switch the SUnit pred/succ sets from being std::sets to being smallvectors.

This reduces selectiondag time on kc++ from 5.43s to 4.98s (9%).  More
significantly, this speeds up the default ppc scheduler from ~1571ms to 1063ms,
a 33% speedup.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@29743 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/include/llvm/CodeGen/ScheduleDAG.h b/include/llvm/CodeGen/ScheduleDAG.h
index ed6ccd0a641431a7011f4d533ef04a765023974d..5d85d374338d79502db0b4bb28b7ec26072f898f 100644 (file)
--- a/include/llvm/CodeGen/ScheduleDAG.h
+++ b/include/llvm/CodeGen/ScheduleDAG.h
@@ -82,9 +82,16 @@ namespace llvm {
     
     // Preds/Succs - The SUnits before/after us in the graph.  The boolean value
     // is true if the edge is a token chain edge, false if it is a value edge. 
-    std::set<std::pair<SUnit*,bool> > Preds;  // All sunit predecessors.
-    std::set<std::pair<SUnit*,bool> > Succs;  // All sunit successors.
+    SmallVector<std::pair<SUnit*,bool>, 4> Preds;  // All sunit predecessors.
+    SmallVector<std::pair<SUnit*,bool>, 4> Succs;  // All sunit successors.
 
+    typedef SmallVector<std::pair<SUnit*,bool>, 4>::iterator pred_iterator;
+    typedef SmallVector<std::pair<SUnit*,bool>, 4>::iterator succ_iterator;
+    typedef SmallVector<std::pair<SUnit*,bool>, 4>::const_iterator 
+      const_pred_iterator;
+    typedef SmallVector<std::pair<SUnit*,bool>, 4>::const_iterator 
+      const_succ_iterator;
+    
     short NumPreds;                     // # of preds.
     short NumSuccs;                     // # of sucss.
     short NumPredsLeft;                 // # of preds not scheduled.
@@ -111,6 +118,26 @@ namespace llvm {
         Latency(0), CycleBound(0), Cycle(0), Depth(0), Height(0),
         NodeNum(nodenum) {}
     
+    /// addPred - This adds the specified node as a pred of the current node if
+    /// not already.  This returns true if this is a new pred.
+    bool addPred(SUnit *N, bool isChain) {
+      for (unsigned i = 0, e = Preds.size(); i != e; ++i)
+        if (Preds[i].first == N && Preds[i].second == isChain)
+          return false;
+      Preds.push_back(std::make_pair(N, isChain));
+      return true;
+    }
+
+    /// addSucc - This adds the specified node as a succ of the current node if
+    /// not already.  This returns true if this is a new succ.
+    bool addSucc(SUnit *N, bool isChain) {
+      for (unsigned i = 0, e = Succs.size(); i != e; ++i)
+        if (Succs[i].first == N && Succs[i].second == isChain)
+          return false;
+      Succs.push_back(std::make_pair(N, isChain));
+      return true;
+    }
+    
     void dump(const SelectionDAG *G) const;
     void dumpAll(const SelectionDAG *G) const;
   };
@@ -127,7 +154,7 @@ namespace llvm {
   public:
     virtual ~SchedulingPriorityQueue() {}
   
-    virtual void initNodes(const std::vector<SUnit> &SUnits) = 0;
+    virtual void initNodes(std::vector<SUnit> &SUnits) = 0;
     virtual void releaseState() = 0;
   
     virtual bool empty() const = 0;

diff --git a/lib/CodeGen/SelectionDAG/ScheduleDAG.cpp b/lib/CodeGen/SelectionDAG/ScheduleDAG.cpp
index 2d2c34340b1cd85cdd5b727de3b2554b636913a3..d33e1ecef7ea8a33ac4abb7d06e8c3827d43773f 100644 (file)
--- a/lib/CodeGen/SelectionDAG/ScheduleDAG.cpp
+++ b/lib/CodeGen/SelectionDAG/ScheduleDAG.cpp
@@ -84,7 +84,7 @@ void ScheduleDAG::BuildSchedUnits() {
           N = *UI;
           break;
         }
-          if (!HasFlagUse) break;
+      if (!HasFlagUse) break;
     }
     
     // Now all flagged nodes are in FlaggedNodes and N is the bottom-most node.
@@ -150,7 +150,7 @@ void ScheduleDAG::BuildSchedUnits() {
         assert(OpVT != MVT::Flag && "Flagged nodes should be in same sunit!");
         bool isChain = OpVT == MVT::Other;
         
-        if (SU->Preds.insert(std::make_pair(OpSU, isChain)).second) {
+        if (SU->addPred(OpSU, isChain)) {
           if (!isChain) {
             SU->NumPreds++;
             SU->NumPredsLeft++;
@@ -158,7 +158,7 @@ void ScheduleDAG::BuildSchedUnits() {
             SU->NumChainPredsLeft++;
           }
         }
-        if (OpSU->Succs.insert(std::make_pair(SU, isChain)).second) {
+        if (OpSU->addSucc(SU, isChain)) {
           if (!isChain) {
             OpSU->NumSuccs++;
             OpSU->NumSuccsLeft++;
@@ -176,35 +176,35 @@ void ScheduleDAG::BuildSchedUnits() {
   return;
 }
 
-static void CalculateDepths(SUnit *SU, unsigned Depth) {
-  if (SU->Depth == 0 || Depth > SU->Depth) {
-    SU->Depth = Depth;
-    for (std::set<std::pair<SUnit*, bool> >::iterator I = SU->Succs.begin(),
-           E = SU->Succs.end(); I != E; ++I)
-      CalculateDepths(I->first, Depth+1);
+static void CalculateDepths(SUnit &SU, unsigned Depth) {
+  if (SU.Depth == 0 || Depth > SU.Depth) {
+    SU.Depth = Depth;
+    for (SUnit::succ_iterator I = SU.Succs.begin(), E = SU.Succs.end();
+         I != E; ++I)
+      CalculateDepths(*I->first, Depth+1);
   }
 }
 
 void ScheduleDAG::CalculateDepths() {
   SUnit *Entry = SUnitMap[DAG.getEntryNode().Val];
-  ::CalculateDepths(Entry, 0U);
+  ::CalculateDepths(*Entry, 0U);
   for (unsigned i = 0, e = SUnits.size(); i != e; ++i)
     if (SUnits[i].Preds.size() == 0 && &SUnits[i] != Entry) {
-      ::CalculateDepths(&SUnits[i], 0U);
+      ::CalculateDepths(SUnits[i], 0U);
     }
 }
 
-static void CalculateHeights(SUnit *SU, unsigned Height) {
-  if (SU->Height == 0 || Height > SU->Height) {
-    SU->Height = Height;
-    for (std::set<std::pair<SUnit*, bool> >::iterator I = SU->Preds.begin(),
-           E = SU->Preds.end(); I != E; ++I)
-      CalculateHeights(I->first, Height+1);
+static void CalculateHeights(SUnit &SU, unsigned Height) {
+  if (SU.Height == 0 || Height > SU.Height) {
+    SU.Height = Height;
+    for (SUnit::pred_iterator I = SU.Preds.begin(), E = SU.Preds.end();
+         I != E; ++I)
+      CalculateHeights(*I->first, Height+1);
   }
 }
 void ScheduleDAG::CalculateHeights() {
   SUnit *Root = SUnitMap[DAG.getRoot().Val];
-  ::CalculateHeights(Root, 0U);
+  ::CalculateHeights(*Root, 0U);
 }
 
 /// CountResults - The results of target nodes have register or immediate
@@ -646,24 +646,24 @@ void SUnit::dumpAll(const SelectionDAG *G) const {
 
   if (Preds.size() != 0) {
     std::cerr << "  Predecessors:\n";
-    for (std::set<std::pair<SUnit*,bool> >::const_iterator I = Preds.begin(),
-           E = Preds.end(); I != E; ++I) {
+    for (SUnit::const_succ_iterator I = Preds.begin(), E = Preds.end();
+         I != E; ++I) {
       if (I->second)
-        std::cerr << "   ch  ";
+        std::cerr << "   ch  #";
       else
-        std::cerr << "   val ";
-      I->first->dump(G);
+        std::cerr << "   val #";
+      std::cerr << I->first << "\n";
     }
   }
   if (Succs.size() != 0) {
     std::cerr << "  Successors:\n";
-    for (std::set<std::pair<SUnit*, bool> >::const_iterator I = Succs.begin(),
-           E = Succs.end(); I != E; ++I) {
+    for (SUnit::const_succ_iterator I = Succs.begin(), E = Succs.end();
+         I != E; ++I) {
       if (I->second)
-        std::cerr << "   ch  ";
+        std::cerr << "   ch  #";
       else
-        std::cerr << "   val ";
-      I->first->dump(G);
+        std::cerr << "   val #";
+      std::cerr << I->first << "\n";
     }
   }
   std::cerr << "\n";

diff --git a/lib/CodeGen/SelectionDAG/ScheduleDAGList.cpp b/lib/CodeGen/SelectionDAG/ScheduleDAGList.cpp
index aa62bd49fce25be22e76ee53c697c68946d99905..15f04cd8b1c5d56866d33f3dcc2ec324a3977d53 100644 (file)
--- a/lib/CodeGen/SelectionDAG/ScheduleDAGList.cpp
+++ b/lib/CodeGen/SelectionDAG/ScheduleDAGList.cpp
@@ -132,15 +132,16 @@ void ScheduleDAGList::ReleaseSucc(SUnit *SuccSU, bool isChain) {
     // available.  This is the max of the start time of all predecessors plus
     // their latencies.
     unsigned AvailableCycle = 0;
-    for (std::set<std::pair<SUnit*, bool> >::iterator I = SuccSU->Preds.begin(),
+    for (SUnit::pred_iterator I = SuccSU->Preds.begin(),
          E = SuccSU->Preds.end(); I != E; ++I) {
       // If this is a token edge, we don't need to wait for the latency of the
       // preceeding instruction (e.g. a long-latency load) unless there is also
       // some other data dependence.
-      unsigned PredDoneCycle = I->first->Cycle;
+      SUnit &Pred = *I->first;
+      unsigned PredDoneCycle = Pred.Cycle;
       if (!I->second)
-        PredDoneCycle += I->first->Latency;
-      else if (I->first->Latency)
+        PredDoneCycle += Pred.Latency;
+      else if (Pred.Latency)
         PredDoneCycle += 1;
 
       AvailableCycle = std::max(AvailableCycle, PredDoneCycle);
@@ -161,8 +162,8 @@ void ScheduleDAGList::ScheduleNodeTopDown(SUnit *SU, unsigned CurCycle) {
   SU->Cycle = CurCycle;
   
   // Bottom up: release successors.
-  for (std::set<std::pair<SUnit*, bool> >::iterator I = SU->Succs.begin(),
-       E = SU->Succs.end(); I != E; ++I)
+  for (SUnit::succ_iterator I = SU->Succs.begin(), E = SU->Succs.end();
+       I != E; ++I)
     ReleaseSucc(I->first, I->second);
 }
 
@@ -313,7 +314,7 @@ namespace {
 namespace {
   class LatencyPriorityQueue : public SchedulingPriorityQueue {
     // SUnits - The SUnits for the current graph.
-    const std::vector<SUnit> *SUnits;
+    std::vector<SUnit> *SUnits;
     
     // Latencies - The latency (max of latency from this node to the bb exit)
     // for each node.
@@ -330,7 +331,7 @@ public:
     LatencyPriorityQueue() : Queue(latency_sort(this)) {
     }
     
-    void initNodes(const std::vector<SUnit> &sunits) {
+    void initNodes(std::vector<SUnit> &sunits) {
       SUnits = &sunits;
       // Calculate node priorities.
       CalculatePriorities();
@@ -379,6 +380,7 @@ private:
     void CalculatePriorities();
     int CalcLatency(const SUnit &SU);
     void AdjustPriorityOfUnscheduledPreds(SUnit *SU);
+    SUnit *getSingleUnscheduledPred(SUnit *SU);
 
     /// RemoveFromPriorityQueue - This is a really inefficient way to remove a
     /// node from a priority queue.  We should roll our own heap to make this
@@ -434,8 +436,8 @@ int LatencyPriorityQueue::CalcLatency(const SUnit &SU) {
     return Latency;
   
   int MaxSuccLatency = 0;
-  for (std::set<std::pair<SUnit*, bool> >::const_iterator I = SU.Succs.begin(),
-       E = SU.Succs.end(); I != E; ++I)
+  for (SUnit::const_succ_iterator I = SU.Succs.begin(), E = SU.Succs.end();
+       I != E; ++I)
     MaxSuccLatency = std::max(MaxSuccLatency, CalcLatency(*I->first));
 
   return Latency = MaxSuccLatency + SU.Latency;
@@ -452,17 +454,19 @@ void LatencyPriorityQueue::CalculatePriorities() {
 
 /// getSingleUnscheduledPred - If there is exactly one unscheduled predecessor
 /// of SU, return it, otherwise return null.
-static SUnit *getSingleUnscheduledPred(SUnit *SU) {
+SUnit *LatencyPriorityQueue::getSingleUnscheduledPred(SUnit *SU) {
   SUnit *OnlyAvailablePred = 0;
-  for (std::set<std::pair<SUnit*, bool> >::const_iterator I = SU->Preds.begin(),
-       E = SU->Preds.end(); I != E; ++I)
-    if (!I->first->isScheduled) {
+  for (SUnit::const_pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
+       I != E; ++I) {
+    SUnit &Pred = *I->first;
+    if (!Pred.isScheduled) {
       // We found an available, but not scheduled, predecessor.  If it's the
       // only one we have found, keep track of it... otherwise give up.
-      if (OnlyAvailablePred && OnlyAvailablePred != I->first)
+      if (OnlyAvailablePred && OnlyAvailablePred != &Pred)
         return 0;
-      OnlyAvailablePred = I->first;
+      OnlyAvailablePred = &Pred;
     }
+  }
       
   return OnlyAvailablePred;
 }
@@ -471,8 +475,8 @@ void LatencyPriorityQueue::push_impl(SUnit *SU) {
   // Look at all of the successors of this node.  Count the number of nodes that
   // this node is the sole unscheduled node for.
   unsigned NumNodesBlocking = 0;
-  for (std::set<std::pair<SUnit*, bool> >::const_iterator I = SU->Succs.begin(),
-       E = SU->Succs.end(); I != E; ++I)
+  for (SUnit::const_succ_iterator I = SU->Succs.begin(), E = SU->Succs.end();
+       I != E; ++I)
     if (getSingleUnscheduledPred(I->first) == SU)
       ++NumNodesBlocking;
   NumNodesSolelyBlocking[SU->NodeNum] = NumNodesBlocking;
@@ -486,8 +490,8 @@ void LatencyPriorityQueue::push_impl(SUnit *SU) {
 // single predecessor has a higher priority, since scheduling it will make
 // the node available.
 void LatencyPriorityQueue::ScheduledNode(SUnit *SU) {
-  for (std::set<std::pair<SUnit*, bool> >::const_iterator I = SU->Succs.begin(),
-       E = SU->Succs.end(); I != E; ++I)
+  for (SUnit::const_succ_iterator I = SU->Succs.begin(), E = SU->Succs.end();
+       I != E; ++I)
     AdjustPriorityOfUnscheduledPreds(I->first);
 }
 

diff --git a/lib/CodeGen/SelectionDAG/ScheduleDAGRRList.cpp b/lib/CodeGen/SelectionDAG/ScheduleDAGRRList.cpp
index 5d7fa5fad16b739e7947a37eb0318413160f24da..f247f7ce765731319f5e98e426822216cd667abb 100644 (file)
--- a/lib/CodeGen/SelectionDAG/ScheduleDAGRRList.cpp
+++ b/lib/CodeGen/SelectionDAG/ScheduleDAGRRList.cpp
@@ -93,7 +93,7 @@ void ScheduleDAGRRList::Schedule() {
   CalculateDepths();
   CalculateHeights();
   DEBUG(for (unsigned su = 0, e = SUnits.size(); su != e; ++su)
-        SUnits[su].dumpAll(&DAG));
+          SUnits[su].dumpAll(&DAG));
 
   AvailableQueue->initNodes(SUnits);
 
@@ -143,8 +143,8 @@ void ScheduleDAGRRList::CommuteNodesToReducePressure() {
       }
     }
 
-    for (std::set<std::pair<SUnit*, bool> >::iterator I = SU->Preds.begin(),
-           E = SU->Preds.end(); I != E; ++I) {
+    for (SUnit::pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
+         I != E; ++I) {
       if (!I->second)
         OperandSeen.insert(I->first);
     }
@@ -235,8 +235,8 @@ void ScheduleDAGRRList::ScheduleNodeBottomUp(SUnit *SU, unsigned CurCycle) {
   Sequence.push_back(SU);
 
   // Bottom up: release predecessors
-  for (std::set<std::pair<SUnit*, bool> >::iterator I = SU->Preds.begin(),
-         E = SU->Preds.end(); I != E; ++I)
+  for (SUnit::pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
+       I != E; ++I)
     ReleasePred(I->first, I->second, CurCycle);
   SU->isScheduled = true;
 }
@@ -347,8 +347,8 @@ void ScheduleDAGRRList::ScheduleNodeTopDown(SUnit *SU, unsigned CurCycle) {
   Sequence.push_back(SU);
 
   // Top down: release successors
-  for (std::set<std::pair<SUnit*, bool> >::iterator I = SU->Succs.begin(),
-         E = SU->Succs.end(); I != E; ++I)
+  for (SUnit::succ_iterator I = SU->Succs.begin(), E = SU->Succs.end();
+       I != E; ++I)
     ReleaseSucc(I->first, I->second, CurCycle);
   SU->isScheduled = true;
 }
@@ -448,7 +448,7 @@ namespace {
     RegReductionPriorityQueue() :
     Queue(SF(this)) {}
     
-    virtual void initNodes(const std::vector<SUnit> &sunits) {}
+    virtual void initNodes(std::vector<SUnit> &sunits) {}
     virtual void releaseState() {}
     
     virtual int getSethiUllmanNumber(unsigned NodeNum) const {
@@ -485,7 +485,7 @@ namespace {
   public:
     BURegReductionPriorityQueue() {}
 
-    void initNodes(const std::vector<SUnit> &sunits) {
+    void initNodes(std::vector<SUnit> &sunits) {
       SUnits = &sunits;
       // Add pseudo dependency edges for two-address nodes.
       AddPseudoTwoAddrDeps();
@@ -521,7 +521,7 @@ namespace {
   public:
     TDRegReductionPriorityQueue() {}
 
-    void initNodes(const std::vector<SUnit> &sunits) {
+    void initNodes(std::vector<SUnit> &sunits) {
       SUnits = &sunits;
       // Calculate node priorities.
       CalculatePriorities();
@@ -548,8 +548,8 @@ static bool isFloater(const SUnit *SU) {
     if (SU->NumPreds == 0)
       return true;
     if (SU->NumPreds == 1) {
-      for (std::set<std::pair<SUnit*, bool> >::iterator I = SU->Preds.begin(),
-             E = SU->Preds.end(); I != E; ++I) {
+      for (SUnit::const_pred_iterator I = SU->Preds.begin(),E = SU->Preds.end();
+           I != E; ++I) {
         if (I->second) continue;
 
         SUnit *PredSU = I->first;
@@ -566,8 +566,8 @@ static bool isFloater(const SUnit *SU) {
 
 static bool isSimpleFloaterUse(const SUnit *SU) {
   unsigned NumOps = 0;
-  for (std::set<std::pair<SUnit*, bool> >::iterator I = SU->Preds.begin(),
-         E = SU->Preds.end(); I != E; ++I) {
+  for (SUnit::const_pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
+       I != E; ++I) {
     if (I->second) continue;
     if (++NumOps > 1)
       return false;
@@ -641,8 +641,8 @@ static void isReachable(SUnit *SU, SUnit *TargetSU,
   }
   if (!Visited.insert(SU).second) return;
 
-  for (std::set<std::pair<SUnit*, bool> >::iterator I = SU->Preds.begin(),
-         E = SU->Preds.end(); I != E; ++I)
+  for (SUnit::pred_iterator I = SU->Preds.begin(), E = SU->Preds.end(); I != E;
+       ++I)
     isReachable(I->first, TargetSU, Visited, Reached);
 }
 
@@ -655,8 +655,8 @@ static bool isReachable(SUnit *SU, SUnit *TargetSU) {
 
 static SUnit *getDefUsePredecessor(SUnit *SU) {
   SDNode *DU = SU->Node->getOperand(0).Val;
-  for (std::set<std::pair<SUnit*, bool> >::iterator
-         I = SU->Preds.begin(), E = SU->Preds.end(); I != E; ++I) {
+  for (SUnit::pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
+       I != E; ++I) {
     if (I->second) continue;  // ignore chain preds
     SUnit *PredSU = I->first;
     if (PredSU->Node == DU)
@@ -689,8 +689,8 @@ void BURegReductionPriorityQueue<SF>::AddPseudoTwoAddrDeps() {
       SUnit *DUSU = getDefUsePredecessor(SU);
       if (!DUSU) continue;
 
-      for (std::set<std::pair<SUnit*, bool> >::iterator I = DUSU->Succs.begin(),
-             E = DUSU->Succs.end(); I != E; ++I) {
+      for (SUnit::succ_iterator I = DUSU->Succs.begin(), E = DUSU->Succs.end();
+           I != E; ++I) {
         if (I->second) continue;
         SUnit *SuccSU = I->first;
         if (SuccSU != SU &&
@@ -699,9 +699,9 @@ void BURegReductionPriorityQueue<SF>::AddPseudoTwoAddrDeps() {
           if (SuccSU->Depth == SU->Depth && !isReachable(SuccSU, SU)) {
             DEBUG(std::cerr << "Adding an edge from SU # " << SU->NodeNum
                   << " to SU #" << SuccSU->NodeNum << "\n");
-            if (SU->Preds.insert(std::make_pair(SuccSU, true)).second)
+            if (SU->addPred(SuccSU, true))
               SU->NumChainPredsLeft++;
-            if (SuccSU->Succs.insert(std::make_pair(SU, true)).second)
+            if (SuccSU->addSucc(SU, true))
               SuccSU->NumChainSuccsLeft++;
           }
         }
@@ -734,8 +734,8 @@ int BURegReductionPriorityQueue<SF>::CalcNodePriority(const SUnit *SU) {
     SethiUllmanNumber = INT_MAX - 10;
   else {
     int Extra = 0;
-    for (std::set<std::pair<SUnit*, bool> >::const_iterator
-         I = SU->Preds.begin(), E = SU->Preds.end(); I != E; ++I) {
+    for (SUnit::const_pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
+         I != E; ++I) {
       if (I->second) continue;  // ignore chain preds
       SUnit *PredSU = I->first;
       int PredSethiUllman = CalcNodePriority(PredSU);
@@ -763,11 +763,11 @@ void BURegReductionPriorityQueue<SF>::CalculatePriorities() {
 
 static unsigned SumOfUnscheduledPredsOfSuccs(const SUnit *SU) {
   unsigned Sum = 0;
-  for (std::set<std::pair<SUnit*, bool> >::const_iterator
-         I = SU->Succs.begin(), E = SU->Succs.end(); I != E; ++I) {
+  for (SUnit::const_succ_iterator I = SU->Succs.begin(), E = SU->Succs.end();
+       I != E; ++I) {
     SUnit *SuccSU = I->first;
-    for (std::set<std::pair<SUnit*, bool> >::const_iterator
-         II = SuccSU->Preds.begin(), EE = SuccSU->Preds.end(); II != EE; ++II) {
+    for (SUnit::const_pred_iterator II = SuccSU->Preds.begin(),
+         EE = SuccSU->Preds.end(); II != EE; ++II) {
       SUnit *PredSU = II->first;
       if (!PredSU->isScheduled)
         Sum++;
@@ -855,8 +855,8 @@ int TDRegReductionPriorityQueue<SF>::CalcNodePriority(const SUnit *SU) {
     SethiUllmanNumber = 1;
   else {
     int Extra = 0;
-    for (std::set<std::pair<SUnit*, bool> >::const_iterator
-         I = SU->Preds.begin(), E = SU->Preds.end(); I != E; ++I) {
+    for (SUnit::const_pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
+         I != E; ++I) {
       if (I->second) continue;  // ignore chain preds
       SUnit *PredSU = I->first;
       int PredSethiUllman = CalcNodePriority(PredSU);