been forgetting to make tabbing
[IRC.git] / Robust / src / Analysis / OwnershipAnalysis / OwnershipAnalysis.java
index e2c2c520fd7926b4deed37f32e4d0479985ac555..2af61b743cd8fa44aca404a325acc298142e3b21 100644 (file)
 package Analysis.OwnershipAnalysis;
 
+import Analysis.CallGraph.*;
 import IR.*;
 import IR.Flat.*;
+import IR.Tree.Modifiers;
 import java.util.*;
 import java.io.*;
 
 
 public class OwnershipAnalysis {
 
-    private State state;
-    private HashSet<FlatNode> visited;
-    private HashSet<FlatNode> toVisit;
 
-    private int labelindex;
-    private Hashtable<FlatNode, Integer> flatnodetolabel;
+  ///////////////////////////////////////////
+  //
+  //  Public interface to discover possible
+  //  aliases in the program under analysis
+  //
+  ///////////////////////////////////////////
+
+  public HashSet<AllocationSite>
+  getFlaggedAllocationSitesReachableFromTask(TaskDescriptor td) {
+    return getFlaggedAllocationSitesReachableFromTaskPRIVATE(td);
+  }
+
+  public AllocationSite getAllocationSiteFromFlatNew(FlatNew fn) {
+    return getAllocationSiteFromFlatNewPRIVATE(fn);
+  }
+
+  public boolean createsPotentialAliases(Descriptor taskOrMethod,
+                                         int paramIndex1,
+                                         int paramIndex2) {
+
+    OwnershipGraph og = mapDescriptorToCompleteOwnershipGraph.get(taskOrMethod);
+    assert(og != null);
+    return og.hasPotentialAlias(paramIndex1, paramIndex2);
+  }
+
+  public boolean createsPotentialAliases(Descriptor taskOrMethod,
+                                         int paramIndex,
+                                         AllocationSite alloc) {
+
+    OwnershipGraph og = mapDescriptorToCompleteOwnershipGraph.get(taskOrMethod);
+    assert(og != null);
+    return og.hasPotentialAlias(paramIndex, alloc);
+  }
+
+  public boolean createsPotentialAliases(Descriptor taskOrMethod,
+                                         AllocationSite alloc,
+                                         int paramIndex) {
+
+    OwnershipGraph og = mapDescriptorToCompleteOwnershipGraph.get(taskOrMethod);
+    assert(og != null);
+    return og.hasPotentialAlias(paramIndex, alloc);
+  }
+
+  public boolean createsPotentialAliases(Descriptor taskOrMethod,
+                                         AllocationSite alloc1,
+                                         AllocationSite alloc2) {
+
+    OwnershipGraph og = mapDescriptorToCompleteOwnershipGraph.get(taskOrMethod);
+    assert(og != null);
+    return og.hasPotentialAlias(alloc1, alloc2);
+  }
+
+  // use the methods given above to check every possible alias
+  // between task parameters and flagged allocation sites reachable
+  // from the task
+  public void writeAllAliases(String outputFile) throws java.io.IOException {
+
+    BufferedWriter bw = new BufferedWriter(new FileWriter(outputFile) );
+
+    // look through every task for potential aliases
+    Iterator taskItr = state.getTaskSymbolTable().getDescriptorsIterator();
+    while( taskItr.hasNext() ) {
+      TaskDescriptor td = (TaskDescriptor) taskItr.next();
+
+      bw.write("\n---------"+td+"--------\n");
+
+      HashSet<AllocationSite> allocSites = getFlaggedAllocationSitesReachableFromTask(td);
+
+      // for each task parameter, check for aliases with
+      // other task parameters and every allocation site
+      // reachable from this task
+      boolean foundSomeAlias = false;
+
+      FlatMethod fm = state.getMethodFlat(td);
+      for( int i = 0; i < fm.numParameters(); ++i ) {
+
+       // for the ith parameter check for aliases to all
+       // higher numbered parameters
+       for( int j = i + 1; j < fm.numParameters(); ++j ) {
+         if( createsPotentialAliases(td, i, j) ) {
+           foundSomeAlias = true;
+           bw.write("Potential alias between parameters "+i+" and "+j+".\n");
+         }
+       }
 
-    private Hashtable<FlatNode, OwnershipGraph> flatNodeToOwnershipGraph;
+       // for the ith parameter, check for aliases against
+       // the set of allocation sites reachable from this
+       // task context
+       Iterator allocItr = allocSites.iterator();
+       while( allocItr.hasNext() ) {
+         AllocationSite as = (AllocationSite) allocItr.next();
+         if( createsPotentialAliases(td, i, as) ) {
+           foundSomeAlias = true;
+           bw.write("Potential alias between parameter "+i+" and "+as+".\n");
+         }
+       }
+      }
+
+      // for each allocation site check for aliases with
+      // other allocation sites in the context of execution
+      // of this task
+      HashSet<AllocationSite> outerChecked = new HashSet<AllocationSite>();
+      Iterator allocItr1 = allocSites.iterator();
+      while( allocItr1.hasNext() ) {
+       AllocationSite as1 = (AllocationSite) allocItr1.next();
+
+       Iterator allocItr2 = allocSites.iterator();
+       while( allocItr2.hasNext() ) {
+         AllocationSite as2 = (AllocationSite) allocItr2.next();
+
+         if( !outerChecked.contains(as2) &&
+             createsPotentialAliases(td, as1, as2) ) {
+           bw.write("Potential alias between "+as1+" and "+as2+".\n");
+         }
+       }
 
+       outerChecked.add(as1);
+      }
 
-    // this analysis generates an ownership graph for every task
-    // in the program
-    public OwnershipAnalysis(State state) throws java.io.IOException {
-       this.state=state;      
-       analyzeTasks();
+      if( !foundSomeAlias ) {
+       bw.write("Task "+td+" contains no aliases between flagged objects.\n");
+      }
     }
 
-    public void analyzeTasks() throws java.io.IOException {
-       for( Iterator it_tasks=state.getTaskSymbolTable().getDescriptorsIterator();
-            it_tasks.hasNext();
-            ) {
+    bw.close();
+  }
+
+  ///////////////////////////////////////////
+  //
+  // end public interface
+  //
+  ///////////////////////////////////////////
+
+
+
+
+
+
+
+
+  // data from the compiler
+  private State state;
+  private CallGraph callGraph;
+  private int allocationDepth;
+
+  // 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 incerement to leave some
+  // reserved IDs for special purposes
+  static private int uniqueIDcount = 10;
+
+
+  // Use these data structures to track progress of
+  // processing all methods in the program, and by methods
+  // TaskDescriptor and MethodDescriptor are combined
+  // together, with a common parent class Descriptor
+  private Hashtable<Descriptor, OwnershipGraph>           mapDescriptorToCompleteOwnershipGraph;
+  private Hashtable<FlatNew,    AllocationSite>           mapFlatNewToAllocationSite;
+  private Hashtable<Descriptor, HashSet<AllocationSite> > mapDescriptorToAllocationSiteSet;
+
+  // Use these data structures to track progress of one pass of
+  // processing the FlatNodes of a particular method
+  private HashSet  <FlatNode>                 flatNodesToVisit;
+  private Hashtable<FlatNode, OwnershipGraph> mapFlatNodeToOwnershipGraph;
+  private HashSet  <FlatReturnNode>           returnNodesToCombineForCompleteOwnershipGraph;
+
+  // descriptorsToAnalyze identifies the set of tasks and methods
+  // that are reachable from the program tasks, this set is initialized
+  // and then remains static
+  private HashSet<Descriptor> descriptorsToAnalyze;
+
+  // descriptorsToVisit is initialized to descriptorsToAnalyze and is
+  // reduced by visiting a descriptor during analysis.  When dependents
+  // must be scheduled, only those contained in descriptorsToAnalyze
+  // should be re-added to this set
+  private HashSet<Descriptor> descriptorsToVisit;
+
+  // a special field descriptor for all array elements
+  private static FieldDescriptor fdElement = new FieldDescriptor(new Modifiers(Modifiers.PUBLIC),
+                                                                 new TypeDescriptor("Array[]"),
+                                                                 "elements",
+                                                                 null,
+                                                                 false);
+
+
+  // this analysis generates an ownership graph for every task
+  // in the program
+  public OwnershipAnalysis(State state,
+                           CallGraph callGraph,
+                           int allocationDepth) throws java.io.IOException {
+    this.state           = state;
+    this.callGraph       = callGraph;
+    this.allocationDepth = allocationDepth;
+
+
+    descriptorsToAnalyze = new HashSet<Descriptor>();
+
+    mapDescriptorToCompleteOwnershipGraph =
+      new Hashtable<Descriptor, OwnershipGraph>();
 
-           // initialize the mapping of flat nodes to ownership graphs
-           // every flat node in the IR graph has its own ownership graph
-           flatNodeToOwnershipGraph = new Hashtable<FlatNode, OwnershipGraph>();
+    mapFlatNewToAllocationSite =
+      new Hashtable<FlatNew, AllocationSite>();
 
-           TaskDescriptor td = (TaskDescriptor)it_tasks.next();
-           FlatMethod     fm = state.getMethodFlat( td );
+    mapDescriptorToAllocationSiteSet =
+      new Hashtable<Descriptor, HashSet<AllocationSite> >();
 
-           // give every node in the flat IR graph a unique label
-           // so a human being can inspect the graph and verify
-           // correctness
-           flatnodetolabel = new Hashtable<FlatNode, Integer>();
-           visited         = new HashSet<FlatNode>();
-           labelindex      = 0;
-           labelFlatNodes( fm );
 
-           String taskname = td.getSymbol();
-           analyzeFlatIRGraph( fm, taskname );
-       }       
+    // initialize methods to visit as the set of all tasks in the
+    // program and then any method that could be called starting
+    // from those tasks
+    Iterator taskItr = state.getTaskSymbolTable().getDescriptorsIterator();
+    while( taskItr.hasNext() ) {
+      Descriptor d = (Descriptor) taskItr.next();
+      scheduleAllCallees(d);
     }
 
-    private void labelFlatNodes(FlatNode fn) {
-       visited.add(fn);
-       flatnodetolabel.put(fn,new Integer(labelindex++));
-       for(int i=0;i<fn.numNext();i++) {
-           FlatNode nn=fn.getNext(i);
-           if(!visited.contains(nn)) {
-               labelFlatNodes(nn);
+    // before beginning analysis, initialize every scheduled method
+    // with an ownership graph that has populated parameter index tables
+    // by analyzing the first node which is always a FlatMethod node
+    Iterator<Descriptor> dItr = descriptorsToAnalyze.iterator();
+    while( dItr.hasNext() ) {
+      Descriptor d  = dItr.next();
+      OwnershipGraph og = new OwnershipGraph(allocationDepth);
+
+      FlatMethod fm;
+      if( d instanceof MethodDescriptor ) {
+       fm = state.getMethodFlat( (MethodDescriptor) d);
+      } else {
+       assert d instanceof TaskDescriptor;
+       fm = state.getMethodFlat( (TaskDescriptor) d);
+      }
+
+      System.out.println("Previsiting " + d);
+
+      analyzeFlatNode(d, fm, null, og);
+      mapDescriptorToCompleteOwnershipGraph.put(d, og);
+    }
+
+    System.out.println("");
+
+    // as mentioned above, analyze methods one-by-one, possibly revisiting
+    // a method if the methods that it calls are updated
+    analyzeMethods();
+
+    writeAllAliases("identifiedAliases.txt");
+  }
+
+  // called from the constructor to help initialize the set
+  // of methods that needs to be analyzed by ownership analysis
+  private void scheduleAllCallees(Descriptor d) {
+    if( descriptorsToAnalyze.contains(d) ) {
+      return;
+    }
+    descriptorsToAnalyze.add(d);
+
+    // start with all method calls to further schedule
+    Set moreMethodsToCheck = moreMethodsToCheck = callGraph.getMethodCalls(d);
+
+    if( d instanceof MethodDescriptor ) {
+      // see if this method has virtual dispatch
+      Set virtualMethods = callGraph.getMethods( (MethodDescriptor)d);
+      moreMethodsToCheck.addAll(virtualMethods);
+    }
+
+    // keep following any further methods identified in
+    // the call chain
+    Iterator methItr = moreMethodsToCheck.iterator();
+    while( methItr.hasNext() ) {
+      Descriptor m = (Descriptor) methItr.next();
+      scheduleAllCallees(m);
+    }
+  }
+
+
+  // manage the set of tasks and methods to be analyzed
+  // and be sure to reschedule tasks/methods when the methods
+  // they call are updated
+  private void analyzeMethods() throws java.io.IOException {
+
+    descriptorsToVisit = (HashSet<Descriptor>)descriptorsToAnalyze.clone();
+
+    while( !descriptorsToVisit.isEmpty() ) {
+      Descriptor d = (Descriptor) descriptorsToVisit.iterator().next();
+      descriptorsToVisit.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 ownership 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);
+
+      FlatMethod fm;
+      if( d instanceof MethodDescriptor ) {
+       fm = state.getMethodFlat( (MethodDescriptor) d);
+      } else {
+       assert d instanceof TaskDescriptor;
+       fm = state.getMethodFlat( (TaskDescriptor) d);
+      }
+
+      OwnershipGraph og = analyzeFlatMethod(d, fm);
+      OwnershipGraph ogPrev = mapDescriptorToCompleteOwnershipGraph.get(d);
+      if( !og.equals(ogPrev) ) {
+       mapDescriptorToCompleteOwnershipGraph.put(d, og);
+
+       /* boolean writeLabels,
+          boolean labelSelect,
+          boolean pruneGarbage,
+          boolean writeReferencers */
+       og.writeGraph(d, true, true, true, false);
+
+       // only methods have dependents, tasks cannot
+       // be invoked by any user program calls
+       if( d instanceof MethodDescriptor ) {
+         MethodDescriptor md = (MethodDescriptor) d;
+         Set dependents = callGraph.getCallerSet(md);
+         if( dependents != null ) {
+           Iterator depItr = dependents.iterator();
+           while( depItr.hasNext() ) {
+             Descriptor dependent = (Descriptor) depItr.next();
+             if( descriptorsToAnalyze.contains(dependent) ) {
+               descriptorsToVisit.add(dependent);
+             }
            }
+         }
+       }
+      }
+    }
+
+  }
+
+
+  // keep passing the Descriptor of the method along for debugging
+  // and dot file writing
+  private OwnershipGraph
+  analyzeFlatMethod(Descriptor mDesc,
+                    FlatMethod flatm) throws java.io.IOException {
+
+    // initialize flat nodes to visit as the flat method
+    // because all other nodes in this flat method are
+    // decendents of the flat method itself
+    flatNodesToVisit = new HashSet<FlatNode>();
+    flatNodesToVisit.add(flatm);
+
+
+    // A YUCKY HACK--this is to make sure that an initially empty
+    // graph (no parameters) will get passed the first "any changes?"
+    // test when it comes up for analysis.  It's ugly but throwing
+    // a child in works.
+    FlatNode fnJ = flatm.getNext(0);
+    assert fnJ != null;
+    flatNodesToVisit.add(fnJ);
+
+
+    // initilize the mapping of flat nodes in this flat method to
+    // ownership graph results to an empty mapping
+    mapFlatNodeToOwnershipGraph = new Hashtable<FlatNode, OwnershipGraph>();
+
+    // initialize the set of return nodes that will be combined as
+    // the final ownership graph result to return as an empty set
+    returnNodesToCombineForCompleteOwnershipGraph = new HashSet<FlatReturnNode>();
+
+
+    while( !flatNodesToVisit.isEmpty() ) {
+      FlatNode fn = (FlatNode) flatNodesToVisit.iterator().next();
+      flatNodesToVisit.remove(fn);
+
+      // perform this node's contributions to the ownership
+      // graph on a new copy, then compare it to the old graph
+      // at this node to see if anything was updated.
+      OwnershipGraph og = new OwnershipGraph(allocationDepth);
+
+      // start by merging all node's parents' graphs
+      for( int i = 0; i < fn.numPrev(); ++i ) {
+       FlatNode pn       = fn.getPrev(i);
+       OwnershipGraph ogParent = getGraphFromFlatNode(pn);
+       og.merge(ogParent);
+      }
+
+      // apply the analysis of the flat node to the
+      // ownership graph made from the merge of the
+      // parent graphs
+      analyzeFlatNode(mDesc,
+                      fn,
+                      returnNodesToCombineForCompleteOwnershipGraph,
+                      og);
+
+      // 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 for
+      // processing
+      OwnershipGraph ogPrev = getGraphFromFlatNode(fn);
+
+      if( !og.equals(ogPrev) ) {
+       setGraphForFlatNode(fn, og);
+
+       for( int i = 0; i < fn.numNext(); i++ ) {
+         FlatNode nn = fn.getNext(i);
+         flatNodesToVisit.add(nn);
        }
+      }
     }
 
-    private OwnershipGraph getGraphFromFlat( FlatNode fn ) {
-       if( !flatNodeToOwnershipGraph.containsKey( fn ) ) {
-           flatNodeToOwnershipGraph.put( fn, new OwnershipGraph() );
+    // end by merging all return nodes into a complete
+    // ownership graph that represents all possible heap
+    // states after the flat method returns
+    OwnershipGraph completeGraph = new OwnershipGraph(allocationDepth);
+    Iterator retItr = returnNodesToCombineForCompleteOwnershipGraph.iterator();
+    while( retItr.hasNext() ) {
+      FlatReturnNode frn = (FlatReturnNode) retItr.next();
+      OwnershipGraph ogr = getGraphFromFlatNode(frn);
+      completeGraph.merge(ogr);
+    }
+    return completeGraph;
+  }
+
+
+  private void
+  analyzeFlatNode(Descriptor methodDesc,
+                  FlatNode fn,
+                  HashSet<FlatReturnNode> setRetNodes,
+                  OwnershipGraph og) throws java.io.IOException {
+
+    TempDescriptor lhs;
+    TempDescriptor rhs;
+    FieldDescriptor fld;
+
+    // use node type to decide what alterations to make
+    // to the ownership graph
+    switch( fn.kind() ) {
+
+    case FKind.FlatMethod:
+      FlatMethod fm = (FlatMethod) fn;
+
+      // there should only be one FlatMethod node as the
+      // parent of all other FlatNode objects, so take
+      // the opportunity to construct the initial graph by
+      // adding parameters labels to new heap regions
+      for( int i = 0; i < fm.numParameters(); ++i ) {
+       TempDescriptor tdParam = fm.getParameter(i);
+
+       og.assignTempEqualToParamAlloc(tdParam,
+                                      methodDesc instanceof TaskDescriptor,
+                                      new Integer(i) );
+      }
+      break;
+
+    case FKind.FlatOpNode:
+      FlatOpNode fon = (FlatOpNode) fn;
+      if( fon.getOp().getOp() == Operation.ASSIGN ) {
+       lhs = fon.getDest();
+       rhs = fon.getLeft();
+       og.assignTempXEqualToTempY(lhs, rhs);
+      }
+      break;
+
+    case FKind.FlatFieldNode:
+      FlatFieldNode ffn = (FlatFieldNode) fn;
+      lhs = ffn.getDst();
+      rhs = ffn.getSrc();
+      fld = ffn.getField();
+      if( !fld.getType().isPrimitive() ) {
+       og.assignTempXEqualToTempYFieldF(lhs, rhs, fld);
+      }
+      break;
+
+    case FKind.FlatSetFieldNode:
+      FlatSetFieldNode fsfn = (FlatSetFieldNode) fn;
+      lhs = fsfn.getDst();
+      fld = fsfn.getField();
+      rhs = fsfn.getSrc();
+      og.assignTempXFieldFEqualToTempY(lhs, fld, rhs);
+      break;
+
+    case FKind.FlatElementNode:
+      FlatElementNode fen = (FlatElementNode) fn;
+      lhs = fen.getDst();
+      rhs = fen.getSrc();
+      if( !lhs.getType().isPrimitive() ) {
+       og.assignTempXEqualToTempYFieldF(lhs, rhs, fdElement);
+      }
+      break;
+
+    case FKind.FlatSetElementNode:
+      FlatSetElementNode fsen = (FlatSetElementNode) fn;
+      lhs = fsen.getDst();
+      rhs = fsen.getSrc();
+      if( !rhs.getType().isPrimitive() ) {
+       og.assignTempXFieldFEqualToTempY(lhs, fdElement, rhs);
+      }
+      break;
+
+    case FKind.FlatNew:
+      FlatNew fnn = (FlatNew) fn;
+      lhs = fnn.getDst();
+      AllocationSite as = getAllocationSiteFromFlatNewPRIVATE(fnn);
+
+      og.assignTempEqualToNewAlloc(lhs, as);
+      break;
+
+    case FKind.FlatCall:
+      FlatCall fc = (FlatCall) fn;
+      MethodDescriptor md = fc.getMethod();
+      FlatMethod flatm = state.getMethodFlat(md);
+      OwnershipGraph ogMergeOfAllPossibleCalleeResults = new OwnershipGraph(allocationDepth);
+
+      if( md.isStatic() ) {
+       // a static method is simply always the same, makes life easy
+       OwnershipGraph onlyPossibleCallee = mapDescriptorToCompleteOwnershipGraph.get(md);
+       ogMergeOfAllPossibleCalleeResults = og;
+       ogMergeOfAllPossibleCalleeResults.resolveMethodCall(fc, md.isStatic(), flatm, onlyPossibleCallee);
+      } else {
+       // if the method descriptor is virtual, then there could be a
+       // set of possible methods that will actually be invoked, so
+       // find all of them and merge all of their results together
+       TypeDescriptor typeDesc = fc.getThis().getType();
+       Set possibleCallees = callGraph.getMethods(md, typeDesc);
+
+       Iterator i = possibleCallees.iterator();
+       while( i.hasNext() ) {
+         MethodDescriptor possibleMd = (MethodDescriptor) i.next();
+
+         // don't alter the working graph (og) until we compute a result for every
+         // possible callee, merge them all together, then set og to that
+         OwnershipGraph ogCopy = new OwnershipGraph(allocationDepth);
+         ogCopy.merge(og);
+
+         OwnershipGraph ogPotentialCallee = mapDescriptorToCompleteOwnershipGraph.get(possibleMd);
+         ogCopy.resolveMethodCall(fc, md.isStatic(), flatm, ogPotentialCallee);
+         ogMergeOfAllPossibleCalleeResults.merge(ogCopy);
        }
+      }
+
+      og = ogMergeOfAllPossibleCalleeResults;
+      break;
 
-       return flatNodeToOwnershipGraph.get( fn );
+    case FKind.FlatReturnNode:
+      FlatReturnNode frn = (FlatReturnNode) fn;
+      rhs = frn.getReturnTemp();
+
+      if( rhs != null ) {
+       og.assignReturnEqualToTemp(rhs);
+      }
+
+      setRetNodes.add(frn);
+      break;
     }
+  }
+
 
-    private void setGraphForFlat( FlatNode fn, OwnershipGraph og ) {
-       flatNodeToOwnershipGraph.put( fn, og );
+  // 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);
+  }
+
+
+  private OwnershipGraph getGraphFromFlatNode(FlatNode fn) {
+    if( !mapFlatNodeToOwnershipGraph.containsKey(fn) ) {
+      mapFlatNodeToOwnershipGraph.put(fn, new OwnershipGraph(allocationDepth) );
     }
 
-    private void analyzeFlatIRGraph( FlatMethod flatm, String taskname ) throws java.io.IOException {
-       visited=new HashSet<FlatNode>();
-       toVisit=new HashSet<FlatNode>();
-       toVisit.add( flatm );
+    return mapFlatNodeToOwnershipGraph.get(fn);
+  }
 
-       while( !toVisit.isEmpty() ) {
-           FlatNode fn = (FlatNode)toVisit.iterator().next();
-           toVisit.remove( fn );
-           visited.add( fn );
+  private void setGraphForFlatNode(FlatNode fn, OwnershipGraph og) {
+    mapFlatNodeToOwnershipGraph.put(fn, og);
+  }
 
-           // perform this node's contributions to the ownership
-           // graph on a new copy, then compare it to the old graph
-           // at this node to see if anything was updated.
-           OwnershipGraph og = new OwnershipGraph();
 
-           // start by merging all incoming node's graphs
-           for( int i = 0; i < fn.numPrev(); ++i ) {
-               FlatNode       pn       = fn.getPrev( i );
-               OwnershipGraph ogParent = getGraphFromFlat( pn );
-               og.merge( ogParent );
-           }
-           
-           TempDescriptor  src;
-           TempDescriptor  dst;
-           FieldDescriptor fld;
-           String nodeDescription = "No description";
-           boolean writeGraph = false;
-
-           // use node type to decide what alterations to make
-           // to the ownership graph       
-           switch( fn.kind() ) {
-               
-           case FKind.FlatMethod:
-               FlatMethod fm = (FlatMethod) fn;
-
-               // add method parameters to the list of heap regions
-               // and remember names for analysis
-               for( int i = 0; i < fm.numParameters(); ++i ) {
-                   TempDescriptor tdParam = fm.getParameter( i );
-                   og.newHeapRegion( tdParam );
-                   og.addAnalysisRegion( tdParam );
-               }
-
-               nodeDescription = "Method";
-               writeGraph = true;
-               break;
-
-           case FKind.FlatOpNode:
-               FlatOpNode fon = (FlatOpNode) fn;
-               if( fon.getOp().getOp() == Operation.ASSIGN ) {
-                   src = fon.getLeft();
-                   dst = fon.getDest();
-                   og.assignTempToTemp( src, dst );
-                   nodeDescription = "Op";
-                   writeGraph = true;
-               }
-               break;
-
-           case FKind.FlatFieldNode:
-               FlatFieldNode ffn = (FlatFieldNode) fn;
-               src = ffn.getSrc();
-               dst = ffn.getDst();
-               fld = ffn.getField();
-               if( !fld.getType().isPrimitive() ) {
-                   og.assignTempToField( src, dst, fld );
-                   nodeDescription = "Field";
-                   writeGraph = true;
-               }
-               break;
-
-           case FKind.FlatSetFieldNode:
-               FlatSetFieldNode fsfn = (FlatSetFieldNode) fn;
-               src = fsfn.getSrc();
-               dst = fsfn.getDst();
-               fld = fsfn.getField();
-               og.assignFieldToTemp( src, dst, fld );
-               nodeDescription = "SetField";
-               writeGraph = true;
-
-               break;
-
-           case FKind.FlatReturnNode:
-               nodeDescription = "Return";
-               writeGraph = true;
-               og.writeCondensedAnalysis( makeCondensedAnalysisName( taskname, flatnodetolabel.get(fn) ) );
-               break;
-           }
 
-           if( writeGraph ) {
-               og.writeGraph( makeNodeName( taskname, 
-                                            flatnodetolabel.get( fn ), 
-                                            nodeDescription ) );
-           }
-           
-           // 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 for
-           // processing
-           OwnershipGraph ogOld = getGraphFromFlat( fn );
-
-           if( !og.equivalent( ogOld ) ) {
-               setGraphForFlat( fn, og );
-
-               for( int i = 0; i < fn.numNext(); i++ ) {
-                   FlatNode nn = fn.getNext( i );
-                   visited.remove( nn );
-                   toVisit.add( nn );
-               }
-           }
-       }
+  // return just the allocation site associated with one FlatNew node
+  private AllocationSite getAllocationSiteFromFlatNewPRIVATE(FlatNew fn) {
+
+    if( !mapFlatNewToAllocationSite.containsKey(fn) ) {
+      AllocationSite as = new AllocationSite(allocationDepth, fn.getType() );
+
+      // the newest nodes are single objects
+      for( int i = 0; i < allocationDepth; ++i ) {
+       Integer id = generateUniqueHeapRegionNodeID();
+       as.setIthOldest(i, id);
+      }
+
+      // the oldest node is a summary node
+      Integer idSummary = generateUniqueHeapRegionNodeID();
+      as.setSummary(idSummary);
+
+      mapFlatNewToAllocationSite.put(fn, as);
     }
 
-    private String makeNodeName( String taskname, Integer id, String type ) {
-       String s = String.format( "%05d", id );
-       return "task"+taskname+"_FN"+s+"_"+type;
+    return mapFlatNewToAllocationSite.get(fn);
+  }
+
+
+  // return all allocation sites in the method (there is one allocation
+  // site per FlatNew node in a method)
+  private HashSet<AllocationSite> getAllocationSiteSet(Descriptor d) {
+    if( !mapDescriptorToAllocationSiteSet.containsKey(d) ) {
+      buildAllocationSiteSet(d);
+    }
+
+    return mapDescriptorToAllocationSiteSet.get(d);
+
+  }
+
+  private void buildAllocationSiteSet(Descriptor d) {
+    HashSet<AllocationSite> s = new HashSet<AllocationSite>();
+
+    FlatMethod fm;
+    if( d instanceof MethodDescriptor ) {
+      fm = state.getMethodFlat( (MethodDescriptor) d);
+    } else {
+      assert d instanceof TaskDescriptor;
+      fm = state.getMethodFlat( (TaskDescriptor) d);
     }
 
-    private String makeCondensedAnalysisName( String taskname, Integer id ) {
-       return "task"+taskname+"_Ownership_from"+id;
+    // 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(getAllocationSiteFromFlatNewPRIVATE( (FlatNew) n) );
+      }
+
+      toVisit.remove(n);
+      visited.add(n);
+
+      for( int i = 0; i < n.numNext(); ++i ) {
+       FlatNode child = n.getNext(i);
+       if( !visited.contains(child) ) {
+         toVisit.add(child);
+       }
+      }
     }
+
+    mapDescriptorToAllocationSiteSet.put(d, s);
+  }
+
+
+  private HashSet<AllocationSite>
+  getFlaggedAllocationSitesReachableFromTaskPRIVATE(TaskDescriptor td) {
+
+    HashSet<AllocationSite> asSetTotal = new HashSet<AllocationSite>();
+    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<AllocationSite> asSet = getAllocationSiteSet(d);
+      Iterator asItr = asSet.iterator();
+      while( asItr.hasNext() ) {
+       AllocationSite as = (AllocationSite) asItr.next();
+       if( as.getType().getClassDesc().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;
+  }
 }