//
//===----------------------------------------------------------------------===//
-#define DEBUG_TYPE "sample-profile"
-
+#include "llvm/Transforms/Scalar.h"
#include "llvm/ADT/DenseMap.h"
-#include "llvm/ADT/OwningPtr.h"
-#include "llvm/ADT/StringMap.h"
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/StringRef.h"
-#include "llvm/DebugInfo/DIContext.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/Metadata.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/InstIterator.h"
-#include "llvm/Support/MemoryBuffer.h"
-#include "llvm/Support/Regex.h"
#include "llvm/Support/raw_ostream.h"
-#include "llvm/Transforms/Scalar.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."));
namespace {
+typedef DenseMap<BasicBlock *, unsigned> BlockWeightMap;
+typedef DenseMap<BasicBlock *, BasicBlock *> EquivalenceClassMap;
+typedef std::pair<BasicBlock *, BasicBlock *> Edge;
+typedef DenseMap<Edge, unsigned> EdgeWeightMap;
+typedef DenseMap<BasicBlock *, SmallVector<BasicBlock *, 8>> BlockEdgeMap;
-typedef DenseMap<uint32_t, uint32_t> BodySampleMap;
-typedef DenseMap<BasicBlock *, uint32_t> BlockWeightMap;
-
-/// \brief Representation of the runtime profile for a function.
+/// \brief Sample profile pass.
///
-/// This data structure contains the runtime profile for a given
-/// function. It contains the total number of samples collected
-/// in the function and a map of samples collected in every statement.
-class SampleFunctionProfile {
+/// 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 FunctionPass {
public:
- SampleFunctionProfile() : TotalSamples(0), TotalHeadSamples(0) {}
+ // Class identification, replacement for typeinfo
+ static char ID;
- bool emitAnnotations(Function &F);
- uint32_t getInstWeight(Instruction &I, unsigned FirstLineno,
- BodySampleMap &BodySamples);
- uint32_t computeBlockWeight(BasicBlock *B, unsigned FirstLineno,
- BodySampleMap &BodySamples);
- void addTotalSamples(unsigned Num) { TotalSamples += Num; }
- void addHeadSamples(unsigned Num) { TotalHeadSamples += Num; }
- void addBodySamples(unsigned LineOffset, unsigned Num) {
- BodySamples[LineOffset] += Num;
+ SampleProfileLoader(StringRef Name = SampleProfileFile)
+ : FunctionPass(ID), DT(nullptr), PDT(nullptr), LI(nullptr), Ctx(nullptr),
+ Reader(), Samples(nullptr), Filename(Name), ProfileIsValid(false) {
+ initializeSampleProfileLoaderPass(*PassRegistry::getPassRegistry());
}
- void print(raw_ostream &OS);
-protected:
- /// \brief Total number of samples collected inside this function.
- ///
- /// Samples are cumulative, they include all the samples collected
- /// inside this function and all its inlined callees.
- unsigned TotalSamples;
+ bool doInitialization(Module &M) override;
- // \brief Total number of samples collected at the head of the function.
- unsigned TotalHeadSamples;
+ void dump() { Reader->dump(); }
- /// \brief Map line offsets to collected samples.
- ///
- /// Each entry in this map contains the number of samples
- /// collected at the corresponding line offset. All line locations
- /// are an offset from the start of the function.
- BodySampleMap BodySamples;
+ const char *getPassName() const override { return "Sample profile pass"; }
- /// \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;
-};
+ bool runOnFunction(Function &F) override;
-/// \brief Sample-based profile reader.
-///
-/// Each profile contains sample counts for all the functions
-/// executed. Inside each function, statements are annotated with the
-/// collected samples on all the instructions associated with that
-/// statement.
-///
-/// For this to produce meaningful data, the program needs to be
-/// compiled with some debug information (at minimum, line numbers:
-/// -gline-tables-only). Otherwise, it will be impossible to match IR
-/// instructions to the line numbers collected by the profiler.
-///
-/// From the profile file, we are interested in collecting the
-/// following information:
-///
-/// * A list of functions included in the profile (mangled names).
-///
-/// * For each function F:
-/// 1. The total number of samples collected in F.
-///
-/// 2. The samples collected at each line in F. To provide some
-/// protection against source code shuffling, line numbers should
-/// be relative to the start of the function.
-class SampleModuleProfile {
-public:
- SampleModuleProfile(StringRef F) : Profiles(0), Filename(F) {}
-
- void dump();
- void loadText();
- void loadNative() { llvm_unreachable("not implemented"); }
- void printFunctionProfile(raw_ostream &OS, StringRef FName);
- void dumpFunctionProfile(StringRef FName);
- SampleFunctionProfile &getProfile(const Function &F) {
- return Profiles[F.getName()];
+ void getAnalysisUsage(AnalysisUsage &AU) const override {
+ AU.setPreservesCFG();
+ AU.addRequired<LoopInfo>();
+ AU.addRequired<DominatorTreeWrapperPass>();
+ AU.addRequired<PostDominatorTree>();
}
protected:
- /// \brief Map every function to its associated profile.
- ///
- /// The profile of every function executed at runtime is collected
- /// in the structure SampleFunctionProfile. This maps function objects
- /// to their corresponding profiles.
- StringMap<SampleFunctionProfile> Profiles;
+ unsigned getFunctionLoc(Function &F);
+ bool emitAnnotations(Function &F);
+ unsigned getInstWeight(Instruction &I);
+ unsigned getBlockWeight(BasicBlock *BB);
+ void printEdgeWeight(raw_ostream &OS, Edge E);
+ void printBlockWeight(raw_ostream &OS, BasicBlock *BB);
+ void printBlockEquivalence(raw_ostream &OS, 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);
+ unsigned visitEdge(Edge E, unsigned *NumUnknownEdges, Edge *UnknownEdge);
+ void buildEdges(Function &F);
+ bool propagateThroughEdges(Function &F);
+
+ /// \brief Line number for the function header. Used to compute absolute
+ /// line numbers from the relative line numbers found in the profile.
+ unsigned HeaderLineno;
- /// \brief Path name to the file holding the profile data.
+ /// \brief Map basic blocks to their computed weights.
///
- /// The format of this file is defined by each profiler
- /// independently. If possible, the profiler should have a text
- /// version of the profile format to be used in constructing test
- /// cases and debugging.
- StringRef Filename;
-};
-
-/// \brief Loader class for text-based profiles.
-///
-/// This class defines a simple interface to read text files containing
-/// profiles. It keeps track of line number information and location of
-/// the file pointer. Users of this class are responsible for actually
-/// parsing the lines returned by the readLine function.
-///
-/// TODO - This does not really belong here. It is a generic text file
-/// reader. It should be moved to the Support library and made more general.
-class ExternalProfileTextLoader {
-public:
- ExternalProfileTextLoader(StringRef F) : Filename(F) {
- error_code EC;
- EC = MemoryBuffer::getFile(Filename, Buffer);
- if (EC)
- report_fatal_error("Could not open profile file " + Filename + ": " +
- EC.message());
- FP = Buffer->getBufferStart();
- Lineno = 0;
- }
-
- /// \brief Read a line from the mapped file.
- StringRef readLine() {
- size_t Length = 0;
- const char *start = FP;
- while (FP != Buffer->getBufferEnd() && *FP != '\n') {
- Length++;
- FP++;
- }
- if (FP != Buffer->getBufferEnd())
- FP++;
- Lineno++;
- return StringRef(start, Length);
- }
-
- /// \brief Return true, if we've reached EOF.
- bool atEOF() const { return FP == Buffer->getBufferEnd(); }
-
- /// \brief Report a parse error message and stop compilation.
- void reportParseError(Twine Msg) const {
- report_fatal_error(Filename + ":" + Twine(Lineno) + ": " + Msg + "\n");
- }
-
-private:
- /// \brief Memory buffer holding the text file.
- OwningPtr<MemoryBuffer> Buffer;
-
- /// \brief Current position into the memory buffer.
- const char *FP;
-
- /// \brief Current line number.
- int64_t Lineno;
+ /// The weight of a basic block is defined to be the maximum
+ /// of all the instruction weights in that block.
+ BlockWeightMap BlockWeights;
- /// \brief Path name where to the profile file.
- StringRef Filename;
-};
+ /// \brief Map edges to their computed weights.
+ ///
+ /// Edge weights are computed by propagating basic block weights in
+ /// SampleProfile::propagateWeights.
+ EdgeWeightMap EdgeWeights;
-/// \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 FunctionPass {
-public:
- // Class identification, replacement for typeinfo
- static char ID;
+ /// \brief Set of visited blocks during propagation.
+ SmallPtrSet<BasicBlock *, 128> VisitedBlocks;
- SampleProfileLoader(StringRef Name = SampleProfileFile)
- : FunctionPass(ID), Profiler(0), Filename(Name) {
- initializeSampleProfileLoaderPass(*PassRegistry::getPassRegistry());
- }
+ /// \brief Set of visited edges during propagation.
+ SmallSet<Edge, 128> VisitedEdges;
- virtual bool doInitialization(Module &M);
+ /// \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;
- void dump() { Profiler->dump(); }
+ /// \brief Dominance, post-dominance and loop information.
+ DominatorTree *DT;
+ PostDominatorTree *PDT;
+ LoopInfo *LI;
- virtual const char *getPassName() const { return "Sample profile pass"; }
+ /// \brief Predecessors for each basic block in the CFG.
+ BlockEdgeMap Predecessors;
- virtual bool runOnFunction(Function &F);
+ /// \brief Successors for each basic block in the CFG.
+ BlockEdgeMap Successors;
- virtual void getAnalysisUsage(AnalysisUsage &AU) const {
- AU.setPreservesCFG();
- }
+ /// \brief LLVM context holding the debug data we need.
+ LLVMContext *Ctx;
-protected:
/// \brief Profile reader object.
- OwningPtr<SampleModuleProfile> Profiler;
+ 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 Print this function profile on stream \p OS.
-///
-/// \param OS Stream to emit the output to.
-void SampleFunctionProfile::print(raw_ostream &OS) {
- OS << TotalSamples << ", " << TotalHeadSamples << ", " << BodySamples.size()
- << " sampled lines\n";
- for (BodySampleMap::const_iterator SI = BodySamples.begin(),
- SE = BodySamples.end();
- SI != SE; ++SI)
- OS << "\tline offset: " << SI->first
- << ", number of samples: " << SI->second << "\n";
- OS << "\n";
+ /// \brief Flag indicating whether the profile input loaded successfully.
+ bool ProfileIsValid;
+};
}
-/// \brief Print the function profile for \p FName on stream \p OS.
+/// \brief Print the weight of edge \p E on stream \p OS.
///
-/// \param OS Stream to emit the output to.
-/// \param FName Name of the function to print.
-void SampleModuleProfile::printFunctionProfile(raw_ostream &OS,
- StringRef FName) {
- OS << "Function: " << FName << ":\n";
- Profiles[FName].print(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 Dump the function profile for \p FName.
+/// \brief Print the equivalence class of block \p BB on stream \p OS.
///
-/// \param FName Name of the function to print.
-void SampleModuleProfile::dumpFunctionProfile(StringRef FName) {
- printFunctionProfile(dbgs(), FName);
+/// \param OS Stream to emit the output to.
+/// \param BB Block to print.
+void SampleProfileLoader::printBlockEquivalence(raw_ostream &OS,
+ BasicBlock *BB) {
+ BasicBlock *Equiv = EquivalenceClass[BB];
+ OS << "equivalence[" << BB->getName()
+ << "]: " << ((Equiv) ? EquivalenceClass[BB]->getName() : "NONE") << "\n";
}
-/// \brief Dump all the function profiles found.
-void SampleModuleProfile::dump() {
- for (StringMap<SampleFunctionProfile>::const_iterator I = Profiles.begin(),
- E = Profiles.end();
- I != E; ++I)
- dumpFunctionProfile(I->getKey());
-}
-
-/// \brief Load samples from a text file.
-///
-/// The file is divided in two segments:
-///
-/// Symbol table (represented with the string "symbol table")
-/// Number of symbols in the table
-/// symbol 1
-/// symbol 2
-/// ...
-/// symbol N
-///
-/// Function body profiles
-/// function1:total_samples:total_head_samples:number_of_locations
-/// location_offset_1: number_of_samples
-/// location_offset_2: number_of_samples
-/// ...
-/// location_offset_N: number_of_samples
-///
-/// Function names must be mangled in order for the profile loader to
-/// match them in the current translation unit.
-///
-/// Since this is a flat profile, a function that shows up more than
-/// once gets all its samples aggregated across all its instances.
-/// TODO - flat profiles are too imprecise to provide good optimization
-/// opportunities. Convert them to context-sensitive profile.
-///
-/// This textual representation is useful to generate unit tests and
-/// for debugging purposes, but it should not be used to generate
-/// profiles for large programs, as the representation is extremely
-/// inefficient.
-void SampleModuleProfile::loadText() {
- ExternalProfileTextLoader Loader(Filename);
-
- // Read the symbol table.
- StringRef Line = Loader.readLine();
- if (Line != "symbol table")
- Loader.reportParseError("Expected 'symbol table', found " + Line);
- int NumSymbols;
- Line = Loader.readLine();
- if (Line.getAsInteger(10, NumSymbols))
- Loader.reportParseError("Expected a number, found " + Line);
- for (int I = 0; I < NumSymbols; I++)
- Profiles[Loader.readLine()] = SampleFunctionProfile();
-
- // Read the profile of each function. Since each function may be
- // mentioned more than once, and we are collecting flat profiles,
- // accumulate samples as we parse them.
- Regex HeadRE("^([^:]+):([0-9]+):([0-9]+):([0-9]+)$");
- Regex LineSample("^([0-9]+): ([0-9]+)$");
- while (!Loader.atEOF()) {
- SmallVector<StringRef, 4> Matches;
- Line = Loader.readLine();
- if (!HeadRE.match(Line, &Matches))
- Loader.reportParseError("Expected 'mangled_name:NUM:NUM:NUM', found " +
- Line);
- assert(Matches.size() == 5);
- StringRef FName = Matches[1];
- unsigned NumSamples, NumHeadSamples, NumSampledLines;
- Matches[2].getAsInteger(10, NumSamples);
- Matches[3].getAsInteger(10, NumHeadSamples);
- Matches[4].getAsInteger(10, NumSampledLines);
- SampleFunctionProfile &FProfile = Profiles[FName];
- FProfile.addTotalSamples(NumSamples);
- FProfile.addHeadSamples(NumHeadSamples);
- unsigned I;
- for (I = 0; I < NumSampledLines && !Loader.atEOF(); I++) {
- Line = Loader.readLine();
- if (!LineSample.match(Line, &Matches))
- Loader.reportParseError("Expected 'NUM: NUM', found " + Line);
- assert(Matches.size() == 3);
- unsigned LineOffset, NumSamples;
- Matches[1].getAsInteger(10, LineOffset);
- Matches[2].getAsInteger(10, NumSamples);
- FProfile.addBodySamples(LineOffset, NumSamples);
- }
-
- if (I < NumSampledLines)
- Loader.reportParseError("Unexpected end of file");
- }
-}
-
-char SampleProfileLoader::ID = 0;
-INITIALIZE_PASS(SampleProfileLoader, "sample-profile", "Sample Profile loader",
- false, false)
-
-bool SampleProfileLoader::doInitialization(Module &M) {
- Profiler.reset(new SampleModuleProfile(Filename));
- Profiler->loadText();
- return true;
-}
-
-FunctionPass *llvm::createSampleProfileLoaderPass() {
- return new SampleProfileLoader(SampleProfileFile);
-}
-
-FunctionPass *llvm::createSampleProfileLoaderPass(StringRef Name) {
- return new SampleProfileLoader(Name);
+/// \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, BasicBlock *BB) {
+ OS << "weight[" << BB->getName() << "]: " << BlockWeights[BB] << "\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 \p FirstLineno to compute the offset. We then
-/// look up the samples collected for \p Inst using \p BodySamples.
+/// 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.
-/// \param FirstLineno Line number of the first instruction in the function.
-/// \param BodySamples Map of relative source line locations to samples.
///
/// \returns The profiled weight of I.
-uint32_t SampleFunctionProfile::getInstWeight(Instruction &Inst,
- unsigned FirstLineno,
- BodySampleMap &BodySamples) {
- unsigned LOffset = Inst.getDebugLoc().getLine() - FirstLineno + 1;
- return BodySamples.lookup(LOffset);
+unsigned SampleProfileLoader::getInstWeight(Instruction &Inst) {
+ DebugLoc DLoc = Inst.getDebugLoc();
+ unsigned Lineno = DLoc.getLine();
+ if (Lineno < HeaderLineno)
+ return 0;
+
+ DILocation DIL(DLoc.getAsMDNode(*Ctx));
+ int LOffset = Lineno - HeaderLineno;
+ unsigned Discriminator = DIL.getDiscriminator();
+ unsigned Weight = Samples->samplesAt(LOffset, Discriminator);
+ DEBUG(dbgs() << " " << Lineno << "." << Discriminator << ":" << Inst
+ << " (line offset: " << LOffset << "." << Discriminator
+ << " - weight: " << Weight << ")\n");
+ return Weight;
}
/// \brief Compute the weight of a basic block.
///
-/// The weight of basic block \p B is the maximum weight of all the
-/// instructions in B.
+/// The weight of basic block \p BB is the maximum weight of all the
+/// instructions in BB. The weight of \p BB is computed and cached in
+/// the BlockWeights map.
///
-/// \param B The basic block to query.
-/// \param FirstLineno The line number for the first line in the
-/// function holding B.
-/// \param BodySamples The map containing all the samples collected in that
-/// function.
+/// \param BB The basic block to query.
///
-/// \returns The computed weight of B.
-uint32_t SampleFunctionProfile::computeBlockWeight(BasicBlock *B,
- unsigned FirstLineno,
- BodySampleMap &BodySamples) {
- // If we've computed B's weight before, return it.
+/// \returns The computed weight of BB.
+unsigned SampleProfileLoader::getBlockWeight(BasicBlock *BB) {
+ // If we've computed BB's weight before, return it.
std::pair<BlockWeightMap::iterator, bool> Entry =
- BlockWeights.insert(std::make_pair(B, 0));
+ BlockWeights.insert(std::make_pair(BB, 0));
if (!Entry.second)
return Entry.first->second;
- // Otherwise, compute and cache B's weight.
- uint32_t Weight = 0;
- for (BasicBlock::iterator I = B->begin(), E = B->end(); I != E; ++I) {
- uint32_t InstWeight = getInstWeight(*I, FirstLineno, BodySamples);
+ // Otherwise, compute and cache BB's weight.
+ unsigned Weight = 0;
+ for (auto &I : BB->getInstList()) {
+ unsigned InstWeight = getInstWeight(I);
if (InstWeight > Weight)
Weight = InstWeight;
}
return Weight;
}
-/// \brief Generate branch weight metadata for all branches in \p F.
+/// \brief Compute and store the weights of every basic block.
///
-/// For every branch instruction B in \p F, we compute the weight of the
-/// target block for each of the edges out of B. This is the weight
-/// that we associate with that branch.
+/// This populates the BlockWeights map by computing
+/// the weights of every basic block in the CFG.
///
-/// TODO - This weight assignment will most likely be wrong if the
-/// target branch has more than two predecessors. This needs to be done
-/// using some form of flow propagation.
+/// \param F The function to query.
+bool SampleProfileLoader::computeBlockWeights(Function &F) {
+ bool Changed = false;
+ DEBUG(dbgs() << "Block weights\n");
+ for (auto &BB : F) {
+ unsigned Weight = getBlockWeight(&BB);
+ Changed |= (Weight > 0);
+ DEBUG(printBlockWeight(dbgs(), &BB));
+ }
+
+ return Changed;
+}
+
+/// \brief Find equivalence classes for the given block.
///
-/// Once all the branch weights are computed, we emit the MD_prof
-/// metadata on B using the computed values.
+/// 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 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) {
+ for (auto *BB2 : Descendants) {
+ bool IsDomParent = DomTree->dominates(BB2, BB1);
+ bool IsInSameLoop = LI->getLoopFor(BB1) == LI->getLoopFor(BB2);
+ if (BB1 != BB2 && VisitedBlocks.insert(BB2) && IsDomParent &&
+ IsInSameLoop) {
+ EquivalenceClass[BB2] = BB1;
+
+ // 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.
+ unsigned &BB1Weight = BlockWeights[BB1];
+ unsigned &BB2Weight = BlockWeights[BB2];
+ BB1Weight = std::max(BB1Weight, BB2Weight);
+ }
+ }
+}
+
+/// \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.
-bool SampleFunctionProfile::emitAnnotations(Function &F) {
+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->DT);
+
+ // Repeat the same logic for all the blocks post-dominated by BB1.
+ // We are looking for every basic block BB2 such that:
+ //
+ // 1- BB1 post-dominates BB2.
+ // 2- BB2 dominates BB1.
+ // 3- BB1 and BB2 are in the same loop nest.
+ //
+ // If all those conditions hold, BB2's equivalence class is BB1.
+ DominatedBBs.clear();
+ PDT->getDescendants(BB1, DominatedBBs);
+ findEquivalencesFor(BB1, DominatedBBs, DT);
+
+ 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) {
+ BasicBlock *BB = &BI;
+ 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.
+unsigned 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;
- unsigned FirstLineno = inst_begin(F)->getDebugLoc().getLine();
- MDBuilder MDB(F.getContext());
+ DEBUG(dbgs() << "\nPropagation through edges\n");
+ for (auto &BI : F) {
+ BasicBlock *BB = &BI;
+
+ // 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++) {
+ unsigned 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) {
+ unsigned &BBWeight = BlockWeights[BB];
+ 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(BB))
+ Changed = true;
+ } else if (NumUnknownEdges == 1 && VisitedBlocks.count(BB)) {
+ // 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(BB)) {
+ unsigned &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))
+ 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))
+ Successors[B1].push_back(B2);
+ }
+ }
+}
- // Clear the block weights cache.
- BlockWeights.clear();
+/// \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;
+
+ // 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);
+ }
- // When we find a branch instruction: For each edge E out of the branch,
- // the weight of E is the weight of the target block.
- for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I) {
- BasicBlock *B = I;
- TerminatorInst *TI = B->getTerminator();
+ // Generate MD_prof metadata for every branch instruction using the
+ // edge weights computed during propagation.
+ DEBUG(dbgs() << "\nPropagation complete. Setting branch weights\n");
+ MDBuilder MDB(F.getContext());
+ for (auto &BI : F) {
+ BasicBlock *BB = &BI;
+ TerminatorInst *TI = BB->getTerminator();
if (TI->getNumSuccessors() == 1)
continue;
if (!isa<BranchInst>(TI) && !isa<SwitchInst>(TI))
continue;
- SmallVector<uint32_t, 4> Weights;
- unsigned NSuccs = TI->getNumSuccessors();
- for (unsigned I = 0; I < NSuccs; ++I) {
+ DEBUG(dbgs() << "\nGetting weights for branch at line "
+ << TI->getDebugLoc().getLine() << ".\n");
+ SmallVector<unsigned, 4> Weights;
+ bool AllWeightsZero = true;
+ for (unsigned I = 0; I < TI->getNumSuccessors(); ++I) {
BasicBlock *Succ = TI->getSuccessor(I);
- uint32_t Weight = computeBlockWeight(Succ, FirstLineno, BodySamples);
+ Edge E = std::make_pair(BB, Succ);
+ unsigned Weight = EdgeWeights[E];
+ DEBUG(dbgs() << "\t"; printEdgeWeight(dbgs(), E));
Weights.push_back(Weight);
+ if (Weight != 0)
+ AllWeightsZero = false;
}
- TI->setMetadata(llvm::LLVMContext::MD_prof,
- MDB.createBranchWeights(Weights));
- Changed = true;
+ // Only set weights if there is at least one non-zero weight.
+ // In any other case, let the analyzer set weights.
+ if (!AllWeightsZero) {
+ DEBUG(dbgs() << "SUCCESS. Found non-zero weights.\n");
+ TI->setMetadata(llvm::LLVMContext::MD_prof,
+ MDB.createBranchWeights(Weights));
+ } 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) {
+ DISubprogram S = getDISubprogram(&F);
+ if (S.isSubprogram())
+ return S.getLineNumber();
+
+ // If could not find the start of \p F, 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;
+}
+
+/// \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;
+
+ // Initialize invariants used during computation and propagation.
+ HeaderLineno = getFunctionLoc(F);
+ if (HeaderLineno == 0)
+ return false;
+
+ DEBUG(dbgs() << "Line number for the first instruction in " << F.getName()
+ << ": " << HeaderLineno << "\n");
+
+ // Compute basic block weights.
+ Changed |= computeBlockWeights(F);
+
+ if (Changed) {
+ // Find equivalence classes.
+ findEquivalenceClasses(F);
+
+ // Propagate weights to all edges.
+ propagateWeights(F);
}
return Changed;
}
+char SampleProfileLoader::ID = 0;
+INITIALIZE_PASS_BEGIN(SampleProfileLoader, "sample-profile",
+ "Sample Profile loader", false, false)
+INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(PostDominatorTree)
+INITIALIZE_PASS_DEPENDENCY(LoopInfo)
+INITIALIZE_PASS_DEPENDENCY(AddDiscriminators)
+INITIALIZE_PASS_END(SampleProfileLoader, "sample-profile",
+ "Sample Profile loader", false, false)
+
+bool SampleProfileLoader::doInitialization(Module &M) {
+ if (std::error_code EC =
+ SampleProfileReader::create(Filename, Reader, M.getContext())) {
+ std::string Msg = "Could not open profile: " + EC.message();
+ M.getContext().diagnose(DiagnosticInfoSampleProfile(Filename.data(), Msg));
+ return false;
+ }
+ ProfileIsValid = (Reader->read() == sampleprof_error::success);
+ return true;
+}
+
+FunctionPass *llvm::createSampleProfileLoaderPass() {
+ return new SampleProfileLoader(SampleProfileFile);
+}
+
+FunctionPass *llvm::createSampleProfileLoaderPass(StringRef Name) {
+ return new SampleProfileLoader(Name);
+}
+
bool SampleProfileLoader::runOnFunction(Function &F) {
- return Profiler->getProfile(F).emitAnnotations(F);
+ if (!ProfileIsValid)
+ return false;
+
+ DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
+ PDT = &getAnalysis<PostDominatorTree>();
+ LI = &getAnalysis<LoopInfo>();
+ Ctx = &F.getParent()->getContext();
+ Samples = Reader->getSamplesFor(F);
+ if (!Samples->empty())
+ return emitAnnotations(F);
+ return false;
}
projects / oota-llvm.git / blobdiff