Experimental post-pass scheduling support. Post-pass scheduling

is currently off by default, and can be enabled with
-disable-post-RA-scheduler=false.

This doesn't have a significant impact on most code yet because it doesn't
yet do anything to address anti-dependencies and it doesn't attempt to
disambiguate memory references. Also, several popular targets
don't have pipeline descriptions yet.

The majority of the changes here are splitting the SelectionDAG-specific
code out of ScheduleDAG, so that ScheduleDAG can be moved to
libLLVMCodeGen.a. The interface between ScheduleDAG-using code and
the rest of the scheduling code is somewhat rough and will evolve.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@59676 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 165 insertions, 0 deletions

diff --git a/lib/CodeGen/LatencyPriorityQueue.cpp b/lib/CodeGen/LatencyPriorityQueue.cpp
new file mode 100644
index 0000000000..70b6574996
--- /dev/null
+++ b/lib/CodeGen/LatencyPriorityQueue.cpp
@@ -0,0 +1,165 @@
+//===---- 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 {
+  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;
+}
+
+
+/// CalcNodePriority - Calculate the maximal path from the node to the exit.
+///
+int LatencyPriorityQueue::CalcLatency(const SUnit &SU) {
+  int &Latency = Latencies[SU.NodeNum];
+  if (Latency != -1)
+    return Latency;
+
+  std::vector<const SUnit*> WorkList;
+  WorkList.push_back(&SU);
+  while (!WorkList.empty()) {
+    const SUnit *Cur = WorkList.back();
+    bool AllDone = true;
+    int MaxSuccLatency = 0;
+    for (SUnit::const_succ_iterator I = Cur->Succs.begin(),E = Cur->Succs.end();
+         I != E; ++I) {
+      int SuccLatency = Latencies[I->Dep->NodeNum];
+      if (SuccLatency == -1) {
+        AllDone = false;
+        WorkList.push_back(I->Dep);
+      } else {
+        MaxSuccLatency = std::max(MaxSuccLatency, SuccLatency);
+      }
+    }
+    if (AllDone) {
+      Latencies[Cur->NodeNum] = MaxSuccLatency + Cur->Latency;
+      WorkList.pop_back();
+    }
+  }
+
+  return Latency;
+}
+
+/// CalculatePriorities - Calculate priorities of all scheduling units.
+void LatencyPriorityQueue::CalculatePriorities() {
+  Latencies.assign(SUnits->size(), -1);
+  NumNodesSolelyBlocking.assign(SUnits->size(), 0);
+
+  // For each node, calculate the maximal path from the node to the exit.
+  std::vector<std::pair<const SUnit*, unsigned> > WorkList;
+  for (unsigned i = 0, e = SUnits->size(); i != e; ++i) {
+    const SUnit *SU = &(*SUnits)[i];
+    if (SU->Succs.empty())
+      WorkList.push_back(std::make_pair(SU, 0U));
+  }
+
+  while (!WorkList.empty()) {
+    const SUnit *SU = WorkList.back().first;
+    unsigned SuccLat = WorkList.back().second;
+    WorkList.pop_back();
+    int &Latency = Latencies[SU->NodeNum];
+    if (Latency == -1 || (SU->Latency + SuccLat) > (unsigned)Latency) {
+      Latency = SU->Latency + SuccLat;
+      for (SUnit::const_pred_iterator I = SU->Preds.begin(),E = SU->Preds.end();
+           I != E; ++I)
+        WorkList.push_back(std::make_pair(I->Dep, Latency));
+    }
+  }
+}
+
+/// 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->Dep;
+    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->Dep) == 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->Dep);
+}
+
+/// 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);
+}