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diff --git a/lib/CodeGen/LatencyPriorityQueue.cpp b/lib/CodeGen/LatencyPriorityQueue.cpp
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+//===---- LatencyPriorityQueue.cpp - A latency-oriented priority queue ----===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements the LatencyPriorityQueue class, which is a
+// SchedulingPriorityQueue that schedules using latency information to
+// reduce the length of the critical path through the basic block.
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "scheduler"
+#include "llvm/CodeGen/LatencyPriorityQueue.h"
+#include "llvm/Support/Debug.h"
+using namespace llvm;
+
+bool latency_sort::operator()(const SUnit *LHS, const SUnit *RHS) const {
+  // The isScheduleHigh flag allows nodes with wraparound dependencies that
+  // cannot easily be modeled as edges with latencies to be scheduled as
+  // soon as possible in a top-down schedule.
+  if (LHS->isScheduleHigh && !RHS->isScheduleHigh)
+    return false;
+  if (!LHS->isScheduleHigh && RHS->isScheduleHigh)
+    return true;
+
+  unsigned LHSNum = LHS->NodeNum;
+  unsigned RHSNum = RHS->NodeNum;
+
+  // The most important heuristic is scheduling the critical path.
+  unsigned LHSLatency = PQ->getLatency(LHSNum);
+  unsigned RHSLatency = PQ->getLatency(RHSNum);
+  if (LHSLatency < RHSLatency) return true;
+  if (LHSLatency > RHSLatency) return false;
+  
+  // After that, if two nodes have identical latencies, look to see if one will
+  // unblock more other nodes than the other.
+  unsigned LHSBlocked = PQ->getNumSolelyBlockNodes(LHSNum);
+  unsigned RHSBlocked = PQ->getNumSolelyBlockNodes(RHSNum);
+  if (LHSBlocked < RHSBlocked) return true;
+  if (LHSBlocked > RHSBlocked) return false;
+  
+  // Finally, just to provide a stable ordering, use the node number as a
+  // deciding factor.
+  return LHSNum < RHSNum;
+}
+
+
+/// getSingleUnscheduledPred - If there is exactly one unscheduled predecessor
+/// of SU, return it, otherwise return null.
+SUnit *LatencyPriorityQueue::getSingleUnscheduledPred(SUnit *SU) {
+  SUnit *OnlyAvailablePred = 0;
+  for (SUnit::const_pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
+       I != E; ++I) {
+    SUnit &Pred = *I->getSUnit();
+    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 != &Pred)
+        return 0;
+      OnlyAvailablePred = &Pred;
+    }
+  }
+      
+  return OnlyAvailablePred;
+}
+
+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 (SUnit::const_succ_iterator I = SU->Succs.begin(), E = SU->Succs.end();
+       I != E; ++I)
+    if (getSingleUnscheduledPred(I->getSUnit()) == SU)
+      ++NumNodesBlocking;
+  NumNodesSolelyBlocking[SU->NodeNum] = NumNodesBlocking;
+  
+  Queue.push(SU);
+}
+
+
+// ScheduledNode - As nodes are scheduled, we look to see if there are any
+// successor nodes that have a single unscheduled predecessor.  If so, that
+// single predecessor has a higher priority, since scheduling it will make
+// the node available.
+void LatencyPriorityQueue::ScheduledNode(SUnit *SU) {
+  for (SUnit::const_succ_iterator I = SU->Succs.begin(), E = SU->Succs.end();
+       I != E; ++I)
+    AdjustPriorityOfUnscheduledPreds(I->getSUnit());
+}
+
+/// AdjustPriorityOfUnscheduledPreds - One of the predecessors of SU was just
+/// scheduled.  If SU is not itself available, then there is at least one
+/// predecessor node that has not been scheduled yet.  If SU has exactly ONE
+/// unscheduled predecessor, we want to increase its priority: it getting
+/// scheduled will make this node available, so it is better than some other
+/// node of the same priority that will not make a node available.
+void LatencyPriorityQueue::AdjustPriorityOfUnscheduledPreds(SUnit *SU) {
+  if (SU->isAvailable) return;  // All preds scheduled.
+  
+  SUnit *OnlyAvailablePred = getSingleUnscheduledPred(SU);
+  if (OnlyAvailablePred == 0 || !OnlyAvailablePred->isAvailable) return;
+  
+  // Okay, we found a single predecessor that is available, but not scheduled.
+  // Since it is available, it must be in the priority queue.  First remove it.
+  remove(OnlyAvailablePred);
+
+  // Reinsert the node into the priority queue, which recomputes its
+  // NumNodesSolelyBlocking value.
+  push(OnlyAvailablePred);
+}