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      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 }
    190