-//===-- ScheduleDAGSimple.cpp - Implement a list scheduler for isel DAG ---===//
+//===---- ScheduleDAGList.cpp - Implement a list scheduler for isel DAG ---===//
//
// The LLVM Compiler Infrastructure
//
-// This file was developed by Evan Cheng and is distributed under the
-// University of Illinois Open Source License. See LICENSE.TXT for details.
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
-// This implements a simple two pass scheduler. The first pass attempts to push
-// backward any lengthy instructions and critical paths. The second pass packs
-// instructions into semi-optimal time slots.
+// This implements a top-down list scheduler, using standard algorithms.
+// The basic approach uses a priority queue of available nodes to schedule.
+// One at a time, nodes are taken from the priority queue (thus in priority
+// order), checked for legality to schedule, and emitted if legal.
+//
+// Nodes may not be legal to schedule either due to structural hazards (e.g.
+// pipeline or resource constraints) or because an input to the instruction has
+// not completed execution.
//
//===----------------------------------------------------------------------===//
-#define DEBUG_TYPE "sched"
+#define DEBUG_TYPE "pre-RA-sched"
#include "llvm/CodeGen/ScheduleDAG.h"
-#include "llvm/CodeGen/SelectionDAG.h"
+#include "llvm/CodeGen/SchedulerRegistry.h"
+#include "llvm/CodeGen/SelectionDAGISel.h"
+#include "llvm/Target/TargetRegisterInfo.h"
+#include "llvm/Target/TargetData.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetInstrInfo.h"
-#include <algorithm>
-#include <queue>
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/Compiler.h"
+#include "llvm/ADT/PriorityQueue.h"
+#include "llvm/ADT/Statistic.h"
+#include <climits>
using namespace llvm;
+STATISTIC(NumNoops , "Number of noops inserted");
+STATISTIC(NumStalls, "Number of pipeline stalls");
-namespace llvm {
-/// Sorting functions for ready queue.
-struct LSSortPred : public std::binary_function<SDOperand, SDOperand, bool> {
- bool operator()(const SDOperand* left, const SDOperand* right) const {
- return true;
- }
-};
-
-/// ScheduleDAGList - List scheduler.
-
-class ScheduleDAGList : public ScheduleDAG {
+static RegisterScheduler
+ tdListDAGScheduler("list-td", " Top-down list scheduler",
+ createTDListDAGScheduler);
+
+namespace {
+//===----------------------------------------------------------------------===//
+/// ScheduleDAGList - The actual list scheduler implementation. This supports
+/// top-down scheduling.
+///
+class VISIBILITY_HIDDEN ScheduleDAGList : public ScheduleDAG {
private:
- LSSortPred &Cmp;
+ /// AvailableQueue - The priority queue to use for the available SUnits.
+ ///
+ SchedulingPriorityQueue *AvailableQueue;
+
+ /// PendingQueue - This contains all of the instructions whose operands have
+ /// been issued, but their results are not ready yet (due to the latency of
+ /// the operation). Once the operands becomes available, the instruction is
+ /// added to the AvailableQueue. This keeps track of each SUnit and the
+ /// number of cycles left to execute before the operation is available.
+ std::vector<std::pair<unsigned, SUnit*> > PendingQueue;
+
+ /// HazardRec - The hazard recognizer to use.
+ HazardRecognizer *HazardRec;
- // Ready queue
- std::priority_queue<SDOperand*, std::vector<SDOperand*>, LSSortPred> Ready;
-
public:
ScheduleDAGList(SelectionDAG &dag, MachineBasicBlock *bb,
- const TargetMachine &tm, LSSortPred cmp)
- : ScheduleDAG(listSchedulingBURR, dag, bb, tm), Cmp(cmp), Ready(Cmp)
- {};
+ const TargetMachine &tm,
+ SchedulingPriorityQueue *availqueue,
+ HazardRecognizer *HR)
+ : ScheduleDAG(dag, bb, tm),
+ AvailableQueue(availqueue), HazardRec(HR) {
+ }
+
+ ~ScheduleDAGList() {
+ delete HazardRec;
+ delete AvailableQueue;
+ }
void Schedule();
+
+private:
+ void ReleaseSucc(SUnit *SuccSU, bool isChain);
+ void ScheduleNodeTopDown(SUnit *SU, unsigned CurCycle);
+ void ListScheduleTopDown();
};
-} // end namespace llvm
+} // end anonymous namespace
+HazardRecognizer::~HazardRecognizer() {}
+
+
+/// Schedule - Schedule the DAG using list scheduling.
void ScheduleDAGList::Schedule() {
+ DOUT << "********** List Scheduling **********\n";
+
+ // Build scheduling units.
+ BuildSchedUnits();
+
+ AvailableQueue->initNodes(SUnits);
+
+ ListScheduleTopDown();
+
+ AvailableQueue->releaseState();
+}
+
+//===----------------------------------------------------------------------===//
+// Top-Down Scheduling
+//===----------------------------------------------------------------------===//
+
+/// ReleaseSucc - Decrement the NumPredsLeft count of a successor. Add it to
+/// the PendingQueue if the count reaches zero.
+void ScheduleDAGList::ReleaseSucc(SUnit *SuccSU, bool isChain) {
+ SuccSU->NumPredsLeft--;
+
+ assert(SuccSU->NumPredsLeft >= 0 &&
+ "List scheduling internal error");
+
+ if (SuccSU->NumPredsLeft == 0) {
+ // 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.
+ unsigned AvailableCycle = 0;
+ for (SUnit::pred_iterator I = SuccSU->Preds.begin(),
+ E = SuccSU->Preds.end(); I != E; ++I) {
+ // If this is a token edge, we don't need to wait for the latency of the
+ // preceeding instruction (e.g. a long-latency load) unless there is also
+ // some other data dependence.
+ SUnit &Pred = *I->Dep;
+ unsigned PredDoneCycle = Pred.Cycle;
+ if (!I->isCtrl)
+ PredDoneCycle += Pred.Latency;
+ else if (Pred.Latency)
+ PredDoneCycle += 1;
+
+ AvailableCycle = std::max(AvailableCycle, PredDoneCycle);
+ }
+
+ PendingQueue.push_back(std::make_pair(AvailableCycle, SuccSU));
+ }
+}
+
+/// ScheduleNodeTopDown - Add the node to the schedule. Decrement the pending
+/// count of its successors. If a successor pending count is zero, add it to
+/// the Available queue.
+void ScheduleDAGList::ScheduleNodeTopDown(SUnit *SU, unsigned CurCycle) {
+ DOUT << "*** Scheduling [" << CurCycle << "]: ";
+ DEBUG(SU->dump(&DAG));
+
+ Sequence.push_back(SU);
+ SU->Cycle = CurCycle;
+
+ // Bottom up: release successors.
+ for (SUnit::succ_iterator I = SU->Succs.begin(), E = SU->Succs.end();
+ I != E; ++I)
+ ReleaseSucc(I->Dep, I->isCtrl);
+}
+
+/// ListScheduleTopDown - The main loop of list scheduling for top-down
+/// schedulers.
+void ScheduleDAGList::ListScheduleTopDown() {
+ unsigned CurCycle = 0;
+
+ // All leaves to Available queue.
+ for (unsigned i = 0, e = SUnits.size(); i != e; ++i) {
+ // It is available if it has no predecessors.
+ if (SUnits[i].Preds.empty()) {
+ AvailableQueue->push(&SUnits[i]);
+ SUnits[i].isAvailable = SUnits[i].isPending = true;
+ }
+ }
+
+ // While Available queue is not empty, grab the node with the highest
+ // priority. If it is not ready put it back. Schedule the node.
+ std::vector<SUnit*> NotReady;
+ Sequence.reserve(SUnits.size());
+ while (!AvailableQueue->empty() || !PendingQueue.empty()) {
+ // Check to see if any of the pending instructions are ready to issue. If
+ // so, add them to the available queue.
+ for (unsigned i = 0, e = PendingQueue.size(); i != e; ++i) {
+ if (PendingQueue[i].first == CurCycle) {
+ AvailableQueue->push(PendingQueue[i].second);
+ PendingQueue[i].second->isAvailable = true;
+ PendingQueue[i] = PendingQueue.back();
+ PendingQueue.pop_back();
+ --i; --e;
+ } else {
+ assert(PendingQueue[i].first > CurCycle && "Negative latency?");
+ }
+ }
+
+ // If there are no instructions available, don't try to issue anything, and
+ // don't advance the hazard recognizer.
+ if (AvailableQueue->empty()) {
+ ++CurCycle;
+ continue;
+ }
+
+ SUnit *FoundSUnit = 0;
+ SDNode *FoundNode = 0;
+
+ bool HasNoopHazards = false;
+ while (!AvailableQueue->empty()) {
+ SUnit *CurSUnit = AvailableQueue->pop();
+
+ // Get the node represented by this SUnit.
+ FoundNode = CurSUnit->Node;
+
+ // If this is a pseudo op, like copyfromreg, look to see if there is a
+ // real target node flagged to it. If so, use the target node.
+ for (unsigned i = 0, e = CurSUnit->FlaggedNodes.size();
+ !FoundNode->isMachineOpcode() && i != e; ++i)
+ FoundNode = CurSUnit->FlaggedNodes[i];
+
+ HazardRecognizer::HazardType HT = HazardRec->getHazardType(FoundNode);
+ if (HT == HazardRecognizer::NoHazard) {
+ FoundSUnit = CurSUnit;
+ break;
+ }
+
+ // Remember if this is a noop hazard.
+ HasNoopHazards |= HT == HazardRecognizer::NoopHazard;
+
+ NotReady.push_back(CurSUnit);
+ }
+
+ // Add the nodes that aren't ready back onto the available list.
+ if (!NotReady.empty()) {
+ AvailableQueue->push_all(NotReady);
+ NotReady.clear();
+ }
+
+ // If we found a node to schedule, do it now.
+ if (FoundSUnit) {
+ ScheduleNodeTopDown(FoundSUnit, CurCycle);
+ HazardRec->EmitInstruction(FoundNode);
+ FoundSUnit->isScheduled = true;
+ AvailableQueue->ScheduledNode(FoundSUnit);
+
+ // If this is a pseudo-op node, we don't want to increment the current
+ // cycle.
+ if (FoundSUnit->Latency) // Don't increment CurCycle for pseudo-ops!
+ ++CurCycle;
+ } else if (!HasNoopHazards) {
+ // Otherwise, we have a pipeline stall, but no other problem, just advance
+ // the current cycle and try again.
+ DOUT << "*** Advancing cycle, no work to do\n";
+ HazardRec->AdvanceCycle();
+ ++NumStalls;
+ ++CurCycle;
+ } else {
+ // Otherwise, we have no instructions to issue and we have instructions
+ // that will fault if we don't do this right. This is the case for
+ // processors without pipeline interlocks and other cases.
+ DOUT << "*** Emitting noop\n";
+ HazardRec->EmitNoop();
+ Sequence.push_back(0); // NULL SUnit* -> noop
+ ++NumNoops;
+ ++CurCycle;
+ }
+ }
+
+#ifndef NDEBUG
+ // Verify that all SUnits were scheduled.
+ bool AnyNotSched = false;
+ for (unsigned i = 0, e = SUnits.size(); i != e; ++i) {
+ if (SUnits[i].NumPredsLeft != 0) {
+ if (!AnyNotSched)
+ cerr << "*** List scheduling failed! ***\n";
+ SUnits[i].dump(&DAG);
+ cerr << "has not been scheduled!\n";
+ AnyNotSched = true;
+ }
+ }
+ assert(!AnyNotSched);
+#endif
+}
+
+//===----------------------------------------------------------------------===//
+// LatencyPriorityQueue Implementation
+//===----------------------------------------------------------------------===//
+//
+// This is a SchedulingPriorityQueue that schedules using latency information to
+// reduce the length of the critical path through the basic block.
+//
+namespace {
+ class LatencyPriorityQueue;
+
+ /// Sorting functions for the Available queue.
+ struct latency_sort : public std::binary_function<SUnit*, SUnit*, bool> {
+ LatencyPriorityQueue *PQ;
+ latency_sort(LatencyPriorityQueue *pq) : PQ(pq) {}
+ latency_sort(const latency_sort &RHS) : PQ(RHS.PQ) {}
+
+ bool operator()(const SUnit* left, const SUnit* right) const;
+ };
+} // end anonymous namespace
+
+namespace {
+ class LatencyPriorityQueue : public SchedulingPriorityQueue {
+ // SUnits - The SUnits for the current graph.
+ std::vector<SUnit> *SUnits;
+
+ // Latencies - The latency (max of latency from this node to the bb exit)
+ // for each node.
+ std::vector<int> Latencies;
+
+ /// NumNodesSolelyBlocking - This vector contains, for every node in the
+ /// Queue, the number of nodes that the node is the sole unscheduled
+ /// predecessor for. This is used as a tie-breaker heuristic for better
+ /// mobility.
+ std::vector<unsigned> NumNodesSolelyBlocking;
+
+ PriorityQueue<SUnit*, std::vector<SUnit*>, latency_sort> Queue;
+public:
+ LatencyPriorityQueue() : Queue(latency_sort(this)) {
+ }
+
+ void initNodes(std::vector<SUnit> &sunits) {
+ SUnits = &sunits;
+ // Calculate node priorities.
+ CalculatePriorities();
+ }
+
+ void addNode(const SUnit *SU) {
+ Latencies.resize(SUnits->size(), -1);
+ NumNodesSolelyBlocking.resize(SUnits->size(), 0);
+ CalcLatency(*SU);
+ }
+
+ void updateNode(const SUnit *SU) {
+ Latencies[SU->NodeNum] = -1;
+ CalcLatency(*SU);
+ }
+
+ void releaseState() {
+ SUnits = 0;
+ Latencies.clear();
+ }
+
+ unsigned getLatency(unsigned NodeNum) const {
+ assert(NodeNum < Latencies.size());
+ return Latencies[NodeNum];
+ }
+
+ unsigned getNumSolelyBlockNodes(unsigned NodeNum) const {
+ assert(NodeNum < NumNodesSolelyBlocking.size());
+ return NumNodesSolelyBlocking[NodeNum];
+ }
+
+ unsigned size() const { return Queue.size(); }
+
+ bool empty() const { return Queue.empty(); }
+
+ virtual void push(SUnit *U) {
+ push_impl(U);
+ }
+ void push_impl(SUnit *U);
+
+ void push_all(const std::vector<SUnit *> &Nodes) {
+ for (unsigned i = 0, e = Nodes.size(); i != e; ++i)
+ push_impl(Nodes[i]);
+ }
+
+ SUnit *pop() {
+ if (empty()) return NULL;
+ SUnit *V = Queue.top();
+ Queue.pop();
+ return V;
+ }
+
+ void remove(SUnit *SU) {
+ assert(!Queue.empty() && "Not in queue!");
+ Queue.erase_one(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 ScheduledNode(SUnit *Node);
+
+private:
+ void CalculatePriorities();
+ int CalcLatency(const SUnit &SU);
+ void AdjustPriorityOfUnscheduledPreds(SUnit *SU);
+ SUnit *getSingleUnscheduledPred(SUnit *SU);
+ };
}
+
+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->isPending) 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);
+}
+
+
+//===----------------------------------------------------------------------===//
+// Public Constructor Functions
+//===----------------------------------------------------------------------===//
-llvm::ScheduleDAG*
-llvm::createBURRListDAGScheduler(SelectionDAG &DAG,
- MachineBasicBlock *BB) {
- return new ScheduleDAGList(DAG, BB, DAG.getTarget(), LSSortPred());
+/// createTDListDAGScheduler - This creates a top-down list scheduler with a
+/// new hazard recognizer. This scheduler takes ownership of the hazard
+/// recognizer and deletes it when done.
+ScheduleDAG* llvm::createTDListDAGScheduler(SelectionDAGISel *IS,
+ SelectionDAG *DAG,
+ MachineBasicBlock *BB, bool Fast) {
+ return new ScheduleDAGList(*DAG, BB, DAG->getTarget(),
+ new LatencyPriorityQueue(),
+ IS->CreateTargetHazardRecognizer());
}
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