diff --git a/lib/CodeGen/PostRASchedulerList.cpp b/lib/CodeGen/PostRASchedulerList.cpp
index 42954ea..5fa598d 100644
--- a/lib/CodeGen/PostRASchedulerList.cpp
+++ b/lib/CodeGen/PostRASchedulerList.cpp
@@ -972,17 +972,17 @@
 /// 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 ff5c236..5a59862 100644
--- a/lib/CodeGen/ScheduleDAG.cpp
+++ b/lib/CodeGen/ScheduleDAG.cpp
@@ -82,13 +82,19 @@
   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 @@
       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 d1930b1..7eac4d8 100644
--- a/lib/CodeGen/SelectionDAG/ScheduleDAGFast.cpp
+++ b/lib/CodeGen/SelectionDAG/ScheduleDAGFast.cpp
@@ -134,17 +134,17 @@
 /// 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 628a2a87..f17fe23 100644
--- a/lib/CodeGen/SelectionDAG/ScheduleDAGList.cpp
+++ b/lib/CodeGen/SelectionDAG/ScheduleDAGList.cpp
@@ -108,17 +108,17 @@
 /// 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 a9d1878..bd6e048 100644
--- a/lib/CodeGen/SelectionDAG/ScheduleDAGRRList.cpp
+++ b/lib/CodeGen/SelectionDAG/ScheduleDAGRRList.cpp
@@ -278,6 +278,7 @@
       AvailableQueue->remove(PredSU);
   }
 
+  assert(PredSU->NumSuccsLeft < UINT_MAX && "NumSuccsLeft will overflow!");
   ++PredSU->NumSuccsLeft;
 }
 
@@ -824,17 +825,17 @@
 /// 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) {