llvm/lib/CodeGen/AsmPrinter/AccelTable.cpp

//===- llvm/CodeGen/AsmPrinter/AccelTable.cpp - Accelerator Tables --------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file contains support for writing accelerator tables.
//
//===----------------------------------------------------------------------===//

#include "llvm/CodeGen/AccelTable.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/StringMap.h"
#include "llvm/ADT/Twine.h"
#include "llvm/BinaryFormat/Dwarf.h"
#include "llvm/CodeGen/AsmPrinter.h"
#include "llvm/CodeGen/DIE.h"
#include "llvm/MC/MCExpr.h"
#include "llvm/MC/MCStreamer.h"
#include "llvm/Support/raw_ostream.h"
#include <algorithm>
#include <cstddef>
#include <cstdint>
#include <limits>
#include <vector>

using namespace llvm;

void AccelTableBase::computeBucketCount() {
  // First get the number of unique hashes.
  std::vector<uint32_t> Uniques;
  Uniques.reserve(Entries.size());
  for (const auto &E : Entries)
    Uniques.push_back(E.second.HashValue);
  array_pod_sort(Uniques.begin(), Uniques.end());
  std::vector<uint32_t>::iterator P =
      std::unique(Uniques.begin(), Uniques.end());

  UniqueHashCount = std::distance(Uniques.begin(), P);

  if (UniqueHashCount > 1024)
    BucketCount = UniqueHashCount / 4;
  else if (UniqueHashCount > 16)
    BucketCount = UniqueHashCount / 2;
  else
    BucketCount = std::max<uint32_t>(UniqueHashCount, 1);
}

void AccelTableBase::finalize(AsmPrinter *Asm, StringRef Prefix) {
  // Create the individual hash data outputs.
  for (auto &E : Entries) {
    // Unique the entries.
    std::stable_sort(E.second.Values.begin(), E.second.Values.end(),
                     [](const AccelTableData *A, const AccelTableData *B) {
                       return *A < *B;
                     });
    E.second.Values.erase(
        std::unique(E.second.Values.begin(), E.second.Values.end()),
        E.second.Values.end());
  }

  // Figure out how many buckets we need, then compute the bucket contents and
  // the final ordering. The hashes and offsets can be emitted by walking these
  // data structures. We add temporary symbols to the data so they can be
  // referenced when emitting the offsets.
  computeBucketCount();

  // Compute bucket contents and final ordering.
  Buckets.resize(BucketCount);
  for (auto &E : Entries) {
    uint32_t Bucket = E.second.HashValue % BucketCount;
    Buckets[Bucket].push_back(&E.second);
    E.second.Sym = Asm->createTempSymbol(Prefix);
  }

  // Sort the contents of the buckets by hash value so that hash collisions end
  // up together. Stable sort makes testing easier and doesn't cost much more.
  for (auto &Bucket : Buckets)
    std::stable_sort(Bucket.begin(), Bucket.end(),
                     [](HashData *LHS, HashData *RHS) {
                       return LHS->HashValue < RHS->HashValue;
                     });
}

namespace {
class AccelTableEmitter {
protected:
  AsmPrinter *const Asm;          ///< Destination.
  const AccelTableBase &Contents; ///< Data to emit.

  /// Controls whether to emit duplicate hash and offset table entries for names
  /// with identical hashes. Apple tables don't emit duplicate entries, DWARF v5
  /// tables do.
  const bool SkipIdenticalHashes;

  void emitHashes() const;

  /// Emit offsets to lists of entries with identical names. The offsets are
  /// relative to the Base argument.
  void emitOffsets(const MCSymbol *Base) const;

public:
  AccelTableEmitter(AsmPrinter *Asm, const AccelTableBase &Contents,
                    bool SkipIdenticalHashes)
      : Asm(Asm), Contents(Contents), SkipIdenticalHashes(SkipIdenticalHashes) {
  }
};

class AppleAccelTableEmitter : public AccelTableEmitter {
  using Atom = AppleAccelTableData::Atom;

  /// The fixed header of an Apple Accelerator Table.
  struct Header {
    uint32_t Magic = MagicHash;
    uint16_t Version = 1;
    uint16_t HashFunction = dwarf::DW_hash_function_djb;
    uint32_t BucketCount;
    uint32_t HashCount;
    uint32_t HeaderDataLength;

    /// 'HASH' magic value to detect endianness.
    static const uint32_t MagicHash = 0x48415348;

    Header(uint32_t BucketCount, uint32_t UniqueHashCount, uint32_t DataLength)
        : BucketCount(BucketCount), HashCount(UniqueHashCount),
          HeaderDataLength(DataLength) {}

    void emit(AsmPrinter *Asm) const;
#ifndef NDEBUG
    void print(raw_ostream &OS) const;
    void dump() const { print(dbgs()); }
#endif
  };

  /// The HeaderData describes the structure of an Apple accelerator table
  /// through a list of Atoms.
  struct HeaderData {
    /// In the case of data that is referenced via DW_FORM_ref_* the offset
    /// base is used to describe the offset for all forms in the list of atoms.
    uint32_t DieOffsetBase;

    const SmallVector<Atom, 4> Atoms;

    HeaderData(ArrayRef<Atom> AtomList, uint32_t Offset = 0)
        : DieOffsetBase(Offset), Atoms(AtomList.begin(), AtomList.end()) {}

    void emit(AsmPrinter *Asm) const;
#ifndef NDEBUG
    void print(raw_ostream &OS) const;
    void dump() const { print(dbgs()); }
#endif
  };

  Header Header;
  HeaderData HeaderData;
  const MCSymbol *SecBegin;

  void emitBuckets() const;
  void emitData() const;

public:
  AppleAccelTableEmitter(AsmPrinter *Asm, const AccelTableBase &Contents,
                         ArrayRef<Atom> Atoms, const MCSymbol *SecBegin)
      : AccelTableEmitter(Asm, Contents, true),
        Header(Contents.getBucketCount(), Contents.getUniqueHashCount(),
               8 + (Atoms.size() * 4)),
        HeaderData(Atoms), SecBegin(SecBegin) {}

  void emit() const;

#ifndef NDEBUG
  void print(raw_ostream &OS) const;
  void dump() const { print(dbgs()); }
#endif
};
} // namespace

void AccelTableEmitter::emitHashes() const {
  uint64_t PrevHash = std::numeric_limits<uint64_t>::max();
  unsigned BucketIdx = 0;
  for (auto &Bucket : Contents.getBuckets()) {
    for (auto &Hash : Bucket) {
      uint32_t HashValue = Hash->HashValue;
      if (SkipIdenticalHashes && PrevHash == HashValue)
        continue;
      Asm->OutStreamer->AddComment("Hash in Bucket " + Twine(BucketIdx));
      Asm->EmitInt32(HashValue);
      PrevHash = HashValue;
    }
    BucketIdx++;
  }
}

void AccelTableEmitter::emitOffsets(const MCSymbol *Base) const {
  const auto &Buckets = Contents.getBuckets();
  uint64_t PrevHash = std::numeric_limits<uint64_t>::max();
  for (size_t i = 0, e = Buckets.size(); i < e; ++i) {
    for (auto *Hash : Buckets[i]) {
      uint32_t HashValue = Hash->HashValue;
      if (SkipIdenticalHashes && PrevHash == HashValue)
        continue;
      PrevHash = HashValue;
      Asm->OutStreamer->AddComment("Offset in Bucket " + Twine(i));
      Asm->EmitLabelDifference(Hash->Sym, Base, sizeof(uint32_t));
    }
  }
}

void AppleAccelTableEmitter::Header::emit(AsmPrinter *Asm) const {
  Asm->OutStreamer->AddComment("Header Magic");
  Asm->EmitInt32(Magic);
  Asm->OutStreamer->AddComment("Header Version");
  Asm->EmitInt16(Version);
  Asm->OutStreamer->AddComment("Header Hash Function");
  Asm->EmitInt16(HashFunction);
  Asm->OutStreamer->AddComment("Header Bucket Count");
  Asm->EmitInt32(BucketCount);
  Asm->OutStreamer->AddComment("Header Hash Count");
  Asm->EmitInt32(HashCount);
  Asm->OutStreamer->AddComment("Header Data Length");
  Asm->EmitInt32(HeaderDataLength);
}

void AppleAccelTableEmitter::HeaderData::emit(AsmPrinter *Asm) const {
  Asm->OutStreamer->AddComment("HeaderData Die Offset Base");
  Asm->EmitInt32(DieOffsetBase);
  Asm->OutStreamer->AddComment("HeaderData Atom Count");
  Asm->EmitInt32(Atoms.size());

  for (const Atom &A : Atoms) {
    Asm->OutStreamer->AddComment(dwarf::AtomTypeString(A.Type));
    Asm->EmitInt16(A.Type);
    Asm->OutStreamer->AddComment(dwarf::FormEncodingString(A.Form));
    Asm->EmitInt16(A.Form);
  }
}

void AppleAccelTableEmitter::emitBuckets() const {
  const auto &Buckets = Contents.getBuckets();
  unsigned index = 0;
  for (size_t i = 0, e = Buckets.size(); i < e; ++i) {
    Asm->OutStreamer->AddComment("Bucket " + Twine(i));
    if (!Buckets[i].empty())
      Asm->EmitInt32(index);
    else
      Asm->EmitInt32(std::numeric_limits<uint32_t>::max());
    // Buckets point in the list of hashes, not to the data. Do not increment
    // the index multiple times in case of hash collisions.
    uint64_t PrevHash = std::numeric_limits<uint64_t>::max();
    for (auto *HD : Buckets[i]) {
      uint32_t HashValue = HD->HashValue;
      if (PrevHash != HashValue)
        ++index;
      PrevHash = HashValue;
    }
  }
}

void AppleAccelTableEmitter::emitData() const {
  const auto &Buckets = Contents.getBuckets();
  for (size_t i = 0, e = Buckets.size(); i < e; ++i) {
    uint64_t PrevHash = std::numeric_limits<uint64_t>::max();
    for (auto &Hash : Buckets[i]) {
      // Terminate the previous entry if there is no hash collision with the
      // current one.
      if (PrevHash != std::numeric_limits<uint64_t>::max() &&
          PrevHash != Hash->HashValue)
        Asm->EmitInt32(0);
      // Remember to emit the label for our offset.
      Asm->OutStreamer->EmitLabel(Hash->Sym);
      Asm->OutStreamer->AddComment(Hash->Name.getString());
      Asm->emitDwarfStringOffset(Hash->Name);
      Asm->OutStreamer->AddComment("Num DIEs");
      Asm->EmitInt32(Hash->Values.size());
      for (const auto *V : Hash->Values)
        static_cast<const AppleAccelTableData *>(V)->emit(Asm);
      PrevHash = Hash->HashValue;
    }
    // Emit the final end marker for the bucket.
    if (!Buckets[i].empty())
      Asm->EmitInt32(0);
  }
}

void AppleAccelTableEmitter::emit() const {
  Header.emit(Asm);
  HeaderData.emit(Asm);
  emitBuckets();
  emitHashes();
  emitOffsets(SecBegin);
  emitData();
}

void llvm::emitAppleAccelTableImpl(AsmPrinter *Asm, AccelTableBase &Contents,
                                   StringRef Prefix, const MCSymbol *SecBegin,
                                   ArrayRef<AppleAccelTableData::Atom> Atoms) {
  Contents.finalize(Asm, Prefix);
  AppleAccelTableEmitter(Asm, Contents, Atoms, SecBegin).emit();
}

void AppleAccelTableOffsetData::emit(AsmPrinter *Asm) const {
  Asm->EmitInt32(Die->getDebugSectionOffset());
}

void AppleAccelTableTypeData::emit(AsmPrinter *Asm) const {
  Asm->EmitInt32(Die->getDebugSectionOffset());
  Asm->EmitInt16(Die->getTag());
  Asm->EmitInt8(0);
}

void AppleAccelTableStaticOffsetData::emit(AsmPrinter *Asm) const {
  Asm->EmitInt32(Offset);
}

void AppleAccelTableStaticTypeData::emit(AsmPrinter *Asm) const {
  Asm->EmitInt32(Offset);
  Asm->EmitInt16(Tag);
  Asm->EmitInt8(ObjCClassIsImplementation ? dwarf::DW_FLAG_type_implementation
                                          : 0);
  Asm->EmitInt32(QualifiedNameHash);
}

#ifndef _MSC_VER
// The lines below are rejected by older versions (TBD) of MSVC.
constexpr AppleAccelTableData::Atom AppleAccelTableTypeData::Atoms[];
constexpr AppleAccelTableData::Atom AppleAccelTableOffsetData::Atoms[];
constexpr AppleAccelTableData::Atom AppleAccelTableStaticOffsetData::Atoms[];
constexpr AppleAccelTableData::Atom AppleAccelTableStaticTypeData::Atoms[];
#else
// FIXME: Erase this path once the minimum MSCV version has been bumped.
const SmallVector<AppleAccelTableData::Atom, 4>
    AppleAccelTableOffsetData::Atoms = {
        Atom(dwarf::DW_ATOM_die_offset, dwarf::DW_FORM_data4)};
const SmallVector<AppleAccelTableData::Atom, 4> AppleAccelTableTypeData::Atoms =
    {Atom(dwarf::DW_ATOM_die_offset, dwarf::DW_FORM_data4),
     Atom(dwarf::DW_ATOM_die_tag, dwarf::DW_FORM_data2),
     Atom(dwarf::DW_ATOM_type_flags, dwarf::DW_FORM_data1)};
const SmallVector<AppleAccelTableData::Atom, 4>
    AppleAccelTableStaticOffsetData::Atoms = {
        Atom(dwarf::DW_ATOM_die_offset, dwarf::DW_FORM_data4)};
const SmallVector<AppleAccelTableData::Atom, 4>
    AppleAccelTableStaticTypeData::Atoms = {
        Atom(dwarf::DW_ATOM_die_offset, dwarf::DW_FORM_data4),
        Atom(dwarf::DW_ATOM_die_tag, dwarf::DW_FORM_data2),
        Atom(5, dwarf::DW_FORM_data1), Atom(6, dwarf::DW_FORM_data4)};
#endif

#ifndef NDEBUG
void AppleAccelTableEmitter::Header::print(raw_ostream &OS) const {
  OS << "Magic: " << format("0x%x", Magic) << "\n"
     << "Version: " << Version << "\n"
     << "Hash Function: " << HashFunction << "\n"
     << "Bucket Count: " << BucketCount << "\n"
     << "Header Data Length: " << HeaderDataLength << "\n";
}

void AppleAccelTableData::Atom::print(raw_ostream &OS) const {
  OS << "Type: " << dwarf::AtomTypeString(Type) << "\n"
     << "Form: " << dwarf::FormEncodingString(Form) << "\n";
}

void AppleAccelTableEmitter::HeaderData::print(raw_ostream &OS) const {
  OS << "DIE Offset Base: " << DieOffsetBase << "\n";
  for (auto Atom : Atoms)
    Atom.print(OS);
}

void AppleAccelTableEmitter::print(raw_ostream &OS) const {
  Header.print(OS);
  HeaderData.print(OS);
  Contents.print(OS);
  SecBegin->print(OS, nullptr);
}

void AccelTableBase::HashData::print(raw_ostream &OS) const {
  OS << "Name: " << Name.getString() << "\n";
  OS << "  Hash Value: " << format("0x%x", HashValue) << "\n";
  OS << "  Symbol: ";
  if (Sym)
    OS << *Sym;
  else
    OS << "<none>";
  OS << "\n";
  for (auto *Value : Values)
    Value->print(OS);
}

void AccelTableBase::print(raw_ostream &OS) const {
  // Print Content.
  OS << "Entries: \n";
  for (const auto &Entry : Entries) {
    OS << "Name: " << Entry.first() << "\n";
    for (auto *V : Entry.second.Values)
      V->print(OS);
  }

  OS << "Buckets and Hashes: \n";
  for (auto &Bucket : Buckets)
    for (auto &Hash : Bucket)
      Hash->print(OS);

  OS << "Data: \n";
  for (auto &E : Entries)
    E.second.print(OS);
}

void AppleAccelTableOffsetData::print(raw_ostream &OS) const {
  OS << "  Offset: " << Die->getOffset() << "\n";
}

void AppleAccelTableTypeData::print(raw_ostream &OS) const {
  OS << "  Offset: " << Die->getOffset() << "\n";
  OS << "  Tag: " << dwarf::TagString(Die->getTag()) << "\n";
}

void AppleAccelTableStaticOffsetData::print(raw_ostream &OS) const {
  OS << "  Static Offset: " << Offset << "\n";
}

void AppleAccelTableStaticTypeData::print(raw_ostream &OS) const {
  OS << "  Static Offset: " << Offset << "\n";
  OS << "  QualifiedNameHash: " << format("%x\n", QualifiedNameHash) << "\n";
  OS << "  Tag: " << dwarf::TagString(Tag) << "\n";
  OS << "  ObjCClassIsImplementation: "
     << (ObjCClassIsImplementation ? "true" : "false");
  OS << "\n";
}
#endif