llvm/lib/CodeGen/AsmPrinter/DwarfAccelTable.cpp

//===- llvm/CodeGen/DwarfAccelTable.cpp - Dwarf 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 dwarf accelerator tables.
//
//===----------------------------------------------------------------------===//

#include "DwarfAccelTable.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 <cassert>
#include <cstddef>
#include <cstdint>
#include <iterator>
#include <limits>
#include <vector>

using namespace llvm;

// The length of the header data is always going to be 4 + 4 + 4*NumAtoms.
DwarfAccelTable::DwarfAccelTable(ArrayRef<DwarfAccelTable::Atom> atomList)
    : Header(8 + (atomList.size() * 4)), HeaderData(atomList),
      Entries(Allocator) {}

void DwarfAccelTable::AddName(DwarfStringPoolEntryRef Name, const DIE *die,
                              char Flags) {
  assert(Data.empty() && "Already finalized!");
  // If the string is in the list already then add this die to the list
  // otherwise add a new one.
  DataArray &DIEs = Entries[Name.getString()];
  assert(!DIEs.Name || DIEs.Name == Name);
  DIEs.Name = Name;
  DIEs.Values.push_back(new (Allocator) HashDataContents(die, Flags));
}

void DwarfAccelTable::ComputeBucketCount() {
  // First get the number of unique hashes.
  std::vector<uint32_t> uniques(Data.size());
  for (size_t i = 0, e = Data.size(); i < e; ++i)
    uniques[i] = Data[i]->HashValue;
  array_pod_sort(uniques.begin(), uniques.end());
  std::vector<uint32_t>::iterator p =
      std::unique(uniques.begin(), uniques.end());
  uint32_t num = std::distance(uniques.begin(), p);

  // Then compute the bucket size, minimum of 1 bucket.
  if (num > 1024)
    Header.bucket_count = num / 4;
  else if (num > 16)
    Header.bucket_count = num / 2;
  else
    Header.bucket_count = num > 0 ? num : 1;

  Header.hashes_count = num;
}

// compareDIEs - comparison predicate that sorts DIEs by their offset.
static bool compareDIEs(const DwarfAccelTable::HashDataContents *A,
                        const DwarfAccelTable::HashDataContents *B) {
  return A->Die->getOffset() < B->Die->getOffset();
}

void DwarfAccelTable::FinalizeTable(AsmPrinter *Asm, StringRef Prefix) {
  // Create the individual hash data outputs.
  Data.reserve(Entries.size());
  for (StringMap<DataArray>::iterator EI = Entries.begin(), EE = Entries.end();
       EI != EE; ++EI) {

    // Unique the entries.
    std::stable_sort(EI->second.Values.begin(), EI->second.Values.end(), compareDIEs);
    EI->second.Values.erase(
        std::unique(EI->second.Values.begin(), EI->second.Values.end()),
        EI->second.Values.end());

    HashData *Entry = new (Allocator) HashData(EI->getKey(), EI->second);
    Data.push_back(Entry);
  }

  // Figure out how many buckets we need, then compute the bucket
  // contents and the final ordering. We'll emit the hashes and offsets
  // by doing a walk during the emission phase. We add temporary
  // symbols to the data so that we can reference them during the offset
  // later, we'll emit them when we emit the data.
  ComputeBucketCount();

  // Compute bucket contents and final ordering.
  Buckets.resize(Header.bucket_count);
  for (size_t i = 0, e = Data.size(); i < e; ++i) {
    uint32_t bucket = Data[i]->HashValue % Header.bucket_count;
    Buckets[bucket].push_back(Data[i]);
    Data[i]->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 (size_t i = 0; i < Buckets.size(); ++i)
    std::stable_sort(Buckets[i].begin(), Buckets[i].end(),
                     [] (HashData *LHS, HashData *RHS) {
                       return LHS->HashValue < RHS->HashValue;
                     });
}

// Emits the header for the table via the AsmPrinter.
void DwarfAccelTable::EmitHeader(AsmPrinter *Asm) {
  Asm->OutStreamer->AddComment("Header Magic");
  Asm->EmitInt32(Header.magic);
  Asm->OutStreamer->AddComment("Header Version");
  Asm->EmitInt16(Header.version);
  Asm->OutStreamer->AddComment("Header Hash Function");
  Asm->EmitInt16(Header.hash_function);
  Asm->OutStreamer->AddComment("Header Bucket Count");
  Asm->EmitInt32(Header.bucket_count);
  Asm->OutStreamer->AddComment("Header Hash Count");
  Asm->EmitInt32(Header.hashes_count);
  Asm->OutStreamer->AddComment("Header Data Length");
  Asm->EmitInt32(Header.header_data_len);
  Asm->OutStreamer->AddComment("HeaderData Die Offset Base");
  Asm->EmitInt32(HeaderData.die_offset_base);
  Asm->OutStreamer->AddComment("HeaderData Atom Count");
  Asm->EmitInt32(HeaderData.Atoms.size());
  for (size_t i = 0; i < HeaderData.Atoms.size(); i++) {
    Atom A = HeaderData.Atoms[i];
    Asm->OutStreamer->AddComment(dwarf::AtomTypeString(A.type));
    Asm->EmitInt16(A.type);
    Asm->OutStreamer->AddComment(dwarf::FormEncodingString(A.form));
    Asm->EmitInt16(A.form);
  }
}

// Walk through and emit the buckets for the table. Each index is
// an offset into the list of hashes.
void DwarfAccelTable::EmitBuckets(AsmPrinter *Asm) {
  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;
    }
  }
}

// Walk through the buckets and emit the individual hashes for each
// bucket.
void DwarfAccelTable::EmitHashes(AsmPrinter *Asm) {
  uint64_t PrevHash = std::numeric_limits<uint64_t>::max();
  for (size_t i = 0, e = Buckets.size(); i < e; ++i) {
    for (HashList::const_iterator HI = Buckets[i].begin(),
                                  HE = Buckets[i].end();
         HI != HE; ++HI) {
      uint32_t HashValue = (*HI)->HashValue;
      if (PrevHash == HashValue)
        continue;
      Asm->OutStreamer->AddComment("Hash in Bucket " + Twine(i));
      Asm->EmitInt32(HashValue);
      PrevHash = HashValue;
    }
  }
}

// Walk through the buckets and emit the individual offsets for each
// element in each bucket. This is done via a symbol subtraction from the
// beginning of the section. The non-section symbol will be output later
// when we emit the actual data.
void DwarfAccelTable::emitOffsets(AsmPrinter *Asm, const MCSymbol *SecBegin) {
  uint64_t PrevHash = std::numeric_limits<uint64_t>::max();
  for (size_t i = 0, e = Buckets.size(); i < e; ++i) {
    for (HashList::const_iterator HI = Buckets[i].begin(),
                                  HE = Buckets[i].end();
         HI != HE; ++HI) {
      uint32_t HashValue = (*HI)->HashValue;
      if (PrevHash == HashValue)
        continue;
      PrevHash = HashValue;
      Asm->OutStreamer->AddComment("Offset in Bucket " + Twine(i));
      MCContext &Context = Asm->OutStreamer->getContext();
      const MCExpr *Sub = MCBinaryExpr::createSub(
          MCSymbolRefExpr::create((*HI)->Sym, Context),
          MCSymbolRefExpr::create(SecBegin, Context), Context);
      Asm->OutStreamer->EmitValue(Sub, sizeof(uint32_t));
    }
  }
}

// Walk through the buckets and emit the full data for each element in
// the bucket. For the string case emit the dies and the various offsets.
// Terminate each HashData bucket with 0.
void DwarfAccelTable::EmitData(AsmPrinter *Asm, DwarfDebug *D) {
  for (size_t i = 0, e = Buckets.size(); i < e; ++i) {
    uint64_t PrevHash = std::numeric_limits<uint64_t>::max();
    for (HashList::const_iterator HI = Buckets[i].begin(),
                                  HE = Buckets[i].end();
         HI != HE; ++HI) {
      // Terminate the previous entry if there is no hash collision
      // with the current one.
      if (PrevHash != std::numeric_limits<uint64_t>::max() &&
          PrevHash != (*HI)->HashValue)
        Asm->EmitInt32(0);
      // Remember to emit the label for our offset.
      Asm->OutStreamer->EmitLabel((*HI)->Sym);
      Asm->OutStreamer->AddComment((*HI)->Str);
      Asm->emitDwarfStringOffset((*HI)->Data.Name);
      Asm->OutStreamer->AddComment("Num DIEs");
      Asm->EmitInt32((*HI)->Data.Values.size());
      for (HashDataContents *HD : (*HI)->Data.Values) {
        // Emit the DIE offset
        Asm->EmitInt32(HD->Die->getDebugSectionOffset());
        // If we have multiple Atoms emit that info too.
        // FIXME: A bit of a hack, we either emit only one atom or all info.
        if (HeaderData.Atoms.size() > 1) {
          Asm->EmitInt16(HD->Die->getTag());
          Asm->EmitInt8(HD->Flags);
        }
      }
      PrevHash = (*HI)->HashValue;
    }
    // Emit the final end marker for the bucket.
    if (!Buckets[i].empty())
      Asm->EmitInt32(0);
  }
}

// Emit the entire data structure to the output file.
void DwarfAccelTable::emit(AsmPrinter *Asm, const MCSymbol *SecBegin,
                           DwarfDebug *D) {
  // Emit the header.
  EmitHeader(Asm);

  // Emit the buckets.
  EmitBuckets(Asm);

  // Emit the hashes.
  EmitHashes(Asm);

  // Emit the offsets.
  emitOffsets(Asm, SecBegin);

  // Emit the hash data.
  EmitData(Asm, D);
}

#ifndef NDEBUG
void DwarfAccelTable::print(raw_ostream &OS) {
  Header.print(OS);
  HeaderData.print(OS);

  OS << "Entries: \n";
  for (StringMap<DataArray>::const_iterator EI = Entries.begin(),
                                            EE = Entries.end();
       EI != EE; ++EI) {
    OS << "Name: " << EI->getKeyData() << "\n";
    for (HashDataContents *HD : EI->second.Values)
      HD->print(OS);
  }

  OS << "Buckets and Hashes: \n";
  for (size_t i = 0, e = Buckets.size(); i < e; ++i)
    for (HashList::const_iterator HI = Buckets[i].begin(),
                                  HE = Buckets[i].end();
         HI != HE; ++HI)
      (*HI)->print(OS);

  OS << "Data: \n";
  for (std::vector<HashData *>::const_iterator DI = Data.begin(),
                                               DE = Data.end();
       DI != DE; ++DI)
    (*DI)->print(OS);
}
#endif