| //===---- LatencyPriorityQueue.cpp - A latency-oriented priority queue ----===// |
| // |
| // 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 |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // 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. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "llvm/CodeGen/LatencyPriorityQueue.h" |
| #include "llvm/Config/llvm-config.h" |
| #include "llvm/Support/Debug.h" |
| #include "llvm/Support/raw_ostream.h" |
| using namespace llvm; |
| |
| #define DEBUG_TYPE "scheduler" |
| |
| bool latency_sort::operator()(const SUnit *LHS, const SUnit *RHS) const { |
| // The isScheduleHigh flag allows nodes with wraparound dependencies that |
| // cannot easily be modeled as edges with latencies to be scheduled as |
| // soon as possible in a top-down schedule. |
| if (LHS->isScheduleHigh && !RHS->isScheduleHigh) |
| return false; |
| if (!LHS->isScheduleHigh && RHS->isScheduleHigh) |
| return true; |
| |
| 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 RHSNum < LHSNum; |
| } |
| |
| |
| /// getSingleUnscheduledPred - If there is exactly one unscheduled predecessor |
| /// of SU, return it, otherwise return null. |
| SUnit *LatencyPriorityQueue::getSingleUnscheduledPred(SUnit *SU) { |
| SUnit *OnlyAvailablePred = nullptr; |
| for (const SDep &P : SU->Preds) { |
| SUnit &Pred = *P.getSUnit(); |
| 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 nullptr; |
| OnlyAvailablePred = &Pred; |
| } |
| } |
| |
| return OnlyAvailablePred; |
| } |
| |
| void LatencyPriorityQueue::push(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 (const SDep &Succ : SU->Succs) |
| if (getSingleUnscheduledPred(Succ.getSUnit()) == SU) |
| ++NumNodesBlocking; |
| NumNodesSolelyBlocking[SU->NodeNum] = NumNodesBlocking; |
| |
| Queue.push_back(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 (const SDep &Succ : SU->Succs) |
| AdjustPriorityOfUnscheduledPreds(Succ.getSUnit()); |
| } |
| |
| /// 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 || !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); |
| } |
| |
| SUnit *LatencyPriorityQueue::pop() { |
| if (empty()) return nullptr; |
| std::vector<SUnit *>::iterator Best = Queue.begin(); |
| for (std::vector<SUnit *>::iterator I = std::next(Queue.begin()), |
| E = Queue.end(); I != E; ++I) |
| if (Picker(*Best, *I)) |
| Best = I; |
| SUnit *V = *Best; |
| if (Best != std::prev(Queue.end())) |
| std::swap(*Best, Queue.back()); |
| Queue.pop_back(); |
| return V; |
| } |
| |
| void LatencyPriorityQueue::remove(SUnit *SU) { |
| assert(!Queue.empty() && "Queue is empty!"); |
| std::vector<SUnit *>::iterator I = find(Queue, SU); |
| assert(I != Queue.end() && "Queue doesn't contain the SU being removed!"); |
| if (I != std::prev(Queue.end())) |
| std::swap(*I, Queue.back()); |
| Queue.pop_back(); |
| } |
| |
| #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP) |
| LLVM_DUMP_METHOD void LatencyPriorityQueue::dump(ScheduleDAG *DAG) const { |
| dbgs() << "Latency Priority Queue\n"; |
| dbgs() << " Number of Queue Entries: " << Queue.size() << "\n"; |
| for (const SUnit *SU : Queue) { |
| dbgs() << " "; |
| DAG->dumpNode(*SU); |
| } |
| } |
| #endif |