@Override
  public void applyTransferFunction(Instr i) {
    IRScope scope = problem.getScope();
    boolean scopeBindingHasEscaped = scope.bindingHasEscaped();

    // Process closure accepting instrs specially -- these are the sites of binding stores!
    if (i instanceof ClosureAcceptingInstr) {
      Operand o = ((ClosureAcceptingInstr) i).getClosureArg();
      // At this site, a binding will get allocated if it has not been already!
      if (o != null && o instanceof WrappedIRClosure) {
        // In this first pass, the current scope and the call's closure are considered
        // independent of each other which means any variable that is used by the variable
        // will get spilled into the binding.  This is clearly conservative, but simplifies
        // the analysis.
        IRClosure cl = ((WrappedIRClosure) o).getClosure();

        // If the call is a dataflow barrier, we have to spill everything here
        boolean spillAllVars = scopeBindingHasEscaped;

        // - If all variables have to be spilled, then those variables will no longer be dirty after
        // the call site
        // - If a variable is used in the closure (FIXME: Strictly only those vars that are live at
        // the call site --
        //   but we dont have this info!), it has to be spilt. So, these variables are no longer
        // dirty after the call site.
        // - If a variable is (re)defined in the closure, it will always be loaded after the call.
        // So, we have to always
        //   spill it before the call in the scenario that the closure never gets executed! So, it
        // won't be dirty after
        //   the call site.
        Set<LocalVariable> newDirtyVars = new HashSet<LocalVariable>(dirtyVars);
        for (LocalVariable v : dirtyVars) {
          if (spillAllVars || cl.usesLocalVariable(v) || cl.definesLocalVariable(v)) {
            newDirtyVars.remove(v);
          }
        }
        dirtyVars = newDirtyVars;
      } else if (scopeBindingHasEscaped) { // Call has no closure && it requires stores
        dirtyVars.clear();
      } else {
        // All variables not local to the current scope have to be always spilled because of
        // multi-threading scenarios where some other scope could load this variable concurrently.
        //
        // Allocate a new hash-set and modify it to get around ConcurrentModificationException on
        // dirtyVars
        Set<LocalVariable> newDirtyVars = new HashSet<LocalVariable>(dirtyVars);
        for (LocalVariable v : dirtyVars) {
          if ((v instanceof ClosureLocalVariable)
              && ((ClosureLocalVariable) v).definingScope != scope) {
            newDirtyVars.remove(v);
          }
        }
        dirtyVars = newDirtyVars;
      }
    }

    if (scopeBindingHasEscaped && (i.getOperation() == Operation.PUT_GLOBAL_VAR)) {
      // global-var tracing can execute closures set up in previous trace-var calls
      // in which case we would have the 'scopeBindingHasEscaped' flag set to true
      dirtyVars.clear();
    }

    // If this instruction can raise an exception and we are going to be rescued,
    // spill all dirty vars before the instruction!
    if (i.canRaiseException() && hasExceptionsRescued()) {
      dirtyVars.clear();
    }

    if (i instanceof ResultInstr) {
      Variable v = ((ResultInstr) i).getResult();

      // %self is local to every scope and never crosses scope boundaries and need not be
      // spilled/refilled
      if (v instanceof LocalVariable && !v.isSelf()) dirtyVars.add((LocalVariable) v);
    }

    if (i.getOperation().isReturn()) dirtyVars.clear();
  }
  public boolean addStores(
      Map<Operand, Operand> varRenameMap, Set<LocalVariable> excTargetDirtyVars) {
    IRScope scope = problem.getScope();

    boolean addedStores = false;
    boolean isClosure = scope instanceof IRClosure;
    boolean scopeBindingHasEscaped = scope.bindingHasEscaped();

    ListIterator<Instr> instrs = basicBlock.getInstrs().listIterator();

    initSolution();

    // If this is the exit BB, we need a binding store on exit only for vars that are both:
    //
    //   (a) dirty,
    //   (b) live on exit from the closure
    //       condition reqd. because the variable could be dirty but not used outside.
    //         Ex: s=0; a.each { |i| j = i+1; sum += j; }; puts sum
    //       i,j are dirty inside the block, but not used outside

    if (basicBlock.isExitBB()) {
      LiveVariablesProblem lvp =
          (LiveVariablesProblem) scope.getDataFlowSolution(DataFlowConstants.LVP_NAME);
      java.util.Collection<LocalVariable> liveVars = lvp.getVarsLiveOnScopeExit();
      if (liveVars != null) {
        dirtyVars.retainAll(liveVars); // Intersection with variables live on exit from the scope
      } else {
        dirtyVars.clear();
      }
    }

    while (instrs.hasNext()) {
      Instr i = instrs.next();

      // Process closure accepting instrs specially -- these are the sites of binding stores!
      if (i instanceof ClosureAcceptingInstr) {
        Operand o = ((ClosureAcceptingInstr) i).getClosureArg();
        if (o != null && o instanceof WrappedIRClosure) {
          IRClosure cl = ((WrappedIRClosure) o).getClosure();

          // Add before call -- hence instrs.previous & instrs.next
          instrs.previous();

          // If the call is a dataflow barrier, we have to spill everything here
          boolean spillAllVars = scopeBindingHasEscaped;

          // Unless we have to spill everything, spill only those dirty variables that are:
          // - used in the closure (FIXME: Strictly only those vars that are live at the call site
          // -- but we dont have this info!)
          Set<LocalVariable> newDirtyVars = new HashSet<LocalVariable>(dirtyVars);
          for (LocalVariable v : dirtyVars) {
            // We have to spill the var that is defined in the closure as well because the load var
            // pass
            // will attempt to load the var always.  So, if the call doesn't actually call the
            // closure,
            // we'll be in trouble in that scenario!
            if (spillAllVars || cl.usesLocalVariable(v) || cl.definesLocalVariable(v)) {
              addedStores = true;
              instrs.add(
                  new StoreLocalVarInstr(
                      problem.getLocalVarReplacement(v, varRenameMap), scope, v));
              newDirtyVars.remove(v);
            }
          }
          dirtyVars = newDirtyVars;
          instrs.next();
        } else if (scopeBindingHasEscaped) { // Call has no closure && it requires stores
          // Add before call -- hence instrs.previous & instrs.next
          instrs.previous();
          for (LocalVariable v : dirtyVars) {
            addedStores = true;
            instrs.add(
                new StoreLocalVarInstr(problem.getLocalVarReplacement(v, varRenameMap), scope, v));
          }
          instrs.next();
          dirtyVars.clear();
        } else {
          instrs.previous();

          // All variables not local to the current scope have to be always spilled because of
          // multi-threading scenarios where some other scope could load this variable concurrently.
          //
          // Allocate a new hash-set and modify it to get around ConcurrentModificationException on
          // dirtyVars
          Set<LocalVariable> newDirtyVars = new HashSet<LocalVariable>(dirtyVars);
          for (LocalVariable v : dirtyVars) {
            // SSS FIXME: I guess we cannot use v.getScopeDepth() > 0 because the variable could be
            // a cloned
            // instance from a different depth and that could mislead us. See if there is a way to
            // fix this.
            // If we introduced 'definingScope' in all local variables, we could simply check for
            // scope match
            // without the instanceof check here.
            if ((v instanceof ClosureLocalVariable
                    && ((ClosureLocalVariable) v).definingScope != scope)
                || (!(v instanceof ClosureLocalVariable) && scope.getScopeType().isClosureType())) {
              addedStores = true;
              instrs.add(
                  new StoreLocalVarInstr(
                      problem.getLocalVarReplacement(v, varRenameMap), scope, v));
              newDirtyVars.remove(v);
            }
          }
          dirtyVars = newDirtyVars;
          instrs.next();
        }
      } else if ((isClosure && (i instanceof ReturnInstr)) || (i instanceof BreakInstr)) {
        // At closure return and break instructions (both of which are exits from the closure),
        // we need a binding store on exit only for vars that are both:
        //
        //   (a) dirty,
        //   (b) live on exit from the closure
        //       condition reqd. because the variable could be dirty but not used outside.
        //         Ex: s=0; a.each { |i| j = i+1; sum += j; return if j < 5; sum += 1; }; puts sum
        //       i,j are dirty inside the block, but not used outside
        //
        // If this also happens to be exit BB, we would have intersected already earlier -- so no
        // need to do it again!

        if (!basicBlock.isExitBB()) {
          LiveVariablesProblem lvp =
              (LiveVariablesProblem) scope.getDataFlowSolution(DataFlowConstants.LVP_NAME);
          if (lvp == null) {
            System.out.println("LVP missing for " + scope);
          }
          java.util.Collection<LocalVariable> liveVars = lvp.getVarsLiveOnScopeExit();
          if (liveVars != null) {
            dirtyVars.retainAll(
                liveVars); // Intersection with variables live on exit from the scope
          } else {
            dirtyVars.clear();
          }
        }

        // Add before call
        instrs.previous();
        boolean f = problem.addClosureExitStoreLocalVars(instrs, dirtyVars, varRenameMap);
        addedStores = addedStores || f;
        instrs.next();

        // Nothing is dirty anymore -- everything that needs spilling has been spilt
        dirtyVars.clear();
      }

      if (scopeBindingHasEscaped && (i.getOperation() == Operation.PUT_GLOBAL_VAR)) {
        // global-var tracing can execute closures set up in previous trace-var calls
        // in which case we would have the 'scopeBindingHasEscaped' flag set to true
        instrs.previous();
        for (LocalVariable v : dirtyVars) {
          addedStores = true;
          instrs.add(
              new StoreLocalVarInstr(problem.getLocalVarReplacement(v, varRenameMap), scope, v));
        }
        instrs.next();
        dirtyVars.clear();
      }

      if (i.canRaiseException()) {
        if (hasExceptionsRescued()) {
          // If exceptions will be rescued, spill every dirty var here
          // Add before excepting instr -- hence instrs.previous & instrs.next
          instrs.previous();
          for (LocalVariable v : dirtyVars) {
            addedStores = true;
            instrs.add(
                new StoreLocalVarInstr(problem.getLocalVarReplacement(v, varRenameMap), scope, v));
          }
          instrs.next();
          dirtyVars.clear();
        } else if (excTargetDirtyVars != null) {
          // If exceptions won't be rescued, pass them back to be spilled in the global ensure block
          excTargetDirtyVars.addAll(dirtyVars);
        }
      }

      if (i instanceof ResultInstr) {
        Variable v = ((ResultInstr) i).getResult();

        // %self is local to every scope and never crosses scope boundaries and need not be
        // spilled/refilled
        if (v instanceof LocalVariable && !v.isSelf()) {
          LocalVariable lv = (LocalVariable) v;
          dirtyVars.add(lv);

          // Make sure there is a replacement tmp-var allocated for lv
          problem.getLocalVarReplacement(lv, varRenameMap);
        }
      }
    }

    // If this is the exit BB, add binding stores for all vars that are still dirty
    if (basicBlock.isExitBB()) {
      // Last instr could be a return -- so, move iterator one position back
      if (instrs.hasPrevious()) instrs.previous();
      boolean f = problem.addClosureExitStoreLocalVars(instrs, dirtyVars, varRenameMap);
      addedStores = addedStores || f;
    }

    return addedStores;
  }