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."));
68 typedef DenseMap<const BasicBlock *, uint64_t> BlockWeightMap;
69 typedef DenseMap<const BasicBlock *, const BasicBlock *> EquivalenceClassMap;
70 typedef std::pair<const BasicBlock *, const BasicBlock *> Edge;
71 typedef DenseMap<Edge, uint64_t> EdgeWeightMap;
72 typedef DenseMap<const BasicBlock *, SmallVector<const BasicBlock *, 8>>
75 /// \brief Sample profile pass.
77 /// This pass reads profile data from the file specified by
78 /// -sample-profile-file and annotates every affected function with the
79 /// profile information found in that file.
80 class SampleProfileLoader : public ModulePass {
82 // Class identification, replacement for typeinfo
85 SampleProfileLoader(StringRef Name = SampleProfileFile)
86 : ModulePass(ID), DT(nullptr), PDT(nullptr), LI(nullptr), Reader(),
87 Samples(nullptr), Filename(Name), ProfileIsValid(false) {
88 initializeSampleProfileLoaderPass(*PassRegistry::getPassRegistry());
91 bool doInitialization(Module &M) override;
93 void dump() { Reader->dump(); }
95 const char *getPassName() const override { return "Sample profile pass"; }
97 bool runOnModule(Module &M) override;
99 void getAnalysisUsage(AnalysisUsage &AU) const override {
100 AU.setPreservesCFG();
104 bool runOnFunction(Function &F);
105 unsigned getFunctionLoc(Function &F);
106 bool emitAnnotations(Function &F);
107 ErrorOr<uint64_t> getInstWeight(const Instruction &I) const;
108 ErrorOr<uint64_t> getBlockWeight(const BasicBlock *BB) const;
109 const FunctionSamples *findCalleeFunctionSamples(const CallInst &I) const;
110 const FunctionSamples *findFunctionSamples(const Instruction &I) const;
111 bool inlineHotFunctions(Function &F);
112 void printEdgeWeight(raw_ostream &OS, Edge E);
113 void printBlockWeight(raw_ostream &OS, const BasicBlock *BB) const;
114 void printBlockEquivalence(raw_ostream &OS, const BasicBlock *BB);
115 bool computeBlockWeights(Function &F);
116 void findEquivalenceClasses(Function &F);
117 void findEquivalencesFor(BasicBlock *BB1,
118 SmallVector<BasicBlock *, 8> Descendants,
119 DominatorTreeBase<BasicBlock> *DomTree);
120 void propagateWeights(Function &F);
121 uint64_t visitEdge(Edge E, unsigned *NumUnknownEdges, Edge *UnknownEdge);
122 void buildEdges(Function &F);
123 bool propagateThroughEdges(Function &F);
124 void computeDominanceAndLoopInfo(Function &F);
125 unsigned getOffset(unsigned L, unsigned H) const;
126 void clearFunctionData();
128 /// \brief Map basic blocks to their computed weights.
130 /// The weight of a basic block is defined to be the maximum
131 /// of all the instruction weights in that block.
132 BlockWeightMap BlockWeights;
134 /// \brief Map edges to their computed weights.
136 /// Edge weights are computed by propagating basic block weights in
137 /// SampleProfile::propagateWeights.
138 EdgeWeightMap EdgeWeights;
140 /// \brief Set of visited blocks during propagation.
141 SmallPtrSet<const BasicBlock *, 128> VisitedBlocks;
143 /// \brief Set of visited edges during propagation.
144 SmallSet<Edge, 128> VisitedEdges;
146 /// \brief Equivalence classes for block weights.
148 /// Two blocks BB1 and BB2 are in the same equivalence class if they
149 /// dominate and post-dominate each other, and they are in the same loop
150 /// nest. When this happens, the two blocks are guaranteed to execute
151 /// the same number of times.
152 EquivalenceClassMap EquivalenceClass;
154 /// \brief Dominance, post-dominance and loop information.
155 std::unique_ptr<DominatorTree> DT;
156 std::unique_ptr<DominatorTreeBase<BasicBlock>> PDT;
157 std::unique_ptr<LoopInfo> LI;
159 /// \brief Predecessors for each basic block in the CFG.
160 BlockEdgeMap Predecessors;
162 /// \brief Successors for each basic block in the CFG.
163 BlockEdgeMap Successors;
165 /// \brief Profile reader object.
166 std::unique_ptr<SampleProfileReader> Reader;
168 /// \brief Samples collected for the body of this function.
169 FunctionSamples *Samples;
171 /// \brief Name of the profile file to load.
174 /// \brief Flag indicating whether the profile input loaded successfully.
179 /// Clear all the per-function data used to load samples and propagate weights.
180 void SampleProfileLoader::clearFunctionData() {
181 BlockWeights.clear();
183 VisitedBlocks.clear();
184 VisitedEdges.clear();
185 EquivalenceClass.clear();
189 Predecessors.clear();
193 /// \brief Returns the offset of lineno \p L to head_lineno \p H
196 /// \param H Header lineno of the function
198 /// \returns offset to the header lineno. 16 bits are used to represent offset.
199 /// We assume that a single function will not exceed 65535 LOC.
200 unsigned SampleProfileLoader::getOffset(unsigned L, unsigned H) const {
201 return (L - H) & 0xffff;
204 /// \brief Print the weight of edge \p E on stream \p OS.
206 /// \param OS Stream to emit the output to.
207 /// \param E Edge to print.
208 void SampleProfileLoader::printEdgeWeight(raw_ostream &OS, Edge E) {
209 OS << "weight[" << E.first->getName() << "->" << E.second->getName()
210 << "]: " << EdgeWeights[E] << "\n";
213 /// \brief Print the equivalence class of block \p BB on stream \p OS.
215 /// \param OS Stream to emit the output to.
216 /// \param BB Block to print.
217 void SampleProfileLoader::printBlockEquivalence(raw_ostream &OS,
218 const BasicBlock *BB) {
219 const BasicBlock *Equiv = EquivalenceClass[BB];
220 OS << "equivalence[" << BB->getName()
221 << "]: " << ((Equiv) ? EquivalenceClass[BB]->getName() : "NONE") << "\n";
224 /// \brief Print the weight of block \p BB on stream \p OS.
226 /// \param OS Stream to emit the output to.
227 /// \param BB Block to print.
228 void SampleProfileLoader::printBlockWeight(raw_ostream &OS,
229 const BasicBlock *BB) const {
230 const auto &I = BlockWeights.find(BB);
231 uint64_t W = (I == BlockWeights.end() ? 0 : I->second);
232 OS << "weight[" << BB->getName() << "]: " << W << "\n";
235 /// \brief Get the weight for an instruction.
237 /// The "weight" of an instruction \p Inst is the number of samples
238 /// collected on that instruction at runtime. To retrieve it, we
239 /// need to compute the line number of \p Inst relative to the start of its
240 /// function. We use HeaderLineno to compute the offset. We then
241 /// look up the samples collected for \p Inst using BodySamples.
243 /// \param Inst Instruction to query.
245 /// \returns the weight of \p Inst.
247 SampleProfileLoader::getInstWeight(const Instruction &Inst) const {
248 DebugLoc DLoc = Inst.getDebugLoc();
250 return std::error_code();
252 const FunctionSamples *FS = findFunctionSamples(Inst);
254 return std::error_code();
256 const DILocation *DIL = DLoc;
257 unsigned Lineno = DLoc.getLine();
258 unsigned HeaderLineno = DIL->getScope()->getSubprogram()->getLine();
260 ErrorOr<uint64_t> R = FS->findSamplesAt(getOffset(Lineno, HeaderLineno),
261 DIL->getDiscriminator());
263 DEBUG(dbgs() << " " << Lineno << "." << DIL->getDiscriminator() << ":"
264 << Inst << " (line offset: " << Lineno - HeaderLineno << "."
265 << DIL->getDiscriminator() << " - weight: " << R.get()
270 /// \brief Compute the weight of a basic block.
272 /// The weight of basic block \p BB is the maximum weight of all the
273 /// instructions in BB.
275 /// \param BB The basic block to query.
277 /// \returns the weight for \p BB.
279 SampleProfileLoader::getBlockWeight(const BasicBlock *BB) const {
282 for (auto &I : BB->getInstList()) {
283 const ErrorOr<uint64_t> &R = getInstWeight(I);
284 if (R && R.get() >= Weight) {
292 return std::error_code();
295 /// \brief Compute and store the weights of every basic block.
297 /// This populates the BlockWeights map by computing
298 /// the weights of every basic block in the CFG.
300 /// \param F The function to query.
301 bool SampleProfileLoader::computeBlockWeights(Function &F) {
302 bool Changed = false;
303 DEBUG(dbgs() << "Block weights\n");
304 for (const auto &BB : F) {
305 ErrorOr<uint64_t> Weight = getBlockWeight(&BB);
307 BlockWeights[&BB] = Weight.get();
308 VisitedBlocks.insert(&BB);
311 DEBUG(printBlockWeight(dbgs(), &BB));
317 /// \brief Get the FunctionSamples for a call instruction.
319 /// The FunctionSamples of a call instruction \p Inst is the inlined
320 /// instance in which that call instruction is calling to. It contains
321 /// all samples that resides in the inlined instance. We first find the
322 /// inlined instance in which the call instruction is from, then we
323 /// traverse its children to find the callsite with the matching
324 /// location and callee function name.
326 /// \param Inst Call instruction to query.
328 /// \returns The FunctionSamples pointer to the inlined instance.
329 const FunctionSamples *
330 SampleProfileLoader::findCalleeFunctionSamples(const CallInst &Inst) const {
331 const DILocation *DIL = Inst.getDebugLoc();
335 DISubprogram *SP = DIL->getScope()->getSubprogram();
339 Function *CalleeFunc = Inst.getCalledFunction();
344 StringRef CalleeName = CalleeFunc->getName();
345 const FunctionSamples *FS = findFunctionSamples(Inst);
349 return FS->findFunctionSamplesAt(
350 CallsiteLocation(getOffset(DIL->getLine(), SP->getLine()),
351 DIL->getDiscriminator(), CalleeName));
354 /// \brief Get the FunctionSamples for an instruction.
356 /// The FunctionSamples of an instruction \p Inst is the inlined instance
357 /// in which that instruction is coming from. We traverse the inline stack
358 /// of that instruction, and match it with the tree nodes in the profile.
360 /// \param Inst Instruction to query.
362 /// \returns the FunctionSamples pointer to the inlined instance.
363 const FunctionSamples *
364 SampleProfileLoader::findFunctionSamples(const Instruction &Inst) const {
365 SmallVector<CallsiteLocation, 10> S;
366 const DILocation *DIL = Inst.getDebugLoc();
370 StringRef CalleeName;
371 for (const DILocation *DIL = Inst.getDebugLoc(); DIL;
372 DIL = DIL->getInlinedAt()) {
373 DISubprogram *SP = DIL->getScope()->getSubprogram();
376 if (!CalleeName.empty()) {
377 S.push_back(CallsiteLocation(getOffset(DIL->getLine(), SP->getLine()),
378 DIL->getDiscriminator(), CalleeName));
380 CalleeName = SP->getLinkageName();
384 const FunctionSamples *FS = Samples;
385 for (int i = S.size() - 1; i >= 0 && FS != nullptr; i--) {
386 FS = FS->findFunctionSamplesAt(S[i]);
391 /// \brief Iteratively inline hot callsites of a function.
393 /// Iteratively traverse all callsites of the function \p F, and find if
394 /// the corresponding inlined instance exists and is hot in profile. If
395 /// it is hot enough, inline the callsites and adds new callsites of the
396 /// callee into the caller.
398 /// TODO: investigate the possibility of not invoking InlineFunction directly.
400 /// \param F function to perform iterative inlining.
402 /// \returns True if there is any inline happened.
403 bool SampleProfileLoader::inlineHotFunctions(Function &F) {
404 bool Changed = false;
405 LLVMContext &Ctx = F.getContext();
407 bool LocalChanged = false;
408 SmallVector<CallInst *, 10> CIS;
410 for (auto &I : BB.getInstList()) {
411 CallInst *CI = dyn_cast<CallInst>(&I);
413 const FunctionSamples *FS = findCalleeFunctionSamples(*CI);
414 if (FS && FS->getTotalSamples() > 0) {
420 for (auto CI : CIS) {
421 InlineFunctionInfo IFI;
422 Function *CalledFunction = CI->getCalledFunction();
423 DebugLoc DLoc = CI->getDebugLoc();
424 uint64_t NumSamples = findCalleeFunctionSamples(*CI)->getTotalSamples();
425 if (InlineFunction(CI, IFI)) {
427 emitOptimizationRemark(Ctx, DEBUG_TYPE, F, DLoc,
428 Twine("inlined hot callee '") +
429 CalledFunction->getName() + "' with " +
430 Twine(NumSamples) + " samples into '" +
443 /// \brief Find equivalence classes for the given block.
445 /// This finds all the blocks that are guaranteed to execute the same
446 /// number of times as \p BB1. To do this, it traverses all the
447 /// descendants of \p BB1 in the dominator or post-dominator tree.
449 /// A block BB2 will be in the same equivalence class as \p BB1 if
450 /// the following holds:
452 /// 1- \p BB1 is a descendant of BB2 in the opposite tree. So, if BB2
453 /// is a descendant of \p BB1 in the dominator tree, then BB2 should
454 /// dominate BB1 in the post-dominator tree.
456 /// 2- Both BB2 and \p BB1 must be in the same loop.
458 /// For every block BB2 that meets those two requirements, we set BB2's
459 /// equivalence class to \p BB1.
461 /// \param BB1 Block to check.
462 /// \param Descendants Descendants of \p BB1 in either the dom or pdom tree.
463 /// \param DomTree Opposite dominator tree. If \p Descendants is filled
464 /// with blocks from \p BB1's dominator tree, then
465 /// this is the post-dominator tree, and vice versa.
466 void SampleProfileLoader::findEquivalencesFor(
467 BasicBlock *BB1, SmallVector<BasicBlock *, 8> Descendants,
468 DominatorTreeBase<BasicBlock> *DomTree) {
469 const BasicBlock *EC = EquivalenceClass[BB1];
470 uint64_t Weight = BlockWeights[EC];
471 for (const auto *BB2 : Descendants) {
472 bool IsDomParent = DomTree->dominates(BB2, BB1);
473 bool IsInSameLoop = LI->getLoopFor(BB1) == LI->getLoopFor(BB2);
474 if (BB1 != BB2 && IsDomParent && IsInSameLoop) {
475 EquivalenceClass[BB2] = EC;
477 // If BB2 is heavier than BB1, make BB2 have the same weight
480 // Note that we don't worry about the opposite situation here
481 // (when BB2 is lighter than BB1). We will deal with this
482 // during the propagation phase. Right now, we just want to
483 // make sure that BB1 has the largest weight of all the
484 // members of its equivalence set.
485 Weight = std::max(Weight, BlockWeights[BB2]);
488 BlockWeights[EC] = Weight;
491 /// \brief Find equivalence classes.
493 /// Since samples may be missing from blocks, we can fill in the gaps by setting
494 /// the weights of all the blocks in the same equivalence class to the same
495 /// weight. To compute the concept of equivalence, we use dominance and loop
496 /// information. Two blocks B1 and B2 are in the same equivalence class if B1
497 /// dominates B2, B2 post-dominates B1 and both are in the same loop.
499 /// \param F The function to query.
500 void SampleProfileLoader::findEquivalenceClasses(Function &F) {
501 SmallVector<BasicBlock *, 8> DominatedBBs;
502 DEBUG(dbgs() << "\nBlock equivalence classes\n");
503 // Find equivalence sets based on dominance and post-dominance information.
505 BasicBlock *BB1 = &BB;
507 // Compute BB1's equivalence class once.
508 if (EquivalenceClass.count(BB1)) {
509 DEBUG(printBlockEquivalence(dbgs(), BB1));
513 // By default, blocks are in their own equivalence class.
514 EquivalenceClass[BB1] = BB1;
516 // Traverse all the blocks dominated by BB1. We are looking for
517 // every basic block BB2 such that:
519 // 1- BB1 dominates BB2.
520 // 2- BB2 post-dominates BB1.
521 // 3- BB1 and BB2 are in the same loop nest.
523 // If all those conditions hold, it means that BB2 is executed
524 // as many times as BB1, so they are placed in the same equivalence
525 // class by making BB2's equivalence class be BB1.
526 DominatedBBs.clear();
527 DT->getDescendants(BB1, DominatedBBs);
528 findEquivalencesFor(BB1, DominatedBBs, PDT.get());
530 DEBUG(printBlockEquivalence(dbgs(), BB1));
533 // Assign weights to equivalence classes.
535 // All the basic blocks in the same equivalence class will execute
536 // the same number of times. Since we know that the head block in
537 // each equivalence class has the largest weight, assign that weight
538 // to all the blocks in that equivalence class.
539 DEBUG(dbgs() << "\nAssign the same weight to all blocks in the same class\n");
541 const BasicBlock *BB = &BI;
542 const BasicBlock *EquivBB = EquivalenceClass[BB];
544 BlockWeights[BB] = BlockWeights[EquivBB];
545 DEBUG(printBlockWeight(dbgs(), BB));
549 /// \brief Visit the given edge to decide if it has a valid weight.
551 /// If \p E has not been visited before, we copy to \p UnknownEdge
552 /// and increment the count of unknown edges.
554 /// \param E Edge to visit.
555 /// \param NumUnknownEdges Current number of unknown edges.
556 /// \param UnknownEdge Set if E has not been visited before.
558 /// \returns E's weight, if known. Otherwise, return 0.
559 uint64_t SampleProfileLoader::visitEdge(Edge E, unsigned *NumUnknownEdges,
561 if (!VisitedEdges.count(E)) {
562 (*NumUnknownEdges)++;
567 return EdgeWeights[E];
570 /// \brief Propagate weights through incoming/outgoing edges.
572 /// If the weight of a basic block is known, and there is only one edge
573 /// with an unknown weight, we can calculate the weight of that edge.
575 /// Similarly, if all the edges have a known count, we can calculate the
576 /// count of the basic block, if needed.
578 /// \param F Function to process.
580 /// \returns True if new weights were assigned to edges or blocks.
581 bool SampleProfileLoader::propagateThroughEdges(Function &F) {
582 bool Changed = false;
583 DEBUG(dbgs() << "\nPropagation through edges\n");
584 for (const auto &BI : F) {
585 const BasicBlock *BB = &BI;
586 const BasicBlock *EC = EquivalenceClass[BB];
588 // Visit all the predecessor and successor edges to determine
589 // which ones have a weight assigned already. Note that it doesn't
590 // matter that we only keep track of a single unknown edge. The
591 // only case we are interested in handling is when only a single
592 // edge is unknown (see setEdgeOrBlockWeight).
593 for (unsigned i = 0; i < 2; i++) {
594 uint64_t TotalWeight = 0;
595 unsigned NumUnknownEdges = 0;
596 Edge UnknownEdge, SelfReferentialEdge;
599 // First, visit all predecessor edges.
600 for (auto *Pred : Predecessors[BB]) {
601 Edge E = std::make_pair(Pred, BB);
602 TotalWeight += visitEdge(E, &NumUnknownEdges, &UnknownEdge);
603 if (E.first == E.second)
604 SelfReferentialEdge = E;
607 // On the second round, visit all successor edges.
608 for (auto *Succ : Successors[BB]) {
609 Edge E = std::make_pair(BB, Succ);
610 TotalWeight += visitEdge(E, &NumUnknownEdges, &UnknownEdge);
614 // After visiting all the edges, there are three cases that we
615 // can handle immediately:
617 // - All the edge weights are known (i.e., NumUnknownEdges == 0).
618 // In this case, we simply check that the sum of all the edges
619 // is the same as BB's weight. If not, we change BB's weight
620 // to match. Additionally, if BB had not been visited before,
621 // we mark it visited.
623 // - Only one edge is unknown and BB has already been visited.
624 // In this case, we can compute the weight of the edge by
625 // subtracting the total block weight from all the known
626 // edge weights. If the edges weight more than BB, then the
627 // edge of the last remaining edge is set to zero.
629 // - There exists a self-referential edge and the weight of BB is
630 // known. In this case, this edge can be based on BB's weight.
631 // We add up all the other known edges and set the weight on
632 // the self-referential edge as we did in the previous case.
634 // In any other case, we must continue iterating. Eventually,
635 // all edges will get a weight, or iteration will stop when
636 // it reaches SampleProfileMaxPropagateIterations.
637 if (NumUnknownEdges <= 1) {
638 uint64_t &BBWeight = BlockWeights[EC];
639 if (NumUnknownEdges == 0) {
640 // If we already know the weight of all edges, the weight of the
641 // basic block can be computed. It should be no larger than the sum
642 // of all edge weights.
643 if (TotalWeight > BBWeight) {
644 BBWeight = TotalWeight;
646 DEBUG(dbgs() << "All edge weights for " << BB->getName()
647 << " known. Set weight for block: ";
648 printBlockWeight(dbgs(), BB););
650 if (VisitedBlocks.insert(EC).second)
652 } else if (NumUnknownEdges == 1 && VisitedBlocks.count(EC)) {
653 // If there is a single unknown edge and the block has been
654 // visited, then we can compute E's weight.
655 if (BBWeight >= TotalWeight)
656 EdgeWeights[UnknownEdge] = BBWeight - TotalWeight;
658 EdgeWeights[UnknownEdge] = 0;
659 VisitedEdges.insert(UnknownEdge);
661 DEBUG(dbgs() << "Set weight for edge: ";
662 printEdgeWeight(dbgs(), UnknownEdge));
664 } else if (SelfReferentialEdge.first && VisitedBlocks.count(EC)) {
665 uint64_t &BBWeight = BlockWeights[BB];
666 // We have a self-referential edge and the weight of BB is known.
667 if (BBWeight >= TotalWeight)
668 EdgeWeights[SelfReferentialEdge] = BBWeight - TotalWeight;
670 EdgeWeights[SelfReferentialEdge] = 0;
671 VisitedEdges.insert(SelfReferentialEdge);
673 DEBUG(dbgs() << "Set self-referential edge weight to: ";
674 printEdgeWeight(dbgs(), SelfReferentialEdge));
682 /// \brief Build in/out edge lists for each basic block in the CFG.
684 /// We are interested in unique edges. If a block B1 has multiple
685 /// edges to another block B2, we only add a single B1->B2 edge.
686 void SampleProfileLoader::buildEdges(Function &F) {
688 BasicBlock *B1 = &BI;
690 // Add predecessors for B1.
691 SmallPtrSet<BasicBlock *, 16> Visited;
692 if (!Predecessors[B1].empty())
693 llvm_unreachable("Found a stale predecessors list in a basic block.");
694 for (pred_iterator PI = pred_begin(B1), PE = pred_end(B1); PI != PE; ++PI) {
695 BasicBlock *B2 = *PI;
696 if (Visited.insert(B2).second)
697 Predecessors[B1].push_back(B2);
700 // Add successors for B1.
702 if (!Successors[B1].empty())
703 llvm_unreachable("Found a stale successors list in a basic block.");
704 for (succ_iterator SI = succ_begin(B1), SE = succ_end(B1); SI != SE; ++SI) {
705 BasicBlock *B2 = *SI;
706 if (Visited.insert(B2).second)
707 Successors[B1].push_back(B2);
712 /// \brief Propagate weights into edges
714 /// The following rules are applied to every block BB in the CFG:
716 /// - If BB has a single predecessor/successor, then the weight
717 /// of that edge is the weight of the block.
719 /// - If all incoming or outgoing edges are known except one, and the
720 /// weight of the block is already known, the weight of the unknown
721 /// edge will be the weight of the block minus the sum of all the known
722 /// edges. If the sum of all the known edges is larger than BB's weight,
723 /// we set the unknown edge weight to zero.
725 /// - If there is a self-referential edge, and the weight of the block is
726 /// known, the weight for that edge is set to the weight of the block
727 /// minus the weight of the other incoming edges to that block (if
729 void SampleProfileLoader::propagateWeights(Function &F) {
733 // Add an entry count to the function using the samples gathered
734 // at the function entry.
735 F.setEntryCount(Samples->getHeadSamples());
737 // Before propagation starts, build, for each block, a list of
738 // unique predecessors and successors. This is necessary to handle
739 // identical edges in multiway branches. Since we visit all blocks and all
740 // edges of the CFG, it is cleaner to build these lists once at the start
744 // Propagate until we converge or we go past the iteration limit.
745 while (Changed && I++ < SampleProfileMaxPropagateIterations) {
746 Changed = propagateThroughEdges(F);
749 // Generate MD_prof metadata for every branch instruction using the
750 // edge weights computed during propagation.
751 DEBUG(dbgs() << "\nPropagation complete. Setting branch weights\n");
752 LLVMContext &Ctx = F.getContext();
755 BasicBlock *BB = &BI;
756 TerminatorInst *TI = BB->getTerminator();
757 if (TI->getNumSuccessors() == 1)
759 if (!isa<BranchInst>(TI) && !isa<SwitchInst>(TI))
762 DEBUG(dbgs() << "\nGetting weights for branch at line "
763 << TI->getDebugLoc().getLine() << ".\n");
764 SmallVector<uint32_t, 4> Weights;
765 uint32_t MaxWeight = 0;
767 for (unsigned I = 0; I < TI->getNumSuccessors(); ++I) {
768 BasicBlock *Succ = TI->getSuccessor(I);
769 Edge E = std::make_pair(BB, Succ);
770 uint64_t Weight = EdgeWeights[E];
771 DEBUG(dbgs() << "\t"; printEdgeWeight(dbgs(), E));
772 // Use uint32_t saturated arithmetic to adjust the incoming weights,
773 // if needed. Sample counts in profiles are 64-bit unsigned values,
774 // but internally branch weights are expressed as 32-bit values.
775 if (Weight > std::numeric_limits<uint32_t>::max()) {
776 DEBUG(dbgs() << " (saturated due to uint32_t overflow)");
777 Weight = std::numeric_limits<uint32_t>::max();
779 Weights.push_back(static_cast<uint32_t>(Weight));
781 if (Weight > MaxWeight) {
783 MaxDestLoc = Succ->getFirstNonPHIOrDbgOrLifetime()->getDebugLoc();
788 // Only set weights if there is at least one non-zero weight.
789 // In any other case, let the analyzer set weights.
791 DEBUG(dbgs() << "SUCCESS. Found non-zero weights.\n");
792 TI->setMetadata(llvm::LLVMContext::MD_prof,
793 MDB.createBranchWeights(Weights));
794 DebugLoc BranchLoc = TI->getDebugLoc();
795 emitOptimizationRemark(
796 Ctx, DEBUG_TYPE, F, MaxDestLoc,
797 Twine("most popular destination for conditional branches at ") +
798 ((BranchLoc) ? Twine(BranchLoc->getFilename() + ":" +
799 Twine(BranchLoc.getLine()) + ":" +
800 Twine(BranchLoc.getCol()))
801 : Twine("<UNKNOWN LOCATION>")));
803 DEBUG(dbgs() << "SKIPPED. All branch weights are zero.\n");
808 /// \brief Get the line number for the function header.
810 /// This looks up function \p F in the current compilation unit and
811 /// retrieves the line number where the function is defined. This is
812 /// line 0 for all the samples read from the profile file. Every line
813 /// number is relative to this line.
815 /// \param F Function object to query.
817 /// \returns the line number where \p F is defined. If it returns 0,
818 /// it means that there is no debug information available for \p F.
819 unsigned SampleProfileLoader::getFunctionLoc(Function &F) {
820 if (DISubprogram *S = getDISubprogram(&F))
823 // If the start of \p F is missing, emit a diagnostic to inform the user
824 // about the missed opportunity.
825 F.getContext().diagnose(DiagnosticInfoSampleProfile(
826 "No debug information found in function " + F.getName() +
827 ": Function profile not used",
832 void SampleProfileLoader::computeDominanceAndLoopInfo(Function &F) {
833 DT.reset(new DominatorTree);
836 PDT.reset(new DominatorTreeBase<BasicBlock>(true));
839 LI.reset(new LoopInfo);
843 /// \brief Generate branch weight metadata for all branches in \p F.
845 /// Branch weights are computed out of instruction samples using a
846 /// propagation heuristic. Propagation proceeds in 3 phases:
848 /// 1- Assignment of block weights. All the basic blocks in the function
849 /// are initial assigned the same weight as their most frequently
850 /// executed instruction.
852 /// 2- Creation of equivalence classes. Since samples may be missing from
853 /// blocks, we can fill in the gaps by setting the weights of all the
854 /// blocks in the same equivalence class to the same weight. To compute
855 /// the concept of equivalence, we use dominance and loop information.
856 /// Two blocks B1 and B2 are in the same equivalence class if B1
857 /// dominates B2, B2 post-dominates B1 and both are in the same loop.
859 /// 3- Propagation of block weights into edges. This uses a simple
860 /// propagation heuristic. The following rules are applied to every
861 /// block BB in the CFG:
863 /// - If BB has a single predecessor/successor, then the weight
864 /// of that edge is the weight of the block.
866 /// - If all the edges are known except one, and the weight of the
867 /// block is already known, the weight of the unknown edge will
868 /// be the weight of the block minus the sum of all the known
869 /// edges. If the sum of all the known edges is larger than BB's weight,
870 /// we set the unknown edge weight to zero.
872 /// - If there is a self-referential edge, and the weight of the block is
873 /// known, the weight for that edge is set to the weight of the block
874 /// minus the weight of the other incoming edges to that block (if
877 /// Since this propagation is not guaranteed to finalize for every CFG, we
878 /// only allow it to proceed for a limited number of iterations (controlled
879 /// by -sample-profile-max-propagate-iterations).
881 /// FIXME: Try to replace this propagation heuristic with a scheme
882 /// that is guaranteed to finalize. A work-list approach similar to
883 /// the standard value propagation algorithm used by SSA-CCP might
886 /// Once all the branch weights are computed, we emit the MD_prof
887 /// metadata on BB using the computed values for each of its branches.
889 /// \param F The function to query.
891 /// \returns true if \p F was modified. Returns false, otherwise.
892 bool SampleProfileLoader::emitAnnotations(Function &F) {
893 bool Changed = false;
895 if (getFunctionLoc(F) == 0)
898 DEBUG(dbgs() << "Line number for the first instruction in " << F.getName()
899 << ": " << getFunctionLoc(F) << "\n");
901 Changed |= inlineHotFunctions(F);
903 // Compute basic block weights.
904 Changed |= computeBlockWeights(F);
907 // Compute dominance and loop info needed for propagation.
908 computeDominanceAndLoopInfo(F);
910 // Find equivalence classes.
911 findEquivalenceClasses(F);
913 // Propagate weights to all edges.
920 char SampleProfileLoader::ID = 0;
921 INITIALIZE_PASS_BEGIN(SampleProfileLoader, "sample-profile",
922 "Sample Profile loader", false, false)
923 INITIALIZE_PASS_DEPENDENCY(AddDiscriminators)
924 INITIALIZE_PASS_END(SampleProfileLoader, "sample-profile",
925 "Sample Profile loader", false, false)
927 bool SampleProfileLoader::doInitialization(Module &M) {
928 auto &Ctx = M.getContext();
929 auto ReaderOrErr = SampleProfileReader::create(Filename, Ctx);
930 if (std::error_code EC = ReaderOrErr.getError()) {
931 std::string Msg = "Could not open profile: " + EC.message();
932 Ctx.diagnose(DiagnosticInfoSampleProfile(Filename.data(), Msg));
935 Reader = std::move(ReaderOrErr.get());
936 ProfileIsValid = (Reader->read() == sampleprof_error::success);
940 ModulePass *llvm::createSampleProfileLoaderPass() {
941 return new SampleProfileLoader(SampleProfileFile);
944 ModulePass *llvm::createSampleProfileLoaderPass(StringRef Name) {
945 return new SampleProfileLoader(Name);
948 bool SampleProfileLoader::runOnModule(Module &M) {
954 if (!F.isDeclaration()) {
956 retval |= runOnFunction(F);
961 bool SampleProfileLoader::runOnFunction(Function &F) {
962 Samples = Reader->getSamplesFor(F);
963 if (!Samples->empty())
964 return emitAnnotations(F);