1 //===- LTO.cpp ------------------------------------------------------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8
9 #include "LTO.h"
10 #include "Config.h"
11 #include "Driver.h"
12 #include "InputFiles.h"
13 #include "Symbols.h"
14 #include "Target.h"
15
16 #include "lld/Common/Args.h"
17 #include "lld/Common/CommonLinkerContext.h"
18 #include "lld/Common/Strings.h"
19 #include "lld/Common/TargetOptionsCommandFlags.h"
20 #include "llvm/Bitcode/BitcodeWriter.h"
21 #include "llvm/LTO/Config.h"
22 #include "llvm/LTO/LTO.h"
23 #include "llvm/Support/Caching.h"
24 #include "llvm/Support/FileSystem.h"
25 #include "llvm/Support/Path.h"
26 #include "llvm/Support/raw_ostream.h"
27 #include "llvm/Transforms/ObjCARC.h"
28
29 using namespace lld;
30 using namespace lld::macho;
31 using namespace llvm;
32 using namespace llvm::MachO;
33 using namespace llvm::sys;
34
35 // Creates an empty file to store a list of object files for final
36 // linking of distributed ThinLTO.
openFile(StringRef file)37 static std::unique_ptr<raw_fd_ostream> openFile(StringRef file) {
38 std::error_code ec;
39 auto ret =
40 std::make_unique<raw_fd_ostream>(file, ec, sys::fs::OpenFlags::OF_None);
41 if (ec) {
42 error("cannot open " + file + ": " + ec.message());
43 return nullptr;
44 }
45 return ret;
46 }
47
getThinLTOOutputFile(StringRef modulePath)48 static std::string getThinLTOOutputFile(StringRef modulePath) {
49 return lto::getThinLTOOutputFile(
50 std::string(modulePath), std::string(config->thinLTOPrefixReplace.first),
51 std::string(config->thinLTOPrefixReplace.second));
52 }
53
createConfig()54 static lto::Config createConfig() {
55 lto::Config c;
56 c.Options = initTargetOptionsFromCodeGenFlags();
57 c.Options.EmitAddrsig = config->icfLevel == ICFLevel::safe;
58 for (StringRef C : config->mllvmOpts)
59 c.MllvmArgs.emplace_back(C.str());
60 c.CodeModel = getCodeModelFromCMModel();
61 c.CPU = getCPUStr();
62 c.MAttrs = getMAttrs();
63 c.DiagHandler = diagnosticHandler;
64 c.PreCodeGenPassesHook = [](legacy::PassManager &pm) {
65 pm.add(createObjCARCContractPass());
66 };
67
68 c.AlwaysEmitRegularLTOObj = !config->ltoObjPath.empty();
69
70 c.TimeTraceEnabled = config->timeTraceEnabled;
71 c.TimeTraceGranularity = config->timeTraceGranularity;
72 c.OptLevel = config->ltoo;
73 c.CGOptLevel = args::getCGOptLevel(config->ltoo);
74 if (config->saveTemps)
75 checkError(c.addSaveTemps(config->outputFile.str() + ".",
76 /*UseInputModulePath=*/true));
77 return c;
78 }
79
80 // If `originalPath` exists, hardlinks `path` to `originalPath`. If that fails,
81 // or `originalPath` is not set, saves `buffer` to `path`.
saveOrHardlinkBuffer(StringRef buffer,const Twine & path,std::optional<StringRef> originalPath)82 static void saveOrHardlinkBuffer(StringRef buffer, const Twine &path,
83 std::optional<StringRef> originalPath) {
84 if (originalPath) {
85 auto err = fs::create_hard_link(*originalPath, path);
86 if (!err)
87 return;
88 }
89 saveBuffer(buffer, path);
90 }
91
BitcodeCompiler()92 BitcodeCompiler::BitcodeCompiler() {
93 // Initialize indexFile.
94 if (!config->thinLTOIndexOnlyArg.empty())
95 indexFile = openFile(config->thinLTOIndexOnlyArg);
96
97 // Initialize ltoObj.
98 lto::ThinBackend backend;
99 auto onIndexWrite = [&](StringRef S) { thinIndices.erase(S); };
100 if (config->thinLTOIndexOnly) {
101 backend = lto::createWriteIndexesThinBackend(
102 std::string(config->thinLTOPrefixReplace.first),
103 std::string(config->thinLTOPrefixReplace.second),
104 config->thinLTOEmitImportsFiles, indexFile.get(), onIndexWrite);
105 } else {
106 backend = lto::createInProcessThinBackend(
107 llvm::heavyweight_hardware_concurrency(config->thinLTOJobs),
108 onIndexWrite, config->thinLTOEmitIndexFiles,
109 config->thinLTOEmitImportsFiles);
110 }
111
112 ltoObj = std::make_unique<lto::LTO>(createConfig(), backend);
113 }
114
add(BitcodeFile & f)115 void BitcodeCompiler::add(BitcodeFile &f) {
116 lto::InputFile &obj = *f.obj;
117
118 if (config->thinLTOEmitIndexFiles)
119 thinIndices.insert(obj.getName());
120
121 ArrayRef<lto::InputFile::Symbol> objSyms = obj.symbols();
122 std::vector<lto::SymbolResolution> resols;
123 resols.reserve(objSyms.size());
124
125 // Provide a resolution to the LTO API for each symbol.
126 bool exportDynamic =
127 config->outputType != MH_EXECUTE || config->exportDynamic;
128 auto symIt = f.symbols.begin();
129 for (const lto::InputFile::Symbol &objSym : objSyms) {
130 resols.emplace_back();
131 lto::SymbolResolution &r = resols.back();
132 Symbol *sym = *symIt++;
133
134 // Ideally we shouldn't check for SF_Undefined but currently IRObjectFile
135 // reports two symbols for module ASM defined. Without this check, lld
136 // flags an undefined in IR with a definition in ASM as prevailing.
137 // Once IRObjectFile is fixed to report only one symbol this hack can
138 // be removed.
139 r.Prevailing = !objSym.isUndefined() && sym->getFile() == &f;
140
141 if (const auto *defined = dyn_cast<Defined>(sym)) {
142 r.ExportDynamic =
143 defined->isExternal() && !defined->privateExtern && exportDynamic;
144 r.FinalDefinitionInLinkageUnit =
145 !defined->isExternalWeakDef() && !defined->interposable;
146 } else if (const auto *common = dyn_cast<CommonSymbol>(sym)) {
147 r.ExportDynamic = !common->privateExtern && exportDynamic;
148 r.FinalDefinitionInLinkageUnit = true;
149 }
150
151 r.VisibleToRegularObj =
152 sym->isUsedInRegularObj || (r.Prevailing && r.ExportDynamic);
153
154 // Un-define the symbol so that we don't get duplicate symbol errors when we
155 // load the ObjFile emitted by LTO compilation.
156 if (r.Prevailing)
157 replaceSymbol<Undefined>(sym, sym->getName(), sym->getFile(),
158 RefState::Strong, /*wasBitcodeSymbol=*/true);
159
160 // TODO: set the other resolution configs properly
161 }
162 checkError(ltoObj->add(std::move(f.obj), resols));
163 }
164
165 // If LazyObjFile has not been added to link, emit empty index files.
166 // This is needed because this is what GNU gold plugin does and we have a
167 // distributed build system that depends on that behavior.
thinLTOCreateEmptyIndexFiles()168 static void thinLTOCreateEmptyIndexFiles() {
169 DenseSet<StringRef> linkedBitCodeFiles;
170 for (InputFile *file : inputFiles)
171 if (auto *f = dyn_cast<BitcodeFile>(file))
172 if (!f->lazy)
173 linkedBitCodeFiles.insert(f->getName());
174
175 for (InputFile *file : inputFiles) {
176 if (auto *f = dyn_cast<BitcodeFile>(file)) {
177 if (!f->lazy)
178 continue;
179 if (linkedBitCodeFiles.contains(f->getName()))
180 continue;
181 std::string path =
182 replaceThinLTOSuffix(getThinLTOOutputFile(f->obj->getName()));
183 std::unique_ptr<raw_fd_ostream> os = openFile(path + ".thinlto.bc");
184 if (!os)
185 continue;
186
187 ModuleSummaryIndex m(/*HaveGVs=*/false);
188 m.setSkipModuleByDistributedBackend();
189 writeIndexToFile(m, *os);
190 if (config->thinLTOEmitImportsFiles)
191 openFile(path + ".imports");
192 }
193 }
194 }
195
196 // Merge all the bitcode files we have seen, codegen the result
197 // and return the resulting ObjectFile(s).
compile()198 std::vector<ObjFile *> BitcodeCompiler::compile() {
199 unsigned maxTasks = ltoObj->getMaxTasks();
200 buf.resize(maxTasks);
201 files.resize(maxTasks);
202
203 // The -cache_path_lto option specifies the path to a directory in which
204 // to cache native object files for ThinLTO incremental builds. If a path was
205 // specified, configure LTO to use it as the cache directory.
206 FileCache cache;
207 if (!config->thinLTOCacheDir.empty())
208 cache = check(localCache("ThinLTO", "Thin", config->thinLTOCacheDir,
209 [&](size_t task, const Twine &moduleName,
210 std::unique_ptr<MemoryBuffer> mb) {
211 files[task] = std::move(mb);
212 }));
213
214 checkError(ltoObj->run(
215 [&](size_t task, const Twine &moduleName) {
216 return std::make_unique<CachedFileStream>(
217 std::make_unique<raw_svector_ostream>(buf[task]));
218 },
219 cache));
220
221 // Emit empty index files for non-indexed files
222 for (StringRef s : thinIndices) {
223 std::string path = getThinLTOOutputFile(s);
224 openFile(path + ".thinlto.bc");
225 if (config->thinLTOEmitImportsFiles)
226 openFile(path + ".imports");
227 }
228
229 if (config->thinLTOEmitIndexFiles)
230 thinLTOCreateEmptyIndexFiles();
231
232 // In ThinLTO mode, Clang passes a temporary directory in -object_path_lto,
233 // while the argument is a single file in FullLTO mode.
234 bool objPathIsDir = true;
235 if (!config->ltoObjPath.empty()) {
236 if (std::error_code ec = fs::create_directories(config->ltoObjPath))
237 fatal("cannot create LTO object path " + config->ltoObjPath + ": " +
238 ec.message());
239
240 if (!fs::is_directory(config->ltoObjPath)) {
241 objPathIsDir = false;
242 unsigned objCount =
243 count_if(buf, [](const SmallString<0> &b) { return !b.empty(); });
244 if (objCount > 1)
245 fatal("-object_path_lto must specify a directory when using ThinLTO");
246 }
247 }
248
249 auto outputFilePath = [objPathIsDir](int i) {
250 SmallString<261> filePath("/tmp/lto.tmp");
251 if (!config->ltoObjPath.empty()) {
252 filePath = config->ltoObjPath;
253 if (objPathIsDir)
254 path::append(filePath, Twine(i) + "." +
255 getArchitectureName(config->arch()) +
256 ".lto.o");
257 }
258 return filePath;
259 };
260
261 // ThinLTO with index only option is required to generate only the index
262 // files. After that, we exit from linker and ThinLTO backend runs in a
263 // distributed environment.
264 if (config->thinLTOIndexOnly) {
265 if (!config->ltoObjPath.empty())
266 saveBuffer(buf[0], outputFilePath(0));
267 if (indexFile)
268 indexFile->close();
269 return {};
270 }
271
272 if (!config->thinLTOCacheDir.empty())
273 pruneCache(config->thinLTOCacheDir, config->thinLTOCachePolicy, files);
274
275 std::vector<ObjFile *> ret;
276 for (unsigned i = 0; i < maxTasks; ++i) {
277 // Get the native object contents either from the cache or from memory. Do
278 // not use the cached MemoryBuffer directly to ensure dsymutil does not
279 // race with the cache pruner.
280 StringRef objBuf;
281 std::optional<StringRef> cachePath;
282 if (files[i]) {
283 objBuf = files[i]->getBuffer();
284 cachePath = files[i]->getBufferIdentifier();
285 } else {
286 objBuf = buf[i];
287 }
288 if (objBuf.empty())
289 continue;
290
291 // FIXME: should `saveTemps` and `ltoObjPath` use the same file name?
292 if (config->saveTemps)
293 saveBuffer(objBuf,
294 config->outputFile + ((i == 0) ? "" : Twine(i)) + ".lto.o");
295
296 auto filePath = outputFilePath(i);
297 uint32_t modTime = 0;
298 if (!config->ltoObjPath.empty()) {
299 saveOrHardlinkBuffer(objBuf, filePath, cachePath);
300 modTime = getModTime(filePath);
301 }
302 ret.push_back(make<ObjFile>(
303 MemoryBufferRef(objBuf, saver().save(filePath.str())), modTime, ""));
304 }
305
306 return ret;
307 }
308