859 lines · cpp
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-exception6//7//===----------------------------------------------------------------------===//8//9// Loops should be simplified before this analysis.10//11//===----------------------------------------------------------------------===//12 13#include "llvm/Analysis/BlockFrequencyInfoImpl.h"14#include "llvm/ADT/APInt.h"15#include "llvm/ADT/DenseMap.h"16#include "llvm/ADT/SCCIterator.h"17#include "llvm/ADT/SmallString.h"18#include "llvm/Config/llvm-config.h"19#include "llvm/IR/Function.h"20#include "llvm/Support/BlockFrequency.h"21#include "llvm/Support/BranchProbability.h"22#include "llvm/Support/Compiler.h"23#include "llvm/Support/Debug.h"24#include "llvm/Support/MathExtras.h"25#include "llvm/Support/ScaledNumber.h"26#include "llvm/Support/raw_ostream.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 {44cl::opt<bool> CheckBFIUnknownBlockQueries(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 50cl::opt<bool> UseIterativeBFIInference(51 "use-iterative-bfi-inference", cl::Hidden,52 cl::desc("Apply an iterative post-processing to infer correct BFI counts"));53 54cl::opt<unsigned> IterativeBFIMaxIterationsPerBlock(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 59cl::opt<double> IterativeBFIPrecision(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 llvm64 65ScaledNumber<uint64_t> BlockMass::toScaled() const {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)72LLVM_DUMP_METHOD void BlockMass::dump() const { print(dbgs()); }73#endif74 75static char getHexDigit(int N) {76 assert(N < 16);77 if (N < 10)78 return '0' + N;79 return 'a' + N - 10;80}81 82raw_ostream &BlockMass::print(raw_ostream &OS) const {83 for (int Digits = 0; Digits < 16; ++Digits)84 OS << getHexDigit(Mass >> (60 - Digits * 4) & 0xf);85 return OS;86}87 88namespace {89 90using BlockNode = BlockFrequencyInfoImplBase::BlockNode;91using Distribution = BlockFrequencyInfoImplBase::Distribution;92using WeightList = BlockFrequencyInfoImplBase::Distribution::WeightList;93using Scaled64 = BlockFrequencyInfoImplBase::Scaled64;94using LoopData = BlockFrequencyInfoImplBase::LoopData;95using Weight = BlockFrequencyInfoImplBase::Weight;96using FrequencyData = BlockFrequencyInfoImplBase::FrequencyData;97 98/// Dithering mass distributer.99///100/// This class splits up a single mass into portions by weight, dithering to101/// spread out error. No mass is lost. The dithering precision depends on the102/// 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 the107/// 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 divided112/// 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 subtracting115/// 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 namespace126 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 else175 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.201 using HashTable = DenseMap<BlockNode::IndexType, Weight>;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) {221 combineWeightsByHashing(Weights);222 return;223 }224 225 combineWeightsBySorting(Weights);226}227 228static uint64_t shiftRightAndRound(uint64_t N, int Shift) {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 1255 // 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 the265 // 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 that275 // 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, we281 // 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 292void BlockFrequencyInfoImplBase::clear() {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.304static void cleanup(BlockFrequencyInfoImplBase &BFI) {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 312bool BlockFrequencyInfoImplBase::addToDist(Distribution &Dist,313 const LoopData *OuterLoop,314 const BlockNode &Pred,315 const BlockNode &Succ,316 uint64_t Weight) {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 NDEBUG327 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#endif338 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 from364 // 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 374bool BlockFrequencyInfoImplBase::addLoopSuccessorsToDist(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.387void BlockFrequencyInfoImplBase::computeLoopScale(LoopData &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 infinite392 // 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 an394 // arbitrary scale to avoid these issues.395 //396 // FIXME: An alternate way would be to select a symbolic scale which is later397 // replaced to be the maximum of all computed scales plus 1. This would398 // appropriately describe the loop as having a large scale, without skewing399 // the final frequency computation.400 const Scaled64 InfiniteLoopScale(1, 12);401 402 // LoopScale == 1 / ExitMass403 // ExitMass == HeadMass - BackedgeMass404 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 the411 // loop scale.412 Loop.Scale =413 ExitMass.isEmpty() ? InfiniteLoopScale : ExitMass.toScaled().inverse();414 415 LLVM_DEBUG(dbgs() << " - exit-mass = " << ExitMass << " ("416 << BlockMass::getFull() << " - " << TotalBackedgeMass417 << ")\n"418 << " - scale = " << Loop.Scale << "\n");419}420 421/// Package up a loop.422void BlockFrequencyInfoImplBase::packageLoop(LoopData &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 NDEBUG435static void debugAssign(const BlockFrequencyInfoImplBase &BFI,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#endif446 447void BlockFrequencyInfoImplBase::distributeMass(const BlockNode &Source,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 482static void convertFloatingToInteger(BlockFrequencyInfoImplBase &BFI,483 const Scaled64 &Min, const Scaled64 &Max) {484 // Scale the Factor to a size that creates integers. If possible scale485 // 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 accurately487 // represented in a 64bit integer without either loosing precision for small488 // values (so small unequal numbers all map to 1) or saturaturing big numbers489 // loosing precision for big numbers (so unequal big numbers may map to490 // 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 with493 // things like instruction costs. Leave some room to avoid saturating494 // 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 = " << Max500 << ", 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 = " << Scaled507 << ", 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 to514/// 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.Scale518 << "\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 in524 // RPO, the head scale will be updated by the loop scale first, and then the525 // 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()->Scale529 : 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 537void BlockFrequencyInfoImplBase::unwrapLoops() {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 546void BlockFrequencyInfoImplBase::finalizeMetrics() {547 // Unwrap loop packages in reverse post-order, tracking min and max548 // 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 567BlockFrequency568BlockFrequencyInfoImplBase::getBlockFreq(const BlockNode &Node) const {569 if (!Node.isValid()) {570#ifndef NDEBUG571 if (CheckBFIUnknownBlockQueries) {572 SmallString<256> Msg;573 raw_svector_ostream OS(Msg);574 OS << "*** Detected BFI query for unknown block " << getBlockName(Node);575 report_fatal_error(OS.str());576 }577#endif578 return BlockFrequency(0);579 }580 return BlockFrequency(Freqs[Node.Index].Integer);581}582 583std::optional<uint64_t>584BlockFrequencyInfoImplBase::getBlockProfileCount(const Function &F,585 const BlockNode &Node,586 bool AllowSynthetic) const {587 return getProfileCountFromFreq(F, getBlockFreq(Node), AllowSynthetic);588}589 590std::optional<uint64_t> BlockFrequencyInfoImplBase::getProfileCountFromFreq(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 unsigned601 // lshr by 1 gives EntryFreq/2.602 BlockCount = (BlockCount + EntryFreq.lshr(1)).udiv(EntryFreq);603 return BlockCount.getLimitedValue();604}605 606bool607BlockFrequencyInfoImplBase::isIrrLoopHeader(const BlockNode &Node) {608 if (!Node.isValid())609 return false;610 return IsIrrLoopHeader.test(Node.Index);611}612 613Scaled64614BlockFrequencyInfoImplBase::getFloatingBlockFreq(const BlockNode &Node) const {615 if (!Node.isValid())616 return Scaled64::getZero();617 return Freqs[Node.Index].Scaled;618}619 620void BlockFrequencyInfoImplBase::setBlockFreq(const BlockNode &Node,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::string628BlockFrequencyInfoImplBase::getBlockName(const BlockNode &Node) const {629 return {};630}631 632std::string633BlockFrequencyInfoImplBase::getLoopName(const LoopData &Loop) const {634 return getBlockName(Loop.getHeader()) + (Loop.isIrreducible() ? "**" : "*");635}636 637void IrreducibleGraph::addNodesInLoop(const BFIBase::LoopData &OuterLoop) {638 Start = OuterLoop.getHeader();639 Nodes.reserve(OuterLoop.Nodes.size());640 for (auto N : OuterLoop.Nodes)641 addNode(N);642 indexNodes();643}644 645void IrreducibleGraph::addNodesInFunction() {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 653void IrreducibleGraph::indexNodes() {654 for (auto &I : Nodes)655 Lookup[I.Node.Index] = &I;656}657 658void IrreducibleGraph::addEdge(IrrNode &Irr, const BlockNode &Succ,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> {674 using GraphT = bfi_detail::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 llvm684 685/// Find extra irreducible headers.686///687/// Find entry blocks and other blocks with backedges, which exist when \c G688/// contains irreducible sub-SCCs.689static void findIrreducibleHeaders(690 const BlockFrequencyInfoImplBase &BFI,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.695 SmallDenseMap<const IrreducibleGraph::IrrNode *, bool, 8> InSCC;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 inverted736 // 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 758static void createIrreducibleLoop(759 BlockFrequencyInfoImplBase &BFI, const IrreducibleGraph &G,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 else777 BFI.Working[N.Index].Loop = &*Loop;778}779 780iterator_range<std::list<LoopData>::iterator>781BlockFrequencyInfoImplBase::analyzeIrreducible(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 800void801BlockFrequencyInfoImplBase::updateLoopWithIrreducible(LoopData &OuterLoop) {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 812void BlockFrequencyInfoImplBase::adjustLoopHeaderMass(LoopData &Loop) {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 into816 // each header will be different. Adjust the mass in each header loop to817 // reflect the masses flowing through back edges.818 //819 // To do this, we distribute the initial mass using the backedge masses820 // 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) << ": " << BackedgeMass830 << "\n");831 if (BackedgeMass.getMass() > 0)832 Dist.addLocal(HeaderNode, BackedgeMass.getMass());833 else834 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 " << LoopMass840 << " 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 849void BlockFrequencyInfoImplBase::distributeIrrLoopHeaderMass(Distribution &Dist) {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}859