1 //===- SampleProfile.cpp - Incorporate sample profiles into the IR --------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements the SampleProfileLoader transformation. This pass
11 // reads a profile file generated by a sampling profiler (e.g. Linux Perf -
12 // http://perf.wiki.kernel.org/) and generates IR metadata to reflect the
13 // profile information in the given profile.
15 // This pass generates branch weight annotations on the IR:
17 // - prof: Represents branch weights. This annotation is added to branches
18 // to indicate the weights of each edge coming out of the branch.
19 // The weight of each edge is the weight of the target block for
20 // that edge. The weight of a block B is computed as the maximum
21 // number of samples found in B.
23 //===----------------------------------------------------------------------===//
25 #include "llvm/ADT/DenseMap.h"
26 #include "llvm/ADT/SmallPtrSet.h"
27 #include "llvm/ADT/SmallSet.h"
28 #include "llvm/ADT/StringRef.h"
29 #include "llvm/Analysis/LoopInfo.h"
30 #include "llvm/Analysis/PostDominators.h"
31 #include "llvm/IR/Constants.h"
32 #include "llvm/IR/DebugInfo.h"
33 #include "llvm/IR/DiagnosticInfo.h"
34 #include "llvm/IR/Dominators.h"
35 #include "llvm/IR/Function.h"
36 #include "llvm/IR/InstIterator.h"
37 #include "llvm/IR/Instructions.h"
38 #include "llvm/IR/LLVMContext.h"
39 #include "llvm/IR/MDBuilder.h"
40 #include "llvm/IR/Metadata.h"
41 #include "llvm/IR/Module.h"
42 #include "llvm/Pass.h"
43 #include "llvm/ProfileData/SampleProfReader.h"
44 #include "llvm/Support/CommandLine.h"
45 #include "llvm/Support/Debug.h"
46 #include "llvm/Support/ErrorOr.h"
47 #include "llvm/Support/raw_ostream.h"
48 #include "llvm/Transforms/IPO.h"
49 #include "llvm/Transforms/Utils/Cloning.h"
53 using namespace sampleprof;
55 #define DEBUG_TYPE "sample-profile"
57 // Command line option to specify the file to read samples from. This is
58 // mainly used for debugging.
59 static cl::opt<std::string> SampleProfileFile(
60 "sample-profile-file", cl::init(""), cl::value_desc("filename"),
61 cl::desc("Profile file loaded by -sample-profile"), cl::Hidden);
62 static cl::opt<unsigned> SampleProfileMaxPropagateIterations(
63 "sample-profile-max-propagate-iterations", cl::init(100),
64 cl::desc("Maximum number of iterations to go through when propagating "
65 "sample block/edge weights through the CFG."));
66 static cl::opt<unsigned> SampleProfileCoverage(
67 "sample-profile-check-coverage", cl::init(0), cl::value_desc("N"),
68 cl::desc("Emit a warning if less than N% of samples in the input profile "
69 "are matched to the IR."));
72 typedef DenseMap<const BasicBlock *, uint64_t> BlockWeightMap;
73 typedef DenseMap<const BasicBlock *, const BasicBlock *> EquivalenceClassMap;
74 typedef std::pair<const BasicBlock *, const BasicBlock *> Edge;
75 typedef DenseMap<Edge, uint64_t> EdgeWeightMap;
76 typedef DenseMap<const BasicBlock *, SmallVector<const BasicBlock *, 8>>
79 /// \brief Sample profile pass.
81 /// This pass reads profile data from the file specified by
82 /// -sample-profile-file and annotates every affected function with the
83 /// profile information found in that file.
84 class SampleProfileLoader : public ModulePass {
86 // Class identification, replacement for typeinfo
89 SampleProfileLoader(StringRef Name = SampleProfileFile)
90 : ModulePass(ID), DT(nullptr), PDT(nullptr), LI(nullptr), Reader(),
91 Samples(nullptr), Filename(Name), ProfileIsValid(false) {
92 initializeSampleProfileLoaderPass(*PassRegistry::getPassRegistry());
95 bool doInitialization(Module &M) override;
97 void dump() { Reader->dump(); }
99 const char *getPassName() const override { return "Sample profile pass"; }
101 bool runOnModule(Module &M) override;
103 void getAnalysisUsage(AnalysisUsage &AU) const override {
104 AU.setPreservesCFG();
108 bool runOnFunction(Function &F);
109 unsigned getFunctionLoc(Function &F);
110 bool emitAnnotations(Function &F);
111 ErrorOr<uint64_t> getInstWeight(const Instruction &I) const;
112 ErrorOr<uint64_t> getBlockWeight(const BasicBlock *BB) const;
113 const FunctionSamples *findCalleeFunctionSamples(const CallInst &I) const;
114 const FunctionSamples *findFunctionSamples(const Instruction &I) const;
115 bool inlineHotFunctions(Function &F);
116 void printEdgeWeight(raw_ostream &OS, Edge E);
117 void printBlockWeight(raw_ostream &OS, const BasicBlock *BB) const;
118 void printBlockEquivalence(raw_ostream &OS, const BasicBlock *BB);
119 bool computeBlockWeights(Function &F);
120 void findEquivalenceClasses(Function &F);
121 void findEquivalencesFor(BasicBlock *BB1,
122 SmallVector<BasicBlock *, 8> Descendants,
123 DominatorTreeBase<BasicBlock> *DomTree);
124 void propagateWeights(Function &F);
125 uint64_t visitEdge(Edge E, unsigned *NumUnknownEdges, Edge *UnknownEdge);
126 void buildEdges(Function &F);
127 bool propagateThroughEdges(Function &F);
128 void computeDominanceAndLoopInfo(Function &F);
129 unsigned getOffset(unsigned L, unsigned H) const;
130 void clearFunctionData();
132 /// \brief Map basic blocks to their computed weights.
134 /// The weight of a basic block is defined to be the maximum
135 /// of all the instruction weights in that block.
136 BlockWeightMap BlockWeights;
138 /// \brief Map edges to their computed weights.
140 /// Edge weights are computed by propagating basic block weights in
141 /// SampleProfile::propagateWeights.
142 EdgeWeightMap EdgeWeights;
144 /// \brief Set of visited blocks during propagation.
145 SmallPtrSet<const BasicBlock *, 128> VisitedBlocks;
147 /// \brief Set of visited edges during propagation.
148 SmallSet<Edge, 128> VisitedEdges;
150 /// \brief Equivalence classes for block weights.
152 /// Two blocks BB1 and BB2 are in the same equivalence class if they
153 /// dominate and post-dominate each other, and they are in the same loop
154 /// nest. When this happens, the two blocks are guaranteed to execute
155 /// the same number of times.
156 EquivalenceClassMap EquivalenceClass;
158 /// \brief Dominance, post-dominance and loop information.
159 std::unique_ptr<DominatorTree> DT;
160 std::unique_ptr<DominatorTreeBase<BasicBlock>> PDT;
161 std::unique_ptr<LoopInfo> LI;
163 /// \brief Predecessors for each basic block in the CFG.
164 BlockEdgeMap Predecessors;
166 /// \brief Successors for each basic block in the CFG.
167 BlockEdgeMap Successors;
169 /// \brief Profile reader object.
170 std::unique_ptr<SampleProfileReader> Reader;
172 /// \brief Samples collected for the body of this function.
173 FunctionSamples *Samples;
175 /// \brief Name of the profile file to load.
178 /// \brief Flag indicating whether the profile input loaded successfully.
182 class SampleCoverageTracker {
184 SampleCoverageTracker() : SampleCoverage() {}
186 bool markSamplesUsed(const FunctionSamples *Samples, uint32_t LineOffset,
187 uint32_t Discriminator);
188 unsigned computeCoverage(unsigned Used, unsigned Total) const;
189 unsigned countUsedSamples(const FunctionSamples *Samples) const;
190 unsigned countBodySamples(const FunctionSamples *Samples) const;
193 typedef DenseMap<LineLocation, unsigned> BodySampleCoverageMap;
194 typedef DenseMap<const FunctionSamples *, BodySampleCoverageMap>
195 FunctionSamplesCoverageMap;
197 /// Coverage map for sampling records.
199 /// This map keeps a record of sampling records that have been matched to
200 /// an IR instruction. This is used to detect some form of staleness in
201 /// profiles (see flag -sample-profile-check-coverage).
203 /// Each entry in the map corresponds to a FunctionSamples instance. This is
204 /// another map that counts how many times the sample record at the
205 /// given location has been used.
206 FunctionSamplesCoverageMap SampleCoverage;
209 SampleCoverageTracker CoverageTracker;
212 /// Mark as used the sample record for the given function samples at
213 /// (LineOffset, Discriminator).
215 /// \returns true if this is the first time we mark the given record.
216 bool SampleCoverageTracker::markSamplesUsed(const FunctionSamples *Samples,
218 uint32_t Discriminator) {
219 LineLocation Loc(LineOffset, Discriminator);
220 unsigned &Count = SampleCoverage[Samples][Loc];
224 /// Return the number of sample records that were applied from this profile.
226 SampleCoverageTracker::countUsedSamples(const FunctionSamples *Samples) const {
227 auto I = SampleCoverage.find(Samples);
228 unsigned Count = (I != SampleCoverage.end()) ? I->second.size() : 0;
229 for (const auto &I : Samples->getCallsiteSamples())
230 Count += countUsedSamples(&I.second);
234 /// Return the number of sample records in the body of this profile.
236 /// The count includes all the samples in inlined callees.
238 SampleCoverageTracker::countBodySamples(const FunctionSamples *Samples) const {
239 unsigned Count = Samples->getBodySamples().size();
240 for (const auto &I : Samples->getCallsiteSamples())
241 Count += countBodySamples(&I.second);
245 /// Return the fraction of sample records used in this profile.
247 /// The returned value is an unsigned integer in the range 0-100 indicating
248 /// the percentage of sample records that were used while applying this
249 /// profile to the associated function.
250 unsigned SampleCoverageTracker::computeCoverage(unsigned Used,
251 unsigned Total) const {
252 assert(Used <= Total &&
253 "number of used records cannot exceed the total number of records");
254 return Total > 0 ? Used * 100 / Total : 100;
257 /// Clear all the per-function data used to load samples and propagate weights.
258 void SampleProfileLoader::clearFunctionData() {
259 BlockWeights.clear();
261 VisitedBlocks.clear();
262 VisitedEdges.clear();
263 EquivalenceClass.clear();
267 Predecessors.clear();
271 /// \brief Returns the offset of lineno \p L to head_lineno \p H
274 /// \param H Header lineno of the function
276 /// \returns offset to the header lineno. 16 bits are used to represent offset.
277 /// We assume that a single function will not exceed 65535 LOC.
278 unsigned SampleProfileLoader::getOffset(unsigned L, unsigned H) const {
279 return (L - H) & 0xffff;
282 /// \brief Print the weight of edge \p E on stream \p OS.
284 /// \param OS Stream to emit the output to.
285 /// \param E Edge to print.
286 void SampleProfileLoader::printEdgeWeight(raw_ostream &OS, Edge E) {
287 OS << "weight[" << E.first->getName() << "->" << E.second->getName()
288 << "]: " << EdgeWeights[E] << "\n";
291 /// \brief Print the equivalence class of block \p BB on stream \p OS.
293 /// \param OS Stream to emit the output to.
294 /// \param BB Block to print.
295 void SampleProfileLoader::printBlockEquivalence(raw_ostream &OS,
296 const BasicBlock *BB) {
297 const BasicBlock *Equiv = EquivalenceClass[BB];
298 OS << "equivalence[" << BB->getName()
299 << "]: " << ((Equiv) ? EquivalenceClass[BB]->getName() : "NONE") << "\n";
302 /// \brief Print the weight of block \p BB on stream \p OS.
304 /// \param OS Stream to emit the output to.
305 /// \param BB Block to print.
306 void SampleProfileLoader::printBlockWeight(raw_ostream &OS,
307 const BasicBlock *BB) const {
308 const auto &I = BlockWeights.find(BB);
309 uint64_t W = (I == BlockWeights.end() ? 0 : I->second);
310 OS << "weight[" << BB->getName() << "]: " << W << "\n";
313 /// \brief Get the weight for an instruction.
315 /// The "weight" of an instruction \p Inst is the number of samples
316 /// collected on that instruction at runtime. To retrieve it, we
317 /// need to compute the line number of \p Inst relative to the start of its
318 /// function. We use HeaderLineno to compute the offset. We then
319 /// look up the samples collected for \p Inst using BodySamples.
321 /// \param Inst Instruction to query.
323 /// \returns the weight of \p Inst.
325 SampleProfileLoader::getInstWeight(const Instruction &Inst) const {
326 DebugLoc DLoc = Inst.getDebugLoc();
328 return std::error_code();
330 const FunctionSamples *FS = findFunctionSamples(Inst);
332 return std::error_code();
334 const DILocation *DIL = DLoc;
335 unsigned Lineno = DLoc.getLine();
336 unsigned HeaderLineno = DIL->getScope()->getSubprogram()->getLine();
338 uint32_t LineOffset = getOffset(Lineno, HeaderLineno);
339 uint32_t Discriminator = DIL->getDiscriminator();
340 ErrorOr<uint64_t> R = FS->findSamplesAt(LineOffset, Discriminator);
343 CoverageTracker.markSamplesUsed(FS, LineOffset, Discriminator);
345 const Function *F = Inst.getParent()->getParent();
346 LLVMContext &Ctx = F->getContext();
347 emitOptimizationRemark(
348 Ctx, DEBUG_TYPE, *F, DLoc,
349 Twine("Applied ") + Twine(*R) + " samples from profile (offset: " +
351 ((Discriminator) ? Twine(".") + Twine(Discriminator) : "") + ")");
353 DEBUG(dbgs() << " " << Lineno << "." << DIL->getDiscriminator() << ":"
354 << Inst << " (line offset: " << Lineno - HeaderLineno << "."
355 << DIL->getDiscriminator() << " - weight: " << R.get()
361 /// \brief Compute the weight of a basic block.
363 /// The weight of basic block \p BB is the maximum weight of all the
364 /// instructions in BB.
366 /// \param BB The basic block to query.
368 /// \returns the weight for \p BB.
370 SampleProfileLoader::getBlockWeight(const BasicBlock *BB) const {
373 for (auto &I : BB->getInstList()) {
374 const ErrorOr<uint64_t> &R = getInstWeight(I);
375 if (R && R.get() >= Weight) {
383 return std::error_code();
386 /// \brief Compute and store the weights of every basic block.
388 /// This populates the BlockWeights map by computing
389 /// the weights of every basic block in the CFG.
391 /// \param F The function to query.
392 bool SampleProfileLoader::computeBlockWeights(Function &F) {
393 bool Changed = false;
394 DEBUG(dbgs() << "Block weights\n");
395 for (const auto &BB : F) {
396 ErrorOr<uint64_t> Weight = getBlockWeight(&BB);
398 BlockWeights[&BB] = Weight.get();
399 VisitedBlocks.insert(&BB);
402 DEBUG(printBlockWeight(dbgs(), &BB));
408 /// \brief Get the FunctionSamples for a call instruction.
410 /// The FunctionSamples of a call instruction \p Inst is the inlined
411 /// instance in which that call instruction is calling to. It contains
412 /// all samples that resides in the inlined instance. We first find the
413 /// inlined instance in which the call instruction is from, then we
414 /// traverse its children to find the callsite with the matching
415 /// location and callee function name.
417 /// \param Inst Call instruction to query.
419 /// \returns The FunctionSamples pointer to the inlined instance.
420 const FunctionSamples *
421 SampleProfileLoader::findCalleeFunctionSamples(const CallInst &Inst) const {
422 const DILocation *DIL = Inst.getDebugLoc();
426 DISubprogram *SP = DIL->getScope()->getSubprogram();
430 Function *CalleeFunc = Inst.getCalledFunction();
435 StringRef CalleeName = CalleeFunc->getName();
436 const FunctionSamples *FS = findFunctionSamples(Inst);
440 return FS->findFunctionSamplesAt(
441 CallsiteLocation(getOffset(DIL->getLine(), SP->getLine()),
442 DIL->getDiscriminator(), CalleeName));
445 /// \brief Get the FunctionSamples for an instruction.
447 /// The FunctionSamples of an instruction \p Inst is the inlined instance
448 /// in which that instruction is coming from. We traverse the inline stack
449 /// of that instruction, and match it with the tree nodes in the profile.
451 /// \param Inst Instruction to query.
453 /// \returns the FunctionSamples pointer to the inlined instance.
454 const FunctionSamples *
455 SampleProfileLoader::findFunctionSamples(const Instruction &Inst) const {
456 SmallVector<CallsiteLocation, 10> S;
457 const DILocation *DIL = Inst.getDebugLoc();
461 StringRef CalleeName;
462 for (const DILocation *DIL = Inst.getDebugLoc(); DIL;
463 DIL = DIL->getInlinedAt()) {
464 DISubprogram *SP = DIL->getScope()->getSubprogram();
467 if (!CalleeName.empty()) {
468 S.push_back(CallsiteLocation(getOffset(DIL->getLine(), SP->getLine()),
469 DIL->getDiscriminator(), CalleeName));
471 CalleeName = SP->getLinkageName();
475 const FunctionSamples *FS = Samples;
476 for (int i = S.size() - 1; i >= 0 && FS != nullptr; i--) {
477 FS = FS->findFunctionSamplesAt(S[i]);
482 /// \brief Iteratively inline hot callsites of a function.
484 /// Iteratively traverse all callsites of the function \p F, and find if
485 /// the corresponding inlined instance exists and is hot in profile. If
486 /// it is hot enough, inline the callsites and adds new callsites of the
487 /// callee into the caller.
489 /// TODO: investigate the possibility of not invoking InlineFunction directly.
491 /// \param F function to perform iterative inlining.
493 /// \returns True if there is any inline happened.
494 bool SampleProfileLoader::inlineHotFunctions(Function &F) {
495 bool Changed = false;
496 LLVMContext &Ctx = F.getContext();
498 bool LocalChanged = false;
499 SmallVector<CallInst *, 10> CIS;
501 for (auto &I : BB.getInstList()) {
502 CallInst *CI = dyn_cast<CallInst>(&I);
504 const FunctionSamples *FS = findCalleeFunctionSamples(*CI);
505 if (FS && FS->getTotalSamples() > 0) {
511 for (auto CI : CIS) {
512 InlineFunctionInfo IFI;
513 Function *CalledFunction = CI->getCalledFunction();
514 DebugLoc DLoc = CI->getDebugLoc();
515 uint64_t NumSamples = findCalleeFunctionSamples(*CI)->getTotalSamples();
516 if (InlineFunction(CI, IFI)) {
518 emitOptimizationRemark(Ctx, DEBUG_TYPE, F, DLoc,
519 Twine("inlined hot callee '") +
520 CalledFunction->getName() + "' with " +
521 Twine(NumSamples) + " samples into '" +
534 /// \brief Find equivalence classes for the given block.
536 /// This finds all the blocks that are guaranteed to execute the same
537 /// number of times as \p BB1. To do this, it traverses all the
538 /// descendants of \p BB1 in the dominator or post-dominator tree.
540 /// A block BB2 will be in the same equivalence class as \p BB1 if
541 /// the following holds:
543 /// 1- \p BB1 is a descendant of BB2 in the opposite tree. So, if BB2
544 /// is a descendant of \p BB1 in the dominator tree, then BB2 should
545 /// dominate BB1 in the post-dominator tree.
547 /// 2- Both BB2 and \p BB1 must be in the same loop.
549 /// For every block BB2 that meets those two requirements, we set BB2's
550 /// equivalence class to \p BB1.
552 /// \param BB1 Block to check.
553 /// \param Descendants Descendants of \p BB1 in either the dom or pdom tree.
554 /// \param DomTree Opposite dominator tree. If \p Descendants is filled
555 /// with blocks from \p BB1's dominator tree, then
556 /// this is the post-dominator tree, and vice versa.
557 void SampleProfileLoader::findEquivalencesFor(
558 BasicBlock *BB1, SmallVector<BasicBlock *, 8> Descendants,
559 DominatorTreeBase<BasicBlock> *DomTree) {
560 const BasicBlock *EC = EquivalenceClass[BB1];
561 uint64_t Weight = BlockWeights[EC];
562 for (const auto *BB2 : Descendants) {
563 bool IsDomParent = DomTree->dominates(BB2, BB1);
564 bool IsInSameLoop = LI->getLoopFor(BB1) == LI->getLoopFor(BB2);
565 if (BB1 != BB2 && IsDomParent && IsInSameLoop) {
566 EquivalenceClass[BB2] = EC;
568 // If BB2 is heavier than BB1, make BB2 have the same weight
571 // Note that we don't worry about the opposite situation here
572 // (when BB2 is lighter than BB1). We will deal with this
573 // during the propagation phase. Right now, we just want to
574 // make sure that BB1 has the largest weight of all the
575 // members of its equivalence set.
576 Weight = std::max(Weight, BlockWeights[BB2]);
579 BlockWeights[EC] = Weight;
582 /// \brief Find equivalence classes.
584 /// Since samples may be missing from blocks, we can fill in the gaps by setting
585 /// the weights of all the blocks in the same equivalence class to the same
586 /// weight. To compute the concept of equivalence, we use dominance and loop
587 /// information. Two blocks B1 and B2 are in the same equivalence class if B1
588 /// dominates B2, B2 post-dominates B1 and both are in the same loop.
590 /// \param F The function to query.
591 void SampleProfileLoader::findEquivalenceClasses(Function &F) {
592 SmallVector<BasicBlock *, 8> DominatedBBs;
593 DEBUG(dbgs() << "\nBlock equivalence classes\n");
594 // Find equivalence sets based on dominance and post-dominance information.
596 BasicBlock *BB1 = &BB;
598 // Compute BB1's equivalence class once.
599 if (EquivalenceClass.count(BB1)) {
600 DEBUG(printBlockEquivalence(dbgs(), BB1));
604 // By default, blocks are in their own equivalence class.
605 EquivalenceClass[BB1] = BB1;
607 // Traverse all the blocks dominated by BB1. We are looking for
608 // every basic block BB2 such that:
610 // 1- BB1 dominates BB2.
611 // 2- BB2 post-dominates BB1.
612 // 3- BB1 and BB2 are in the same loop nest.
614 // If all those conditions hold, it means that BB2 is executed
615 // as many times as BB1, so they are placed in the same equivalence
616 // class by making BB2's equivalence class be BB1.
617 DominatedBBs.clear();
618 DT->getDescendants(BB1, DominatedBBs);
619 findEquivalencesFor(BB1, DominatedBBs, PDT.get());
621 DEBUG(printBlockEquivalence(dbgs(), BB1));
624 // Assign weights to equivalence classes.
626 // All the basic blocks in the same equivalence class will execute
627 // the same number of times. Since we know that the head block in
628 // each equivalence class has the largest weight, assign that weight
629 // to all the blocks in that equivalence class.
630 DEBUG(dbgs() << "\nAssign the same weight to all blocks in the same class\n");
632 const BasicBlock *BB = &BI;
633 const BasicBlock *EquivBB = EquivalenceClass[BB];
635 BlockWeights[BB] = BlockWeights[EquivBB];
636 DEBUG(printBlockWeight(dbgs(), BB));
640 /// \brief Visit the given edge to decide if it has a valid weight.
642 /// If \p E has not been visited before, we copy to \p UnknownEdge
643 /// and increment the count of unknown edges.
645 /// \param E Edge to visit.
646 /// \param NumUnknownEdges Current number of unknown edges.
647 /// \param UnknownEdge Set if E has not been visited before.
649 /// \returns E's weight, if known. Otherwise, return 0.
650 uint64_t SampleProfileLoader::visitEdge(Edge E, unsigned *NumUnknownEdges,
652 if (!VisitedEdges.count(E)) {
653 (*NumUnknownEdges)++;
658 return EdgeWeights[E];
661 /// \brief Propagate weights through incoming/outgoing edges.
663 /// If the weight of a basic block is known, and there is only one edge
664 /// with an unknown weight, we can calculate the weight of that edge.
666 /// Similarly, if all the edges have a known count, we can calculate the
667 /// count of the basic block, if needed.
669 /// \param F Function to process.
671 /// \returns True if new weights were assigned to edges or blocks.
672 bool SampleProfileLoader::propagateThroughEdges(Function &F) {
673 bool Changed = false;
674 DEBUG(dbgs() << "\nPropagation through edges\n");
675 for (const auto &BI : F) {
676 const BasicBlock *BB = &BI;
677 const BasicBlock *EC = EquivalenceClass[BB];
679 // Visit all the predecessor and successor edges to determine
680 // which ones have a weight assigned already. Note that it doesn't
681 // matter that we only keep track of a single unknown edge. The
682 // only case we are interested in handling is when only a single
683 // edge is unknown (see setEdgeOrBlockWeight).
684 for (unsigned i = 0; i < 2; i++) {
685 uint64_t TotalWeight = 0;
686 unsigned NumUnknownEdges = 0;
687 Edge UnknownEdge, SelfReferentialEdge;
690 // First, visit all predecessor edges.
691 for (auto *Pred : Predecessors[BB]) {
692 Edge E = std::make_pair(Pred, BB);
693 TotalWeight += visitEdge(E, &NumUnknownEdges, &UnknownEdge);
694 if (E.first == E.second)
695 SelfReferentialEdge = E;
698 // On the second round, visit all successor edges.
699 for (auto *Succ : Successors[BB]) {
700 Edge E = std::make_pair(BB, Succ);
701 TotalWeight += visitEdge(E, &NumUnknownEdges, &UnknownEdge);
705 // After visiting all the edges, there are three cases that we
706 // can handle immediately:
708 // - All the edge weights are known (i.e., NumUnknownEdges == 0).
709 // In this case, we simply check that the sum of all the edges
710 // is the same as BB's weight. If not, we change BB's weight
711 // to match. Additionally, if BB had not been visited before,
712 // we mark it visited.
714 // - Only one edge is unknown and BB has already been visited.
715 // In this case, we can compute the weight of the edge by
716 // subtracting the total block weight from all the known
717 // edge weights. If the edges weight more than BB, then the
718 // edge of the last remaining edge is set to zero.
720 // - There exists a self-referential edge and the weight of BB is
721 // known. In this case, this edge can be based on BB's weight.
722 // We add up all the other known edges and set the weight on
723 // the self-referential edge as we did in the previous case.
725 // In any other case, we must continue iterating. Eventually,
726 // all edges will get a weight, or iteration will stop when
727 // it reaches SampleProfileMaxPropagateIterations.
728 if (NumUnknownEdges <= 1) {
729 uint64_t &BBWeight = BlockWeights[EC];
730 if (NumUnknownEdges == 0) {
731 // If we already know the weight of all edges, the weight of the
732 // basic block can be computed. It should be no larger than the sum
733 // of all edge weights.
734 if (TotalWeight > BBWeight) {
735 BBWeight = TotalWeight;
737 DEBUG(dbgs() << "All edge weights for " << BB->getName()
738 << " known. Set weight for block: ";
739 printBlockWeight(dbgs(), BB););
741 if (VisitedBlocks.insert(EC).second)
743 } else if (NumUnknownEdges == 1 && VisitedBlocks.count(EC)) {
744 // If there is a single unknown edge and the block has been
745 // visited, then we can compute E's weight.
746 if (BBWeight >= TotalWeight)
747 EdgeWeights[UnknownEdge] = BBWeight - TotalWeight;
749 EdgeWeights[UnknownEdge] = 0;
750 VisitedEdges.insert(UnknownEdge);
752 DEBUG(dbgs() << "Set weight for edge: ";
753 printEdgeWeight(dbgs(), UnknownEdge));
755 } else if (SelfReferentialEdge.first && VisitedBlocks.count(EC)) {
756 uint64_t &BBWeight = BlockWeights[BB];
757 // We have a self-referential edge and the weight of BB is known.
758 if (BBWeight >= TotalWeight)
759 EdgeWeights[SelfReferentialEdge] = BBWeight - TotalWeight;
761 EdgeWeights[SelfReferentialEdge] = 0;
762 VisitedEdges.insert(SelfReferentialEdge);
764 DEBUG(dbgs() << "Set self-referential edge weight to: ";
765 printEdgeWeight(dbgs(), SelfReferentialEdge));
773 /// \brief Build in/out edge lists for each basic block in the CFG.
775 /// We are interested in unique edges. If a block B1 has multiple
776 /// edges to another block B2, we only add a single B1->B2 edge.
777 void SampleProfileLoader::buildEdges(Function &F) {
779 BasicBlock *B1 = &BI;
781 // Add predecessors for B1.
782 SmallPtrSet<BasicBlock *, 16> Visited;
783 if (!Predecessors[B1].empty())
784 llvm_unreachable("Found a stale predecessors list in a basic block.");
785 for (pred_iterator PI = pred_begin(B1), PE = pred_end(B1); PI != PE; ++PI) {
786 BasicBlock *B2 = *PI;
787 if (Visited.insert(B2).second)
788 Predecessors[B1].push_back(B2);
791 // Add successors for B1.
793 if (!Successors[B1].empty())
794 llvm_unreachable("Found a stale successors list in a basic block.");
795 for (succ_iterator SI = succ_begin(B1), SE = succ_end(B1); SI != SE; ++SI) {
796 BasicBlock *B2 = *SI;
797 if (Visited.insert(B2).second)
798 Successors[B1].push_back(B2);
803 /// \brief Propagate weights into edges
805 /// The following rules are applied to every block BB in the CFG:
807 /// - If BB has a single predecessor/successor, then the weight
808 /// of that edge is the weight of the block.
810 /// - If all incoming or outgoing edges are known except one, and the
811 /// weight of the block is already known, the weight of the unknown
812 /// edge will be the weight of the block minus the sum of all the known
813 /// edges. If the sum of all the known edges is larger than BB's weight,
814 /// we set the unknown edge weight to zero.
816 /// - If there is a self-referential edge, and the weight of the block is
817 /// known, the weight for that edge is set to the weight of the block
818 /// minus the weight of the other incoming edges to that block (if
820 void SampleProfileLoader::propagateWeights(Function &F) {
824 // Add an entry count to the function using the samples gathered
825 // at the function entry.
826 F.setEntryCount(Samples->getHeadSamples());
828 // Before propagation starts, build, for each block, a list of
829 // unique predecessors and successors. This is necessary to handle
830 // identical edges in multiway branches. Since we visit all blocks and all
831 // edges of the CFG, it is cleaner to build these lists once at the start
835 // Propagate until we converge or we go past the iteration limit.
836 while (Changed && I++ < SampleProfileMaxPropagateIterations) {
837 Changed = propagateThroughEdges(F);
840 // Generate MD_prof metadata for every branch instruction using the
841 // edge weights computed during propagation.
842 DEBUG(dbgs() << "\nPropagation complete. Setting branch weights\n");
843 LLVMContext &Ctx = F.getContext();
846 BasicBlock *BB = &BI;
847 TerminatorInst *TI = BB->getTerminator();
848 if (TI->getNumSuccessors() == 1)
850 if (!isa<BranchInst>(TI) && !isa<SwitchInst>(TI))
853 DEBUG(dbgs() << "\nGetting weights for branch at line "
854 << TI->getDebugLoc().getLine() << ".\n");
855 SmallVector<uint32_t, 4> Weights;
856 uint32_t MaxWeight = 0;
858 for (unsigned I = 0; I < TI->getNumSuccessors(); ++I) {
859 BasicBlock *Succ = TI->getSuccessor(I);
860 Edge E = std::make_pair(BB, Succ);
861 uint64_t Weight = EdgeWeights[E];
862 DEBUG(dbgs() << "\t"; printEdgeWeight(dbgs(), E));
863 // Use uint32_t saturated arithmetic to adjust the incoming weights,
864 // if needed. Sample counts in profiles are 64-bit unsigned values,
865 // but internally branch weights are expressed as 32-bit values.
866 if (Weight > std::numeric_limits<uint32_t>::max()) {
867 DEBUG(dbgs() << " (saturated due to uint32_t overflow)");
868 Weight = std::numeric_limits<uint32_t>::max();
870 Weights.push_back(static_cast<uint32_t>(Weight));
872 if (Weight > MaxWeight) {
874 MaxDestLoc = Succ->getFirstNonPHIOrDbgOrLifetime()->getDebugLoc();
879 // Only set weights if there is at least one non-zero weight.
880 // In any other case, let the analyzer set weights.
882 DEBUG(dbgs() << "SUCCESS. Found non-zero weights.\n");
883 TI->setMetadata(llvm::LLVMContext::MD_prof,
884 MDB.createBranchWeights(Weights));
885 DebugLoc BranchLoc = TI->getDebugLoc();
886 emitOptimizationRemark(
887 Ctx, DEBUG_TYPE, F, MaxDestLoc,
888 Twine("most popular destination for conditional branches at ") +
889 ((BranchLoc) ? Twine(BranchLoc->getFilename() + ":" +
890 Twine(BranchLoc.getLine()) + ":" +
891 Twine(BranchLoc.getCol()))
892 : Twine("<UNKNOWN LOCATION>")));
894 DEBUG(dbgs() << "SKIPPED. All branch weights are zero.\n");
899 /// \brief Get the line number for the function header.
901 /// This looks up function \p F in the current compilation unit and
902 /// retrieves the line number where the function is defined. This is
903 /// line 0 for all the samples read from the profile file. Every line
904 /// number is relative to this line.
906 /// \param F Function object to query.
908 /// \returns the line number where \p F is defined. If it returns 0,
909 /// it means that there is no debug information available for \p F.
910 unsigned SampleProfileLoader::getFunctionLoc(Function &F) {
911 if (DISubprogram *S = getDISubprogram(&F))
914 // If the start of \p F is missing, emit a diagnostic to inform the user
915 // about the missed opportunity.
916 F.getContext().diagnose(DiagnosticInfoSampleProfile(
917 "No debug information found in function " + F.getName() +
918 ": Function profile not used",
923 void SampleProfileLoader::computeDominanceAndLoopInfo(Function &F) {
924 DT.reset(new DominatorTree);
927 PDT.reset(new DominatorTreeBase<BasicBlock>(true));
930 LI.reset(new LoopInfo);
934 /// \brief Generate branch weight metadata for all branches in \p F.
936 /// Branch weights are computed out of instruction samples using a
937 /// propagation heuristic. Propagation proceeds in 3 phases:
939 /// 1- Assignment of block weights. All the basic blocks in the function
940 /// are initial assigned the same weight as their most frequently
941 /// executed instruction.
943 /// 2- Creation of equivalence classes. Since samples may be missing from
944 /// blocks, we can fill in the gaps by setting the weights of all the
945 /// blocks in the same equivalence class to the same weight. To compute
946 /// the concept of equivalence, we use dominance and loop information.
947 /// Two blocks B1 and B2 are in the same equivalence class if B1
948 /// dominates B2, B2 post-dominates B1 and both are in the same loop.
950 /// 3- Propagation of block weights into edges. This uses a simple
951 /// propagation heuristic. The following rules are applied to every
952 /// block BB in the CFG:
954 /// - If BB has a single predecessor/successor, then the weight
955 /// of that edge is the weight of the block.
957 /// - If all the edges are known except one, and the weight of the
958 /// block is already known, the weight of the unknown edge will
959 /// be the weight of the block minus the sum of all the known
960 /// edges. If the sum of all the known edges is larger than BB's weight,
961 /// we set the unknown edge weight to zero.
963 /// - If there is a self-referential edge, and the weight of the block is
964 /// known, the weight for that edge is set to the weight of the block
965 /// minus the weight of the other incoming edges to that block (if
968 /// Since this propagation is not guaranteed to finalize for every CFG, we
969 /// only allow it to proceed for a limited number of iterations (controlled
970 /// by -sample-profile-max-propagate-iterations).
972 /// FIXME: Try to replace this propagation heuristic with a scheme
973 /// that is guaranteed to finalize. A work-list approach similar to
974 /// the standard value propagation algorithm used by SSA-CCP might
977 /// Once all the branch weights are computed, we emit the MD_prof
978 /// metadata on BB using the computed values for each of its branches.
980 /// \param F The function to query.
982 /// \returns true if \p F was modified. Returns false, otherwise.
983 bool SampleProfileLoader::emitAnnotations(Function &F) {
984 bool Changed = false;
986 if (getFunctionLoc(F) == 0)
989 DEBUG(dbgs() << "Line number for the first instruction in " << F.getName()
990 << ": " << getFunctionLoc(F) << "\n");
992 Changed |= inlineHotFunctions(F);
994 // Compute basic block weights.
995 Changed |= computeBlockWeights(F);
998 // Compute dominance and loop info needed for propagation.
999 computeDominanceAndLoopInfo(F);
1001 // Find equivalence classes.
1002 findEquivalenceClasses(F);
1004 // Propagate weights to all edges.
1005 propagateWeights(F);
1008 // If coverage checking was requested, compute it now.
1009 if (SampleProfileCoverage) {
1010 unsigned Used = CoverageTracker.countUsedSamples(Samples);
1011 unsigned Total = CoverageTracker.countBodySamples(Samples);
1012 unsigned Coverage = CoverageTracker.computeCoverage(Used, Total);
1013 if (Coverage < SampleProfileCoverage) {
1014 F.getContext().diagnose(DiagnosticInfoSampleProfile(
1015 getDISubprogram(&F)->getFilename(), getFunctionLoc(F),
1016 Twine(Used) + " of " + Twine(Total) + " available profile records (" +
1017 Twine(Coverage) + "%) were applied",
1025 char SampleProfileLoader::ID = 0;
1026 INITIALIZE_PASS_BEGIN(SampleProfileLoader, "sample-profile",
1027 "Sample Profile loader", false, false)
1028 INITIALIZE_PASS_DEPENDENCY(AddDiscriminators)
1029 INITIALIZE_PASS_END(SampleProfileLoader, "sample-profile",
1030 "Sample Profile loader", false, false)
1032 bool SampleProfileLoader::doInitialization(Module &M) {
1033 auto &Ctx = M.getContext();
1034 auto ReaderOrErr = SampleProfileReader::create(Filename, Ctx);
1035 if (std::error_code EC = ReaderOrErr.getError()) {
1036 std::string Msg = "Could not open profile: " + EC.message();
1037 Ctx.diagnose(DiagnosticInfoSampleProfile(Filename, Msg));
1040 Reader = std::move(ReaderOrErr.get());
1041 ProfileIsValid = (Reader->read() == sampleprof_error::success);
1045 ModulePass *llvm::createSampleProfileLoaderPass() {
1046 return new SampleProfileLoader(SampleProfileFile);
1049 ModulePass *llvm::createSampleProfileLoaderPass(StringRef Name) {
1050 return new SampleProfileLoader(Name);
1053 bool SampleProfileLoader::runOnModule(Module &M) {
1054 if (!ProfileIsValid)
1057 bool retval = false;
1059 if (!F.isDeclaration()) {
1060 clearFunctionData();
1061 retval |= runOnFunction(F);
1066 bool SampleProfileLoader::runOnFunction(Function &F) {
1067 Samples = Reader->getSamplesFor(F);
1068 if (!Samples->empty())
1069 return emitAnnotations(F);