| //===---- 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 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 "pre-RA-sched" |
| #include "llvm/CodeGen/ScheduleDAG.h" |
| #include "llvm/CodeGen/SchedulerRegistry.h" |
| #include "llvm/CodeGen/SelectionDAGISel.h" |
| #include "llvm/CodeGen/SSARegMap.h" |
| #include "llvm/Target/MRegisterInfo.h" |
| #include "llvm/Target/TargetData.h" |
| #include "llvm/Target/TargetMachine.h" |
| #include "llvm/Target/TargetInstrInfo.h" |
| #include "llvm/Support/Debug.h" |
| #include "llvm/Support/Compiler.h" |
| #include "llvm/ADT/Statistic.h" |
| #include <climits> |
| #include <queue> |
| using namespace llvm; |
| |
| STATISTIC(NumNoops , "Number of noops inserted"); |
| STATISTIC(NumStalls, "Number of pipeline stalls"); |
| |
| 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: |
| /// 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; |
| |
| public: |
| ScheduleDAGList(SelectionDAG &dag, MachineBasicBlock *bb, |
| 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 anonymous namespace |
| |
| HazardRecognizer::~HazardRecognizer() {} |
| |
| |
| /// Schedule - Schedule the DAG using list scheduling. |
| void ScheduleDAGList::Schedule() { |
| DOUT << "********** List Scheduling **********\n"; |
| |
| // Build scheduling units. |
| BuildSchedUnits(); |
| |
| AvailableQueue->initNodes(SUnitMap, SUnits); |
| |
| ListScheduleTopDown(); |
| |
| AvailableQueue->releaseState(); |
| |
| DOUT << "*** Final schedule ***\n"; |
| DEBUG(dumpSchedule()); |
| DOUT << "\n"; |
| |
| // Emit in scheduled order |
| EmitSchedule(); |
| } |
| |
| //===----------------------------------------------------------------------===// |
| // 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; |
| SUnit *Entry = SUnitMap[DAG.getEntryNode().Val].front(); |
| |
| // 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.size() == 0 && &SUnits[i] != Entry) { |
| AvailableQueue->push(&SUnits[i]); |
| SUnits[i].isAvailable = SUnits[i].isPending = true; |
| } |
| } |
| |
| // Emit the entry node first. |
| ScheduleNodeTopDown(Entry, CurCycle); |
| HazardRec->EmitInstruction(Entry->Node); |
| |
| // 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; |
| 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->getOpcode() < ISD::BUILTIN_OP_END && 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; |
| |
| std::priority_queue<SUnit*, std::vector<SUnit*>, latency_sort> Queue; |
| public: |
| LatencyPriorityQueue() : Queue(latency_sort(this)) { |
| } |
| |
| void initNodes(DenseMap<SDNode*, std::vector<SUnit*> > &sumap, |
| 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; |
| } |
| |
| /// remove - This is a really inefficient way to remove a node from a |
| /// priority queue. We should roll our own heap to make this better or |
| /// something. |
| void remove(SUnit *SU) { |
| std::vector<SUnit*> Temp; |
| |
| assert(!Queue.empty() && "Not in queue!"); |
| while (Queue.top() != SU) { |
| Temp.push_back(Queue.top()); |
| Queue.pop(); |
| assert(!Queue.empty() && "Not in queue!"); |
| } |
| |
| // Remove the node from the PQ. |
| Queue.pop(); |
| |
| // Add all the other nodes back. |
| for (unsigned i = 0, e = Temp.size(); i != e; ++i) |
| Queue.push(Temp[i]); |
| } |
| |
| // 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.size() == 0) |
| 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 |
| //===----------------------------------------------------------------------===// |
| |
| /// 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) { |
| return new ScheduleDAGList(*DAG, BB, DAG->getTarget(), |
| new LatencyPriorityQueue(), |
| IS->CreateTargetHazardRecognizer()); |
| } |