SampleProfReader.h

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//===- SampleProfReader.h - Read 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 reading sample profiles.
//
// NOTE: If you are making changes to this file format, please remember
//       to document them in the Clang documentation at
//       tools/clang/docs/UsersManual.rst.
//
// Text format
// -----------
//
// Sample profiles are written as ASCII text. The file is divided into
// sections, which correspond to each of the functions executed at runtime.
// Each section has the following format
//
//     function1:total_samples:total_head_samples
//      offset1[.discriminator]: number_of_samples [fn1:num fn2:num ... ]
//      offset2[.discriminator]: number_of_samples [fn3:num fn4:num ... ]
//      ...
//      offsetN[.discriminator]: number_of_samples [fn5:num fn6:num ... ]
//      offsetA[.discriminator]: fnA:num_of_total_samples
//       offsetA1[.discriminator]: number_of_samples [fn7:num fn8:num ... ]
//       ...
//      !CFGChecksum: num
//      !Attribute: flags
//
// This is a nested tree in which the indentation represents the nesting level
// of the inline stack. There are no blank lines in the file. And the spacing
// within a single line is fixed. Additional spaces will result in an error
// while reading the file.
//
// Any line starting with the '#' character is completely ignored.
//
// Inlined calls are represented with indentation. The Inline stack is a
// stack of source locations in which the top of the stack represents the
// leaf function, and the bottom of the stack represents the actual
// symbol to which the instruction belongs.
//
// Function names must be mangled in order for the profile loader to
// match them in the current translation unit. The two numbers in the
// function header specify how many total samples were accumulated in the
// function (first number), and the total number of samples accumulated
// in the prologue of the function (second number). This head sample
// count provides an indicator of how frequently the function is invoked.
//
// There are three types of lines in the function body.
//
// * Sampled line represents the profile information of a source location.
// * Callsite line represents the profile information of a callsite.
// * Metadata line represents extra metadata of the function.
//
// Each sampled line may contain several items. Some are optional (marked
// below):
//
// a. Source line offset. This number represents the line number
//    in the function where the sample was collected. The line number is
//    always relative to the line where symbol of the function is
//    defined. So, if the function has its header at line 280, the offset
//    13 is at line 293 in the file.
//
//    Note that this offset should never be a negative number. This could
//    happen in cases like macros. The debug machinery will register the
//    line number at the point of macro expansion. So, if the macro was
//    expanded in a line before the start of the function, the profile
//    converter should emit a 0 as the offset (this means that the optimizers
//    will not be able to associate a meaningful weight to the instructions
//    in the macro).
//
// b. [OPTIONAL] Discriminator. This is used if the sampled program
//    was compiled with DWARF discriminator support
//    (http://wiki.dwarfstd.org/index.php?title=Path_Discriminators).
//    DWARF discriminators are unsigned integer values that allow the
//    compiler to distinguish between multiple execution paths on the
//    same source line location.
//
//    For example, consider the line of code ``if (cond) foo(); else bar();``.
//    If the predicate ``cond`` is true 80% of the time, then the edge
//    into function ``foo`` should be considered to be taken most of the
//    time. But both calls to ``foo`` and ``bar`` are at the same source
//    line, so a sample count at that line is not sufficient. The
//    compiler needs to know which part of that line is taken more
//    frequently.
//
//    This is what discriminators provide. In this case, the calls to
//    ``foo`` and ``bar`` will be at the same line, but will have
//    different discriminator values. This allows the compiler to correctly
//    set edge weights into ``foo`` and ``bar``.
//
// c. Number of samples. This is an integer quantity representing the
//    number of samples collected by the profiler at this source
//    location.
//
// d. [OPTIONAL] Potential call targets and samples. If present, this
//    line contains a call instruction. This models both direct and
//    number of samples. For example,
//
//      130: 7  foo:3  bar:2  baz:7
//
//    The above means that at relative line offset 130 there is a call
//    instruction that calls one of ``foo()``, ``bar()`` and ``baz()``,
//    with ``baz()`` being the relatively more frequently called target.
//
// Each callsite line may contain several items. Some are optional.
//
// a. Source line offset. This number represents the line number of the
//    callsite that is inlined in the profiled binary.
//
// b. [OPTIONAL] Discriminator. Same as the discriminator for sampled line.
//
// c. Number of samples. This is an integer quantity representing the
//    total number of samples collected for the inlined instance at this
//    callsite
//
// Metadata line can occur in lines with one indent only, containing extra
// information for the top-level function. Furthermore, metadata can only
// occur after all the body samples and callsite samples.
// Each metadata line may contain a particular type of metadata, marked by
// the starting characters annotated with !. We process each metadata line
// independently, hence each metadata line has to form an independent piece
// of information that does not require cross-line reference.
// We support the following types of metadata:
//
// a. CFG Checksum (a.k.a. function hash):
//   !CFGChecksum: 12345
// b. CFG Checksum (see ContextAttributeMask):
//   !Atribute: 1
//
//
// Binary format
// -------------
//
// This is a more compact encoding. Numbers are encoded as ULEB128 values
// and all strings are encoded in a name table. The file is organized in
// the following sections:
//
// MAGIC (uint64_t)
//    File identifier computed by function SPMagic() (0x5350524f463432ff)
//
// VERSION (uint32_t)
//    File format version number computed by SPVersion()
//
// SUMMARY
//    TOTAL_COUNT (uint64_t)
//        Total number of samples in the profile.
//    MAX_COUNT (uint64_t)
//        Maximum value of samples on a line.
//    MAX_FUNCTION_COUNT (uint64_t)
//        Maximum number of samples at function entry (head samples).
//    NUM_COUNTS (uint64_t)
//        Number of lines with samples.
//    NUM_FUNCTIONS (uint64_t)
//        Number of functions with samples.
//    NUM_DETAILED_SUMMARY_ENTRIES (size_t)
//        Number of entries in detailed summary
//    DETAILED_SUMMARY
//        A list of detailed summary entry. Each entry consists of
//        CUTOFF (uint32_t)
//            Required percentile of total sample count expressed as a fraction
//            multiplied by 1000000.
//        MIN_COUNT (uint64_t)
//            The minimum number of samples required to reach the target
//            CUTOFF.
//        NUM_COUNTS (uint64_t)
//            Number of samples to get to the desrired percentile.
//
// NAME TABLE
//    SIZE (uint64_t)
//        Number of entries in the name table.
//    NAMES
//        A NUL-separated list of SIZE strings.
//
// FUNCTION BODY (one for each uninlined function body present in the profile)
//    HEAD_SAMPLES (uint64_t) [only for top-level functions]
//        Total number of samples collected at the head (prologue) of the
//        function.
//        NOTE: This field should only be present for top-level functions
//              (i.e., not inlined into any caller). Inlined function calls
//              have no prologue, so they don't need this.
//    NAME_IDX (uint64_t)
//        Index into the name table indicating the function name.
//    SAMPLES (uint64_t)
//        Total number of samples collected in this function.
//    NRECS (uint32_t)
//        Total number of sampling records this function's profile.
//    BODY RECORDS
//        A list of NRECS entries. Each entry contains:
//          OFFSET (uint32_t)
//            Line offset from the start of the function.
//          DISCRIMINATOR (uint32_t)
//            Discriminator value (see description of discriminators
//            in the text format documentation above).
//          SAMPLES (uint64_t)
//            Number of samples collected at this location.
//          NUM_CALLS (uint32_t)
//            Number of non-inlined function calls made at this location. In the
//            case of direct calls, this number will always be 1. For indirect
//            calls (virtual functions and function pointers) this will
//            represent all the actual functions called at runtime.
//          CALL_TARGETS
//            A list of NUM_CALLS entries for each called function:
//               NAME_IDX (uint64_t)
//                  Index into the name table with the callee name.
//               SAMPLES (uint64_t)
//                  Number of samples collected at the call site.
//    NUM_INLINED_FUNCTIONS (uint32_t)
//      Number of callees inlined into this function.
//    INLINED FUNCTION RECORDS
//      A list of NUM_INLINED_FUNCTIONS entries describing each of the inlined
//      callees.
//        OFFSET (uint32_t)
//          Line offset from the start of the function.
//        DISCRIMINATOR (uint32_t)
//          Discriminator value (see description of discriminators
//          in the text format documentation above).
//        FUNCTION BODY
//          A FUNCTION BODY entry describing the inlined function.
//===----------------------------------------------------------------------===//
 
#ifndef LLVM_PROFILEDATA_SAMPLEPROFREADER_H
#define LLVM_PROFILEDATA_SAMPLEPROFREADER_H
 
#include "llvm/ADT/Eytzinger.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/STLForwardCompat.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/ADT/StringSet.h"
#include "llvm/IR/DiagnosticInfo.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/ProfileSummary.h"
#include "llvm/ProfileData/GCOV.h"
#include "llvm/ProfileData/SampleProf.h"
#include "llvm/ProfileData/SymbolRemappingReader.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/Discriminator.h"
#include "llvm/Support/ErrorOr.h"
#include "llvm/Support/MemoryBuffer.h"
#include "llvm/Support/OnDiskHashTable.h"
#include <array>
#include <cstdint>
#include <list>
#include <memory>
#include <optional>
#include <string>
#include <system_error>
#include <vector>
 
namespace llvm {
 
class raw_ostream;
class Twine;
 
namespace vfs {
class FileSystem;
} // namespace vfs
 
namespace sampleprof {
 
class SampleProfileReader;
 
/// SampleProfileReaderItaniumRemapper remaps the profile data from a
/// sample profile data reader, by applying a provided set of equivalences
/// between components of the symbol names in the profile.
class SampleProfileReaderItaniumRemapper {
public:
  SampleProfileReaderItaniumRemapper(std::unique_ptr<MemoryBuffer> B,
                                     std::unique_ptr<SymbolRemappingReader> SRR,
                                     SampleProfileReader &R)
      : Buffer(std::move(B)), Remappings(std::move(SRR)), Reader(R) {
    assert(Remappings && "Remappings cannot be nullptr");
  }
 
  /// Create a remapper from the given remapping file. The remapper will
  /// be used for profile read in by Reader.
  LLVM_ABI static ErrorOr<std::unique_ptr<SampleProfileReaderItaniumRemapper>>
  create(StringRef Filename, vfs::FileSystem &FS, SampleProfileReader &Reader,
         LLVMContext &C);
 
  /// Create a remapper from the given Buffer. The remapper will
  /// be used for profile read in by Reader.
  LLVM_ABI static ErrorOr<std::unique_ptr<SampleProfileReaderItaniumRemapper>>
  create(std::unique_ptr<MemoryBuffer> &B, SampleProfileReader &Reader,
         LLVMContext &C);
 
  /// Apply remappings to the profile read by Reader.
  LLVM_ABI void applyRemapping(LLVMContext &Ctx);
 
  bool hasApplied() { return RemappingApplied; }
 
  /// Insert function name into remapper.
  void insert(StringRef FunctionName) { Remappings->insert(FunctionName); }
 
  /// Query whether there is equivalent in the remapper which has been
  /// inserted.
  bool exist(StringRef FunctionName) {
    return Remappings->lookup(FunctionName);
  }
 
  /// Return the equivalent name in the profile for \p FunctionName if
  /// it exists.
  LLVM_ABI std::optional<StringRef> lookUpNameInProfile(StringRef FunctionName);
 
private:
  // The buffer holding the content read from remapping file.
  std::unique_ptr<MemoryBuffer> Buffer;
  std::unique_ptr<SymbolRemappingReader> Remappings;
  // Map remapping key to the name in the profile. By looking up the
  // key in the remapper, a given new name can be mapped to the
  // cannonical name using the NameMap.
  DenseMap<SymbolRemappingReader::Key, StringRef> NameMap;
  // The Reader the remapper is servicing.
  SampleProfileReader &Reader;
  // Indicate whether remapping has been applied to the profile read
  // by Reader -- by calling applyRemapping.
  bool RemappingApplied = false;
};
 
/// 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.
///
/// The reader supports two file formats: text and binary. The text format
/// is useful for debugging and testing, while the binary format is more
/// compact and I/O efficient. They can both be used interchangeably.
 
/// Manages the sample profile name table, supporting both an eagerly loaded
/// std::vector of FunctionId objects and lazy-loaded MD5 hashes read directly
/// from the memory-mapped buffer. It enforces the exclusivity of these
/// two formats and provides a unified read-only container interface.
class SampleProfileNameTable {
public:
  class iterator
      : public llvm::iterator_facade_base<iterator, std::input_iterator_tag,
                                          FunctionId, std::ptrdiff_t,
                                          const FunctionId *, FunctionId> {
  public:
    iterator() = default;
    iterator(const SampleProfileNameTable *Table, size_t Idx)
        : Table(Table), Idx(Idx) {}
 
    bool operator==(const iterator &RHS) const {
      return Table == RHS.Table && Idx == RHS.Idx;
    }
 
    iterator &operator++() {
      ++Idx;
      return *this;
    }
 
    FunctionId operator*() const {
      assert(Table && Idx < Table->size() &&
             "Dereferencing invalid or out-of-bounds iterator");
      return (*Table)[Idx];
    }
 
  private:
    const SampleProfileNameTable *Table = nullptr;
    size_t Idx = 0;
  };
 
  using const_iterator = iterator;
 
  SampleProfileNameTable() = default;
  SampleProfileNameTable(const SampleProfileNameTable &) = delete;
  SampleProfileNameTable(SampleProfileNameTable &&) = delete;
  SampleProfileNameTable &operator=(const SampleProfileNameTable &) = delete;
  SampleProfileNameTable &operator=(SampleProfileNameTable &&) = delete;
  virtual ~SampleProfileNameTable() = default;
 
  virtual size_t size() const = 0;
  bool empty() const { return size() == 0; }
  virtual FunctionId operator[](size_t Idx) const = 0;
 
  virtual EytzingerTableSpan<support::ulittle64_t>
  getEytzingerSpan(bool IsNested) const {
    llvm_unreachable(
        "getEytzingerSpan is exclusively supported for Eytzinger layout");
  }
  virtual bool contains(StringRef Key) const {
    return contains(FunctionId(Key).getHashCode());
  }
  virtual bool contains(uint64_t GUID) const {
    return getOrCreateSet(GUIDSet, *this, GetFunctionIdHash).contains(GUID);
  }
 
  iterator begin() const { return iterator(this, 0); }
  iterator end() const { return iterator(this, size()); }
 
protected:
  mutable std::optional<DenseSet<uint64_t>> GUIDSet;
 
  static constexpr auto GetFunctionIdHash = [](FunctionId F) {
    return F.getHashCode();
  };
  static constexpr auto GetFunctionIdString = [](FunctionId F) {
    return F.stringRef();
  };
 
  template <typename SetT, typename RangeT, typename ProjT = llvm::identity>
  static const SetT &getOrCreateSet(std::optional<SetT> &Set,
                                    const RangeT &Range, ProjT Proj = ProjT()) {
    if (!Set) {
      Set.emplace();
      Set->reserve(Range.size());
      for (const auto &Item : Range)
        Set->insert(Proj(Item));
    }
    return *Set;
  }
};
 
class LazySampleProfileNameTable final : public SampleProfileNameTable {
  const uint8_t *Start = nullptr;
  size_t Size = 0;
 
public:
  LazySampleProfileNameTable(const uint8_t *Start, size_t Size)
      : Start(Start), Size(Size) {}
 
  size_t size() const override { return Size; }
 
  FunctionId operator[](size_t Idx) const override {
    assert(Idx < Size && "Index out of bounds");
    using namespace support;
    return FunctionId(endian::read<uint64_t, unaligned>(
        Start + Idx * sizeof(uint64_t), endianness::little));
  }
 
  bool contains(uint64_t GUID) const override {
    ArrayRef<support::ulittle64_t> Table(
        reinterpret_cast<const support::ulittle64_t *>(Start), Size);
    return getOrCreateSet(GUIDSet, Table).contains(GUID);
  }
};
 
class StringSampleProfileNameTable final : public SampleProfileNameTable {
  std::vector<FunctionId> Vec;
  mutable std::optional<DenseSet<StringRef>> NameSet;
 
public:
  explicit StringSampleProfileNameTable(std::vector<FunctionId> &&Vec)
      : Vec(std::move(Vec)) {}
  explicit StringSampleProfileNameTable(const std::vector<FunctionId> &Vec)
      : Vec(Vec) {}
 
  size_t size() const override { return Vec.size(); }
 
  FunctionId operator[](size_t Idx) const override {
    assert(Idx < Vec.size() && "Index out of bounds");
    return Vec[Idx];
  }
 
  bool contains(StringRef Key) const override {
    return getOrCreateSet(NameSet, Vec, GetFunctionIdString).contains(Key);
  }
};
 
class MD5SampleProfileNameTable final : public SampleProfileNameTable {
  std::vector<FunctionId> Vec;
 
public:
  explicit MD5SampleProfileNameTable(std::vector<FunctionId> &&Vec)
      : Vec(std::move(Vec)) {}
  explicit MD5SampleProfileNameTable(const std::vector<FunctionId> &Vec)
      : Vec(Vec) {}
 
  size_t size() const override { return Vec.size(); }
 
  FunctionId operator[](size_t Idx) const override {
    assert(Idx < Vec.size() && "Index out of bounds");
    return Vec[Idx];
  }
};
 
class EytzingerSampleProfileNameTable final : public SampleProfileNameTable {
  ArrayRef<support::ulittle64_t> Array;
  std::array<EytzingerTableSpan<support::ulittle64_t>,
             static_cast<size_t>(EytzingerSpan::NumSpans)>
      Spans;
 
public:
  EytzingerSampleProfileNameTable(const support::ulittle64_t *Data,
                                  size_t NumNested, size_t NumFlat,
                                  size_t NumInlinees)
      : Array(Data, NumNested + NumFlat + NumInlinees),
        Spans{{{Data, NumNested},
               {Data + NumNested, NumFlat},
               {Data + NumNested + NumFlat, NumInlinees}}} {}
 
  size_t size() const override { return Array.size(); }
 
  FunctionId operator[](size_t Idx) const override {
    return FunctionId(Array[Idx]);
  }
 
  EytzingerTableSpan<support::ulittle64_t>
  getEytzingerSpan(bool IsNested) const override {
    return Spans[static_cast<size_t>(IsNested ? EytzingerSpan::Nested
                                              : EytzingerSpan::Flat)];
  }
 
  bool contains(uint64_t GUID) const override {
    return llvm::any_of(Spans,
                        [&](const auto &Span) { return Span.contains(GUID); });
  }
};
 
class SampleProfileReader {
public:
  SampleProfileReader(std::unique_ptr<MemoryBuffer> B, LLVMContext &C,
                      SampleProfileFormat Format = SPF_None)
      : Profiles(), Ctx(C), Buffer(std::move(B)), Format(Format) {}
 
  virtual ~SampleProfileReader() = default;
 
  /// Read and validate the file header.
  virtual std::error_code readHeader() = 0;
 
  /// Set the bits for FS discriminators. Parameter Pass specify the sequence
  /// number, Pass == i is for the i-th round of adding FS discriminators.
  /// Pass == 0 is for using base discriminators.
  void setDiscriminatorMaskedBitFrom(FSDiscriminatorPass P) {
    MaskedBitFrom = getFSPassBitEnd(P);
  }
 
  /// Get the bitmask the discriminators: For FS profiles, return the bit
  /// mask for this pass. For non FS profiles, return (unsigned) -1.
  uint32_t getDiscriminatorMask() const {
    if (!ProfileIsFS)
      return 0xFFFFFFFF;
    assert((MaskedBitFrom != 0) && "MaskedBitFrom is not set properly");
    return getN1Bits(MaskedBitFrom);
  }
 
  /// The interface to read sample profiles from the associated file.
  std::error_code read() {
    if (std::error_code EC = readImpl())
      return EC;
    if (Remapper)
      Remapper->applyRemapping(Ctx);
    FunctionSamples::UseMD5 = useMD5();
    return sampleprof_error::success;
  }
 
  /// Read sample profiles for the given functions.
  std::error_code read(const DenseSet<StringRef> &FuncsToUse) {
    DenseSet<StringRef> S;
    for (StringRef F : FuncsToUse)
      if (Profiles.find(FunctionId(F)) == Profiles.end())
        S.insert(F);
    if (std::error_code EC = read(S, Profiles))
      return EC;
    return sampleprof_error::success;
  }
 
  /// The implementaion to read sample profiles from the associated file.
  virtual std::error_code readImpl() = 0;
 
  /// Print the profile for \p FunctionSamples on stream \p OS.
  LLVM_ABI void dumpFunctionProfile(const FunctionSamples &FS,
                                    raw_ostream &OS = dbgs());
 
  /// Collect functions with definitions in Module M. For reader which
  /// support loading function profiles on demand, return true when the
  /// reader has been given a module. Always return false for reader
  /// which doesn't support loading function profiles on demand.
  virtual bool collectFuncsFromModule() { return false; }
 
  /// Print all the profiles on stream \p OS.
  LLVM_ABI void dump(raw_ostream &OS = dbgs());
 
  /// Print all the profiles on stream \p OS in the JSON format.
  LLVM_ABI void dumpJson(raw_ostream &OS = dbgs());
 
  /// Return the format version of the profile. For tests only.
  uint64_t getFormatVersion() const { return FormatVersion; }
 
  /// Return the samples collected for function \p F.
  FunctionSamples *getSamplesFor(const Function &F) {
    // The function name may have been updated by adding suffix. Call
    // a helper to (optionally) strip off suffixes so that we can
    // match against the original function name in the profile.
    StringRef CanonName = FunctionSamples::getCanonicalFnName(F);
    return getSamplesFor(CanonName);
  }
 
  /// Return the samples collected for function \p F.
  FunctionSamples *getSamplesFor(StringRef Fname) {
    auto It = Profiles.find(FunctionId(Fname));
    if (It != Profiles.end())
      return &It->second;
 
    if (FuncNameToProfNameMap && !FuncNameToProfNameMap->empty()) {
      auto R = FuncNameToProfNameMap->find(FunctionId(Fname));
      if (R != FuncNameToProfNameMap->end()) {
        Fname = R->second.stringRef();
        auto It = Profiles.find(FunctionId(Fname));
        if (It != Profiles.end())
          return &It->second;
      }
    }
 
    if (Remapper) {
      if (auto NameInProfile = Remapper->lookUpNameInProfile(Fname)) {
        auto It = Profiles.find(FunctionId(*NameInProfile));
        if (It != Profiles.end())
          return &It->second;
      }
    }
    return nullptr;
  }
 
  /// Return all the profiles.
  SampleProfileMap &getProfiles() { return Profiles; }
 
  /// Report a parse error message.
  void reportError(int64_t LineNumber, const Twine &Msg) const {
    Ctx.diagnose(DiagnosticInfoSampleProfile(Buffer->getBufferIdentifier(),
                                             LineNumber, Msg));
  }
 
  /// Create a sample profile reader appropriate to the file format.
  /// Create a remapper underlying if RemapFilename is not empty.
  /// Parameter P specifies the FSDiscriminatorPass.
  LLVM_ABI static ErrorOr<std::unique_ptr<SampleProfileReader>>
  create(StringRef Filename, LLVMContext &C, vfs::FileSystem &FS,
         FSDiscriminatorPass P = FSDiscriminatorPass::Base,
         StringRef RemapFilename = "");
 
  /// Create a sample profile reader from the supplied memory buffer.
  /// Create a remapper underlying if RemapFilename is not empty.
  /// Parameter P specifies the FSDiscriminatorPass.
  LLVM_ABI static ErrorOr<std::unique_ptr<SampleProfileReader>>
  create(std::unique_ptr<MemoryBuffer> &B, LLVMContext &C, vfs::FileSystem &FS,
         FSDiscriminatorPass P = FSDiscriminatorPass::Base,
         StringRef RemapFilename = "");
 
  /// Return the profile summary.
  ProfileSummary &getSummary() const { return *Summary; }
 
  MemoryBuffer *getBuffer() const { return Buffer.get(); }
 
  /// \brief Return the profile format.
  SampleProfileFormat getFormat() const { return Format; }
 
  /// Whether input profile is based on pseudo probes.
  bool profileIsProbeBased() const { return ProfileIsProbeBased; }
 
  /// Whether input profile is fully context-sensitive.
  bool profileIsCS() const { return ProfileIsCS; }
 
  /// Whether input profile contains ShouldBeInlined contexts.
  bool profileIsPreInlined() const { return ProfileIsPreInlined; }
 
  /// Whether input profile is flow-sensitive.
  bool profileIsFS() const { return ProfileIsFS; }
 
  virtual std::unique_ptr<ProfileSymbolList> getProfileSymbolList() {
    return nullptr;
  };
 
  /// It includes all the names that have samples either in outline instance
  /// or inline instance.
  virtual llvm::iterator_range<SampleProfileNameTable::iterator>
  getNameTable() const {
    return {SampleProfileNameTable::iterator(),
            SampleProfileNameTable::iterator()};
  }
  virtual bool dumpSectionInfo(raw_ostream &OS = dbgs()) { return false; };
  virtual bool contains(StringRef Key) const { return false; }
  virtual bool contains(uint64_t GUID) const { return false; }
 
  /// Return whether names in the profile are all MD5 numbers.
  bool useMD5() const { return ProfileIsMD5; }
 
  /// Force the profile to use MD5 in Sample contexts, even if function names
  /// are present.
  virtual void setProfileUseMD5() { ProfileIsMD5 = true; }
 
  /// Don't read profile without context if the flag is set.
  void setSkipFlatProf(bool Skip) { SkipFlatProf = Skip; }
 
  /// Return whether any name in the profile contains ".__uniq." suffix.
  virtual bool hasUniqSuffix() { return false; }
 
  SampleProfileReaderItaniumRemapper *getRemapper() { return Remapper.get(); }
 
  void setModule(const Module *Mod) { M = Mod; }
 
  void setFuncNameToProfNameMap(
      const HashKeyMap<DenseMap, FunctionId, FunctionId> &FPMap) {
    FuncNameToProfNameMap = &FPMap;
  }
 
protected:
  /// Map every function to its associated profile.
  ///
  /// The profile of every function executed at runtime is collected
  /// in the structure FunctionSamples. This maps function objects
  /// to their corresponding profiles.
  SampleProfileMap Profiles;
 
  /// LLVM context used to emit diagnostics.
  LLVMContext &Ctx;
 
  /// Memory buffer holding the profile file.
  std::unique_ptr<MemoryBuffer> Buffer;
 
  /// Profile summary information.
  std::unique_ptr<ProfileSummary> Summary;
 
  /// Take ownership of the summary of this reader.
  static std::unique_ptr<ProfileSummary>
  takeSummary(SampleProfileReader &Reader) {
    return std::move(Reader.Summary);
  }
 
  /// Compute summary for this profile.
  LLVM_ABI void computeSummary();
 
  /// Read sample profiles for the given functions and write them to the given
  /// profile map. Currently it's only used for extended binary format to load
  /// the profiles on-demand.
  virtual std::error_code read(const DenseSet<StringRef> &FuncsToUse,
                               SampleProfileMap &Profiles) {
    return sampleprof_error::not_implemented;
  }
 
  std::unique_ptr<SampleProfileReaderItaniumRemapper> Remapper;
 
  // A map pointer to the FuncNameToProfNameMap in SampleProfileLoader,
  // which maps the function name to the matched profile name. This is used
  // for sample loader to look up profile using the new name.
  const HashKeyMap<DenseMap, FunctionId, FunctionId> *FuncNameToProfNameMap =
      nullptr;
 
  // A map from a function's context hash to its meta data section range, used
  // for on-demand read function profile metadata.
  DenseMap<uint64_t, std::pair<const uint8_t *, const uint8_t *>>
      FuncMetadataIndex;
 
  std::pair<const uint8_t *, const uint8_t *> ProfileSecRange;
 
  /// Whether the profile has attribute metadata.
  bool ProfileHasAttribute = false;
 
  /// \brief Whether samples are collected based on pseudo probes.
  bool ProfileIsProbeBased = false;
 
  /// Whether function profiles are context-sensitive flat profiles.
  bool ProfileIsCS = false;
 
  /// Whether function profile contains ShouldBeInlined contexts.
  bool ProfileIsPreInlined = false;
 
  /// Number of context-sensitive profiles.
  uint32_t CSProfileCount = 0;
 
  /// Whether the function profiles use FS discriminators.
  bool ProfileIsFS = false;
 
  /// Format version of the profile.
  uint64_t FormatVersion = 0;
 
  /// If true, the profile has vtable profiles and reader should decode them
  /// to parse profiles correctly.
  bool ReadVTableProf = false;
 
  /// \brief The format of sample.
  SampleProfileFormat Format = SPF_None;
 
  /// \brief The current module being compiled if SampleProfileReader
  /// is used by compiler. If SampleProfileReader is used by other
  /// tools which are not compiler, M is usually nullptr.
  const Module *M = nullptr;
 
  /// Zero out the discriminator bits higher than bit MaskedBitFrom (0 based).
  /// The default is to keep all the bits.
  uint32_t MaskedBitFrom = 31;
 
  /// Whether the profile uses MD5 for Sample Contexts and function names. This
  /// can be one-way overriden by the user to force use MD5.
  bool ProfileIsMD5 = false;
 
  /// If SkipFlatProf is true, skip functions marked with !Flat in text mode or
  /// sections with SecFlagFlat flag in ExtBinary mode.
  bool SkipFlatProf = false;
};
 
class LLVM_ABI SampleProfileReaderText : public SampleProfileReader {
public:
  SampleProfileReaderText(std::unique_ptr<MemoryBuffer> B, LLVMContext &C)
      : SampleProfileReader(std::move(B), C, SPF_Text) {}
 
  /// Read and validate the file header.
  std::error_code readHeader() override { return sampleprof_error::success; }
 
  /// Read sample profiles from the associated file.
  std::error_code readImpl() override;
 
  /// Return true if \p Buffer is in the format supported by this class.
  static bool hasFormat(const MemoryBuffer &Buffer);
 
  /// Text format sample profile does not support MD5 for now.
  void setProfileUseMD5() override {}
 
private:
  /// CSNameTable is used to save full context vectors. This serves as an
  /// underlying immutable buffer for all clients.
  std::list<SampleContextFrameVector> CSNameTable;
};
 
class LLVM_ABI SampleProfileReaderBinary : public SampleProfileReader {
public:
  SampleProfileReaderBinary(std::unique_ptr<MemoryBuffer> B, LLVMContext &C,
                            SampleProfileFormat Format = SPF_None)
      : SampleProfileReader(std::move(B), C, Format) {}
 
  /// Read and validate the file header.
  std::error_code readHeader() override;
 
  /// Read sample profiles from the associated file.
  std::error_code readImpl() override;
 
  /// It includes all the names that have samples either in outline instance
  /// or inline instance.
  llvm::iterator_range<SampleProfileNameTable::iterator>
  getNameTable() const override {
    if (!NameTable)
      return {SampleProfileNameTable::iterator(),
              SampleProfileNameTable::iterator()};
    return {NameTable->begin(), NameTable->end()};
  }
 
  bool contains(StringRef Key) const override {
    assert(NameTable && "NameTable should be populated before querying");
    return NameTable->contains(Key);
  }
 
  bool contains(uint64_t GUID) const override {
    assert(NameTable && "NameTable should be populated before querying");
    return NameTable->contains(GUID);
  }
 
protected:
  /// Read a numeric value of type T from the profile.
  ///
  /// If an error occurs during decoding, a diagnostic message is emitted and
  /// EC is set.
  ///
  /// \returns the read value.
  template <typename T> ErrorOr<T> readNumber();
 
  /// Read a numeric value of type T from the profile. The value is saved
  /// without encoded.
  template <typename T> ErrorOr<T> readUnencodedNumber();
 
  /// Read a string from the profile.
  ///
  /// If an error occurs during decoding, a diagnostic message is emitted and
  /// EC is set.
  ///
  /// \returns the read value.
  ErrorOr<StringRef> readString();
 
  /// Read the string index and check whether it overflows the table.
  template <typename T> inline ErrorOr<size_t> readStringIndex(T &Table);
 
  /// Read the next function profile instance.
  std::error_code readFuncProfile(const uint8_t *Start);
  std::error_code readFuncProfile(const uint8_t *Start,
                                  SampleProfileMap &Profiles);
 
  /// Read the contents of the given profile instance.
  std::error_code readProfile(FunctionSamples &FProfile);
 
  /// Read the contents of Magic number and Version number.
  std::error_code readMagicIdent();
 
  /// Read profile summary.
  std::error_code readSummary();
 
  /// Read the whole name table.
  std::error_code readNameTable();
 
  /// Read a string indirectly via the name table. Optionally return the index.
  ErrorOr<FunctionId> readStringFromTable(size_t *RetIdx = nullptr);
 
  /// Read a context indirectly via the CSNameTable. Optionally return the
  /// index.
  ErrorOr<SampleContextFrames> readContextFromTable(size_t *RetIdx = nullptr);
 
  /// Read a context indirectly via the CSNameTable if the profile has context,
  /// otherwise same as readStringFromTable, also return its hash value.
  ErrorOr<std::pair<SampleContext, uint64_t>> readSampleContextFromTable();
 
  /// Read all virtual functions' vtable access counts for \p FProfile.
  std::error_code readCallsiteVTableProf(FunctionSamples &FProfile);
 
  /// Read bytes from the input buffer pointed by `Data` and decode them into
  /// \p M. `Data` will be advanced to the end of the read bytes when this
  /// function returns. Returns error if any.
  std::error_code readVTableTypeCountMap(TypeCountMap &M);
 
  /// Points to the current location in the buffer.
  const uint8_t *Data = nullptr;
 
  /// Points to the end of the buffer.
  const uint8_t *End = nullptr;
 
  /// Function name table.
  std::unique_ptr<SampleProfileNameTable> NameTable;
 
  /// CSNameTable is used to save full context vectors. It is the backing buffer
  /// for SampleContextFrames.
  std::vector<SampleContextFrameVector> CSNameTable;
 
  /// Table to cache MD5 values of sample contexts corresponding to
  /// readSampleContextFromTable(), used to index into Profiles or
  /// FuncOffsetTable.
  std::vector<uint64_t> MD5SampleContextTable;
 
  /// The starting address of the table of MD5 values of sample contexts. For
  /// fixed length MD5 non-CS profile it is same as MD5NameMemStart because
  /// hashes of non-CS contexts are already in the profile. Otherwise it points
  /// to the start of MD5SampleContextTable.
  const uint64_t *MD5SampleContextStart = nullptr;
 
private:
  std::error_code readSummaryEntry(std::vector<ProfileSummaryEntry> &Entries);
  virtual std::error_code verifySPMagic(uint64_t Magic) = 0;
};
 
class LLVM_ABI SampleProfileReaderRawBinary : public SampleProfileReaderBinary {
private:
  std::error_code verifySPMagic(uint64_t Magic) override;
 
public:
  SampleProfileReaderRawBinary(std::unique_ptr<MemoryBuffer> B, LLVMContext &C,
                               SampleProfileFormat Format = SPF_Binary)
      : SampleProfileReaderBinary(std::move(B), C, Format) {}
 
  /// \brief Return true if \p Buffer is in the format supported by this class.
  static bool hasFormat(const MemoryBuffer &Buffer);
};
 
/// Trait class for reading the on-disk function offset hash table mapping
/// function name GUIDs to their offsets in the SecLBRProfile section.
class FuncOffsetHashTableInfo {
public:
  using key_type = uint64_t;
  using key_type_ref = uint64_t;
  using data_type = uint32_t; // Offset
  using data_type_ref = uint32_t;
  using hash_value_type = uint32_t;
  using offset_type = uint32_t;
  using internal_key_type = uint64_t;
  using external_key_type = uint64_t;
 
  static hash_value_type ComputeHash(key_type_ref Key) {
    return static_cast<hash_value_type>(Key);
  }
 
  static bool EqualKey(key_type_ref LHS, key_type_ref RHS) {
    return LHS == RHS;
  }
 
  static key_type GetInternalKey(key_type_ref Key) { return Key; }
  static external_key_type GetExternalKey(internal_key_type Key) { return Key; }
 
  static std::pair<offset_type, offset_type>
  ReadKeyDataLength(const unsigned char *&D) {
    // Implicit lengths: do NOT read or advance pointer D.
    return {sizeof(key_type), sizeof(data_type)};
  }
 
  static key_type ReadKey(const unsigned char *D, offset_type Len) {
    assert(Len == sizeof(key_type) && "Key length mismatch");
    return support::endian::read64le(D);
  }
 
  static data_type ReadData(key_type_ref K, const unsigned char *D,
                            offset_type Len) {
    assert(Len == sizeof(data_type) && "Data length mismatch");
    return support::endian::read32le(D);
  }
};
 
/// Tags to select the initialization mode of SampleProfileFuncOffsetTable.
struct InMemoryModeT {};
struct OnDiskModeT {};
struct EytzingerModeT {};
 
inline constexpr InMemoryModeT InMemoryMode{};
inline constexpr OnDiskModeT OnDiskMode{};
inline constexpr EytzingerModeT EytzingerMode{};
 
/// A unified wrapper representing the function offset table.
///
/// This class abstracts away the physical representation of the offset table,
/// which can either be:
///
/// - An llvm::DenseMap mapping function GUIDs (or context hashes) to their
///   profile offsets, populated when reading the array of offsets in
///   context-sensitive (CS) profiles or version 103 profiles.
///
/// - An OnDiskIterableChainedHashTable providing the same mapping directly from
///   the file in (non-context-sensitive) version 104 profiles.
///
/// - A raw slice of 32-bit relative offsets for Eytzinger parallel lookups.
///
/// It exposes a single, type-agnostic lookup interface, shielding the reader
/// from the underlying container types. To prevent hybrid-state corruption, the
/// table's mode is locked at construction time, and assertions prevent
/// modification in on-disk mode.
class SampleProfileFuncOffsetTable {
public:
  enum class TableMode { InMemory, OnDisk, Eytzinger };
 
  using OnDiskTableType =
      llvm::OnDiskIterableChainedHashTable<FuncOffsetHashTableInfo>;
 
  SampleProfileFuncOffsetTable() = delete;
  SampleProfileFuncOffsetTable(const SampleProfileFuncOffsetTable &) = delete;
  SampleProfileFuncOffsetTable &
  operator=(const SampleProfileFuncOffsetTable &) = delete;
  SampleProfileFuncOffsetTable(SampleProfileFuncOffsetTable &&) = delete;
  SampleProfileFuncOffsetTable &
  operator=(SampleProfileFuncOffsetTable &&) = delete;
 
  explicit SampleProfileFuncOffsetTable(InMemoryModeT,
                                        size_t InitialCapacity = 0)
      : Mode(TableMode::InMemory) {
    InMemoryTable.reserve(InitialCapacity);
  }
 
  SampleProfileFuncOffsetTable(
      EytzingerModeT, EytzingerTableSpan<support::ulittle64_t> NameSpan,
      ArrayRef<support::ulittle32_t> FuncOffsetSpan)
      : Mode(TableMode::Eytzinger), NameSpan(NameSpan),
        FuncOffsetSpan(FuncOffsetSpan) {}
 
  /// Insert a function GUID and its profile offset into the in-memory map.
  /// Enforces that the on-disk table must not have been set first.
  void insert(uint64_t GUID, uint64_t Offset) {
    assert(!OnDiskTable &&
           "Cannot insert in-memory elements after on-disk table has been set");
    InMemoryTable[GUID] = Offset;
  }
 
  /// Instantiate the on-disk chained hash table using raw stream pointers.
  SampleProfileFuncOffsetTable(OnDiskModeT, const uint8_t *Buckets,
                               const uint8_t *Payload, const uint8_t *Base)
      : Mode(TableMode::OnDisk) {
    OnDiskTable.reset(OnDiskTableType::Create(Buckets, Payload, Base));
  }
 
  /// Query the offset table for the profile offset associated with the given
  /// GUID. Returns the offset if found, or std::nullopt if the key is missing.
  std::optional<uint64_t> lookup(uint64_t GUID) const {
    if (isEytzinger()) {
      if (std::optional<size_t> Idx = NameSpan.findIndex(GUID)) {
        uint32_t RelOffset = FuncOffsetSpan[*Idx];
        if (RelOffset != UINT32_MAX)
          return RelOffset;
      }
      return std::nullopt;
    }
    if (OnDiskTable) {
      auto Iter = OnDiskTable->find(GUID);
      if (Iter != OnDiskTable->end())
        return *Iter;
    } else {
      auto Iter = InMemoryTable.find(GUID);
      if (Iter != InMemoryTable.end())
        return Iter->second;
    }
    return std::nullopt;
  }
 
  /// Direct read-only array (`ArrayRef`) of function offsets aligned parallel
  /// to the corresponding Eytzinger name span.
  ArrayRef<support::ulittle32_t> getFuncOffsets() const {
    assert(isEytzinger() &&
           "Cannot call getFuncOffsets() on non-Eytzinger table");
    return FuncOffsetSpan;
  }
 
  size_t getExpectedSize() const {
    assert(isEytzinger() &&
           "Cannot call getExpectedSize() on non-Eytzinger table");
    return NameSpan.size();
  }
 
  bool isEytzinger() const { return Mode == TableMode::Eytzinger; }
 
private:
  TableMode Mode;
  llvm::DenseMap<hash_code, uint64_t> InMemoryTable;
  std::unique_ptr<OnDiskTableType> OnDiskTable;
  EytzingerTableSpan<support::ulittle64_t> NameSpan;
  ArrayRef<support::ulittle32_t> FuncOffsetSpan;
};
 
/// SampleProfileReaderExtBinaryBase/SampleProfileWriterExtBinaryBase defines
/// the basic structure of the extensible binary format.
/// The format is organized in sections except the magic and version number
/// at the beginning. There is a section table before all the sections, and
/// each entry in the table describes the entry type, start, size and
/// attributes. The format in each section is defined by the section itself.
///
/// It is easy to add a new section while maintaining the backward
/// compatibility of the profile. Nothing extra needs to be done. If we want
/// to extend an existing section, like add cache misses information in
/// addition to the sample count in the profile body, we can add a new section
/// with the extension and retire the existing section, and we could choose
/// to keep the parser of the old section if we want the reader to be able
/// to read both new and old format profile.
///
/// SampleProfileReaderExtBinary/SampleProfileWriterExtBinary define the
/// commonly used sections of a profile in extensible binary format. It is
/// possible to define other types of profile inherited from
/// SampleProfileReaderExtBinaryBase/SampleProfileWriterExtBinaryBase.
class LLVM_ABI SampleProfileReaderExtBinaryBase
    : public SampleProfileReaderBinary {
private:
  std::error_code decompressSection(const uint8_t *SecStart,
                                    const uint64_t SecSize,
                                    const uint8_t *&DecompressBuf,
                                    uint64_t &DecompressBufSize);
 
  BumpPtrAllocator Allocator;
 
protected:
  std::vector<SecHdrTableEntry> SecHdrTable;
  std::error_code readSecHdrTableEntry(uint64_t Idx);
  std::error_code readSecHdrTable();
 
  std::error_code readFuncMetadata(DenseSet<FunctionSamples *> &Profiles);
  std::error_code readFuncMetadata();
  std::error_code readFuncMetadata(FunctionSamples *FProfile);
  std::error_code readFuncOffsetTable(bool IsEytzinger, bool IsNested);
  std::error_code readEytzingerFuncOffsetTable(bool IsNested);
  std::error_code readLegacyFuncOffsetTable();
  std::error_code readFuncProfiles();
  std::error_code readFuncProfiles(const DenseSet<StringRef> &FuncsToUse,
                                   SampleProfileMap &Profiles);
  std::error_code readNameTableSec(bool IsMD5, bool FixedLengthMD5,
                                   bool IsEytzinger = false);
  std::error_code readNameTableSecEytzinger(bool IsMD5, bool FixedLengthMD5);
  std::error_code readNameTableSecLegacy(bool IsMD5, bool FixedLengthMD5);
  std::error_code readCSNameTableSec();
  std::error_code readProfileSymbolList(bool IsMD5);
  std::error_code readStringBasedProfileSymbolList();
  std::error_code readMD5ProfileSymbolList();
 
  std::error_code readHeader() override;
  std::error_code verifySPMagic(uint64_t Magic) override = 0;
  virtual std::error_code readOneSection(const uint8_t *Start, uint64_t Size,
                                         const SecHdrTableEntry &Entry);
  // placeholder for subclasses to dispatch their own section readers.
  virtual std::error_code readCustomSection(const SecHdrTableEntry &Entry) = 0;
 
  /// Determine which container readFuncOffsetTable() should populate, the list
  /// FuncOffsetList or the map FuncOffsetTable.
  bool useFuncOffsetList() const;
 
  std::unique_ptr<ProfileSymbolList> ProfSymList;
 
  /// The table mapping from a function context's MD5 to the offset of its
  /// FunctionSample towards file start.
  /// At most one of FuncOffsetTable and FuncOffsetList is populated.
  std::optional<SampleProfileFuncOffsetTable> FuncOffsetTable;
 
  /// The list version of FuncOffsetTable. This is used if every entry is
  /// being accessed.
  std::vector<std::pair<SampleContext, uint64_t>> FuncOffsetList;
 
  /// The set containing the functions to use when compiling a module.
  DenseSet<StringRef> FuncsToUse;
 
public:
  SampleProfileReaderExtBinaryBase(std::unique_ptr<MemoryBuffer> B,
                                   LLVMContext &C, SampleProfileFormat Format)
      : SampleProfileReaderBinary(std::move(B), C, Format) {
    FuncOffsetTable.emplace(InMemoryMode);
  }
 
  /// Read sample profiles in extensible format from the associated file.
  std::error_code readImpl() override;
 
  /// Get the total size of all \p Type sections.
  uint64_t getSectionSize(SecType Type);
  /// Get the total size of header and all sections.
  uint64_t getFileSize();
  bool dumpSectionInfo(raw_ostream &OS = dbgs()) override;
 
  /// Collect functions with definitions in Module M. Return true if
  /// the reader has been given a module.
  bool collectFuncsFromModule() override;
 
  std::unique_ptr<ProfileSymbolList> getProfileSymbolList() override {
    return std::move(ProfSymList);
  };
 
private:
  /// Read the profiles on-demand for the given functions. This is used after
  /// stale call graph matching finds new functions whose profiles aren't loaded
  /// at the beginning and we need to loaded the profiles explicitly for
  /// potential matching.
  std::error_code read(const DenseSet<StringRef> &FuncsToUse,
                       SampleProfileMap &Profiles) override;
};
 
class LLVM_ABI SampleProfileReaderExtBinary
    : public SampleProfileReaderExtBinaryBase {
private:
  std::error_code verifySPMagic(uint64_t Magic) override;
  std::error_code readCustomSection(const SecHdrTableEntry &Entry) override {
    // Update the data reader pointer to the end of the section.
    Data = End;
    return sampleprof_error::success;
  };
 
public:
  SampleProfileReaderExtBinary(std::unique_ptr<MemoryBuffer> B, LLVMContext &C,
                               SampleProfileFormat Format = SPF_Ext_Binary)
      : SampleProfileReaderExtBinaryBase(std::move(B), C, Format) {}
 
  /// \brief Return true if \p Buffer is in the format supported by this class.
  static bool hasFormat(const MemoryBuffer &Buffer);
};
 
using InlineCallStack = SmallVector<FunctionSamples *, 10>;
 
// Supported histogram types in GCC.  Currently, we only need support for
// call target histograms.
enum HistType {
  HIST_TYPE_INTERVAL,
  HIST_TYPE_POW2,
  HIST_TYPE_SINGLE_VALUE,
  HIST_TYPE_CONST_DELTA,
  HIST_TYPE_INDIR_CALL,
  HIST_TYPE_AVERAGE,
  HIST_TYPE_IOR,
  HIST_TYPE_INDIR_CALL_TOPN
};
 
class LLVM_ABI SampleProfileReaderGCC : public SampleProfileReader {
public:
  SampleProfileReaderGCC(std::unique_ptr<MemoryBuffer> B, LLVMContext &C)
      : SampleProfileReader(std::move(B), C, SPF_GCC),
        GcovBuffer(Buffer.get()) {}
 
  /// Read and validate the file header.
  std::error_code readHeader() override;
 
  /// Read sample profiles from the associated file.
  std::error_code readImpl() override;
 
  /// Return true if \p Buffer is in the format supported by this class.
  static bool hasFormat(const MemoryBuffer &Buffer);
 
protected:
  std::error_code readNameTable();
  std::error_code readOneFunctionProfile(const InlineCallStack &InlineStack,
                                         bool Update, uint32_t Offset);
  std::error_code readFunctionProfiles();
  std::error_code skipNextWord();
  template <typename T> ErrorOr<T> readNumber();
  ErrorOr<StringRef> readString();
 
  /// Read the section tag and check that it's the same as \p Expected.
  std::error_code readSectionTag(uint32_t Expected);
 
  /// GCOV buffer containing the profile.
  GCOVBuffer GcovBuffer;
 
  /// Function names in this profile.
  std::vector<std::string> Names;
 
  /// GCOV tags used to separate sections in the profile file.
  static const uint32_t GCOVTagAFDOFileNames = 0xaa000000;
  static const uint32_t GCOVTagAFDOFunction = 0xac000000;
};
 
} // end namespace sampleprof
 
} // end namespace llvm
 
#endif // LLVM_PROFILEDATA_SAMPLEPROFREADER_H