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 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 WinCOFF: 42 // Make room to write the table size later. 43 Size = 4; 44 break; 45 } 46 } 47 48 StringTableBuilder::StringTableBuilder(Kind K, unsigned Alignment) 49 : K(K), Alignment(Alignment) { 50 initSize(); 51 } 52 53 void StringTableBuilder::write(raw_ostream &OS) const { 54 assert(isFinalized()); 55 SmallString<0> Data; 56 Data.resize(getSize()); 57 write((uint8_t *)Data.data()); 58 OS << Data; 59 } 60 61 using StringPair = std::pair<CachedHashStringRef, size_t>; 62 63 void StringTableBuilder::write(uint8_t *Buf) const { 64 assert(isFinalized()); 65 for (const StringPair &P : StringIndexMap) { 66 StringRef Data = P.first.val(); 67 if (!Data.empty()) 68 memcpy(Buf + P.second, Data.data(), Data.size()); 69 } 70 if (K != WinCOFF) 71 return; 72 support::endian::write32le(Buf, Size); 73 } 74 75 // Returns the character at Pos from end of a string. 76 static int charTailAt(StringPair *P, size_t Pos) { 77 StringRef S = P->first.val(); 78 if (Pos >= S.size()) 79 return -1; 80 return (unsigned char)S[S.size() - Pos - 1]; 81 } 82 83 // Three-way radix quicksort. This is much faster than std::sort with strcmp 84 // because it does not compare characters that we already know the same. 85 static void multikey_qsort(StringPair **Begin, StringPair **End, int Pos) { 86 tailcall: 87 if (End - Begin <= 1) 88 return; 89 90 // Partition items. Items in [Begin, P) are greater than the pivot, 91 // [P, Q) are the same as the pivot, and [Q, End) are less than the pivot. 92 int Pivot = charTailAt(*Begin, Pos); 93 StringPair **P = Begin; 94 StringPair **Q = End; 95 for (StringPair **R = Begin + 1; R < Q;) { 96 int C = charTailAt(*R, Pos); 97 if (C > Pivot) 98 std::swap(*P++, *R++); 99 else if (C < Pivot) 100 std::swap(*--Q, *R); 101 else 102 R++; 103 } 104 105 multikey_qsort(Begin, P, Pos); 106 multikey_qsort(Q, End, Pos); 107 if (Pivot != -1) { 108 // qsort(P, Q, Pos + 1), but with tail call optimization. 109 Begin = P; 110 End = Q; 111 ++Pos; 112 goto tailcall; 113 } 114 } 115 116 void StringTableBuilder::finalize() { 117 finalizeStringTable(/*Optimize=*/true); 118 } 119 120 void StringTableBuilder::finalizeInOrder() { 121 finalizeStringTable(/*Optimize=*/false); 122 } 123 124 void StringTableBuilder::finalizeStringTable(bool Optimize) { 125 Finalized = true; 126 127 if (Optimize) { 128 std::vector<StringPair *> Strings; 129 Strings.reserve(StringIndexMap.size()); 130 for (StringPair &P : StringIndexMap) 131 Strings.push_back(&P); 132 133 if (!Strings.empty()) { 134 // If we're optimizing, sort by name. If not, sort by previously assigned 135 // offset. 136 multikey_qsort(&Strings[0], &Strings[0] + Strings.size(), 0); 137 } 138 139 initSize(); 140 141 StringRef Previous; 142 for (StringPair *P : Strings) { 143 StringRef S = P->first.val(); 144 if (Previous.endswith(S)) { 145 size_t Pos = Size - S.size() - (K != RAW); 146 if (!(Pos & (Alignment - 1))) { 147 P->second = Pos; 148 continue; 149 } 150 } 151 152 Size = alignTo(Size, Alignment); 153 P->second = Size; 154 155 Size += S.size(); 156 if (K != RAW) 157 ++Size; 158 Previous = S; 159 } 160 } 161 162 if (K == MachO) 163 Size = alignTo(Size, 4); // Pad to multiple of 4. 164 } 165 166 void StringTableBuilder::clear() { 167 Finalized = false; 168 StringIndexMap.clear(); 169 } 170 171 size_t StringTableBuilder::getOffset(CachedHashStringRef S) const { 172 assert(isFinalized()); 173 auto I = StringIndexMap.find(S); 174 assert(I != StringIndexMap.end() && "String is not in table!"); 175 return I->second; 176 } 177 178 size_t StringTableBuilder::add(CachedHashStringRef S) { 179 if (K == WinCOFF) 180 assert(S.size() > COFF::NameSize && "Short string in COFF string table!"); 181 182 assert(!isFinalized()); 183 auto P = StringIndexMap.insert(std::make_pair(S, 0)); 184 if (P.second) { 185 size_t Start = alignTo(Size, Alignment); 186 P.first->second = Start; 187 Size = Start + S.size() + (K != RAW); 188 } 189 return P.first->second; 190 } 191