1 files changed, 363 insertions, 0 deletions
diff --git a/llvm/lib/Target/AMDGPU/GCNILPSched.cpp b/llvm/lib/Target/AMDGPU/GCNILPSched.cpp
new file mode 100644
index 000000000000..39072af7d871
--- /dev/null
+++ b/llvm/lib/Target/AMDGPU/GCNILPSched.cpp
@@ -0,0 +1,363 @@
+//===---------------------------- GCNILPSched.cpp - -----------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+/// \file
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/CodeGen/ScheduleDAG.h"
+#include "llvm/Support/Debug.h"
+
+using namespace llvm;
+
+#define DEBUG_TYPE "machine-scheduler"
+
+namespace {
+
+class GCNILPScheduler {
+  struct Candidate : ilist_node<Candidate> {
+    SUnit *SU;
+
+    Candidate(SUnit *SU_)
+      : SU(SU_) {}
+  };
+
+  SpecificBumpPtrAllocator<Candidate> Alloc;
+  typedef simple_ilist<Candidate> Queue;
+  Queue PendingQueue;
+  Queue AvailQueue;
+  unsigned CurQueueId = 0;
+
+  std::vector<unsigned> SUNumbers;
+
+  /// CurCycle - The current scheduler state corresponds to this cycle.
+  unsigned CurCycle = 0;
+
+  unsigned getNodePriority(const SUnit *SU) const;
+
+  const SUnit *pickBest(const SUnit *left, const SUnit *right);
+  Candidate* pickCandidate();
+
+  void releasePending();
+  void advanceToCycle(unsigned NextCycle);
+  void releasePredecessors(const SUnit* SU);
+
+public:
+  std::vector<const SUnit*> schedule(ArrayRef<const SUnit*> TopRoots,
+                                     const ScheduleDAG &DAG);
+};
+} // namespace
+
+/// CalcNodeSethiUllmanNumber - Compute Sethi Ullman number.
+/// Smaller number is the higher priority.
+static unsigned
+CalcNodeSethiUllmanNumber(const SUnit *SU, std::vector<unsigned> &SUNumbers) {
+  unsigned &SethiUllmanNumber = SUNumbers[SU->NodeNum];
+  if (SethiUllmanNumber != 0)
+    return SethiUllmanNumber;
+
+  unsigned Extra = 0;
+  for (const SDep &Pred : SU->Preds) {
+    if (Pred.isCtrl()) continue;  // ignore chain preds
+    SUnit *PredSU = Pred.getSUnit();
+    unsigned PredSethiUllman = CalcNodeSethiUllmanNumber(PredSU, SUNumbers);
+    if (PredSethiUllman > SethiUllmanNumber) {
+      SethiUllmanNumber = PredSethiUllman;
+      Extra = 0;
+    }
+    else if (PredSethiUllman == SethiUllmanNumber)
+      ++Extra;
+  }
+
+  SethiUllmanNumber += Extra;
+
+  if (SethiUllmanNumber == 0)
+    SethiUllmanNumber = 1;
+
+  return SethiUllmanNumber;
+}
+
+// Lower priority means schedule further down. For bottom-up scheduling, lower
+// priority SUs are scheduled before higher priority SUs.
+unsigned GCNILPScheduler::getNodePriority(const SUnit *SU) const {
+  assert(SU->NodeNum < SUNumbers.size());
+  if (SU->NumSuccs == 0 && SU->NumPreds != 0)
+    // If SU does not have a register use, i.e. it doesn't produce a value
+    // that would be consumed (e.g. store), then it terminates a chain of
+    // computation.  Give it a large SethiUllman number so it will be
+    // scheduled right before its predecessors that it doesn't lengthen
+    // their live ranges.
+    return 0xffff;
+
+  if (SU->NumPreds == 0 && SU->NumSuccs != 0)
+    // If SU does not have a register def, schedule it close to its uses
+    // because it does not lengthen any live ranges.
+    return 0;
+
+  return SUNumbers[SU->NodeNum];
+}
+
+/// closestSucc - Returns the scheduled cycle of the successor which is
+/// closest to the current cycle.
+static unsigned closestSucc(const SUnit *SU) {
+  unsigned MaxHeight = 0;
+  for (const SDep &Succ : SU->Succs) {
+    if (Succ.isCtrl()) continue;  // ignore chain succs
+    unsigned Height = Succ.getSUnit()->getHeight();
+    // If there are bunch of CopyToRegs stacked up, they should be considered
+    // to be at the same position.
+    if (Height > MaxHeight)
+      MaxHeight = Height;
+  }
+  return MaxHeight;
+}
+
+/// calcMaxScratches - Returns an cost estimate of the worse case requirement
+/// for scratch registers, i.e. number of data dependencies.
+static unsigned calcMaxScratches(const SUnit *SU) {
+  unsigned Scratches = 0;
+  for (const SDep &Pred : SU->Preds) {
+    if (Pred.isCtrl()) continue;  // ignore chain preds
+    Scratches++;
+  }
+  return Scratches;
+}
+
+// Return -1 if left has higher priority, 1 if right has higher priority.
+// Return 0 if latency-based priority is equivalent.
+static int BUCompareLatency(const SUnit *left, const SUnit *right) {
+  // Scheduling an instruction that uses a VReg whose postincrement has not yet
+  // been scheduled will induce a copy. Model this as an extra cycle of latency.
+  int LHeight = (int)left->getHeight();
+  int RHeight = (int)right->getHeight();
+
+  // If either node is scheduling for latency, sort them by height/depth
+  // and latency.
+
+  // If neither instruction stalls (!LStall && !RStall) and HazardRecognizer
+  // is enabled, grouping instructions by cycle, then its height is already
+  // covered so only its depth matters. We also reach this point if both stall
+  // but have the same height.
+  if (LHeight != RHeight)
+    return LHeight > RHeight ? 1 : -1;
+
+  int LDepth = left->getDepth();
+  int RDepth = right->getDepth();
+  if (LDepth != RDepth) {
+    LLVM_DEBUG(dbgs() << "  Comparing latency of SU (" << left->NodeNum
+                      << ") depth " << LDepth << " vs SU (" << right->NodeNum
+                      << ") depth " << RDepth << "\n");
+    return LDepth < RDepth ? 1 : -1;
+  }
+  if (left->Latency != right->Latency)
+    return left->Latency > right->Latency ? 1 : -1;
+
+  return 0;
+}
+
+const SUnit *GCNILPScheduler::pickBest(const SUnit *left, const SUnit *right)
+{
+  // TODO: add register pressure lowering checks
+
+  bool const DisableSchedCriticalPath = false;
+  int MaxReorderWindow = 6;
+  if (!DisableSchedCriticalPath) {
+    int spread = (int)left->getDepth() - (int)right->getDepth();
+    if (std::abs(spread) > MaxReorderWindow) {
+      LLVM_DEBUG(dbgs() << "Depth of SU(" << left->NodeNum << "): "
+                        << left->getDepth() << " != SU(" << right->NodeNum
+                        << "): " << right->getDepth() << "\n");
+      return left->getDepth() < right->getDepth() ? right : left;
+    }
+  }
+
+  bool const DisableSchedHeight = false;
+  if (!DisableSchedHeight && left->getHeight() != right->getHeight()) {
+    int spread = (int)left->getHeight() - (int)right->getHeight();
+    if (std::abs(spread) > MaxReorderWindow)
+      return left->getHeight() > right->getHeight() ? right : left;
+  }
+
+  // Prioritize by Sethi-Ulmann number and push CopyToReg nodes down.
+  unsigned LPriority = getNodePriority(left);
+  unsigned RPriority = getNodePriority(right);
+
+  if (LPriority != RPriority)
+    return LPriority > RPriority ? right : left;
+
+  // Try schedule def + use closer when Sethi-Ullman numbers are the same.
+  // e.g.
+  // t1 = op t2, c1
+  // t3 = op t4, c2
+  //
+  // and the following instructions are both ready.
+  // t2 = op c3
+  // t4 = op c4
+  //
+  // Then schedule t2 = op first.
+  // i.e.
+  // t4 = op c4
+  // t2 = op c3
+  // t1 = op t2, c1
+  // t3 = op t4, c2
+  //
+  // This creates more short live intervals.
+  unsigned LDist = closestSucc(left);
+  unsigned RDist = closestSucc(right);
+  if (LDist != RDist)
+    return LDist < RDist ? right : left;
+
+  // How many registers becomes live when the node is scheduled.
+  unsigned LScratch = calcMaxScratches(left);
+  unsigned RScratch = calcMaxScratches(right);
+  if (LScratch != RScratch)
+    return LScratch > RScratch ? right : left;
+
+  bool const DisableSchedCycles = false;
+  if (!DisableSchedCycles) {
+    int result = BUCompareLatency(left, right);
+    if (result != 0)
+      return result > 0 ? right : left;
+    return left;
+  }
+  else {
+    if (left->getHeight() != right->getHeight())
+      return (left->getHeight() > right->getHeight()) ? right : left;
+
+    if (left->getDepth() != right->getDepth())
+      return (left->getDepth() < right->getDepth()) ? right : left;
+  }
+
+  assert(left->NodeQueueId && right->NodeQueueId &&
+        "NodeQueueId cannot be zero");
+  return (left->NodeQueueId > right->NodeQueueId) ? right : left;
+}
+
+GCNILPScheduler::Candidate* GCNILPScheduler::pickCandidate() {
+  if (AvailQueue.empty())
+    return nullptr;
+  auto Best = AvailQueue.begin();
+  for (auto I = std::next(AvailQueue.begin()), E = AvailQueue.end(); I != E; ++I) {
+    auto NewBestSU = pickBest(Best->SU, I->SU);
+    if (NewBestSU != Best->SU) {
+      assert(NewBestSU == I->SU);
+      Best = I;
+    }
+  }
+  return &*Best;
+}
+
+void GCNILPScheduler::releasePending() {
+  // Check to see if any of the pending instructions are ready to issue.  If
+  // so, add them to the available queue.
+  for(auto I = PendingQueue.begin(), E = PendingQueue.end(); I != E;) {
+    auto &C = *I++;
+    if (C.SU->getHeight() <= CurCycle) {
+      PendingQueue.remove(C);
+      AvailQueue.push_back(C);
+      C.SU->NodeQueueId = CurQueueId++;
+    }
+  }
+}
+
+/// Move the scheduler state forward by the specified number of Cycles.
+void GCNILPScheduler::advanceToCycle(unsigned NextCycle) {
+  if (NextCycle <= CurCycle)
+    return;
+  CurCycle = NextCycle;
+  releasePending();
+}
+
+void GCNILPScheduler::releasePredecessors(const SUnit* SU) {
+  for (const auto &PredEdge : SU->Preds) {
+    auto PredSU = PredEdge.getSUnit();
+    if (PredEdge.isWeak())
+      continue;
+    assert(PredSU->isBoundaryNode() || PredSU->NumSuccsLeft > 0);
+
+    PredSU->setHeightToAtLeast(SU->getHeight() + PredEdge.getLatency());
+
+    if (!PredSU->isBoundaryNode() && --PredSU->NumSuccsLeft == 0)
+      PendingQueue.push_front(*new (Alloc.Allocate()) Candidate(PredSU));
+  }
+}
+
+std::vector<const SUnit*>
+GCNILPScheduler::schedule(ArrayRef<const SUnit*> BotRoots,
+                          const ScheduleDAG &DAG) {
+  auto &SUnits = const_cast<ScheduleDAG&>(DAG).SUnits;
+
+  std::vector<SUnit> SUSavedCopy;
+  SUSavedCopy.resize(SUnits.size());
+
+  // we cannot save only those fields we touch: some of them are private
+  // so save units verbatim: this assumes SUnit should have value semantics
+  for (const SUnit &SU : SUnits)
+    SUSavedCopy[SU.NodeNum] = SU;
+
+  SUNumbers.assign(SUnits.size(), 0);
+  for (const SUnit &SU : SUnits)
+    CalcNodeSethiUllmanNumber(&SU, SUNumbers);
+
+  for (auto SU : BotRoots) {
+    AvailQueue.push_back(
+      *new (Alloc.Allocate()) Candidate(const_cast<SUnit*>(SU)));
+  }
+  releasePredecessors(&DAG.ExitSU);
+
+  std::vector<const SUnit*> Schedule;
+  Schedule.reserve(SUnits.size());
+  while (true) {
+    if (AvailQueue.empty() && !PendingQueue.empty()) {
+      auto EarliestSU = std::min_element(
+        PendingQueue.begin(), PendingQueue.end(),
+        [=](const Candidate& C1, const Candidate& C2) {
+        return C1.SU->getHeight() < C2.SU->getHeight();
+      })->SU;
+      advanceToCycle(std::max(CurCycle + 1, EarliestSU->getHeight()));
+    }
+    if (AvailQueue.empty())
+      break;
+
+    LLVM_DEBUG(dbgs() << "\n=== Picking candidate\n"
+                         "Ready queue:";
+               for (auto &C
+                    : AvailQueue) dbgs()
+               << ' ' << C.SU->NodeNum;
+               dbgs() << '\n';);
+
+    auto C = pickCandidate();
+    assert(C);
+    AvailQueue.remove(*C);
+    auto SU = C->SU;
+    LLVM_DEBUG(dbgs() << "Selected "; DAG.dumpNode(*SU));
+
+    advanceToCycle(SU->getHeight());
+
+    releasePredecessors(SU);
+    Schedule.push_back(SU);
+    SU->isScheduled = true;
+  }
+  assert(SUnits.size() == Schedule.size());
+
+  std::reverse(Schedule.begin(), Schedule.end());
+
+  // restore units
+  for (auto &SU : SUnits)
+    SU = SUSavedCopy[SU.NodeNum];
+
+  return Schedule;
+}
+
+namespace llvm {
+std::vector<const SUnit*> makeGCNILPScheduler(ArrayRef<const SUnit*> BotRoots,
+                                              const ScheduleDAG &DAG) {
+  GCNILPScheduler S;
+  return S.schedule(BotRoots, DAG);
+}
+}