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Diffstat (limited to 'lib/CodeGen/SelectionDAG/ScheduleDAGList.cpp')
| -rw-r--r-- | lib/CodeGen/SelectionDAG/ScheduleDAGList.cpp | 531 |
1 files changed, 531 insertions, 0 deletions
diff --git a/lib/CodeGen/SelectionDAG/ScheduleDAGList.cpp b/lib/CodeGen/SelectionDAG/ScheduleDAGList.cpp new file mode 100644 index 0000000..9e4e46f --- /dev/null +++ b/lib/CodeGen/SelectionDAG/ScheduleDAGList.cpp @@ -0,0 +1,531 @@ +//===---- 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) { + if (!isChain) + SuccSU->NumPredsLeft--; + else + SuccSU->NumChainPredsLeft--; + + assert(SuccSU->NumPredsLeft >= 0 && SuccSU->NumChainPredsLeft >= 0 && + "List scheduling internal error"); + + if ((SuccSU->NumPredsLeft + SuccSU->NumChainPredsLeft) == 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->first; + unsigned PredDoneCycle = Pred.Cycle; + if (!I->second) + 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->first, I->second); +} + +/// ListScheduleTopDown - The main loop of list scheduling for top-down +/// schedulers. +void ScheduleDAGList::ListScheduleTopDown() { + unsigned CurCycle = 0; + SUnit *Entry = SUnitMap[DAG.getEntryNode().Val]; + + // 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 || SUnits[i].NumChainPredsLeft != 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*, SUnit*> &sumap, + std::vector<SUnit> &sunits) { + SUnits = &sunits; + // Calculate node priorities. + CalculatePriorities(); + } + 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]; + } + + 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; + } + + // 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); + + /// RemoveFromPriorityQueue - 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 RemoveFromPriorityQueue(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]); + } + }; +} + +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; + + int MaxSuccLatency = 0; + for (SUnit::const_succ_iterator I = SU.Succs.begin(), E = SU.Succs.end(); + I != E; ++I) + MaxSuccLatency = std::max(MaxSuccLatency, CalcLatency(*I->first)); + + return Latency = MaxSuccLatency + SU.Latency; +} + +/// CalculatePriorities - Calculate priorities of all scheduling units. +void LatencyPriorityQueue::CalculatePriorities() { + Latencies.assign(SUnits->size(), -1); + NumNodesSolelyBlocking.assign(SUnits->size(), 0); + + for (unsigned i = 0, e = SUnits->size(); i != e; ++i) + CalcLatency((*SUnits)[i]); +} + +/// 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->first; + 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->first) == 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->first); +} + +/// 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. + RemoveFromPriorityQueue(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()); +} |