1 //===- BlockFrequencyImplInfo.cpp - Block Frequency Info Implementation ---===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // Loops should be simplified before this analysis.
11 //
12 //===----------------------------------------------------------------------===//
13
14 #include "llvm/Analysis/BlockFrequencyInfoImpl.h"
15 #include "llvm/ADT/SCCIterator.h"
16 #include "llvm/IR/Function.h"
17 #include "llvm/Support/raw_ostream.h"
18 #include <numeric>
19
20 using namespace llvm;
21 using namespace llvm::bfi_detail;
22
23 #define DEBUG_TYPE "block-freq"
24
toScaled() const25 ScaledNumber<uint64_t> BlockMass::toScaled() const {
26 if (isFull())
27 return ScaledNumber<uint64_t>(1, 0);
28 return ScaledNumber<uint64_t>(getMass() + 1, -64);
29 }
30
dump() const31 LLVM_DUMP_METHOD void BlockMass::dump() const { print(dbgs()); }
32
getHexDigit(int N)33 static char getHexDigit(int N) {
34 assert(N < 16);
35 if (N < 10)
36 return '0' + N;
37 return 'a' + N - 10;
38 }
39
print(raw_ostream & OS) const40 raw_ostream &BlockMass::print(raw_ostream &OS) const {
41 for (int Digits = 0; Digits < 16; ++Digits)
42 OS << getHexDigit(Mass >> (60 - Digits * 4) & 0xf);
43 return OS;
44 }
45
46 namespace {
47
48 typedef BlockFrequencyInfoImplBase::BlockNode BlockNode;
49 typedef BlockFrequencyInfoImplBase::Distribution Distribution;
50 typedef BlockFrequencyInfoImplBase::Distribution::WeightList WeightList;
51 typedef BlockFrequencyInfoImplBase::Scaled64 Scaled64;
52 typedef BlockFrequencyInfoImplBase::LoopData LoopData;
53 typedef BlockFrequencyInfoImplBase::Weight Weight;
54 typedef BlockFrequencyInfoImplBase::FrequencyData FrequencyData;
55
56 /// \brief Dithering mass distributer.
57 ///
58 /// This class splits up a single mass into portions by weight, dithering to
59 /// spread out error. No mass is lost. The dithering precision depends on the
60 /// precision of the product of \a BlockMass and \a BranchProbability.
61 ///
62 /// The distribution algorithm follows.
63 ///
64 /// 1. Initialize by saving the sum of the weights in \a RemWeight and the
65 /// mass to distribute in \a RemMass.
66 ///
67 /// 2. For each portion:
68 ///
69 /// 1. Construct a branch probability, P, as the portion's weight divided
70 /// by the current value of \a RemWeight.
71 /// 2. Calculate the portion's mass as \a RemMass times P.
72 /// 3. Update \a RemWeight and \a RemMass at each portion by subtracting
73 /// the current portion's weight and mass.
74 struct DitheringDistributer {
75 uint32_t RemWeight;
76 BlockMass RemMass;
77
78 DitheringDistributer(Distribution &Dist, const BlockMass &Mass);
79
80 BlockMass takeMass(uint32_t Weight);
81 };
82
83 } // end anonymous namespace
84
DitheringDistributer(Distribution & Dist,const BlockMass & Mass)85 DitheringDistributer::DitheringDistributer(Distribution &Dist,
86 const BlockMass &Mass) {
87 Dist.normalize();
88 RemWeight = Dist.Total;
89 RemMass = Mass;
90 }
91
takeMass(uint32_t Weight)92 BlockMass DitheringDistributer::takeMass(uint32_t Weight) {
93 assert(Weight && "invalid weight");
94 assert(Weight <= RemWeight);
95 BlockMass Mass = RemMass * BranchProbability(Weight, RemWeight);
96
97 // Decrement totals (dither).
98 RemWeight -= Weight;
99 RemMass -= Mass;
100 return Mass;
101 }
102
add(const BlockNode & Node,uint64_t Amount,Weight::DistType Type)103 void Distribution::add(const BlockNode &Node, uint64_t Amount,
104 Weight::DistType Type) {
105 assert(Amount && "invalid weight of 0");
106 uint64_t NewTotal = Total + Amount;
107
108 // Check for overflow. It should be impossible to overflow twice.
109 bool IsOverflow = NewTotal < Total;
110 assert(!(DidOverflow && IsOverflow) && "unexpected repeated overflow");
111 DidOverflow |= IsOverflow;
112
113 // Update the total.
114 Total = NewTotal;
115
116 // Save the weight.
117 Weights.push_back(Weight(Type, Node, Amount));
118 }
119
combineWeight(Weight & W,const Weight & OtherW)120 static void combineWeight(Weight &W, const Weight &OtherW) {
121 assert(OtherW.TargetNode.isValid());
122 if (!W.Amount) {
123 W = OtherW;
124 return;
125 }
126 assert(W.Type == OtherW.Type);
127 assert(W.TargetNode == OtherW.TargetNode);
128 assert(OtherW.Amount && "Expected non-zero weight");
129 if (W.Amount > W.Amount + OtherW.Amount)
130 // Saturate on overflow.
131 W.Amount = UINT64_MAX;
132 else
133 W.Amount += OtherW.Amount;
134 }
135
combineWeightsBySorting(WeightList & Weights)136 static void combineWeightsBySorting(WeightList &Weights) {
137 // Sort so edges to the same node are adjacent.
138 std::sort(Weights.begin(), Weights.end(),
139 [](const Weight &L,
140 const Weight &R) { return L.TargetNode < R.TargetNode; });
141
142 // Combine adjacent edges.
143 WeightList::iterator O = Weights.begin();
144 for (WeightList::const_iterator I = O, L = O, E = Weights.end(); I != E;
145 ++O, (I = L)) {
146 *O = *I;
147
148 // Find the adjacent weights to the same node.
149 for (++L; L != E && I->TargetNode == L->TargetNode; ++L)
150 combineWeight(*O, *L);
151 }
152
153 // Erase extra entries.
154 Weights.erase(O, Weights.end());
155 }
156
combineWeightsByHashing(WeightList & Weights)157 static void combineWeightsByHashing(WeightList &Weights) {
158 // Collect weights into a DenseMap.
159 typedef DenseMap<BlockNode::IndexType, Weight> HashTable;
160 HashTable Combined(NextPowerOf2(2 * Weights.size()));
161 for (const Weight &W : Weights)
162 combineWeight(Combined[W.TargetNode.Index], W);
163
164 // Check whether anything changed.
165 if (Weights.size() == Combined.size())
166 return;
167
168 // Fill in the new weights.
169 Weights.clear();
170 Weights.reserve(Combined.size());
171 for (const auto &I : Combined)
172 Weights.push_back(I.second);
173 }
174
combineWeights(WeightList & Weights)175 static void combineWeights(WeightList &Weights) {
176 // Use a hash table for many successors to keep this linear.
177 if (Weights.size() > 128) {
178 combineWeightsByHashing(Weights);
179 return;
180 }
181
182 combineWeightsBySorting(Weights);
183 }
184
shiftRightAndRound(uint64_t N,int Shift)185 static uint64_t shiftRightAndRound(uint64_t N, int Shift) {
186 assert(Shift >= 0);
187 assert(Shift < 64);
188 if (!Shift)
189 return N;
190 return (N >> Shift) + (UINT64_C(1) & N >> (Shift - 1));
191 }
192
normalize()193 void Distribution::normalize() {
194 // Early exit for termination nodes.
195 if (Weights.empty())
196 return;
197
198 // Only bother if there are multiple successors.
199 if (Weights.size() > 1)
200 combineWeights(Weights);
201
202 // Early exit when combined into a single successor.
203 if (Weights.size() == 1) {
204 Total = 1;
205 Weights.front().Amount = 1;
206 return;
207 }
208
209 // Determine how much to shift right so that the total fits into 32-bits.
210 //
211 // If we shift at all, shift by 1 extra. Otherwise, the lower limit of 1
212 // for each weight can cause a 32-bit overflow.
213 int Shift = 0;
214 if (DidOverflow)
215 Shift = 33;
216 else if (Total > UINT32_MAX)
217 Shift = 33 - countLeadingZeros(Total);
218
219 // Early exit if nothing needs to be scaled.
220 if (!Shift) {
221 // If we didn't overflow then combineWeights() shouldn't have changed the
222 // sum of the weights, but let's double-check.
223 assert(Total == std::accumulate(Weights.begin(), Weights.end(), UINT64_C(0),
224 [](uint64_t Sum, const Weight &W) {
225 return Sum + W.Amount;
226 }) &&
227 "Expected total to be correct");
228 return;
229 }
230
231 // Recompute the total through accumulation (rather than shifting it) so that
232 // it's accurate after shifting and any changes combineWeights() made above.
233 Total = 0;
234
235 // Sum the weights to each node and shift right if necessary.
236 for (Weight &W : Weights) {
237 // Scale down below UINT32_MAX. Since Shift is larger than necessary, we
238 // can round here without concern about overflow.
239 assert(W.TargetNode.isValid());
240 W.Amount = std::max(UINT64_C(1), shiftRightAndRound(W.Amount, Shift));
241 assert(W.Amount <= UINT32_MAX);
242
243 // Update the total.
244 Total += W.Amount;
245 }
246 assert(Total <= UINT32_MAX);
247 }
248
clear()249 void BlockFrequencyInfoImplBase::clear() {
250 // Swap with a default-constructed std::vector, since std::vector<>::clear()
251 // does not actually clear heap storage.
252 std::vector<FrequencyData>().swap(Freqs);
253 std::vector<WorkingData>().swap(Working);
254 Loops.clear();
255 }
256
257 /// \brief Clear all memory not needed downstream.
258 ///
259 /// Releases all memory not used downstream. In particular, saves Freqs.
cleanup(BlockFrequencyInfoImplBase & BFI)260 static void cleanup(BlockFrequencyInfoImplBase &BFI) {
261 std::vector<FrequencyData> SavedFreqs(std::move(BFI.Freqs));
262 BFI.clear();
263 BFI.Freqs = std::move(SavedFreqs);
264 }
265
addToDist(Distribution & Dist,const LoopData * OuterLoop,const BlockNode & Pred,const BlockNode & Succ,uint64_t Weight)266 bool BlockFrequencyInfoImplBase::addToDist(Distribution &Dist,
267 const LoopData *OuterLoop,
268 const BlockNode &Pred,
269 const BlockNode &Succ,
270 uint64_t Weight) {
271 if (!Weight)
272 Weight = 1;
273
274 auto isLoopHeader = [&OuterLoop](const BlockNode &Node) {
275 return OuterLoop && OuterLoop->isHeader(Node);
276 };
277
278 BlockNode Resolved = Working[Succ.Index].getResolvedNode();
279
280 #ifndef NDEBUG
281 auto debugSuccessor = [&](const char *Type) {
282 dbgs() << " =>"
283 << " [" << Type << "] weight = " << Weight;
284 if (!isLoopHeader(Resolved))
285 dbgs() << ", succ = " << getBlockName(Succ);
286 if (Resolved != Succ)
287 dbgs() << ", resolved = " << getBlockName(Resolved);
288 dbgs() << "\n";
289 };
290 (void)debugSuccessor;
291 #endif
292
293 if (isLoopHeader(Resolved)) {
294 DEBUG(debugSuccessor("backedge"));
295 Dist.addBackedge(Resolved, Weight);
296 return true;
297 }
298
299 if (Working[Resolved.Index].getContainingLoop() != OuterLoop) {
300 DEBUG(debugSuccessor(" exit "));
301 Dist.addExit(Resolved, Weight);
302 return true;
303 }
304
305 if (Resolved < Pred) {
306 if (!isLoopHeader(Pred)) {
307 // If OuterLoop is an irreducible loop, we can't actually handle this.
308 assert((!OuterLoop || !OuterLoop->isIrreducible()) &&
309 "unhandled irreducible control flow");
310
311 // Irreducible backedge. Abort.
312 DEBUG(debugSuccessor("abort!!!"));
313 return false;
314 }
315
316 // If "Pred" is a loop header, then this isn't really a backedge; rather,
317 // OuterLoop must be irreducible. These false backedges can come only from
318 // secondary loop headers.
319 assert(OuterLoop && OuterLoop->isIrreducible() && !isLoopHeader(Resolved) &&
320 "unhandled irreducible control flow");
321 }
322
323 DEBUG(debugSuccessor(" local "));
324 Dist.addLocal(Resolved, Weight);
325 return true;
326 }
327
addLoopSuccessorsToDist(const LoopData * OuterLoop,LoopData & Loop,Distribution & Dist)328 bool BlockFrequencyInfoImplBase::addLoopSuccessorsToDist(
329 const LoopData *OuterLoop, LoopData &Loop, Distribution &Dist) {
330 // Copy the exit map into Dist.
331 for (const auto &I : Loop.Exits)
332 if (!addToDist(Dist, OuterLoop, Loop.getHeader(), I.first,
333 I.second.getMass()))
334 // Irreducible backedge.
335 return false;
336
337 return true;
338 }
339
340 /// \brief Compute the loop scale for a loop.
computeLoopScale(LoopData & Loop)341 void BlockFrequencyInfoImplBase::computeLoopScale(LoopData &Loop) {
342 // Compute loop scale.
343 DEBUG(dbgs() << "compute-loop-scale: " << getLoopName(Loop) << "\n");
344
345 // Infinite loops need special handling. If we give the back edge an infinite
346 // mass, they may saturate all the other scales in the function down to 1,
347 // making all the other region temperatures look exactly the same. Choose an
348 // arbitrary scale to avoid these issues.
349 //
350 // FIXME: An alternate way would be to select a symbolic scale which is later
351 // replaced to be the maximum of all computed scales plus 1. This would
352 // appropriately describe the loop as having a large scale, without skewing
353 // the final frequency computation.
354 const Scaled64 InfiniteLoopScale(1, 12);
355
356 // LoopScale == 1 / ExitMass
357 // ExitMass == HeadMass - BackedgeMass
358 BlockMass TotalBackedgeMass;
359 for (auto &Mass : Loop.BackedgeMass)
360 TotalBackedgeMass += Mass;
361 BlockMass ExitMass = BlockMass::getFull() - TotalBackedgeMass;
362
363 // Block scale stores the inverse of the scale. If this is an infinite loop,
364 // its exit mass will be zero. In this case, use an arbitrary scale for the
365 // loop scale.
366 Loop.Scale =
367 ExitMass.isEmpty() ? InfiniteLoopScale : ExitMass.toScaled().inverse();
368
369 DEBUG(dbgs() << " - exit-mass = " << ExitMass << " (" << BlockMass::getFull()
370 << " - " << TotalBackedgeMass << ")\n"
371 << " - scale = " << Loop.Scale << "\n");
372 }
373
374 /// \brief Package up a loop.
packageLoop(LoopData & Loop)375 void BlockFrequencyInfoImplBase::packageLoop(LoopData &Loop) {
376 DEBUG(dbgs() << "packaging-loop: " << getLoopName(Loop) << "\n");
377
378 // Clear the subloop exits to prevent quadratic memory usage.
379 for (const BlockNode &M : Loop.Nodes) {
380 if (auto *Loop = Working[M.Index].getPackagedLoop())
381 Loop->Exits.clear();
382 DEBUG(dbgs() << " - node: " << getBlockName(M.Index) << "\n");
383 }
384 Loop.IsPackaged = true;
385 }
386
387 #ifndef NDEBUG
debugAssign(const BlockFrequencyInfoImplBase & BFI,const DitheringDistributer & D,const BlockNode & T,const BlockMass & M,const char * Desc)388 static void debugAssign(const BlockFrequencyInfoImplBase &BFI,
389 const DitheringDistributer &D, const BlockNode &T,
390 const BlockMass &M, const char *Desc) {
391 dbgs() << " => assign " << M << " (" << D.RemMass << ")";
392 if (Desc)
393 dbgs() << " [" << Desc << "]";
394 if (T.isValid())
395 dbgs() << " to " << BFI.getBlockName(T);
396 dbgs() << "\n";
397 }
398 #endif
399
distributeMass(const BlockNode & Source,LoopData * OuterLoop,Distribution & Dist)400 void BlockFrequencyInfoImplBase::distributeMass(const BlockNode &Source,
401 LoopData *OuterLoop,
402 Distribution &Dist) {
403 BlockMass Mass = Working[Source.Index].getMass();
404 DEBUG(dbgs() << " => mass: " << Mass << "\n");
405
406 // Distribute mass to successors as laid out in Dist.
407 DitheringDistributer D(Dist, Mass);
408
409 for (const Weight &W : Dist.Weights) {
410 // Check for a local edge (non-backedge and non-exit).
411 BlockMass Taken = D.takeMass(W.Amount);
412 if (W.Type == Weight::Local) {
413 Working[W.TargetNode.Index].getMass() += Taken;
414 DEBUG(debugAssign(*this, D, W.TargetNode, Taken, nullptr));
415 continue;
416 }
417
418 // Backedges and exits only make sense if we're processing a loop.
419 assert(OuterLoop && "backedge or exit outside of loop");
420
421 // Check for a backedge.
422 if (W.Type == Weight::Backedge) {
423 OuterLoop->BackedgeMass[OuterLoop->getHeaderIndex(W.TargetNode)] += Taken;
424 DEBUG(debugAssign(*this, D, W.TargetNode, Taken, "back"));
425 continue;
426 }
427
428 // This must be an exit.
429 assert(W.Type == Weight::Exit);
430 OuterLoop->Exits.push_back(std::make_pair(W.TargetNode, Taken));
431 DEBUG(debugAssign(*this, D, W.TargetNode, Taken, "exit"));
432 }
433 }
434
convertFloatingToInteger(BlockFrequencyInfoImplBase & BFI,const Scaled64 & Min,const Scaled64 & Max)435 static void convertFloatingToInteger(BlockFrequencyInfoImplBase &BFI,
436 const Scaled64 &Min, const Scaled64 &Max) {
437 // Scale the Factor to a size that creates integers. Ideally, integers would
438 // be scaled so that Max == UINT64_MAX so that they can be best
439 // differentiated. However, in the presence of large frequency values, small
440 // frequencies are scaled down to 1, making it impossible to differentiate
441 // small, unequal numbers. When the spread between Min and Max frequencies
442 // fits well within MaxBits, we make the scale be at least 8.
443 const unsigned MaxBits = 64;
444 const unsigned SpreadBits = (Max / Min).lg();
445 Scaled64 ScalingFactor;
446 if (SpreadBits <= MaxBits - 3) {
447 // If the values are small enough, make the scaling factor at least 8 to
448 // allow distinguishing small values.
449 ScalingFactor = Min.inverse();
450 ScalingFactor <<= 3;
451 } else {
452 // If the values need more than MaxBits to be represented, saturate small
453 // frequency values down to 1 by using a scaling factor that benefits large
454 // frequency values.
455 ScalingFactor = Scaled64(1, MaxBits) / Max;
456 }
457
458 // Translate the floats to integers.
459 DEBUG(dbgs() << "float-to-int: min = " << Min << ", max = " << Max
460 << ", factor = " << ScalingFactor << "\n");
461 for (size_t Index = 0; Index < BFI.Freqs.size(); ++Index) {
462 Scaled64 Scaled = BFI.Freqs[Index].Scaled * ScalingFactor;
463 BFI.Freqs[Index].Integer = std::max(UINT64_C(1), Scaled.toInt<uint64_t>());
464 DEBUG(dbgs() << " - " << BFI.getBlockName(Index) << ": float = "
465 << BFI.Freqs[Index].Scaled << ", scaled = " << Scaled
466 << ", int = " << BFI.Freqs[Index].Integer << "\n");
467 }
468 }
469
470 /// \brief Unwrap a loop package.
471 ///
472 /// Visits all the members of a loop, adjusting their BlockData according to
473 /// the loop's pseudo-node.
unwrapLoop(BlockFrequencyInfoImplBase & BFI,LoopData & Loop)474 static void unwrapLoop(BlockFrequencyInfoImplBase &BFI, LoopData &Loop) {
475 DEBUG(dbgs() << "unwrap-loop-package: " << BFI.getLoopName(Loop)
476 << ": mass = " << Loop.Mass << ", scale = " << Loop.Scale
477 << "\n");
478 Loop.Scale *= Loop.Mass.toScaled();
479 Loop.IsPackaged = false;
480 DEBUG(dbgs() << " => combined-scale = " << Loop.Scale << "\n");
481
482 // Propagate the head scale through the loop. Since members are visited in
483 // RPO, the head scale will be updated by the loop scale first, and then the
484 // final head scale will be used for updated the rest of the members.
485 for (const BlockNode &N : Loop.Nodes) {
486 const auto &Working = BFI.Working[N.Index];
487 Scaled64 &F = Working.isAPackage() ? Working.getPackagedLoop()->Scale
488 : BFI.Freqs[N.Index].Scaled;
489 Scaled64 New = Loop.Scale * F;
490 DEBUG(dbgs() << " - " << BFI.getBlockName(N) << ": " << F << " => " << New
491 << "\n");
492 F = New;
493 }
494 }
495
unwrapLoops()496 void BlockFrequencyInfoImplBase::unwrapLoops() {
497 // Set initial frequencies from loop-local masses.
498 for (size_t Index = 0; Index < Working.size(); ++Index)
499 Freqs[Index].Scaled = Working[Index].Mass.toScaled();
500
501 for (LoopData &Loop : Loops)
502 unwrapLoop(*this, Loop);
503 }
504
finalizeMetrics()505 void BlockFrequencyInfoImplBase::finalizeMetrics() {
506 // Unwrap loop packages in reverse post-order, tracking min and max
507 // frequencies.
508 auto Min = Scaled64::getLargest();
509 auto Max = Scaled64::getZero();
510 for (size_t Index = 0; Index < Working.size(); ++Index) {
511 // Update min/max scale.
512 Min = std::min(Min, Freqs[Index].Scaled);
513 Max = std::max(Max, Freqs[Index].Scaled);
514 }
515
516 // Convert to integers.
517 convertFloatingToInteger(*this, Min, Max);
518
519 // Clean up data structures.
520 cleanup(*this);
521
522 // Print out the final stats.
523 DEBUG(dump());
524 }
525
526 BlockFrequency
getBlockFreq(const BlockNode & Node) const527 BlockFrequencyInfoImplBase::getBlockFreq(const BlockNode &Node) const {
528 if (!Node.isValid())
529 return 0;
530 return Freqs[Node.Index].Integer;
531 }
532
533 Optional<uint64_t>
getBlockProfileCount(const Function & F,const BlockNode & Node) const534 BlockFrequencyInfoImplBase::getBlockProfileCount(const Function &F,
535 const BlockNode &Node) const {
536 auto EntryCount = F.getEntryCount();
537 if (!EntryCount)
538 return None;
539 // Use 128 bit APInt to do the arithmetic to avoid overflow.
540 APInt BlockCount(128, EntryCount.getValue());
541 APInt BlockFreq(128, getBlockFreq(Node).getFrequency());
542 APInt EntryFreq(128, getEntryFreq());
543 BlockCount *= BlockFreq;
544 BlockCount = BlockCount.udiv(EntryFreq);
545 return BlockCount.getLimitedValue();
546 }
547
548 Scaled64
getFloatingBlockFreq(const BlockNode & Node) const549 BlockFrequencyInfoImplBase::getFloatingBlockFreq(const BlockNode &Node) const {
550 if (!Node.isValid())
551 return Scaled64::getZero();
552 return Freqs[Node.Index].Scaled;
553 }
554
setBlockFreq(const BlockNode & Node,uint64_t Freq)555 void BlockFrequencyInfoImplBase::setBlockFreq(const BlockNode &Node,
556 uint64_t Freq) {
557 assert(Node.isValid() && "Expected valid node");
558 assert(Node.Index < Freqs.size() && "Expected legal index");
559 Freqs[Node.Index].Integer = Freq;
560 }
561
562 std::string
getBlockName(const BlockNode & Node) const563 BlockFrequencyInfoImplBase::getBlockName(const BlockNode &Node) const {
564 return std::string();
565 }
566
567 std::string
getLoopName(const LoopData & Loop) const568 BlockFrequencyInfoImplBase::getLoopName(const LoopData &Loop) const {
569 return getBlockName(Loop.getHeader()) + (Loop.isIrreducible() ? "**" : "*");
570 }
571
572 raw_ostream &
printBlockFreq(raw_ostream & OS,const BlockNode & Node) const573 BlockFrequencyInfoImplBase::printBlockFreq(raw_ostream &OS,
574 const BlockNode &Node) const {
575 return OS << getFloatingBlockFreq(Node);
576 }
577
578 raw_ostream &
printBlockFreq(raw_ostream & OS,const BlockFrequency & Freq) const579 BlockFrequencyInfoImplBase::printBlockFreq(raw_ostream &OS,
580 const BlockFrequency &Freq) const {
581 Scaled64 Block(Freq.getFrequency(), 0);
582 Scaled64 Entry(getEntryFreq(), 0);
583
584 return OS << Block / Entry;
585 }
586
addNodesInLoop(const BFIBase::LoopData & OuterLoop)587 void IrreducibleGraph::addNodesInLoop(const BFIBase::LoopData &OuterLoop) {
588 Start = OuterLoop.getHeader();
589 Nodes.reserve(OuterLoop.Nodes.size());
590 for (auto N : OuterLoop.Nodes)
591 addNode(N);
592 indexNodes();
593 }
594
addNodesInFunction()595 void IrreducibleGraph::addNodesInFunction() {
596 Start = 0;
597 for (uint32_t Index = 0; Index < BFI.Working.size(); ++Index)
598 if (!BFI.Working[Index].isPackaged())
599 addNode(Index);
600 indexNodes();
601 }
602
indexNodes()603 void IrreducibleGraph::indexNodes() {
604 for (auto &I : Nodes)
605 Lookup[I.Node.Index] = &I;
606 }
607
addEdge(IrrNode & Irr,const BlockNode & Succ,const BFIBase::LoopData * OuterLoop)608 void IrreducibleGraph::addEdge(IrrNode &Irr, const BlockNode &Succ,
609 const BFIBase::LoopData *OuterLoop) {
610 if (OuterLoop && OuterLoop->isHeader(Succ))
611 return;
612 auto L = Lookup.find(Succ.Index);
613 if (L == Lookup.end())
614 return;
615 IrrNode &SuccIrr = *L->second;
616 Irr.Edges.push_back(&SuccIrr);
617 SuccIrr.Edges.push_front(&Irr);
618 ++SuccIrr.NumIn;
619 }
620
621 namespace llvm {
622 template <> struct GraphTraits<IrreducibleGraph> {
623 typedef bfi_detail::IrreducibleGraph GraphT;
624
625 typedef const GraphT::IrrNode NodeType;
626 typedef GraphT::IrrNode::iterator ChildIteratorType;
627
getEntryNodellvm::GraphTraits628 static const NodeType *getEntryNode(const GraphT &G) {
629 return G.StartIrr;
630 }
child_beginllvm::GraphTraits631 static ChildIteratorType child_begin(NodeType *N) { return N->succ_begin(); }
child_endllvm::GraphTraits632 static ChildIteratorType child_end(NodeType *N) { return N->succ_end(); }
633 };
634 } // end namespace llvm
635
636 /// \brief Find extra irreducible headers.
637 ///
638 /// Find entry blocks and other blocks with backedges, which exist when \c G
639 /// contains irreducible sub-SCCs.
findIrreducibleHeaders(const BlockFrequencyInfoImplBase & BFI,const IrreducibleGraph & G,const std::vector<const IrreducibleGraph::IrrNode * > & SCC,LoopData::NodeList & Headers,LoopData::NodeList & Others)640 static void findIrreducibleHeaders(
641 const BlockFrequencyInfoImplBase &BFI,
642 const IrreducibleGraph &G,
643 const std::vector<const IrreducibleGraph::IrrNode *> &SCC,
644 LoopData::NodeList &Headers, LoopData::NodeList &Others) {
645 // Map from nodes in the SCC to whether it's an entry block.
646 SmallDenseMap<const IrreducibleGraph::IrrNode *, bool, 8> InSCC;
647
648 // InSCC also acts the set of nodes in the graph. Seed it.
649 for (const auto *I : SCC)
650 InSCC[I] = false;
651
652 for (auto I = InSCC.begin(), E = InSCC.end(); I != E; ++I) {
653 auto &Irr = *I->first;
654 for (const auto *P : make_range(Irr.pred_begin(), Irr.pred_end())) {
655 if (InSCC.count(P))
656 continue;
657
658 // This is an entry block.
659 I->second = true;
660 Headers.push_back(Irr.Node);
661 DEBUG(dbgs() << " => entry = " << BFI.getBlockName(Irr.Node) << "\n");
662 break;
663 }
664 }
665 assert(Headers.size() >= 2 &&
666 "Expected irreducible CFG; -loop-info is likely invalid");
667 if (Headers.size() == InSCC.size()) {
668 // Every block is a header.
669 std::sort(Headers.begin(), Headers.end());
670 return;
671 }
672
673 // Look for extra headers from irreducible sub-SCCs.
674 for (const auto &I : InSCC) {
675 // Entry blocks are already headers.
676 if (I.second)
677 continue;
678
679 auto &Irr = *I.first;
680 for (const auto *P : make_range(Irr.pred_begin(), Irr.pred_end())) {
681 // Skip forward edges.
682 if (P->Node < Irr.Node)
683 continue;
684
685 // Skip predecessors from entry blocks. These can have inverted
686 // ordering.
687 if (InSCC.lookup(P))
688 continue;
689
690 // Store the extra header.
691 Headers.push_back(Irr.Node);
692 DEBUG(dbgs() << " => extra = " << BFI.getBlockName(Irr.Node) << "\n");
693 break;
694 }
695 if (Headers.back() == Irr.Node)
696 // Added this as a header.
697 continue;
698
699 // This is not a header.
700 Others.push_back(Irr.Node);
701 DEBUG(dbgs() << " => other = " << BFI.getBlockName(Irr.Node) << "\n");
702 }
703 std::sort(Headers.begin(), Headers.end());
704 std::sort(Others.begin(), Others.end());
705 }
706
createIrreducibleLoop(BlockFrequencyInfoImplBase & BFI,const IrreducibleGraph & G,LoopData * OuterLoop,std::list<LoopData>::iterator Insert,const std::vector<const IrreducibleGraph::IrrNode * > & SCC)707 static void createIrreducibleLoop(
708 BlockFrequencyInfoImplBase &BFI, const IrreducibleGraph &G,
709 LoopData *OuterLoop, std::list<LoopData>::iterator Insert,
710 const std::vector<const IrreducibleGraph::IrrNode *> &SCC) {
711 // Translate the SCC into RPO.
712 DEBUG(dbgs() << " - found-scc\n");
713
714 LoopData::NodeList Headers;
715 LoopData::NodeList Others;
716 findIrreducibleHeaders(BFI, G, SCC, Headers, Others);
717
718 auto Loop = BFI.Loops.emplace(Insert, OuterLoop, Headers.begin(),
719 Headers.end(), Others.begin(), Others.end());
720
721 // Update loop hierarchy.
722 for (const auto &N : Loop->Nodes)
723 if (BFI.Working[N.Index].isLoopHeader())
724 BFI.Working[N.Index].Loop->Parent = &*Loop;
725 else
726 BFI.Working[N.Index].Loop = &*Loop;
727 }
728
729 iterator_range<std::list<LoopData>::iterator>
analyzeIrreducible(const IrreducibleGraph & G,LoopData * OuterLoop,std::list<LoopData>::iterator Insert)730 BlockFrequencyInfoImplBase::analyzeIrreducible(
731 const IrreducibleGraph &G, LoopData *OuterLoop,
732 std::list<LoopData>::iterator Insert) {
733 assert((OuterLoop == nullptr) == (Insert == Loops.begin()));
734 auto Prev = OuterLoop ? std::prev(Insert) : Loops.end();
735
736 for (auto I = scc_begin(G); !I.isAtEnd(); ++I) {
737 if (I->size() < 2)
738 continue;
739
740 // Translate the SCC into RPO.
741 createIrreducibleLoop(*this, G, OuterLoop, Insert, *I);
742 }
743
744 if (OuterLoop)
745 return make_range(std::next(Prev), Insert);
746 return make_range(Loops.begin(), Insert);
747 }
748
749 void
updateLoopWithIrreducible(LoopData & OuterLoop)750 BlockFrequencyInfoImplBase::updateLoopWithIrreducible(LoopData &OuterLoop) {
751 OuterLoop.Exits.clear();
752 for (auto &Mass : OuterLoop.BackedgeMass)
753 Mass = BlockMass::getEmpty();
754 auto O = OuterLoop.Nodes.begin() + 1;
755 for (auto I = O, E = OuterLoop.Nodes.end(); I != E; ++I)
756 if (!Working[I->Index].isPackaged())
757 *O++ = *I;
758 OuterLoop.Nodes.erase(O, OuterLoop.Nodes.end());
759 }
760
adjustLoopHeaderMass(LoopData & Loop)761 void BlockFrequencyInfoImplBase::adjustLoopHeaderMass(LoopData &Loop) {
762 assert(Loop.isIrreducible() && "this only makes sense on irreducible loops");
763
764 // Since the loop has more than one header block, the mass flowing back into
765 // each header will be different. Adjust the mass in each header loop to
766 // reflect the masses flowing through back edges.
767 //
768 // To do this, we distribute the initial mass using the backedge masses
769 // as weights for the distribution.
770 BlockMass LoopMass = BlockMass::getFull();
771 Distribution Dist;
772
773 DEBUG(dbgs() << "adjust-loop-header-mass:\n");
774 for (uint32_t H = 0; H < Loop.NumHeaders; ++H) {
775 auto &HeaderNode = Loop.Nodes[H];
776 auto &BackedgeMass = Loop.BackedgeMass[Loop.getHeaderIndex(HeaderNode)];
777 DEBUG(dbgs() << " - Add back edge mass for node "
778 << getBlockName(HeaderNode) << ": " << BackedgeMass << "\n");
779 if (BackedgeMass.getMass() > 0)
780 Dist.addLocal(HeaderNode, BackedgeMass.getMass());
781 else
782 DEBUG(dbgs() << " Nothing added. Back edge mass is zero\n");
783 }
784
785 DitheringDistributer D(Dist, LoopMass);
786
787 DEBUG(dbgs() << " Distribute loop mass " << LoopMass
788 << " to headers using above weights\n");
789 for (const Weight &W : Dist.Weights) {
790 BlockMass Taken = D.takeMass(W.Amount);
791 assert(W.Type == Weight::Local && "all weights should be local");
792 Working[W.TargetNode.Index].getMass() = Taken;
793 DEBUG(debugAssign(*this, D, W.TargetNode, Taken, nullptr));
794 }
795 }
796