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1 //===- ProfileSummaryInfo.cpp - Global profile summary information --------===//
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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 // This file contains a pass that provides access to the global profile summary
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11 // information.
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12 //
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13 //===----------------------------------------------------------------------===//
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14
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15 #include "llvm/Analysis/BlockFrequencyInfo.h"
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16 #include "llvm/Analysis/ProfileSummaryInfo.h"
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17 #include "llvm/IR/BasicBlock.h"
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18 #include "llvm/IR/Metadata.h"
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19 #include "llvm/IR/Module.h"
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20 #include "llvm/IR/ProfileSummary.h"
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21 using namespace llvm;
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22
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23 // The following two parameters determine the threshold for a count to be
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24 // considered hot/cold. These two parameters are percentile values (multiplied
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25 // by 10000). If the counts are sorted in descending order, the minimum count to
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26 // reach ProfileSummaryCutoffHot gives the threshold to determine a hot count.
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27 // Similarly, the minimum count to reach ProfileSummaryCutoffCold gives the
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28 // threshold for determining cold count (everything <= this threshold is
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29 // considered cold).
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30
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31 static cl::opt<int> ProfileSummaryCutoffHot(
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32 "profile-summary-cutoff-hot", cl::Hidden, cl::init(999000), cl::ZeroOrMore,
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33 cl::desc("A count is hot if it exceeds the minimum count to"
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34 " reach this percentile of total counts."));
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35
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36 static cl::opt<int> ProfileSummaryCutoffCold(
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37 "profile-summary-cutoff-cold", cl::Hidden, cl::init(999999), cl::ZeroOrMore,
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38 cl::desc("A count is cold if it is below the minimum count"
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39 " to reach this percentile of total counts."));
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40
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41 // Find the minimum count to reach a desired percentile of counts.
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42 static uint64_t getMinCountForPercentile(SummaryEntryVector &DS,
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43 uint64_t Percentile) {
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44 auto Compare = [](const ProfileSummaryEntry &Entry, uint64_t Percentile) {
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45 return Entry.Cutoff < Percentile;
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46 };
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47 auto It = std::lower_bound(DS.begin(), DS.end(), Percentile, Compare);
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48 // The required percentile has to be <= one of the percentiles in the
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49 // detailed summary.
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50 if (It == DS.end())
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51 report_fatal_error("Desired percentile exceeds the maximum cutoff");
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52 return It->MinCount;
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53 }
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54
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55 // The profile summary metadata may be attached either by the frontend or by
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56 // any backend passes (IR level instrumentation, for example). This method
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57 // checks if the Summary is null and if so checks if the summary metadata is now
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58 // available in the module and parses it to get the Summary object.
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59 void ProfileSummaryInfo::computeSummary() {
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60 if (Summary)
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61 return;
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62 auto *SummaryMD = M.getProfileSummary();
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63 if (!SummaryMD)
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64 return;
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65 Summary.reset(ProfileSummary::getFromMD(SummaryMD));
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66 }
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67
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68 /// Returns true if the function's entry is hot. If it returns false, it
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69 /// either means it is not hot or it is unknown whether it is hot or not (for
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70 /// example, no profile data is available).
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71 bool ProfileSummaryInfo::isFunctionEntryHot(const Function *F) {
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72 computeSummary();
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73 if (!F || !Summary)
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74 return false;
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75 auto FunctionCount = F->getEntryCount();
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76 // FIXME: The heuristic used below for determining hotness is based on
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77 // preliminary SPEC tuning for inliner. This will eventually be a
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78 // convenience method that calls isHotCount.
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79 return FunctionCount && isHotCount(FunctionCount.getValue());
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80 }
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81
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82 /// Returns true if the function's entry is a cold. If it returns false, it
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83 /// either means it is not cold or it is unknown whether it is cold or not (for
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84 /// example, no profile data is available).
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85 bool ProfileSummaryInfo::isFunctionEntryCold(const Function *F) {
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86 computeSummary();
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87 if (!F)
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88 return false;
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89 if (F->hasFnAttribute(Attribute::Cold)) {
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90 return true;
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91 }
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92 if (!Summary)
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93 return false;
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94 auto FunctionCount = F->getEntryCount();
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95 // FIXME: The heuristic used below for determining coldness is based on
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96 // preliminary SPEC tuning for inliner. This will eventually be a
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97 // convenience method that calls isHotCount.
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98 return FunctionCount && isColdCount(FunctionCount.getValue());
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99 }
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100
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101 /// Compute the hot and cold thresholds.
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102 void ProfileSummaryInfo::computeThresholds() {
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103 if (!Summary)
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104 computeSummary();
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105 if (!Summary)
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106 return;
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107 auto &DetailedSummary = Summary->getDetailedSummary();
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108 HotCountThreshold =
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109 getMinCountForPercentile(DetailedSummary, ProfileSummaryCutoffHot);
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110 ColdCountThreshold =
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111 getMinCountForPercentile(DetailedSummary, ProfileSummaryCutoffCold);
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112 }
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113
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114 bool ProfileSummaryInfo::isHotCount(uint64_t C) {
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115 if (!HotCountThreshold)
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116 computeThresholds();
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117 return HotCountThreshold && C >= HotCountThreshold.getValue();
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118 }
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119
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120 bool ProfileSummaryInfo::isColdCount(uint64_t C) {
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121 if (!ColdCountThreshold)
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122 computeThresholds();
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123 return ColdCountThreshold && C <= ColdCountThreshold.getValue();
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124 }
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125
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126 bool ProfileSummaryInfo::isHotBB(const BasicBlock *B, BlockFrequencyInfo *BFI) {
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127 auto Count = BFI->getBlockProfileCount(B);
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128 if (Count && isHotCount(*Count))
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129 return true;
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130 // Use extractProfTotalWeight to get BB count.
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131 // For Sample PGO, BFI may not provide accurate BB count due to errors
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132 // magnified during sample count propagation. This serves as a backup plan
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133 // to ensure all hot BB will not be missed.
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134 // The query currently has false positives as branch instruction cloning does
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135 // not update/scale branch weights. Unlike false negatives, this will not cause
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136 // performance problem.
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137 uint64_t TotalCount;
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138 if (B->getTerminator()->extractProfTotalWeight(TotalCount) &&
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139 isHotCount(TotalCount))
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140 return true;
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141 return false;
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142 }
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143
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144 INITIALIZE_PASS(ProfileSummaryInfoWrapperPass, "profile-summary-info",
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145 "Profile summary info", false, true)
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146
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147 ProfileSummaryInfoWrapperPass::ProfileSummaryInfoWrapperPass()
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148 : ImmutablePass(ID) {
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149 initializeProfileSummaryInfoWrapperPassPass(*PassRegistry::getPassRegistry());
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150 }
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151
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152 bool ProfileSummaryInfoWrapperPass::doInitialization(Module &M) {
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153 PSI.reset(new ProfileSummaryInfo(M));
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154 return false;
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155 }
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156
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157 bool ProfileSummaryInfoWrapperPass::doFinalization(Module &M) {
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158 PSI.reset();
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159 return false;
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160 }
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161
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162 AnalysisKey ProfileSummaryAnalysis::Key;
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163 ProfileSummaryInfo ProfileSummaryAnalysis::run(Module &M,
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164 ModuleAnalysisManager &) {
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165 return ProfileSummaryInfo(M);
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166 }
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167
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168 PreservedAnalyses ProfileSummaryPrinterPass::run(Module &M,
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169 ModuleAnalysisManager &AM) {
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170 ProfileSummaryInfo &PSI = AM.getResult<ProfileSummaryAnalysis>(M);
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171
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172 OS << "Functions in " << M.getName() << " with hot/cold annotations: \n";
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173 for (auto &F : M) {
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174 OS << F.getName();
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175 if (PSI.isFunctionEntryHot(&F))
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176 OS << " :hot entry ";
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177 else if (PSI.isFunctionEntryCold(&F))
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178 OS << " :cold entry ";
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179 OS << "\n";
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180 }
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181 return PreservedAnalyses::all();
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182 }
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183
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184 char ProfileSummaryInfoWrapperPass::ID = 0;
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