lib/MC/StringTableBuilder.cpp

   1 //===- StringTableBuilder.cpp - String table building utility -------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #include "llvm/MC/StringTableBuilder.h"
  10 #include "llvm/ADT/CachedHashString.h"
  11 #include "llvm/ADT/SmallString.h"
  12 #include "llvm/ADT/StringRef.h"
  13 #include "llvm/BinaryFormat/COFF.h"
  14 #include "llvm/Support/Endian.h"
  15 #include "llvm/Support/MathExtras.h"
  16 #include "llvm/Support/raw_ostream.h"
  17 #include <cassert>
  18 #include <cstddef>
  19 #include <cstdint>
  20 #include <cstring>
  21 #include <utility>
  22 #include <vector>
  23
  24 using namespace llvm;
  25
  26 StringTableBuilder::~StringTableBuilder() = default;
  27
  28 void StringTableBuilder::initSize() {
  29   // Account for leading bytes in table so that offsets returned from add are
  30   // correct.
  31   switch (K) {
  32   case RAW:
  33   case DWARF:
  34     Size = 0;
  35     break;
  36   case MachO:
  37   case ELF:
  38     // Start the table with a NUL byte.
  39     Size = 1;
  40     break;
  41   case XCOFF:
  42   case WinCOFF:
  43     // Make room to write the table size later.
  44     Size = 4;
  45     break;
  46   }
  47 }
  48
  49 StringTableBuilder::StringTableBuilder(Kind K, unsigned Alignment)
  50     : K(K), Alignment(Alignment) {
  51   initSize();
  52 }
  53
  54 void StringTableBuilder::write(raw_ostream &OS) const {
  55   assert(isFinalized());
  56   SmallString<0> Data;
  57   Data.resize(getSize());
  58   write((uint8_t *)Data.data());
  59   OS << Data;
  60 }
  61
  62 using StringPair = std::pair<CachedHashStringRef, size_t>;
  63
  64 void StringTableBuilder::write(uint8_t *Buf) const {
  65   assert(isFinalized());
  66   for (const StringPair &P : StringIndexMap) {
  67     StringRef Data = P.first.val();
  68     if (!Data.empty())
  69       memcpy(Buf + P.second, Data.data(), Data.size());
  70   }
  71   // The COFF formats store the size of the string table in the first 4 bytes.
  72   // For Windows, the format is little-endian; for AIX, it is big-endian.
  73   if (K == WinCOFF)
  74     support::endian::write32le(Buf, Size);
  75   else if (K == XCOFF)
  76     support::endian::write32be(Buf, Size);
  77 }
  78
  79 // Returns the character at Pos from end of a string.
  80 static int charTailAt(StringPair *P, size_t Pos) {
  81   StringRef S = P->first.val();
  82   if (Pos >= S.size())
  83     return -1;
  84   return (unsigned char)S[S.size() - Pos - 1];
  85 }
  86
  87 // Three-way radix quicksort. This is much faster than std::sort with strcmp
  88 // because it does not compare characters that we already know the same.
  89 static void multikeySort(MutableArrayRef<StringPair *> Vec, int Pos) {
  90 tailcall:
  91   if (Vec.size() <= 1)
  92     return;
  93
  94   // Partition items so that items in [0, I) are greater than the pivot,
  95   // [I, J) are the same as the pivot, and [J, Vec.size()) are less than
  96   // the pivot.
  97   int Pivot = charTailAt(Vec[0], Pos);
  98   size_t I = 0;
  99   size_t J = Vec.size();
 100   for (size_t K = 1; K < J;) {
 101     int C = charTailAt(Vec[K], Pos);
 102     if (C > Pivot)
 103       std::swap(Vec[I++], Vec[K++]);
 104     else if (C < Pivot)
 105       std::swap(Vec[--J], Vec[K]);
 106     else
 107       K++;
 108   }
 109
 110   multikeySort(Vec.slice(0, I), Pos);
 111   multikeySort(Vec.slice(J), Pos);
 112
 113   // multikeySort(Vec.slice(I, J - I), Pos + 1), but with
 114   // tail call optimization.
 115   if (Pivot != -1) {
 116     Vec = Vec.slice(I, J - I);
 117     ++Pos;
 118     goto tailcall;
 119   }
 120 }
 121
 122 void StringTableBuilder::finalize() {
 123   assert(K != DWARF);
 124   finalizeStringTable(/*Optimize=*/true);
 125 }
 126
 127 void StringTableBuilder::finalizeInOrder() {
 128   finalizeStringTable(/*Optimize=*/false);
 129 }
 130
 131 void StringTableBuilder::finalizeStringTable(bool Optimize) {
 132   Finalized = true;
 133
 134   if (Optimize) {
 135     std::vector<StringPair *> Strings;
 136     Strings.reserve(StringIndexMap.size());
 137     for (StringPair &P : StringIndexMap)
 138       Strings.push_back(&P);
 139
 140     multikeySort(Strings, 0);
 141     initSize();
 142
 143     StringRef Previous;
 144     for (StringPair *P : Strings) {
 145       StringRef S = P->first.val();
 146       if (Previous.endswith(S)) {
 147         size_t Pos = Size - S.size() - (K != RAW);
 148         if (!(Pos & (Alignment - 1))) {
 149           P->second = Pos;
 150           continue;
 151         }
 152       }
 153
 154       Size = alignTo(Size, Alignment);
 155       P->second = Size;
 156
 157       Size += S.size();
 158       if (K != RAW)
 159         ++Size;
 160       Previous = S;
 161     }
 162   }
 163
 164   if (K == MachO)
 165     Size = alignTo(Size, 4); // Pad to multiple of 4.
 166
 167   // The first byte in an ELF string table must be null, according to the ELF
 168   // specification. In 'initSize()' we reserved the first byte to hold null for
 169   // this purpose and here we actually add the string to allow 'getOffset()' to
 170   // be called on an empty string.
 171   if (K == ELF)
 172     StringIndexMap[CachedHashStringRef("")] = 0;
 173 }
 174
 175 void StringTableBuilder::clear() {
 176   Finalized = false;
 177   StringIndexMap.clear();
 178 }
 179
 180 size_t StringTableBuilder::getOffset(CachedHashStringRef S) const {
 181   assert(isFinalized());
 182   auto I = StringIndexMap.find(S);
 183   assert(I != StringIndexMap.end() && "String is not in table!");
 184   return I->second;
 185 }
 186
 187 size_t StringTableBuilder::add(CachedHashStringRef S) {
 188   if (K == WinCOFF)
 189     assert(S.size() > COFF::NameSize && "Short string in COFF string table!");
 190
 191   assert(!isFinalized());
 192   auto P = StringIndexMap.insert(std::make_pair(S, 0));
 193   if (P.second) {
 194     size_t Start = alignTo(Size, Alignment);
 195     P.first->second = Start;
 196     Size = Start + S.size() + (K != RAW);
 197   }
 198   return P.first->second;
 199 }