SampleProfWriter.h

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//===- SampleProfWriter.h - Write LLVM sample profile data ------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file contains definitions needed for writing sample profiles.
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_PROFILEDATA_SAMPLEPROFWRITER_H
#define LLVM_PROFILEDATA_SAMPLEPROFWRITER_H
 
#include "llvm/ADT/MapVector.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/IR/ProfileSummary.h"
#include "llvm/ProfileData/SampleProf.h"
#include "llvm/Support/ErrorOr.h"
#include "llvm/Support/raw_ostream.h"
#include <cstdint>
#include <memory>
#include <set>
#include <system_error>
 
namespace llvm {
namespace sampleprof {
 
enum SectionLayout {
  DefaultLayout,
  // The layout splits profile with context information from profile without
  // context information. When Thinlto is enabled, ThinLTO postlink phase only
  // has to load profile with context information and can skip the other part.
  CtxSplitLayout,
  NumOfLayout,
};
 
/// When writing a profile with size limit, user may want to use a different
/// strategy to reduce function count other than dropping functions with fewest
/// samples first. In this case a class implementing the same interfaces should
/// be provided to SampleProfileWriter::writeWithSizeLimit().
class FunctionPruningStrategy {
protected:
  SampleProfileMap &ProfileMap;
  size_t OutputSizeLimit;
 
public:
  /// \p ProfileMap A reference to the original profile map. It will be modified
  /// by Erase().
  /// \p OutputSizeLimit Size limit in bytes of the output profile. This is
  /// necessary to estimate how many functions to remove.
  FunctionPruningStrategy(SampleProfileMap &ProfileMap, size_t OutputSizeLimit)
      : ProfileMap(ProfileMap), OutputSizeLimit(OutputSizeLimit) {}
 
  virtual ~FunctionPruningStrategy() = default;
 
  /// SampleProfileWriter::writeWithSizeLimit() calls this after every write
  /// iteration if the output size still exceeds the limit. This function
  /// should erase some functions from the profile map so that the writer tries
  /// to write the profile again with fewer functions. At least 1 entry from the
  /// profile map must be erased.
  ///
  /// \p CurrentOutputSize Number of bytes in the output if current profile map
  /// is written.
  virtual void Erase(size_t CurrentOutputSize) = 0;
};
 
class DefaultFunctionPruningStrategy : public FunctionPruningStrategy {
  std::vector<NameFunctionSamples> SortedFunctions;
 
public:
  DefaultFunctionPruningStrategy(SampleProfileMap &ProfileMap,
                                 size_t OutputSizeLimit);
 
  /// In this default implementation, functions with fewest samples are dropped
  /// first. Since the exact size of the output cannot be easily calculated due
  /// to compression, we use a heuristic to remove as many functions as
  /// necessary but not too many, aiming to minimize the number of write
  /// iterations.
  /// Empirically, functions with larger total sample count contain linearly
  /// more sample entries, meaning it takes linearly more space to write them.
  /// The cumulative length is therefore quadratic if all functions are sorted
  /// by total sample count.
  /// TODO: Find better heuristic.
  void Erase(size_t CurrentOutputSize) override;
};
 
/// Sample-based profile writer. Base class.
class SampleProfileWriter {
public:
  virtual ~SampleProfileWriter() = default;
 
  /// Write sample profiles in \p S.
  ///
  /// \returns status code of the file update operation.
  virtual std::error_code writeSample(const FunctionSamples &S) = 0;
 
  /// Write all the sample profiles in the given map of samples.
  ///
  /// \returns status code of the file update operation.
  virtual std::error_code write(const SampleProfileMap &ProfileMap);
 
  /// Write sample profiles up to given size limit, using the pruning strategy
  /// to drop some functions if necessary.
  ///
  /// \returns status code of the file update operation.
  template <typename FunctionPruningStrategy = DefaultFunctionPruningStrategy>
  std::error_code writeWithSizeLimit(SampleProfileMap &ProfileMap,
                                     size_t OutputSizeLimit) {
    FunctionPruningStrategy Strategy(ProfileMap, OutputSizeLimit);
    return writeWithSizeLimitInternal(ProfileMap, OutputSizeLimit, &Strategy);
  }
 
  raw_ostream &getOutputStream() { return *OutputStream; }
 
  /// Profile writer factory.
  ///
  /// Create a new file writer based on the value of \p Format.
  static ErrorOr<std::unique_ptr<SampleProfileWriter>>
  create(StringRef Filename, SampleProfileFormat Format);
 
  /// Create a new stream writer based on the value of \p Format.
  /// For testing.
  static ErrorOr<std::unique_ptr<SampleProfileWriter>>
  create(std::unique_ptr<raw_ostream> &OS, SampleProfileFormat Format);
 
  virtual void setProfileSymbolList(ProfileSymbolList *PSL) {}
  virtual void setToCompressAllSections() {}
  virtual void setUseMD5() {}
  virtual void setPartialProfile() {}
  virtual void resetSecLayout(SectionLayout SL) {}
 
protected:
  SampleProfileWriter(std::unique_ptr<raw_ostream> &OS)
      : OutputStream(std::move(OS)) {}
 
  /// Write a file header for the profile file.
  virtual std::error_code writeHeader(const SampleProfileMap &ProfileMap) = 0;
 
  // Write function profiles to the profile file.
  virtual std::error_code writeFuncProfiles(const SampleProfileMap &ProfileMap);
 
  std::error_code writeWithSizeLimitInternal(SampleProfileMap &ProfileMap,
                                             size_t OutputSizeLimit,
                                             FunctionPruningStrategy *Strategy);
 
  /// For writeWithSizeLimit in text mode, each newline takes 1 additional byte
  /// on Windows when actually written to the file, but not written to a memory
  /// buffer. This needs to be accounted for when rewriting the profile.
  size_t LineCount;
 
  /// Output stream where to emit the profile to.
  std::unique_ptr<raw_ostream> OutputStream;
 
  /// Profile summary.
  std::unique_ptr<ProfileSummary> Summary;
 
  /// Compute summary for this profile.
  void computeSummary(const SampleProfileMap &ProfileMap);
 
  /// Profile format.
  SampleProfileFormat Format = SPF_None;
};
 
/// Sample-based profile writer (text format).
class SampleProfileWriterText : public SampleProfileWriter {
public:
  std::error_code writeSample(const FunctionSamples &S) override;
 
protected:
  SampleProfileWriterText(std::unique_ptr<raw_ostream> &OS)
      : SampleProfileWriter(OS), Indent(0) {}
 
  std::error_code writeHeader(const SampleProfileMap &ProfileMap) override {
    LineCount = 0;
    return sampleprof_error::success;
  }
 
private:
  /// Indent level to use when writing.
  ///
  /// This is used when printing inlined callees.
  unsigned Indent;
 
  friend ErrorOr<std::unique_ptr<SampleProfileWriter>>
  SampleProfileWriter::create(std::unique_ptr<raw_ostream> &OS,
                              SampleProfileFormat Format);
};
 
/// Sample-based profile writer (binary format).
class SampleProfileWriterBinary : public SampleProfileWriter {
public:
  SampleProfileWriterBinary(std::unique_ptr<raw_ostream> &OS)
      : SampleProfileWriter(OS) {}
 
  std::error_code writeSample(const FunctionSamples &S) override;
 
protected:
  virtual MapVector<StringRef, uint32_t> &getNameTable() { return NameTable; }
  virtual std::error_code writeMagicIdent(SampleProfileFormat Format);
  virtual std::error_code writeNameTable();
  std::error_code writeHeader(const SampleProfileMap &ProfileMap) override;
  std::error_code writeSummary();
  virtual std::error_code writeContextIdx(const SampleContext &Context);
  std::error_code writeNameIdx(StringRef FName);
  std::error_code writeBody(const FunctionSamples &S);
  inline void stablizeNameTable(MapVector<StringRef, uint32_t> &NameTable,
                                std::set<StringRef> &V);
 
  MapVector<StringRef, uint32_t> NameTable;
 
  void addName(StringRef FName);
  virtual void addContext(const SampleContext &Context);
  void addNames(const FunctionSamples &S);
 
private:
  friend ErrorOr<std::unique_ptr<SampleProfileWriter>>
  SampleProfileWriter::create(std::unique_ptr<raw_ostream> &OS,
                              SampleProfileFormat Format);
};
 
class SampleProfileWriterRawBinary : public SampleProfileWriterBinary {
  using SampleProfileWriterBinary::SampleProfileWriterBinary;
};
 
const std::array<SmallVector<SecHdrTableEntry, 8>, NumOfLayout>
    ExtBinaryHdrLayoutTable = {
        // Note that SecFuncOffsetTable section is written after SecLBRProfile
        // in the profile, but is put before SecLBRProfile in SectionHdrLayout.
        // This is because sample reader follows the order in SectionHdrLayout
        // to read each section. To read function profiles on demand, sample
        // reader need to get the offset of each function profile first.
        //
        // DefaultLayout
        SmallVector<SecHdrTableEntry, 8>({{SecProfSummary, 0, 0, 0, 0},
                                          {SecNameTable, 0, 0, 0, 0},
                                          {SecCSNameTable, 0, 0, 0, 0},
                                          {SecFuncOffsetTable, 0, 0, 0, 0},
                                          {SecLBRProfile, 0, 0, 0, 0},
                                          {SecProfileSymbolList, 0, 0, 0, 0},
                                          {SecFuncMetadata, 0, 0, 0, 0}}),
        // CtxSplitLayout
        SmallVector<SecHdrTableEntry, 8>({{SecProfSummary, 0, 0, 0, 0},
                                          {SecNameTable, 0, 0, 0, 0},
                                          // profile with context
                                          // for next two sections
                                          {SecFuncOffsetTable, 0, 0, 0, 0},
                                          {SecLBRProfile, 0, 0, 0, 0},
                                          // profile without context
                                          // for next two sections
                                          {SecFuncOffsetTable, 0, 0, 0, 0},
                                          {SecLBRProfile, 0, 0, 0, 0},
                                          {SecProfileSymbolList, 0, 0, 0, 0},
                                          {SecFuncMetadata, 0, 0, 0, 0}}),
};
 
class SampleProfileWriterExtBinaryBase : public SampleProfileWriterBinary {
  using SampleProfileWriterBinary::SampleProfileWriterBinary;
public:
  std::error_code write(const SampleProfileMap &ProfileMap) override;
 
  void setToCompressAllSections() override;
  void setToCompressSection(SecType Type);
  std::error_code writeSample(const FunctionSamples &S) override;
 
  // Set to use MD5 to represent string in NameTable.
  void setUseMD5() override {
    UseMD5 = true;
    addSectionFlag(SecNameTable, SecNameTableFlags::SecFlagMD5Name);
    // MD5 will be stored as plain uint64_t instead of variable-length
    // quantity format in NameTable section.
    addSectionFlag(SecNameTable, SecNameTableFlags::SecFlagFixedLengthMD5);
  }
 
  // Set the profile to be partial. It means the profile is for
  // common/shared code. The common profile is usually merged from
  // profiles collected from running other targets.
  void setPartialProfile() override {
    addSectionFlag(SecProfSummary, SecProfSummaryFlags::SecFlagPartial);
  }
 
  void setProfileSymbolList(ProfileSymbolList *PSL) override {
    ProfSymList = PSL;
  };
 
  void resetSecLayout(SectionLayout SL) override {
    verifySecLayout(SL);
#ifndef NDEBUG
    // Make sure resetSecLayout is called before any flag setting.
    for (auto &Entry : SectionHdrLayout) {
      assert(Entry.Flags == 0 &&
             "resetSecLayout has to be called before any flag setting");
    }
#endif
    SecLayout = SL;
    SectionHdrLayout = ExtBinaryHdrLayoutTable[SL];
  }
 
protected:
  uint64_t markSectionStart(SecType Type, uint32_t LayoutIdx);
  std::error_code addNewSection(SecType Sec, uint32_t LayoutIdx,
                                uint64_t SectionStart);
  template <class SecFlagType>
  void addSectionFlag(SecType Type, SecFlagType Flag) {
    for (auto &Entry : SectionHdrLayout) {
      if (Entry.Type == Type)
        addSecFlag(Entry, Flag);
    }
  }
  template <class SecFlagType>
  void addSectionFlag(uint32_t SectionIdx, SecFlagType Flag) {
    addSecFlag(SectionHdrLayout[SectionIdx], Flag);
  }
 
  void addContext(const SampleContext &Context) override;
 
  // placeholder for subclasses to dispatch their own section writers.
  virtual std::error_code writeCustomSection(SecType Type) = 0;
  // Verify the SecLayout is supported by the format.
  virtual void verifySecLayout(SectionLayout SL) = 0;
 
  // specify the order to write sections.
  virtual std::error_code writeSections(const SampleProfileMap &ProfileMap) = 0;
 
  // Dispatch section writer for each section. \p LayoutIdx is the sequence
  // number indicating where the section is located in SectionHdrLayout.
  virtual std::error_code writeOneSection(SecType Type, uint32_t LayoutIdx,
                                          const SampleProfileMap &ProfileMap);
 
  // Helper function to write name table.
  std::error_code writeNameTable() override;
  std::error_code writeContextIdx(const SampleContext &Context) override;
  std::error_code writeCSNameIdx(const SampleContext &Context);
  std::error_code writeCSNameTableSection();
 
  std::error_code writeFuncMetadata(const SampleProfileMap &Profiles);
  std::error_code writeFuncMetadata(const FunctionSamples &Profile);
 
  // Functions to write various kinds of sections.
  std::error_code writeNameTableSection(const SampleProfileMap &ProfileMap);
  std::error_code writeFuncOffsetTable();
  std::error_code writeProfileSymbolListSection();
 
  SectionLayout SecLayout = DefaultLayout;
  // Specifiy the order of sections in section header table. Note
  // the order of sections in SecHdrTable may be different that the
  // order in SectionHdrLayout. sample Reader will follow the order
  // in SectionHdrLayout to read each section.
  SmallVector<SecHdrTableEntry, 8> SectionHdrLayout =
      ExtBinaryHdrLayoutTable[DefaultLayout];
 
  // Save the start of SecLBRProfile so we can compute the offset to the
  // start of SecLBRProfile for each Function's Profile and will keep it
  // in FuncOffsetTable.
  uint64_t SecLBRProfileStart = 0;
 
private:
  void allocSecHdrTable();
  std::error_code writeSecHdrTable();
  std::error_code writeHeader(const SampleProfileMap &ProfileMap) override;
  std::error_code compressAndOutput();
 
  // We will swap the raw_ostream held by LocalBufStream and that
  // held by OutputStream if we try to add a section which needs
  // compression. After the swap, all the data written to output
  // will be temporarily buffered into the underlying raw_string_ostream
  // originally held by LocalBufStream. After the data writing for the
  // section is completed, compress the data in the local buffer,
  // swap the raw_ostream back and write the compressed data to the
  // real output.
  std::unique_ptr<raw_ostream> LocalBufStream;
  // The location where the output stream starts.
  uint64_t FileStart;
  // The location in the output stream where the SecHdrTable should be
  // written to.
  uint64_t SecHdrTableOffset;
  // The table contains SecHdrTableEntry entries in order of how they are
  // populated in the writer. It may be different from the order in
  // SectionHdrLayout which specifies the sequence in which sections will
  // be read.
  std::vector<SecHdrTableEntry> SecHdrTable;
 
  // FuncOffsetTable maps function context to its profile offset in
  // SecLBRProfile section. It is used to load function profile on demand.
  MapVector<SampleContext, uint64_t> FuncOffsetTable;
  // Whether to use MD5 to represent string.
  bool UseMD5 = false;
 
  /// CSNameTable maps function context to its offset in SecCSNameTable section.
  /// The offset will be used everywhere where the context is referenced.
  MapVector<SampleContext, uint32_t> CSNameTable;
 
  ProfileSymbolList *ProfSymList = nullptr;
};
 
class SampleProfileWriterExtBinary : public SampleProfileWriterExtBinaryBase {
public:
  SampleProfileWriterExtBinary(std::unique_ptr<raw_ostream> &OS)
      : SampleProfileWriterExtBinaryBase(OS) {}
 
private:
  std::error_code writeDefaultLayout(const SampleProfileMap &ProfileMap);
  std::error_code writeCtxSplitLayout(const SampleProfileMap &ProfileMap);
 
  std::error_code writeSections(const SampleProfileMap &ProfileMap) override;
 
  std::error_code writeCustomSection(SecType Type) override {
    return sampleprof_error::success;
  };
 
  void verifySecLayout(SectionLayout SL) override {
    assert((SL == DefaultLayout || SL == CtxSplitLayout) &&
           "Unsupported layout");
  }
};
 
// CompactBinary is a compact format of binary profile which both reduces
// the profile size and the load time needed when compiling. It has two
// major difference with Binary format.
// 1. It represents all the strings in name table using md5 hash.
// 2. It saves a function offset table which maps function name index to
// the offset of its function profile to the start of the binary profile,
// so by using the function offset table, for those function profiles which
// will not be needed when compiling a module, the profile reader does't
// have to read them and it saves compile time if the profile size is huge.
// The layout of the compact format is shown as follows:
//
//    Part1: Profile header, the same as binary format, containing magic
//           number, version, summary, name table...
//    Part2: Function Offset Table Offset, which saves the position of
//           Part4.
//    Part3: Function profile collection
//             function1 profile start
//                 ....
//             function2 profile start
//                 ....
//             function3 profile start
//                 ....
//                ......
//    Part4: Function Offset Table
//             function1 name index --> function1 profile start
//             function2 name index --> function2 profile start
//             function3 name index --> function3 profile start
//
// We need Part2 because profile reader can use it to find out and read
// function offset table without reading Part3 first.
class SampleProfileWriterCompactBinary : public SampleProfileWriterBinary {
  using SampleProfileWriterBinary::SampleProfileWriterBinary;
 
public:
  std::error_code writeSample(const FunctionSamples &S) override;
  std::error_code write(const SampleProfileMap &ProfileMap) override;
 
protected:
  /// The table mapping from function name to the offset of its FunctionSample
  /// towards profile start.
  MapVector<StringRef, uint64_t> FuncOffsetTable;
  /// The offset of the slot to be filled with the offset of FuncOffsetTable
  /// towards profile start.
  uint64_t TableOffset;
  std::error_code writeNameTable() override;
  std::error_code writeHeader(const SampleProfileMap &ProfileMap) override;
  std::error_code writeFuncOffsetTable();
};
 
} // end namespace sampleprof
} // end namespace llvm
 
#endif // LLVM_PROFILEDATA_SAMPLEPROFWRITER_H