141 lines
5.2 KiB
C++
141 lines
5.2 KiB
C++
//===---- LatencyPriorityQueue.cpp - A latency-oriented priority queue ----===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements the LatencyPriorityQueue class, which is a
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// SchedulingPriorityQueue that schedules using latency information to
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// reduce the length of the critical path through the basic block.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/CodeGen/LatencyPriorityQueue.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/raw_ostream.h"
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using namespace llvm;
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#define DEBUG_TYPE "scheduler"
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bool latency_sort::operator()(const SUnit *LHS, const SUnit *RHS) const {
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// The isScheduleHigh flag allows nodes with wraparound dependencies that
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// cannot easily be modeled as edges with latencies to be scheduled as
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// soon as possible in a top-down schedule.
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if (LHS->isScheduleHigh && !RHS->isScheduleHigh)
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return false;
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if (!LHS->isScheduleHigh && RHS->isScheduleHigh)
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return true;
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unsigned LHSNum = LHS->NodeNum;
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unsigned RHSNum = RHS->NodeNum;
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// The most important heuristic is scheduling the critical path.
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unsigned LHSLatency = PQ->getLatency(LHSNum);
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unsigned RHSLatency = PQ->getLatency(RHSNum);
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if (LHSLatency < RHSLatency) return true;
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if (LHSLatency > RHSLatency) return false;
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// After that, if two nodes have identical latencies, look to see if one will
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// unblock more other nodes than the other.
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unsigned LHSBlocked = PQ->getNumSolelyBlockNodes(LHSNum);
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unsigned RHSBlocked = PQ->getNumSolelyBlockNodes(RHSNum);
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if (LHSBlocked < RHSBlocked) return true;
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if (LHSBlocked > RHSBlocked) return false;
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// Finally, just to provide a stable ordering, use the node number as a
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// deciding factor.
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return RHSNum < LHSNum;
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}
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/// getSingleUnscheduledPred - If there is exactly one unscheduled predecessor
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/// of SU, return it, otherwise return null.
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SUnit *LatencyPriorityQueue::getSingleUnscheduledPred(SUnit *SU) {
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SUnit *OnlyAvailablePred = nullptr;
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for (SUnit::const_pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
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I != E; ++I) {
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SUnit &Pred = *I->getSUnit();
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if (!Pred.isScheduled) {
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// We found an available, but not scheduled, predecessor. If it's the
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// only one we have found, keep track of it... otherwise give up.
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if (OnlyAvailablePred && OnlyAvailablePred != &Pred)
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return nullptr;
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OnlyAvailablePred = &Pred;
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}
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}
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return OnlyAvailablePred;
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}
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void LatencyPriorityQueue::push(SUnit *SU) {
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// Look at all of the successors of this node. Count the number of nodes that
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// this node is the sole unscheduled node for.
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unsigned NumNodesBlocking = 0;
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for (SUnit::const_succ_iterator I = SU->Succs.begin(), E = SU->Succs.end();
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I != E; ++I) {
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if (getSingleUnscheduledPred(I->getSUnit()) == SU)
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++NumNodesBlocking;
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}
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NumNodesSolelyBlocking[SU->NodeNum] = NumNodesBlocking;
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Queue.push_back(SU);
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}
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// scheduledNode - As nodes are scheduled, we look to see if there are any
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// successor nodes that have a single unscheduled predecessor. If so, that
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// single predecessor has a higher priority, since scheduling it will make
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// the node available.
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void LatencyPriorityQueue::scheduledNode(SUnit *SU) {
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for (SUnit::const_succ_iterator I = SU->Succs.begin(), E = SU->Succs.end();
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I != E; ++I) {
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AdjustPriorityOfUnscheduledPreds(I->getSUnit());
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}
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}
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/// AdjustPriorityOfUnscheduledPreds - One of the predecessors of SU was just
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/// scheduled. If SU is not itself available, then there is at least one
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/// predecessor node that has not been scheduled yet. If SU has exactly ONE
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/// unscheduled predecessor, we want to increase its priority: it getting
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/// scheduled will make this node available, so it is better than some other
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/// node of the same priority that will not make a node available.
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void LatencyPriorityQueue::AdjustPriorityOfUnscheduledPreds(SUnit *SU) {
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if (SU->isAvailable) return; // All preds scheduled.
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SUnit *OnlyAvailablePred = getSingleUnscheduledPred(SU);
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if (!OnlyAvailablePred || !OnlyAvailablePred->isAvailable) return;
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// Okay, we found a single predecessor that is available, but not scheduled.
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// Since it is available, it must be in the priority queue. First remove it.
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remove(OnlyAvailablePred);
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// Reinsert the node into the priority queue, which recomputes its
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// NumNodesSolelyBlocking value.
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push(OnlyAvailablePred);
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}
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SUnit *LatencyPriorityQueue::pop() {
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if (empty()) return nullptr;
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std::vector<SUnit *>::iterator Best = Queue.begin();
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for (std::vector<SUnit *>::iterator I = std::next(Queue.begin()),
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E = Queue.end(); I != E; ++I)
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if (Picker(*Best, *I))
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Best = I;
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SUnit *V = *Best;
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if (Best != std::prev(Queue.end()))
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std::swap(*Best, Queue.back());
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Queue.pop_back();
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return V;
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}
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void LatencyPriorityQueue::remove(SUnit *SU) {
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assert(!Queue.empty() && "Queue is empty!");
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std::vector<SUnit *>::iterator I = find(Queue, SU);
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if (I != std::prev(Queue.end()))
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std::swap(*I, Queue.back());
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Queue.pop_back();
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}
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