LLVM 19.0.0git
BlockFrequencyInfoImpl.cpp
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1//===- BlockFrequencyImplInfo.cpp - Block Frequency Info Implementation ---===//
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// Loops should be simplified before this analysis.
10//
11//===----------------------------------------------------------------------===//
12
14#include "llvm/ADT/APInt.h"
15#include "llvm/ADT/DenseMap.h"
18#include "llvm/Config/llvm-config.h"
19#include "llvm/IR/Function.h"
23#include "llvm/Support/Debug.h"
27#include <algorithm>
28#include <cassert>
29#include <cstddef>
30#include <cstdint>
31#include <iterator>
32#include <list>
33#include <numeric>
34#include <optional>
35#include <utility>
36#include <vector>
37
38using namespace llvm;
39using namespace llvm::bfi_detail;
40
41#define DEBUG_TYPE "block-freq"
42
43namespace llvm {
45 "check-bfi-unknown-block-queries",
46 cl::init(false), cl::Hidden,
47 cl::desc("Check if block frequency is queried for an unknown block "
48 "for debugging missed BFI updates"));
49
51 "use-iterative-bfi-inference", cl::Hidden,
52 cl::desc("Apply an iterative post-processing to infer correct BFI counts"));
53
55 "iterative-bfi-max-iterations-per-block", cl::init(1000), cl::Hidden,
56 cl::desc("Iterative inference: maximum number of update iterations "
57 "per block"));
58
60 "iterative-bfi-precision", cl::init(1e-12), cl::Hidden,
61 cl::desc("Iterative inference: delta convergence precision; smaller values "
62 "typically lead to better results at the cost of worsen runtime"));
63} // namespace llvm
64
66 if (isFull())
67 return ScaledNumber<uint64_t>(1, 0);
68 return ScaledNumber<uint64_t>(getMass() + 1, -64);
69}
70
71#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
73#endif
74
75static char getHexDigit(int N) {
76 assert(N < 16);
77 if (N < 10)
78 return '0' + N;
79 return 'a' + N - 10;
80}
81
83 for (int Digits = 0; Digits < 16; ++Digits)
84 OS << getHexDigit(Mass >> (60 - Digits * 4) & 0xf);
85 return OS;
86}
87
88namespace {
89
97
98/// Dithering mass distributer.
99///
100/// This class splits up a single mass into portions by weight, dithering to
101/// spread out error. No mass is lost. The dithering precision depends on the
102/// precision of the product of \a BlockMass and \a BranchProbability.
103///
104/// The distribution algorithm follows.
105///
106/// 1. Initialize by saving the sum of the weights in \a RemWeight and the
107/// mass to distribute in \a RemMass.
108///
109/// 2. For each portion:
110///
111/// 1. Construct a branch probability, P, as the portion's weight divided
112/// by the current value of \a RemWeight.
113/// 2. Calculate the portion's mass as \a RemMass times P.
114/// 3. Update \a RemWeight and \a RemMass at each portion by subtracting
115/// the current portion's weight and mass.
116struct DitheringDistributer {
117 uint32_t RemWeight;
118 BlockMass RemMass;
119
120 DitheringDistributer(Distribution &Dist, const BlockMass &Mass);
121
122 BlockMass takeMass(uint32_t Weight);
123};
124
125} // end anonymous namespace
126
127DitheringDistributer::DitheringDistributer(Distribution &Dist,
128 const BlockMass &Mass) {
129 Dist.normalize();
130 RemWeight = Dist.Total;
131 RemMass = Mass;
132}
133
134BlockMass DitheringDistributer::takeMass(uint32_t Weight) {
135 assert(Weight && "invalid weight");
136 assert(Weight <= RemWeight);
137 BlockMass Mass = RemMass * BranchProbability(Weight, RemWeight);
138
139 // Decrement totals (dither).
140 RemWeight -= Weight;
141 RemMass -= Mass;
142 return Mass;
143}
144
145void Distribution::add(const BlockNode &Node, uint64_t Amount,
146 Weight::DistType Type) {
147 assert(Amount && "invalid weight of 0");
148 uint64_t NewTotal = Total + Amount;
149
150 // Check for overflow. It should be impossible to overflow twice.
151 bool IsOverflow = NewTotal < Total;
152 assert(!(DidOverflow && IsOverflow) && "unexpected repeated overflow");
153 DidOverflow |= IsOverflow;
154
155 // Update the total.
156 Total = NewTotal;
157
158 // Save the weight.
159 Weights.push_back(Weight(Type, Node, Amount));
160}
161
162static void combineWeight(Weight &W, const Weight &OtherW) {
163 assert(OtherW.TargetNode.isValid());
164 if (!W.Amount) {
165 W = OtherW;
166 return;
167 }
168 assert(W.Type == OtherW.Type);
169 assert(W.TargetNode == OtherW.TargetNode);
170 assert(OtherW.Amount && "Expected non-zero weight");
171 if (W.Amount > W.Amount + OtherW.Amount)
172 // Saturate on overflow.
173 W.Amount = UINT64_MAX;
174 else
175 W.Amount += OtherW.Amount;
176}
177
178static void combineWeightsBySorting(WeightList &Weights) {
179 // Sort so edges to the same node are adjacent.
180 llvm::sort(Weights, [](const Weight &L, const Weight &R) {
181 return L.TargetNode < R.TargetNode;
182 });
183
184 // Combine adjacent edges.
185 WeightList::iterator O = Weights.begin();
186 for (WeightList::const_iterator I = O, L = O, E = Weights.end(); I != E;
187 ++O, (I = L)) {
188 *O = *I;
189
190 // Find the adjacent weights to the same node.
191 for (++L; L != E && I->TargetNode == L->TargetNode; ++L)
192 combineWeight(*O, *L);
193 }
194
195 // Erase extra entries.
196 Weights.erase(O, Weights.end());
197}
198
199static void combineWeightsByHashing(WeightList &Weights) {
200 // Collect weights into a DenseMap.
202
203 HashTable Combined(NextPowerOf2(2 * Weights.size()));
204 for (const Weight &W : Weights)
205 combineWeight(Combined[W.TargetNode.Index], W);
206
207 // Check whether anything changed.
208 if (Weights.size() == Combined.size())
209 return;
210
211 // Fill in the new weights.
212 Weights.clear();
213 Weights.reserve(Combined.size());
214 for (const auto &I : Combined)
215 Weights.push_back(I.second);
216}
217
218static void combineWeights(WeightList &Weights) {
219 // Use a hash table for many successors to keep this linear.
220 if (Weights.size() > 128) {
222 return;
223 }
224
226}
227
229 assert(Shift >= 0);
230 assert(Shift < 64);
231 if (!Shift)
232 return N;
233 return (N >> Shift) + (UINT64_C(1) & N >> (Shift - 1));
234}
235
236void Distribution::normalize() {
237 // Early exit for termination nodes.
238 if (Weights.empty())
239 return;
240
241 // Only bother if there are multiple successors.
242 if (Weights.size() > 1)
243 combineWeights(Weights);
244
245 // Early exit when combined into a single successor.
246 if (Weights.size() == 1) {
247 Total = 1;
248 Weights.front().Amount = 1;
249 return;
250 }
251
252 // Determine how much to shift right so that the total fits into 32-bits.
253 //
254 // If we shift at all, shift by 1 extra. Otherwise, the lower limit of 1
255 // for each weight can cause a 32-bit overflow.
256 int Shift = 0;
257 if (DidOverflow)
258 Shift = 33;
259 else if (Total > UINT32_MAX)
260 Shift = 33 - llvm::countl_zero(Total);
261
262 // Early exit if nothing needs to be scaled.
263 if (!Shift) {
264 // If we didn't overflow then combineWeights() shouldn't have changed the
265 // sum of the weights, but let's double-check.
266 assert(Total == std::accumulate(Weights.begin(), Weights.end(), UINT64_C(0),
267 [](uint64_t Sum, const Weight &W) {
268 return Sum + W.Amount;
269 }) &&
270 "Expected total to be correct");
271 return;
272 }
273
274 // Recompute the total through accumulation (rather than shifting it) so that
275 // it's accurate after shifting and any changes combineWeights() made above.
276 Total = 0;
277
278 // Sum the weights to each node and shift right if necessary.
279 for (Weight &W : Weights) {
280 // Scale down below UINT32_MAX. Since Shift is larger than necessary, we
281 // can round here without concern about overflow.
282 assert(W.TargetNode.isValid());
283 W.Amount = std::max(UINT64_C(1), shiftRightAndRound(W.Amount, Shift));
284 assert(W.Amount <= UINT32_MAX);
285
286 // Update the total.
287 Total += W.Amount;
288 }
289 assert(Total <= UINT32_MAX);
290}
291
293 // Swap with a default-constructed std::vector, since std::vector<>::clear()
294 // does not actually clear heap storage.
295 std::vector<FrequencyData>().swap(Freqs);
296 IsIrrLoopHeader.clear();
297 std::vector<WorkingData>().swap(Working);
298 Loops.clear();
299}
300
301/// Clear all memory not needed downstream.
302///
303/// Releases all memory not used downstream. In particular, saves Freqs.
305 std::vector<FrequencyData> SavedFreqs(std::move(BFI.Freqs));
306 SparseBitVector<> SavedIsIrrLoopHeader(std::move(BFI.IsIrrLoopHeader));
307 BFI.clear();
308 BFI.Freqs = std::move(SavedFreqs);
309 BFI.IsIrrLoopHeader = std::move(SavedIsIrrLoopHeader);
310}
311
313 const LoopData *OuterLoop,
314 const BlockNode &Pred,
315 const BlockNode &Succ,
317 if (!Weight)
318 Weight = 1;
319
320 auto isLoopHeader = [&OuterLoop](const BlockNode &Node) {
321 return OuterLoop && OuterLoop->isHeader(Node);
322 };
323
324 BlockNode Resolved = Working[Succ.Index].getResolvedNode();
325
326#ifndef NDEBUG
327 auto debugSuccessor = [&](const char *Type) {
328 dbgs() << " =>"
329 << " [" << Type << "] weight = " << Weight;
330 if (!isLoopHeader(Resolved))
331 dbgs() << ", succ = " << getBlockName(Succ);
332 if (Resolved != Succ)
333 dbgs() << ", resolved = " << getBlockName(Resolved);
334 dbgs() << "\n";
335 };
336 (void)debugSuccessor;
337#endif
338
339 if (isLoopHeader(Resolved)) {
340 LLVM_DEBUG(debugSuccessor("backedge"));
341 Dist.addBackedge(Resolved, Weight);
342 return true;
343 }
344
345 if (Working[Resolved.Index].getContainingLoop() != OuterLoop) {
346 LLVM_DEBUG(debugSuccessor(" exit "));
347 Dist.addExit(Resolved, Weight);
348 return true;
349 }
350
351 if (Resolved < Pred) {
352 if (!isLoopHeader(Pred)) {
353 // If OuterLoop is an irreducible loop, we can't actually handle this.
354 assert((!OuterLoop || !OuterLoop->isIrreducible()) &&
355 "unhandled irreducible control flow");
356
357 // Irreducible backedge. Abort.
358 LLVM_DEBUG(debugSuccessor("abort!!!"));
359 return false;
360 }
361
362 // If "Pred" is a loop header, then this isn't really a backedge; rather,
363 // OuterLoop must be irreducible. These false backedges can come only from
364 // secondary loop headers.
365 assert(OuterLoop && OuterLoop->isIrreducible() && !isLoopHeader(Resolved) &&
366 "unhandled irreducible control flow");
367 }
368
369 LLVM_DEBUG(debugSuccessor(" local "));
370 Dist.addLocal(Resolved, Weight);
371 return true;
372}
373
375 const LoopData *OuterLoop, LoopData &Loop, Distribution &Dist) {
376 // Copy the exit map into Dist.
377 for (const auto &I : Loop.Exits)
378 if (!addToDist(Dist, OuterLoop, Loop.getHeader(), I.first,
379 I.second.getMass()))
380 // Irreducible backedge.
381 return false;
382
383 return true;
384}
385
386/// Compute the loop scale for a loop.
388 // Compute loop scale.
389 LLVM_DEBUG(dbgs() << "compute-loop-scale: " << getLoopName(Loop) << "\n");
390
391 // Infinite loops need special handling. If we give the back edge an infinite
392 // mass, they may saturate all the other scales in the function down to 1,
393 // making all the other region temperatures look exactly the same. Choose an
394 // arbitrary scale to avoid these issues.
395 //
396 // FIXME: An alternate way would be to select a symbolic scale which is later
397 // replaced to be the maximum of all computed scales plus 1. This would
398 // appropriately describe the loop as having a large scale, without skewing
399 // the final frequency computation.
400 const Scaled64 InfiniteLoopScale(1, 12);
401
402 // LoopScale == 1 / ExitMass
403 // ExitMass == HeadMass - BackedgeMass
404 BlockMass TotalBackedgeMass;
405 for (auto &Mass : Loop.BackedgeMass)
406 TotalBackedgeMass += Mass;
407 BlockMass ExitMass = BlockMass::getFull() - TotalBackedgeMass;
408
409 // Block scale stores the inverse of the scale. If this is an infinite loop,
410 // its exit mass will be zero. In this case, use an arbitrary scale for the
411 // loop scale.
412 Loop.Scale =
413 ExitMass.isEmpty() ? InfiniteLoopScale : ExitMass.toScaled().inverse();
414
415 LLVM_DEBUG(dbgs() << " - exit-mass = " << ExitMass << " ("
416 << BlockMass::getFull() << " - " << TotalBackedgeMass
417 << ")\n"
418 << " - scale = " << Loop.Scale << "\n");
419}
420
421/// Package up a loop.
423 LLVM_DEBUG(dbgs() << "packaging-loop: " << getLoopName(Loop) << "\n");
424
425 // Clear the subloop exits to prevent quadratic memory usage.
426 for (const BlockNode &M : Loop.Nodes) {
427 if (auto *Loop = Working[M.Index].getPackagedLoop())
428 Loop->Exits.clear();
429 LLVM_DEBUG(dbgs() << " - node: " << getBlockName(M.Index) << "\n");
430 }
431 Loop.IsPackaged = true;
432}
433
434#ifndef NDEBUG
436 const DitheringDistributer &D, const BlockNode &T,
437 const BlockMass &M, const char *Desc) {
438 dbgs() << " => assign " << M << " (" << D.RemMass << ")";
439 if (Desc)
440 dbgs() << " [" << Desc << "]";
441 if (T.isValid())
442 dbgs() << " to " << BFI.getBlockName(T);
443 dbgs() << "\n";
444}
445#endif
446
448 LoopData *OuterLoop,
449 Distribution &Dist) {
450 BlockMass Mass = Working[Source.Index].getMass();
451 LLVM_DEBUG(dbgs() << " => mass: " << Mass << "\n");
452
453 // Distribute mass to successors as laid out in Dist.
454 DitheringDistributer D(Dist, Mass);
455
456 for (const Weight &W : Dist.Weights) {
457 // Check for a local edge (non-backedge and non-exit).
458 BlockMass Taken = D.takeMass(W.Amount);
459 if (W.Type == Weight::Local) {
460 Working[W.TargetNode.Index].getMass() += Taken;
461 LLVM_DEBUG(debugAssign(*this, D, W.TargetNode, Taken, nullptr));
462 continue;
463 }
464
465 // Backedges and exits only make sense if we're processing a loop.
466 assert(OuterLoop && "backedge or exit outside of loop");
467
468 // Check for a backedge.
469 if (W.Type == Weight::Backedge) {
470 OuterLoop->BackedgeMass[OuterLoop->getHeaderIndex(W.TargetNode)] += Taken;
471 LLVM_DEBUG(debugAssign(*this, D, W.TargetNode, Taken, "back"));
472 continue;
473 }
474
475 // This must be an exit.
476 assert(W.Type == Weight::Exit);
477 OuterLoop->Exits.push_back(std::make_pair(W.TargetNode, Taken));
478 LLVM_DEBUG(debugAssign(*this, D, W.TargetNode, Taken, "exit"));
479 }
480}
481
483 const Scaled64 &Min, const Scaled64 &Max) {
484 // Scale the Factor to a size that creates integers. If possible scale
485 // integers so that Max == UINT64_MAX so that they can be best differentiated.
486 // Is is possible that the range between min and max cannot be accurately
487 // represented in a 64bit integer without either loosing precision for small
488 // values (so small unequal numbers all map to 1) or saturaturing big numbers
489 // loosing precision for big numbers (so unequal big numbers may map to
490 // UINT64_MAX). We choose to loose precision for small numbers.
491 const unsigned MaxBits = sizeof(Scaled64::DigitsType) * CHAR_BIT;
492 // Users often add up multiple BlockFrequency values or multiply them with
493 // things like instruction costs. Leave some room to avoid saturating
494 // operations reaching UIN64_MAX too early.
495 const unsigned Slack = 10;
496 Scaled64 ScalingFactor = Scaled64(1, MaxBits - Slack) / Max;
497
498 // Translate the floats to integers.
499 LLVM_DEBUG(dbgs() << "float-to-int: min = " << Min << ", max = " << Max
500 << ", factor = " << ScalingFactor << "\n");
501 (void)Min;
502 for (size_t Index = 0; Index < BFI.Freqs.size(); ++Index) {
503 Scaled64 Scaled = BFI.Freqs[Index].Scaled * ScalingFactor;
504 BFI.Freqs[Index].Integer = std::max(UINT64_C(1), Scaled.toInt<uint64_t>());
505 LLVM_DEBUG(dbgs() << " - " << BFI.getBlockName(Index) << ": float = "
506 << BFI.Freqs[Index].Scaled << ", scaled = " << Scaled
507 << ", int = " << BFI.Freqs[Index].Integer << "\n");
508 }
509}
510
511/// Unwrap a loop package.
512///
513/// Visits all the members of a loop, adjusting their BlockData according to
514/// the loop's pseudo-node.
515static void unwrapLoop(BlockFrequencyInfoImplBase &BFI, LoopData &Loop) {
516 LLVM_DEBUG(dbgs() << "unwrap-loop-package: " << BFI.getLoopName(Loop)
517 << ": mass = " << Loop.Mass << ", scale = " << Loop.Scale
518 << "\n");
519 Loop.Scale *= Loop.Mass.toScaled();
520 Loop.IsPackaged = false;
521 LLVM_DEBUG(dbgs() << " => combined-scale = " << Loop.Scale << "\n");
522
523 // Propagate the head scale through the loop. Since members are visited in
524 // RPO, the head scale will be updated by the loop scale first, and then the
525 // final head scale will be used for updated the rest of the members.
526 for (const BlockNode &N : Loop.Nodes) {
527 const auto &Working = BFI.Working[N.Index];
528 Scaled64 &F = Working.isAPackage() ? Working.getPackagedLoop()->Scale
529 : BFI.Freqs[N.Index].Scaled;
530 Scaled64 New = Loop.Scale * F;
531 LLVM_DEBUG(dbgs() << " - " << BFI.getBlockName(N) << ": " << F << " => "
532 << New << "\n");
533 F = New;
534 }
535}
536
538 // Set initial frequencies from loop-local masses.
539 for (size_t Index = 0; Index < Working.size(); ++Index)
540 Freqs[Index].Scaled = Working[Index].Mass.toScaled();
541
542 for (LoopData &Loop : Loops)
543 unwrapLoop(*this, Loop);
544}
545
547 // Unwrap loop packages in reverse post-order, tracking min and max
548 // frequencies.
549 auto Min = Scaled64::getLargest();
550 auto Max = Scaled64::getZero();
551 for (size_t Index = 0; Index < Working.size(); ++Index) {
552 // Update min/max scale.
553 Min = std::min(Min, Freqs[Index].Scaled);
554 Max = std::max(Max, Freqs[Index].Scaled);
555 }
556
557 // Convert to integers.
558 convertFloatingToInteger(*this, Min, Max);
559
560 // Clean up data structures.
561 cleanup(*this);
562
563 // Print out the final stats.
564 LLVM_DEBUG(dump());
565}
566
569 if (!Node.isValid()) {
570#ifndef NDEBUG
574 OS << "*** Detected BFI query for unknown block " << getBlockName(Node);
575 report_fatal_error(OS.str());
576 }
577#endif
578 return BlockFrequency(0);
579 }
580 return BlockFrequency(Freqs[Node.Index].Integer);
581}
582
583std::optional<uint64_t>
585 const BlockNode &Node,
586 bool AllowSynthetic) const {
587 return getProfileCountFromFreq(F, getBlockFreq(Node), AllowSynthetic);
588}
589
591 const Function &F, BlockFrequency Freq, bool AllowSynthetic) const {
592 auto EntryCount = F.getEntryCount(AllowSynthetic);
593 if (!EntryCount)
594 return std::nullopt;
595 // Use 128 bit APInt to do the arithmetic to avoid overflow.
596 APInt BlockCount(128, EntryCount->getCount());
597 APInt BlockFreq(128, Freq.getFrequency());
598 APInt EntryFreq(128, getEntryFreq().getFrequency());
599 BlockCount *= BlockFreq;
600 // Rounded division of BlockCount by EntryFreq. Since EntryFreq is unsigned
601 // lshr by 1 gives EntryFreq/2.
602 BlockCount = (BlockCount + EntryFreq.lshr(1)).udiv(EntryFreq);
603 return BlockCount.getLimitedValue();
604}
605
606bool
608 if (!Node.isValid())
609 return false;
610 return IsIrrLoopHeader.test(Node.Index);
611}
612
615 if (!Node.isValid())
616 return Scaled64::getZero();
617 return Freqs[Node.Index].Scaled;
618}
619
621 BlockFrequency Freq) {
622 assert(Node.isValid() && "Expected valid node");
623 assert(Node.Index < Freqs.size() && "Expected legal index");
624 Freqs[Node.Index].Integer = Freq.getFrequency();
625}
626
627std::string
629 return {};
630}
631
632std::string
634 return getBlockName(Loop.getHeader()) + (Loop.isIrreducible() ? "**" : "*");
635}
636
638 Start = OuterLoop.getHeader();
639 Nodes.reserve(OuterLoop.Nodes.size());
640 for (auto N : OuterLoop.Nodes)
641 addNode(N);
642 indexNodes();
643}
644
646 Start = 0;
647 for (uint32_t Index = 0; Index < BFI.Working.size(); ++Index)
648 if (!BFI.Working[Index].isPackaged())
649 addNode(Index);
650 indexNodes();
651}
652
654 for (auto &I : Nodes)
655 Lookup[I.Node.Index] = &I;
656}
657
659 const BFIBase::LoopData *OuterLoop) {
660 if (OuterLoop && OuterLoop->isHeader(Succ))
661 return;
662 auto L = Lookup.find(Succ.Index);
663 if (L == Lookup.end())
664 return;
665 IrrNode &SuccIrr = *L->second;
666 Irr.Edges.push_back(&SuccIrr);
667 SuccIrr.Edges.push_front(&Irr);
668 ++SuccIrr.NumIn;
669}
670
671namespace llvm {
672
673template <> struct GraphTraits<IrreducibleGraph> {
675 using NodeRef = const GraphT::IrrNode *;
676 using ChildIteratorType = GraphT::IrrNode::iterator;
677
678 static NodeRef getEntryNode(const GraphT &G) { return G.StartIrr; }
679 static ChildIteratorType child_begin(NodeRef N) { return N->succ_begin(); }
680 static ChildIteratorType child_end(NodeRef N) { return N->succ_end(); }
681};
682
683} // end namespace llvm
684
685/// Find extra irreducible headers.
686///
687/// Find entry blocks and other blocks with backedges, which exist when \c G
688/// contains irreducible sub-SCCs.
691 const IrreducibleGraph &G,
692 const std::vector<const IrreducibleGraph::IrrNode *> &SCC,
693 LoopData::NodeList &Headers, LoopData::NodeList &Others) {
694 // Map from nodes in the SCC to whether it's an entry block.
696
697 // InSCC also acts the set of nodes in the graph. Seed it.
698 for (const auto *I : SCC)
699 InSCC[I] = false;
700
701 for (auto I = InSCC.begin(), E = InSCC.end(); I != E; ++I) {
702 auto &Irr = *I->first;
703 for (const auto *P : make_range(Irr.pred_begin(), Irr.pred_end())) {
704 if (InSCC.count(P))
705 continue;
706
707 // This is an entry block.
708 I->second = true;
709 Headers.push_back(Irr.Node);
710 LLVM_DEBUG(dbgs() << " => entry = " << BFI.getBlockName(Irr.Node)
711 << "\n");
712 break;
713 }
714 }
715 assert(Headers.size() >= 2 &&
716 "Expected irreducible CFG; -loop-info is likely invalid");
717 if (Headers.size() == InSCC.size()) {
718 // Every block is a header.
719 llvm::sort(Headers);
720 return;
721 }
722
723 // Look for extra headers from irreducible sub-SCCs.
724 for (const auto &I : InSCC) {
725 // Entry blocks are already headers.
726 if (I.second)
727 continue;
728
729 auto &Irr = *I.first;
730 for (const auto *P : make_range(Irr.pred_begin(), Irr.pred_end())) {
731 // Skip forward edges.
732 if (P->Node < Irr.Node)
733 continue;
734
735 // Skip predecessors from entry blocks. These can have inverted
736 // ordering.
737 if (InSCC.lookup(P))
738 continue;
739
740 // Store the extra header.
741 Headers.push_back(Irr.Node);
742 LLVM_DEBUG(dbgs() << " => extra = " << BFI.getBlockName(Irr.Node)
743 << "\n");
744 break;
745 }
746 if (Headers.back() == Irr.Node)
747 // Added this as a header.
748 continue;
749
750 // This is not a header.
751 Others.push_back(Irr.Node);
752 LLVM_DEBUG(dbgs() << " => other = " << BFI.getBlockName(Irr.Node) << "\n");
753 }
754 llvm::sort(Headers);
755 llvm::sort(Others);
756}
757
760 LoopData *OuterLoop, std::list<LoopData>::iterator Insert,
761 const std::vector<const IrreducibleGraph::IrrNode *> &SCC) {
762 // Translate the SCC into RPO.
763 LLVM_DEBUG(dbgs() << " - found-scc\n");
764
765 LoopData::NodeList Headers;
766 LoopData::NodeList Others;
767 findIrreducibleHeaders(BFI, G, SCC, Headers, Others);
768
769 auto Loop = BFI.Loops.emplace(Insert, OuterLoop, Headers.begin(),
770 Headers.end(), Others.begin(), Others.end());
771
772 // Update loop hierarchy.
773 for (const auto &N : Loop->Nodes)
774 if (BFI.Working[N.Index].isLoopHeader())
775 BFI.Working[N.Index].Loop->Parent = &*Loop;
776 else
777 BFI.Working[N.Index].Loop = &*Loop;
778}
779
782 const IrreducibleGraph &G, LoopData *OuterLoop,
783 std::list<LoopData>::iterator Insert) {
784 assert((OuterLoop == nullptr) == (Insert == Loops.begin()));
785 auto Prev = OuterLoop ? std::prev(Insert) : Loops.end();
786
787 for (auto I = scc_begin(G); !I.isAtEnd(); ++I) {
788 if (I->size() < 2)
789 continue;
790
791 // Translate the SCC into RPO.
792 createIrreducibleLoop(*this, G, OuterLoop, Insert, *I);
793 }
794
795 if (OuterLoop)
796 return make_range(std::next(Prev), Insert);
797 return make_range(Loops.begin(), Insert);
798}
799
800void
802 OuterLoop.Exits.clear();
803 for (auto &Mass : OuterLoop.BackedgeMass)
804 Mass = BlockMass::getEmpty();
805 auto O = OuterLoop.Nodes.begin() + 1;
806 for (auto I = O, E = OuterLoop.Nodes.end(); I != E; ++I)
807 if (!Working[I->Index].isPackaged())
808 *O++ = *I;
809 OuterLoop.Nodes.erase(O, OuterLoop.Nodes.end());
810}
811
813 assert(Loop.isIrreducible() && "this only makes sense on irreducible loops");
814
815 // Since the loop has more than one header block, the mass flowing back into
816 // each header will be different. Adjust the mass in each header loop to
817 // reflect the masses flowing through back edges.
818 //
819 // To do this, we distribute the initial mass using the backedge masses
820 // as weights for the distribution.
821 BlockMass LoopMass = BlockMass::getFull();
822 Distribution Dist;
823
824 LLVM_DEBUG(dbgs() << "adjust-loop-header-mass:\n");
825 for (uint32_t H = 0; H < Loop.NumHeaders; ++H) {
826 auto &HeaderNode = Loop.Nodes[H];
827 auto &BackedgeMass = Loop.BackedgeMass[Loop.getHeaderIndex(HeaderNode)];
828 LLVM_DEBUG(dbgs() << " - Add back edge mass for node "
829 << getBlockName(HeaderNode) << ": " << BackedgeMass
830 << "\n");
831 if (BackedgeMass.getMass() > 0)
832 Dist.addLocal(HeaderNode, BackedgeMass.getMass());
833 else
834 LLVM_DEBUG(dbgs() << " Nothing added. Back edge mass is zero\n");
835 }
836
837 DitheringDistributer D(Dist, LoopMass);
838
839 LLVM_DEBUG(dbgs() << " Distribute loop mass " << LoopMass
840 << " to headers using above weights\n");
841 for (const Weight &W : Dist.Weights) {
842 BlockMass Taken = D.takeMass(W.Amount);
843 assert(W.Type == Weight::Local && "all weights should be local");
844 Working[W.TargetNode.Index].getMass() = Taken;
845 LLVM_DEBUG(debugAssign(*this, D, W.TargetNode, Taken, nullptr));
846 }
847}
848
850 BlockMass LoopMass = BlockMass::getFull();
851 DitheringDistributer D(Dist, LoopMass);
852 for (const Weight &W : Dist.Weights) {
853 BlockMass Taken = D.takeMass(W.Amount);
854 assert(W.Type == Weight::Local && "all weights should be local");
855 Working[W.TargetNode.Index].getMass() = Taken;
856 LLVM_DEBUG(debugAssign(*this, D, W.TargetNode, Taken, nullptr));
857 }
858}
This file implements a class to represent arbitrary precision integral constant values and operations...
@ Scaled
static void combineWeightsBySorting(WeightList &Weights)
static void cleanup(BlockFrequencyInfoImplBase &BFI)
Clear all memory not needed downstream.
static void combineWeightsByHashing(WeightList &Weights)
static void unwrapLoop(BlockFrequencyInfoImplBase &BFI, LoopData &Loop)
Unwrap a loop package.
static void combineWeight(Weight &W, const Weight &OtherW)
static void debugAssign(const BlockFrequencyInfoImplBase &BFI, const DitheringDistributer &D, const BlockNode &T, const BlockMass &M, const char *Desc)
static void combineWeights(WeightList &Weights)
static char getHexDigit(int N)
static void findIrreducibleHeaders(const BlockFrequencyInfoImplBase &BFI, const IrreducibleGraph &G, const std::vector< const IrreducibleGraph::IrrNode * > &SCC, LoopData::NodeList &Headers, LoopData::NodeList &Others)
Find extra irreducible headers.
static void convertFloatingToInteger(BlockFrequencyInfoImplBase &BFI, const Scaled64 &Min, const Scaled64 &Max)
static void createIrreducibleLoop(BlockFrequencyInfoImplBase &BFI, const IrreducibleGraph &G, LoopData *OuterLoop, std::list< LoopData >::iterator Insert, const std::vector< const IrreducibleGraph::IrrNode * > &SCC)
static uint64_t shiftRightAndRound(uint64_t N, int Shift)
static GCRegistry::Add< StatepointGC > D("statepoint-example", "an example strategy for statepoint")
#define LLVM_DUMP_METHOD
Mark debug helper function definitions like dump() that should not be stripped from debug builds.
Definition: Compiler.h:537
#define LLVM_DEBUG(X)
Definition: Debug.h:101
This file defines the DenseMap class.
Hexagon Hardware Loops
#define F(x, y, z)
Definition: MD5.cpp:55
#define I(x, y, z)
Definition: MD5.cpp:58
#define G(x, y, z)
Definition: MD5.cpp:56
#define H(x, y, z)
Definition: MD5.cpp:57
#define P(N)
This builds on the llvm/ADT/GraphTraits.h file to find the strongly connected components (SCCs) of a ...
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
raw_pwrite_stream & OS
This file defines the SmallString class.
ScaledNumber< uint64_t > Scaled64
Class for arbitrary precision integers.
Definition: APInt.h:77
uint64_t getLimitedValue(uint64_t Limit=UINT64_MAX) const
If this value is smaller than the specified limit, return it, otherwise return the limit value.
Definition: APInt.h:454
APInt lshr(unsigned shiftAmt) const
Logical right-shift function.
Definition: APInt.h:830
Base class for BlockFrequencyInfoImpl.
std::vector< WorkingData > Working
Loop data: see initializeLoops().
bool addLoopSuccessorsToDist(const LoopData *OuterLoop, LoopData &Loop, Distribution &Dist)
Add all edges out of a packaged loop to the distribution.
std::string getLoopName(const LoopData &Loop) const
bool isIrrLoopHeader(const BlockNode &Node)
void computeLoopScale(LoopData &Loop)
Compute the loop scale for a loop.
void packageLoop(LoopData &Loop)
Package up a loop.
virtual std::string getBlockName(const BlockNode &Node) const
void finalizeMetrics()
Finalize frequency metrics.
void setBlockFreq(const BlockNode &Node, BlockFrequency Freq)
void updateLoopWithIrreducible(LoopData &OuterLoop)
Update a loop after packaging irreducible SCCs inside of it.
std::optional< uint64_t > getBlockProfileCount(const Function &F, const BlockNode &Node, bool AllowSynthetic=false) const
BlockFrequency getBlockFreq(const BlockNode &Node) const
void distributeIrrLoopHeaderMass(Distribution &Dist)
iterator_range< std::list< LoopData >::iterator > analyzeIrreducible(const bfi_detail::IrreducibleGraph &G, LoopData *OuterLoop, std::list< LoopData >::iterator Insert)
Analyze irreducible SCCs.
bool addToDist(Distribution &Dist, const LoopData *OuterLoop, const BlockNode &Pred, const BlockNode &Succ, uint64_t Weight)
Add an edge to the distribution.
std::optional< uint64_t > getProfileCountFromFreq(const Function &F, BlockFrequency Freq, bool AllowSynthetic=false) const
Scaled64 getFloatingBlockFreq(const BlockNode &Node) const
void distributeMass(const BlockNode &Source, LoopData *OuterLoop, Distribution &Dist)
Distribute mass according to a distribution.
void adjustLoopHeaderMass(LoopData &Loop)
Adjust the mass of all headers in an irreducible loop.
uint64_t getFrequency() const
Returns the frequency as a fixpoint number scaled by the entry frequency.
ValueT lookup(const_arg_type_t< KeyT > Val) const
lookup - Return the entry for the specified key, or a default constructed value if no such entry exis...
Definition: DenseMap.h:202
unsigned size() const
Definition: DenseMap.h:99
iterator begin()
Definition: DenseMap.h:75
size_type count(const_arg_type_t< KeyT > Val) const
Return 1 if the specified key is in the map, 0 otherwise.
Definition: DenseMap.h:151
iterator end()
Definition: DenseMap.h:84
BlockT * getHeader() const
Represents a single loop in the control flow graph.
Definition: LoopInfo.h:44
Simple representation of a scaled number.
Definition: ScaledNumber.h:493
static ScaledNumber getLargest()
Definition: ScaledNumber.h:523
ScaledNumber inverse() const
Definition: ScaledNumber.h:678
static ScaledNumber getZero()
Definition: ScaledNumber.h:521
SmallString - A SmallString is just a SmallVector with methods and accessors that make it work better...
Definition: SmallString.h:26
size_t size() const
Definition: SmallVector.h:91
iterator erase(const_iterator CI)
Definition: SmallVector.h:750
void push_back(const T &Elt)
Definition: SmallVector.h:426
The instances of the Type class are immutable: once they are created, they are never changed.
Definition: Type.h:45
raw_ostream & print(raw_ostream &OS) const
ScaledNumber< uint64_t > toScaled() const
Convert to scaled number.
A range adaptor for a pair of iterators.
This class implements an extremely fast bulk output stream that can only output to a stream.
Definition: raw_ostream.h:52
A raw_ostream that writes to an SmallVector or SmallString.
Definition: raw_ostream.h:690
#define UINT64_MAX
Definition: DataTypes.h:77
std::string getBlockName(const BlockT *BB)
Get the name of a MachineBasicBlock.
initializer< Ty > init(const Ty &Val)
Definition: CommandLine.h:450
This is an optimization pass for GlobalISel generic memory operations.
Definition: AddressRanges.h:18
void dump(const SparseBitVector< ElementSize > &LHS, raw_ostream &out)
iterator_range< T > make_range(T x, T y)
Convenience function for iterating over sub-ranges.
scc_iterator< T > scc_begin(const T &G)
Construct the begin iterator for a deduced graph type T.
Definition: SCCIterator.h:233
llvm::cl::opt< unsigned > IterativeBFIMaxIterationsPerBlock
int countl_zero(T Val)
Count number of 0's from the most significant bit to the least stopping at the first 1.
Definition: bit.h:281
void sort(IteratorTy Start, IteratorTy End)
Definition: STLExtras.h:1647
llvm::cl::opt< bool > UseIterativeBFIInference
raw_ostream & dbgs()
dbgs() - This returns a reference to a raw_ostream for debugging messages.
Definition: Debug.cpp:163
void report_fatal_error(Error Err, bool gen_crash_diag=true)
Report a serious error, calling any installed error handler.
Definition: Error.cpp:159
llvm::cl::opt< bool > CheckBFIUnknownBlockQueries
llvm::cl::opt< double > IterativeBFIPrecision
constexpr uint64_t NextPowerOf2(uint64_t A)
Returns the next power of two (in 64-bits) that is strictly greater than A.
Definition: MathExtras.h:360
#define N
Distribution of unscaled probability weight.
void addBackedge(const BlockNode &Node, uint64_t Amount)
WeightList Weights
Individual successor weights.
void addExit(const BlockNode &Node, uint64_t Amount)
void addLocal(const BlockNode &Node, uint64_t Amount)
bool isHeader(const BlockNode &Node) const
ExitMap Exits
Successor edges (and weights).
NodeList Nodes
Header and the members of the loop.
HeaderMassList BackedgeMass
Mass returned to each loop header.
HeaderMassList::difference_type getHeaderIndex(const BlockNode &B)
Description of the encoding of one expression Op.
static ChildIteratorType child_begin(NodeRef N)
static ChildIteratorType child_end(NodeRef N)
static NodeRef getEntryNode(const GraphT &G)
Graph of irreducible control flow.
void addEdge(IrrNode &Irr, const BlockNode &Succ, const BFIBase::LoopData *OuterLoop)
SmallDenseMap< uint32_t, IrrNode *, 4 > Lookup
void addNodesInLoop(const BFIBase::LoopData &OuterLoop)