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1 //===- LTO.cpp ------------------------------------------------------------===//
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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 #include "LTO.h"
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10 #include "Config.h"
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11 #include "InputFiles.h"
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12 #include "Symbols.h"
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13 #include "lld/Common/Args.h"
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14 #include "lld/Common/ErrorHandler.h"
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15 #include "lld/Common/Strings.h"
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16 #include "lld/Common/TargetOptionsCommandFlags.h"
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17 #include "llvm/ADT/STLExtras.h"
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18 #include "llvm/ADT/SmallString.h"
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19 #include "llvm/ADT/StringRef.h"
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20 #include "llvm/ADT/Twine.h"
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21 #include "llvm/Bitcode/BitcodeWriter.h"
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22 #include "llvm/IR/DiagnosticPrinter.h"
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23 #include "llvm/LTO/Caching.h"
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24 #include "llvm/LTO/Config.h"
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25 #include "llvm/LTO/LTO.h"
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26 #include "llvm/Object/SymbolicFile.h"
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27 #include "llvm/Support/CodeGen.h"
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28 #include "llvm/Support/Error.h"
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29 #include "llvm/Support/FileSystem.h"
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30 #include "llvm/Support/MemoryBuffer.h"
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31 #include "llvm/Support/raw_ostream.h"
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32 #include <algorithm>
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33 #include <cstddef>
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34 #include <memory>
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35 #include <string>
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36 #include <system_error>
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37 #include <vector>
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38
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39 using namespace llvm;
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40 using namespace llvm::object;
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173
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41 using namespace lld;
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42 using namespace lld::coff;
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150
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43
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44 // Creates an empty file to and returns a raw_fd_ostream to write to it.
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45 static std::unique_ptr<raw_fd_ostream> openFile(StringRef file) {
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46 std::error_code ec;
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47 auto ret =
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48 std::make_unique<raw_fd_ostream>(file, ec, sys::fs::OpenFlags::OF_None);
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49 if (ec) {
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50 error("cannot open " + file + ": " + ec.message());
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51 return nullptr;
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52 }
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53 return ret;
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54 }
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55
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56 static std::string getThinLTOOutputFile(StringRef path) {
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57 return lto::getThinLTOOutputFile(
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58 std::string(path), std::string(config->thinLTOPrefixReplace.first),
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59 std::string(config->thinLTOPrefixReplace.second));
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60 }
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61
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62 static lto::Config createConfig() {
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63 lto::Config c;
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64 c.Options = initTargetOptionsFromCodeGenFlags();
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65
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66 // Always emit a section per function/datum with LTO. LLVM LTO should get most
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67 // of the benefit of linker GC, but there are still opportunities for ICF.
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68 c.Options.FunctionSections = true;
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69 c.Options.DataSections = true;
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70
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71 // Use static reloc model on 32-bit x86 because it usually results in more
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72 // compact code, and because there are also known code generation bugs when
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73 // using the PIC model (see PR34306).
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74 if (config->machine == COFF::IMAGE_FILE_MACHINE_I386)
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75 c.RelocModel = Reloc::Static;
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76 else
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77 c.RelocModel = Reloc::PIC_;
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78 c.DisableVerify = true;
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79 c.DiagHandler = diagnosticHandler;
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80 c.OptLevel = config->ltoo;
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81 c.CPU = getCPUStr();
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82 c.MAttrs = getMAttrs();
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83 c.CGOptLevel = args::getCGOptLevel(config->ltoo);
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173
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84 c.AlwaysEmitRegularLTOObj = !config->ltoObjPath.empty();
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150
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85
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86 if (config->saveTemps)
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87 checkError(c.addSaveTemps(std::string(config->outputFile) + ".",
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88 /*UseInputModulePath*/ true));
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89 return c;
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90 }
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91
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92 BitcodeCompiler::BitcodeCompiler() {
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93 // Initialize indexFile.
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94 if (!config->thinLTOIndexOnlyArg.empty())
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95 indexFile = openFile(config->thinLTOIndexOnlyArg);
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96
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97 // Initialize ltoObj.
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98 lto::ThinBackend backend;
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99 if (config->thinLTOIndexOnly) {
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100 auto OnIndexWrite = [&](StringRef S) { thinIndices.erase(S); };
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101 backend = lto::createWriteIndexesThinBackend(
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102 std::string(config->thinLTOPrefixReplace.first),
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103 std::string(config->thinLTOPrefixReplace.second),
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104 config->thinLTOEmitImportsFiles, indexFile.get(), OnIndexWrite);
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173
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105 } else {
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106 backend = lto::createInProcessThinBackend(
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107 llvm::heavyweight_hardware_concurrency(config->thinLTOJobs));
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150
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108 }
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109
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110 ltoObj = std::make_unique<lto::LTO>(createConfig(), backend,
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111 config->ltoPartitions);
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112 }
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113
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114 BitcodeCompiler::~BitcodeCompiler() = default;
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115
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116 static void undefine(Symbol *s) { replaceSymbol<Undefined>(s, s->getName()); }
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117
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118 void BitcodeCompiler::add(BitcodeFile &f) {
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119 lto::InputFile &obj = *f.obj;
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120 unsigned symNum = 0;
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121 std::vector<Symbol *> symBodies = f.getSymbols();
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122 std::vector<lto::SymbolResolution> resols(symBodies.size());
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123
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124 if (config->thinLTOIndexOnly)
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125 thinIndices.insert(obj.getName());
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126
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127 // Provide a resolution to the LTO API for each symbol.
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128 for (const lto::InputFile::Symbol &objSym : obj.symbols()) {
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129 Symbol *sym = symBodies[symNum];
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130 lto::SymbolResolution &r = resols[symNum];
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131 ++symNum;
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132
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133 // Ideally we shouldn't check for SF_Undefined but currently IRObjectFile
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134 // reports two symbols for module ASM defined. Without this check, lld
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135 // flags an undefined in IR with a definition in ASM as prevailing.
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136 // Once IRObjectFile is fixed to report only one symbol this hack can
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137 // be removed.
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138 r.Prevailing = !objSym.isUndefined() && sym->getFile() == &f;
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139 r.VisibleToRegularObj = sym->isUsedInRegularObj;
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140 if (r.Prevailing)
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141 undefine(sym);
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142 }
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143 checkError(ltoObj->add(std::move(f.obj), resols));
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144 }
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145
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146 // Merge all the bitcode files we have seen, codegen the result
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147 // and return the resulting objects.
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173
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148 std::vector<InputFile *> BitcodeCompiler::compile() {
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150
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149 unsigned maxTasks = ltoObj->getMaxTasks();
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150 buf.resize(maxTasks);
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151 files.resize(maxTasks);
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152
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153 // The /lldltocache option specifies the path to a directory in which to cache
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154 // native object files for ThinLTO incremental builds. If a path was
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155 // specified, configure LTO to use it as the cache directory.
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156 lto::NativeObjectCache cache;
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157 if (!config->ltoCache.empty())
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158 cache = check(lto::localCache(
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159 config->ltoCache, [&](size_t task, std::unique_ptr<MemoryBuffer> mb) {
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160 files[task] = std::move(mb);
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161 }));
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162
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163 checkError(ltoObj->run(
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164 [&](size_t task) {
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165 return std::make_unique<lto::NativeObjectStream>(
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166 std::make_unique<raw_svector_ostream>(buf[task]));
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167 },
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168 cache));
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169
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170 // Emit empty index files for non-indexed files
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171 for (StringRef s : thinIndices) {
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172 std::string path = getThinLTOOutputFile(s);
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173 openFile(path + ".thinlto.bc");
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174 if (config->thinLTOEmitImportsFiles)
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175 openFile(path + ".imports");
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176 }
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177
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178 // ThinLTO with index only option is required to generate only the index
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179 // files. After that, we exit from linker and ThinLTO backend runs in a
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180 // distributed environment.
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181 if (config->thinLTOIndexOnly) {
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182 if (!config->ltoObjPath.empty())
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183 saveBuffer(buf[0], config->ltoObjPath);
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184 if (indexFile)
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185 indexFile->close();
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186 return {};
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187 }
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188
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189 if (!config->ltoCache.empty())
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190 pruneCache(config->ltoCache, config->ltoCachePolicy);
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191
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192 std::vector<InputFile *> ret;
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193 for (unsigned i = 0; i != maxTasks; ++i) {
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173
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194 // Assign unique names to LTO objects. This ensures they have unique names
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195 // in the PDB if one is produced. The names should look like:
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196 // - foo.exe.lto.obj
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197 // - foo.exe.lto.1.obj
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198 // - ...
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199 StringRef ltoObjName =
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200 saver.save(Twine(config->outputFile) + ".lto" +
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201 (i == 0 ? Twine("") : Twine('.') + Twine(i)) + ".obj");
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202
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203 // Get the native object contents either from the cache or from memory. Do
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204 // not use the cached MemoryBuffer directly, or the PDB will not be
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205 // deterministic.
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206 StringRef objBuf;
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207 if (files[i])
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208 objBuf = files[i]->getBuffer();
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209 else
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210 objBuf = buf[i];
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211 if (objBuf.empty())
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150
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212 continue;
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173
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213
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214 if (config->saveTemps)
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215 saveBuffer(buf[i], ltoObjName);
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216 ret.push_back(make<ObjFile>(MemoryBufferRef(objBuf, ltoObjName)));
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150
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217 }
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218
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219 return ret;
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220 }
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