ) {

    if( !descriptorsToVisitSet.contains( d ) ) {

      if( state.DISJOINTDVISITSTACK ||
          state.DISJOINTDVISITSTACKEESONTOP
          ) {
        descriptorsToVisitStack.add( d );

      } else if( state.DISJOINTDVISITPQUE ) {
        Integer priority = mapDescriptorToPriority.get( d );
        descriptorsToVisitQ.add( new DescriptorQWrapper( priority, 
                                                         d ) 
                                 );
      }

      descriptorsToVisitSet.add( d );
    }
  }


  // a dependent of a method decriptor d for this analysis is:
  //  1) a method or task that invokes d
  //  2) in the descriptorsToAnalyze set
  protected void addDependent( Descriptor callee, Descriptor caller ) {
    Set<Descriptor> deps = mapDescriptorToSetDependents.get( callee );
    if( deps == null ) {
      deps = new HashSet<Descriptor>();
    }
    deps.add( caller );
    mapDescriptorToSetDependents.put( callee, deps );
  }
  
  protected Set<Descriptor> getDependents( Descriptor callee ) {
    Set<Descriptor> deps = mapDescriptorToSetDependents.get( callee );
    if( deps == null ) {
      deps = new HashSet<Descriptor>();
      mapDescriptorToSetDependents.put( callee, deps );
    }
    return deps;
  }

  
  public Hashtable<FlatCall, ReachGraph> getIHMcontributions( Descriptor d ) {

    Hashtable<FlatCall, ReachGraph> heapsFromCallers = 
      mapDescriptorToIHMcontributions.get( d );
    
    if( heapsFromCallers == null ) {
      heapsFromCallers = new Hashtable<FlatCall, ReachGraph>();
      mapDescriptorToIHMcontributions.put( d, heapsFromCallers );
    }
    
    return heapsFromCallers;
  }

  public ReachGraph getIHMcontribution( Descriptor d, 
                                        FlatCall   fc
                                        ) {
    Hashtable<FlatCall, ReachGraph> heapsFromCallers = 
      getIHMcontributions( d );

    if( !heapsFromCallers.containsKey( fc ) ) {
      return null;
    }

    return heapsFromCallers.get( fc );
  }


  public void addIHMcontribution( Descriptor d,
                                  FlatCall   fc,
                                  ReachGraph rg
                                  ) {
    Hashtable<FlatCall, ReachGraph> heapsFromCallers = 
      getIHMcontributions( d );

    heapsFromCallers.put( fc, rg );
  }


  private AllocSite createParameterAllocSite( ReachGraph     rg, 
                                              TempDescriptor tempDesc,
                                              boolean        flagRegions
                                              ) {
    
    FlatNew flatNew;
    if( flagRegions ) {
      flatNew = new FlatNew( tempDesc.getType(), // type
                             tempDesc,           // param temp
                             false,              // global alloc?
                             "param"+tempDesc    // disjoint site ID string
                             );
    } else {
      flatNew = new FlatNew( tempDesc.getType(), // type
                             tempDesc,           // param temp
                             false,              // global alloc?
                             null                // disjoint site ID string
                             );
    }

    // create allocation site
    AllocSite as = AllocSite.factory( allocationDepth, 
                                      flatNew, 
                                      flatNew.getDisjointId()
                                      );
    for (int i = 0; i < allocationDepth; ++i) {
        Integer id = generateUniqueHeapRegionNodeID();
        as.setIthOldest(i, id);
        mapHrnIdToAllocSite.put(id, as);
    }
    // the oldest node is a summary node
    as.setSummary( generateUniqueHeapRegionNodeID() );
    
    rg.age(as);
    
    return as;
    
  }

private Set<FieldDescriptor> getFieldSetTobeAnalyzed(TypeDescriptor typeDesc){
        
        Set<FieldDescriptor> fieldSet=new HashSet<FieldDescriptor>();
    if(!typeDesc.isImmutable()){
            ClassDescriptor classDesc = typeDesc.getClassDesc();                    
            for (Iterator it = classDesc.getFields(); it.hasNext();) {
                    FieldDescriptor field = (FieldDescriptor) it.next();
                    TypeDescriptor fieldType = field.getType();
                    if (shouldAnalysisTrack( fieldType )) {
                        fieldSet.add(field);                    
                    }
            }
    }
    return fieldSet;
        
}

  private HeapRegionNode createMultiDeimensionalArrayHRN(ReachGraph rg, AllocSite alloc, HeapRegionNode srcHRN, FieldDescriptor fd, Hashtable<HeapRegionNode, HeapRegionNode> map, Hashtable<TypeDescriptor, HeapRegionNode> mapToExistingNode, ReachSet alpha ){

        int dimCount=fd.getType().getArrayCount();
        HeapRegionNode prevNode=null;
        HeapRegionNode arrayEntryNode=null;
        for(int i=dimCount;i>0;i--){
                TypeDescriptor typeDesc=fd.getType().dereference();//hack to get instance of type desc
                typeDesc.setArrayCount(i);
                TempDescriptor tempDesc=new TempDescriptor(typeDesc.getSymbol(),typeDesc);
                HeapRegionNode hrnSummary ;
                if(!mapToExistingNode.containsKey(typeDesc)){
                        AllocSite as;
                        if(i==dimCount){
                                as = alloc;
                        }else{
                          as = createParameterAllocSite(rg, tempDesc, false);
                        }
                        // make a new reference to allocated node
                    hrnSummary = 
                                rg.createNewHeapRegionNode(as.getSummary(), // id or null to generate a new one
                                                           false, // single object?
                                                           true, // summary?
                                                           false, // out-of-context?
                                                           as.getType(), // type
                                                           as, // allocation site
                                                           alpha, // inherent reach
                                                           alpha, // current reach
                                                           ExistPredSet.factory(rg.predTrue), // predicates
                                                           tempDesc.toString() // description
                                                           );
                    rg.id2hrn.put(as.getSummary(),hrnSummary);
                    
                    mapToExistingNode.put(typeDesc, hrnSummary);
                }else{
                        hrnSummary=mapToExistingNode.get(typeDesc);
                }
            
            if(prevNode==null){
                    // make a new reference between new summary node and source
                    RefEdge edgeToSummary = new RefEdge(srcHRN, // source
                                                        hrnSummary, // dest
                                                        typeDesc, // type
                                                        fd.getSymbol(), // field name
                                                        alpha, // beta
                                                        ExistPredSet.factory(rg.predTrue) // predicates
                                                        );
                    
                    rg.addRefEdge(srcHRN, hrnSummary, edgeToSummary);
                    prevNode=hrnSummary;
                    arrayEntryNode=hrnSummary;
            }else{
                    // make a new reference between summary nodes of array
                    RefEdge edgeToSummary = new RefEdge(prevNode, // source
                                                        hrnSummary, // dest
                                                        typeDesc, // type
                                                        arrayElementFieldName, // field name
                                                        alpha, // beta
                                                        ExistPredSet.factory(rg.predTrue) // predicates
                                                        );
                    
                    rg.addRefEdge(prevNode, hrnSummary, edgeToSummary);
                    prevNode=hrnSummary;
            }
            
        }
        
        // create a new obj node if obj has at least one non-primitive field
        TypeDescriptor type=fd.getType();
    if(getFieldSetTobeAnalyzed(type).size()>0){
        TypeDescriptor typeDesc=type.dereference();
        typeDesc.setArrayCount(0);
        if(!mapToExistingNode.containsKey(typeDesc)){
                TempDescriptor tempDesc=new TempDescriptor(type.getSymbol(),typeDesc);
                AllocSite as = createParameterAllocSite(rg, tempDesc, false);
                // make a new reference to allocated node
                    HeapRegionNode hrnSummary = 
                                rg.createNewHeapRegionNode(as.getSummary(), // id or null to generate a new one
                                                           false, // single object?
                                                           true, // summary?
                                                           false, // out-of-context?
                                                           typeDesc, // type
                                                           as, // allocation site
                                                           alpha, // inherent reach
                                                           alpha, // current reach
                                                           ExistPredSet.factory(rg.predTrue), // predicates
                                                           tempDesc.toString() // description
                                                           );
                    rg.id2hrn.put(as.getSummary(),hrnSummary);
                    mapToExistingNode.put(typeDesc, hrnSummary);
                    RefEdge edgeToSummary = new RefEdge(prevNode, // source
                                        hrnSummary, // dest
                                        typeDesc, // type
                                        arrayElementFieldName, // field name
                                        alpha, // beta
                                        ExistPredSet.factory(rg.predTrue) // predicates
                                        );
                    rg.addRefEdge(prevNode, hrnSummary, edgeToSummary);
                    prevNode=hrnSummary;
        }else{
                HeapRegionNode hrnSummary=mapToExistingNode.get(typeDesc);
                if(prevNode.getReferenceTo(hrnSummary, typeDesc, arrayElementFieldName)==null){
                        RefEdge edgeToSummary = new RefEdge(prevNode, // source
                                        hrnSummary, // dest
                                        typeDesc, // type
                                        arrayElementFieldName, // field name
                                        alpha, // beta
                                        ExistPredSet.factory(rg.predTrue) // predicates
                                        );
                    rg.addRefEdge(prevNode, hrnSummary, edgeToSummary);
                }
                 prevNode=hrnSummary;
        }
    }
        
        map.put(arrayEntryNode, prevNode);
        return arrayEntryNode;
}

private ReachGraph createInitialTaskReachGraph(FlatMethod fm) {
    ReachGraph rg = new ReachGraph();
    TaskDescriptor taskDesc = fm.getTask();
    
    for (int idx = 0; idx < taskDesc.numParameters(); idx++) {
        Descriptor paramDesc = taskDesc.getParameter(idx);
        TypeDescriptor paramTypeDesc = taskDesc.getParamType(idx);
        
        // setup data structure
        Set<HashMap<HeapRegionNode, FieldDescriptor>> workSet = 
            new HashSet<HashMap<HeapRegionNode, FieldDescriptor>>();
        Hashtable<TypeDescriptor, HeapRegionNode> mapTypeToExistingSummaryNode = 
            new Hashtable<TypeDescriptor, HeapRegionNode>();
        Hashtable<HeapRegionNode, HeapRegionNode> mapToFirstDimensionArrayNode = 
            new Hashtable<HeapRegionNode, HeapRegionNode>();
        Set<String> doneSet = new HashSet<String>();
        
        TempDescriptor tempDesc = fm.getParameter(idx);
        
        AllocSite as = createParameterAllocSite(rg, tempDesc, true);
        VariableNode lnX = rg.getVariableNodeFromTemp(tempDesc);
        Integer idNewest = as.getIthOldest(0);
        HeapRegionNode hrnNewest = rg.id2hrn.get(idNewest);

        // make a new reference to allocated node
        RefEdge edgeNew = new RefEdge(lnX, // source
                                      hrnNewest, // dest
                                      taskDesc.getParamType(idx), // type
                                      null, // field name
                                      hrnNewest.getAlpha(), // beta
                                      ExistPredSet.factory(rg.predTrue) // predicates
                                      );
        rg.addRefEdge(lnX, hrnNewest, edgeNew);

        // set-up a work set for class field
        ClassDescriptor classDesc = paramTypeDesc.getClassDesc();
        for (Iterator it = classDesc.getFields(); it.hasNext();) {
            FieldDescriptor fd = (FieldDescriptor) it.next();
            TypeDescriptor fieldType = fd.getType();
            if (shouldAnalysisTrack( fieldType )) {
                HashMap<HeapRegionNode, FieldDescriptor> newMap = new HashMap<HeapRegionNode, FieldDescriptor>();
                newMap.put(hrnNewest, fd);
                workSet.add(newMap);
            }
        }
        
        int uniqueIdentifier = 0;
        while (!workSet.isEmpty()) {
            HashMap<HeapRegionNode, FieldDescriptor> map = workSet
                .iterator().next();
            workSet.remove(map);
            
            Set<HeapRegionNode> key = map.keySet();
            HeapRegionNode srcHRN = key.iterator().next();
            FieldDescriptor fd = map.get(srcHRN);
            TypeDescriptor type = fd.getType();
            String doneSetIdentifier = srcHRN.getIDString() + "_" + fd;
            
            if (!doneSet.contains(doneSetIdentifier)) {
                doneSet.add(doneSetIdentifier);
                if (!mapTypeToExistingSummaryNode.containsKey(type)) {
                    // create new summary Node
                    TempDescriptor td = new TempDescriptor("temp"
                                                           + uniqueIdentifier, type);
                    
                    AllocSite allocSite;
                    if(type.equals(paramTypeDesc)){
                    //corresponding allocsite has already been created for a parameter variable.
                        allocSite=as;
                    }else{
                      allocSite = createParameterAllocSite(rg, td, false);
                    }
                    String strDesc = allocSite.toStringForDOT()
                        + "\\nsummary";
                    TypeDescriptor allocType=allocSite.getType();
                    
                    HeapRegionNode      hrnSummary;
                    if(allocType.isArray() && allocType.getArrayCount()>0){
                      hrnSummary=createMultiDeimensionalArrayHRN(rg,allocSite,srcHRN,fd,mapToFirstDimensionArrayNode,mapTypeToExistingSummaryNode,hrnNewest.getAlpha());
                    }else{                  
                        hrnSummary = 
                                        rg.createNewHeapRegionNode(allocSite.getSummary(), // id or null to generate a new one
                                                                   false, // single object?
                                                                   true, // summary?
                                                                   false, // out-of-context?
                                                                   allocSite.getType(), // type
                                                                   allocSite, // allocation site
                                                                   hrnNewest.getAlpha(), // inherent reach
                                                                   hrnNewest.getAlpha(), // current reach
                                                                   ExistPredSet.factory(rg.predTrue), // predicates
                                                                   strDesc // description
                                                                   );
                                    rg.id2hrn.put(allocSite.getSummary(),hrnSummary);
                    
                    // make a new reference to summary node
                    RefEdge edgeToSummary = new RefEdge(srcHRN, // source
                                                        hrnSummary, // dest
                                                        type, // type
                                                        fd.getSymbol(), // field name
                                                        hrnNewest.getAlpha(), // beta
                                                        ExistPredSet.factory(rg.predTrue) // predicates
                                                        );
                    
                    rg.addRefEdge(srcHRN, hrnSummary, edgeToSummary);
                    }               
                    uniqueIdentifier++;
                    
                    mapTypeToExistingSummaryNode.put(type, hrnSummary);
                    
                    // set-up a work set for  fields of the class
                    Set<FieldDescriptor> fieldTobeAnalyzed=getFieldSetTobeAnalyzed(type);
                    for (Iterator iterator = fieldTobeAnalyzed.iterator(); iterator
                                        .hasNext();) {
                                FieldDescriptor fieldDescriptor = (FieldDescriptor) iterator
                                                .next();
                                HeapRegionNode newDstHRN;
                                if(mapToFirstDimensionArrayNode.containsKey(hrnSummary)){
                                        //related heap region node is already exsited.
                                        newDstHRN=mapToFirstDimensionArrayNode.get(hrnSummary);
                                }else{
                                        newDstHRN=hrnSummary;
                                }
                                 doneSetIdentifier = newDstHRN.getIDString() + "_" + fieldDescriptor;                                                            
                                 if(!doneSet.contains(doneSetIdentifier)){
                                 // add new work item
                                         HashMap<HeapRegionNode, FieldDescriptor> newMap = 
                                            new HashMap<HeapRegionNode, FieldDescriptor>();
                                         newMap.put(newDstHRN, fieldDescriptor);
                                         workSet.add(newMap);
                                  }                             
                        }
                    
                }else{
                    // if there exists corresponding summary node
                    HeapRegionNode hrnDst=mapTypeToExistingSummaryNode.get(type);
                    
                    RefEdge edgeToSummary = new RefEdge(srcHRN, // source
                                                        hrnDst, // dest
                                                        fd.getType(), // type
                                                        fd.getSymbol(), // field name
                                                        srcHRN.getAlpha(), // beta
                                                        ExistPredSet.factory(rg.predTrue) // predicates
                                                        );
                    rg.addRefEdge(srcHRN, hrnDst, edgeToSummary);
                    
                }               
            }       
        }           
    }   
//    debugSnapshot(rg, fm, true);
    return rg;
}

// return all allocation sites in the method (there is one allocation
// site per FlatNew node in a method)
private HashSet<AllocSite> getAllocationSiteSet(Descriptor d) {
  if( !mapDescriptorToAllocSiteSet.containsKey(d) ) {
    buildAllocationSiteSet(d);
  }

  return mapDescriptorToAllocSiteSet.get(d);

}

private void buildAllocationSiteSet(Descriptor d) {
    HashSet<AllocSite> s = new HashSet<AllocSite>();

    FlatMethod fm;
    if( d instanceof MethodDescriptor ) {
      fm = state.getMethodFlat( (MethodDescriptor) d);
    } else {
      assert d instanceof TaskDescriptor;
      fm = state.getMethodFlat( (TaskDescriptor) d);
    }
    pm.analyzeMethod(fm);

    // visit every node in this FlatMethod's IR graph
    // and make a set of the allocation sites from the
    // FlatNew node's visited
    HashSet<FlatNode> visited = new HashSet<FlatNode>();
    HashSet<FlatNode> toVisit = new HashSet<FlatNode>();
    toVisit.add(fm);

    while( !toVisit.isEmpty() ) {
      FlatNode n = toVisit.iterator().next();

      if( n instanceof FlatNew ) {
        s.add(getAllocSiteFromFlatNewPRIVATE( (FlatNew) n) );
      }

      toVisit.remove(n);
      visited.add(n);

      for( int i = 0; i < pm.numNext(n); ++i ) {
        FlatNode child = pm.getNext(n, i);
        if( !visited.contains(child) ) {
          toVisit.add(child);
        }
      }
    }

    mapDescriptorToAllocSiteSet.put(d, s);
  }

        private HashSet<AllocSite> getFlaggedAllocationSites(Descriptor dIn) {

                HashSet<AllocSite> out = new HashSet<AllocSite>();
                HashSet<Descriptor> toVisit = new HashSet<Descriptor>();
                HashSet<Descriptor> visited = new HashSet<Descriptor>();

                toVisit.add(dIn);

                while (!toVisit.isEmpty()) {
                        Descriptor d = toVisit.iterator().next();
                        toVisit.remove(d);
                        visited.add(d);

                        HashSet<AllocSite> asSet = getAllocationSiteSet(d);
                        Iterator asItr = asSet.iterator();
                        while (asItr.hasNext()) {
                                AllocSite as = (AllocSite) asItr.next();
                                if (as.getDisjointAnalysisId() != null) {
                                        out.add(as);
                                }
                        }

                        // enqueue callees of this method to be searched for
                        // allocation sites also
                        Set callees = callGraph.getCalleeSet(d);
                        if (callees != null) {
                                Iterator methItr = callees.iterator();
                                while (methItr.hasNext()) {
                                        MethodDescriptor md = (MethodDescriptor) methItr.next();

                                        if (!visited.contains(md)) {
                                                toVisit.add(md);
                                        }
                                }
                        }
                }

                return out;
        }
 
    
private HashSet<AllocSite>
getFlaggedAllocationSitesReachableFromTaskPRIVATE(TaskDescriptor td) {

  HashSet<AllocSite> asSetTotal = new HashSet<AllocSite>();
  HashSet<Descriptor>     toVisit    = new HashSet<Descriptor>();
  HashSet<Descriptor>     visited    = new HashSet<Descriptor>();

  toVisit.add(td);

  // traverse this task and all methods reachable from this task
  while( !toVisit.isEmpty() ) {
    Descriptor d = toVisit.iterator().next();
    toVisit.remove(d);
    visited.add(d);

    HashSet<AllocSite> asSet = getAllocationSiteSet(d);
    Iterator asItr = asSet.iterator();
    while( asItr.hasNext() ) {
        AllocSite as = (AllocSite) asItr.next();
        TypeDescriptor typed = as.getType();
        if( typed != null ) {
          ClassDescriptor cd = typed.getClassDesc();
          if( cd != null && cd.hasFlags() ) {
            asSetTotal.add(as);
          }
        }
    }

    // enqueue callees of this method to be searched for
    // allocation sites also
    Set callees = callGraph.getCalleeSet(d);
    if( callees != null ) {
        Iterator methItr = callees.iterator();
        while( methItr.hasNext() ) {
          MethodDescriptor md = (MethodDescriptor) methItr.next();

          if( !visited.contains(md) ) {
            toVisit.add(md);
          }
        }
    }
  }

  return asSetTotal;
}


  
  
  // get successive captures of the analysis state, use compiler
  // flags to control
  boolean takeDebugSnapshots = false;
  String  descSymbolDebug    = null;
  boolean stopAfterCapture   = false;
  int     snapVisitCounter   = 0;
  int     snapNodeCounter    = 0;
  int     visitStartCapture  = 0;
  int     numVisitsToCapture = 0;


  void debugSnapshot( ReachGraph rg, FlatNode fn, boolean in ) {
    if( snapVisitCounter > visitStartCapture + numVisitsToCapture ) {
      return;
    }

    if( in ) {

    }

    if( snapVisitCounter >= visitStartCapture ) {
      System.out.println( "    @@@ snapping visit="+snapVisitCounter+
                          ", node="+snapNodeCounter+
                          " @@@" );
      String graphName;
      if( in ) {
        graphName = String.format( "snap%03d_%04din",
                                   snapVisitCounter,
                                   snapNodeCounter );
      } else {
        graphName = String.format( "snap%03d_%04dout",
                                   snapVisitCounter,
                                   snapNodeCounter );
      }
      if( fn != null ) {
        graphName = graphName + fn;
      }
      rg.writeGraph( graphName,
                     true,  // write labels (variables)
                     true,  // selectively hide intermediate temp vars
                     true,  // prune unreachable heap regions
                     true, // hide subset reachability states
                     true );// hide edge taints
    }
  }

}