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1 //===- llvm/Support/Parallel.h - Parallel algorithms ----------------------===//
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2 //
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3 // The LLVM Compiler Infrastructure
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4 //
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5 // This file is distributed under the University of Illinois Open Source
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6 // License. See LICENSE.TXT for details.
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7 //
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8 //===----------------------------------------------------------------------===//
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9
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10 #ifndef LLVM_SUPPORT_PARALLEL_H
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11 #define LLVM_SUPPORT_PARALLEL_H
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12
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13 #include "llvm/ADT/STLExtras.h"
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14 #include "llvm/Config/llvm-config.h"
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15 #include "llvm/Support/MathExtras.h"
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16
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17 #include <algorithm>
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18 #include <condition_variable>
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19 #include <functional>
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20 #include <mutex>
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21
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22 #if defined(_MSC_VER) && LLVM_ENABLE_THREADS
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23 #pragma warning(push)
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24 #pragma warning(disable : 4530)
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25 #include <concrt.h>
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26 #include <ppl.h>
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27 #pragma warning(pop)
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28 #endif
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29
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30 namespace llvm {
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31
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32 namespace parallel {
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33 struct sequential_execution_policy {};
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34 struct parallel_execution_policy {};
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35
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36 template <typename T>
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37 struct is_execution_policy
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38 : public std::integral_constant<
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39 bool, llvm::is_one_of<T, sequential_execution_policy,
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40 parallel_execution_policy>::value> {};
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41
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42 constexpr sequential_execution_policy seq{};
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43 constexpr parallel_execution_policy par{};
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44
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45 namespace detail {
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46
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47 #if LLVM_ENABLE_THREADS
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48
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49 class Latch {
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50 uint32_t Count;
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51 mutable std::mutex Mutex;
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52 mutable std::condition_variable Cond;
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53
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54 public:
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55 explicit Latch(uint32_t Count = 0) : Count(Count) {}
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56 ~Latch() { sync(); }
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57
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58 void inc() {
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59 std::unique_lock<std::mutex> lock(Mutex);
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60 ++Count;
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61 }
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62
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63 void dec() {
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64 std::unique_lock<std::mutex> lock(Mutex);
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65 if (--Count == 0)
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66 Cond.notify_all();
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67 }
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68
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69 void sync() const {
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70 std::unique_lock<std::mutex> lock(Mutex);
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71 Cond.wait(lock, [&] { return Count == 0; });
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72 }
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73 };
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74
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75 class TaskGroup {
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76 Latch L;
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77
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78 public:
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79 void spawn(std::function<void()> f);
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80
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81 void sync() const { L.sync(); }
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82 };
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83
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84 #if defined(_MSC_VER)
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85 template <class RandomAccessIterator, class Comparator>
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86 void parallel_sort(RandomAccessIterator Start, RandomAccessIterator End,
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87 const Comparator &Comp) {
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88 concurrency::parallel_sort(Start, End, Comp);
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89 }
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90 template <class IterTy, class FuncTy>
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91 void parallel_for_each(IterTy Begin, IterTy End, FuncTy Fn) {
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92 concurrency::parallel_for_each(Begin, End, Fn);
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93 }
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94
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95 template <class IndexTy, class FuncTy>
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96 void parallel_for_each_n(IndexTy Begin, IndexTy End, FuncTy Fn) {
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97 concurrency::parallel_for(Begin, End, Fn);
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98 }
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99
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100 #else
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101 const ptrdiff_t MinParallelSize = 1024;
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102
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103 /// \brief Inclusive median.
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104 template <class RandomAccessIterator, class Comparator>
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105 RandomAccessIterator medianOf3(RandomAccessIterator Start,
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106 RandomAccessIterator End,
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107 const Comparator &Comp) {
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108 RandomAccessIterator Mid = Start + (std::distance(Start, End) / 2);
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109 return Comp(*Start, *(End - 1))
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110 ? (Comp(*Mid, *(End - 1)) ? (Comp(*Start, *Mid) ? Mid : Start)
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111 : End - 1)
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112 : (Comp(*Mid, *Start) ? (Comp(*(End - 1), *Mid) ? Mid : End - 1)
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113 : Start);
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114 }
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115
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116 template <class RandomAccessIterator, class Comparator>
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117 void parallel_quick_sort(RandomAccessIterator Start, RandomAccessIterator End,
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118 const Comparator &Comp, TaskGroup &TG, size_t Depth) {
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119 // Do a sequential sort for small inputs.
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120 if (std::distance(Start, End) < detail::MinParallelSize || Depth == 0) {
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121 std::sort(Start, End, Comp);
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122 return;
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123 }
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124
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125 // Partition.
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126 auto Pivot = medianOf3(Start, End, Comp);
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127 // Move Pivot to End.
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128 std::swap(*(End - 1), *Pivot);
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129 Pivot = std::partition(Start, End - 1, [&Comp, End](decltype(*Start) V) {
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130 return Comp(V, *(End - 1));
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131 });
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132 // Move Pivot to middle of partition.
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133 std::swap(*Pivot, *(End - 1));
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134
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135 // Recurse.
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136 TG.spawn([=, &Comp, &TG] {
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137 parallel_quick_sort(Start, Pivot, Comp, TG, Depth - 1);
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138 });
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139 parallel_quick_sort(Pivot + 1, End, Comp, TG, Depth - 1);
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140 }
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141
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142 template <class RandomAccessIterator, class Comparator>
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143 void parallel_sort(RandomAccessIterator Start, RandomAccessIterator End,
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144 const Comparator &Comp) {
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145 TaskGroup TG;
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146 parallel_quick_sort(Start, End, Comp, TG,
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147 llvm::Log2_64(std::distance(Start, End)) + 1);
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148 }
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149
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150 template <class IterTy, class FuncTy>
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151 void parallel_for_each(IterTy Begin, IterTy End, FuncTy Fn) {
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152 // TaskGroup has a relatively high overhead, so we want to reduce
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153 // the number of spawn() calls. We'll create up to 1024 tasks here.
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154 // (Note that 1024 is an arbitrary number. This code probably needs
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155 // improving to take the number of available cores into account.)
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156 ptrdiff_t TaskSize = std::distance(Begin, End) / 1024;
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157 if (TaskSize == 0)
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158 TaskSize = 1;
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159
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160 TaskGroup TG;
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161 while (TaskSize < std::distance(Begin, End)) {
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162 TG.spawn([=, &Fn] { std::for_each(Begin, Begin + TaskSize, Fn); });
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163 Begin += TaskSize;
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164 }
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165 std::for_each(Begin, End, Fn);
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166 }
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167
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168 template <class IndexTy, class FuncTy>
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169 void parallel_for_each_n(IndexTy Begin, IndexTy End, FuncTy Fn) {
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170 ptrdiff_t TaskSize = (End - Begin) / 1024;
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171 if (TaskSize == 0)
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172 TaskSize = 1;
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173
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174 TaskGroup TG;
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175 IndexTy I = Begin;
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176 for (; I + TaskSize < End; I += TaskSize) {
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177 TG.spawn([=, &Fn] {
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178 for (IndexTy J = I, E = I + TaskSize; J != E; ++J)
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179 Fn(J);
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180 });
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181 }
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182 for (IndexTy J = I; J < End; ++J)
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183 Fn(J);
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184 }
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185
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186 #endif
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187
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188 #endif
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189
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190 template <typename Iter>
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191 using DefComparator =
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192 std::less<typename std::iterator_traits<Iter>::value_type>;
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193
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194 } // namespace detail
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195
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196 // sequential algorithm implementations.
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197 template <class Policy, class RandomAccessIterator,
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198 class Comparator = detail::DefComparator<RandomAccessIterator>>
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199 void sort(Policy policy, RandomAccessIterator Start, RandomAccessIterator End,
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200 const Comparator &Comp = Comparator()) {
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201 static_assert(is_execution_policy<Policy>::value,
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202 "Invalid execution policy!");
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203 std::sort(Start, End, Comp);
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204 }
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205
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206 template <class Policy, class IterTy, class FuncTy>
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207 void for_each(Policy policy, IterTy Begin, IterTy End, FuncTy Fn) {
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208 static_assert(is_execution_policy<Policy>::value,
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209 "Invalid execution policy!");
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210 std::for_each(Begin, End, Fn);
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211 }
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212
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213 template <class Policy, class IndexTy, class FuncTy>
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214 void for_each_n(Policy policy, IndexTy Begin, IndexTy End, FuncTy Fn) {
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215 static_assert(is_execution_policy<Policy>::value,
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216 "Invalid execution policy!");
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217 for (IndexTy I = Begin; I != End; ++I)
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218 Fn(I);
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219 }
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220
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221 // Parallel algorithm implementations, only available when LLVM_ENABLE_THREADS
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222 // is true.
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223 #if LLVM_ENABLE_THREADS
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224 template <class RandomAccessIterator,
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225 class Comparator = detail::DefComparator<RandomAccessIterator>>
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226 void sort(parallel_execution_policy policy, RandomAccessIterator Start,
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227 RandomAccessIterator End, const Comparator &Comp = Comparator()) {
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228 detail::parallel_sort(Start, End, Comp);
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229 }
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230
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231 template <class IterTy, class FuncTy>
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232 void for_each(parallel_execution_policy policy, IterTy Begin, IterTy End,
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233 FuncTy Fn) {
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234 detail::parallel_for_each(Begin, End, Fn);
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235 }
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236
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237 template <class IndexTy, class FuncTy>
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238 void for_each_n(parallel_execution_policy policy, IndexTy Begin, IndexTy End,
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239 FuncTy Fn) {
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240 detail::parallel_for_each_n(Begin, End, Fn);
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241 }
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242 #endif
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243
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244 } // namespace parallel
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245 } // namespace llvm
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246
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247 #endif // LLVM_SUPPORT_PARALLEL_H
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