1 //===- LTO.cpp ------------------------------------------------------------===//
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
7 //===----------------------------------------------------------------------===//
11 #include "InputFiles.h"
12 #include "SymbolTable.h"
14 #include "lld/Common/Args.h"
15 #include "lld/Common/ErrorHandler.h"
16 #include "lld/Common/Strings.h"
17 #include "lld/Common/TargetOptionsCommandFlags.h"
18 #include "llvm/ADT/SmallString.h"
19 #include "llvm/ADT/StringRef.h"
20 #include "llvm/ADT/Twine.h"
21 #include "llvm/BinaryFormat/ELF.h"
22 #include "llvm/Bitcode/BitcodeWriter.h"
23 #include "llvm/LTO/Config.h"
24 #include "llvm/LTO/LTO.h"
25 #include "llvm/Support/Caching.h"
26 #include "llvm/Support/CodeGen.h"
27 #include "llvm/Support/Error.h"
28 #include "llvm/Support/FileSystem.h"
29 #include "llvm/Support/MemoryBuffer.h"
34 #include <system_error>
38 using namespace llvm::object;
39 using namespace llvm::ELF;
41 using namespace lld::elf;
43 // Creates an empty file to store a list of object files for final
44 // linking of distributed ThinLTO.
45 static std::unique_ptr<raw_fd_ostream> openFile(StringRef file) {
48 std::make_unique<raw_fd_ostream>(file, ec, sys::fs::OpenFlags::OF_None);
50 error("cannot open " + file + ": " + ec.message());
56 // The merged bitcode after LTO is large. Try opening a file stream that
57 // supports reading, seeking and writing. Such a file allows BitcodeWriter to
58 // flush buffered data to reduce memory consumption. If this fails, open a file
59 // stream that supports only write.
60 static std::unique_ptr<raw_fd_ostream> openLTOOutputFile(StringRef file) {
62 std::unique_ptr<raw_fd_ostream> fs =
63 std::make_unique<raw_fd_stream>(file, ec);
66 return openFile(file);
69 static std::string getThinLTOOutputFile(StringRef modulePath) {
70 return lto::getThinLTOOutputFile(
71 std::string(modulePath), std::string(config->thinLTOPrefixReplace.first),
72 std::string(config->thinLTOPrefixReplace.second));
75 static lto::Config createConfig() {
78 // LLD supports the new relocations and address-significance tables.
79 c.Options = initTargetOptionsFromCodeGenFlags();
80 c.Options.RelaxELFRelocations = true;
81 c.Options.EmitAddrsig = true;
83 // Always emit a section per function/datum with LTO.
84 c.Options.FunctionSections = true;
85 c.Options.DataSections = true;
87 // Check if basic block sections must be used.
88 // Allowed values for --lto-basic-block-sections are "all", "labels",
89 // "<file name specifying basic block ids>", or none. This is the equivalent
90 // of -fbasic-block-sections= flag in clang.
91 if (!config->ltoBasicBlockSections.empty()) {
92 if (config->ltoBasicBlockSections == "all") {
93 c.Options.BBSections = BasicBlockSection::All;
94 } else if (config->ltoBasicBlockSections == "labels") {
95 c.Options.BBSections = BasicBlockSection::Labels;
96 } else if (config->ltoBasicBlockSections == "none") {
97 c.Options.BBSections = BasicBlockSection::None;
99 ErrorOr<std::unique_ptr<MemoryBuffer>> MBOrErr =
100 MemoryBuffer::getFile(config->ltoBasicBlockSections.str());
102 error("cannot open " + config->ltoBasicBlockSections + ":" +
103 MBOrErr.getError().message());
105 c.Options.BBSectionsFuncListBuf = std::move(*MBOrErr);
107 c.Options.BBSections = BasicBlockSection::List;
111 c.Options.UniqueBasicBlockSectionNames =
112 config->ltoUniqueBasicBlockSectionNames;
114 if (auto relocModel = getRelocModelFromCMModel())
115 c.RelocModel = *relocModel;
116 else if (config->relocatable)
118 else if (config->isPic)
119 c.RelocModel = Reloc::PIC_;
121 c.RelocModel = Reloc::Static;
123 c.CodeModel = getCodeModelFromCMModel();
124 c.DisableVerify = config->disableVerify;
125 c.DiagHandler = diagnosticHandler;
126 c.OptLevel = config->ltoo;
128 c.MAttrs = getMAttrs();
129 c.CGOptLevel = args::getCGOptLevel(config->ltoo);
131 c.PTO.LoopVectorization = c.OptLevel > 1;
132 c.PTO.SLPVectorization = c.OptLevel > 1;
134 // Set up a custom pipeline if we've been asked to.
135 c.OptPipeline = std::string(config->ltoNewPmPasses);
136 c.AAPipeline = std::string(config->ltoAAPipeline);
138 // Set up optimization remarks if we've been asked to.
139 c.RemarksFilename = std::string(config->optRemarksFilename);
140 c.RemarksPasses = std::string(config->optRemarksPasses);
141 c.RemarksWithHotness = config->optRemarksWithHotness;
142 c.RemarksHotnessThreshold = config->optRemarksHotnessThreshold;
143 c.RemarksFormat = std::string(config->optRemarksFormat);
145 // Set up output file to emit statistics.
146 c.StatsFile = std::string(config->optStatsFilename);
148 c.SampleProfile = std::string(config->ltoSampleProfile);
149 for (StringRef pluginFn : config->passPlugins)
150 c.PassPlugins.push_back(std::string(pluginFn));
151 c.DebugPassManager = config->ltoDebugPassManager;
152 c.DwoDir = std::string(config->dwoDir);
154 c.HasWholeProgramVisibility = config->ltoWholeProgramVisibility;
155 c.AlwaysEmitRegularLTOObj = !config->ltoObjPath.empty();
157 for (const llvm::StringRef &name : config->thinLTOModulesToCompile)
158 c.ThinLTOModulesToCompile.emplace_back(name);
160 c.TimeTraceEnabled = config->timeTraceEnabled;
161 c.TimeTraceGranularity = config->timeTraceGranularity;
163 c.CSIRProfile = std::string(config->ltoCSProfileFile);
164 c.RunCSIRInstr = config->ltoCSProfileGenerate;
165 c.PGOWarnMismatch = config->ltoPGOWarnMismatch;
167 c.OpaquePointers = config->opaquePointers;
169 if (config->emitLLVM) {
170 c.PostInternalizeModuleHook = [](size_t task, const Module &m) {
171 if (std::unique_ptr<raw_fd_ostream> os =
172 openLTOOutputFile(config->outputFile))
173 WriteBitcodeToFile(m, *os, false);
178 if (config->ltoEmitAsm)
179 c.CGFileType = CGFT_AssemblyFile;
181 if (config->saveTemps)
182 checkError(c.addSaveTemps(config->outputFile.str() + ".",
183 /*UseInputModulePath*/ true));
187 BitcodeCompiler::BitcodeCompiler() {
188 // Initialize indexFile.
189 if (!config->thinLTOIndexOnlyArg.empty())
190 indexFile = openFile(config->thinLTOIndexOnlyArg);
192 // Initialize ltoObj.
193 lto::ThinBackend backend;
194 auto onIndexWrite = [&](StringRef s) { thinIndices.erase(s); };
195 if (config->thinLTOIndexOnly) {
196 backend = lto::createWriteIndexesThinBackend(
197 std::string(config->thinLTOPrefixReplace.first),
198 std::string(config->thinLTOPrefixReplace.second),
199 config->thinLTOEmitImportsFiles, indexFile.get(), onIndexWrite);
201 backend = lto::createInProcessThinBackend(
202 llvm::heavyweight_hardware_concurrency(config->thinLTOJobs),
203 onIndexWrite, config->thinLTOEmitIndexFiles,
204 config->thinLTOEmitImportsFiles);
207 ltoObj = std::make_unique<lto::LTO>(createConfig(), backend,
208 config->ltoPartitions);
210 // Initialize usedStartStop.
211 if (ctx->bitcodeFiles.empty())
213 for (Symbol *sym : symtab->symbols()) {
214 if (sym->isPlaceholder())
216 StringRef s = sym->getName();
217 for (StringRef prefix : {"__start_", "__stop_"})
218 if (s.startswith(prefix))
219 usedStartStop.insert(s.substr(prefix.size()));
223 BitcodeCompiler::~BitcodeCompiler() = default;
225 void BitcodeCompiler::add(BitcodeFile &f) {
226 lto::InputFile &obj = *f.obj;
227 bool isExec = !config->shared && !config->relocatable;
229 if (config->thinLTOEmitIndexFiles)
230 thinIndices.insert(obj.getName());
232 ArrayRef<Symbol *> syms = f.getSymbols();
233 ArrayRef<lto::InputFile::Symbol> objSyms = obj.symbols();
234 std::vector<lto::SymbolResolution> resols(syms.size());
236 // Provide a resolution to the LTO API for each symbol.
237 for (size_t i = 0, e = syms.size(); i != e; ++i) {
238 Symbol *sym = syms[i];
239 const lto::InputFile::Symbol &objSym = objSyms[i];
240 lto::SymbolResolution &r = resols[i];
242 // Ideally we shouldn't check for SF_Undefined but currently IRObjectFile
243 // reports two symbols for module ASM defined. Without this check, lld
244 // flags an undefined in IR with a definition in ASM as prevailing.
245 // Once IRObjectFile is fixed to report only one symbol this hack can
247 r.Prevailing = !objSym.isUndefined() && sym->file == &f;
249 // We ask LTO to preserve following global symbols:
250 // 1) All symbols when doing relocatable link, so that them can be used
251 // for doing final link.
252 // 2) Symbols that are used in regular objects.
253 // 3) C named sections if we have corresponding __start_/__stop_ symbol.
254 // 4) Symbols that are defined in bitcode files and used for dynamic
256 // 5) Symbols that will be referenced after linker wrapping is performed.
257 r.VisibleToRegularObj = config->relocatable || sym->isUsedInRegularObj ||
258 sym->referencedAfterWrap ||
259 (r.Prevailing && sym->includeInDynsym()) ||
260 usedStartStop.count(objSym.getSectionName());
261 // Identify symbols exported dynamically, and that therefore could be
262 // referenced by a shared library not visible to the linker.
264 sym->computeBinding() != STB_LOCAL &&
265 (config->exportDynamic || sym->exportDynamic || sym->inDynamicList);
266 const auto *dr = dyn_cast<Defined>(sym);
267 r.FinalDefinitionInLinkageUnit =
268 (isExec || sym->visibility != STV_DEFAULT) && dr &&
269 // Skip absolute symbols from ELF objects, otherwise PC-rel relocations
270 // will be generated by for them, triggering linker errors.
271 // Symbol section is always null for bitcode symbols, hence the check
272 // for isElf(). Skip linker script defined symbols as well: they have
274 !(dr->section == nullptr && (!sym->file || sym->file->isElf()));
278 Undefined{nullptr, StringRef(), STB_GLOBAL, STV_DEFAULT, sym->type});
280 // We tell LTO to not apply interprocedural optimization for wrapped
281 // (with --wrap) symbols because otherwise LTO would inline them while
282 // their values are still not final.
283 r.LinkerRedefined = sym->scriptDefined;
285 checkError(ltoObj->add(std::move(f.obj), resols));
288 // If LazyObjFile has not been added to link, emit empty index files.
289 // This is needed because this is what GNU gold plugin does and we have a
290 // distributed build system that depends on that behavior.
291 static void thinLTOCreateEmptyIndexFiles() {
292 for (BitcodeFile *f : ctx->lazyBitcodeFiles) {
295 std::string path = replaceThinLTOSuffix(getThinLTOOutputFile(f->getName()));
296 std::unique_ptr<raw_fd_ostream> os = openFile(path + ".thinlto.bc");
300 ModuleSummaryIndex m(/*HaveGVs*/ false);
301 m.setSkipModuleByDistributedBackend();
302 writeIndexToFile(m, *os);
303 if (config->thinLTOEmitImportsFiles)
304 openFile(path + ".imports");
308 // Merge all the bitcode files we have seen, codegen the result
309 // and return the resulting ObjectFile(s).
310 std::vector<InputFile *> BitcodeCompiler::compile() {
311 unsigned maxTasks = ltoObj->getMaxTasks();
312 buf.resize(maxTasks);
313 files.resize(maxTasks);
315 // The --thinlto-cache-dir option specifies the path to a directory in which
316 // to cache native object files for ThinLTO incremental builds. If a path was
317 // specified, configure LTO to use it as the cache directory.
319 if (!config->thinLTOCacheDir.empty())
321 check(localCache("ThinLTO", "Thin", config->thinLTOCacheDir,
322 [&](size_t task, std::unique_ptr<MemoryBuffer> mb) {
323 files[task] = std::move(mb);
326 if (!ctx->bitcodeFiles.empty())
327 checkError(ltoObj->run(
329 return std::make_unique<CachedFileStream>(
330 std::make_unique<raw_svector_ostream>(buf[task]));
334 // Emit empty index files for non-indexed files but not in single-module mode.
335 if (config->thinLTOModulesToCompile.empty()) {
336 for (StringRef s : thinIndices) {
337 std::string path = getThinLTOOutputFile(s);
338 openFile(path + ".thinlto.bc");
339 if (config->thinLTOEmitImportsFiles)
340 openFile(path + ".imports");
344 if (config->thinLTOEmitIndexFiles)
345 thinLTOCreateEmptyIndexFiles();
347 if (config->thinLTOIndexOnly) {
348 if (!config->ltoObjPath.empty())
349 saveBuffer(buf[0], config->ltoObjPath);
351 // ThinLTO with index only option is required to generate only the index
352 // files. After that, we exit from linker and ThinLTO backend runs in a
353 // distributed environment.
359 if (!config->thinLTOCacheDir.empty())
360 pruneCache(config->thinLTOCacheDir, config->thinLTOCachePolicy);
362 if (!config->ltoObjPath.empty()) {
363 saveBuffer(buf[0], config->ltoObjPath);
364 for (unsigned i = 1; i != maxTasks; ++i)
365 saveBuffer(buf[i], config->ltoObjPath + Twine(i));
368 if (config->saveTemps) {
370 saveBuffer(buf[0], config->outputFile + ".lto.o");
371 for (unsigned i = 1; i != maxTasks; ++i)
372 saveBuffer(buf[i], config->outputFile + Twine(i) + ".lto.o");
375 if (config->ltoEmitAsm) {
376 saveBuffer(buf[0], config->outputFile);
377 for (unsigned i = 1; i != maxTasks; ++i)
378 saveBuffer(buf[i], config->outputFile + Twine(i));
382 std::vector<InputFile *> ret;
383 for (unsigned i = 0; i != maxTasks; ++i)
385 ret.push_back(createObjectFile(MemoryBufferRef(buf[i], "lto.tmp")));
387 for (std::unique_ptr<MemoryBuffer> &file : files)
389 ret.push_back(createObjectFile(*file));