llvm/lib/Analysis/BlockFrequencyInfoImpl.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-exception
   6 //
   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
  38 using namespace llvm;
  39 using namespace llvm::bfi_detail;
  40
  41 #define DEBUG_TYPE "block-freq"
  42
  43 namespace llvm {
  44 cl::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
  50 cl::opt<bool> UseIterativeBFIInference(
  51     "use-iterative-bfi-inference", cl::Hidden,
  52     cl::desc("Apply an iterative post-processing to infer correct BFI counts"));
  53
  54 cl::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
  59 cl::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 llvm
  64
  65 ScaledNumber<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)
  72 LLVM_DUMP_METHOD void BlockMass::dump() const { print(dbgs()); }
  73 #endif
  74
  75 static char getHexDigit(int N) {
  76   assert(N < 16);
  77   if (N < 10)
  78     return '0' + N;
  79   return 'a' + N - 10;
  80 }
  81
  82 raw_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
  88 namespace {
  89
  90 using BlockNode = BlockFrequencyInfoImplBase::BlockNode;
  91 using Distribution = BlockFrequencyInfoImplBase::Distribution;
  92 using WeightList = BlockFrequencyInfoImplBase::Distribution::WeightList;
  93 using Scaled64 = BlockFrequencyInfoImplBase::Scaled64;
  94 using LoopData = BlockFrequencyInfoImplBase::LoopData;
  95 using Weight = BlockFrequencyInfoImplBase::Weight;
  96 using FrequencyData = BlockFrequencyInfoImplBase::FrequencyData;
  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.
 116 struct 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
 127 DitheringDistributer::DitheringDistributer(Distribution &Dist,
 128                                            const BlockMass &Mass) {
 129   Dist.normalize();
 130   RemWeight = Dist.Total;
 131   RemMass = Mass;
 132 }
 133
 134 BlockMass 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
 145 void 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
 162 static 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
 178 static 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
 199 static 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
 218 static 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
 228 static 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
 236 void 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
 292 void 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.
 304 static 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
 312 bool 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 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
 374 bool 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.
 387 void 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 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.
 422 void 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 NDEBUG
 435 static 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 #endif
 446
 447 void 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
 482 static void convertFloatingToInteger(BlockFrequencyInfoImplBase &BFI,
 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.
 515 static 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
 537 void 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
 546 void BlockFrequencyInfoImplBase::finalizeMetrics() {
 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
 567 BlockFrequency
 568 BlockFrequencyInfoImplBase::getBlockFreq(const BlockNode &Node) const {
 569   if (!Node.isValid()) {
 570 #ifndef NDEBUG
 571     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 #endif
 578     return BlockFrequency(0);
 579   }
 580   return BlockFrequency(Freqs[Node.Index].Integer);
 581 }
 582
 583 std::optional<uint64_t>
 584 BlockFrequencyInfoImplBase::getBlockProfileCount(const Function &F,
 585                                                  const BlockNode &Node,
 586                                                  bool AllowSynthetic) const {
 587   return getProfileCountFromFreq(F, getBlockFreq(Node), AllowSynthetic);
 588 }
 589
 590 std::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 unsigned
 601   // lshr by 1 gives EntryFreq/2.
 602   BlockCount = (BlockCount + EntryFreq.lshr(1)).udiv(EntryFreq);
 603   return BlockCount.getLimitedValue();
 604 }
 605
 606 bool
 607 BlockFrequencyInfoImplBase::isIrrLoopHeader(const BlockNode &Node) {
 608   if (!Node.isValid())
 609     return false;
 610   return IsIrrLoopHeader.test(Node.Index);
 611 }
 612
 613 Scaled64
 614 BlockFrequencyInfoImplBase::getFloatingBlockFreq(const BlockNode &Node) const {
 615   if (!Node.isValid())
 616     return Scaled64::getZero();
 617   return Freqs[Node.Index].Scaled;
 618 }
 619
 620 void 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
 627 std::string
 628 BlockFrequencyInfoImplBase::getBlockName(const BlockNode &Node) const {
 629   return {};
 630 }
 631
 632 std::string
 633 BlockFrequencyInfoImplBase::getLoopName(const LoopData &Loop) const {
 634   return getBlockName(Loop.getHeader()) + (Loop.isIrreducible() ? "**" : "*");
 635 }
 636
 637 void 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
 645 void 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
 653 void IrreducibleGraph::indexNodes() {
 654   for (auto &I : Nodes)
 655     Lookup[I.Node.Index] = &I;
 656 }
 657
 658 void 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
 671 namespace llvm {
 672
 673 template <> 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 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.
 689 static 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 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
 758 static 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     else
 777       BFI.Working[N.Index].Loop = &*Loop;
 778 }
 779
 780 iterator_range<std::list<LoopData>::iterator>
 781 BlockFrequencyInfoImplBase::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
 800 void
 801 BlockFrequencyInfoImplBase::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
 812 void 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 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
 849 void 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 }