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llvm-project/llvm/lib/CodeGen/VLIWMachineScheduler.cpp

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//===- VLIWMachineScheduler.cpp - VLIW-Focused Scheduling Pass ------------===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// MachineScheduler schedules machine instructions after phi elimination. It
// preserves LiveIntervals so it can be invoked before register allocation.
//
//===----------------------------------------------------------------------===//
#include "llvm/CodeGen/VLIWMachineScheduler.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/CodeGen/DFAPacketizer.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineLoopInfo.h"
#include "llvm/CodeGen/RegisterClassInfo.h"
#include "llvm/CodeGen/RegisterPressure.h"
#include "llvm/CodeGen/ScheduleDAG.h"
#include "llvm/CodeGen/ScheduleHazardRecognizer.h"
#include "llvm/CodeGen/TargetInstrInfo.h"
#include "llvm/CodeGen/TargetOpcodes.h"
#include "llvm/CodeGen/TargetRegisterInfo.h"
#include "llvm/CodeGen/TargetSchedule.h"
#include "llvm/CodeGen/TargetSubtargetInfo.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include <algorithm>
#include <cassert>
#include <iomanip>
#include <limits>
#include <memory>
#include <sstream>
using namespace llvm;
#define DEBUG_TYPE "machine-scheduler"
static cl::opt<bool> IgnoreBBRegPressure("ignore-bb-reg-pressure", cl::Hidden,
cl::init(false));
static cl::opt<bool> UseNewerCandidate("use-newer-candidate", cl::Hidden,
cl::init(true));
static cl::opt<unsigned> SchedDebugVerboseLevel("misched-verbose-level",
cl::Hidden, cl::init(1));
// Check if the scheduler should penalize instructions that are available to
// early due to a zero-latency dependence.
static cl::opt<bool> CheckEarlyAvail("check-early-avail", cl::Hidden,
cl::init(true));
// This value is used to determine if a register class is a high pressure set.
// We compute the maximum number of registers needed and divided by the total
// available. Then, we compare the result to this value.
static cl::opt<float> RPThreshold("vliw-misched-reg-pressure", cl::Hidden,
cl::init(0.75f),
cl::desc("High register pressure threhold."));
VLIWResourceModel::VLIWResourceModel(const TargetSubtargetInfo &STI,
const TargetSchedModel *SM)
: TII(STI.getInstrInfo()), SchedModel(SM) {
ResourcesModel = createPacketizer(STI);
// This hard requirement could be relaxed,
// but for now do not let it proceed.
assert(ResourcesModel && "Unimplemented CreateTargetScheduleState.");
Packet.reserve(SchedModel->getIssueWidth());
Packet.clear();
ResourcesModel->clearResources();
}
void VLIWResourceModel::reset() {
Packet.clear();
ResourcesModel->clearResources();
}
VLIWResourceModel::~VLIWResourceModel() { delete ResourcesModel; }
/// Return true if there is a dependence between SUd and SUu.
bool VLIWResourceModel::hasDependence(const SUnit *SUd, const SUnit *SUu) {
if (SUd->Succs.size() == 0)
return false;
for (const auto &S : SUd->Succs) {
// Since we do not add pseudos to packets, might as well
// ignore order dependencies.
if (S.isCtrl())
continue;
if (S.getSUnit() == SUu && S.getLatency() > 0)
return true;
}
return false;
}
/// Check if scheduling of this SU is possible
/// in the current packet.
/// It is _not_ precise (statefull), it is more like
/// another heuristic. Many corner cases are figured
/// empirically.
bool VLIWResourceModel::isResourceAvailable(SUnit *SU, bool IsTop) {
if (!SU || !SU->getInstr())
return false;
// First see if the pipeline could receive this instruction
// in the current cycle.
switch (SU->getInstr()->getOpcode()) {
default:
if (!ResourcesModel->canReserveResources(*SU->getInstr()))
return false;
break;
case TargetOpcode::EXTRACT_SUBREG:
case TargetOpcode::INSERT_SUBREG:
case TargetOpcode::SUBREG_TO_REG:
case TargetOpcode::REG_SEQUENCE:
case TargetOpcode::IMPLICIT_DEF:
case TargetOpcode::COPY:
case TargetOpcode::INLINEASM:
case TargetOpcode::INLINEASM_BR:
break;
}
// Now see if there are no other dependencies to instructions already
// in the packet.
if (IsTop) {
for (unsigned i = 0, e = Packet.size(); i != e; ++i)
if (hasDependence(Packet[i], SU))
return false;
} else {
for (unsigned i = 0, e = Packet.size(); i != e; ++i)
if (hasDependence(SU, Packet[i]))
return false;
}
return true;
}
/// Keep track of available resources.
bool VLIWResourceModel::reserveResources(SUnit *SU, bool IsTop) {
bool startNewCycle = false;
// Artificially reset state.
if (!SU) {
reset();
TotalPackets++;
return false;
}
// If this SU does not fit in the packet or the packet is now full
// start a new one.
if (!isResourceAvailable(SU, IsTop) ||
Packet.size() >= SchedModel->getIssueWidth()) {
reset();
TotalPackets++;
startNewCycle = true;
}
switch (SU->getInstr()->getOpcode()) {
default:
ResourcesModel->reserveResources(*SU->getInstr());
break;
case TargetOpcode::EXTRACT_SUBREG:
case TargetOpcode::INSERT_SUBREG:
case TargetOpcode::SUBREG_TO_REG:
case TargetOpcode::REG_SEQUENCE:
case TargetOpcode::IMPLICIT_DEF:
case TargetOpcode::KILL:
case TargetOpcode::CFI_INSTRUCTION:
case TargetOpcode::EH_LABEL:
case TargetOpcode::COPY:
case TargetOpcode::INLINEASM:
case TargetOpcode::INLINEASM_BR:
break;
}
Packet.push_back(SU);
#ifndef NDEBUG
LLVM_DEBUG(dbgs() << "Packet[" << TotalPackets << "]:\n");
for (unsigned i = 0, e = Packet.size(); i != e; ++i) {
LLVM_DEBUG(dbgs() << "\t[" << i << "] SU(");
LLVM_DEBUG(dbgs() << Packet[i]->NodeNum << ")\t");
LLVM_DEBUG(Packet[i]->getInstr()->dump());
}
#endif
return startNewCycle;
}
DFAPacketizer *
VLIWResourceModel::createPacketizer(const TargetSubtargetInfo &STI) const {
return STI.getInstrInfo()->CreateTargetScheduleState(STI);
}
/// schedule - Called back from MachineScheduler::runOnMachineFunction
/// after setting up the current scheduling region. [RegionBegin, RegionEnd)
/// only includes instructions that have DAG nodes, not scheduling boundaries.
void VLIWMachineScheduler::schedule() {
LLVM_DEBUG(dbgs() << "********** MI Converging Scheduling VLIW "
<< printMBBReference(*BB) << " " << BB->getName()
<< " in_func " << BB->getParent()->getName()
<< " at loop depth " << MLI->getLoopDepth(BB) << " \n");
buildDAGWithRegPressure();
Topo.InitDAGTopologicalSorting();
// Postprocess the DAG to add platform-specific artificial dependencies.
postprocessDAG();
SmallVector<SUnit *, 8> TopRoots, BotRoots;
findRootsAndBiasEdges(TopRoots, BotRoots);
// Initialize the strategy before modifying the DAG.
SchedImpl->initialize(this);
LLVM_DEBUG({
unsigned maxH = 0;
for (const SUnit &SU : SUnits)
if (SU.getHeight() > maxH)
maxH = SU.getHeight();
dbgs() << "Max Height " << maxH << "\n";
});
LLVM_DEBUG({
unsigned maxD = 0;
for (const SUnit &SU : SUnits)
if (SU.getDepth() > maxD)
maxD = SU.getDepth();
dbgs() << "Max Depth " << maxD << "\n";
});
LLVM_DEBUG(dump());
if (ViewMISchedDAGs)
viewGraph();
initQueues(TopRoots, BotRoots);
bool IsTopNode = false;
while (true) {
LLVM_DEBUG(
dbgs() << "** VLIWMachineScheduler::schedule picking next node\n");
SUnit *SU = SchedImpl->pickNode(IsTopNode);
if (!SU)
break;
if (!checkSchedLimit())
break;
scheduleMI(SU, IsTopNode);
// Notify the scheduling strategy after updating the DAG.
SchedImpl->schedNode(SU, IsTopNode);
updateQueues(SU, IsTopNode);
}
assert(CurrentTop == CurrentBottom && "Nonempty unscheduled zone.");
placeDebugValues();
LLVM_DEBUG({
dbgs() << "*** Final schedule for "
<< printMBBReference(*begin()->getParent()) << " ***\n";
dumpSchedule();
dbgs() << '\n';
});
}
void ConvergingVLIWScheduler::initialize(ScheduleDAGMI *dag) {
DAG = static_cast<VLIWMachineScheduler *>(dag);
SchedModel = DAG->getSchedModel();
Top.init(DAG, SchedModel);
Bot.init(DAG, SchedModel);
// Initialize the HazardRecognizers. If itineraries don't exist, are empty, or
// are disabled, then these HazardRecs will be disabled.
const InstrItineraryData *Itin = DAG->getSchedModel()->getInstrItineraries();
const TargetSubtargetInfo &STI = DAG->MF.getSubtarget();
const TargetInstrInfo *TII = STI.getInstrInfo();
delete Top.HazardRec;
delete Bot.HazardRec;
Top.HazardRec = TII->CreateTargetMIHazardRecognizer(Itin, DAG);
Bot.HazardRec = TII->CreateTargetMIHazardRecognizer(Itin, DAG);
delete Top.ResourceModel;
delete Bot.ResourceModel;
Top.ResourceModel = createVLIWResourceModel(STI, DAG->getSchedModel());
Bot.ResourceModel = createVLIWResourceModel(STI, DAG->getSchedModel());
const std::vector<unsigned> &MaxPressure =
DAG->getRegPressure().MaxSetPressure;
HighPressureSets.assign(MaxPressure.size(), false);
for (unsigned i = 0, e = MaxPressure.size(); i < e; ++i) {
unsigned Limit = DAG->getRegClassInfo()->getRegPressureSetLimit(i);
HighPressureSets[i] =
((float)MaxPressure[i] > ((float)Limit * RPThreshold));
}
assert((!ForceTopDown || !ForceBottomUp) &&
"-misched-topdown incompatible with -misched-bottomup");
}
VLIWResourceModel *ConvergingVLIWScheduler::createVLIWResourceModel(
const TargetSubtargetInfo &STI, const TargetSchedModel *SchedModel) const {
return new VLIWResourceModel(STI, SchedModel);
}
void ConvergingVLIWScheduler::releaseTopNode(SUnit *SU) {
for (const SDep &PI : SU->Preds) {
unsigned PredReadyCycle = PI.getSUnit()->TopReadyCycle;
unsigned MinLatency = PI.getLatency();
#ifndef NDEBUG
Top.MaxMinLatency = std::max(MinLatency, Top.MaxMinLatency);
#endif
if (SU->TopReadyCycle < PredReadyCycle + MinLatency)
SU->TopReadyCycle = PredReadyCycle + MinLatency;
}
if (!SU->isScheduled)
Top.releaseNode(SU, SU->TopReadyCycle);
}
void ConvergingVLIWScheduler::releaseBottomNode(SUnit *SU) {
assert(SU->getInstr() && "Scheduled SUnit must have instr");
for (SUnit::succ_iterator I = SU->Succs.begin(), E = SU->Succs.end(); I != E;
++I) {
unsigned SuccReadyCycle = I->getSUnit()->BotReadyCycle;
unsigned MinLatency = I->getLatency();
#ifndef NDEBUG
Bot.MaxMinLatency = std::max(MinLatency, Bot.MaxMinLatency);
#endif
if (SU->BotReadyCycle < SuccReadyCycle + MinLatency)
SU->BotReadyCycle = SuccReadyCycle + MinLatency;
}
if (!SU->isScheduled)
Bot.releaseNode(SU, SU->BotReadyCycle);
}
ConvergingVLIWScheduler::VLIWSchedBoundary::~VLIWSchedBoundary() {
delete ResourceModel;
delete HazardRec;
}
/// Does this SU have a hazard within the current instruction group.
///
/// The scheduler supports two modes of hazard recognition. The first is the
/// ScheduleHazardRecognizer API. It is a fully general hazard recognizer that
/// supports highly complicated in-order reservation tables
/// (ScoreboardHazardRecognizer) and arbitrary target-specific logic.
///
/// The second is a streamlined mechanism that checks for hazards based on
/// simple counters that the scheduler itself maintains. It explicitly checks
/// for instruction dispatch limitations, including the number of micro-ops that
/// can dispatch per cycle.
///
/// TODO: Also check whether the SU must start a new group.
bool ConvergingVLIWScheduler::VLIWSchedBoundary::checkHazard(SUnit *SU) {
if (HazardRec->isEnabled())
return HazardRec->getHazardType(SU) != ScheduleHazardRecognizer::NoHazard;
unsigned uops = SchedModel->getNumMicroOps(SU->getInstr());
if (IssueCount + uops > SchedModel->getIssueWidth())
return true;
return false;
}
void ConvergingVLIWScheduler::VLIWSchedBoundary::releaseNode(
SUnit *SU, unsigned ReadyCycle) {
if (ReadyCycle < MinReadyCycle)
MinReadyCycle = ReadyCycle;
// Check for interlocks first. For the purpose of other heuristics, an
// instruction that cannot issue appears as if it's not in the ReadyQueue.
if (ReadyCycle > CurrCycle || checkHazard(SU))
Pending.push(SU);
else
Available.push(SU);
}
/// Move the boundary of scheduled code by one cycle.
void ConvergingVLIWScheduler::VLIWSchedBoundary::bumpCycle() {
unsigned Width = SchedModel->getIssueWidth();
IssueCount = (IssueCount <= Width) ? 0 : IssueCount - Width;
assert(MinReadyCycle < std::numeric_limits<unsigned>::max() &&
"MinReadyCycle uninitialized");
unsigned NextCycle = std::max(CurrCycle + 1, MinReadyCycle);
if (!HazardRec->isEnabled()) {
// Bypass HazardRec virtual calls.
CurrCycle = NextCycle;
} else {
// Bypass getHazardType calls in case of long latency.
for (; CurrCycle != NextCycle; ++CurrCycle) {
if (isTop())
HazardRec->AdvanceCycle();
else
HazardRec->RecedeCycle();
}
}
CheckPending = true;
LLVM_DEBUG(dbgs() << "*** Next cycle " << Available.getName() << " cycle "
<< CurrCycle << '\n');
}
/// Move the boundary of scheduled code by one SUnit.
void ConvergingVLIWScheduler::VLIWSchedBoundary::bumpNode(SUnit *SU) {
bool startNewCycle = false;
// Update the reservation table.
if (HazardRec->isEnabled()) {
if (!isTop() && SU->isCall) {
// Calls are scheduled with their preceding instructions. For bottom-up
// scheduling, clear the pipeline state before emitting.
HazardRec->Reset();
}
HazardRec->EmitInstruction(SU);
}
// Update DFA model.
startNewCycle = ResourceModel->reserveResources(SU, isTop());
// Check the instruction group dispatch limit.
// TODO: Check if this SU must end a dispatch group.
IssueCount += SchedModel->getNumMicroOps(SU->getInstr());
if (startNewCycle) {
LLVM_DEBUG(dbgs() << "*** Max instrs at cycle " << CurrCycle << '\n');
bumpCycle();
} else
LLVM_DEBUG(dbgs() << "*** IssueCount " << IssueCount << " at cycle "
<< CurrCycle << '\n');
}
/// Release pending ready nodes in to the available queue. This makes them
/// visible to heuristics.
void ConvergingVLIWScheduler::VLIWSchedBoundary::releasePending() {
// If the available queue is empty, it is safe to reset MinReadyCycle.
if (Available.empty())
MinReadyCycle = std::numeric_limits<unsigned>::max();
// 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 = Pending.size(); i != e; ++i) {
SUnit *SU = *(Pending.begin() + i);
unsigned ReadyCycle = isTop() ? SU->TopReadyCycle : SU->BotReadyCycle;
if (ReadyCycle < MinReadyCycle)
MinReadyCycle = ReadyCycle;
if (ReadyCycle > CurrCycle)
continue;
if (checkHazard(SU))
continue;
Available.push(SU);
Pending.remove(Pending.begin() + i);
--i;
--e;
}
CheckPending = false;
}
/// Remove SU from the ready set for this boundary.
void ConvergingVLIWScheduler::VLIWSchedBoundary::removeReady(SUnit *SU) {
if (Available.isInQueue(SU))
Available.remove(Available.find(SU));
else {
assert(Pending.isInQueue(SU) && "bad ready count");
Pending.remove(Pending.find(SU));
}
}
/// If this queue only has one ready candidate, return it. As a side effect,
/// advance the cycle until at least one node is ready. If multiple instructions
/// are ready, return NULL.
SUnit *ConvergingVLIWScheduler::VLIWSchedBoundary::pickOnlyChoice() {
if (CheckPending)
releasePending();
auto AdvanceCycle = [this]() {
if (Available.empty())
return true;
if (Available.size() == 1 && Pending.size() > 0)
return !ResourceModel->isResourceAvailable(*Available.begin(), isTop()) ||
getWeakLeft(*Available.begin(), isTop()) != 0;
return false;
};
for (unsigned i = 0; AdvanceCycle(); ++i) {
assert(i <= (HazardRec->getMaxLookAhead() + MaxMinLatency) &&
"permanent hazard");
(void)i;
ResourceModel->reserveResources(nullptr, isTop());
bumpCycle();
releasePending();
}
if (Available.size() == 1)
return *Available.begin();
return nullptr;
}
#ifndef NDEBUG
void ConvergingVLIWScheduler::traceCandidate(const char *Label,
const ReadyQueue &Q, SUnit *SU,
int Cost, PressureChange P) {
dbgs() << Label << " " << Q.getName() << " ";
if (P.isValid())
dbgs() << DAG->TRI->getRegPressureSetName(P.getPSet()) << ":"
<< P.getUnitInc() << " ";
else
dbgs() << " ";
dbgs() << "cost(" << Cost << ")\t";
DAG->dumpNode(*SU);
}
// Very detailed queue dump, to be used with higher verbosity levels.
void ConvergingVLIWScheduler::readyQueueVerboseDump(
const RegPressureTracker &RPTracker, SchedCandidate &Candidate,
ReadyQueue &Q) {
RegPressureTracker &TempTracker = const_cast<RegPressureTracker &>(RPTracker);
dbgs() << ">>> " << Q.getName() << "\n";
for (ReadyQueue::iterator I = Q.begin(), E = Q.end(); I != E; ++I) {
RegPressureDelta RPDelta;
TempTracker.getMaxPressureDelta((*I)->getInstr(), RPDelta,
DAG->getRegionCriticalPSets(),
DAG->getRegPressure().MaxSetPressure);
std::stringstream dbgstr;
dbgstr << "SU(" << std::setw(3) << (*I)->NodeNum << ")";
dbgs() << dbgstr.str();
SchedulingCost(Q, *I, Candidate, RPDelta, true);
dbgs() << "\t";
(*I)->getInstr()->dump();
}
dbgs() << "\n";
}
#endif
/// isSingleUnscheduledPred - If SU2 is the only unscheduled predecessor
/// of SU, return true (we may have duplicates)
static inline bool isSingleUnscheduledPred(SUnit *SU, SUnit *SU2) {
if (SU->NumPredsLeft == 0)
return false;
for (auto &Pred : SU->Preds) {
// We found an available, but not scheduled, predecessor.
if (!Pred.getSUnit()->isScheduled && (Pred.getSUnit() != SU2))
return false;
}
return true;
}
/// isSingleUnscheduledSucc - If SU2 is the only unscheduled successor
/// of SU, return true (we may have duplicates)
static inline bool isSingleUnscheduledSucc(SUnit *SU, SUnit *SU2) {
if (SU->NumSuccsLeft == 0)
return false;
for (auto &Succ : SU->Succs) {
// We found an available, but not scheduled, successor.
if (!Succ.getSUnit()->isScheduled && (Succ.getSUnit() != SU2))
return false;
}
return true;
}
/// Check if the instruction changes the register pressure of a register in the
/// high pressure set. The function returns a negative value if the pressure
/// decreases and a positive value is the pressure increases. If the instruction
/// doesn't use a high pressure register or doesn't change the register
/// pressure, then return 0.
int ConvergingVLIWScheduler::pressureChange(const SUnit *SU, bool isBotUp) {
PressureDiff &PD = DAG->getPressureDiff(SU);
for (const auto &P : PD) {
if (!P.isValid())
continue;
// The pressure differences are computed bottom-up, so the comparison for
// an increase is positive in the bottom direction, but negative in the
// top-down direction.
if (HighPressureSets[P.getPSet()])
return (isBotUp ? P.getUnitInc() : -P.getUnitInc());
}
return 0;
}
/// Single point to compute overall scheduling cost.
/// TODO: More heuristics will be used soon.
int ConvergingVLIWScheduler::SchedulingCost(ReadyQueue &Q, SUnit *SU,
SchedCandidate &Candidate,
RegPressureDelta &Delta,
bool verbose) {
// Initial trivial priority.
int ResCount = 1;
// Do not waste time on a node that is already scheduled.
if (!SU || SU->isScheduled)
return ResCount;
LLVM_DEBUG(if (verbose) dbgs()
<< ((Q.getID() == TopQID) ? "(top|" : "(bot|"));
// Forced priority is high.
if (SU->isScheduleHigh) {
ResCount += PriorityOne;
LLVM_DEBUG(dbgs() << "H|");
}
unsigned IsAvailableAmt = 0;
// Critical path first.
if (Q.getID() == TopQID) {
if (Top.isLatencyBound(SU)) {
LLVM_DEBUG(if (verbose) dbgs() << "LB|");
ResCount += (SU->getHeight() * ScaleTwo);
}
LLVM_DEBUG(if (verbose) {
std::stringstream dbgstr;
dbgstr << "h" << std::setw(3) << SU->getHeight() << "|";
dbgs() << dbgstr.str();
});
// If resources are available for it, multiply the
// chance of scheduling.
if (Top.ResourceModel->isResourceAvailable(SU, true)) {
IsAvailableAmt = (PriorityTwo + PriorityThree);
ResCount += IsAvailableAmt;
LLVM_DEBUG(if (verbose) dbgs() << "A|");
} else
LLVM_DEBUG(if (verbose) dbgs() << " |");
} else {
if (Bot.isLatencyBound(SU)) {
LLVM_DEBUG(if (verbose) dbgs() << "LB|");
ResCount += (SU->getDepth() * ScaleTwo);
}
LLVM_DEBUG(if (verbose) {
std::stringstream dbgstr;
dbgstr << "d" << std::setw(3) << SU->getDepth() << "|";
dbgs() << dbgstr.str();
});
// If resources are available for it, multiply the
// chance of scheduling.
if (Bot.ResourceModel->isResourceAvailable(SU, false)) {
IsAvailableAmt = (PriorityTwo + PriorityThree);
ResCount += IsAvailableAmt;
LLVM_DEBUG(if (verbose) dbgs() << "A|");
} else
LLVM_DEBUG(if (verbose) dbgs() << " |");
}
unsigned NumNodesBlocking = 0;
if (Q.getID() == TopQID) {
// How many SUs does it block from scheduling?
// Look at all of the successors of this node.
// Count the number of nodes that
// this node is the sole unscheduled node for.
if (Top.isLatencyBound(SU))
for (const SDep &SI : SU->Succs)
if (isSingleUnscheduledPred(SI.getSUnit(), SU))
++NumNodesBlocking;
} else {
// How many unscheduled predecessors block this node?
if (Bot.isLatencyBound(SU))
for (const SDep &PI : SU->Preds)
if (isSingleUnscheduledSucc(PI.getSUnit(), SU))
++NumNodesBlocking;
}
ResCount += (NumNodesBlocking * ScaleTwo);
LLVM_DEBUG(if (verbose) {
std::stringstream dbgstr;
dbgstr << "blk " << std::setw(2) << NumNodesBlocking << ")|";
dbgs() << dbgstr.str();
});
// Factor in reg pressure as a heuristic.
if (!IgnoreBBRegPressure) {
// Decrease priority by the amount that register pressure exceeds the limit.
ResCount -= (Delta.Excess.getUnitInc() * PriorityOne);
// Decrease priority if register pressure exceeds the limit.
ResCount -= (Delta.CriticalMax.getUnitInc() * PriorityOne);
// Decrease priority slightly if register pressure would increase over the
// current maximum.
ResCount -= (Delta.CurrentMax.getUnitInc() * PriorityTwo);
// If there are register pressure issues, then we remove the value added for
// the instruction being available. The rationale is that we really don't
// want to schedule an instruction that causes a spill.
if (IsAvailableAmt && pressureChange(SU, Q.getID() != TopQID) > 0 &&
(Delta.Excess.getUnitInc() || Delta.CriticalMax.getUnitInc() ||
Delta.CurrentMax.getUnitInc()))
ResCount -= IsAvailableAmt;
LLVM_DEBUG(if (verbose) {
dbgs() << "RP " << Delta.Excess.getUnitInc() << "/"
<< Delta.CriticalMax.getUnitInc() << "/"
<< Delta.CurrentMax.getUnitInc() << ")|";
});
}
// Give preference to a zero latency instruction if the dependent
// instruction is in the current packet.
if (Q.getID() == TopQID && getWeakLeft(SU, true) == 0) {
for (const SDep &PI : SU->Preds) {
if (!PI.getSUnit()->getInstr()->isPseudo() && PI.isAssignedRegDep() &&
PI.getLatency() == 0 &&
Top.ResourceModel->isInPacket(PI.getSUnit())) {
ResCount += PriorityThree;
LLVM_DEBUG(if (verbose) dbgs() << "Z|");
}
}
} else if (Q.getID() == BotQID && getWeakLeft(SU, false) == 0) {
for (const SDep &SI : SU->Succs) {
if (!SI.getSUnit()->getInstr()->isPseudo() && SI.isAssignedRegDep() &&
SI.getLatency() == 0 &&
Bot.ResourceModel->isInPacket(SI.getSUnit())) {
ResCount += PriorityThree;
LLVM_DEBUG(if (verbose) dbgs() << "Z|");
}
}
}
// If the instruction has a non-zero latency dependence with an instruction in
// the current packet, then it should not be scheduled yet. The case occurs
// when the dependent instruction is scheduled in a new packet, so the
// scheduler updates the current cycle and pending instructions become
// available.
if (CheckEarlyAvail) {
if (Q.getID() == TopQID) {
for (const auto &PI : SU->Preds) {
if (PI.getLatency() > 0 &&
Top.ResourceModel->isInPacket(PI.getSUnit())) {
ResCount -= PriorityOne;
LLVM_DEBUG(if (verbose) dbgs() << "D|");
}
}
} else {
for (const auto &SI : SU->Succs) {
if (SI.getLatency() > 0 &&
Bot.ResourceModel->isInPacket(SI.getSUnit())) {
ResCount -= PriorityOne;
LLVM_DEBUG(if (verbose) dbgs() << "D|");
}
}
}
}
LLVM_DEBUG(if (verbose) {
std::stringstream dbgstr;
dbgstr << "Total " << std::setw(4) << ResCount << ")";
dbgs() << dbgstr.str();
});
return ResCount;
}
/// Pick the best candidate from the top queue.
///
/// TODO: getMaxPressureDelta results can be mostly cached for each SUnit during
/// DAG building. To adjust for the current scheduling location we need to
/// maintain the number of vreg uses remaining to be top-scheduled.
ConvergingVLIWScheduler::CandResult
ConvergingVLIWScheduler::pickNodeFromQueue(VLIWSchedBoundary &Zone,
const RegPressureTracker &RPTracker,
SchedCandidate &Candidate) {
ReadyQueue &Q = Zone.Available;
LLVM_DEBUG(if (SchedDebugVerboseLevel > 1)
readyQueueVerboseDump(RPTracker, Candidate, Q);
else Q.dump(););
// getMaxPressureDelta temporarily modifies the tracker.
RegPressureTracker &TempTracker = const_cast<RegPressureTracker &>(RPTracker);
// BestSU remains NULL if no top candidates beat the best existing candidate.
CandResult FoundCandidate = NoCand;
for (ReadyQueue::iterator I = Q.begin(), E = Q.end(); I != E; ++I) {
RegPressureDelta RPDelta;
TempTracker.getMaxPressureDelta((*I)->getInstr(), RPDelta,
DAG->getRegionCriticalPSets(),
DAG->getRegPressure().MaxSetPressure);
int CurrentCost = SchedulingCost(Q, *I, Candidate, RPDelta, false);
// Initialize the candidate if needed.
if (!Candidate.SU) {
LLVM_DEBUG(traceCandidate("DCAND", Q, *I, CurrentCost));
Candidate.SU = *I;
Candidate.RPDelta = RPDelta;
Candidate.SCost = CurrentCost;
FoundCandidate = NodeOrder;
continue;
}
// Choose node order for negative cost candidates. There is no good
// candidate in this case.
if (CurrentCost < 0 && Candidate.SCost < 0) {
if ((Q.getID() == TopQID && (*I)->NodeNum < Candidate.SU->NodeNum) ||
(Q.getID() == BotQID && (*I)->NodeNum > Candidate.SU->NodeNum)) {
LLVM_DEBUG(traceCandidate("NCAND", Q, *I, CurrentCost));
Candidate.SU = *I;
Candidate.RPDelta = RPDelta;
Candidate.SCost = CurrentCost;
FoundCandidate = NodeOrder;
}
continue;
}
// Best cost.
if (CurrentCost > Candidate.SCost) {
LLVM_DEBUG(traceCandidate("CCAND", Q, *I, CurrentCost));
Candidate.SU = *I;
Candidate.RPDelta = RPDelta;
Candidate.SCost = CurrentCost;
FoundCandidate = BestCost;
continue;
}
// Choose an instruction that does not depend on an artificial edge.
unsigned CurrWeak = getWeakLeft(*I, (Q.getID() == TopQID));
unsigned CandWeak = getWeakLeft(Candidate.SU, (Q.getID() == TopQID));
if (CurrWeak != CandWeak) {
if (CurrWeak < CandWeak) {
LLVM_DEBUG(traceCandidate("WCAND", Q, *I, CurrentCost));
Candidate.SU = *I;
Candidate.RPDelta = RPDelta;
Candidate.SCost = CurrentCost;
FoundCandidate = Weak;
}
continue;
}
if (CurrentCost == Candidate.SCost && Zone.isLatencyBound(*I)) {
unsigned CurrSize, CandSize;
if (Q.getID() == TopQID) {
CurrSize = (*I)->Succs.size();
CandSize = Candidate.SU->Succs.size();
} else {
CurrSize = (*I)->Preds.size();
CandSize = Candidate.SU->Preds.size();
}
if (CurrSize > CandSize) {
LLVM_DEBUG(traceCandidate("SPCAND", Q, *I, CurrentCost));
Candidate.SU = *I;
Candidate.RPDelta = RPDelta;
Candidate.SCost = CurrentCost;
FoundCandidate = BestCost;
}
// Keep the old candidate if it's a better candidate. That is, don't use
// the subsequent tie breaker.
if (CurrSize != CandSize)
continue;
}
// Tie breaker.
// To avoid scheduling indeterminism, we need a tie breaker
// for the case when cost is identical for two nodes.
if (UseNewerCandidate && CurrentCost == Candidate.SCost) {
if ((Q.getID() == TopQID && (*I)->NodeNum < Candidate.SU->NodeNum) ||
(Q.getID() == BotQID && (*I)->NodeNum > Candidate.SU->NodeNum)) {
LLVM_DEBUG(traceCandidate("TCAND", Q, *I, CurrentCost));
Candidate.SU = *I;
Candidate.RPDelta = RPDelta;
Candidate.SCost = CurrentCost;
FoundCandidate = NodeOrder;
continue;
}
}
// Fall through to original instruction order.
// Only consider node order if Candidate was chosen from this Q.
if (FoundCandidate == NoCand)
continue;
}
return FoundCandidate;
}
/// Pick the best candidate node from either the top or bottom queue.
SUnit *ConvergingVLIWScheduler::pickNodeBidrectional(bool &IsTopNode) {
// Schedule as far as possible in the direction of no choice. This is most
// efficient, but also provides the best heuristics for CriticalPSets.
if (SUnit *SU = Bot.pickOnlyChoice()) {
LLVM_DEBUG(dbgs() << "Picked only Bottom\n");
IsTopNode = false;
return SU;
}
if (SUnit *SU = Top.pickOnlyChoice()) {
LLVM_DEBUG(dbgs() << "Picked only Top\n");
IsTopNode = true;
return SU;
}
SchedCandidate BotCand;
// Prefer bottom scheduling when heuristics are silent.
CandResult BotResult =
pickNodeFromQueue(Bot, DAG->getBotRPTracker(), BotCand);
assert(BotResult != NoCand && "failed to find the first candidate");
// If either Q has a single candidate that provides the least increase in
// Excess pressure, we can immediately schedule from that Q.
//
// RegionCriticalPSets summarizes the pressure within the scheduled region and
// affects picking from either Q. If scheduling in one direction must
// increase pressure for one of the excess PSets, then schedule in that
// direction first to provide more freedom in the other direction.
if (BotResult == SingleExcess || BotResult == SingleCritical) {
LLVM_DEBUG(dbgs() << "Prefered Bottom Node\n");
IsTopNode = false;
return BotCand.SU;
}
// Check if the top Q has a better candidate.
SchedCandidate TopCand;
CandResult TopResult =
pickNodeFromQueue(Top, DAG->getTopRPTracker(), TopCand);
assert(TopResult != NoCand && "failed to find the first candidate");
if (TopResult == SingleExcess || TopResult == SingleCritical) {
LLVM_DEBUG(dbgs() << "Prefered Top Node\n");
IsTopNode = true;
return TopCand.SU;
}
// If either Q has a single candidate that minimizes pressure above the
// original region's pressure pick it.
if (BotResult == SingleMax) {
LLVM_DEBUG(dbgs() << "Prefered Bottom Node SingleMax\n");
IsTopNode = false;
return BotCand.SU;
}
if (TopResult == SingleMax) {
LLVM_DEBUG(dbgs() << "Prefered Top Node SingleMax\n");
IsTopNode = true;
return TopCand.SU;
}
if (TopCand.SCost > BotCand.SCost) {
LLVM_DEBUG(dbgs() << "Prefered Top Node Cost\n");
IsTopNode = true;
return TopCand.SU;
}
// Otherwise prefer the bottom candidate in node order.
LLVM_DEBUG(dbgs() << "Prefered Bottom in Node order\n");
IsTopNode = false;
return BotCand.SU;
}
/// Pick the best node to balance the schedule. Implements MachineSchedStrategy.
SUnit *ConvergingVLIWScheduler::pickNode(bool &IsTopNode) {
if (DAG->top() == DAG->bottom()) {
assert(Top.Available.empty() && Top.Pending.empty() &&
Bot.Available.empty() && Bot.Pending.empty() && "ReadyQ garbage");
return nullptr;
}
SUnit *SU;
if (ForceTopDown) {
SU = Top.pickOnlyChoice();
if (!SU) {
SchedCandidate TopCand;
CandResult TopResult =
pickNodeFromQueue(Top, DAG->getTopRPTracker(), TopCand);
assert(TopResult != NoCand && "failed to find the first candidate");
(void)TopResult;
SU = TopCand.SU;
}
IsTopNode = true;
} else if (ForceBottomUp) {
SU = Bot.pickOnlyChoice();
if (!SU) {
SchedCandidate BotCand;
CandResult BotResult =
pickNodeFromQueue(Bot, DAG->getBotRPTracker(), BotCand);
assert(BotResult != NoCand && "failed to find the first candidate");
(void)BotResult;
SU = BotCand.SU;
}
IsTopNode = false;
} else {
SU = pickNodeBidrectional(IsTopNode);
}
if (SU->isTopReady())
Top.removeReady(SU);
if (SU->isBottomReady())
Bot.removeReady(SU);
LLVM_DEBUG(dbgs() << "*** " << (IsTopNode ? "Top" : "Bottom")
<< " Scheduling instruction in cycle "
<< (IsTopNode ? Top.CurrCycle : Bot.CurrCycle) << " ("
<< reportPackets() << ")\n";
DAG->dumpNode(*SU));
return SU;
}
/// Update the scheduler's state after scheduling a node. This is the same node
/// that was just returned by pickNode(). However, VLIWMachineScheduler needs
/// to update it's state based on the current cycle before MachineSchedStrategy
/// does.
void ConvergingVLIWScheduler::schedNode(SUnit *SU, bool IsTopNode) {
if (IsTopNode) {
Top.bumpNode(SU);
SU->TopReadyCycle = Top.CurrCycle;
} else {
Bot.bumpNode(SU);
SU->BotReadyCycle = Bot.CurrCycle;
}
}
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