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/GraphTraits.h"
  17 #include "llvm/ADT/None.h"
  18 #include "llvm/ADT/SCCIterator.h"
  19 #include "llvm/Config/llvm-config.h"
  20 #include "llvm/IR/Function.h"
  21 #include "llvm/Support/BlockFrequency.h"
  22 #include "llvm/Support/BranchProbability.h"
  23 #include "llvm/Support/Compiler.h"
  24 #include "llvm/Support/Debug.h"
  25 #include "llvm/Support/ScaledNumber.h"
  26 #include "llvm/Support/MathExtras.h"
  27 #include "llvm/Support/raw_ostream.h"
  28 #include <algorithm>
  29 #include <cassert>
  30 #include <cstddef>
  31 #include <cstdint>
  32 #include <iterator>
  33 #include <list>
  34 #include <numeric>
  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::init(false), cl::Hidden, cl::ZeroOrMore,
  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 }
  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 - countLeadingZeros(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.  Ideally, integers would
 485   // be scaled so that Max == UINT64_MAX so that they can be best
 486   // differentiated.  However, in the presence of large frequency values, small
 487   // frequencies are scaled down to 1, making it impossible to differentiate
 488   // small, unequal numbers. When the spread between Min and Max frequencies
 489   // fits well within MaxBits, we make the scale be at least 8.
 490   const unsigned MaxBits = 64;
 491   const unsigned SpreadBits = (Max / Min).lg();
 492   Scaled64 ScalingFactor;
 493   if (SpreadBits <= MaxBits - 3) {
 494     // If the values are small enough, make the scaling factor at least 8 to
 495     // allow distinguishing small values.
 496     ScalingFactor = Min.inverse();
 497     ScalingFactor <<= 3;
 498   } else {
 499     // If the values need more than MaxBits to be represented, saturate small
 500     // frequency values down to 1 by using a scaling factor that benefits large
 501     // frequency values.
 502     ScalingFactor = Scaled64(1, MaxBits) / Max;
 503   }
 504
 505   // Translate the floats to integers.
 506   LLVM_DEBUG(dbgs() << "float-to-int: min = " << Min << ", max = " << Max
 507                     << ", factor = " << ScalingFactor << "\n");
 508   for (size_t Index = 0; Index < BFI.Freqs.size(); ++Index) {
 509     Scaled64 Scaled = BFI.Freqs[Index].Scaled * ScalingFactor;
 510     BFI.Freqs[Index].Integer = std::max(UINT64_C(1), Scaled.toInt<uint64_t>());
 511     LLVM_DEBUG(dbgs() << " - " << BFI.getBlockName(Index) << ": float = "
 512                       << BFI.Freqs[Index].Scaled << ", scaled = " << Scaled
 513                       << ", int = " << BFI.Freqs[Index].Integer << "\n");
 514   }
 515 }
 516
 517 /// Unwrap a loop package.
 518 ///
 519 /// Visits all the members of a loop, adjusting their BlockData according to
 520 /// the loop's pseudo-node.
 521 static void unwrapLoop(BlockFrequencyInfoImplBase &BFI, LoopData &Loop) {
 522   LLVM_DEBUG(dbgs() << "unwrap-loop-package: " << BFI.getLoopName(Loop)
 523                     << ": mass = " << Loop.Mass << ", scale = " << Loop.Scale
 524                     << "\n");
 525   Loop.Scale *= Loop.Mass.toScaled();
 526   Loop.IsPackaged = false;
 527   LLVM_DEBUG(dbgs() << "  => combined-scale = " << Loop.Scale << "\n");
 528
 529   // Propagate the head scale through the loop.  Since members are visited in
 530   // RPO, the head scale will be updated by the loop scale first, and then the
 531   // final head scale will be used for updated the rest of the members.
 532   for (const BlockNode &N : Loop.Nodes) {
 533     const auto &Working = BFI.Working[N.Index];
 534     Scaled64 &F = Working.isAPackage() ? Working.getPackagedLoop()->Scale
 535                                        : BFI.Freqs[N.Index].Scaled;
 536     Scaled64 New = Loop.Scale * F;
 537     LLVM_DEBUG(dbgs() << " - " << BFI.getBlockName(N) << ": " << F << " => "
 538                       << New << "\n");
 539     F = New;
 540   }
 541 }
 542
 543 void BlockFrequencyInfoImplBase::unwrapLoops() {
 544   // Set initial frequencies from loop-local masses.
 545   for (size_t Index = 0; Index < Working.size(); ++Index)
 546     Freqs[Index].Scaled = Working[Index].Mass.toScaled();
 547
 548   for (LoopData &Loop : Loops)
 549     unwrapLoop(*this, Loop);
 550 }
 551
 552 void BlockFrequencyInfoImplBase::finalizeMetrics() {
 553   // Unwrap loop packages in reverse post-order, tracking min and max
 554   // frequencies.
 555   auto Min = Scaled64::getLargest();
 556   auto Max = Scaled64::getZero();
 557   for (size_t Index = 0; Index < Working.size(); ++Index) {
 558     // Update min/max scale.
 559     Min = std::min(Min, Freqs[Index].Scaled);
 560     Max = std::max(Max, Freqs[Index].Scaled);
 561   }
 562
 563   // Convert to integers.
 564   convertFloatingToInteger(*this, Min, Max);
 565
 566   // Clean up data structures.
 567   cleanup(*this);
 568
 569   // Print out the final stats.
 570   LLVM_DEBUG(dump());
 571 }
 572
 573 BlockFrequency
 574 BlockFrequencyInfoImplBase::getBlockFreq(const BlockNode &Node) const {
 575   if (!Node.isValid()) {
 576 #ifndef NDEBUG
 577     if (CheckBFIUnknownBlockQueries) {
 578       SmallString<256> Msg;
 579       raw_svector_ostream OS(Msg);
 580       OS << "*** Detected BFI query for unknown block " << getBlockName(Node);
 581       report_fatal_error(OS.str());
 582     }
 583 #endif
 584     return 0;
 585   }
 586   return Freqs[Node.Index].Integer;
 587 }
 588
 589 Optional<uint64_t>
 590 BlockFrequencyInfoImplBase::getBlockProfileCount(const Function &F,
 591                                                  const BlockNode &Node,
 592                                                  bool AllowSynthetic) const {
 593   return getProfileCountFromFreq(F, getBlockFreq(Node).getFrequency(),
 594                                  AllowSynthetic);
 595 }
 596
 597 Optional<uint64_t>
 598 BlockFrequencyInfoImplBase::getProfileCountFromFreq(const Function &F,
 599                                                     uint64_t Freq,
 600                                                     bool AllowSynthetic) const {
 601   auto EntryCount = F.getEntryCount(AllowSynthetic);
 602   if (!EntryCount)
 603     return None;
 604   // Use 128 bit APInt to do the arithmetic to avoid overflow.
 605   APInt BlockCount(128, EntryCount.getCount());
 606   APInt BlockFreq(128, Freq);
 607   APInt EntryFreq(128, getEntryFreq());
 608   BlockCount *= BlockFreq;
 609   // Rounded division of BlockCount by EntryFreq. Since EntryFreq is unsigned
 610   // lshr by 1 gives EntryFreq/2.
 611   BlockCount = (BlockCount + EntryFreq.lshr(1)).udiv(EntryFreq);
 612   return BlockCount.getLimitedValue();
 613 }
 614
 615 bool
 616 BlockFrequencyInfoImplBase::isIrrLoopHeader(const BlockNode &Node) {
 617   if (!Node.isValid())
 618     return false;
 619   return IsIrrLoopHeader.test(Node.Index);
 620 }
 621
 622 Scaled64
 623 BlockFrequencyInfoImplBase::getFloatingBlockFreq(const BlockNode &Node) const {
 624   if (!Node.isValid())
 625     return Scaled64::getZero();
 626   return Freqs[Node.Index].Scaled;
 627 }
 628
 629 void BlockFrequencyInfoImplBase::setBlockFreq(const BlockNode &Node,
 630                                               uint64_t Freq) {
 631   assert(Node.isValid() && "Expected valid node");
 632   assert(Node.Index < Freqs.size() && "Expected legal index");
 633   Freqs[Node.Index].Integer = Freq;
 634 }
 635
 636 std::string
 637 BlockFrequencyInfoImplBase::getBlockName(const BlockNode &Node) const {
 638   return {};
 639 }
 640
 641 std::string
 642 BlockFrequencyInfoImplBase::getLoopName(const LoopData &Loop) const {
 643   return getBlockName(Loop.getHeader()) + (Loop.isIrreducible() ? "**" : "*");
 644 }
 645
 646 raw_ostream &
 647 BlockFrequencyInfoImplBase::printBlockFreq(raw_ostream &OS,
 648                                            const BlockNode &Node) const {
 649   return OS << getFloatingBlockFreq(Node);
 650 }
 651
 652 raw_ostream &
 653 BlockFrequencyInfoImplBase::printBlockFreq(raw_ostream &OS,
 654                                            const BlockFrequency &Freq) const {
 655   Scaled64 Block(Freq.getFrequency(), 0);
 656   Scaled64 Entry(getEntryFreq(), 0);
 657
 658   return OS << Block / Entry;
 659 }
 660
 661 void IrreducibleGraph::addNodesInLoop(const BFIBase::LoopData &OuterLoop) {
 662   Start = OuterLoop.getHeader();
 663   Nodes.reserve(OuterLoop.Nodes.size());
 664   for (auto N : OuterLoop.Nodes)
 665     addNode(N);
 666   indexNodes();
 667 }
 668
 669 void IrreducibleGraph::addNodesInFunction() {
 670   Start = 0;
 671   for (uint32_t Index = 0; Index < BFI.Working.size(); ++Index)
 672     if (!BFI.Working[Index].isPackaged())
 673       addNode(Index);
 674   indexNodes();
 675 }
 676
 677 void IrreducibleGraph::indexNodes() {
 678   for (auto &I : Nodes)
 679     Lookup[I.Node.Index] = &I;
 680 }
 681
 682 void IrreducibleGraph::addEdge(IrrNode &Irr, const BlockNode &Succ,
 683                                const BFIBase::LoopData *OuterLoop) {
 684   if (OuterLoop && OuterLoop->isHeader(Succ))
 685     return;
 686   auto L = Lookup.find(Succ.Index);
 687   if (L == Lookup.end())
 688     return;
 689   IrrNode &SuccIrr = *L->second;
 690   Irr.Edges.push_back(&SuccIrr);
 691   SuccIrr.Edges.push_front(&Irr);
 692   ++SuccIrr.NumIn;
 693 }
 694
 695 namespace llvm {
 696
 697 template <> struct GraphTraits<IrreducibleGraph> {
 698   using GraphT = bfi_detail::IrreducibleGraph;
 699   using NodeRef = const GraphT::IrrNode *;
 700   using ChildIteratorType = GraphT::IrrNode::iterator;
 701
 702   static NodeRef getEntryNode(const GraphT &G) { return G.StartIrr; }
 703   static ChildIteratorType child_begin(NodeRef N) { return N->succ_begin(); }
 704   static ChildIteratorType child_end(NodeRef N) { return N->succ_end(); }
 705 };
 706
 707 } // end namespace llvm
 708
 709 /// Find extra irreducible headers.
 710 ///
 711 /// Find entry blocks and other blocks with backedges, which exist when \c G
 712 /// contains irreducible sub-SCCs.
 713 static void findIrreducibleHeaders(
 714     const BlockFrequencyInfoImplBase &BFI,
 715     const IrreducibleGraph &G,
 716     const std::vector<const IrreducibleGraph::IrrNode *> &SCC,
 717     LoopData::NodeList &Headers, LoopData::NodeList &Others) {
 718   // Map from nodes in the SCC to whether it's an entry block.
 719   SmallDenseMap<const IrreducibleGraph::IrrNode *, bool, 8> InSCC;
 720
 721   // InSCC also acts the set of nodes in the graph.  Seed it.
 722   for (const auto *I : SCC)
 723     InSCC[I] = false;
 724
 725   for (auto I = InSCC.begin(), E = InSCC.end(); I != E; ++I) {
 726     auto &Irr = *I->first;
 727     for (const auto *P : make_range(Irr.pred_begin(), Irr.pred_end())) {
 728       if (InSCC.count(P))
 729         continue;
 730
 731       // This is an entry block.
 732       I->second = true;
 733       Headers.push_back(Irr.Node);
 734       LLVM_DEBUG(dbgs() << "  => entry = " << BFI.getBlockName(Irr.Node)
 735                         << "\n");
 736       break;
 737     }
 738   }
 739   assert(Headers.size() >= 2 &&
 740          "Expected irreducible CFG; -loop-info is likely invalid");
 741   if (Headers.size() == InSCC.size()) {
 742     // Every block is a header.
 743     llvm::sort(Headers);
 744     return;
 745   }
 746
 747   // Look for extra headers from irreducible sub-SCCs.
 748   for (const auto &I : InSCC) {
 749     // Entry blocks are already headers.
 750     if (I.second)
 751       continue;
 752
 753     auto &Irr = *I.first;
 754     for (const auto *P : make_range(Irr.pred_begin(), Irr.pred_end())) {
 755       // Skip forward edges.
 756       if (P->Node < Irr.Node)
 757         continue;
 758
 759       // Skip predecessors from entry blocks.  These can have inverted
 760       // ordering.
 761       if (InSCC.lookup(P))
 762         continue;
 763
 764       // Store the extra header.
 765       Headers.push_back(Irr.Node);
 766       LLVM_DEBUG(dbgs() << "  => extra = " << BFI.getBlockName(Irr.Node)
 767                         << "\n");
 768       break;
 769     }
 770     if (Headers.back() == Irr.Node)
 771       // Added this as a header.
 772       continue;
 773
 774     // This is not a header.
 775     Others.push_back(Irr.Node);
 776     LLVM_DEBUG(dbgs() << "  => other = " << BFI.getBlockName(Irr.Node) << "\n");
 777   }
 778   llvm::sort(Headers);
 779   llvm::sort(Others);
 780 }
 781
 782 static void createIrreducibleLoop(
 783     BlockFrequencyInfoImplBase &BFI, const IrreducibleGraph &G,
 784     LoopData *OuterLoop, std::list<LoopData>::iterator Insert,
 785     const std::vector<const IrreducibleGraph::IrrNode *> &SCC) {
 786   // Translate the SCC into RPO.
 787   LLVM_DEBUG(dbgs() << " - found-scc\n");
 788
 789   LoopData::NodeList Headers;
 790   LoopData::NodeList Others;
 791   findIrreducibleHeaders(BFI, G, SCC, Headers, Others);
 792
 793   auto Loop = BFI.Loops.emplace(Insert, OuterLoop, Headers.begin(),
 794                                 Headers.end(), Others.begin(), Others.end());
 795
 796   // Update loop hierarchy.
 797   for (const auto &N : Loop->Nodes)
 798     if (BFI.Working[N.Index].isLoopHeader())
 799       BFI.Working[N.Index].Loop->Parent = &*Loop;
 800     else
 801       BFI.Working[N.Index].Loop = &*Loop;
 802 }
 803
 804 iterator_range<std::list<LoopData>::iterator>
 805 BlockFrequencyInfoImplBase::analyzeIrreducible(
 806     const IrreducibleGraph &G, LoopData *OuterLoop,
 807     std::list<LoopData>::iterator Insert) {
 808   assert((OuterLoop == nullptr) == (Insert == Loops.begin()));
 809   auto Prev = OuterLoop ? std::prev(Insert) : Loops.end();
 810
 811   for (auto I = scc_begin(G); !I.isAtEnd(); ++I) {
 812     if (I->size() < 2)
 813       continue;
 814
 815     // Translate the SCC into RPO.
 816     createIrreducibleLoop(*this, G, OuterLoop, Insert, *I);
 817   }
 818
 819   if (OuterLoop)
 820     return make_range(std::next(Prev), Insert);
 821   return make_range(Loops.begin(), Insert);
 822 }
 823
 824 void
 825 BlockFrequencyInfoImplBase::updateLoopWithIrreducible(LoopData &OuterLoop) {
 826   OuterLoop.Exits.clear();
 827   for (auto &Mass : OuterLoop.BackedgeMass)
 828     Mass = BlockMass::getEmpty();
 829   auto O = OuterLoop.Nodes.begin() + 1;
 830   for (auto I = O, E = OuterLoop.Nodes.end(); I != E; ++I)
 831     if (!Working[I->Index].isPackaged())
 832       *O++ = *I;
 833   OuterLoop.Nodes.erase(O, OuterLoop.Nodes.end());
 834 }
 835
 836 void BlockFrequencyInfoImplBase::adjustLoopHeaderMass(LoopData &Loop) {
 837   assert(Loop.isIrreducible() && "this only makes sense on irreducible loops");
 838
 839   // Since the loop has more than one header block, the mass flowing back into
 840   // each header will be different. Adjust the mass in each header loop to
 841   // reflect the masses flowing through back edges.
 842   //
 843   // To do this, we distribute the initial mass using the backedge masses
 844   // as weights for the distribution.
 845   BlockMass LoopMass = BlockMass::getFull();
 846   Distribution Dist;
 847
 848   LLVM_DEBUG(dbgs() << "adjust-loop-header-mass:\n");
 849   for (uint32_t H = 0; H < Loop.NumHeaders; ++H) {
 850     auto &HeaderNode = Loop.Nodes[H];
 851     auto &BackedgeMass = Loop.BackedgeMass[Loop.getHeaderIndex(HeaderNode)];
 852     LLVM_DEBUG(dbgs() << " - Add back edge mass for node "
 853                       << getBlockName(HeaderNode) << ": " << BackedgeMass
 854                       << "\n");
 855     if (BackedgeMass.getMass() > 0)
 856       Dist.addLocal(HeaderNode, BackedgeMass.getMass());
 857     else
 858       LLVM_DEBUG(dbgs() << "   Nothing added. Back edge mass is zero\n");
 859   }
 860
 861   DitheringDistributer D(Dist, LoopMass);
 862
 863   LLVM_DEBUG(dbgs() << " Distribute loop mass " << LoopMass
 864                     << " to headers using above weights\n");
 865   for (const Weight &W : Dist.Weights) {
 866     BlockMass Taken = D.takeMass(W.Amount);
 867     assert(W.Type == Weight::Local && "all weights should be local");
 868     Working[W.TargetNode.Index].getMass() = Taken;
 869     LLVM_DEBUG(debugAssign(*this, D, W.TargetNode, Taken, nullptr));
 870   }
 871 }
 872
 873 void BlockFrequencyInfoImplBase::distributeIrrLoopHeaderMass(Distribution &Dist) {
 874   BlockMass LoopMass = BlockMass::getFull();
 875   DitheringDistributer D(Dist, LoopMass);
 876   for (const Weight &W : Dist.Weights) {
 877     BlockMass Taken = D.takeMass(W.Amount);
 878     assert(W.Type == Weight::Local && "all weights should be local");
 879     Working[W.TargetNode.Index].getMass() = Taken;
 880     LLVM_DEBUG(debugAssign(*this, D, W.TargetNode, Taken, nullptr));
 881   }
 882 }