[IRC.git] / Robust / src / Analysis / MLP / MLPAnalysis.java

package Analysis.MLP;

import Analysis.CallGraph.*;
import Analysis.OwnershipAnalysis.*;
import IR.*;
import IR.Flat.*;
import IR.Tree.*;
import java.util.*;
import java.io.*;


public class MLPAnalysis {

  // data from the compiler
  private State             state;
  private TypeUtil          typeUtil;
  private CallGraph         callGraph;
  private OwnershipAnalysis ownAnalysis;

  private FlatSESEEnterNode      rootSESE;  
  private Set<FlatSESEEnterNode> allSESEs;

  private Hashtable< FlatNode, Stack<FlatSESEEnterNode> > seseStacks;
  private Hashtable< FlatNode, Set<TempDescriptor>      > livenessRootView;
  private Hashtable< FlatNode, Set<TempDescriptor>      > livenessVirtualReads;
  private Hashtable< FlatNode, VarSrcTokTable           > variableResults;
  private Hashtable< FlatNode, Set<TempDescriptor>      > notAvailableResults;
  private Hashtable< FlatNode, CodePlan                 > codePlans;

  private Hashtable<FlatEdge, FlatWriteDynamicVarNode> wdvNodesToSpliceIn;

  public static int maxSESEage = -1;


  // use these methods in BuildCode to have access to analysis results
  public FlatSESEEnterNode getRootSESE() {
    return rootSESE;
  }

  public Set<FlatSESEEnterNode> getAllSESEs() {
    return allSESEs;
  }

  public int getMaxSESEage() {
    return maxSESEage;
  }

  // may be null
  public CodePlan getCodePlan( FlatNode fn ) {
    CodePlan cp = codePlans.get( fn );
    return cp;
  }


  public MLPAnalysis( State             state,
                      TypeUtil          tu,
                      CallGraph         callGraph,
                      OwnershipAnalysis ownAnalysis
                      ) {

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

    this.state       = state;
    this.typeUtil    = tu;
    this.callGraph   = callGraph;
    this.ownAnalysis = ownAnalysis;
    this.maxSESEage  = state.MLP_MAXSESEAGE;

    // initialize analysis data structures
    allSESEs = new HashSet<FlatSESEEnterNode>();

    seseStacks           = new Hashtable< FlatNode, Stack<FlatSESEEnterNode> >();
    livenessVirtualReads = new Hashtable< FlatNode, Set<TempDescriptor>      >();
    variableResults      = new Hashtable< FlatNode, VarSrcTokTable           >();
    notAvailableResults  = new Hashtable< FlatNode, Set<TempDescriptor>      >();
    codePlans            = new Hashtable< FlatNode, CodePlan                 >();

    wdvNodesToSpliceIn = new Hashtable<FlatEdge, FlatWriteDynamicVarNode>();


    FlatMethod fmMain = state.getMethodFlat( tu.getMain() );

    rootSESE = (FlatSESEEnterNode) fmMain.getNext(0);    
    rootSESE.setfmEnclosing( fmMain );
    rootSESE.setmdEnclosing( fmMain.getMethod() );
    rootSESE.setcdEnclosing( fmMain.getMethod().getClassDesc() );

    if( state.MLPDEBUG ) {      
      System.out.println( "" );
    }

    // 1st pass
    // run analysis on each method that is actually called
    // reachability analysis already computed this so reuse
    Iterator<Descriptor> methItr = ownAnalysis.descriptorsToAnalyze.iterator();
    while( methItr.hasNext() ) {
      Descriptor d  = methItr.next();      
      FlatMethod fm = state.getMethodFlat( d );

      // find every SESE from methods that may be called
      // and organize them into roots and children
      buildForestForward( fm );
    }
    if( state.MLPDEBUG ) {      
      //System.out.println( "\nSESE Hierarchy\n--------------\n" ); printSESEHierarchy();
    }


    // 2nd pass, results are saved in FlatSESEEnterNode, so
    // intermediate results, for safety, are discarded
    livenessAnalysisBackward( rootSESE, true, null, fmMain.getFlatExit() );


    // 3rd pass
    methItr = ownAnalysis.descriptorsToAnalyze.iterator();
    while( methItr.hasNext() ) {
      Descriptor d  = methItr.next();      
      FlatMethod fm = state.getMethodFlat( d );

      // starting from roots do a forward, fixed-point
      // variable analysis for refinement and stalls
      variableAnalysisForward( fm );
    }


    // 4th pass, compute liveness contribution from
    // virtual reads discovered in variable pass
    livenessAnalysisBackward( rootSESE, true, null, fmMain.getFlatExit() );        
    if( state.MLPDEBUG ) {      
      //System.out.println( "\nLive-In, SESE View\n-------------\n" ); printSESELiveness();
      //System.out.println( "\nLive-In, Root View\n------------------\n"+fmMain.printMethod( livenessRootView ) );
    }


    // 5th pass
    methItr = ownAnalysis.descriptorsToAnalyze.iterator();
    while( methItr.hasNext() ) {
      Descriptor d  = methItr.next();      
      FlatMethod fm = state.getMethodFlat( d );

      // prune variable results in one traversal
      // by removing reference variables that are not live
      pruneVariableResultsWithLiveness( fm );
    }
    if( state.MLPDEBUG ) {      
      System.out.println( "\nVariable Results-Out\n----------------\n"+fmMain.printMethod( variableResults ) );
    }
    

    // 6th pass
    methItr = ownAnalysis.descriptorsToAnalyze.iterator();
    while( methItr.hasNext() ) {
      Descriptor d  = methItr.next();      
      FlatMethod fm = state.getMethodFlat( d );

      // compute what is not available at every program
      // point, in a forward fixed-point pass
      notAvailableForward( fm );
    }
    if( state.MLPDEBUG ) {      
      //System.out.println( "\nNot Available Results-Out\n---------------------\n"+fmMain.printMethod( notAvailableResults ) );
    }


    // 7th pass
    methItr = ownAnalysis.descriptorsToAnalyze.iterator();
    while( methItr.hasNext() ) {
      Descriptor d  = methItr.next();      
      FlatMethod fm = state.getMethodFlat( d );

      // compute a plan for code injections
      computeStallsForward( fm );
    }
    if( state.MLPDEBUG ) {
      //System.out.println( "\nCode Plans\n----------\n"+fmMain.printMethod( codePlans ) );
    }

    // splice new IR nodes into graph after all
    // analysis passes are complete
    Iterator spliceItr = wdvNodesToSpliceIn.entrySet().iterator();
    while( spliceItr.hasNext() ) {
      Map.Entry               me    = (Map.Entry)               spliceItr.next();
      FlatWriteDynamicVarNode fwdvn = (FlatWriteDynamicVarNode) me.getValue();
      fwdvn.spliceIntoIR();
    }

    // detailed per-SESE information
    if( state.MLPDEBUG ) {
      System.out.println( "\nSESE info\n-------------\n" ); printSESEInfo();
    }

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


  private void buildForestForward( FlatMethod fm ) {
    
    // start from flat method top, visit every node in
    // method exactly once, find SESEs and remember
    // roots and child relationships
    Set<FlatNode> flatNodesToVisit = new HashSet<FlatNode>();
    flatNodesToVisit.add( fm );

    Set<FlatNode> visited = new HashSet<FlatNode>();    

    Stack<FlatSESEEnterNode> seseStackFirst = new Stack<FlatSESEEnterNode>();
    seseStacks.put( fm, seseStackFirst );

    while( !flatNodesToVisit.isEmpty() ) {
      Iterator<FlatNode> fnItr = flatNodesToVisit.iterator();
      FlatNode fn = fnItr.next();

      Stack<FlatSESEEnterNode> seseStack = seseStacks.get( fn );
      assert seseStack != null;      

      flatNodesToVisit.remove( fn );
      visited.add( fn );      

      buildForest_nodeActions( fn, seseStack, fm );

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

        if( !visited.contains( nn ) ) {
          flatNodesToVisit.add( nn );

          // clone stack and send along each analysis path
          seseStacks.put( nn, (Stack<FlatSESEEnterNode>)seseStack.clone() );
        }
      }
    }      
  }

  private void buildForest_nodeActions( FlatNode fn,                                                       
                                        Stack<FlatSESEEnterNode> seseStack,
                                        FlatMethod fm ) {
    switch( fn.kind() ) {

    case FKind.FlatSESEEnterNode: {
      FlatSESEEnterNode fsen = (FlatSESEEnterNode) fn;

      allSESEs.add( fsen );
      fsen.setfmEnclosing( fm );
      fsen.setmdEnclosing( fm.getMethod() );
      fsen.setcdEnclosing( fm.getMethod().getClassDesc() );

      if( !seseStack.empty() ) {
        seseStack.peek().addChild( fsen );
        fsen.setParent( seseStack.peek() );
      }

      seseStack.push( fsen );
    } break;

    case FKind.FlatSESEExitNode: {
      FlatSESEExitNode fsexn = (FlatSESEExitNode) fn;
      assert !seseStack.empty();
      FlatSESEEnterNode fsen = seseStack.pop();
    } break;

    case FKind.FlatReturnNode: {
      FlatReturnNode frn = (FlatReturnNode) fn;
      if( !seseStack.empty() ) {
        throw new Error( "Error: return statement enclosed within SESE "+
                         seseStack.peek().getPrettyIdentifier() );
      }
    } break;
      
    }
  }

  private void printSESEHierarchy() {
    // our forest is actually a tree now that
    // there is an implicit root SESE
    printSESEHierarchyTree( rootSESE, 0 );
    System.out.println( "" );
  }

  private void printSESEHierarchyTree( FlatSESEEnterNode fsen, int depth ) {
    for( int i = 0; i < depth; ++i ) {
      System.out.print( "  " );
    }
    System.out.println( "- "+fsen.getPrettyIdentifier() );

    Iterator<FlatSESEEnterNode> childItr = fsen.getChildren().iterator();
    while( childItr.hasNext() ) {
      FlatSESEEnterNode fsenChild = childItr.next();
      printSESEHierarchyTree( fsenChild, depth + 1 );
    }
  }


  private void livenessAnalysisBackward( FlatSESEEnterNode fsen, 
                                         boolean toplevel, 
                                         Hashtable< FlatSESEExitNode, Set<TempDescriptor> > liveout, 
                                         FlatExit fexit ) {

    // start from an SESE exit, visit nodes in reverse up to
    // SESE enter in a fixed-point scheme, where children SESEs
    // should already be analyzed and therefore can be skipped 
    // because child SESE enter node has all necessary info
    Set<FlatNode> flatNodesToVisit = new HashSet<FlatNode>();

    FlatSESEExitNode fsexn = fsen.getFlatExit();
    if (toplevel) {
        //handle root SESE
        flatNodesToVisit.add( fexit );
    } else
        flatNodesToVisit.add( fsexn );
    Hashtable<FlatNode, Set<TempDescriptor>> livenessResults=new Hashtable<FlatNode, Set<TempDescriptor>>();

    if (toplevel==true)
        liveout=new Hashtable<FlatSESEExitNode, Set<TempDescriptor>>();
    
    while( !flatNodesToVisit.isEmpty() ) {
      FlatNode fn = (FlatNode) flatNodesToVisit.iterator().next();
      flatNodesToVisit.remove( fn );      
      
      Set<TempDescriptor> prev = livenessResults.get( fn );

      // merge sets from control flow joins
      Set<TempDescriptor> u = new HashSet<TempDescriptor>();
      for( int i = 0; i < fn.numNext(); i++ ) {
        FlatNode nn = fn.getNext( i );
        Set<TempDescriptor> s = livenessResults.get( nn );
        if( s != null ) {
          u.addAll( s );
        }
      }
      
      Set<TempDescriptor> curr = liveness_nodeActions( fn, u, fsen, toplevel, liveout);

      // if a new result, schedule backward nodes for analysis
      if( !curr.equals( prev ) ) {
        livenessResults.put( fn, curr );

        // don't flow backwards past current SESE enter
        if( !fn.equals( fsen ) ) {
          for( int i = 0; i < fn.numPrev(); i++ ) {
            FlatNode nn = fn.getPrev( i );
            flatNodesToVisit.add( nn );
          }
        }
      }
    }
    
    Set<TempDescriptor> s = livenessResults.get( fsen );
    if( s != null ) {
      fsen.addInVarSet( s );
    }
    
    // remember liveness per node from the root view as the
    // global liveness of variables for later passes to use
    if( toplevel == true ) {
      livenessRootView = livenessResults;
    }

    // post-order traversal, so do children first
    Iterator<FlatSESEEnterNode> childItr = fsen.getChildren().iterator();
    while( childItr.hasNext() ) {
      FlatSESEEnterNode fsenChild = childItr.next();
      livenessAnalysisBackward( fsenChild, false, liveout, null );
    }
  }

  private Set<TempDescriptor> liveness_nodeActions( FlatNode fn, 
                                                    Set<TempDescriptor> liveIn,
                                                    FlatSESEEnterNode currentSESE,
                                                    boolean toplevel,
                                                    Hashtable< FlatSESEExitNode, Set<TempDescriptor> > liveout ) {

    switch( fn.kind() ) {

    case FKind.FlatSESEExitNode:
      if (toplevel==true) {
          FlatSESEExitNode exitn=(FlatSESEExitNode) fn;
        //update liveout set for FlatSESEExitNode
          if (!liveout.containsKey(exitn))
            liveout.put(exitn, new HashSet<TempDescriptor>());
          liveout.get(exitn).addAll(liveIn);
      }
      // no break, sese exits should also execute default actions
      
    default: {
      // handle effects of statement in reverse, writes then reads
      TempDescriptor [] writeTemps = fn.writesTemps();
      for( int i = 0; i < writeTemps.length; ++i ) {
        liveIn.remove( writeTemps[i] );

        if (!toplevel) {
          FlatSESEExitNode exitnode=currentSESE.getFlatExit();
          Set<TempDescriptor> livetemps=liveout.get(exitnode);
          if (livetemps.contains(writeTemps[i])) {
            //write to a live out temp...
            //need to put in SESE liveout set
            currentSESE.addOutVar(writeTemps[i]);
          }
        }
      }

      TempDescriptor [] readTemps = fn.readsTemps();
      for( int i = 0; i < readTemps.length; ++i ) {
        liveIn.add( readTemps[i] );
      }

      Set<TempDescriptor> virtualReadTemps = livenessVirtualReads.get( fn );
      if( virtualReadTemps != null ) {
        Iterator<TempDescriptor> vrItr = virtualReadTemps.iterator();
        while( vrItr.hasNext() ) {
          TempDescriptor vrt = vrItr.next();
          liveIn.add( vrt );
        }
      }
    } break;

    } // end switch

    return liveIn;
  }

  private void printSESELiveness() {
    // our forest is actually a tree now that
    // there is an implicit root SESE
    printSESELivenessTree( rootSESE );
    System.out.println( "" );
  }

  private void printSESELivenessTree( FlatSESEEnterNode fsen ) {

    System.out.println( "SESE "+fsen.getPrettyIdentifier()+" has in-set:" );
    Iterator<TempDescriptor> tItr = fsen.getInVarSet().iterator();
    while( tItr.hasNext() ) {
      System.out.println( "  "+tItr.next() );
    }
    System.out.println( "and out-set:" );
    tItr = fsen.getOutVarSet().iterator();
    while( tItr.hasNext() ) {
      System.out.println( "  "+tItr.next() );
    }
    System.out.println( "" );


    Iterator<FlatSESEEnterNode> childItr = fsen.getChildren().iterator();
    while( childItr.hasNext() ) {
      FlatSESEEnterNode fsenChild = childItr.next();
      printSESELivenessTree( fsenChild );
    }
  }

  private void printSESEInfo() {
    printSESEInfoTree( rootSESE );
    System.out.println( "" );
  }

  private void printSESEInfoTree( FlatSESEEnterNode fsen ) {

    System.out.println( "SESE "+fsen.getPrettyIdentifier()+" {" );

    System.out.println( "  in-set: "+fsen.getInVarSet() );
    Iterator<TempDescriptor> tItr = fsen.getInVarSet().iterator();
    while( tItr.hasNext() ) {
      TempDescriptor inVar = tItr.next();
      if( fsen.getReadyInVarSet().contains( inVar ) ) {
        System.out.println( "    (ready)  "+inVar );
      }
      if( fsen.getStaticInVarSet().contains( inVar ) ) {
        System.out.println( "    (static) "+inVar );
      } 
      if( fsen.getDynamicInVarSet().contains( inVar ) ) {
        System.out.println( "    (dynamic)"+inVar );
      }
    }

    System.out.println( "  out-set: "+fsen.getOutVarSet() );

    /*
    System.out.println( "  static names to track:" );
    tItr = fsen.getOutVarSet().iterator();
    while( tItr.hasNext() ) {
      System.out.println( "    "+tItr.next() );
    }
    */

    System.out.println( "}" );

    Iterator<FlatSESEEnterNode> childItr = fsen.getChildren().iterator();
    while( childItr.hasNext() ) {
      FlatSESEEnterNode fsenChild = childItr.next();
      printSESEInfoTree( fsenChild );
    }
  }


  private void variableAnalysisForward( FlatMethod fm ) {

    Set<FlatNode> flatNodesToVisit = new HashSet<FlatNode>();
    flatNodesToVisit.add( fm );  

    while( !flatNodesToVisit.isEmpty() ) {
      FlatNode fn = (FlatNode) flatNodesToVisit.iterator().next();
      flatNodesToVisit.remove( fn );      

      Stack<FlatSESEEnterNode> seseStack = seseStacks.get( fn );
      assert seseStack != null;      

      VarSrcTokTable prev = variableResults.get( fn );

      // merge sets from control flow joins
      VarSrcTokTable curr = new VarSrcTokTable();
      for( int i = 0; i < fn.numPrev(); i++ ) {
        FlatNode nn = fn.getPrev( i );          
        VarSrcTokTable incoming = variableResults.get( nn );
        curr.merge( incoming );
      }

      if( !seseStack.empty() ) {
        variable_nodeActions( fn, curr, seseStack.peek() );
      }

      // if a new result, schedule forward nodes for analysis
      if( !curr.equals( prev ) ) {       
        variableResults.put( fn, curr );

        for( int i = 0; i < fn.numNext(); i++ ) {
          FlatNode nn = fn.getNext( i );         
          flatNodesToVisit.add( nn );    
        }
      }
    }
  }

  private void variable_nodeActions( FlatNode fn, 
                                     VarSrcTokTable vstTable,
                                     FlatSESEEnterNode currentSESE ) {
    switch( fn.kind() ) {

    case FKind.FlatSESEEnterNode: {
      FlatSESEEnterNode fsen = (FlatSESEEnterNode) fn;
      assert fsen.equals( currentSESE );

      vstTable.age( currentSESE );
      vstTable.assertConsistency();

      vstTable.ownInSet( currentSESE );
      vstTable.assertConsistency();
    } break;

    case FKind.FlatSESEExitNode: {
      FlatSESEExitNode  fsexn = (FlatSESEExitNode)  fn;
      FlatSESEEnterNode fsen  = fsexn.getFlatEnter();
      assert currentSESE.getChildren().contains( fsen );
      vstTable.remapChildTokens( fsen );

      Set<TempDescriptor> liveIn       = currentSESE.getInVarSet();
      Set<TempDescriptor> virLiveIn    = vstTable.removeParentAndSiblingTokens( fsen, liveIn );
      Set<TempDescriptor> virLiveInOld = livenessVirtualReads.get( fn );
      if( virLiveInOld != null ) {
        virLiveIn.addAll( virLiveInOld );
      }
      livenessVirtualReads.put( fn, virLiveIn );
      vstTable.assertConsistency();

      // then all child out-set tokens are guaranteed
      // to be filled in, so clobber those entries with
      // the latest, clean sources
      Iterator<TempDescriptor> outVarItr = fsen.getOutVarSet().iterator();
      while( outVarItr.hasNext() ) {
        TempDescriptor outVar = outVarItr.next();
        HashSet<TempDescriptor> ts = new HashSet<TempDescriptor>();
        ts.add( outVar );
        VariableSourceToken vst = new VariableSourceToken( ts,
                                                           fsen,
                                                           new Integer( 0 ),
                                                           outVar
                                                           );
        vstTable.remove( outVar );
        vstTable.add( vst );
      }
      vstTable.assertConsistency();

    } break;

    case FKind.FlatOpNode: {
      FlatOpNode fon = (FlatOpNode) fn;

      if( fon.getOp().getOp() == Operation.ASSIGN ) {
        TempDescriptor lhs = fon.getDest();
        TempDescriptor rhs = fon.getLeft();        

        vstTable.remove( lhs );

        Set<VariableSourceToken> forAddition = new HashSet<VariableSourceToken>();

        Iterator<VariableSourceToken> itr = vstTable.get( rhs ).iterator();
        while( itr.hasNext() ) {
          VariableSourceToken vst = itr.next();

          HashSet<TempDescriptor> ts = new HashSet<TempDescriptor>();
          ts.add( lhs );

          forAddition.add( new VariableSourceToken( ts,
                                                    vst.getSESE(),
                                                    vst.getAge(),
                                                    vst.getAddrVar()
                                                    )
                           );
        }

        vstTable.addAll( forAddition );

        // only break if this is an ASSIGN op node,
        // otherwise fall through to default case
        vstTable.assertConsistency();
        break;
      }
    }

    // note that FlatOpNode's that aren't ASSIGN
    // fall through to this default case
    default: {
      TempDescriptor [] writeTemps = fn.writesTemps();
      if( writeTemps.length > 0 ) {


        // for now, when writeTemps > 1, make sure
        // its a call node, programmer enforce only
        // doing stuff like calling a print routine
        //assert writeTemps.length == 1;
        if( writeTemps.length > 1 ) {
          assert fn.kind() == FKind.FlatCall ||
                 fn.kind() == FKind.FlatMethod;
          break;
        }


        vstTable.remove( writeTemps[0] );

        HashSet<TempDescriptor> ts = new HashSet<TempDescriptor>();
        ts.add( writeTemps[0] );

        vstTable.add( new VariableSourceToken( ts,
                                               currentSESE,
                                               new Integer( 0 ),
                                               writeTemps[0]
                                             )
                      );
      }      

      vstTable.assertConsistency();
    } break;

    } // end switch
  }


  private void pruneVariableResultsWithLiveness( FlatMethod fm ) {
    
    // start from flat method top, visit every node in
    // method exactly once
    Set<FlatNode> flatNodesToVisit = new HashSet<FlatNode>();
    flatNodesToVisit.add( fm );

    Set<FlatNode> visited = new HashSet<FlatNode>();    

    while( !flatNodesToVisit.isEmpty() ) {
      Iterator<FlatNode> fnItr = flatNodesToVisit.iterator();
      FlatNode fn = fnItr.next();

      flatNodesToVisit.remove( fn );
      visited.add( fn );      

      Set<TempDescriptor> rootLiveSet = livenessRootView.get( fn );
      VarSrcTokTable      vstTable    = variableResults.get( fn );
      
      // fix later, not working, only wanted it to make tables easier to read
      //vstTable.pruneByLiveness( rootLiveSet );
      
      for( int i = 0; i < fn.numNext(); i++ ) {
        FlatNode nn = fn.getNext( i );

        if( !visited.contains( nn ) ) {
          flatNodesToVisit.add( nn );
        }
      }
    }
  }


  private void notAvailableForward( FlatMethod fm ) {

    Set<FlatNode> flatNodesToVisit = new HashSet<FlatNode>();
    flatNodesToVisit.add( fm );  

    while( !flatNodesToVisit.isEmpty() ) {
      FlatNode fn = (FlatNode) flatNodesToVisit.iterator().next();
      flatNodesToVisit.remove( fn );      

      Stack<FlatSESEEnterNode> seseStack = seseStacks.get( fn );
      assert seseStack != null;      

      Set<TempDescriptor> prev = notAvailableResults.get( fn );

      Set<TempDescriptor> curr = new HashSet<TempDescriptor>();      
      for( int i = 0; i < fn.numPrev(); i++ ) {
        FlatNode nn = fn.getPrev( i );       
        Set<TempDescriptor> notAvailIn = notAvailableResults.get( nn );
        if( notAvailIn != null ) {
          curr.addAll( notAvailIn );
        }
      }
      
      if( !seseStack.empty() ) {
        notAvailable_nodeActions( fn, curr, seseStack.peek() );     
      }

      // if a new result, schedule forward nodes for analysis
      if( !curr.equals( prev ) ) {
        notAvailableResults.put( fn, curr );

        for( int i = 0; i < fn.numNext(); i++ ) {
          FlatNode nn = fn.getNext( i );         
          flatNodesToVisit.add( nn );    
        }
      }
    }
  }

  private void notAvailable_nodeActions( FlatNode fn, 
                                         Set<TempDescriptor> notAvailSet,
                                         FlatSESEEnterNode currentSESE ) {

    // any temps that are removed from the not available set
    // at this node should be marked in this node's code plan
    // as temps to be grabbed at runtime!

    switch( fn.kind() ) {

    case FKind.FlatSESEEnterNode: {
      FlatSESEEnterNode fsen = (FlatSESEEnterNode) fn;
      assert fsen.equals( currentSESE );
      notAvailSet.clear();
    } break;

    case FKind.FlatSESEExitNode: {
      FlatSESEExitNode  fsexn = (FlatSESEExitNode)  fn;
      FlatSESEEnterNode fsen  = fsexn.getFlatEnter();
      assert currentSESE.getChildren().contains( fsen );

      Set<TempDescriptor> liveTemps = livenessRootView.get( fn );
      assert liveTemps != null;

      notAvailSet.addAll( liveTemps );
    } break;

    case FKind.FlatOpNode: {
      FlatOpNode fon = (FlatOpNode) fn;

      if( fon.getOp().getOp() == Operation.ASSIGN ) {
        TempDescriptor lhs = fon.getDest();
        TempDescriptor rhs = fon.getLeft();

        // copy makes lhs same availability as rhs
        if( notAvailSet.contains( rhs ) ) {
          notAvailSet.add( lhs );
        } else {
          notAvailSet.remove( lhs );
        }

        // only break if this is an ASSIGN op node,
        // otherwise fall through to default case
        break;
      }
    }

    // note that FlatOpNode's that aren't ASSIGN
    // fall through to this default case
    default: {
      TempDescriptor [] writeTemps = fn.writesTemps();
      for( int i = 0; i < writeTemps.length; i++ ) {
        TempDescriptor wTemp = writeTemps[i];
        notAvailSet.remove( wTemp );
      }
      TempDescriptor [] readTemps = fn.readsTemps();
      for( int i = 0; i < readTemps.length; i++ ) {
        TempDescriptor rTemp = readTemps[i];
        notAvailSet.remove( rTemp );

        // if this variable has exactly one source, potentially
        // get other things from this source as well
        VarSrcTokTable vstTable = variableResults.get( fn );

        Integer srcType = 
          vstTable.getRefVarSrcType( rTemp, 
                                     currentSESE,
                                     currentSESE.getParent() );

        if( srcType.equals( VarSrcTokTable.SrcType_STATIC ) ) {

          VariableSourceToken vst = vstTable.get( rTemp ).iterator().next();

          Iterator<VariableSourceToken> availItr = vstTable.get( vst.getSESE(),
                                                                 vst.getAge()
                                                                 ).iterator();

          // look through things that are also available from same source
          while( availItr.hasNext() ) {
            VariableSourceToken vstAlsoAvail = availItr.next();
          
            Iterator<TempDescriptor> refVarItr = vstAlsoAvail.getRefVars().iterator();
            while( refVarItr.hasNext() ) {
              TempDescriptor refVarAlso = refVarItr.next();

              // if a variable is available from the same source, AND it ALSO
              // only comes from one statically known source, mark it available
              Integer srcTypeAlso = 
                vstTable.getRefVarSrcType( refVarAlso, 
                                           currentSESE,
                                           currentSESE.getParent() );
              if( srcTypeAlso.equals( VarSrcTokTable.SrcType_STATIC ) ) {
                notAvailSet.remove( refVarAlso );
              }
            }
          }
        }
      }
    } break;

    } // end switch
  }


  private void computeStallsForward( FlatMethod fm ) {
    
    // start from flat method top, visit every node in
    // method exactly once
    Set<FlatNode> flatNodesToVisit = new HashSet<FlatNode>();
    flatNodesToVisit.add( fm );

    Set<FlatNode> visited = new HashSet<FlatNode>();    

    while( !flatNodesToVisit.isEmpty() ) {
      Iterator<FlatNode> fnItr = flatNodesToVisit.iterator();
      FlatNode fn = fnItr.next();

      flatNodesToVisit.remove( fn );
      visited.add( fn );      

      Stack<FlatSESEEnterNode> seseStack = seseStacks.get( fn );
      assert seseStack != null;      

      // use incoming results as "dot statement" or just
      // before the current statement
      VarSrcTokTable dotSTtable = new VarSrcTokTable();
      for( int i = 0; i < fn.numPrev(); i++ ) {
        FlatNode nn = fn.getPrev( i );
        dotSTtable.merge( variableResults.get( nn ) );
      }

      // find dt-st notAvailableSet also
      Set<TempDescriptor> dotSTnotAvailSet = new HashSet<TempDescriptor>();      
      for( int i = 0; i < fn.numPrev(); i++ ) {
        FlatNode nn = fn.getPrev( i );       
        Set<TempDescriptor> notAvailIn = notAvailableResults.get( nn );
        if( notAvailIn != null ) {
          dotSTnotAvailSet.addAll( notAvailIn );
        }
      }

      Set<TempDescriptor> dotSTlive = livenessRootView.get( fn );

      if( !seseStack.empty() ) {
        computeStalls_nodeActions( fn, 
                                   dotSTlive,
                                   dotSTtable,
                                   dotSTnotAvailSet,
                                   seseStack.peek()
                                   );
      }

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

        if( !visited.contains( nn ) ) {
          flatNodesToVisit.add( nn );
        }
      }
    }
  }

  private void computeStalls_nodeActions( FlatNode fn,
                                          Set<TempDescriptor> liveSetIn,
                                          VarSrcTokTable vstTableIn,
                                          Set<TempDescriptor> notAvailSetIn,
                                          FlatSESEEnterNode currentSESE ) {

    CodePlan plan = new CodePlan( currentSESE);

    switch( fn.kind() ) {

    case FKind.FlatSESEEnterNode: {
      FlatSESEEnterNode fsen = (FlatSESEEnterNode) fn;

      // track the source types of the in-var set so generated
      // code at this SESE issue can compute the number of
      // dependencies properly
      Iterator<TempDescriptor> inVarItr = fsen.getInVarSet().iterator();
      while( inVarItr.hasNext() ) {
        TempDescriptor inVar = inVarItr.next();
        Integer srcType = 
          vstTableIn.getRefVarSrcType( inVar, 
                                       fsen,
                                       fsen.getParent() );

        // the current SESE needs a local space to track the dynamic
        // variable and the child needs space in its SESE record
        if( srcType.equals( VarSrcTokTable.SrcType_DYNAMIC ) ) {
          fsen.addDynamicInVar( inVar );
          fsen.getParent().addDynamicVar( inVar );

        } else if( srcType.equals( VarSrcTokTable.SrcType_STATIC ) ) {
          fsen.addStaticInVar( inVar );
          VariableSourceToken vst = vstTableIn.get( inVar ).iterator().next();
          fsen.putStaticInVar2src( inVar, vst );
          fsen.addStaticInVarSrc( new SESEandAgePair( vst.getSESE(), 
                                                      vst.getAge() 
                                                    ) 
                                );

        } else {
          assert srcType.equals( VarSrcTokTable.SrcType_READY );
          fsen.addReadyInVar( inVar );
        }       
      }

    } break;

    case FKind.FlatSESEExitNode: {
      FlatSESEExitNode fsexn = (FlatSESEExitNode) fn;
    } break;

    case FKind.FlatOpNode: {
      FlatOpNode fon = (FlatOpNode) fn;

      if( fon.getOp().getOp() == Operation.ASSIGN ) {
        TempDescriptor lhs = fon.getDest();
        TempDescriptor rhs = fon.getLeft();        

        // if this is an op node, don't stall, copy
        // source and delay until we need to use value

        // but check the source type of rhs variable
        // and if dynamic, lhs becomes dynamic, too,
        // and we need to keep dynamic sources during
        Integer srcType 
          = vstTableIn.getRefVarSrcType( rhs,
                                         currentSESE,
                                         currentSESE.getParent() );

        if( srcType.equals( VarSrcTokTable.SrcType_DYNAMIC ) ) {
          plan.addDynAssign( lhs, rhs );
          currentSESE.addDynamicVar( lhs );
          currentSESE.addDynamicVar( rhs );
        }

        // only break if this is an ASSIGN op node,
        // otherwise fall through to default case
        break;
      }
    }

    // note that FlatOpNode's that aren't ASSIGN
    // fall through to this default case
    default: {          

      // a node with no live set has nothing to stall for
      if( liveSetIn == null ) {
        break;
      }

      TempDescriptor[] readarray = fn.readsTemps();
      for( int i = 0; i < readarray.length; i++ ) {
        TempDescriptor readtmp = readarray[i];

        // ignore temps that are definitely available 
        // when considering to stall on it
        if( !notAvailSetIn.contains( readtmp ) ) {
          continue;
        }

        // check the source type of this variable
        Integer srcType 
          = vstTableIn.getRefVarSrcType( readtmp,
                                       currentSESE,
                                       currentSESE.getParent() );

        if( srcType.equals( VarSrcTokTable.SrcType_DYNAMIC ) ) {
          // 1) It is not clear statically where this variable will
          // come from statically, so dynamically we must keep track
          // along various control paths, and therefore when we stall,
          // just stall for the exact thing we need and move on
          plan.addDynamicStall( readtmp );
          currentSESE.addDynamicVar( readtmp );

        } else if( srcType.equals( VarSrcTokTable.SrcType_STATIC ) ) {    
          // 2) Single token/age pair: Stall for token/age pair, and copy
          // all live variables with same token/age pair at the same
          // time.  This is the same stuff that the notavaialable analysis 
          // marks as now available.      

          VariableSourceToken vst = vstTableIn.get( readtmp ).iterator().next();

          Iterator<VariableSourceToken> availItr = 
            vstTableIn.get( vst.getSESE(), vst.getAge() ).iterator();

          while( availItr.hasNext() ) {
            VariableSourceToken vstAlsoAvail = availItr.next();

            // only grab additional stuff that is live
            Set<TempDescriptor> copySet = new HashSet<TempDescriptor>();

            Iterator<TempDescriptor> refVarItr = vstAlsoAvail.getRefVars().iterator();
            while( refVarItr.hasNext() ) {
              TempDescriptor refVar = refVarItr.next();
              if( liveSetIn.contains( refVar ) ) {
                copySet.add( refVar );
              }
            }

            if( !copySet.isEmpty() ) {
              plan.addStall2CopySet( vstAlsoAvail, copySet );
            }
          }                      

        } else {
          // the other case for srcs is READY from a parent, however
          // since we are only examining variables that come from
          // children tokens, this should never occur
          assert false;
        }

        // assert that everything being stalled for is in the
        // "not available" set coming into this flat node and
        // that every VST identified is in the possible "stall set"
        // that represents VST's from children SESE's

      }      
    } break;
      
    } // end switch


    // identify sese-age pairs that are statically useful
    // and should have an associated SESE variable in code
    Set<VariableSourceToken> staticSet = vstTableIn.getStaticSet();
    Iterator<VariableSourceToken> vstItr = staticSet.iterator();
    while( vstItr.hasNext() ) {
      VariableSourceToken vst = vstItr.next();
      currentSESE.addNeededStaticName( 
        new SESEandAgePair( vst.getSESE(), vst.getAge() ) 
                                     );
      currentSESE.mustTrackAtLeastAge( vst.getAge() );
    }


    codePlans.put( fn, plan );


    // if any variables at this-node-*dot* have a static source (exactly one vst)
    // but go to a dynamic source at next-node-*dot*, create a new IR graph
    // node on that edge to track the sources dynamically
    VarSrcTokTable thisVstTable = variableResults.get( fn );
    for( int i = 0; i < fn.numNext(); i++ ) {
      FlatNode            nn           = fn.getNext( i );
      VarSrcTokTable      nextVstTable = variableResults.get( nn );
      Set<TempDescriptor> nextLiveIn   = livenessRootView.get( nn );

      // the table can be null if it is one of the few IR nodes
      // completely outside of the root SESE scope
      if( nextVstTable != null && nextLiveIn != null ) {

        Hashtable<TempDescriptor, VariableSourceToken> static2dynamicSet = 
          thisVstTable.getStatic2DynamicSet( nextVstTable, nextLiveIn );
        
        if( !static2dynamicSet.isEmpty() ) {

          // either add these results to partial fixed-point result
          // or make a new one if we haven't made any here yet
          FlatEdge fe = new FlatEdge( fn, nn );
          FlatWriteDynamicVarNode fwdvn = wdvNodesToSpliceIn.get( fe );

          if( fwdvn == null ) {
            fwdvn = new FlatWriteDynamicVarNode( fn, 
                                                 nn,
                                                 static2dynamicSet,
                                                 currentSESE
                                                 );
            wdvNodesToSpliceIn.put( fe, fwdvn );
          } else {
            fwdvn.addMoreVar2Src( static2dynamicSet );
          }
        }
      }
    }
  }
}