1//===- VLIWMachineScheduler.cpp - VLIW-Focused Scheduling Pass ------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// MachineScheduler schedules machine instructions after phi elimination. It
10// preserves LiveIntervals so it can be invoked before register allocation.
11//
12//===----------------------------------------------------------------------===//
13
14#include "llvm/CodeGen/VLIWMachineScheduler.h"
15#include "llvm/ADT/SmallVector.h"
16#include "llvm/CodeGen/DFAPacketizer.h"
17#include "llvm/CodeGen/MachineBasicBlock.h"
18#include "llvm/CodeGen/MachineFunction.h"
19#include "llvm/CodeGen/MachineInstr.h"
20#include "llvm/CodeGen/MachineLoopInfo.h"
21#include "llvm/CodeGen/RegisterClassInfo.h"
22#include "llvm/CodeGen/RegisterPressure.h"
23#include "llvm/CodeGen/ScheduleDAG.h"
24#include "llvm/CodeGen/ScheduleHazardRecognizer.h"
25#include "llvm/CodeGen/TargetInstrInfo.h"
26#include "llvm/CodeGen/TargetOpcodes.h"
27#include "llvm/CodeGen/TargetRegisterInfo.h"
28#include "llvm/CodeGen/TargetSchedule.h"
29#include "llvm/CodeGen/TargetSubtargetInfo.h"
30#include "llvm/Support/CommandLine.h"
31#include "llvm/Support/Debug.h"
32#include "llvm/Support/raw_ostream.h"
33#include <algorithm>
34#include <cassert>
35#include <iomanip>
36#include <limits>
37#include <memory>
38#include <sstream>
39
40using namespace llvm;
41
42#define DEBUG_TYPE "machine-scheduler"
43
44static cl::opt<bool> IgnoreBBRegPressure("ignore-bb-reg-pressure", cl::Hidden,
45 cl::init(Val: false));
46
47static cl::opt<bool> UseNewerCandidate("use-newer-candidate", cl::Hidden,
48 cl::init(Val: true));
49
50static cl::opt<unsigned> SchedDebugVerboseLevel("misched-verbose-level",
51 cl::Hidden, cl::init(Val: 1));
52
53// Check if the scheduler should penalize instructions that are available to
54// early due to a zero-latency dependence.
55static cl::opt<bool> CheckEarlyAvail("check-early-avail", cl::Hidden,
56 cl::init(Val: true));
57
58// This value is used to determine if a register class is a high pressure set.
59// We compute the maximum number of registers needed and divided by the total
60// available. Then, we compare the result to this value.
61static cl::opt<float> RPThreshold("vliw-misched-reg-pressure", cl::Hidden,
62 cl::init(Val: 0.75f),
63 cl::desc("High register pressure threhold."));
64
65VLIWResourceModel::VLIWResourceModel(const TargetSubtargetInfo &STI,
66 const TargetSchedModel *SM)
67 : TII(STI.getInstrInfo()), SchedModel(SM) {
68 ResourcesModel = createPacketizer(STI);
69
70 // This hard requirement could be relaxed,
71 // but for now do not let it proceed.
72 assert(ResourcesModel && "Unimplemented CreateTargetScheduleState.");
73
74 Packet.reserve(N: SchedModel->getIssueWidth());
75 Packet.clear();
76 ResourcesModel->clearResources();
77}
78
79void VLIWResourceModel::reset() {
80 Packet.clear();
81 ResourcesModel->clearResources();
82}
83
84VLIWResourceModel::~VLIWResourceModel() { delete ResourcesModel; }
85
86/// Return true if there is a dependence between SUd and SUu.
87bool VLIWResourceModel::hasDependence(const SUnit *SUd, const SUnit *SUu) {
88 if (SUd->Succs.size() == 0)
89 return false;
90
91 for (const auto &S : SUd->Succs) {
92 // Since we do not add pseudos to packets, might as well
93 // ignore order dependencies.
94 if (S.isCtrl())
95 continue;
96
97 if (S.getSUnit() == SUu && S.getLatency() > 0)
98 return true;
99 }
100 return false;
101}
102
103/// Check if scheduling of this SU is possible
104/// in the current packet.
105/// It is _not_ precise (statefull), it is more like
106/// another heuristic. Many corner cases are figured
107/// empirically.
108bool VLIWResourceModel::isResourceAvailable(SUnit *SU, bool IsTop) {
109 if (!SU || !SU->getInstr())
110 return false;
111
112 // First see if the pipeline could receive this instruction
113 // in the current cycle.
114 switch (SU->getInstr()->getOpcode()) {
115 default:
116 if (!ResourcesModel->canReserveResources(MI&: *SU->getInstr()))
117 return false;
118 break;
119 case TargetOpcode::EXTRACT_SUBREG:
120 case TargetOpcode::INSERT_SUBREG:
121 case TargetOpcode::SUBREG_TO_REG:
122 case TargetOpcode::REG_SEQUENCE:
123 case TargetOpcode::IMPLICIT_DEF:
124 case TargetOpcode::COPY:
125 case TargetOpcode::INLINEASM:
126 case TargetOpcode::INLINEASM_BR:
127 break;
128 }
129
130 // Now see if there are no other dependencies to instructions already
131 // in the packet.
132 if (IsTop) {
133 for (unsigned i = 0, e = Packet.size(); i != e; ++i)
134 if (hasDependence(SUd: Packet[i], SUu: SU))
135 return false;
136 } else {
137 for (unsigned i = 0, e = Packet.size(); i != e; ++i)
138 if (hasDependence(SUd: SU, SUu: Packet[i]))
139 return false;
140 }
141 return true;
142}
143
144/// Keep track of available resources.
145bool VLIWResourceModel::reserveResources(SUnit *SU, bool IsTop) {
146 bool startNewCycle = false;
147 // Artificially reset state.
148 if (!SU) {
149 reset();
150 TotalPackets++;
151 return false;
152 }
153 // If this SU does not fit in the packet or the packet is now full
154 // start a new one.
155 if (!isResourceAvailable(SU, IsTop) ||
156 Packet.size() >= SchedModel->getIssueWidth()) {
157 reset();
158 TotalPackets++;
159 startNewCycle = true;
160 }
161
162 switch (SU->getInstr()->getOpcode()) {
163 default:
164 ResourcesModel->reserveResources(MI&: *SU->getInstr());
165 break;
166 case TargetOpcode::EXTRACT_SUBREG:
167 case TargetOpcode::INSERT_SUBREG:
168 case TargetOpcode::SUBREG_TO_REG:
169 case TargetOpcode::REG_SEQUENCE:
170 case TargetOpcode::IMPLICIT_DEF:
171 case TargetOpcode::KILL:
172 case TargetOpcode::CFI_INSTRUCTION:
173 case TargetOpcode::EH_LABEL:
174 case TargetOpcode::COPY:
175 case TargetOpcode::INLINEASM:
176 case TargetOpcode::INLINEASM_BR:
177 break;
178 }
179 Packet.push_back(Elt: SU);
180
181#ifndef NDEBUG
182 LLVM_DEBUG(dbgs() << "Packet[" << TotalPackets << "]:\n");
183 for (unsigned i = 0, e = Packet.size(); i != e; ++i) {
184 LLVM_DEBUG(dbgs() << "\t[" << i << "] SU(");
185 LLVM_DEBUG(dbgs() << Packet[i]->NodeNum << ")\t");
186 LLVM_DEBUG(Packet[i]->getInstr()->dump());
187 }
188#endif
189
190 return startNewCycle;
191}
192
193DFAPacketizer *
194VLIWResourceModel::createPacketizer(const TargetSubtargetInfo &STI) const {
195 return STI.getInstrInfo()->CreateTargetScheduleState(STI);
196}
197
198/// schedule - Called back from MachineScheduler::runOnMachineFunction
199/// after setting up the current scheduling region. [RegionBegin, RegionEnd)
200/// only includes instructions that have DAG nodes, not scheduling boundaries.
201void VLIWMachineScheduler::schedule() {
202 LLVM_DEBUG(dbgs() << "********** MI Converging Scheduling VLIW "
203 << printMBBReference(*BB) << " " << BB->getName()
204 << " in_func " << BB->getParent()->getName()
205 << " at loop depth " << MLI->getLoopDepth(BB) << " \n");
206
207 buildDAGWithRegPressure();
208
209 Topo.InitDAGTopologicalSorting();
210
211 // Postprocess the DAG to add platform-specific artificial dependencies.
212 postProcessDAG();
213
214 SmallVector<SUnit *, 8> TopRoots, BotRoots;
215 findRootsAndBiasEdges(TopRoots, BotRoots);
216
217 // Initialize the strategy before modifying the DAG.
218 SchedImpl->initialize(DAG: this);
219
220 LLVM_DEBUG({
221 unsigned maxH = 0;
222 for (const SUnit &SU : SUnits)
223 if (SU.getHeight() > maxH)
224 maxH = SU.getHeight();
225 dbgs() << "Max Height " << maxH << "\n";
226 });
227 LLVM_DEBUG({
228 unsigned maxD = 0;
229 for (const SUnit &SU : SUnits)
230 if (SU.getDepth() > maxD)
231 maxD = SU.getDepth();
232 dbgs() << "Max Depth " << maxD << "\n";
233 });
234 LLVM_DEBUG(dump());
235 if (ViewMISchedDAGs)
236 viewGraph();
237
238 initQueues(TopRoots, BotRoots);
239
240 bool IsTopNode = false;
241 while (true) {
242 LLVM_DEBUG(
243 dbgs() << "** VLIWMachineScheduler::schedule picking next node\n");
244 SUnit *SU = SchedImpl->pickNode(IsTopNode);
245 if (!SU)
246 break;
247
248 if (!checkSchedLimit())
249 break;
250
251 scheduleMI(SU, IsTopNode);
252
253 // Notify the scheduling strategy after updating the DAG.
254 SchedImpl->schedNode(SU, IsTopNode);
255
256 updateQueues(SU, IsTopNode);
257 }
258 assert(CurrentTop == CurrentBottom && "Nonempty unscheduled zone.");
259
260 placeDebugValues();
261
262 LLVM_DEBUG({
263 dbgs() << "*** Final schedule for "
264 << printMBBReference(*begin()->getParent()) << " ***\n";
265 dumpSchedule();
266 dbgs() << '\n';
267 });
268}
269
270void ConvergingVLIWScheduler::initialize(ScheduleDAGMI *dag) {
271 DAG = static_cast<VLIWMachineScheduler *>(dag);
272 SchedModel = DAG->getSchedModel();
273
274 Top.init(dag: DAG, smodel: SchedModel);
275 Bot.init(dag: DAG, smodel: SchedModel);
276
277 // Initialize the HazardRecognizers. If itineraries don't exist, are empty, or
278 // are disabled, then these HazardRecs will be disabled.
279 const InstrItineraryData *Itin = DAG->getSchedModel()->getInstrItineraries();
280 const TargetSubtargetInfo &STI = DAG->MF.getSubtarget();
281 const TargetInstrInfo *TII = STI.getInstrInfo();
282 delete Top.HazardRec;
283 delete Bot.HazardRec;
284 Top.HazardRec = TII->CreateTargetMIHazardRecognizer(Itin, DAG);
285 Bot.HazardRec = TII->CreateTargetMIHazardRecognizer(Itin, DAG);
286
287 delete Top.ResourceModel;
288 delete Bot.ResourceModel;
289 Top.ResourceModel = createVLIWResourceModel(STI, SchedModel: DAG->getSchedModel());
290 Bot.ResourceModel = createVLIWResourceModel(STI, SchedModel: DAG->getSchedModel());
291
292 const std::vector<unsigned> &MaxPressure =
293 DAG->getRegPressure().MaxSetPressure;
294 HighPressureSets.assign(NumElts: MaxPressure.size(), Elt: false);
295 for (unsigned i = 0, e = MaxPressure.size(); i < e; ++i) {
296 unsigned Limit = DAG->getRegClassInfo()->getRegPressureSetLimit(Idx: i);
297 HighPressureSets[i] =
298 ((float)MaxPressure[i] > ((float)Limit * RPThreshold));
299 }
300
301 assert((!ForceTopDown || !ForceBottomUp) &&
302 "-misched-topdown incompatible with -misched-bottomup");
303}
304
305VLIWResourceModel *ConvergingVLIWScheduler::createVLIWResourceModel(
306 const TargetSubtargetInfo &STI, const TargetSchedModel *SchedModel) const {
307 return new VLIWResourceModel(STI, SchedModel);
308}
309
310void ConvergingVLIWScheduler::releaseTopNode(SUnit *SU) {
311 for (const SDep &PI : SU->Preds) {
312 unsigned PredReadyCycle = PI.getSUnit()->TopReadyCycle;
313 unsigned MinLatency = PI.getLatency();
314#ifndef NDEBUG
315 Top.MaxMinLatency = std::max(a: MinLatency, b: Top.MaxMinLatency);
316#endif
317 if (SU->TopReadyCycle < PredReadyCycle + MinLatency)
318 SU->TopReadyCycle = PredReadyCycle + MinLatency;
319 }
320
321 if (!SU->isScheduled)
322 Top.releaseNode(SU, ReadyCycle: SU->TopReadyCycle);
323}
324
325void ConvergingVLIWScheduler::releaseBottomNode(SUnit *SU) {
326 assert(SU->getInstr() && "Scheduled SUnit must have instr");
327
328 for (SUnit::succ_iterator I = SU->Succs.begin(), E = SU->Succs.end(); I != E;
329 ++I) {
330 unsigned SuccReadyCycle = I->getSUnit()->BotReadyCycle;
331 unsigned MinLatency = I->getLatency();
332#ifndef NDEBUG
333 Bot.MaxMinLatency = std::max(a: MinLatency, b: Bot.MaxMinLatency);
334#endif
335 if (SU->BotReadyCycle < SuccReadyCycle + MinLatency)
336 SU->BotReadyCycle = SuccReadyCycle + MinLatency;
337 }
338
339 if (!SU->isScheduled)
340 Bot.releaseNode(SU, ReadyCycle: SU->BotReadyCycle);
341}
342
343ConvergingVLIWScheduler::VLIWSchedBoundary::~VLIWSchedBoundary() {
344 delete ResourceModel;
345 delete HazardRec;
346}
347
348/// Does this SU have a hazard within the current instruction group.
349///
350/// The scheduler supports two modes of hazard recognition. The first is the
351/// ScheduleHazardRecognizer API. It is a fully general hazard recognizer that
352/// supports highly complicated in-order reservation tables
353/// (ScoreboardHazardRecognizer) and arbitrary target-specific logic.
354///
355/// The second is a streamlined mechanism that checks for hazards based on
356/// simple counters that the scheduler itself maintains. It explicitly checks
357/// for instruction dispatch limitations, including the number of micro-ops that
358/// can dispatch per cycle.
359///
360/// TODO: Also check whether the SU must start a new group.
361bool ConvergingVLIWScheduler::VLIWSchedBoundary::checkHazard(SUnit *SU) {
362 if (HazardRec->isEnabled())
363 return HazardRec->getHazardType(SU) != ScheduleHazardRecognizer::NoHazard;
364
365 unsigned uops = SchedModel->getNumMicroOps(MI: SU->getInstr());
366 if (IssueCount + uops > SchedModel->getIssueWidth())
367 return true;
368
369 return false;
370}
371
372void ConvergingVLIWScheduler::VLIWSchedBoundary::releaseNode(
373 SUnit *SU, unsigned ReadyCycle) {
374 if (ReadyCycle < MinReadyCycle)
375 MinReadyCycle = ReadyCycle;
376
377 // Check for interlocks first. For the purpose of other heuristics, an
378 // instruction that cannot issue appears as if it's not in the ReadyQueue.
379 if (ReadyCycle > CurrCycle || checkHazard(SU))
380
381 Pending.push(SU);
382 else
383 Available.push(SU);
384}
385
386/// Move the boundary of scheduled code by one cycle.
387void ConvergingVLIWScheduler::VLIWSchedBoundary::bumpCycle() {
388 unsigned Width = SchedModel->getIssueWidth();
389 IssueCount = (IssueCount <= Width) ? 0 : IssueCount - Width;
390
391 assert(MinReadyCycle < std::numeric_limits<unsigned>::max() &&
392 "MinReadyCycle uninitialized");
393 unsigned NextCycle = std::max(a: CurrCycle + 1, b: MinReadyCycle);
394
395 if (!HazardRec->isEnabled()) {
396 // Bypass HazardRec virtual calls.
397 CurrCycle = NextCycle;
398 } else {
399 // Bypass getHazardType calls in case of long latency.
400 for (; CurrCycle != NextCycle; ++CurrCycle) {
401 if (isTop())
402 HazardRec->AdvanceCycle();
403 else
404 HazardRec->RecedeCycle();
405 }
406 }
407 CheckPending = true;
408
409 LLVM_DEBUG(dbgs() << "*** Next cycle " << Available.getName() << " cycle "
410 << CurrCycle << '\n');
411}
412
413/// Move the boundary of scheduled code by one SUnit.
414void ConvergingVLIWScheduler::VLIWSchedBoundary::bumpNode(SUnit *SU) {
415 bool startNewCycle = false;
416
417 // Update the reservation table.
418 if (HazardRec->isEnabled()) {
419 if (!isTop() && SU->isCall) {
420 // Calls are scheduled with their preceding instructions. For bottom-up
421 // scheduling, clear the pipeline state before emitting.
422 HazardRec->Reset();
423 }
424 HazardRec->EmitInstruction(SU);
425 }
426
427 // Update DFA model.
428 startNewCycle = ResourceModel->reserveResources(SU, IsTop: isTop());
429
430 // Check the instruction group dispatch limit.
431 // TODO: Check if this SU must end a dispatch group.
432 IssueCount += SchedModel->getNumMicroOps(MI: SU->getInstr());
433 if (startNewCycle) {
434 LLVM_DEBUG(dbgs() << "*** Max instrs at cycle " << CurrCycle << '\n');
435 bumpCycle();
436 } else
437 LLVM_DEBUG(dbgs() << "*** IssueCount " << IssueCount << " at cycle "
438 << CurrCycle << '\n');
439}
440
441/// Release pending ready nodes in to the available queue. This makes them
442/// visible to heuristics.
443void ConvergingVLIWScheduler::VLIWSchedBoundary::releasePending() {
444 // If the available queue is empty, it is safe to reset MinReadyCycle.
445 if (Available.empty())
446 MinReadyCycle = std::numeric_limits<unsigned>::max();
447
448 // Check to see if any of the pending instructions are ready to issue. If
449 // so, add them to the available queue.
450 for (unsigned i = 0, e = Pending.size(); i != e; ++i) {
451 SUnit *SU = *(Pending.begin() + i);
452 unsigned ReadyCycle = isTop() ? SU->TopReadyCycle : SU->BotReadyCycle;
453
454 if (ReadyCycle < MinReadyCycle)
455 MinReadyCycle = ReadyCycle;
456
457 if (ReadyCycle > CurrCycle)
458 continue;
459
460 if (checkHazard(SU))
461 continue;
462
463 Available.push(SU);
464 Pending.remove(I: Pending.begin() + i);
465 --i;
466 --e;
467 }
468 CheckPending = false;
469}
470
471/// Remove SU from the ready set for this boundary.
472void ConvergingVLIWScheduler::VLIWSchedBoundary::removeReady(SUnit *SU) {
473 if (Available.isInQueue(SU))
474 Available.remove(I: Available.find(SU));
475 else {
476 assert(Pending.isInQueue(SU) && "bad ready count");
477 Pending.remove(I: Pending.find(SU));
478 }
479}
480
481/// If this queue only has one ready candidate, return it. As a side effect,
482/// advance the cycle until at least one node is ready. If multiple instructions
483/// are ready, return NULL.
484SUnit *ConvergingVLIWScheduler::VLIWSchedBoundary::pickOnlyChoice() {
485 if (CheckPending)
486 releasePending();
487
488 auto AdvanceCycle = [this]() {
489 if (Available.empty())
490 return true;
491 if (Available.size() == 1 && Pending.size() > 0)
492 return !ResourceModel->isResourceAvailable(SU: *Available.begin(), IsTop: isTop()) ||
493 getWeakLeft(SU: *Available.begin(), isTop: isTop()) != 0;
494 return false;
495 };
496 for (unsigned i = 0; AdvanceCycle(); ++i) {
497 assert(i <= (HazardRec->getMaxLookAhead() + MaxMinLatency) &&
498 "permanent hazard");
499 (void)i;
500 ResourceModel->reserveResources(SU: nullptr, IsTop: isTop());
501 bumpCycle();
502 releasePending();
503 }
504 if (Available.size() == 1)
505 return *Available.begin();
506 return nullptr;
507}
508
509#ifndef NDEBUG
510void ConvergingVLIWScheduler::traceCandidate(const char *Label,
511 const ReadyQueue &Q, SUnit *SU,
512 int Cost, PressureChange P) {
513 dbgs() << Label << " " << Q.getName() << " ";
514 if (P.isValid())
515 dbgs() << DAG->TRI->getRegPressureSetName(Idx: P.getPSet()) << ":"
516 << P.getUnitInc() << " ";
517 else
518 dbgs() << " ";
519 dbgs() << "cost(" << Cost << ")\t";
520 DAG->dumpNode(SU: *SU);
521}
522
523// Very detailed queue dump, to be used with higher verbosity levels.
524void ConvergingVLIWScheduler::readyQueueVerboseDump(
525 const RegPressureTracker &RPTracker, SchedCandidate &Candidate,
526 ReadyQueue &Q) {
527 RegPressureTracker &TempTracker = const_cast<RegPressureTracker &>(RPTracker);
528
529 dbgs() << ">>> " << Q.getName() << "\n";
530 for (ReadyQueue::iterator I = Q.begin(), E = Q.end(); I != E; ++I) {
531 RegPressureDelta RPDelta;
532 TempTracker.getMaxPressureDelta(MI: (*I)->getInstr(), Delta&: RPDelta,
533 CriticalPSets: DAG->getRegionCriticalPSets(),
534 MaxPressureLimit: DAG->getRegPressure().MaxSetPressure);
535 std::stringstream dbgstr;
536 dbgstr << "SU(" << std::setw(3) << (*I)->NodeNum << ")";
537 dbgs() << dbgstr.str();
538 SchedulingCost(Q, SU: *I, Candidate, Delta&: RPDelta, verbose: true);
539 dbgs() << "\t";
540 (*I)->getInstr()->dump();
541 }
542 dbgs() << "\n";
543}
544#endif
545
546/// isSingleUnscheduledPred - If SU2 is the only unscheduled predecessor
547/// of SU, return true (we may have duplicates)
548static inline bool isSingleUnscheduledPred(SUnit *SU, SUnit *SU2) {
549 if (SU->NumPredsLeft == 0)
550 return false;
551
552 for (auto &Pred : SU->Preds) {
553 // We found an available, but not scheduled, predecessor.
554 if (!Pred.getSUnit()->isScheduled && (Pred.getSUnit() != SU2))
555 return false;
556 }
557
558 return true;
559}
560
561/// isSingleUnscheduledSucc - If SU2 is the only unscheduled successor
562/// of SU, return true (we may have duplicates)
563static inline bool isSingleUnscheduledSucc(SUnit *SU, SUnit *SU2) {
564 if (SU->NumSuccsLeft == 0)
565 return false;
566
567 for (auto &Succ : SU->Succs) {
568 // We found an available, but not scheduled, successor.
569 if (!Succ.getSUnit()->isScheduled && (Succ.getSUnit() != SU2))
570 return false;
571 }
572 return true;
573}
574
575/// Check if the instruction changes the register pressure of a register in the
576/// high pressure set. The function returns a negative value if the pressure
577/// decreases and a positive value is the pressure increases. If the instruction
578/// doesn't use a high pressure register or doesn't change the register
579/// pressure, then return 0.
580int ConvergingVLIWScheduler::pressureChange(const SUnit *SU, bool isBotUp) {
581 PressureDiff &PD = DAG->getPressureDiff(SU);
582 for (const auto &P : PD) {
583 if (!P.isValid())
584 continue;
585 // The pressure differences are computed bottom-up, so the comparison for
586 // an increase is positive in the bottom direction, but negative in the
587 // top-down direction.
588 if (HighPressureSets[P.getPSet()])
589 return (isBotUp ? P.getUnitInc() : -P.getUnitInc());
590 }
591 return 0;
592}
593
594/// Single point to compute overall scheduling cost.
595/// TODO: More heuristics will be used soon.
596int ConvergingVLIWScheduler::SchedulingCost(ReadyQueue &Q, SUnit *SU,
597 SchedCandidate &Candidate,
598 RegPressureDelta &Delta,
599 bool verbose) {
600 // Initial trivial priority.
601 int ResCount = 1;
602
603 // Do not waste time on a node that is already scheduled.
604 if (!SU || SU->isScheduled)
605 return ResCount;
606
607 LLVM_DEBUG(if (verbose) dbgs()
608 << ((Q.getID() == TopQID) ? "(top|" : "(bot|"));
609 // Forced priority is high.
610 if (SU->isScheduleHigh) {
611 ResCount += PriorityOne;
612 LLVM_DEBUG(dbgs() << "H|");
613 }
614
615 unsigned IsAvailableAmt = 0;
616 // Critical path first.
617 if (Q.getID() == TopQID) {
618 if (Top.isLatencyBound(SU)) {
619 LLVM_DEBUG(if (verbose) dbgs() << "LB|");
620 ResCount += (SU->getHeight() * ScaleTwo);
621 }
622
623 LLVM_DEBUG(if (verbose) {
624 std::stringstream dbgstr;
625 dbgstr << "h" << std::setw(3) << SU->getHeight() << "|";
626 dbgs() << dbgstr.str();
627 });
628
629 // If resources are available for it, multiply the
630 // chance of scheduling.
631 if (Top.ResourceModel->isResourceAvailable(SU, IsTop: true)) {
632 IsAvailableAmt = (PriorityTwo + PriorityThree);
633 ResCount += IsAvailableAmt;
634 LLVM_DEBUG(if (verbose) dbgs() << "A|");
635 } else
636 LLVM_DEBUG(if (verbose) dbgs() << " |");
637 } else {
638 if (Bot.isLatencyBound(SU)) {
639 LLVM_DEBUG(if (verbose) dbgs() << "LB|");
640 ResCount += (SU->getDepth() * ScaleTwo);
641 }
642
643 LLVM_DEBUG(if (verbose) {
644 std::stringstream dbgstr;
645 dbgstr << "d" << std::setw(3) << SU->getDepth() << "|";
646 dbgs() << dbgstr.str();
647 });
648
649 // If resources are available for it, multiply the
650 // chance of scheduling.
651 if (Bot.ResourceModel->isResourceAvailable(SU, IsTop: false)) {
652 IsAvailableAmt = (PriorityTwo + PriorityThree);
653 ResCount += IsAvailableAmt;
654 LLVM_DEBUG(if (verbose) dbgs() << "A|");
655 } else
656 LLVM_DEBUG(if (verbose) dbgs() << " |");
657 }
658
659 unsigned NumNodesBlocking = 0;
660 if (Q.getID() == TopQID) {
661 // How many SUs does it block from scheduling?
662 // Look at all of the successors of this node.
663 // Count the number of nodes that
664 // this node is the sole unscheduled node for.
665 if (Top.isLatencyBound(SU))
666 for (const SDep &SI : SU->Succs)
667 if (isSingleUnscheduledPred(SU: SI.getSUnit(), SU2: SU))
668 ++NumNodesBlocking;
669 } else {
670 // How many unscheduled predecessors block this node?
671 if (Bot.isLatencyBound(SU))
672 for (const SDep &PI : SU->Preds)
673 if (isSingleUnscheduledSucc(SU: PI.getSUnit(), SU2: SU))
674 ++NumNodesBlocking;
675 }
676 ResCount += (NumNodesBlocking * ScaleTwo);
677
678 LLVM_DEBUG(if (verbose) {
679 std::stringstream dbgstr;
680 dbgstr << "blk " << std::setw(2) << NumNodesBlocking << ")|";
681 dbgs() << dbgstr.str();
682 });
683
684 // Factor in reg pressure as a heuristic.
685 if (!IgnoreBBRegPressure) {
686 // Decrease priority by the amount that register pressure exceeds the limit.
687 ResCount -= (Delta.Excess.getUnitInc() * PriorityOne);
688 // Decrease priority if register pressure exceeds the limit.
689 ResCount -= (Delta.CriticalMax.getUnitInc() * PriorityOne);
690 // Decrease priority slightly if register pressure would increase over the
691 // current maximum.
692 ResCount -= (Delta.CurrentMax.getUnitInc() * PriorityTwo);
693 // If there are register pressure issues, then we remove the value added for
694 // the instruction being available. The rationale is that we really don't
695 // want to schedule an instruction that causes a spill.
696 if (IsAvailableAmt && pressureChange(SU, isBotUp: Q.getID() != TopQID) > 0 &&
697 (Delta.Excess.getUnitInc() || Delta.CriticalMax.getUnitInc() ||
698 Delta.CurrentMax.getUnitInc()))
699 ResCount -= IsAvailableAmt;
700 LLVM_DEBUG(if (verbose) {
701 dbgs() << "RP " << Delta.Excess.getUnitInc() << "/"
702 << Delta.CriticalMax.getUnitInc() << "/"
703 << Delta.CurrentMax.getUnitInc() << ")|";
704 });
705 }
706
707 // Give preference to a zero latency instruction if the dependent
708 // instruction is in the current packet.
709 if (Q.getID() == TopQID && getWeakLeft(SU, isTop: true) == 0) {
710 for (const SDep &PI : SU->Preds) {
711 if (!PI.getSUnit()->getInstr()->isPseudo() && PI.isAssignedRegDep() &&
712 PI.getLatency() == 0 &&
713 Top.ResourceModel->isInPacket(SU: PI.getSUnit())) {
714 ResCount += PriorityThree;
715 LLVM_DEBUG(if (verbose) dbgs() << "Z|");
716 }
717 }
718 } else if (Q.getID() == BotQID && getWeakLeft(SU, isTop: false) == 0) {
719 for (const SDep &SI : SU->Succs) {
720 if (!SI.getSUnit()->getInstr()->isPseudo() && SI.isAssignedRegDep() &&
721 SI.getLatency() == 0 &&
722 Bot.ResourceModel->isInPacket(SU: SI.getSUnit())) {
723 ResCount += PriorityThree;
724 LLVM_DEBUG(if (verbose) dbgs() << "Z|");
725 }
726 }
727 }
728
729 // If the instruction has a non-zero latency dependence with an instruction in
730 // the current packet, then it should not be scheduled yet. The case occurs
731 // when the dependent instruction is scheduled in a new packet, so the
732 // scheduler updates the current cycle and pending instructions become
733 // available.
734 if (CheckEarlyAvail) {
735 if (Q.getID() == TopQID) {
736 for (const auto &PI : SU->Preds) {
737 if (PI.getLatency() > 0 &&
738 Top.ResourceModel->isInPacket(SU: PI.getSUnit())) {
739 ResCount -= PriorityOne;
740 LLVM_DEBUG(if (verbose) dbgs() << "D|");
741 }
742 }
743 } else {
744 for (const auto &SI : SU->Succs) {
745 if (SI.getLatency() > 0 &&
746 Bot.ResourceModel->isInPacket(SU: SI.getSUnit())) {
747 ResCount -= PriorityOne;
748 LLVM_DEBUG(if (verbose) dbgs() << "D|");
749 }
750 }
751 }
752 }
753
754 LLVM_DEBUG(if (verbose) {
755 std::stringstream dbgstr;
756 dbgstr << "Total " << std::setw(4) << ResCount << ")";
757 dbgs() << dbgstr.str();
758 });
759
760 return ResCount;
761}
762
763/// Pick the best candidate from the top queue.
764///
765/// TODO: getMaxPressureDelta results can be mostly cached for each SUnit during
766/// DAG building. To adjust for the current scheduling location we need to
767/// maintain the number of vreg uses remaining to be top-scheduled.
768ConvergingVLIWScheduler::CandResult
769ConvergingVLIWScheduler::pickNodeFromQueue(VLIWSchedBoundary &Zone,
770 const RegPressureTracker &RPTracker,
771 SchedCandidate &Candidate) {
772 ReadyQueue &Q = Zone.Available;
773 LLVM_DEBUG(if (SchedDebugVerboseLevel > 1)
774 readyQueueVerboseDump(RPTracker, Candidate, Q);
775 else Q.dump(););
776
777 // getMaxPressureDelta temporarily modifies the tracker.
778 RegPressureTracker &TempTracker = const_cast<RegPressureTracker &>(RPTracker);
779
780 // BestSU remains NULL if no top candidates beat the best existing candidate.
781 CandResult FoundCandidate = NoCand;
782 for (ReadyQueue::iterator I = Q.begin(), E = Q.end(); I != E; ++I) {
783 RegPressureDelta RPDelta;
784 TempTracker.getMaxPressureDelta(MI: (*I)->getInstr(), Delta&: RPDelta,
785 CriticalPSets: DAG->getRegionCriticalPSets(),
786 MaxPressureLimit: DAG->getRegPressure().MaxSetPressure);
787
788 int CurrentCost = SchedulingCost(Q, SU: *I, Candidate, Delta&: RPDelta, verbose: false);
789
790 // Initialize the candidate if needed.
791 if (!Candidate.SU) {
792 LLVM_DEBUG(traceCandidate("DCAND", Q, *I, CurrentCost));
793 Candidate.SU = *I;
794 Candidate.RPDelta = RPDelta;
795 Candidate.SCost = CurrentCost;
796 FoundCandidate = NodeOrder;
797 continue;
798 }
799
800 // Choose node order for negative cost candidates. There is no good
801 // candidate in this case.
802 if (CurrentCost < 0 && Candidate.SCost < 0) {
803 if ((Q.getID() == TopQID && (*I)->NodeNum < Candidate.SU->NodeNum) ||
804 (Q.getID() == BotQID && (*I)->NodeNum > Candidate.SU->NodeNum)) {
805 LLVM_DEBUG(traceCandidate("NCAND", Q, *I, CurrentCost));
806 Candidate.SU = *I;
807 Candidate.RPDelta = RPDelta;
808 Candidate.SCost = CurrentCost;
809 FoundCandidate = NodeOrder;
810 }
811 continue;
812 }
813
814 // Best cost.
815 if (CurrentCost > Candidate.SCost) {
816 LLVM_DEBUG(traceCandidate("CCAND", Q, *I, CurrentCost));
817 Candidate.SU = *I;
818 Candidate.RPDelta = RPDelta;
819 Candidate.SCost = CurrentCost;
820 FoundCandidate = BestCost;
821 continue;
822 }
823
824 // Choose an instruction that does not depend on an artificial edge.
825 unsigned CurrWeak = getWeakLeft(SU: *I, isTop: (Q.getID() == TopQID));
826 unsigned CandWeak = getWeakLeft(SU: Candidate.SU, isTop: (Q.getID() == TopQID));
827 if (CurrWeak != CandWeak) {
828 if (CurrWeak < CandWeak) {
829 LLVM_DEBUG(traceCandidate("WCAND", Q, *I, CurrentCost));
830 Candidate.SU = *I;
831 Candidate.RPDelta = RPDelta;
832 Candidate.SCost = CurrentCost;
833 FoundCandidate = Weak;
834 }
835 continue;
836 }
837
838 if (CurrentCost == Candidate.SCost && Zone.isLatencyBound(SU: *I)) {
839 unsigned CurrSize, CandSize;
840 if (Q.getID() == TopQID) {
841 CurrSize = (*I)->Succs.size();
842 CandSize = Candidate.SU->Succs.size();
843 } else {
844 CurrSize = (*I)->Preds.size();
845 CandSize = Candidate.SU->Preds.size();
846 }
847 if (CurrSize > CandSize) {
848 LLVM_DEBUG(traceCandidate("SPCAND", Q, *I, CurrentCost));
849 Candidate.SU = *I;
850 Candidate.RPDelta = RPDelta;
851 Candidate.SCost = CurrentCost;
852 FoundCandidate = BestCost;
853 }
854 // Keep the old candidate if it's a better candidate. That is, don't use
855 // the subsequent tie breaker.
856 if (CurrSize != CandSize)
857 continue;
858 }
859
860 // Tie breaker.
861 // To avoid scheduling indeterminism, we need a tie breaker
862 // for the case when cost is identical for two nodes.
863 if (UseNewerCandidate && CurrentCost == Candidate.SCost) {
864 if ((Q.getID() == TopQID && (*I)->NodeNum < Candidate.SU->NodeNum) ||
865 (Q.getID() == BotQID && (*I)->NodeNum > Candidate.SU->NodeNum)) {
866 LLVM_DEBUG(traceCandidate("TCAND", Q, *I, CurrentCost));
867 Candidate.SU = *I;
868 Candidate.RPDelta = RPDelta;
869 Candidate.SCost = CurrentCost;
870 FoundCandidate = NodeOrder;
871 continue;
872 }
873 }
874
875 // Fall through to original instruction order.
876 // Only consider node order if Candidate was chosen from this Q.
877 if (FoundCandidate == NoCand)
878 continue;
879 }
880 return FoundCandidate;
881}
882
883/// Pick the best candidate node from either the top or bottom queue.
884SUnit *ConvergingVLIWScheduler::pickNodeBidrectional(bool &IsTopNode) {
885 // Schedule as far as possible in the direction of no choice. This is most
886 // efficient, but also provides the best heuristics for CriticalPSets.
887 if (SUnit *SU = Bot.pickOnlyChoice()) {
888 LLVM_DEBUG(dbgs() << "Picked only Bottom\n");
889 IsTopNode = false;
890 return SU;
891 }
892 if (SUnit *SU = Top.pickOnlyChoice()) {
893 LLVM_DEBUG(dbgs() << "Picked only Top\n");
894 IsTopNode = true;
895 return SU;
896 }
897 SchedCandidate BotCand;
898 // Prefer bottom scheduling when heuristics are silent.
899 CandResult BotResult =
900 pickNodeFromQueue(Zone&: Bot, RPTracker: DAG->getBotRPTracker(), Candidate&: BotCand);
901 assert(BotResult != NoCand && "failed to find the first candidate");
902
903 // If either Q has a single candidate that provides the least increase in
904 // Excess pressure, we can immediately schedule from that Q.
905 //
906 // RegionCriticalPSets summarizes the pressure within the scheduled region and
907 // affects picking from either Q. If scheduling in one direction must
908 // increase pressure for one of the excess PSets, then schedule in that
909 // direction first to provide more freedom in the other direction.
910 if (BotResult == SingleExcess || BotResult == SingleCritical) {
911 LLVM_DEBUG(dbgs() << "Prefered Bottom Node\n");
912 IsTopNode = false;
913 return BotCand.SU;
914 }
915 // Check if the top Q has a better candidate.
916 SchedCandidate TopCand;
917 CandResult TopResult =
918 pickNodeFromQueue(Zone&: Top, RPTracker: DAG->getTopRPTracker(), Candidate&: TopCand);
919 assert(TopResult != NoCand && "failed to find the first candidate");
920
921 if (TopResult == SingleExcess || TopResult == SingleCritical) {
922 LLVM_DEBUG(dbgs() << "Prefered Top Node\n");
923 IsTopNode = true;
924 return TopCand.SU;
925 }
926 // If either Q has a single candidate that minimizes pressure above the
927 // original region's pressure pick it.
928 if (BotResult == SingleMax) {
929 LLVM_DEBUG(dbgs() << "Prefered Bottom Node SingleMax\n");
930 IsTopNode = false;
931 return BotCand.SU;
932 }
933 if (TopResult == SingleMax) {
934 LLVM_DEBUG(dbgs() << "Prefered Top Node SingleMax\n");
935 IsTopNode = true;
936 return TopCand.SU;
937 }
938 if (TopCand.SCost > BotCand.SCost) {
939 LLVM_DEBUG(dbgs() << "Prefered Top Node Cost\n");
940 IsTopNode = true;
941 return TopCand.SU;
942 }
943 // Otherwise prefer the bottom candidate in node order.
944 LLVM_DEBUG(dbgs() << "Prefered Bottom in Node order\n");
945 IsTopNode = false;
946 return BotCand.SU;
947}
948
949/// Pick the best node to balance the schedule. Implements MachineSchedStrategy.
950SUnit *ConvergingVLIWScheduler::pickNode(bool &IsTopNode) {
951 if (DAG->top() == DAG->bottom()) {
952 assert(Top.Available.empty() && Top.Pending.empty() &&
953 Bot.Available.empty() && Bot.Pending.empty() && "ReadyQ garbage");
954 return nullptr;
955 }
956 SUnit *SU;
957 if (ForceTopDown) {
958 SU = Top.pickOnlyChoice();
959 if (!SU) {
960 SchedCandidate TopCand;
961 CandResult TopResult =
962 pickNodeFromQueue(Zone&: Top, RPTracker: DAG->getTopRPTracker(), Candidate&: TopCand);
963 assert(TopResult != NoCand && "failed to find the first candidate");
964 (void)TopResult;
965 SU = TopCand.SU;
966 }
967 IsTopNode = true;
968 } else if (ForceBottomUp) {
969 SU = Bot.pickOnlyChoice();
970 if (!SU) {
971 SchedCandidate BotCand;
972 CandResult BotResult =
973 pickNodeFromQueue(Zone&: Bot, RPTracker: DAG->getBotRPTracker(), Candidate&: BotCand);
974 assert(BotResult != NoCand && "failed to find the first candidate");
975 (void)BotResult;
976 SU = BotCand.SU;
977 }
978 IsTopNode = false;
979 } else {
980 SU = pickNodeBidrectional(IsTopNode);
981 }
982 if (SU->isTopReady())
983 Top.removeReady(SU);
984 if (SU->isBottomReady())
985 Bot.removeReady(SU);
986
987 LLVM_DEBUG(dbgs() << "*** " << (IsTopNode ? "Top" : "Bottom")
988 << " Scheduling instruction in cycle "
989 << (IsTopNode ? Top.CurrCycle : Bot.CurrCycle) << " ("
990 << reportPackets() << ")\n";
991 DAG->dumpNode(*SU));
992 return SU;
993}
994
995/// Update the scheduler's state after scheduling a node. This is the same node
996/// that was just returned by pickNode(). However, VLIWMachineScheduler needs
997/// to update it's state based on the current cycle before MachineSchedStrategy
998/// does.
999void ConvergingVLIWScheduler::schedNode(SUnit *SU, bool IsTopNode) {
1000 if (IsTopNode) {
1001 Top.bumpNode(SU);
1002 SU->TopReadyCycle = Top.CurrCycle;
1003 } else {
1004 Bot.bumpNode(SU);
1005 SU->BotReadyCycle = Bot.CurrCycle;
1006 }
1007}
1008

source code of llvm/lib/CodeGen/VLIWMachineScheduler.cpp