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1 //===--- HeaderMap.cpp - A file that acts like dir of symlinks ------------===//
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2 //
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3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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4 // See https://llvm.org/LICENSE.txt for license information.
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5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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6 //
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7 //===----------------------------------------------------------------------===//
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8 //
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9 // This file implements the HeaderMap interface.
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10 //
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11 //===----------------------------------------------------------------------===//
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12
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13 #include "clang/Lex/HeaderMap.h"
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14 #include "clang/Lex/HeaderMapTypes.h"
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15 #include "clang/Basic/CharInfo.h"
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16 #include "clang/Basic/FileManager.h"
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17 #include "llvm/ADT/SmallString.h"
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18 #include "llvm/Support/Compiler.h"
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19 #include "llvm/Support/DataTypes.h"
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20 #include "llvm/Support/MathExtras.h"
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21 #include "llvm/Support/MemoryBuffer.h"
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22 #include "llvm/Support/SwapByteOrder.h"
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23 #include "llvm/Support/Debug.h"
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24 #include <cstring>
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25 #include <memory>
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26 using namespace clang;
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27
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28 /// HashHMapKey - This is the 'well known' hash function required by the file
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29 /// format, used to look up keys in the hash table. The hash table uses simple
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30 /// linear probing based on this function.
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31 static inline unsigned HashHMapKey(StringRef Str) {
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32 unsigned Result = 0;
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33 const char *S = Str.begin(), *End = Str.end();
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34
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35 for (; S != End; S++)
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36 Result += toLowercase(*S) * 13;
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37 return Result;
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38 }
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39
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40
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41
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42 //===----------------------------------------------------------------------===//
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43 // Verification and Construction
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44 //===----------------------------------------------------------------------===//
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45
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46 /// HeaderMap::Create - This attempts to load the specified file as a header
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47 /// map. If it doesn't look like a HeaderMap, it gives up and returns null.
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48 /// If it looks like a HeaderMap but is obviously corrupted, it puts a reason
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49 /// into the string error argument and returns null.
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50 std::unique_ptr<HeaderMap> HeaderMap::Create(const FileEntry *FE,
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51 FileManager &FM) {
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52 // If the file is too small to be a header map, ignore it.
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53 unsigned FileSize = FE->getSize();
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54 if (FileSize <= sizeof(HMapHeader)) return nullptr;
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55
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56 auto FileBuffer = FM.getBufferForFile(FE);
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57 if (!FileBuffer || !*FileBuffer)
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58 return nullptr;
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59 bool NeedsByteSwap;
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60 if (!checkHeader(**FileBuffer, NeedsByteSwap))
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61 return nullptr;
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62 return std::unique_ptr<HeaderMap>(new HeaderMap(std::move(*FileBuffer), NeedsByteSwap));
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63 }
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64
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65 bool HeaderMapImpl::checkHeader(const llvm::MemoryBuffer &File,
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66 bool &NeedsByteSwap) {
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67 if (File.getBufferSize() <= sizeof(HMapHeader))
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68 return false;
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69 const char *FileStart = File.getBufferStart();
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70
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71 // We know the file is at least as big as the header, check it now.
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72 const HMapHeader *Header = reinterpret_cast<const HMapHeader*>(FileStart);
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73
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74 // Sniff it to see if it's a headermap by checking the magic number and
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75 // version.
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76 if (Header->Magic == HMAP_HeaderMagicNumber &&
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77 Header->Version == HMAP_HeaderVersion)
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78 NeedsByteSwap = false;
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79 else if (Header->Magic == llvm::ByteSwap_32(HMAP_HeaderMagicNumber) &&
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80 Header->Version == llvm::ByteSwap_16(HMAP_HeaderVersion))
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81 NeedsByteSwap = true; // Mixed endianness headermap.
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82 else
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83 return false; // Not a header map.
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84
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85 if (Header->Reserved != 0)
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86 return false;
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87
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88 // Check the number of buckets. It should be a power of two, and there
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89 // should be enough space in the file for all of them.
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90 uint32_t NumBuckets = NeedsByteSwap
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91 ? llvm::sys::getSwappedBytes(Header->NumBuckets)
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92 : Header->NumBuckets;
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93 if (!llvm::isPowerOf2_32(NumBuckets))
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94 return false;
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95 if (File.getBufferSize() <
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96 sizeof(HMapHeader) + sizeof(HMapBucket) * NumBuckets)
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97 return false;
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98
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99 // Okay, everything looks good.
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100 return true;
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101 }
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102
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103 //===----------------------------------------------------------------------===//
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104 // Utility Methods
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105 //===----------------------------------------------------------------------===//
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106
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107
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108 /// getFileName - Return the filename of the headermap.
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109 StringRef HeaderMapImpl::getFileName() const {
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110 return FileBuffer->getBufferIdentifier();
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111 }
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112
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113 unsigned HeaderMapImpl::getEndianAdjustedWord(unsigned X) const {
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114 if (!NeedsBSwap) return X;
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115 return llvm::ByteSwap_32(X);
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116 }
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117
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118 /// getHeader - Return a reference to the file header, in unbyte-swapped form.
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119 /// This method cannot fail.
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120 const HMapHeader &HeaderMapImpl::getHeader() const {
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121 // We know the file is at least as big as the header. Return it.
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122 return *reinterpret_cast<const HMapHeader*>(FileBuffer->getBufferStart());
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123 }
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124
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125 /// getBucket - Return the specified hash table bucket from the header map,
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126 /// bswap'ing its fields as appropriate. If the bucket number is not valid,
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127 /// this return a bucket with an empty key (0).
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128 HMapBucket HeaderMapImpl::getBucket(unsigned BucketNo) const {
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129 assert(FileBuffer->getBufferSize() >=
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130 sizeof(HMapHeader) + sizeof(HMapBucket) * BucketNo &&
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131 "Expected bucket to be in range");
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132
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133 HMapBucket Result;
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134 Result.Key = HMAP_EmptyBucketKey;
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135
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136 const HMapBucket *BucketArray =
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137 reinterpret_cast<const HMapBucket*>(FileBuffer->getBufferStart() +
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138 sizeof(HMapHeader));
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139 const HMapBucket *BucketPtr = BucketArray+BucketNo;
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140
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141 // Load the values, bswapping as needed.
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142 Result.Key = getEndianAdjustedWord(BucketPtr->Key);
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143 Result.Prefix = getEndianAdjustedWord(BucketPtr->Prefix);
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144 Result.Suffix = getEndianAdjustedWord(BucketPtr->Suffix);
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145 return Result;
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146 }
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147
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148 Optional<StringRef> HeaderMapImpl::getString(unsigned StrTabIdx) const {
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149 // Add the start of the string table to the idx.
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150 StrTabIdx += getEndianAdjustedWord(getHeader().StringsOffset);
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151
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152 // Check for invalid index.
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153 if (StrTabIdx >= FileBuffer->getBufferSize())
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154 return None;
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155
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156 const char *Data = FileBuffer->getBufferStart() + StrTabIdx;
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157 unsigned MaxLen = FileBuffer->getBufferSize() - StrTabIdx;
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158 unsigned Len = strnlen(Data, MaxLen);
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159
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160 // Check whether the buffer is null-terminated.
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161 if (Len == MaxLen && Data[Len - 1])
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162 return None;
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163
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164 return StringRef(Data, Len);
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165 }
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166
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167 //===----------------------------------------------------------------------===//
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168 // The Main Drivers
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169 //===----------------------------------------------------------------------===//
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170
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171 /// dump - Print the contents of this headermap to stderr.
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172 LLVM_DUMP_METHOD void HeaderMapImpl::dump() const {
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173 const HMapHeader &Hdr = getHeader();
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174 unsigned NumBuckets = getEndianAdjustedWord(Hdr.NumBuckets);
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175
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176 llvm::dbgs() << "Header Map " << getFileName() << ":\n " << NumBuckets
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177 << ", " << getEndianAdjustedWord(Hdr.NumEntries) << "\n";
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178
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179 auto getStringOrInvalid = [this](unsigned Id) -> StringRef {
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180 if (Optional<StringRef> S = getString(Id))
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181 return *S;
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182 return "<invalid>";
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183 };
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184
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185 for (unsigned i = 0; i != NumBuckets; ++i) {
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186 HMapBucket B = getBucket(i);
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187 if (B.Key == HMAP_EmptyBucketKey) continue;
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188
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189 StringRef Key = getStringOrInvalid(B.Key);
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190 StringRef Prefix = getStringOrInvalid(B.Prefix);
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191 StringRef Suffix = getStringOrInvalid(B.Suffix);
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192 llvm::dbgs() << " " << i << ". " << Key << " -> '" << Prefix << "' '"
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193 << Suffix << "'\n";
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194 }
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195 }
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196
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197 /// LookupFile - Check to see if the specified relative filename is located in
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198 /// this HeaderMap. If so, open it and return its FileEntry.
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199 Optional<FileEntryRef> HeaderMap::LookupFile(StringRef Filename,
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200 FileManager &FM) const {
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201
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202 SmallString<1024> Path;
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203 StringRef Dest = HeaderMapImpl::lookupFilename(Filename, Path);
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204 if (Dest.empty())
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205 return None;
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206
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207 return FM.getOptionalFileRef(Dest);
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208 }
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209
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210 StringRef HeaderMapImpl::lookupFilename(StringRef Filename,
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211 SmallVectorImpl<char> &DestPath) const {
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212 const HMapHeader &Hdr = getHeader();
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213 unsigned NumBuckets = getEndianAdjustedWord(Hdr.NumBuckets);
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214
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215 // Don't probe infinitely. This should be checked before constructing.
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216 assert(llvm::isPowerOf2_32(NumBuckets) && "Expected power of 2");
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217
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218 // Linearly probe the hash table.
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219 for (unsigned Bucket = HashHMapKey(Filename);; ++Bucket) {
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220 HMapBucket B = getBucket(Bucket & (NumBuckets-1));
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221 if (B.Key == HMAP_EmptyBucketKey) return StringRef(); // Hash miss.
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222
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223 // See if the key matches. If not, probe on.
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224 Optional<StringRef> Key = getString(B.Key);
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225 if (LLVM_UNLIKELY(!Key))
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226 continue;
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227 if (!Filename.equals_lower(*Key))
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228 continue;
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229
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230 // If so, we have a match in the hash table. Construct the destination
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231 // path.
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232 Optional<StringRef> Prefix = getString(B.Prefix);
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233 Optional<StringRef> Suffix = getString(B.Suffix);
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234
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235 DestPath.clear();
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236 if (LLVM_LIKELY(Prefix && Suffix)) {
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237 DestPath.append(Prefix->begin(), Prefix->end());
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238 DestPath.append(Suffix->begin(), Suffix->end());
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239 }
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240 return StringRef(DestPath.begin(), DestPath.size());
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241 }
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242 }
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221
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243
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244 StringRef HeaderMapImpl::reverseLookupFilename(StringRef DestPath) const {
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245 if (!ReverseMap.empty())
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246 return ReverseMap.lookup(DestPath);
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247
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248 const HMapHeader &Hdr = getHeader();
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249 unsigned NumBuckets = getEndianAdjustedWord(Hdr.NumBuckets);
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250 StringRef RetKey;
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251 for (unsigned i = 0; i != NumBuckets; ++i) {
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252 HMapBucket B = getBucket(i);
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253 if (B.Key == HMAP_EmptyBucketKey)
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254 continue;
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255
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256 Optional<StringRef> Key = getString(B.Key);
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257 Optional<StringRef> Prefix = getString(B.Prefix);
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258 Optional<StringRef> Suffix = getString(B.Suffix);
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259 if (LLVM_LIKELY(Key && Prefix && Suffix)) {
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260 SmallVector<char, 1024> Buf;
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261 Buf.append(Prefix->begin(), Prefix->end());
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262 Buf.append(Suffix->begin(), Suffix->end());
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263 StringRef Value(Buf.begin(), Buf.size());
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264 ReverseMap[Value] = *Key;
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265
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266 if (DestPath == Value)
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267 RetKey = *Key;
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268 }
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269 }
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270 return RetKey;
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271 }
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