diff --git a/include/llvm/CodeGen/ScheduleDAG.h b/include/llvm/CodeGen/ScheduleDAG.h
index c5e12a6019d..2de095b8857 100644
--- a/include/llvm/CodeGen/ScheduleDAG.h
+++ b/include/llvm/CodeGen/ScheduleDAG.h
@@ -243,10 +243,10 @@ namespace llvm {
     unsigned NodeNum;                   // Entry # of node in the node vector.
     unsigned NodeQueueId;               // Queue id of node.
     unsigned short Latency;             // Node latency.
-    short NumPreds;                     // # of SDep::Data preds.
-    short NumSuccs;                     // # of SDep::Data sucss.
-    short NumPredsLeft;                 // # of preds not scheduled.
-    short NumSuccsLeft;                 // # of succs not scheduled.
+    unsigned NumPreds;                  // # of SDep::Data preds.
+    unsigned NumSuccs;                  // # of SDep::Data sucss.
+    unsigned NumPredsLeft;              // # of preds not scheduled.
+    unsigned NumSuccsLeft;              // # of succs not scheduled.
     bool isTwoAddress     : 1;          // Is a two-address instruction.
     bool isCommutable     : 1;          // Is a commutable instruction.
     bool hasPhysRegDefs   : 1;          // Has physreg defs that are being used.
diff --git a/lib/CodeGen/PostRASchedulerList.cpp b/lib/CodeGen/PostRASchedulerList.cpp
index 42954eac4f6..5fa598d95b7 100644
--- a/lib/CodeGen/PostRASchedulerList.cpp
+++ b/lib/CodeGen/PostRASchedulerList.cpp
@@ -972,17 +972,17 @@ void SchedulePostRATDList::FixupKills(MachineBasicBlock *MBB) {
 /// the PendingQueue if the count reaches zero. Also update its cycle bound.
 void SchedulePostRATDList::ReleaseSucc(SUnit *SU, SDep *SuccEdge) {
   SUnit *SuccSU = SuccEdge->getSUnit();
-  --SuccSU->NumPredsLeft;
-  
+
 #ifndef NDEBUG
-  if (SuccSU->NumPredsLeft < 0) {
+  if (SuccSU->NumPredsLeft == 0) {
     errs() << "*** Scheduling failed! ***\n";
     SuccSU->dump(this);
     errs() << " has been released too many times!\n";
     llvm_unreachable(0);
   }
 #endif
-  
+  --SuccSU->NumPredsLeft;
+
   // Compute how many cycles it will be before this actually becomes
   // available.  This is the max of the start time of all predecessors plus
   // their latencies.
diff --git a/lib/CodeGen/ScheduleDAG.cpp b/lib/CodeGen/ScheduleDAG.cpp
index ff5c236e379..5a59862090b 100644
--- a/lib/CodeGen/ScheduleDAG.cpp
+++ b/lib/CodeGen/ScheduleDAG.cpp
@@ -82,13 +82,19 @@ void SUnit::addPred(const SDep &D) {
   SUnit *N = D.getSUnit();
   // Update the bookkeeping.
   if (D.getKind() == SDep::Data) {
+    assert(NumPreds < UINT_MAX && "NumPreds will overflow!");
+    assert(N->NumSuccs < UINT_MAX && "NumSuccs will overflow!");
     ++NumPreds;
     ++N->NumSuccs;
   }
-  if (!N->isScheduled)
+  if (!N->isScheduled) {
+    assert(NumPredsLeft < UINT_MAX && "NumPredsLeft will overflow!");
     ++NumPredsLeft;
-  if (!isScheduled)
+  }
+  if (!isScheduled) {
+    assert(N->NumSuccsLeft < UINT_MAX && "NumSuccsLeft will overflow!");
     ++N->NumSuccsLeft;
+  }
   Preds.push_back(D);
   N->Succs.push_back(P);
   if (P.getLatency() != 0) {
@@ -121,13 +127,19 @@ void SUnit::removePred(const SDep &D) {
       Preds.erase(I);
       // Update the bookkeeping.
       if (P.getKind() == SDep::Data) {
+        assert(NumPreds > 0 && "NumPreds will underflow!");
+        assert(N->NumSuccs > 0 && "NumSuccs will underflow!");
         --NumPreds;
         --N->NumSuccs;
       }
-      if (!N->isScheduled)
+      if (!N->isScheduled) {
+        assert(NumPredsLeft > 0 && "NumPredsLeft will underflow!");
         --NumPredsLeft;
-      if (!isScheduled)
+      }
+      if (!isScheduled) {
+        assert(N->NumSuccsLeft > 0 && "NumSuccsLeft will underflow!");
         --N->NumSuccsLeft;
+      }
       if (P.getLatency() != 0) {
         this->setDepthDirty();
         N->setHeightDirty();
diff --git a/lib/CodeGen/SelectionDAG/ScheduleDAGFast.cpp b/lib/CodeGen/SelectionDAG/ScheduleDAGFast.cpp
index d1930b1a2c7..7eac4d81bb8 100644
--- a/lib/CodeGen/SelectionDAG/ScheduleDAGFast.cpp
+++ b/lib/CodeGen/SelectionDAG/ScheduleDAGFast.cpp
@@ -134,17 +134,17 @@ void ScheduleDAGFast::Schedule() {
 /// the AvailableQueue if the count reaches zero. Also update its cycle bound.
 void ScheduleDAGFast::ReleasePred(SUnit *SU, SDep *PredEdge) {
   SUnit *PredSU = PredEdge->getSUnit();
-  --PredSU->NumSuccsLeft;
-  
+
 #ifndef NDEBUG
-  if (PredSU->NumSuccsLeft < 0) {
+  if (PredSU->NumSuccsLeft == 0) {
     errs() << "*** Scheduling failed! ***\n";
     PredSU->dump(this);
     errs() << " has been released too many times!\n";
     llvm_unreachable(0);
   }
 #endif
-  
+  --PredSU->NumSuccsLeft;
+
   // If all the node's successors are scheduled, this node is ready
   // to be scheduled. Ignore the special EntrySU node.
   if (PredSU->NumSuccsLeft == 0 && PredSU != &EntrySU) {
diff --git a/lib/CodeGen/SelectionDAG/ScheduleDAGList.cpp b/lib/CodeGen/SelectionDAG/ScheduleDAGList.cpp
index 628a2a87ee6..f17fe23fc75 100644
--- a/lib/CodeGen/SelectionDAG/ScheduleDAGList.cpp
+++ b/lib/CodeGen/SelectionDAG/ScheduleDAGList.cpp
@@ -108,17 +108,17 @@ void ScheduleDAGList::Schedule() {
 /// the PendingQueue if the count reaches zero. Also update its cycle bound.
 void ScheduleDAGList::ReleaseSucc(SUnit *SU, const SDep &D) {
   SUnit *SuccSU = D.getSUnit();
-  --SuccSU->NumPredsLeft;
-  
+
 #ifndef NDEBUG
-  if (SuccSU->NumPredsLeft < 0) {
+  if (SuccSU->NumPredsLeft == 0) {
     errs() << "*** Scheduling failed! ***\n";
     SuccSU->dump(this);
     errs() << " has been released too many times!\n";
     llvm_unreachable(0);
   }
 #endif
-  
+  --SuccSU->NumPredsLeft;
+
   SuccSU->setDepthToAtLeast(SU->getDepth() + D.getLatency());
   
   // If all the node's predecessors are scheduled, this node is ready
diff --git a/lib/CodeGen/SelectionDAG/ScheduleDAGRRList.cpp b/lib/CodeGen/SelectionDAG/ScheduleDAGRRList.cpp
index a9d18784608..bd6e04805f1 100644
--- a/lib/CodeGen/SelectionDAG/ScheduleDAGRRList.cpp
+++ b/lib/CodeGen/SelectionDAG/ScheduleDAGRRList.cpp
@@ -278,6 +278,7 @@ void ScheduleDAGRRList::CapturePred(SDep *PredEdge) {
       AvailableQueue->remove(PredSU);
   }
 
+  assert(PredSU->NumSuccsLeft < UINT_MAX && "NumSuccsLeft will overflow!");
   ++PredSU->NumSuccsLeft;
 }
 
@@ -824,17 +825,17 @@ void ScheduleDAGRRList::ListScheduleBottomUp() {
 /// the AvailableQueue if the count reaches zero. Also update its cycle bound.
 void ScheduleDAGRRList::ReleaseSucc(SUnit *SU, const SDep *SuccEdge) {
   SUnit *SuccSU = SuccEdge->getSUnit();
-  --SuccSU->NumPredsLeft;
-  
+
 #ifndef NDEBUG
-  if (SuccSU->NumPredsLeft < 0) {
+  if (SuccSU->NumPredsLeft == 0) {
     errs() << "*** Scheduling failed! ***\n";
     SuccSU->dump(this);
     errs() << " has been released too many times!\n";
     llvm_unreachable(0);
   }
 #endif
-  
+  --SuccSU->NumPredsLeft;
+
   // If all the node's predecessors are scheduled, this node is ready
   // to be scheduled. Ignore the special ExitSU node.
   if (SuccSU->NumPredsLeft == 0 && SuccSU != &ExitSU) {