1 ////===- SampleProfileLoadBaseImpl.h - Profile loader base impl --*- C++-*-===// 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 /// \file 10 /// This file provides the interface for the sampled PGO profile loader base 11 /// implementation. 12 // 13 //===----------------------------------------------------------------------===// 14 15 #ifndef LLVM_TRANSFORMS_UTILS_SAMPLEPROFILELOADERBASEIMPL_H 16 #define LLVM_TRANSFORMS_UTILS_SAMPLEPROFILELOADERBASEIMPL_H 17 18 #include "llvm/ADT/ArrayRef.h" 19 #include "llvm/ADT/DenseMap.h" 20 #include "llvm/ADT/DenseSet.h" 21 #include "llvm/ADT/SmallPtrSet.h" 22 #include "llvm/ADT/SmallSet.h" 23 #include "llvm/ADT/SmallVector.h" 24 #include "llvm/Analysis/LoopInfo.h" 25 #include "llvm/Analysis/OptimizationRemarkEmitter.h" 26 #include "llvm/Analysis/PostDominators.h" 27 #include "llvm/IR/BasicBlock.h" 28 #include "llvm/IR/CFG.h" 29 #include "llvm/IR/DebugInfoMetadata.h" 30 #include "llvm/IR/DebugLoc.h" 31 #include "llvm/IR/Dominators.h" 32 #include "llvm/IR/Function.h" 33 #include "llvm/IR/Instruction.h" 34 #include "llvm/IR/Instructions.h" 35 #include "llvm/IR/Module.h" 36 #include "llvm/ProfileData/SampleProf.h" 37 #include "llvm/ProfileData/SampleProfReader.h" 38 #include "llvm/Support/CommandLine.h" 39 #include "llvm/Support/GenericDomTree.h" 40 #include "llvm/Support/raw_ostream.h" 41 #include "llvm/Transforms/Utils/SampleProfileLoaderBaseUtil.h" 42 43 namespace llvm { 44 using namespace sampleprof; 45 using namespace sampleprofutil; 46 using ProfileCount = Function::ProfileCount; 47 48 #define DEBUG_TYPE "sample-profile-impl" 49 50 namespace afdo_detail { 51 52 template <typename BlockT> struct IRTraits; 53 template <> struct IRTraits<BasicBlock> { 54 using InstructionT = Instruction; 55 using BasicBlockT = BasicBlock; 56 using FunctionT = Function; 57 using BlockFrequencyInfoT = BlockFrequencyInfo; 58 using LoopT = Loop; 59 using LoopInfoT = LoopInfo; 60 using OptRemarkEmitterT = OptimizationRemarkEmitter; 61 using OptRemarkAnalysisT = OptimizationRemarkAnalysis; 62 using DominatorTreeT = DominatorTree; 63 using PostDominatorTreeT = PostDominatorTree; 64 static Function &getFunction(Function &F) { return F; } 65 static const BasicBlock *getEntryBB(const Function *F) { 66 return &F->getEntryBlock(); 67 } 68 }; 69 70 } // end namespace afdo_detail 71 72 extern cl::opt<unsigned> SampleProfileMaxPropagateIterations; 73 extern cl::opt<unsigned> SampleProfileRecordCoverage; 74 extern cl::opt<unsigned> SampleProfileSampleCoverage; 75 extern cl::opt<bool> NoWarnSampleUnused; 76 77 template <typename BT> class SampleProfileLoaderBaseImpl { 78 public: 79 SampleProfileLoaderBaseImpl(std::string Name) : Filename(Name) {} 80 void dump() { Reader->dump(); } 81 82 using InstructionT = typename afdo_detail::IRTraits<BT>::InstructionT; 83 using BasicBlockT = typename afdo_detail::IRTraits<BT>::BasicBlockT; 84 using BlockFrequencyInfoT = 85 typename afdo_detail::IRTraits<BT>::BlockFrequencyInfoT; 86 using FunctionT = typename afdo_detail::IRTraits<BT>::FunctionT; 87 using LoopT = typename afdo_detail::IRTraits<BT>::LoopT; 88 using LoopInfoT = typename afdo_detail::IRTraits<BT>::LoopInfoT; 89 using OptRemarkEmitterT = 90 typename afdo_detail::IRTraits<BT>::OptRemarkEmitterT; 91 using OptRemarkAnalysisT = 92 typename afdo_detail::IRTraits<BT>::OptRemarkAnalysisT; 93 using DominatorTreeT = typename afdo_detail::IRTraits<BT>::DominatorTreeT; 94 using PostDominatorTreeT = 95 typename afdo_detail::IRTraits<BT>::PostDominatorTreeT; 96 97 using BlockWeightMap = DenseMap<const BasicBlockT *, uint64_t>; 98 using EquivalenceClassMap = 99 DenseMap<const BasicBlockT *, const BasicBlockT *>; 100 using Edge = std::pair<const BasicBlockT *, const BasicBlockT *>; 101 using EdgeWeightMap = DenseMap<Edge, uint64_t>; 102 using BlockEdgeMap = 103 DenseMap<const BasicBlockT *, SmallVector<const BasicBlockT *, 8>>; 104 105 protected: 106 ~SampleProfileLoaderBaseImpl() = default; 107 friend class SampleCoverageTracker; 108 109 Function &getFunction(FunctionT &F) { 110 return afdo_detail::IRTraits<BT>::getFunction(F); 111 } 112 const BasicBlockT *getEntryBB(const FunctionT *F) { 113 return afdo_detail::IRTraits<BT>::getEntryBB(F); 114 } 115 116 unsigned getFunctionLoc(FunctionT &Func); 117 virtual ErrorOr<uint64_t> getInstWeight(const InstructionT &Inst); 118 ErrorOr<uint64_t> getInstWeightImpl(const InstructionT &Inst); 119 ErrorOr<uint64_t> getBlockWeight(const BasicBlockT *BB); 120 mutable DenseMap<const DILocation *, const FunctionSamples *> 121 DILocation2SampleMap; 122 virtual const FunctionSamples * 123 findFunctionSamples(const InstructionT &I) const; 124 void printEdgeWeight(raw_ostream &OS, Edge E); 125 void printBlockWeight(raw_ostream &OS, const BasicBlockT *BB) const; 126 void printBlockEquivalence(raw_ostream &OS, const BasicBlockT *BB); 127 bool computeBlockWeights(FunctionT &F); 128 void findEquivalenceClasses(FunctionT &F); 129 void findEquivalencesFor(BasicBlockT *BB1, 130 ArrayRef<BasicBlockT *> Descendants, 131 PostDominatorTreeT *DomTree); 132 133 void propagateWeights(FunctionT &F); 134 uint64_t visitEdge(Edge E, unsigned *NumUnknownEdges, Edge *UnknownEdge); 135 void buildEdges(FunctionT &F); 136 bool propagateThroughEdges(FunctionT &F, bool UpdateBlockCount); 137 void clearFunctionData(); 138 void computeDominanceAndLoopInfo(FunctionT &F); 139 bool 140 computeAndPropagateWeights(FunctionT &F, 141 const DenseSet<GlobalValue::GUID> &InlinedGUIDs); 142 void emitCoverageRemarks(FunctionT &F); 143 144 /// Map basic blocks to their computed weights. 145 /// 146 /// The weight of a basic block is defined to be the maximum 147 /// of all the instruction weights in that block. 148 BlockWeightMap BlockWeights; 149 150 /// Map edges to their computed weights. 151 /// 152 /// Edge weights are computed by propagating basic block weights in 153 /// SampleProfile::propagateWeights. 154 EdgeWeightMap EdgeWeights; 155 156 /// Set of visited blocks during propagation. 157 SmallPtrSet<const BasicBlockT *, 32> VisitedBlocks; 158 159 /// Set of visited edges during propagation. 160 SmallSet<Edge, 32> VisitedEdges; 161 162 /// Equivalence classes for block weights. 163 /// 164 /// Two blocks BB1 and BB2 are in the same equivalence class if they 165 /// dominate and post-dominate each other, and they are in the same loop 166 /// nest. When this happens, the two blocks are guaranteed to execute 167 /// the same number of times. 168 EquivalenceClassMap EquivalenceClass; 169 170 /// Dominance, post-dominance and loop information. 171 std::unique_ptr<DominatorTreeT> DT; 172 std::unique_ptr<PostDominatorTreeT> PDT; 173 std::unique_ptr<LoopInfoT> LI; 174 175 /// Predecessors for each basic block in the CFG. 176 BlockEdgeMap Predecessors; 177 178 /// Successors for each basic block in the CFG. 179 BlockEdgeMap Successors; 180 181 /// Profile coverage tracker. 182 SampleCoverageTracker CoverageTracker; 183 184 /// Profile reader object. 185 std::unique_ptr<SampleProfileReader> Reader; 186 187 /// Samples collected for the body of this function. 188 FunctionSamples *Samples = nullptr; 189 190 /// Name of the profile file to load. 191 std::string Filename; 192 193 /// Profile Summary Info computed from sample profile. 194 ProfileSummaryInfo *PSI = nullptr; 195 196 /// Optimization Remark Emitter used to emit diagnostic remarks. 197 OptRemarkEmitterT *ORE = nullptr; 198 }; 199 200 /// Clear all the per-function data used to load samples and propagate weights. 201 template <typename BT> 202 void SampleProfileLoaderBaseImpl<BT>::clearFunctionData() { 203 BlockWeights.clear(); 204 EdgeWeights.clear(); 205 VisitedBlocks.clear(); 206 VisitedEdges.clear(); 207 EquivalenceClass.clear(); 208 DT = nullptr; 209 PDT = nullptr; 210 LI = nullptr; 211 Predecessors.clear(); 212 Successors.clear(); 213 CoverageTracker.clear(); 214 } 215 216 #ifndef NDEBUG 217 /// Print the weight of edge \p E on stream \p OS. 218 /// 219 /// \param OS Stream to emit the output to. 220 /// \param E Edge to print. 221 template <typename BT> 222 void SampleProfileLoaderBaseImpl<BT>::printEdgeWeight(raw_ostream &OS, Edge E) { 223 OS << "weight[" << E.first->getName() << "->" << E.second->getName() 224 << "]: " << EdgeWeights[E] << "\n"; 225 } 226 227 /// Print the equivalence class of block \p BB on stream \p OS. 228 /// 229 /// \param OS Stream to emit the output to. 230 /// \param BB Block to print. 231 template <typename BT> 232 void SampleProfileLoaderBaseImpl<BT>::printBlockEquivalence( 233 raw_ostream &OS, const BasicBlockT *BB) { 234 const BasicBlockT *Equiv = EquivalenceClass[BB]; 235 OS << "equivalence[" << BB->getName() 236 << "]: " << ((Equiv) ? EquivalenceClass[BB]->getName() : "NONE") << "\n"; 237 } 238 239 /// Print the weight of block \p BB on stream \p OS. 240 /// 241 /// \param OS Stream to emit the output to. 242 /// \param BB Block to print. 243 template <typename BT> 244 void SampleProfileLoaderBaseImpl<BT>::printBlockWeight( 245 raw_ostream &OS, const BasicBlockT *BB) const { 246 const auto &I = BlockWeights.find(BB); 247 uint64_t W = (I == BlockWeights.end() ? 0 : I->second); 248 OS << "weight[" << BB->getName() << "]: " << W << "\n"; 249 } 250 #endif 251 252 /// Get the weight for an instruction. 253 /// 254 /// The "weight" of an instruction \p Inst is the number of samples 255 /// collected on that instruction at runtime. To retrieve it, we 256 /// need to compute the line number of \p Inst relative to the start of its 257 /// function. We use HeaderLineno to compute the offset. We then 258 /// look up the samples collected for \p Inst using BodySamples. 259 /// 260 /// \param Inst Instruction to query. 261 /// 262 /// \returns the weight of \p Inst. 263 template <typename BT> 264 ErrorOr<uint64_t> 265 SampleProfileLoaderBaseImpl<BT>::getInstWeight(const InstructionT &Inst) { 266 return getInstWeightImpl(Inst); 267 } 268 269 template <typename BT> 270 ErrorOr<uint64_t> 271 SampleProfileLoaderBaseImpl<BT>::getInstWeightImpl(const InstructionT &Inst) { 272 const FunctionSamples *FS = findFunctionSamples(Inst); 273 if (!FS) 274 return std::error_code(); 275 276 const DebugLoc &DLoc = Inst.getDebugLoc(); 277 if (!DLoc) 278 return std::error_code(); 279 280 const DILocation *DIL = DLoc; 281 uint32_t LineOffset = FunctionSamples::getOffset(DIL); 282 uint32_t Discriminator = DIL->getBaseDiscriminator(); 283 ErrorOr<uint64_t> R = FS->findSamplesAt(LineOffset, Discriminator); 284 if (R) { 285 bool FirstMark = 286 CoverageTracker.markSamplesUsed(FS, LineOffset, Discriminator, R.get()); 287 if (FirstMark) { 288 ORE->emit([&]() { 289 OptRemarkAnalysisT Remark(DEBUG_TYPE, "AppliedSamples", &Inst); 290 Remark << "Applied " << ore::NV("NumSamples", *R); 291 Remark << " samples from profile (offset: "; 292 Remark << ore::NV("LineOffset", LineOffset); 293 if (Discriminator) { 294 Remark << "."; 295 Remark << ore::NV("Discriminator", Discriminator); 296 } 297 Remark << ")"; 298 return Remark; 299 }); 300 } 301 LLVM_DEBUG(dbgs() << " " << DLoc.getLine() << "." 302 << DIL->getBaseDiscriminator() << ":" << Inst 303 << " (line offset: " << LineOffset << "." 304 << DIL->getBaseDiscriminator() << " - weight: " << R.get() 305 << ")\n"); 306 } 307 return R; 308 } 309 310 /// Compute the weight of a basic block. 311 /// 312 /// The weight of basic block \p BB is the maximum weight of all the 313 /// instructions in BB. 314 /// 315 /// \param BB The basic block to query. 316 /// 317 /// \returns the weight for \p BB. 318 template <typename BT> 319 ErrorOr<uint64_t> 320 SampleProfileLoaderBaseImpl<BT>::getBlockWeight(const BasicBlockT *BB) { 321 uint64_t Max = 0; 322 bool HasWeight = false; 323 for (auto &I : *BB) { 324 const ErrorOr<uint64_t> &R = getInstWeight(I); 325 if (R) { 326 Max = std::max(Max, R.get()); 327 HasWeight = true; 328 } 329 } 330 return HasWeight ? ErrorOr<uint64_t>(Max) : std::error_code(); 331 } 332 333 /// Compute and store the weights of every basic block. 334 /// 335 /// This populates the BlockWeights map by computing 336 /// the weights of every basic block in the CFG. 337 /// 338 /// \param F The function to query. 339 template <typename BT> 340 bool SampleProfileLoaderBaseImpl<BT>::computeBlockWeights(FunctionT &F) { 341 bool Changed = false; 342 LLVM_DEBUG(dbgs() << "Block weights\n"); 343 for (const auto &BB : F) { 344 ErrorOr<uint64_t> Weight = getBlockWeight(&BB); 345 if (Weight) { 346 BlockWeights[&BB] = Weight.get(); 347 VisitedBlocks.insert(&BB); 348 Changed = true; 349 } 350 LLVM_DEBUG(printBlockWeight(dbgs(), &BB)); 351 } 352 353 return Changed; 354 } 355 356 /// Get the FunctionSamples for an instruction. 357 /// 358 /// The FunctionSamples of an instruction \p Inst is the inlined instance 359 /// in which that instruction is coming from. We traverse the inline stack 360 /// of that instruction, and match it with the tree nodes in the profile. 361 /// 362 /// \param Inst Instruction to query. 363 /// 364 /// \returns the FunctionSamples pointer to the inlined instance. 365 template <typename BT> 366 const FunctionSamples *SampleProfileLoaderBaseImpl<BT>::findFunctionSamples( 367 const InstructionT &Inst) const { 368 const DILocation *DIL = Inst.getDebugLoc(); 369 if (!DIL) 370 return Samples; 371 372 auto it = DILocation2SampleMap.try_emplace(DIL, nullptr); 373 if (it.second) { 374 it.first->second = Samples->findFunctionSamples(DIL, Reader->getRemapper()); 375 } 376 return it.first->second; 377 } 378 379 /// Find equivalence classes for the given block. 380 /// 381 /// This finds all the blocks that are guaranteed to execute the same 382 /// number of times as \p BB1. To do this, it traverses all the 383 /// descendants of \p BB1 in the dominator or post-dominator tree. 384 /// 385 /// A block BB2 will be in the same equivalence class as \p BB1 if 386 /// the following holds: 387 /// 388 /// 1- \p BB1 is a descendant of BB2 in the opposite tree. So, if BB2 389 /// is a descendant of \p BB1 in the dominator tree, then BB2 should 390 /// dominate BB1 in the post-dominator tree. 391 /// 392 /// 2- Both BB2 and \p BB1 must be in the same loop. 393 /// 394 /// For every block BB2 that meets those two requirements, we set BB2's 395 /// equivalence class to \p BB1. 396 /// 397 /// \param BB1 Block to check. 398 /// \param Descendants Descendants of \p BB1 in either the dom or pdom tree. 399 /// \param DomTree Opposite dominator tree. If \p Descendants is filled 400 /// with blocks from \p BB1's dominator tree, then 401 /// this is the post-dominator tree, and vice versa. 402 template <typename BT> 403 void SampleProfileLoaderBaseImpl<BT>::findEquivalencesFor( 404 BasicBlockT *BB1, ArrayRef<BasicBlockT *> Descendants, 405 PostDominatorTreeT *DomTree) { 406 const BasicBlockT *EC = EquivalenceClass[BB1]; 407 uint64_t Weight = BlockWeights[EC]; 408 for (const auto *BB2 : Descendants) { 409 bool IsDomParent = DomTree->dominates(BB2, BB1); 410 bool IsInSameLoop = LI->getLoopFor(BB1) == LI->getLoopFor(BB2); 411 if (BB1 != BB2 && IsDomParent && IsInSameLoop) { 412 EquivalenceClass[BB2] = EC; 413 // If BB2 is visited, then the entire EC should be marked as visited. 414 if (VisitedBlocks.count(BB2)) { 415 VisitedBlocks.insert(EC); 416 } 417 418 // If BB2 is heavier than BB1, make BB2 have the same weight 419 // as BB1. 420 // 421 // Note that we don't worry about the opposite situation here 422 // (when BB2 is lighter than BB1). We will deal with this 423 // during the propagation phase. Right now, we just want to 424 // make sure that BB1 has the largest weight of all the 425 // members of its equivalence set. 426 Weight = std::max(Weight, BlockWeights[BB2]); 427 } 428 } 429 const BasicBlockT *EntryBB = getEntryBB(EC->getParent()); 430 if (EC == EntryBB) { 431 BlockWeights[EC] = Samples->getHeadSamples() + 1; 432 } else { 433 BlockWeights[EC] = Weight; 434 } 435 } 436 437 /// Find equivalence classes. 438 /// 439 /// Since samples may be missing from blocks, we can fill in the gaps by setting 440 /// the weights of all the blocks in the same equivalence class to the same 441 /// weight. To compute the concept of equivalence, we use dominance and loop 442 /// information. Two blocks B1 and B2 are in the same equivalence class if B1 443 /// dominates B2, B2 post-dominates B1 and both are in the same loop. 444 /// 445 /// \param F The function to query. 446 template <typename BT> 447 void SampleProfileLoaderBaseImpl<BT>::findEquivalenceClasses(FunctionT &F) { 448 SmallVector<BasicBlockT *, 8> DominatedBBs; 449 LLVM_DEBUG(dbgs() << "\nBlock equivalence classes\n"); 450 // Find equivalence sets based on dominance and post-dominance information. 451 for (auto &BB : F) { 452 BasicBlockT *BB1 = &BB; 453 454 // Compute BB1's equivalence class once. 455 if (EquivalenceClass.count(BB1)) { 456 LLVM_DEBUG(printBlockEquivalence(dbgs(), BB1)); 457 continue; 458 } 459 460 // By default, blocks are in their own equivalence class. 461 EquivalenceClass[BB1] = BB1; 462 463 // Traverse all the blocks dominated by BB1. We are looking for 464 // every basic block BB2 such that: 465 // 466 // 1- BB1 dominates BB2. 467 // 2- BB2 post-dominates BB1. 468 // 3- BB1 and BB2 are in the same loop nest. 469 // 470 // If all those conditions hold, it means that BB2 is executed 471 // as many times as BB1, so they are placed in the same equivalence 472 // class by making BB2's equivalence class be BB1. 473 DominatedBBs.clear(); 474 DT->getDescendants(BB1, DominatedBBs); 475 findEquivalencesFor(BB1, DominatedBBs, PDT.get()); 476 477 LLVM_DEBUG(printBlockEquivalence(dbgs(), BB1)); 478 } 479 480 // Assign weights to equivalence classes. 481 // 482 // All the basic blocks in the same equivalence class will execute 483 // the same number of times. Since we know that the head block in 484 // each equivalence class has the largest weight, assign that weight 485 // to all the blocks in that equivalence class. 486 LLVM_DEBUG( 487 dbgs() << "\nAssign the same weight to all blocks in the same class\n"); 488 for (auto &BI : F) { 489 const BasicBlockT *BB = &BI; 490 const BasicBlockT *EquivBB = EquivalenceClass[BB]; 491 if (BB != EquivBB) 492 BlockWeights[BB] = BlockWeights[EquivBB]; 493 LLVM_DEBUG(printBlockWeight(dbgs(), BB)); 494 } 495 } 496 497 /// Visit the given edge to decide if it has a valid weight. 498 /// 499 /// If \p E has not been visited before, we copy to \p UnknownEdge 500 /// and increment the count of unknown edges. 501 /// 502 /// \param E Edge to visit. 503 /// \param NumUnknownEdges Current number of unknown edges. 504 /// \param UnknownEdge Set if E has not been visited before. 505 /// 506 /// \returns E's weight, if known. Otherwise, return 0. 507 template <typename BT> 508 uint64_t SampleProfileLoaderBaseImpl<BT>::visitEdge(Edge E, 509 unsigned *NumUnknownEdges, 510 Edge *UnknownEdge) { 511 if (!VisitedEdges.count(E)) { 512 (*NumUnknownEdges)++; 513 *UnknownEdge = E; 514 return 0; 515 } 516 517 return EdgeWeights[E]; 518 } 519 520 /// Propagate weights through incoming/outgoing edges. 521 /// 522 /// If the weight of a basic block is known, and there is only one edge 523 /// with an unknown weight, we can calculate the weight of that edge. 524 /// 525 /// Similarly, if all the edges have a known count, we can calculate the 526 /// count of the basic block, if needed. 527 /// 528 /// \param F Function to process. 529 /// \param UpdateBlockCount Whether we should update basic block counts that 530 /// has already been annotated. 531 /// 532 /// \returns True if new weights were assigned to edges or blocks. 533 template <typename BT> 534 bool SampleProfileLoaderBaseImpl<BT>::propagateThroughEdges( 535 FunctionT &F, bool UpdateBlockCount) { 536 bool Changed = false; 537 LLVM_DEBUG(dbgs() << "\nPropagation through edges\n"); 538 for (const auto &BI : F) { 539 const BasicBlockT *BB = &BI; 540 const BasicBlockT *EC = EquivalenceClass[BB]; 541 542 // Visit all the predecessor and successor edges to determine 543 // which ones have a weight assigned already. Note that it doesn't 544 // matter that we only keep track of a single unknown edge. The 545 // only case we are interested in handling is when only a single 546 // edge is unknown (see setEdgeOrBlockWeight). 547 for (unsigned i = 0; i < 2; i++) { 548 uint64_t TotalWeight = 0; 549 unsigned NumUnknownEdges = 0, NumTotalEdges = 0; 550 Edge UnknownEdge, SelfReferentialEdge, SingleEdge; 551 552 if (i == 0) { 553 // First, visit all predecessor edges. 554 NumTotalEdges = Predecessors[BB].size(); 555 for (auto *Pred : Predecessors[BB]) { 556 Edge E = std::make_pair(Pred, BB); 557 TotalWeight += visitEdge(E, &NumUnknownEdges, &UnknownEdge); 558 if (E.first == E.second) 559 SelfReferentialEdge = E; 560 } 561 if (NumTotalEdges == 1) { 562 SingleEdge = std::make_pair(Predecessors[BB][0], BB); 563 } 564 } else { 565 // On the second round, visit all successor edges. 566 NumTotalEdges = Successors[BB].size(); 567 for (auto *Succ : Successors[BB]) { 568 Edge E = std::make_pair(BB, Succ); 569 TotalWeight += visitEdge(E, &NumUnknownEdges, &UnknownEdge); 570 } 571 if (NumTotalEdges == 1) { 572 SingleEdge = std::make_pair(BB, Successors[BB][0]); 573 } 574 } 575 576 // After visiting all the edges, there are three cases that we 577 // can handle immediately: 578 // 579 // - All the edge weights are known (i.e., NumUnknownEdges == 0). 580 // In this case, we simply check that the sum of all the edges 581 // is the same as BB's weight. If not, we change BB's weight 582 // to match. Additionally, if BB had not been visited before, 583 // we mark it visited. 584 // 585 // - Only one edge is unknown and BB has already been visited. 586 // In this case, we can compute the weight of the edge by 587 // subtracting the total block weight from all the known 588 // edge weights. If the edges weight more than BB, then the 589 // edge of the last remaining edge is set to zero. 590 // 591 // - There exists a self-referential edge and the weight of BB is 592 // known. In this case, this edge can be based on BB's weight. 593 // We add up all the other known edges and set the weight on 594 // the self-referential edge as we did in the previous case. 595 // 596 // In any other case, we must continue iterating. Eventually, 597 // all edges will get a weight, or iteration will stop when 598 // it reaches SampleProfileMaxPropagateIterations. 599 if (NumUnknownEdges <= 1) { 600 uint64_t &BBWeight = BlockWeights[EC]; 601 if (NumUnknownEdges == 0) { 602 if (!VisitedBlocks.count(EC)) { 603 // If we already know the weight of all edges, the weight of the 604 // basic block can be computed. It should be no larger than the sum 605 // of all edge weights. 606 if (TotalWeight > BBWeight) { 607 BBWeight = TotalWeight; 608 Changed = true; 609 LLVM_DEBUG(dbgs() << "All edge weights for " << BB->getName() 610 << " known. Set weight for block: "; 611 printBlockWeight(dbgs(), BB);); 612 } 613 } else if (NumTotalEdges == 1 && 614 EdgeWeights[SingleEdge] < BlockWeights[EC]) { 615 // If there is only one edge for the visited basic block, use the 616 // block weight to adjust edge weight if edge weight is smaller. 617 EdgeWeights[SingleEdge] = BlockWeights[EC]; 618 Changed = true; 619 } 620 } else if (NumUnknownEdges == 1 && VisitedBlocks.count(EC)) { 621 // If there is a single unknown edge and the block has been 622 // visited, then we can compute E's weight. 623 if (BBWeight >= TotalWeight) 624 EdgeWeights[UnknownEdge] = BBWeight - TotalWeight; 625 else 626 EdgeWeights[UnknownEdge] = 0; 627 const BasicBlockT *OtherEC; 628 if (i == 0) 629 OtherEC = EquivalenceClass[UnknownEdge.first]; 630 else 631 OtherEC = EquivalenceClass[UnknownEdge.second]; 632 // Edge weights should never exceed the BB weights it connects. 633 if (VisitedBlocks.count(OtherEC) && 634 EdgeWeights[UnknownEdge] > BlockWeights[OtherEC]) 635 EdgeWeights[UnknownEdge] = BlockWeights[OtherEC]; 636 VisitedEdges.insert(UnknownEdge); 637 Changed = true; 638 LLVM_DEBUG(dbgs() << "Set weight for edge: "; 639 printEdgeWeight(dbgs(), UnknownEdge)); 640 } 641 } else if (VisitedBlocks.count(EC) && BlockWeights[EC] == 0) { 642 // If a block Weights 0, all its in/out edges should weight 0. 643 if (i == 0) { 644 for (auto *Pred : Predecessors[BB]) { 645 Edge E = std::make_pair(Pred, BB); 646 EdgeWeights[E] = 0; 647 VisitedEdges.insert(E); 648 } 649 } else { 650 for (auto *Succ : Successors[BB]) { 651 Edge E = std::make_pair(BB, Succ); 652 EdgeWeights[E] = 0; 653 VisitedEdges.insert(E); 654 } 655 } 656 } else if (SelfReferentialEdge.first && VisitedBlocks.count(EC)) { 657 uint64_t &BBWeight = BlockWeights[BB]; 658 // We have a self-referential edge and the weight of BB is known. 659 if (BBWeight >= TotalWeight) 660 EdgeWeights[SelfReferentialEdge] = BBWeight - TotalWeight; 661 else 662 EdgeWeights[SelfReferentialEdge] = 0; 663 VisitedEdges.insert(SelfReferentialEdge); 664 Changed = true; 665 LLVM_DEBUG(dbgs() << "Set self-referential edge weight to: "; 666 printEdgeWeight(dbgs(), SelfReferentialEdge)); 667 } 668 if (UpdateBlockCount && !VisitedBlocks.count(EC) && TotalWeight > 0) { 669 BlockWeights[EC] = TotalWeight; 670 VisitedBlocks.insert(EC); 671 Changed = true; 672 } 673 } 674 } 675 676 return Changed; 677 } 678 679 /// Build in/out edge lists for each basic block in the CFG. 680 /// 681 /// We are interested in unique edges. If a block B1 has multiple 682 /// edges to another block B2, we only add a single B1->B2 edge. 683 template <typename BT> 684 void SampleProfileLoaderBaseImpl<BT>::buildEdges(FunctionT &F) { 685 for (auto &BI : F) { 686 BasicBlockT *B1 = &BI; 687 688 // Add predecessors for B1. 689 SmallPtrSet<BasicBlockT *, 16> Visited; 690 if (!Predecessors[B1].empty()) 691 llvm_unreachable("Found a stale predecessors list in a basic block."); 692 for (BasicBlockT *B2 : predecessors(B1)) 693 if (Visited.insert(B2).second) 694 Predecessors[B1].push_back(B2); 695 696 // Add successors for B1. 697 Visited.clear(); 698 if (!Successors[B1].empty()) 699 llvm_unreachable("Found a stale successors list in a basic block."); 700 for (BasicBlockT *B2 : successors(B1)) 701 if (Visited.insert(B2).second) 702 Successors[B1].push_back(B2); 703 } 704 } 705 706 /// Propagate weights into edges 707 /// 708 /// The following rules are applied to every block BB in the CFG: 709 /// 710 /// - If BB has a single predecessor/successor, then the weight 711 /// of that edge is the weight of the block. 712 /// 713 /// - If all incoming or outgoing edges are known except one, and the 714 /// weight of the block is already known, the weight of the unknown 715 /// edge will be the weight of the block minus the sum of all the known 716 /// edges. If the sum of all the known edges is larger than BB's weight, 717 /// we set the unknown edge weight to zero. 718 /// 719 /// - If there is a self-referential edge, and the weight of the block is 720 /// known, the weight for that edge is set to the weight of the block 721 /// minus the weight of the other incoming edges to that block (if 722 /// known). 723 template <typename BT> 724 void SampleProfileLoaderBaseImpl<BT>::propagateWeights(FunctionT &F) { 725 bool Changed = true; 726 unsigned I = 0; 727 728 // If BB weight is larger than its corresponding loop's header BB weight, 729 // use the BB weight to replace the loop header BB weight. 730 for (auto &BI : F) { 731 BasicBlockT *BB = &BI; 732 LoopT *L = LI->getLoopFor(BB); 733 if (!L) { 734 continue; 735 } 736 BasicBlockT *Header = L->getHeader(); 737 if (Header && BlockWeights[BB] > BlockWeights[Header]) { 738 BlockWeights[Header] = BlockWeights[BB]; 739 } 740 } 741 742 // Before propagation starts, build, for each block, a list of 743 // unique predecessors and successors. This is necessary to handle 744 // identical edges in multiway branches. Since we visit all blocks and all 745 // edges of the CFG, it is cleaner to build these lists once at the start 746 // of the pass. 747 buildEdges(F); 748 749 // Propagate until we converge or we go past the iteration limit. 750 while (Changed && I++ < SampleProfileMaxPropagateIterations) { 751 Changed = propagateThroughEdges(F, false); 752 } 753 754 // The first propagation propagates BB counts from annotated BBs to unknown 755 // BBs. The 2nd propagation pass resets edges weights, and use all BB weights 756 // to propagate edge weights. 757 VisitedEdges.clear(); 758 Changed = true; 759 while (Changed && I++ < SampleProfileMaxPropagateIterations) { 760 Changed = propagateThroughEdges(F, false); 761 } 762 763 // The 3rd propagation pass allows adjust annotated BB weights that are 764 // obviously wrong. 765 Changed = true; 766 while (Changed && I++ < SampleProfileMaxPropagateIterations) { 767 Changed = propagateThroughEdges(F, true); 768 } 769 } 770 771 /// Generate branch weight metadata for all branches in \p F. 772 /// 773 /// Branch weights are computed out of instruction samples using a 774 /// propagation heuristic. Propagation proceeds in 3 phases: 775 /// 776 /// 1- Assignment of block weights. All the basic blocks in the function 777 /// are initial assigned the same weight as their most frequently 778 /// executed instruction. 779 /// 780 /// 2- Creation of equivalence classes. Since samples may be missing from 781 /// blocks, we can fill in the gaps by setting the weights of all the 782 /// blocks in the same equivalence class to the same weight. To compute 783 /// the concept of equivalence, we use dominance and loop information. 784 /// Two blocks B1 and B2 are in the same equivalence class if B1 785 /// dominates B2, B2 post-dominates B1 and both are in the same loop. 786 /// 787 /// 3- Propagation of block weights into edges. This uses a simple 788 /// propagation heuristic. The following rules are applied to every 789 /// block BB in the CFG: 790 /// 791 /// - If BB has a single predecessor/successor, then the weight 792 /// of that edge is the weight of the block. 793 /// 794 /// - If all the edges are known except one, and the weight of the 795 /// block is already known, the weight of the unknown edge will 796 /// be the weight of the block minus the sum of all the known 797 /// edges. If the sum of all the known edges is larger than BB's weight, 798 /// we set the unknown edge weight to zero. 799 /// 800 /// - If there is a self-referential edge, and the weight of the block is 801 /// known, the weight for that edge is set to the weight of the block 802 /// minus the weight of the other incoming edges to that block (if 803 /// known). 804 /// 805 /// Since this propagation is not guaranteed to finalize for every CFG, we 806 /// only allow it to proceed for a limited number of iterations (controlled 807 /// by -sample-profile-max-propagate-iterations). 808 /// 809 /// FIXME: Try to replace this propagation heuristic with a scheme 810 /// that is guaranteed to finalize. A work-list approach similar to 811 /// the standard value propagation algorithm used by SSA-CCP might 812 /// work here. 813 /// 814 /// \param F The function to query. 815 /// 816 /// \returns true if \p F was modified. Returns false, otherwise. 817 template <typename BT> 818 bool SampleProfileLoaderBaseImpl<BT>::computeAndPropagateWeights( 819 FunctionT &F, const DenseSet<GlobalValue::GUID> &InlinedGUIDs) { 820 bool Changed = (InlinedGUIDs.size() != 0); 821 822 // Compute basic block weights. 823 Changed |= computeBlockWeights(F); 824 825 if (Changed) { 826 // Add an entry count to the function using the samples gathered at the 827 // function entry. 828 // Sets the GUIDs that are inlined in the profiled binary. This is used 829 // for ThinLink to make correct liveness analysis, and also make the IR 830 // match the profiled binary before annotation. 831 getFunction(F).setEntryCount( 832 ProfileCount(Samples->getHeadSamples() + 1, Function::PCT_Real), 833 &InlinedGUIDs); 834 835 // Compute dominance and loop info needed for propagation. 836 computeDominanceAndLoopInfo(F); 837 838 // Find equivalence classes. 839 findEquivalenceClasses(F); 840 841 // Propagate weights to all edges. 842 propagateWeights(F); 843 } 844 845 return Changed; 846 } 847 848 template <typename BT> 849 void SampleProfileLoaderBaseImpl<BT>::emitCoverageRemarks(FunctionT &F) { 850 // If coverage checking was requested, compute it now. 851 const Function &Func = getFunction(F); 852 if (SampleProfileRecordCoverage) { 853 unsigned Used = CoverageTracker.countUsedRecords(Samples, PSI); 854 unsigned Total = CoverageTracker.countBodyRecords(Samples, PSI); 855 unsigned Coverage = CoverageTracker.computeCoverage(Used, Total); 856 if (Coverage < SampleProfileRecordCoverage) { 857 Func.getContext().diagnose(DiagnosticInfoSampleProfile( 858 Func.getSubprogram()->getFilename(), getFunctionLoc(F), 859 Twine(Used) + " of " + Twine(Total) + " available profile records (" + 860 Twine(Coverage) + "%) were applied", 861 DS_Warning)); 862 } 863 } 864 865 if (SampleProfileSampleCoverage) { 866 uint64_t Used = CoverageTracker.getTotalUsedSamples(); 867 uint64_t Total = CoverageTracker.countBodySamples(Samples, PSI); 868 unsigned Coverage = CoverageTracker.computeCoverage(Used, Total); 869 if (Coverage < SampleProfileSampleCoverage) { 870 Func.getContext().diagnose(DiagnosticInfoSampleProfile( 871 Func.getSubprogram()->getFilename(), getFunctionLoc(F), 872 Twine(Used) + " of " + Twine(Total) + " available profile samples (" + 873 Twine(Coverage) + "%) were applied", 874 DS_Warning)); 875 } 876 } 877 } 878 879 /// Get the line number for the function header. 880 /// 881 /// This looks up function \p F in the current compilation unit and 882 /// retrieves the line number where the function is defined. This is 883 /// line 0 for all the samples read from the profile file. Every line 884 /// number is relative to this line. 885 /// 886 /// \param F Function object to query. 887 /// 888 /// \returns the line number where \p F is defined. If it returns 0, 889 /// it means that there is no debug information available for \p F. 890 template <typename BT> 891 unsigned SampleProfileLoaderBaseImpl<BT>::getFunctionLoc(FunctionT &F) { 892 const Function &Func = getFunction(F); 893 if (DISubprogram *S = Func.getSubprogram()) 894 return S->getLine(); 895 896 if (NoWarnSampleUnused) 897 return 0; 898 899 // If the start of \p F is missing, emit a diagnostic to inform the user 900 // about the missed opportunity. 901 Func.getContext().diagnose(DiagnosticInfoSampleProfile( 902 "No debug information found in function " + Func.getName() + 903 ": Function profile not used", 904 DS_Warning)); 905 return 0; 906 } 907 908 template <typename BT> 909 void SampleProfileLoaderBaseImpl<BT>::computeDominanceAndLoopInfo( 910 FunctionT &F) { 911 DT.reset(new DominatorTreeT); 912 DT->recalculate(F); 913 914 PDT.reset(new PostDominatorTree(F)); 915 916 LI.reset(new LoopInfoT); 917 LI->analyze(*DT); 918 } 919 920 #undef DEBUG_TYPE 921 922 } // namespace llvm 923 #endif // LLVM_TRANSFORMS_UTILS_SAMPLEPROFILELOADERBASEIMPL_H 924