1 //===- MachineScheduler.cpp - Machine Instruction Scheduler ---------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // MachineScheduler schedules machine instructions after phi elimination. It
11 // preserves LiveIntervals so it can be invoked before register allocation.
13 //===----------------------------------------------------------------------===//
15 #define DEBUG_TYPE "misched"
17 #include "RegisterClassInfo.h"
18 #include "RegisterPressure.h"
19 #include "llvm/CodeGen/LiveIntervalAnalysis.h"
20 #include "llvm/CodeGen/MachineScheduler.h"
21 #include "llvm/CodeGen/Passes.h"
22 #include "llvm/CodeGen/ScheduleDAGInstrs.h"
23 #include "llvm/Analysis/AliasAnalysis.h"
24 #include "llvm/Target/TargetInstrInfo.h"
25 #include "llvm/Support/CommandLine.h"
26 #include "llvm/Support/Debug.h"
27 #include "llvm/Support/ErrorHandling.h"
28 #include "llvm/Support/raw_ostream.h"
29 #include "llvm/ADT/OwningPtr.h"
30 #include "llvm/ADT/PriorityQueue.h"
36 static cl::opt<bool> ForceTopDown("misched-topdown", cl::Hidden,
37 cl::desc("Force top-down list scheduling"));
38 static cl::opt<bool> ForceBottomUp("misched-bottomup", cl::Hidden,
39 cl::desc("Force bottom-up list scheduling"));
42 static cl::opt<bool> ViewMISchedDAGs("view-misched-dags", cl::Hidden,
43 cl::desc("Pop up a window to show MISched dags after they are processed"));
45 static cl::opt<unsigned> MISchedCutoff("misched-cutoff", cl::Hidden,
46 cl::desc("Stop scheduling after N instructions"), cl::init(~0U));
48 static bool ViewMISchedDAGs = false;
51 //===----------------------------------------------------------------------===//
52 // Machine Instruction Scheduling Pass and Registry
53 //===----------------------------------------------------------------------===//
55 MachineSchedContext::MachineSchedContext():
56 MF(0), MLI(0), MDT(0), PassConfig(0), AA(0), LIS(0) {
57 RegClassInfo = new RegisterClassInfo();
60 MachineSchedContext::~MachineSchedContext() {
65 /// MachineScheduler runs after coalescing and before register allocation.
66 class MachineScheduler : public MachineSchedContext,
67 public MachineFunctionPass {
71 virtual void getAnalysisUsage(AnalysisUsage &AU) const;
73 virtual void releaseMemory() {}
75 virtual bool runOnMachineFunction(MachineFunction&);
77 virtual void print(raw_ostream &O, const Module* = 0) const;
79 static char ID; // Class identification, replacement for typeinfo
83 char MachineScheduler::ID = 0;
85 char &llvm::MachineSchedulerID = MachineScheduler::ID;
87 INITIALIZE_PASS_BEGIN(MachineScheduler, "misched",
88 "Machine Instruction Scheduler", false, false)
89 INITIALIZE_AG_DEPENDENCY(AliasAnalysis)
90 INITIALIZE_PASS_DEPENDENCY(SlotIndexes)
91 INITIALIZE_PASS_DEPENDENCY(LiveIntervals)
92 INITIALIZE_PASS_END(MachineScheduler, "misched",
93 "Machine Instruction Scheduler", false, false)
95 MachineScheduler::MachineScheduler()
96 : MachineFunctionPass(ID) {
97 initializeMachineSchedulerPass(*PassRegistry::getPassRegistry());
100 void MachineScheduler::getAnalysisUsage(AnalysisUsage &AU) const {
101 AU.setPreservesCFG();
102 AU.addRequiredID(MachineDominatorsID);
103 AU.addRequired<MachineLoopInfo>();
104 AU.addRequired<AliasAnalysis>();
105 AU.addRequired<TargetPassConfig>();
106 AU.addRequired<SlotIndexes>();
107 AU.addPreserved<SlotIndexes>();
108 AU.addRequired<LiveIntervals>();
109 AU.addPreserved<LiveIntervals>();
110 MachineFunctionPass::getAnalysisUsage(AU);
113 MachinePassRegistry MachineSchedRegistry::Registry;
115 /// A dummy default scheduler factory indicates whether the scheduler
116 /// is overridden on the command line.
117 static ScheduleDAGInstrs *useDefaultMachineSched(MachineSchedContext *C) {
121 /// MachineSchedOpt allows command line selection of the scheduler.
122 static cl::opt<MachineSchedRegistry::ScheduleDAGCtor, false,
123 RegisterPassParser<MachineSchedRegistry> >
124 MachineSchedOpt("misched",
125 cl::init(&useDefaultMachineSched), cl::Hidden,
126 cl::desc("Machine instruction scheduler to use"));
128 static MachineSchedRegistry
129 DefaultSchedRegistry("default", "Use the target's default scheduler choice.",
130 useDefaultMachineSched);
132 /// Forward declare the standard machine scheduler. This will be used as the
133 /// default scheduler if the target does not set a default.
134 static ScheduleDAGInstrs *createConvergingSched(MachineSchedContext *C);
137 /// Decrement this iterator until reaching the top or a non-debug instr.
138 static MachineBasicBlock::iterator
139 priorNonDebug(MachineBasicBlock::iterator I, MachineBasicBlock::iterator Beg) {
140 assert(I != Beg && "reached the top of the region, cannot decrement");
142 if (!I->isDebugValue())
148 /// If this iterator is a debug value, increment until reaching the End or a
149 /// non-debug instruction.
150 static MachineBasicBlock::iterator
151 nextIfDebug(MachineBasicBlock::iterator I, MachineBasicBlock::iterator End) {
153 if (!I->isDebugValue())
159 /// Top-level MachineScheduler pass driver.
161 /// Visit blocks in function order. Divide each block into scheduling regions
162 /// and visit them bottom-up. Visiting regions bottom-up is not required, but is
163 /// consistent with the DAG builder, which traverses the interior of the
164 /// scheduling regions bottom-up.
166 /// This design avoids exposing scheduling boundaries to the DAG builder,
167 /// simplifying the DAG builder's support for "special" target instructions.
168 /// At the same time the design allows target schedulers to operate across
169 /// scheduling boundaries, for example to bundle the boudary instructions
170 /// without reordering them. This creates complexity, because the target
171 /// scheduler must update the RegionBegin and RegionEnd positions cached by
172 /// ScheduleDAGInstrs whenever adding or removing instructions. A much simpler
173 /// design would be to split blocks at scheduling boundaries, but LLVM has a
174 /// general bias against block splitting purely for implementation simplicity.
175 bool MachineScheduler::runOnMachineFunction(MachineFunction &mf) {
176 // Initialize the context of the pass.
178 MLI = &getAnalysis<MachineLoopInfo>();
179 MDT = &getAnalysis<MachineDominatorTree>();
180 PassConfig = &getAnalysis<TargetPassConfig>();
181 AA = &getAnalysis<AliasAnalysis>();
183 LIS = &getAnalysis<LiveIntervals>();
184 const TargetInstrInfo *TII = MF->getTarget().getInstrInfo();
186 RegClassInfo->runOnMachineFunction(*MF);
188 // Select the scheduler, or set the default.
189 MachineSchedRegistry::ScheduleDAGCtor Ctor = MachineSchedOpt;
190 if (Ctor == useDefaultMachineSched) {
191 // Get the default scheduler set by the target.
192 Ctor = MachineSchedRegistry::getDefault();
194 Ctor = createConvergingSched;
195 MachineSchedRegistry::setDefault(Ctor);
198 // Instantiate the selected scheduler.
199 OwningPtr<ScheduleDAGInstrs> Scheduler(Ctor(this));
201 // Visit all machine basic blocks.
203 // TODO: Visit blocks in global postorder or postorder within the bottom-up
204 // loop tree. Then we can optionally compute global RegPressure.
205 for (MachineFunction::iterator MBB = MF->begin(), MBBEnd = MF->end();
206 MBB != MBBEnd; ++MBB) {
208 Scheduler->startBlock(MBB);
210 // Break the block into scheduling regions [I, RegionEnd), and schedule each
211 // region as soon as it is discovered. RegionEnd points the the scheduling
212 // boundary at the bottom of the region. The DAG does not include RegionEnd,
213 // but the region does (i.e. the next RegionEnd is above the previous
214 // RegionBegin). If the current block has no terminator then RegionEnd ==
215 // MBB->end() for the bottom region.
217 // The Scheduler may insert instructions during either schedule() or
218 // exitRegion(), even for empty regions. So the local iterators 'I' and
219 // 'RegionEnd' are invalid across these calls.
220 unsigned RemainingCount = MBB->size();
221 for(MachineBasicBlock::iterator RegionEnd = MBB->end();
222 RegionEnd != MBB->begin(); RegionEnd = Scheduler->begin()) {
224 // Avoid decrementing RegionEnd for blocks with no terminator.
225 if (RegionEnd != MBB->end()
226 || TII->isSchedulingBoundary(llvm::prior(RegionEnd), MBB, *MF)) {
228 // Count the boundary instruction.
232 // The next region starts above the previous region. Look backward in the
233 // instruction stream until we find the nearest boundary.
234 MachineBasicBlock::iterator I = RegionEnd;
235 for(;I != MBB->begin(); --I, --RemainingCount) {
236 if (TII->isSchedulingBoundary(llvm::prior(I), MBB, *MF))
239 // Notify the scheduler of the region, even if we may skip scheduling
240 // it. Perhaps it still needs to be bundled.
241 Scheduler->enterRegion(MBB, I, RegionEnd, RemainingCount);
243 // Skip empty scheduling regions (0 or 1 schedulable instructions).
244 if (I == RegionEnd || I == llvm::prior(RegionEnd)) {
245 // Close the current region. Bundle the terminator if needed.
246 // This invalidates 'RegionEnd' and 'I'.
247 Scheduler->exitRegion();
250 DEBUG(dbgs() << "MachineScheduling " << MF->getFunction()->getName()
251 << ":BB#" << MBB->getNumber() << "\n From: " << *I << " To: ";
252 if (RegionEnd != MBB->end()) dbgs() << *RegionEnd;
253 else dbgs() << "End";
254 dbgs() << " Remaining: " << RemainingCount << "\n");
256 // Schedule a region: possibly reorder instructions.
257 // This invalidates 'RegionEnd' and 'I'.
258 Scheduler->schedule();
260 // Close the current region.
261 Scheduler->exitRegion();
263 // Scheduling has invalidated the current iterator 'I'. Ask the
264 // scheduler for the top of it's scheduled region.
265 RegionEnd = Scheduler->begin();
267 assert(RemainingCount == 0 && "Instruction count mismatch!");
268 Scheduler->finishBlock();
270 Scheduler->finalizeSchedule();
271 DEBUG(LIS->print(dbgs()));
275 void MachineScheduler::print(raw_ostream &O, const Module* m) const {
279 //===----------------------------------------------------------------------===//
280 // MachineSchedStrategy - Interface to a machine scheduling algorithm.
281 //===----------------------------------------------------------------------===//
286 /// MachineSchedStrategy - Interface used by ScheduleDAGMI to drive the selected
287 /// scheduling algorithm.
289 /// If this works well and targets wish to reuse ScheduleDAGMI, we may expose it
290 /// in ScheduleDAGInstrs.h
291 class MachineSchedStrategy {
293 virtual ~MachineSchedStrategy() {}
295 /// Initialize the strategy after building the DAG for a new region.
296 virtual void initialize(ScheduleDAGMI *DAG) = 0;
298 /// Pick the next node to schedule, or return NULL. Set IsTopNode to true to
299 /// schedule the node at the top of the unscheduled region. Otherwise it will
300 /// be scheduled at the bottom.
301 virtual SUnit *pickNode(bool &IsTopNode) = 0;
303 /// When all predecessor dependencies have been resolved, free this node for
304 /// top-down scheduling.
305 virtual void releaseTopNode(SUnit *SU) = 0;
306 /// When all successor dependencies have been resolved, free this node for
307 /// bottom-up scheduling.
308 virtual void releaseBottomNode(SUnit *SU) = 0;
312 //===----------------------------------------------------------------------===//
313 // ScheduleDAGMI - Base class for MachineInstr scheduling with LiveIntervals
315 //===----------------------------------------------------------------------===//
318 /// ScheduleDAGMI is an implementation of ScheduleDAGInstrs that schedules
319 /// machine instructions while updating LiveIntervals.
320 class ScheduleDAGMI : public ScheduleDAGInstrs {
322 RegisterClassInfo *RegClassInfo;
323 MachineSchedStrategy *SchedImpl;
325 // Register pressure in this region computed by buildSchedGraph.
326 IntervalPressure RegPressure;
327 RegPressureTracker RPTracker;
329 /// The top of the unscheduled zone.
330 MachineBasicBlock::iterator CurrentTop;
332 /// The bottom of the unscheduled zone.
333 MachineBasicBlock::iterator CurrentBottom;
335 /// The number of instructions scheduled so far. Used to cut off the
336 /// scheduler at the point determined by misched-cutoff.
337 unsigned NumInstrsScheduled;
339 ScheduleDAGMI(MachineSchedContext *C, MachineSchedStrategy *S):
340 ScheduleDAGInstrs(*C->MF, *C->MLI, *C->MDT, /*IsPostRA=*/false, C->LIS),
341 AA(C->AA), RegClassInfo(C->RegClassInfo), SchedImpl(S),
342 RPTracker(RegPressure), CurrentTop(), CurrentBottom(),
343 NumInstrsScheduled(0) {}
349 MachineBasicBlock::iterator top() const { return CurrentTop; }
350 MachineBasicBlock::iterator bottom() const { return CurrentBottom; }
352 /// Implement the ScheduleDAGInstrs interface for handling the next scheduling
353 /// region. This covers all instructions in a block, while schedule() may only
355 void enterRegion(MachineBasicBlock *bb,
356 MachineBasicBlock::iterator begin,
357 MachineBasicBlock::iterator end,
360 /// Implement ScheduleDAGInstrs interface for scheduling a sequence of
361 /// reorderable instructions.
365 void moveInstruction(MachineInstr *MI, MachineBasicBlock::iterator InsertPos);
366 bool checkSchedLimit();
368 void releaseSucc(SUnit *SU, SDep *SuccEdge);
369 void releaseSuccessors(SUnit *SU);
370 void releasePred(SUnit *SU, SDep *PredEdge);
371 void releasePredecessors(SUnit *SU);
373 void placeDebugValues();
377 /// ReleaseSucc - Decrement the NumPredsLeft count of a successor. When
378 /// NumPredsLeft reaches zero, release the successor node.
379 void ScheduleDAGMI::releaseSucc(SUnit *SU, SDep *SuccEdge) {
380 SUnit *SuccSU = SuccEdge->getSUnit();
383 if (SuccSU->NumPredsLeft == 0) {
384 dbgs() << "*** Scheduling failed! ***\n";
386 dbgs() << " has been released too many times!\n";
390 --SuccSU->NumPredsLeft;
391 if (SuccSU->NumPredsLeft == 0 && SuccSU != &ExitSU)
392 SchedImpl->releaseTopNode(SuccSU);
395 /// releaseSuccessors - Call releaseSucc on each of SU's successors.
396 void ScheduleDAGMI::releaseSuccessors(SUnit *SU) {
397 for (SUnit::succ_iterator I = SU->Succs.begin(), E = SU->Succs.end();
399 releaseSucc(SU, &*I);
403 /// ReleasePred - Decrement the NumSuccsLeft count of a predecessor. When
404 /// NumSuccsLeft reaches zero, release the predecessor node.
405 void ScheduleDAGMI::releasePred(SUnit *SU, SDep *PredEdge) {
406 SUnit *PredSU = PredEdge->getSUnit();
409 if (PredSU->NumSuccsLeft == 0) {
410 dbgs() << "*** Scheduling failed! ***\n";
412 dbgs() << " has been released too many times!\n";
416 --PredSU->NumSuccsLeft;
417 if (PredSU->NumSuccsLeft == 0 && PredSU != &EntrySU)
418 SchedImpl->releaseBottomNode(PredSU);
421 /// releasePredecessors - Call releasePred on each of SU's predecessors.
422 void ScheduleDAGMI::releasePredecessors(SUnit *SU) {
423 for (SUnit::pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
425 releasePred(SU, &*I);
429 void ScheduleDAGMI::moveInstruction(MachineInstr *MI,
430 MachineBasicBlock::iterator InsertPos) {
431 // Fix RegionBegin if the first instruction moves down.
432 if (&*RegionBegin == MI)
433 RegionBegin = llvm::next(RegionBegin);
434 BB->splice(InsertPos, BB, MI);
436 // Fix RegionBegin if another instruction moves above the first instruction.
437 if (RegionBegin == InsertPos)
441 bool ScheduleDAGMI::checkSchedLimit() {
443 if (NumInstrsScheduled == MISchedCutoff && MISchedCutoff != ~0U) {
444 CurrentTop = CurrentBottom;
447 ++NumInstrsScheduled;
452 /// enterRegion - Called back from MachineScheduler::runOnMachineFunction after
453 /// crossing a scheduling boundary. [begin, end) includes all instructions in
454 /// the region, including the boundary itself and single-instruction regions
455 /// that don't get scheduled.
456 void ScheduleDAGMI::enterRegion(MachineBasicBlock *bb,
457 MachineBasicBlock::iterator begin,
458 MachineBasicBlock::iterator end,
461 ScheduleDAGInstrs::enterRegion(bb, begin, end, endcount);
462 // Setup the register pressure tracker to begin tracking at the end of this
464 RPTracker.init(&MF, RegClassInfo, LIS, BB, end);
467 /// schedule - Called back from MachineScheduler::runOnMachineFunction
468 /// after setting up the current scheduling region. [RegionBegin, RegionEnd)
469 /// only includes instructions that have DAG nodes, not scheduling boundaries.
470 void ScheduleDAGMI::schedule() {
471 while(RPTracker.getPos() != RegionEnd) {
472 bool Moved = RPTracker.recede();
473 assert(Moved && "Regpressure tracker cannot find RegionEnd"); (void)Moved;
477 buildSchedGraph(AA, &RPTracker);
479 DEBUG(dbgs() << "********** MI Scheduling **********\n");
480 DEBUG(for (unsigned su = 0, e = SUnits.size(); su != e; ++su)
481 SUnits[su].dumpAll(this));
483 if (ViewMISchedDAGs) viewGraph();
485 SchedImpl->initialize(this);
487 // Release edges from the special Entry node or to the special Exit node.
488 releaseSuccessors(&EntrySU);
489 releasePredecessors(&ExitSU);
491 // Release all DAG roots for scheduling.
492 for (std::vector<SUnit>::iterator I = SUnits.begin(), E = SUnits.end();
494 // A SUnit is ready to top schedule if it has no predecessors.
495 if (I->Preds.empty())
496 SchedImpl->releaseTopNode(&(*I));
497 // A SUnit is ready to bottom schedule if it has no successors.
498 if (I->Succs.empty())
499 SchedImpl->releaseBottomNode(&(*I));
502 CurrentTop = nextIfDebug(RegionBegin, RegionEnd);
503 CurrentBottom = RegionEnd;
504 bool IsTopNode = false;
505 while (SUnit *SU = SchedImpl->pickNode(IsTopNode)) {
506 DEBUG(dbgs() << "*** " << (IsTopNode ? "Top" : "Bottom")
507 << " Scheduling Instruction:\n"; SU->dump(this));
508 if (!checkSchedLimit())
511 // Move the instruction to its new location in the instruction stream.
512 MachineInstr *MI = SU->getInstr();
515 assert(SU->isTopReady() && "node still has unscheduled dependencies");
516 if (&*CurrentTop == MI)
517 CurrentTop = nextIfDebug(++CurrentTop, CurrentBottom);
519 moveInstruction(MI, CurrentTop);
520 // Release dependent instructions for scheduling.
521 releaseSuccessors(SU);
524 assert(SU->isBottomReady() && "node still has unscheduled dependencies");
525 MachineBasicBlock::iterator priorII =
526 priorNonDebug(CurrentBottom, CurrentTop);
528 CurrentBottom = priorII;
530 if (&*CurrentTop == MI)
531 CurrentTop = nextIfDebug(++CurrentTop, CurrentBottom);
532 moveInstruction(MI, CurrentBottom);
535 // Release dependent instructions for scheduling.
536 releasePredecessors(SU);
538 SU->isScheduled = true;
540 assert(CurrentTop == CurrentBottom && "Nonempty unscheduled zone.");
545 /// Reinsert any remaining debug_values, just like the PostRA scheduler.
546 void ScheduleDAGMI::placeDebugValues() {
547 // If first instruction was a DBG_VALUE then put it back.
549 BB->splice(RegionBegin, BB, FirstDbgValue);
550 RegionBegin = FirstDbgValue;
553 for (std::vector<std::pair<MachineInstr *, MachineInstr *> >::iterator
554 DI = DbgValues.end(), DE = DbgValues.begin(); DI != DE; --DI) {
555 std::pair<MachineInstr *, MachineInstr *> P = *prior(DI);
556 MachineInstr *DbgValue = P.first;
557 MachineBasicBlock::iterator OrigPrevMI = P.second;
558 BB->splice(++OrigPrevMI, BB, DbgValue);
559 if (OrigPrevMI == llvm::prior(RegionEnd))
560 RegionEnd = DbgValue;
563 FirstDbgValue = NULL;
566 //===----------------------------------------------------------------------===//
567 // ConvergingScheduler - Implementation of the standard MachineSchedStrategy.
568 //===----------------------------------------------------------------------===//
571 /// ConvergingScheduler shrinks the unscheduled zone using heuristics to balance
573 class ConvergingScheduler : public MachineSchedStrategy {
576 unsigned NumTopReady;
577 unsigned NumBottomReady;
580 virtual void initialize(ScheduleDAGMI *dag) {
583 assert((!ForceTopDown || !ForceBottomUp) &&
584 "-misched-topdown incompatible with -misched-bottomup");
587 virtual SUnit *pickNode(bool &IsTopNode) {
588 if (DAG->top() == DAG->bottom())
591 // As an initial placeholder heuristic, schedule in the direction that has
592 // the fewest choices.
594 if (ForceTopDown || (!ForceBottomUp && NumTopReady <= NumBottomReady)) {
595 SU = DAG->getSUnit(DAG->top());
599 SU = DAG->getSUnit(priorNonDebug(DAG->bottom(), DAG->top()));
602 if (SU->isTopReady()) {
603 assert(NumTopReady > 0 && "bad ready count");
606 if (SU->isBottomReady()) {
607 assert(NumBottomReady > 0 && "bad ready count");
613 virtual void releaseTopNode(SUnit *SU) {
616 virtual void releaseBottomNode(SUnit *SU) {
622 /// Create the standard converging machine scheduler. This will be used as the
623 /// default scheduler if the target does not set a default.
624 static ScheduleDAGInstrs *createConvergingSched(MachineSchedContext *C) {
625 assert((!ForceTopDown || !ForceBottomUp) &&
626 "-misched-topdown incompatible with -misched-bottomup");
627 return new ScheduleDAGMI(C, new ConvergingScheduler());
629 static MachineSchedRegistry
630 ConvergingSchedRegistry("converge", "Standard converging scheduler.",
631 createConvergingSched);
633 //===----------------------------------------------------------------------===//
634 // Machine Instruction Shuffler for Correctness Testing
635 //===----------------------------------------------------------------------===//
639 /// Apply a less-than relation on the node order, which corresponds to the
640 /// instruction order prior to scheduling. IsReverse implements greater-than.
641 template<bool IsReverse>
643 bool operator()(SUnit *A, SUnit *B) const {
645 return A->NodeNum > B->NodeNum;
647 return A->NodeNum < B->NodeNum;
651 /// Reorder instructions as much as possible.
652 class InstructionShuffler : public MachineSchedStrategy {
656 // Using a less-than relation (SUnitOrder<false>) for the TopQ priority
657 // gives nodes with a higher number higher priority causing the latest
658 // instructions to be scheduled first.
659 PriorityQueue<SUnit*, std::vector<SUnit*>, SUnitOrder<false> >
661 // When scheduling bottom-up, use greater-than as the queue priority.
662 PriorityQueue<SUnit*, std::vector<SUnit*>, SUnitOrder<true> >
665 InstructionShuffler(bool alternate, bool topdown)
666 : IsAlternating(alternate), IsTopDown(topdown) {}
668 virtual void initialize(ScheduleDAGMI *) {
673 /// Implement MachineSchedStrategy interface.
674 /// -----------------------------------------
676 virtual SUnit *pickNode(bool &IsTopNode) {
680 if (TopQ.empty()) return NULL;
683 } while (SU->isScheduled);
688 if (BottomQ.empty()) return NULL;
691 } while (SU->isScheduled);
695 IsTopDown = !IsTopDown;
699 virtual void releaseTopNode(SUnit *SU) {
702 virtual void releaseBottomNode(SUnit *SU) {
708 static ScheduleDAGInstrs *createInstructionShuffler(MachineSchedContext *C) {
709 bool Alternate = !ForceTopDown && !ForceBottomUp;
710 bool TopDown = !ForceBottomUp;
711 assert((TopDown || !ForceTopDown) &&
712 "-misched-topdown incompatible with -misched-bottomup");
713 return new ScheduleDAGMI(C, new InstructionShuffler(Alternate, TopDown));
715 static MachineSchedRegistry ShufflerRegistry(
716 "shuffle", "Shuffle machine instructions alternating directions",
717 createInstructionShuffler);