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Diffstat (limited to 'contrib/llvm/lib/Transforms/IPO/SampleProfile.cpp')
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diff --git a/contrib/llvm/lib/Transforms/IPO/SampleProfile.cpp b/contrib/llvm/lib/Transforms/IPO/SampleProfile.cpp new file mode 100644 index 0000000..928d92e --- /dev/null +++ b/contrib/llvm/lib/Transforms/IPO/SampleProfile.cpp @@ -0,0 +1,1265 @@ +//===- SampleProfile.cpp - Incorporate sample profiles into the IR --------===// +// +// The LLVM Compiler Infrastructure +// +// This file is distributed under the University of Illinois Open Source +// License. See LICENSE.TXT for details. +// +//===----------------------------------------------------------------------===// +// +// This file implements the SampleProfileLoader transformation. This pass +// reads a profile file generated by a sampling profiler (e.g. Linux Perf - +// http://perf.wiki.kernel.org/) and generates IR metadata to reflect the +// profile information in the given profile. +// +// This pass generates branch weight annotations on the IR: +// +// - prof: Represents branch weights. This annotation is added to branches +// to indicate the weights of each edge coming out of the branch. +// The weight of each edge is the weight of the target block for +// that edge. The weight of a block B is computed as the maximum +// number of samples found in B. +// +//===----------------------------------------------------------------------===// + +#include "llvm/ADT/DenseMap.h" +#include "llvm/ADT/SmallPtrSet.h" +#include "llvm/ADT/SmallSet.h" +#include "llvm/ADT/StringRef.h" +#include "llvm/Analysis/LoopInfo.h" +#include "llvm/Analysis/PostDominators.h" +#include "llvm/IR/Constants.h" +#include "llvm/IR/DebugInfo.h" +#include "llvm/IR/DiagnosticInfo.h" +#include "llvm/IR/Dominators.h" +#include "llvm/IR/Function.h" +#include "llvm/IR/InstIterator.h" +#include "llvm/IR/Instructions.h" +#include "llvm/IR/LLVMContext.h" +#include "llvm/IR/MDBuilder.h" +#include "llvm/IR/Metadata.h" +#include "llvm/IR/Module.h" +#include "llvm/Pass.h" +#include "llvm/ProfileData/SampleProfReader.h" +#include "llvm/Support/CommandLine.h" +#include "llvm/Support/Debug.h" +#include "llvm/Support/ErrorOr.h" +#include "llvm/Support/Format.h" +#include "llvm/Support/raw_ostream.h" +#include "llvm/Transforms/IPO.h" +#include "llvm/Transforms/Utils/Cloning.h" +#include <cctype> + +using namespace llvm; +using namespace sampleprof; + +#define DEBUG_TYPE "sample-profile" + +// Command line option to specify the file to read samples from. This is +// mainly used for debugging. +static cl::opt<std::string> SampleProfileFile( + "sample-profile-file", cl::init(""), cl::value_desc("filename"), + cl::desc("Profile file loaded by -sample-profile"), cl::Hidden); +static cl::opt<unsigned> SampleProfileMaxPropagateIterations( + "sample-profile-max-propagate-iterations", cl::init(100), + cl::desc("Maximum number of iterations to go through when propagating " + "sample block/edge weights through the CFG.")); +static cl::opt<unsigned> SampleProfileRecordCoverage( + "sample-profile-check-record-coverage", cl::init(0), cl::value_desc("N"), + cl::desc("Emit a warning if less than N% of records in the input profile " + "are matched to the IR.")); +static cl::opt<unsigned> SampleProfileSampleCoverage( + "sample-profile-check-sample-coverage", cl::init(0), cl::value_desc("N"), + cl::desc("Emit a warning if less than N% of samples in the input profile " + "are matched to the IR.")); +static cl::opt<double> SampleProfileHotThreshold( + "sample-profile-inline-hot-threshold", cl::init(0.1), cl::value_desc("N"), + cl::desc("Inlined functions that account for more than N% of all samples " + "collected in the parent function, will be inlined again.")); +static cl::opt<double> SampleProfileGlobalHotThreshold( + "sample-profile-global-hot-threshold", cl::init(30), cl::value_desc("N"), + cl::desc("Top-level functions that account for more than N% of all samples " + "collected in the profile, will be marked as hot for the inliner " + "to consider.")); +static cl::opt<double> SampleProfileGlobalColdThreshold( + "sample-profile-global-cold-threshold", cl::init(0.5), cl::value_desc("N"), + cl::desc("Top-level functions that account for less than N% of all samples " + "collected in the profile, will be marked as cold for the inliner " + "to consider.")); + +namespace { +typedef DenseMap<const BasicBlock *, uint64_t> BlockWeightMap; +typedef DenseMap<const BasicBlock *, const BasicBlock *> EquivalenceClassMap; +typedef std::pair<const BasicBlock *, const BasicBlock *> Edge; +typedef DenseMap<Edge, uint64_t> EdgeWeightMap; +typedef DenseMap<const BasicBlock *, SmallVector<const BasicBlock *, 8>> + BlockEdgeMap; + +/// \brief Sample profile pass. +/// +/// This pass reads profile data from the file specified by +/// -sample-profile-file and annotates every affected function with the +/// profile information found in that file. +class SampleProfileLoader : public ModulePass { +public: + // Class identification, replacement for typeinfo + static char ID; + + SampleProfileLoader(StringRef Name = SampleProfileFile) + : ModulePass(ID), DT(nullptr), PDT(nullptr), LI(nullptr), Reader(), + Samples(nullptr), Filename(Name), ProfileIsValid(false), + TotalCollectedSamples(0) { + initializeSampleProfileLoaderPass(*PassRegistry::getPassRegistry()); + } + + bool doInitialization(Module &M) override; + + void dump() { Reader->dump(); } + + const char *getPassName() const override { return "Sample profile pass"; } + + bool runOnModule(Module &M) override; + + void getAnalysisUsage(AnalysisUsage &AU) const override { + AU.setPreservesCFG(); + } + +protected: + bool runOnFunction(Function &F); + unsigned getFunctionLoc(Function &F); + bool emitAnnotations(Function &F); + ErrorOr<uint64_t> getInstWeight(const Instruction &I) const; + ErrorOr<uint64_t> getBlockWeight(const BasicBlock *BB) const; + const FunctionSamples *findCalleeFunctionSamples(const CallInst &I) const; + const FunctionSamples *findFunctionSamples(const Instruction &I) const; + bool inlineHotFunctions(Function &F); + bool emitInlineHints(Function &F); + void printEdgeWeight(raw_ostream &OS, Edge E); + void printBlockWeight(raw_ostream &OS, const BasicBlock *BB) const; + void printBlockEquivalence(raw_ostream &OS, const BasicBlock *BB); + bool computeBlockWeights(Function &F); + void findEquivalenceClasses(Function &F); + void findEquivalencesFor(BasicBlock *BB1, + SmallVector<BasicBlock *, 8> Descendants, + DominatorTreeBase<BasicBlock> *DomTree); + void propagateWeights(Function &F); + uint64_t visitEdge(Edge E, unsigned *NumUnknownEdges, Edge *UnknownEdge); + void buildEdges(Function &F); + bool propagateThroughEdges(Function &F); + void computeDominanceAndLoopInfo(Function &F); + unsigned getOffset(unsigned L, unsigned H) const; + void clearFunctionData(); + + /// \brief Map basic blocks to their computed weights. + /// + /// The weight of a basic block is defined to be the maximum + /// of all the instruction weights in that block. + BlockWeightMap BlockWeights; + + /// \brief Map edges to their computed weights. + /// + /// Edge weights are computed by propagating basic block weights in + /// SampleProfile::propagateWeights. + EdgeWeightMap EdgeWeights; + + /// \brief Set of visited blocks during propagation. + SmallPtrSet<const BasicBlock *, 128> VisitedBlocks; + + /// \brief Set of visited edges during propagation. + SmallSet<Edge, 128> VisitedEdges; + + /// \brief Equivalence classes for block weights. + /// + /// Two blocks BB1 and BB2 are in the same equivalence class if they + /// dominate and post-dominate each other, and they are in the same loop + /// nest. When this happens, the two blocks are guaranteed to execute + /// the same number of times. + EquivalenceClassMap EquivalenceClass; + + /// \brief Dominance, post-dominance and loop information. + std::unique_ptr<DominatorTree> DT; + std::unique_ptr<DominatorTreeBase<BasicBlock>> PDT; + std::unique_ptr<LoopInfo> LI; + + /// \brief Predecessors for each basic block in the CFG. + BlockEdgeMap Predecessors; + + /// \brief Successors for each basic block in the CFG. + BlockEdgeMap Successors; + + /// \brief Profile reader object. + std::unique_ptr<SampleProfileReader> Reader; + + /// \brief Samples collected for the body of this function. + FunctionSamples *Samples; + + /// \brief Name of the profile file to load. + StringRef Filename; + + /// \brief Flag indicating whether the profile input loaded successfully. + bool ProfileIsValid; + + /// \brief Total number of samples collected in this profile. + /// + /// This is the sum of all the samples collected in all the functions executed + /// at runtime. + uint64_t TotalCollectedSamples; +}; + +class SampleCoverageTracker { +public: + SampleCoverageTracker() : SampleCoverage(), TotalUsedSamples(0) {} + + bool markSamplesUsed(const FunctionSamples *FS, uint32_t LineOffset, + uint32_t Discriminator, uint64_t Samples); + unsigned computeCoverage(unsigned Used, unsigned Total) const; + unsigned countUsedRecords(const FunctionSamples *FS) const; + unsigned countBodyRecords(const FunctionSamples *FS) const; + uint64_t getTotalUsedSamples() const { return TotalUsedSamples; } + uint64_t countBodySamples(const FunctionSamples *FS) const; + void clear() { + SampleCoverage.clear(); + TotalUsedSamples = 0; + } + +private: + typedef std::map<LineLocation, unsigned> BodySampleCoverageMap; + typedef DenseMap<const FunctionSamples *, BodySampleCoverageMap> + FunctionSamplesCoverageMap; + + /// Coverage map for sampling records. + /// + /// This map keeps a record of sampling records that have been matched to + /// an IR instruction. This is used to detect some form of staleness in + /// profiles (see flag -sample-profile-check-coverage). + /// + /// Each entry in the map corresponds to a FunctionSamples instance. This is + /// another map that counts how many times the sample record at the + /// given location has been used. + FunctionSamplesCoverageMap SampleCoverage; + + /// Number of samples used from the profile. + /// + /// When a sampling record is used for the first time, the samples from + /// that record are added to this accumulator. Coverage is later computed + /// based on the total number of samples available in this function and + /// its callsites. + /// + /// Note that this accumulator tracks samples used from a single function + /// and all the inlined callsites. Strictly, we should have a map of counters + /// keyed by FunctionSamples pointers, but these stats are cleared after + /// every function, so we just need to keep a single counter. + uint64_t TotalUsedSamples; +}; + +SampleCoverageTracker CoverageTracker; + +/// Return true if the given callsite is hot wrt to its caller. +/// +/// Functions that were inlined in the original binary will be represented +/// in the inline stack in the sample profile. If the profile shows that +/// the original inline decision was "good" (i.e., the callsite is executed +/// frequently), then we will recreate the inline decision and apply the +/// profile from the inlined callsite. +/// +/// To decide whether an inlined callsite is hot, we compute the fraction +/// of samples used by the callsite with respect to the total number of samples +/// collected in the caller. +/// +/// If that fraction is larger than the default given by +/// SampleProfileHotThreshold, the callsite will be inlined again. +bool callsiteIsHot(const FunctionSamples *CallerFS, + const FunctionSamples *CallsiteFS) { + if (!CallsiteFS) + return false; // The callsite was not inlined in the original binary. + + uint64_t ParentTotalSamples = CallerFS->getTotalSamples(); + if (ParentTotalSamples == 0) + return false; // Avoid division by zero. + + uint64_t CallsiteTotalSamples = CallsiteFS->getTotalSamples(); + if (CallsiteTotalSamples == 0) + return false; // Callsite is trivially cold. + + double PercentSamples = + (double)CallsiteTotalSamples / (double)ParentTotalSamples * 100.0; + return PercentSamples >= SampleProfileHotThreshold; +} + +} + +/// Mark as used the sample record for the given function samples at +/// (LineOffset, Discriminator). +/// +/// \returns true if this is the first time we mark the given record. +bool SampleCoverageTracker::markSamplesUsed(const FunctionSamples *FS, + uint32_t LineOffset, + uint32_t Discriminator, + uint64_t Samples) { + LineLocation Loc(LineOffset, Discriminator); + unsigned &Count = SampleCoverage[FS][Loc]; + bool FirstTime = (++Count == 1); + if (FirstTime) + TotalUsedSamples += Samples; + return FirstTime; +} + +/// Return the number of sample records that were applied from this profile. +/// +/// This count does not include records from cold inlined callsites. +unsigned +SampleCoverageTracker::countUsedRecords(const FunctionSamples *FS) const { + auto I = SampleCoverage.find(FS); + + // The size of the coverage map for FS represents the number of records + // that were marked used at least once. + unsigned Count = (I != SampleCoverage.end()) ? I->second.size() : 0; + + // If there are inlined callsites in this function, count the samples found + // in the respective bodies. However, do not bother counting callees with 0 + // total samples, these are callees that were never invoked at runtime. + for (const auto &I : FS->getCallsiteSamples()) { + const FunctionSamples *CalleeSamples = &I.second; + if (callsiteIsHot(FS, CalleeSamples)) + Count += countUsedRecords(CalleeSamples); + } + + return Count; +} + +/// Return the number of sample records in the body of this profile. +/// +/// This count does not include records from cold inlined callsites. +unsigned +SampleCoverageTracker::countBodyRecords(const FunctionSamples *FS) const { + unsigned Count = FS->getBodySamples().size(); + + // Only count records in hot callsites. + for (const auto &I : FS->getCallsiteSamples()) { + const FunctionSamples *CalleeSamples = &I.second; + if (callsiteIsHot(FS, CalleeSamples)) + Count += countBodyRecords(CalleeSamples); + } + + return Count; +} + +/// Return the number of samples collected in the body of this profile. +/// +/// This count does not include samples from cold inlined callsites. +uint64_t +SampleCoverageTracker::countBodySamples(const FunctionSamples *FS) const { + uint64_t Total = 0; + for (const auto &I : FS->getBodySamples()) + Total += I.second.getSamples(); + + // Only count samples in hot callsites. + for (const auto &I : FS->getCallsiteSamples()) { + const FunctionSamples *CalleeSamples = &I.second; + if (callsiteIsHot(FS, CalleeSamples)) + Total += countBodySamples(CalleeSamples); + } + + return Total; +} + +/// Return the fraction of sample records used in this profile. +/// +/// The returned value is an unsigned integer in the range 0-100 indicating +/// the percentage of sample records that were used while applying this +/// profile to the associated function. +unsigned SampleCoverageTracker::computeCoverage(unsigned Used, + unsigned Total) const { + assert(Used <= Total && + "number of used records cannot exceed the total number of records"); + return Total > 0 ? Used * 100 / Total : 100; +} + +/// Clear all the per-function data used to load samples and propagate weights. +void SampleProfileLoader::clearFunctionData() { + BlockWeights.clear(); + EdgeWeights.clear(); + VisitedBlocks.clear(); + VisitedEdges.clear(); + EquivalenceClass.clear(); + DT = nullptr; + PDT = nullptr; + LI = nullptr; + Predecessors.clear(); + Successors.clear(); + CoverageTracker.clear(); +} + +/// \brief Returns the offset of lineno \p L to head_lineno \p H +/// +/// \param L Lineno +/// \param H Header lineno of the function +/// +/// \returns offset to the header lineno. 16 bits are used to represent offset. +/// We assume that a single function will not exceed 65535 LOC. +unsigned SampleProfileLoader::getOffset(unsigned L, unsigned H) const { + return (L - H) & 0xffff; +} + +/// \brief Print the weight of edge \p E on stream \p OS. +/// +/// \param OS Stream to emit the output to. +/// \param E Edge to print. +void SampleProfileLoader::printEdgeWeight(raw_ostream &OS, Edge E) { + OS << "weight[" << E.first->getName() << "->" << E.second->getName() + << "]: " << EdgeWeights[E] << "\n"; +} + +/// \brief Print the equivalence class of block \p BB on stream \p OS. +/// +/// \param OS Stream to emit the output to. +/// \param BB Block to print. +void SampleProfileLoader::printBlockEquivalence(raw_ostream &OS, + const BasicBlock *BB) { + const BasicBlock *Equiv = EquivalenceClass[BB]; + OS << "equivalence[" << BB->getName() + << "]: " << ((Equiv) ? EquivalenceClass[BB]->getName() : "NONE") << "\n"; +} + +/// \brief Print the weight of block \p BB on stream \p OS. +/// +/// \param OS Stream to emit the output to. +/// \param BB Block to print. +void SampleProfileLoader::printBlockWeight(raw_ostream &OS, + const BasicBlock *BB) const { + const auto &I = BlockWeights.find(BB); + uint64_t W = (I == BlockWeights.end() ? 0 : I->second); + OS << "weight[" << BB->getName() << "]: " << W << "\n"; +} + +/// \brief Get the weight for an instruction. +/// +/// The "weight" of an instruction \p Inst is the number of samples +/// collected on that instruction at runtime. To retrieve it, we +/// need to compute the line number of \p Inst relative to the start of its +/// function. We use HeaderLineno to compute the offset. We then +/// look up the samples collected for \p Inst using BodySamples. +/// +/// \param Inst Instruction to query. +/// +/// \returns the weight of \p Inst. +ErrorOr<uint64_t> +SampleProfileLoader::getInstWeight(const Instruction &Inst) const { + DebugLoc DLoc = Inst.getDebugLoc(); + if (!DLoc) + return std::error_code(); + + const FunctionSamples *FS = findFunctionSamples(Inst); + if (!FS) + return std::error_code(); + + const DILocation *DIL = DLoc; + unsigned Lineno = DLoc.getLine(); + unsigned HeaderLineno = DIL->getScope()->getSubprogram()->getLine(); + + uint32_t LineOffset = getOffset(Lineno, HeaderLineno); + uint32_t Discriminator = DIL->getDiscriminator(); + ErrorOr<uint64_t> R = FS->findSamplesAt(LineOffset, Discriminator); + if (R) { + bool FirstMark = + CoverageTracker.markSamplesUsed(FS, LineOffset, Discriminator, R.get()); + if (FirstMark) { + const Function *F = Inst.getParent()->getParent(); + LLVMContext &Ctx = F->getContext(); + emitOptimizationRemark( + Ctx, DEBUG_TYPE, *F, DLoc, + Twine("Applied ") + Twine(*R) + " samples from profile (offset: " + + Twine(LineOffset) + + ((Discriminator) ? Twine(".") + Twine(Discriminator) : "") + ")"); + } + DEBUG(dbgs() << " " << Lineno << "." << DIL->getDiscriminator() << ":" + << Inst << " (line offset: " << Lineno - HeaderLineno << "." + << DIL->getDiscriminator() << " - weight: " << R.get() + << ")\n"); + } + return R; +} + +/// \brief Compute the weight of a basic block. +/// +/// The weight of basic block \p BB is the maximum weight of all the +/// instructions in BB. +/// +/// \param BB The basic block to query. +/// +/// \returns the weight for \p BB. +ErrorOr<uint64_t> +SampleProfileLoader::getBlockWeight(const BasicBlock *BB) const { + bool Found = false; + uint64_t Weight = 0; + for (auto &I : BB->getInstList()) { + const ErrorOr<uint64_t> &R = getInstWeight(I); + if (R && R.get() >= Weight) { + Weight = R.get(); + Found = true; + } + } + if (Found) + return Weight; + else + return std::error_code(); +} + +/// \brief Compute and store the weights of every basic block. +/// +/// This populates the BlockWeights map by computing +/// the weights of every basic block in the CFG. +/// +/// \param F The function to query. +bool SampleProfileLoader::computeBlockWeights(Function &F) { + bool Changed = false; + DEBUG(dbgs() << "Block weights\n"); + for (const auto &BB : F) { + ErrorOr<uint64_t> Weight = getBlockWeight(&BB); + if (Weight) { + BlockWeights[&BB] = Weight.get(); + VisitedBlocks.insert(&BB); + Changed = true; + } + DEBUG(printBlockWeight(dbgs(), &BB)); + } + + return Changed; +} + +/// \brief Get the FunctionSamples for a call instruction. +/// +/// The FunctionSamples of a call instruction \p Inst is the inlined +/// instance in which that call instruction is calling to. It contains +/// all samples that resides in the inlined instance. We first find the +/// inlined instance in which the call instruction is from, then we +/// traverse its children to find the callsite with the matching +/// location and callee function name. +/// +/// \param Inst Call instruction to query. +/// +/// \returns The FunctionSamples pointer to the inlined instance. +const FunctionSamples * +SampleProfileLoader::findCalleeFunctionSamples(const CallInst &Inst) const { + const DILocation *DIL = Inst.getDebugLoc(); + if (!DIL) { + return nullptr; + } + DISubprogram *SP = DIL->getScope()->getSubprogram(); + if (!SP) + return nullptr; + + Function *CalleeFunc = Inst.getCalledFunction(); + if (!CalleeFunc) { + return nullptr; + } + + StringRef CalleeName = CalleeFunc->getName(); + const FunctionSamples *FS = findFunctionSamples(Inst); + if (FS == nullptr) + return nullptr; + + return FS->findFunctionSamplesAt( + CallsiteLocation(getOffset(DIL->getLine(), SP->getLine()), + DIL->getDiscriminator(), CalleeName)); +} + +/// \brief Get the FunctionSamples for an instruction. +/// +/// The FunctionSamples of an instruction \p Inst is the inlined instance +/// in which that instruction is coming from. We traverse the inline stack +/// of that instruction, and match it with the tree nodes in the profile. +/// +/// \param Inst Instruction to query. +/// +/// \returns the FunctionSamples pointer to the inlined instance. +const FunctionSamples * +SampleProfileLoader::findFunctionSamples(const Instruction &Inst) const { + SmallVector<CallsiteLocation, 10> S; + const DILocation *DIL = Inst.getDebugLoc(); + if (!DIL) { + return Samples; + } + StringRef CalleeName; + for (const DILocation *DIL = Inst.getDebugLoc(); DIL; + DIL = DIL->getInlinedAt()) { + DISubprogram *SP = DIL->getScope()->getSubprogram(); + if (!SP) + return nullptr; + if (!CalleeName.empty()) { + S.push_back(CallsiteLocation(getOffset(DIL->getLine(), SP->getLine()), + DIL->getDiscriminator(), CalleeName)); + } + CalleeName = SP->getLinkageName(); + } + if (S.size() == 0) + return Samples; + const FunctionSamples *FS = Samples; + for (int i = S.size() - 1; i >= 0 && FS != nullptr; i--) { + FS = FS->findFunctionSamplesAt(S[i]); + } + return FS; +} + +/// \brief Emit an inline hint if \p F is globally hot or cold. +/// +/// If \p F consumes a significant fraction of samples (indicated by +/// SampleProfileGlobalHotThreshold), apply the InlineHint attribute for the +/// inliner to consider the function hot. +/// +/// If \p F consumes a small fraction of samples (indicated by +/// SampleProfileGlobalColdThreshold), apply the Cold attribute for the inliner +/// to consider the function cold. +/// +/// FIXME - This setting of inline hints is sub-optimal. Instead of marking a +/// function globally hot or cold, we should be annotating individual callsites. +/// This is not currently possible, but work on the inliner will eventually +/// provide this ability. See http://reviews.llvm.org/D15003 for details and +/// discussion. +/// +/// \returns True if either attribute was applied to \p F. +bool SampleProfileLoader::emitInlineHints(Function &F) { + if (TotalCollectedSamples == 0) + return false; + + uint64_t FunctionSamples = Samples->getTotalSamples(); + double SamplesPercent = + (double)FunctionSamples / (double)TotalCollectedSamples * 100.0; + + // If the function collected more samples than the hot threshold, mark + // it globally hot. + if (SamplesPercent >= SampleProfileGlobalHotThreshold) { + F.addFnAttr(llvm::Attribute::InlineHint); + std::string Msg; + raw_string_ostream S(Msg); + S << "Applied inline hint to globally hot function '" << F.getName() + << "' with " << format("%.2f", SamplesPercent) + << "% of samples (threshold: " + << format("%.2f", SampleProfileGlobalHotThreshold.getValue()) << "%)"; + S.flush(); + emitOptimizationRemark(F.getContext(), DEBUG_TYPE, F, DebugLoc(), Msg); + return true; + } + + // If the function collected fewer samples than the cold threshold, mark + // it globally cold. + if (SamplesPercent <= SampleProfileGlobalColdThreshold) { + F.addFnAttr(llvm::Attribute::Cold); + std::string Msg; + raw_string_ostream S(Msg); + S << "Applied cold hint to globally cold function '" << F.getName() + << "' with " << format("%.2f", SamplesPercent) + << "% of samples (threshold: " + << format("%.2f", SampleProfileGlobalColdThreshold.getValue()) << "%)"; + S.flush(); + emitOptimizationRemark(F.getContext(), DEBUG_TYPE, F, DebugLoc(), Msg); + return true; + } + + return false; +} + +/// \brief Iteratively inline hot callsites of a function. +/// +/// Iteratively traverse all callsites of the function \p F, and find if +/// the corresponding inlined instance exists and is hot in profile. If +/// it is hot enough, inline the callsites and adds new callsites of the +/// callee into the caller. +/// +/// TODO: investigate the possibility of not invoking InlineFunction directly. +/// +/// \param F function to perform iterative inlining. +/// +/// \returns True if there is any inline happened. +bool SampleProfileLoader::inlineHotFunctions(Function &F) { + bool Changed = false; + LLVMContext &Ctx = F.getContext(); + while (true) { + bool LocalChanged = false; + SmallVector<CallInst *, 10> CIS; + for (auto &BB : F) { + for (auto &I : BB.getInstList()) { + CallInst *CI = dyn_cast<CallInst>(&I); + if (CI && callsiteIsHot(Samples, findCalleeFunctionSamples(*CI))) + CIS.push_back(CI); + } + } + for (auto CI : CIS) { + InlineFunctionInfo IFI; + Function *CalledFunction = CI->getCalledFunction(); + DebugLoc DLoc = CI->getDebugLoc(); + uint64_t NumSamples = findCalleeFunctionSamples(*CI)->getTotalSamples(); + if (InlineFunction(CI, IFI)) { + LocalChanged = true; + emitOptimizationRemark(Ctx, DEBUG_TYPE, F, DLoc, + Twine("inlined hot callee '") + + CalledFunction->getName() + "' with " + + Twine(NumSamples) + " samples into '" + + F.getName() + "'"); + } + } + if (LocalChanged) { + Changed = true; + } else { + break; + } + } + return Changed; +} + +/// \brief Find equivalence classes for the given block. +/// +/// This finds all the blocks that are guaranteed to execute the same +/// number of times as \p BB1. To do this, it traverses all the +/// descendants of \p BB1 in the dominator or post-dominator tree. +/// +/// A block BB2 will be in the same equivalence class as \p BB1 if +/// the following holds: +/// +/// 1- \p BB1 is a descendant of BB2 in the opposite tree. So, if BB2 +/// is a descendant of \p BB1 in the dominator tree, then BB2 should +/// dominate BB1 in the post-dominator tree. +/// +/// 2- Both BB2 and \p BB1 must be in the same loop. +/// +/// For every block BB2 that meets those two requirements, we set BB2's +/// equivalence class to \p BB1. +/// +/// \param BB1 Block to check. +/// \param Descendants Descendants of \p BB1 in either the dom or pdom tree. +/// \param DomTree Opposite dominator tree. If \p Descendants is filled +/// with blocks from \p BB1's dominator tree, then +/// this is the post-dominator tree, and vice versa. +void SampleProfileLoader::findEquivalencesFor( + BasicBlock *BB1, SmallVector<BasicBlock *, 8> Descendants, + DominatorTreeBase<BasicBlock> *DomTree) { + const BasicBlock *EC = EquivalenceClass[BB1]; + uint64_t Weight = BlockWeights[EC]; + for (const auto *BB2 : Descendants) { + bool IsDomParent = DomTree->dominates(BB2, BB1); + bool IsInSameLoop = LI->getLoopFor(BB1) == LI->getLoopFor(BB2); + if (BB1 != BB2 && IsDomParent && IsInSameLoop) { + EquivalenceClass[BB2] = EC; + + // If BB2 is heavier than BB1, make BB2 have the same weight + // as BB1. + // + // Note that we don't worry about the opposite situation here + // (when BB2 is lighter than BB1). We will deal with this + // during the propagation phase. Right now, we just want to + // make sure that BB1 has the largest weight of all the + // members of its equivalence set. + Weight = std::max(Weight, BlockWeights[BB2]); + } + } + BlockWeights[EC] = Weight; +} + +/// \brief Find equivalence classes. +/// +/// Since samples may be missing from blocks, we can fill in the gaps by setting +/// the weights of all the blocks in the same equivalence class to the same +/// weight. To compute the concept of equivalence, we use dominance and loop +/// information. Two blocks B1 and B2 are in the same equivalence class if B1 +/// dominates B2, B2 post-dominates B1 and both are in the same loop. +/// +/// \param F The function to query. +void SampleProfileLoader::findEquivalenceClasses(Function &F) { + SmallVector<BasicBlock *, 8> DominatedBBs; + DEBUG(dbgs() << "\nBlock equivalence classes\n"); + // Find equivalence sets based on dominance and post-dominance information. + for (auto &BB : F) { + BasicBlock *BB1 = &BB; + + // Compute BB1's equivalence class once. + if (EquivalenceClass.count(BB1)) { + DEBUG(printBlockEquivalence(dbgs(), BB1)); + continue; + } + + // By default, blocks are in their own equivalence class. + EquivalenceClass[BB1] = BB1; + + // Traverse all the blocks dominated by BB1. We are looking for + // every basic block BB2 such that: + // + // 1- BB1 dominates BB2. + // 2- BB2 post-dominates BB1. + // 3- BB1 and BB2 are in the same loop nest. + // + // If all those conditions hold, it means that BB2 is executed + // as many times as BB1, so they are placed in the same equivalence + // class by making BB2's equivalence class be BB1. + DominatedBBs.clear(); + DT->getDescendants(BB1, DominatedBBs); + findEquivalencesFor(BB1, DominatedBBs, PDT.get()); + + DEBUG(printBlockEquivalence(dbgs(), BB1)); + } + + // Assign weights to equivalence classes. + // + // All the basic blocks in the same equivalence class will execute + // the same number of times. Since we know that the head block in + // each equivalence class has the largest weight, assign that weight + // to all the blocks in that equivalence class. + DEBUG(dbgs() << "\nAssign the same weight to all blocks in the same class\n"); + for (auto &BI : F) { + const BasicBlock *BB = &BI; + const BasicBlock *EquivBB = EquivalenceClass[BB]; + if (BB != EquivBB) + BlockWeights[BB] = BlockWeights[EquivBB]; + DEBUG(printBlockWeight(dbgs(), BB)); + } +} + +/// \brief Visit the given edge to decide if it has a valid weight. +/// +/// If \p E has not been visited before, we copy to \p UnknownEdge +/// and increment the count of unknown edges. +/// +/// \param E Edge to visit. +/// \param NumUnknownEdges Current number of unknown edges. +/// \param UnknownEdge Set if E has not been visited before. +/// +/// \returns E's weight, if known. Otherwise, return 0. +uint64_t SampleProfileLoader::visitEdge(Edge E, unsigned *NumUnknownEdges, + Edge *UnknownEdge) { + if (!VisitedEdges.count(E)) { + (*NumUnknownEdges)++; + *UnknownEdge = E; + return 0; + } + + return EdgeWeights[E]; +} + +/// \brief Propagate weights through incoming/outgoing edges. +/// +/// If the weight of a basic block is known, and there is only one edge +/// with an unknown weight, we can calculate the weight of that edge. +/// +/// Similarly, if all the edges have a known count, we can calculate the +/// count of the basic block, if needed. +/// +/// \param F Function to process. +/// +/// \returns True if new weights were assigned to edges or blocks. +bool SampleProfileLoader::propagateThroughEdges(Function &F) { + bool Changed = false; + DEBUG(dbgs() << "\nPropagation through edges\n"); + for (const auto &BI : F) { + const BasicBlock *BB = &BI; + const BasicBlock *EC = EquivalenceClass[BB]; + + // Visit all the predecessor and successor edges to determine + // which ones have a weight assigned already. Note that it doesn't + // matter that we only keep track of a single unknown edge. The + // only case we are interested in handling is when only a single + // edge is unknown (see setEdgeOrBlockWeight). + for (unsigned i = 0; i < 2; i++) { + uint64_t TotalWeight = 0; + unsigned NumUnknownEdges = 0; + Edge UnknownEdge, SelfReferentialEdge; + + if (i == 0) { + // First, visit all predecessor edges. + for (auto *Pred : Predecessors[BB]) { + Edge E = std::make_pair(Pred, BB); + TotalWeight += visitEdge(E, &NumUnknownEdges, &UnknownEdge); + if (E.first == E.second) + SelfReferentialEdge = E; + } + } else { + // On the second round, visit all successor edges. + for (auto *Succ : Successors[BB]) { + Edge E = std::make_pair(BB, Succ); + TotalWeight += visitEdge(E, &NumUnknownEdges, &UnknownEdge); + } + } + + // After visiting all the edges, there are three cases that we + // can handle immediately: + // + // - All the edge weights are known (i.e., NumUnknownEdges == 0). + // In this case, we simply check that the sum of all the edges + // is the same as BB's weight. If not, we change BB's weight + // to match. Additionally, if BB had not been visited before, + // we mark it visited. + // + // - Only one edge is unknown and BB has already been visited. + // In this case, we can compute the weight of the edge by + // subtracting the total block weight from all the known + // edge weights. If the edges weight more than BB, then the + // edge of the last remaining edge is set to zero. + // + // - There exists a self-referential edge and the weight of BB is + // known. In this case, this edge can be based on BB's weight. + // We add up all the other known edges and set the weight on + // the self-referential edge as we did in the previous case. + // + // In any other case, we must continue iterating. Eventually, + // all edges will get a weight, or iteration will stop when + // it reaches SampleProfileMaxPropagateIterations. + if (NumUnknownEdges <= 1) { + uint64_t &BBWeight = BlockWeights[EC]; + if (NumUnknownEdges == 0) { + // If we already know the weight of all edges, the weight of the + // basic block can be computed. It should be no larger than the sum + // of all edge weights. + if (TotalWeight > BBWeight) { + BBWeight = TotalWeight; + Changed = true; + DEBUG(dbgs() << "All edge weights for " << BB->getName() + << " known. Set weight for block: "; + printBlockWeight(dbgs(), BB);); + } + if (VisitedBlocks.insert(EC).second) + Changed = true; + } else if (NumUnknownEdges == 1 && VisitedBlocks.count(EC)) { + // If there is a single unknown edge and the block has been + // visited, then we can compute E's weight. + if (BBWeight >= TotalWeight) + EdgeWeights[UnknownEdge] = BBWeight - TotalWeight; + else + EdgeWeights[UnknownEdge] = 0; + VisitedEdges.insert(UnknownEdge); + Changed = true; + DEBUG(dbgs() << "Set weight for edge: "; + printEdgeWeight(dbgs(), UnknownEdge)); + } + } else if (SelfReferentialEdge.first && VisitedBlocks.count(EC)) { + uint64_t &BBWeight = BlockWeights[BB]; + // We have a self-referential edge and the weight of BB is known. + if (BBWeight >= TotalWeight) + EdgeWeights[SelfReferentialEdge] = BBWeight - TotalWeight; + else + EdgeWeights[SelfReferentialEdge] = 0; + VisitedEdges.insert(SelfReferentialEdge); + Changed = true; + DEBUG(dbgs() << "Set self-referential edge weight to: "; + printEdgeWeight(dbgs(), SelfReferentialEdge)); + } + } + } + + return Changed; +} + +/// \brief Build in/out edge lists for each basic block in the CFG. +/// +/// We are interested in unique edges. If a block B1 has multiple +/// edges to another block B2, we only add a single B1->B2 edge. +void SampleProfileLoader::buildEdges(Function &F) { + for (auto &BI : F) { + BasicBlock *B1 = &BI; + + // Add predecessors for B1. + SmallPtrSet<BasicBlock *, 16> Visited; + if (!Predecessors[B1].empty()) + llvm_unreachable("Found a stale predecessors list in a basic block."); + for (pred_iterator PI = pred_begin(B1), PE = pred_end(B1); PI != PE; ++PI) { + BasicBlock *B2 = *PI; + if (Visited.insert(B2).second) + Predecessors[B1].push_back(B2); + } + + // Add successors for B1. + Visited.clear(); + if (!Successors[B1].empty()) + llvm_unreachable("Found a stale successors list in a basic block."); + for (succ_iterator SI = succ_begin(B1), SE = succ_end(B1); SI != SE; ++SI) { + BasicBlock *B2 = *SI; + if (Visited.insert(B2).second) + Successors[B1].push_back(B2); + } + } +} + +/// \brief Propagate weights into edges +/// +/// The following rules are applied to every block BB in the CFG: +/// +/// - If BB has a single predecessor/successor, then the weight +/// of that edge is the weight of the block. +/// +/// - If all incoming or outgoing edges are known except one, and the +/// weight of the block is already known, the weight of the unknown +/// edge will be the weight of the block minus the sum of all the known +/// edges. If the sum of all the known edges is larger than BB's weight, +/// we set the unknown edge weight to zero. +/// +/// - If there is a self-referential edge, and the weight of the block is +/// known, the weight for that edge is set to the weight of the block +/// minus the weight of the other incoming edges to that block (if +/// known). +void SampleProfileLoader::propagateWeights(Function &F) { + bool Changed = true; + unsigned I = 0; + + // Add an entry count to the function using the samples gathered + // at the function entry. + F.setEntryCount(Samples->getHeadSamples()); + + // Before propagation starts, build, for each block, a list of + // unique predecessors and successors. This is necessary to handle + // identical edges in multiway branches. Since we visit all blocks and all + // edges of the CFG, it is cleaner to build these lists once at the start + // of the pass. + buildEdges(F); + + // Propagate until we converge or we go past the iteration limit. + while (Changed && I++ < SampleProfileMaxPropagateIterations) { + Changed = propagateThroughEdges(F); + } + + // Generate MD_prof metadata for every branch instruction using the + // edge weights computed during propagation. + DEBUG(dbgs() << "\nPropagation complete. Setting branch weights\n"); + LLVMContext &Ctx = F.getContext(); + MDBuilder MDB(Ctx); + for (auto &BI : F) { + BasicBlock *BB = &BI; + TerminatorInst *TI = BB->getTerminator(); + if (TI->getNumSuccessors() == 1) + continue; + if (!isa<BranchInst>(TI) && !isa<SwitchInst>(TI)) + continue; + + DEBUG(dbgs() << "\nGetting weights for branch at line " + << TI->getDebugLoc().getLine() << ".\n"); + SmallVector<uint32_t, 4> Weights; + uint32_t MaxWeight = 0; + DebugLoc MaxDestLoc; + for (unsigned I = 0; I < TI->getNumSuccessors(); ++I) { + BasicBlock *Succ = TI->getSuccessor(I); + Edge E = std::make_pair(BB, Succ); + uint64_t Weight = EdgeWeights[E]; + DEBUG(dbgs() << "\t"; printEdgeWeight(dbgs(), E)); + // Use uint32_t saturated arithmetic to adjust the incoming weights, + // if needed. Sample counts in profiles are 64-bit unsigned values, + // but internally branch weights are expressed as 32-bit values. + if (Weight > std::numeric_limits<uint32_t>::max()) { + DEBUG(dbgs() << " (saturated due to uint32_t overflow)"); + Weight = std::numeric_limits<uint32_t>::max(); + } + Weights.push_back(static_cast<uint32_t>(Weight)); + if (Weight != 0) { + if (Weight > MaxWeight) { + MaxWeight = Weight; + MaxDestLoc = Succ->getFirstNonPHIOrDbgOrLifetime()->getDebugLoc(); + } + } + } + + // Only set weights if there is at least one non-zero weight. + // In any other case, let the analyzer set weights. + if (MaxWeight > 0) { + DEBUG(dbgs() << "SUCCESS. Found non-zero weights.\n"); + TI->setMetadata(llvm::LLVMContext::MD_prof, + MDB.createBranchWeights(Weights)); + DebugLoc BranchLoc = TI->getDebugLoc(); + emitOptimizationRemark( + Ctx, DEBUG_TYPE, F, MaxDestLoc, + Twine("most popular destination for conditional branches at ") + + ((BranchLoc) ? Twine(BranchLoc->getFilename() + ":" + + Twine(BranchLoc.getLine()) + ":" + + Twine(BranchLoc.getCol())) + : Twine("<UNKNOWN LOCATION>"))); + } else { + DEBUG(dbgs() << "SKIPPED. All branch weights are zero.\n"); + } + } +} + +/// \brief Get the line number for the function header. +/// +/// This looks up function \p F in the current compilation unit and +/// retrieves the line number where the function is defined. This is +/// line 0 for all the samples read from the profile file. Every line +/// number is relative to this line. +/// +/// \param F Function object to query. +/// +/// \returns the line number where \p F is defined. If it returns 0, +/// it means that there is no debug information available for \p F. +unsigned SampleProfileLoader::getFunctionLoc(Function &F) { + if (DISubprogram *S = getDISubprogram(&F)) + return S->getLine(); + + // If the start of \p F is missing, emit a diagnostic to inform the user + // about the missed opportunity. + F.getContext().diagnose(DiagnosticInfoSampleProfile( + "No debug information found in function " + F.getName() + + ": Function profile not used", + DS_Warning)); + return 0; +} + +void SampleProfileLoader::computeDominanceAndLoopInfo(Function &F) { + DT.reset(new DominatorTree); + DT->recalculate(F); + + PDT.reset(new DominatorTreeBase<BasicBlock>(true)); + PDT->recalculate(F); + + LI.reset(new LoopInfo); + LI->analyze(*DT); +} + +/// \brief Generate branch weight metadata for all branches in \p F. +/// +/// Branch weights are computed out of instruction samples using a +/// propagation heuristic. Propagation proceeds in 3 phases: +/// +/// 1- Assignment of block weights. All the basic blocks in the function +/// are initial assigned the same weight as their most frequently +/// executed instruction. +/// +/// 2- Creation of equivalence classes. Since samples may be missing from +/// blocks, we can fill in the gaps by setting the weights of all the +/// blocks in the same equivalence class to the same weight. To compute +/// the concept of equivalence, we use dominance and loop information. +/// Two blocks B1 and B2 are in the same equivalence class if B1 +/// dominates B2, B2 post-dominates B1 and both are in the same loop. +/// +/// 3- Propagation of block weights into edges. This uses a simple +/// propagation heuristic. The following rules are applied to every +/// block BB in the CFG: +/// +/// - If BB has a single predecessor/successor, then the weight +/// of that edge is the weight of the block. +/// +/// - If all the edges are known except one, and the weight of the +/// block is already known, the weight of the unknown edge will +/// be the weight of the block minus the sum of all the known +/// edges. If the sum of all the known edges is larger than BB's weight, +/// we set the unknown edge weight to zero. +/// +/// - If there is a self-referential edge, and the weight of the block is +/// known, the weight for that edge is set to the weight of the block +/// minus the weight of the other incoming edges to that block (if +/// known). +/// +/// Since this propagation is not guaranteed to finalize for every CFG, we +/// only allow it to proceed for a limited number of iterations (controlled +/// by -sample-profile-max-propagate-iterations). +/// +/// FIXME: Try to replace this propagation heuristic with a scheme +/// that is guaranteed to finalize. A work-list approach similar to +/// the standard value propagation algorithm used by SSA-CCP might +/// work here. +/// +/// Once all the branch weights are computed, we emit the MD_prof +/// metadata on BB using the computed values for each of its branches. +/// +/// \param F The function to query. +/// +/// \returns true if \p F was modified. Returns false, otherwise. +bool SampleProfileLoader::emitAnnotations(Function &F) { + bool Changed = false; + + if (getFunctionLoc(F) == 0) + return false; + + DEBUG(dbgs() << "Line number for the first instruction in " << F.getName() + << ": " << getFunctionLoc(F) << "\n"); + + Changed |= emitInlineHints(F); + + Changed |= inlineHotFunctions(F); + + // Compute basic block weights. + Changed |= computeBlockWeights(F); + + if (Changed) { + // Compute dominance and loop info needed for propagation. + computeDominanceAndLoopInfo(F); + + // Find equivalence classes. + findEquivalenceClasses(F); + + // Propagate weights to all edges. + propagateWeights(F); + } + + // If coverage checking was requested, compute it now. + if (SampleProfileRecordCoverage) { + unsigned Used = CoverageTracker.countUsedRecords(Samples); + unsigned Total = CoverageTracker.countBodyRecords(Samples); + unsigned Coverage = CoverageTracker.computeCoverage(Used, Total); + if (Coverage < SampleProfileRecordCoverage) { + F.getContext().diagnose(DiagnosticInfoSampleProfile( + getDISubprogram(&F)->getFilename(), getFunctionLoc(F), + Twine(Used) + " of " + Twine(Total) + " available profile records (" + + Twine(Coverage) + "%) were applied", + DS_Warning)); + } + } + + if (SampleProfileSampleCoverage) { + uint64_t Used = CoverageTracker.getTotalUsedSamples(); + uint64_t Total = CoverageTracker.countBodySamples(Samples); + unsigned Coverage = CoverageTracker.computeCoverage(Used, Total); + if (Coverage < SampleProfileSampleCoverage) { + F.getContext().diagnose(DiagnosticInfoSampleProfile( + getDISubprogram(&F)->getFilename(), getFunctionLoc(F), + Twine(Used) + " of " + Twine(Total) + " available profile samples (" + + Twine(Coverage) + "%) were applied", + DS_Warning)); + } + } + return Changed; +} + +char SampleProfileLoader::ID = 0; +INITIALIZE_PASS_BEGIN(SampleProfileLoader, "sample-profile", + "Sample Profile loader", false, false) +INITIALIZE_PASS_DEPENDENCY(AddDiscriminators) +INITIALIZE_PASS_END(SampleProfileLoader, "sample-profile", + "Sample Profile loader", false, false) + +bool SampleProfileLoader::doInitialization(Module &M) { + auto &Ctx = M.getContext(); + auto ReaderOrErr = SampleProfileReader::create(Filename, Ctx); + if (std::error_code EC = ReaderOrErr.getError()) { + std::string Msg = "Could not open profile: " + EC.message(); + Ctx.diagnose(DiagnosticInfoSampleProfile(Filename, Msg)); + return false; + } + Reader = std::move(ReaderOrErr.get()); + ProfileIsValid = (Reader->read() == sampleprof_error::success); + return true; +} + +ModulePass *llvm::createSampleProfileLoaderPass() { + return new SampleProfileLoader(SampleProfileFile); +} + +ModulePass *llvm::createSampleProfileLoaderPass(StringRef Name) { + return new SampleProfileLoader(Name); +} + +bool SampleProfileLoader::runOnModule(Module &M) { + if (!ProfileIsValid) + return false; + + // Compute the total number of samples collected in this profile. + for (const auto &I : Reader->getProfiles()) + TotalCollectedSamples += I.second.getTotalSamples(); + + bool retval = false; + for (auto &F : M) + if (!F.isDeclaration()) { + clearFunctionData(); + retval |= runOnFunction(F); + } + return retval; +} + +bool SampleProfileLoader::runOnFunction(Function &F) { + Samples = Reader->getSamplesFor(F); + if (!Samples->empty()) + return emitAnnotations(F); + return false; +} |
