269 lines
9.0 KiB
C++
269 lines
9.0 KiB
C++
//===---- ScheduleDAGList.cpp - Implement a list scheduler for isel DAG ---===//
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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 implements a top-down list scheduler, using standard algorithms.
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// The basic approach uses a priority queue of available nodes to schedule.
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// One at a time, nodes are taken from the priority queue (thus in priority
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// order), checked for legality to schedule, and emitted if legal.
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//
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// Nodes may not be legal to schedule either due to structural hazards (e.g.
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// pipeline or resource constraints) or because an input to the instruction has
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// not completed execution.
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "pre-RA-sched"
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#include "ScheduleDAGSDNodes.h"
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#include "llvm/CodeGen/LatencyPriorityQueue.h"
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#include "llvm/CodeGen/ScheduleHazardRecognizer.h"
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#include "llvm/CodeGen/SchedulerRegistry.h"
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#include "llvm/CodeGen/SelectionDAGISel.h"
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#include "llvm/Target/TargetRegisterInfo.h"
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#include "llvm/Target/TargetData.h"
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#include "llvm/Target/TargetInstrInfo.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/Compiler.h"
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#include "llvm/ADT/PriorityQueue.h"
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#include "llvm/ADT/Statistic.h"
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#include <climits>
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using namespace llvm;
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STATISTIC(NumNoops , "Number of noops inserted");
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STATISTIC(NumStalls, "Number of pipeline stalls");
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static RegisterScheduler
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tdListDAGScheduler("list-td", "Top-down list scheduler",
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createTDListDAGScheduler);
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namespace {
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//===----------------------------------------------------------------------===//
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/// ScheduleDAGList - The actual list scheduler implementation. This supports
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/// top-down scheduling.
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///
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class VISIBILITY_HIDDEN ScheduleDAGList : public ScheduleDAGSDNodes {
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private:
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/// AvailableQueue - The priority queue to use for the available SUnits.
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///
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SchedulingPriorityQueue *AvailableQueue;
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/// PendingQueue - This contains all of the instructions whose operands have
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/// been issued, but their results are not ready yet (due to the latency of
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/// the operation). Once the operands become available, the instruction is
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/// added to the AvailableQueue.
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std::vector<SUnit*> PendingQueue;
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/// HazardRec - The hazard recognizer to use.
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ScheduleHazardRecognizer *HazardRec;
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public:
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ScheduleDAGList(MachineFunction &mf,
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SchedulingPriorityQueue *availqueue,
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ScheduleHazardRecognizer *HR)
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: ScheduleDAGSDNodes(mf),
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AvailableQueue(availqueue), HazardRec(HR) {
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}
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~ScheduleDAGList() {
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delete HazardRec;
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delete AvailableQueue;
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}
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void Schedule();
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private:
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void ReleaseSucc(SUnit *SU, const SDep &D);
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void ReleaseSuccessors(SUnit *SU);
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void ScheduleNodeTopDown(SUnit *SU, unsigned CurCycle);
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void ListScheduleTopDown();
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};
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} // end anonymous namespace
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/// Schedule - Schedule the DAG using list scheduling.
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void ScheduleDAGList::Schedule() {
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DOUT << "********** List Scheduling **********\n";
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// Build the scheduling graph.
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BuildSchedGraph();
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AvailableQueue->initNodes(SUnits);
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ListScheduleTopDown();
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AvailableQueue->releaseState();
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}
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//===----------------------------------------------------------------------===//
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// Top-Down Scheduling
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//===----------------------------------------------------------------------===//
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/// ReleaseSucc - Decrement the NumPredsLeft count of a successor. Add it to
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/// the PendingQueue if the count reaches zero. Also update its cycle bound.
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void ScheduleDAGList::ReleaseSucc(SUnit *SU, const SDep &D) {
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SUnit *SuccSU = D.getSUnit();
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--SuccSU->NumPredsLeft;
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#ifndef NDEBUG
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if (SuccSU->NumPredsLeft < 0) {
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cerr << "*** Scheduling failed! ***\n";
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SuccSU->dump(this);
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cerr << " has been released too many times!\n";
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assert(0);
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}
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#endif
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SuccSU->setDepthToAtLeast(SU->getDepth() + D.getLatency());
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// If all the node's predecessors are scheduled, this node is ready
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// to be scheduled. Ignore the special ExitSU node.
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if (SuccSU->NumPredsLeft == 0 && SuccSU != &ExitSU)
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PendingQueue.push_back(SuccSU);
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}
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void ScheduleDAGList::ReleaseSuccessors(SUnit *SU) {
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// Top down: release successors.
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for (SUnit::succ_iterator I = SU->Succs.begin(), E = SU->Succs.end();
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I != E; ++I) {
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assert(!I->isAssignedRegDep() &&
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"The list-td scheduler doesn't yet support physreg dependencies!");
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ReleaseSucc(SU, *I);
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}
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}
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/// ScheduleNodeTopDown - Add the node to the schedule. Decrement the pending
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/// count of its successors. If a successor pending count is zero, add it to
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/// the Available queue.
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void ScheduleDAGList::ScheduleNodeTopDown(SUnit *SU, unsigned CurCycle) {
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DOUT << "*** Scheduling [" << CurCycle << "]: ";
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DEBUG(SU->dump(this));
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Sequence.push_back(SU);
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assert(CurCycle >= SU->getDepth() && "Node scheduled above its depth!");
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SU->setDepthToAtLeast(CurCycle);
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ReleaseSuccessors(SU);
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SU->isScheduled = true;
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AvailableQueue->ScheduledNode(SU);
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}
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/// ListScheduleTopDown - The main loop of list scheduling for top-down
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/// schedulers.
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void ScheduleDAGList::ListScheduleTopDown() {
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unsigned CurCycle = 0;
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// Release any successors of the special Entry node.
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ReleaseSuccessors(&EntrySU);
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// All leaves to Available queue.
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for (unsigned i = 0, e = SUnits.size(); i != e; ++i) {
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// It is available if it has no predecessors.
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if (SUnits[i].Preds.empty()) {
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AvailableQueue->push(&SUnits[i]);
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SUnits[i].isAvailable = true;
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}
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}
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// While Available queue is not empty, grab the node with the highest
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// priority. If it is not ready put it back. Schedule the node.
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std::vector<SUnit*> NotReady;
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Sequence.reserve(SUnits.size());
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while (!AvailableQueue->empty() || !PendingQueue.empty()) {
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// Check to see if any of the pending instructions are ready to issue. If
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// so, add them to the available queue.
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for (unsigned i = 0, e = PendingQueue.size(); i != e; ++i) {
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if (PendingQueue[i]->getDepth() == CurCycle) {
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AvailableQueue->push(PendingQueue[i]);
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PendingQueue[i]->isAvailable = true;
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PendingQueue[i] = PendingQueue.back();
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PendingQueue.pop_back();
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--i; --e;
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} else {
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assert(PendingQueue[i]->getDepth() > CurCycle && "Negative latency?");
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}
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}
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// If there are no instructions available, don't try to issue anything, and
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// don't advance the hazard recognizer.
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if (AvailableQueue->empty()) {
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++CurCycle;
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continue;
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}
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SUnit *FoundSUnit = 0;
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bool HasNoopHazards = false;
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while (!AvailableQueue->empty()) {
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SUnit *CurSUnit = AvailableQueue->pop();
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ScheduleHazardRecognizer::HazardType HT =
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HazardRec->getHazardType(CurSUnit);
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if (HT == ScheduleHazardRecognizer::NoHazard) {
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FoundSUnit = CurSUnit;
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break;
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}
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// Remember if this is a noop hazard.
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HasNoopHazards |= HT == ScheduleHazardRecognizer::NoopHazard;
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NotReady.push_back(CurSUnit);
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}
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// Add the nodes that aren't ready back onto the available list.
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if (!NotReady.empty()) {
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AvailableQueue->push_all(NotReady);
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NotReady.clear();
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}
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// If we found a node to schedule, do it now.
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if (FoundSUnit) {
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ScheduleNodeTopDown(FoundSUnit, CurCycle);
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HazardRec->EmitInstruction(FoundSUnit);
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// If this is a pseudo-op node, we don't want to increment the current
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// cycle.
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if (FoundSUnit->Latency) // Don't increment CurCycle for pseudo-ops!
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++CurCycle;
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} else if (!HasNoopHazards) {
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// Otherwise, we have a pipeline stall, but no other problem, just advance
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// the current cycle and try again.
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DOUT << "*** Advancing cycle, no work to do\n";
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HazardRec->AdvanceCycle();
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++NumStalls;
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++CurCycle;
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} else {
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// Otherwise, we have no instructions to issue and we have instructions
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// that will fault if we don't do this right. This is the case for
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// processors without pipeline interlocks and other cases.
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DOUT << "*** Emitting noop\n";
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HazardRec->EmitNoop();
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Sequence.push_back(0); // NULL here means noop
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++NumNoops;
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++CurCycle;
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}
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}
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#ifndef NDEBUG
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VerifySchedule(/*isBottomUp=*/false);
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#endif
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}
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//===----------------------------------------------------------------------===//
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// Public Constructor Functions
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//===----------------------------------------------------------------------===//
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/// createTDListDAGScheduler - This creates a top-down list scheduler with a
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/// new hazard recognizer. This scheduler takes ownership of the hazard
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/// recognizer and deletes it when done.
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ScheduleDAGSDNodes *
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llvm::createTDListDAGScheduler(SelectionDAGISel *IS, CodeGenOpt::Level) {
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return new ScheduleDAGList(*IS->MF,
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new LatencyPriorityQueue(),
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IS->CreateTargetHazardRecognizer());
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}
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