lib/MC/StringTableBuilder.cpp

   1 //===- StringTableBuilder.cpp - String table building utility -------------===//
   2 //
   3 //                     The LLVM Compiler Infrastructure
   4 //
   5 // This file is distributed under the University of Illinois Open Source
   6 // License. See LICENSE.TXT for details.
   7 //
   8 //===----------------------------------------------------------------------===//
   9
  10 #include "llvm/MC/StringTableBuilder.h"
  11 #include "llvm/ADT/CachedHashString.h"
  12 #include "llvm/ADT/SmallString.h"
  13 #include "llvm/ADT/StringRef.h"
  14 #include "llvm/BinaryFormat/COFF.h"
  15 #include "llvm/Support/Endian.h"
  16 #include "llvm/Support/MathExtras.h"
  17 #include "llvm/Support/raw_ostream.h"
  18 #include <cassert>
  19 #include <cstddef>
  20 #include <cstdint>
  21 #include <cstring>
  22 #include <utility>
  23 #include <vector>
  24
  25 using namespace llvm;
  26
  27 StringTableBuilder::~StringTableBuilder() = default;
  28
  29 void StringTableBuilder::initSize() {
  30   // Account for leading bytes in table so that offsets returned from add are
  31   // correct.
  32   switch (K) {
  33   case RAW:
  34   case DWARF:
  35     Size = 0;
  36     break;
  37   case MachO:
  38   case ELF:
  39     // Start the table with a NUL byte.
  40     Size = 1;
  41     break;
  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   if (K != WinCOFF)
  72     return;
  73   support::endian::write32le(Buf, Size);
  74 }
  75
  76 // Returns the character at Pos from end of a string.
  77 static int charTailAt(StringPair *P, size_t Pos) {
  78   StringRef S = P->first.val();
  79   if (Pos >= S.size())
  80     return -1;
  81   return (unsigned char)S[S.size() - Pos - 1];
  82 }
  83
  84 // Three-way radix quicksort. This is much faster than std::sort with strcmp
  85 // because it does not compare characters that we already know the same.
  86 static void multikeySort(MutableArrayRef<StringPair *> Vec, int Pos) {
  87 tailcall:
  88   if (Vec.size() <= 1)
  89     return;
  90
  91   // Partition items so that items in [0, I) are greater than the pivot,
  92   // [I, J) are the same as the pivot, and [J, Vec.size()) are less than
  93   // the pivot.
  94   int Pivot = charTailAt(Vec[0], Pos);
  95   size_t I = 0;
  96   size_t J = Vec.size();
  97   for (size_t K = 1; K < J;) {
  98     int C = charTailAt(Vec[K], Pos);
  99     if (C > Pivot)
 100       std::swap(Vec[I++], Vec[K++]);
 101     else if (C < Pivot)
 102       std::swap(Vec[--J], Vec[K]);
 103     else
 104       K++;
 105   }
 106
 107   multikeySort(Vec.slice(0, I), Pos);
 108   multikeySort(Vec.slice(J), Pos);
 109
 110   // multikeySort(Vec.slice(I, J - I), Pos + 1), but with
 111   // tail call optimization.
 112   if (Pivot != -1) {
 113     Vec = Vec.slice(I, J - I);
 114     ++Pos;
 115     goto tailcall;
 116   }
 117 }
 118
 119 void StringTableBuilder::finalize() {
 120   assert(K != DWARF);
 121   finalizeStringTable(/*Optimize=*/true);
 122 }
 123
 124 void StringTableBuilder::finalizeInOrder() {
 125   finalizeStringTable(/*Optimize=*/false);
 126 }
 127
 128 void StringTableBuilder::finalizeStringTable(bool Optimize) {
 129   Finalized = true;
 130
 131   if (Optimize) {
 132     std::vector<StringPair *> Strings;
 133     Strings.reserve(StringIndexMap.size());
 134     for (StringPair &P : StringIndexMap)
 135       Strings.push_back(&P);
 136
 137     multikeySort(Strings, 0);
 138     initSize();
 139
 140     StringRef Previous;
 141     for (StringPair *P : Strings) {
 142       StringRef S = P->first.val();
 143       if (Previous.endswith(S)) {
 144         size_t Pos = Size - S.size() - (K != RAW);
 145         if (!(Pos & (Alignment - 1))) {
 146           P->second = Pos;
 147           continue;
 148         }
 149       }
 150
 151       Size = alignTo(Size, Alignment);
 152       P->second = Size;
 153
 154       Size += S.size();
 155       if (K != RAW)
 156         ++Size;
 157       Previous = S;
 158     }
 159   }
 160
 161   if (K == MachO)
 162     Size = alignTo(Size, 4); // Pad to multiple of 4.
 163 }
 164
 165 void StringTableBuilder::clear() {
 166   Finalized = false;
 167   StringIndexMap.clear();
 168 }
 169
 170 size_t StringTableBuilder::getOffset(CachedHashStringRef S) const {
 171   assert(isFinalized());
 172   auto I = StringIndexMap.find(S);
 173   assert(I != StringIndexMap.end() && "String is not in table!");
 174   return I->second;
 175 }
 176
 177 size_t StringTableBuilder::add(CachedHashStringRef S) {
 178   if (K == WinCOFF)
 179     assert(S.size() > COFF::NameSize && "Short string in COFF string table!");
 180
 181   assert(!isFinalized());
 182   auto P = StringIndexMap.insert(std::make_pair(S, 0));
 183   if (P.second) {
 184     size_t Start = alignTo(Size, Alignment);
 185     P.first->second = Start;
 186     Size = Start + S.size() + (K != RAW);
 187   }
 188   return P.first->second;
 189 }