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 "InputFiles.h"
12 #include "SymbolTable.h"
13 #include "Symbols.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"
30 #include <algorithm>
31 #include <cstddef>
32 #include <memory>
33 #include <string>
34 #include <system_error>
35 #include <vector>
36
37 using namespace llvm;
38 using namespace llvm::object;
39 using namespace llvm::ELF;
40 using namespace lld;
41 using namespace lld::elf;
42
43 // Creates an empty file to store a list of object files for final
44 // linking of distributed ThinLTO.
openFile(StringRef file)45 static std::unique_ptr<raw_fd_ostream> openFile(StringRef file) {
46 std::error_code ec;
47 auto ret =
48 std::make_unique<raw_fd_ostream>(file, ec, sys::fs::OpenFlags::OF_None);
49 if (ec) {
50 error("cannot open " + file + ": " + ec.message());
51 return nullptr;
52 }
53 return ret;
54 }
55
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.
openLTOOutputFile(StringRef file)60 static std::unique_ptr<raw_fd_ostream> openLTOOutputFile(StringRef file) {
61 std::error_code ec;
62 std::unique_ptr<raw_fd_ostream> fs =
63 std::make_unique<raw_fd_stream>(file, ec);
64 if (!ec)
65 return fs;
66 return openFile(file);
67 }
68
getThinLTOOutputFile(StringRef modulePath)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));
73 }
74
createConfig()75 static lto::Config createConfig() {
76 lto::Config c;
77
78 // LLD supports the new relocations and address-significance tables.
79 c.Options = initTargetOptionsFromCodeGenFlags();
80 c.Options.EmitAddrsig = true;
81 for (StringRef C : config->mllvmOpts)
82 c.MllvmArgs.emplace_back(C.str());
83
84 // Always emit a section per function/datum with LTO.
85 c.Options.FunctionSections = true;
86 c.Options.DataSections = true;
87
88 // Check if basic block sections must be used.
89 // Allowed values for --lto-basic-block-sections are "all", "labels",
90 // "<file name specifying basic block ids>", or none. This is the equivalent
91 // of -fbasic-block-sections= flag in clang.
92 if (!config->ltoBasicBlockSections.empty()) {
93 if (config->ltoBasicBlockSections == "all") {
94 c.Options.BBSections = BasicBlockSection::All;
95 } else if (config->ltoBasicBlockSections == "labels") {
96 c.Options.BBSections = BasicBlockSection::Labels;
97 } else if (config->ltoBasicBlockSections == "none") {
98 c.Options.BBSections = BasicBlockSection::None;
99 } else {
100 ErrorOr<std::unique_ptr<MemoryBuffer>> MBOrErr =
101 MemoryBuffer::getFile(config->ltoBasicBlockSections.str());
102 if (!MBOrErr) {
103 error("cannot open " + config->ltoBasicBlockSections + ":" +
104 MBOrErr.getError().message());
105 } else {
106 c.Options.BBSectionsFuncListBuf = std::move(*MBOrErr);
107 }
108 c.Options.BBSections = BasicBlockSection::List;
109 }
110 }
111
112 c.Options.UniqueBasicBlockSectionNames =
113 config->ltoUniqueBasicBlockSectionNames;
114
115 if (auto relocModel = getRelocModelFromCMModel())
116 c.RelocModel = *relocModel;
117 else if (config->relocatable)
118 c.RelocModel = std::nullopt;
119 else if (config->isPic)
120 c.RelocModel = Reloc::PIC_;
121 else
122 c.RelocModel = Reloc::Static;
123
124 c.CodeModel = getCodeModelFromCMModel();
125 c.DisableVerify = config->disableVerify;
126 c.DiagHandler = diagnosticHandler;
127 c.OptLevel = config->ltoo;
128 c.CPU = getCPUStr();
129 c.MAttrs = getMAttrs();
130 c.CGOptLevel = args::getCGOptLevel(config->ltoo);
131
132 c.PTO.LoopVectorization = c.OptLevel > 1;
133 c.PTO.SLPVectorization = c.OptLevel > 1;
134
135 // Set up a custom pipeline if we've been asked to.
136 c.OptPipeline = std::string(config->ltoNewPmPasses);
137 c.AAPipeline = std::string(config->ltoAAPipeline);
138
139 // Set up optimization remarks if we've been asked to.
140 c.RemarksFilename = std::string(config->optRemarksFilename);
141 c.RemarksPasses = std::string(config->optRemarksPasses);
142 c.RemarksWithHotness = config->optRemarksWithHotness;
143 c.RemarksHotnessThreshold = config->optRemarksHotnessThreshold;
144 c.RemarksFormat = std::string(config->optRemarksFormat);
145
146 // Set up output file to emit statistics.
147 c.StatsFile = std::string(config->optStatsFilename);
148
149 c.SampleProfile = std::string(config->ltoSampleProfile);
150 for (StringRef pluginFn : config->passPlugins)
151 c.PassPlugins.push_back(std::string(pluginFn));
152 c.DebugPassManager = config->ltoDebugPassManager;
153 c.DwoDir = std::string(config->dwoDir);
154
155 c.HasWholeProgramVisibility = config->ltoWholeProgramVisibility;
156 c.AlwaysEmitRegularLTOObj = !config->ltoObjPath.empty();
157
158 for (const llvm::StringRef &name : config->thinLTOModulesToCompile)
159 c.ThinLTOModulesToCompile.emplace_back(name);
160
161 c.TimeTraceEnabled = config->timeTraceEnabled;
162 c.TimeTraceGranularity = config->timeTraceGranularity;
163
164 c.CSIRProfile = std::string(config->ltoCSProfileFile);
165 c.RunCSIRInstr = config->ltoCSProfileGenerate;
166 c.PGOWarnMismatch = config->ltoPGOWarnMismatch;
167
168 c.OpaquePointers = config->opaquePointers;
169
170 if (config->emitLLVM) {
171 c.PostInternalizeModuleHook = [](size_t task, const Module &m) {
172 if (std::unique_ptr<raw_fd_ostream> os =
173 openLTOOutputFile(config->outputFile))
174 WriteBitcodeToFile(m, *os, false);
175 return false;
176 };
177 }
178
179 if (config->ltoEmitAsm) {
180 c.CGFileType = CGFT_AssemblyFile;
181 c.Options.MCOptions.AsmVerbose = true;
182 }
183
184 if (!config->saveTempsArgs.empty())
185 checkError(c.addSaveTemps(config->outputFile.str() + ".",
186 /*UseInputModulePath*/ true,
187 config->saveTempsArgs));
188 return c;
189 }
190
BitcodeCompiler()191 BitcodeCompiler::BitcodeCompiler() {
192 // Initialize indexFile.
193 if (!config->thinLTOIndexOnlyArg.empty())
194 indexFile = openFile(config->thinLTOIndexOnlyArg);
195
196 // Initialize ltoObj.
197 lto::ThinBackend backend;
198 auto onIndexWrite = [&](StringRef s) { thinIndices.erase(s); };
199 if (config->thinLTOIndexOnly) {
200 backend = lto::createWriteIndexesThinBackend(
201 std::string(config->thinLTOPrefixReplace.first),
202 std::string(config->thinLTOPrefixReplace.second),
203 config->thinLTOEmitImportsFiles, indexFile.get(), onIndexWrite);
204 } else {
205 backend = lto::createInProcessThinBackend(
206 llvm::heavyweight_hardware_concurrency(config->thinLTOJobs),
207 onIndexWrite, config->thinLTOEmitIndexFiles,
208 config->thinLTOEmitImportsFiles);
209 }
210
211 ltoObj = std::make_unique<lto::LTO>(createConfig(), backend,
212 config->ltoPartitions);
213
214 // Initialize usedStartStop.
215 if (ctx.bitcodeFiles.empty())
216 return;
217 for (Symbol *sym : symtab.getSymbols()) {
218 if (sym->isPlaceholder())
219 continue;
220 StringRef s = sym->getName();
221 for (StringRef prefix : {"__start_", "__stop_"})
222 if (s.startswith(prefix))
223 usedStartStop.insert(s.substr(prefix.size()));
224 }
225 }
226
227 BitcodeCompiler::~BitcodeCompiler() = default;
228
add(BitcodeFile & f)229 void BitcodeCompiler::add(BitcodeFile &f) {
230 lto::InputFile &obj = *f.obj;
231 bool isExec = !config->shared && !config->relocatable;
232
233 if (config->thinLTOEmitIndexFiles)
234 thinIndices.insert(obj.getName());
235
236 ArrayRef<Symbol *> syms = f.getSymbols();
237 ArrayRef<lto::InputFile::Symbol> objSyms = obj.symbols();
238 std::vector<lto::SymbolResolution> resols(syms.size());
239
240 // Provide a resolution to the LTO API for each symbol.
241 for (size_t i = 0, e = syms.size(); i != e; ++i) {
242 Symbol *sym = syms[i];
243 const lto::InputFile::Symbol &objSym = objSyms[i];
244 lto::SymbolResolution &r = resols[i];
245
246 // Ideally we shouldn't check for SF_Undefined but currently IRObjectFile
247 // reports two symbols for module ASM defined. Without this check, lld
248 // flags an undefined in IR with a definition in ASM as prevailing.
249 // Once IRObjectFile is fixed to report only one symbol this hack can
250 // be removed.
251 r.Prevailing = !objSym.isUndefined() && sym->file == &f;
252
253 // We ask LTO to preserve following global symbols:
254 // 1) All symbols when doing relocatable link, so that them can be used
255 // for doing final link.
256 // 2) Symbols that are used in regular objects.
257 // 3) C named sections if we have corresponding __start_/__stop_ symbol.
258 // 4) Symbols that are defined in bitcode files and used for dynamic
259 // linking.
260 // 5) Symbols that will be referenced after linker wrapping is performed.
261 r.VisibleToRegularObj = config->relocatable || sym->isUsedInRegularObj ||
262 sym->referencedAfterWrap ||
263 (r.Prevailing && sym->includeInDynsym()) ||
264 usedStartStop.count(objSym.getSectionName());
265 // Identify symbols exported dynamically, and that therefore could be
266 // referenced by a shared library not visible to the linker.
267 r.ExportDynamic =
268 sym->computeBinding() != STB_LOCAL &&
269 (config->exportDynamic || sym->exportDynamic || sym->inDynamicList);
270 const auto *dr = dyn_cast<Defined>(sym);
271 r.FinalDefinitionInLinkageUnit =
272 (isExec || sym->visibility() != STV_DEFAULT) && dr &&
273 // Skip absolute symbols from ELF objects, otherwise PC-rel relocations
274 // will be generated by for them, triggering linker errors.
275 // Symbol section is always null for bitcode symbols, hence the check
276 // for isElf(). Skip linker script defined symbols as well: they have
277 // no File defined.
278 !(dr->section == nullptr && (!sym->file || sym->file->isElf()));
279
280 if (r.Prevailing)
281 Undefined(nullptr, StringRef(), STB_GLOBAL, STV_DEFAULT, sym->type)
282 .overwrite(*sym);
283
284 // We tell LTO to not apply interprocedural optimization for wrapped
285 // (with --wrap) symbols because otherwise LTO would inline them while
286 // their values are still not final.
287 r.LinkerRedefined = sym->scriptDefined;
288 }
289 checkError(ltoObj->add(std::move(f.obj), resols));
290 }
291
292 // If LazyObjFile has not been added to link, emit empty index files.
293 // This is needed because this is what GNU gold plugin does and we have a
294 // distributed build system that depends on that behavior.
thinLTOCreateEmptyIndexFiles()295 static void thinLTOCreateEmptyIndexFiles() {
296 DenseSet<StringRef> linkedBitCodeFiles;
297 for (BitcodeFile *f : ctx.bitcodeFiles)
298 linkedBitCodeFiles.insert(f->getName());
299
300 for (BitcodeFile *f : ctx.lazyBitcodeFiles) {
301 if (!f->lazy)
302 continue;
303 if (linkedBitCodeFiles.contains(f->getName()))
304 continue;
305 std::string path =
306 replaceThinLTOSuffix(getThinLTOOutputFile(f->obj->getName()));
307 std::unique_ptr<raw_fd_ostream> os = openFile(path + ".thinlto.bc");
308 if (!os)
309 continue;
310
311 ModuleSummaryIndex m(/*HaveGVs*/ false);
312 m.setSkipModuleByDistributedBackend();
313 writeIndexToFile(m, *os);
314 if (config->thinLTOEmitImportsFiles)
315 openFile(path + ".imports");
316 }
317 }
318
319 // Merge all the bitcode files we have seen, codegen the result
320 // and return the resulting ObjectFile(s).
compile()321 std::vector<InputFile *> BitcodeCompiler::compile() {
322 unsigned maxTasks = ltoObj->getMaxTasks();
323 buf.resize(maxTasks);
324 files.resize(maxTasks);
325
326 // The --thinlto-cache-dir option specifies the path to a directory in which
327 // to cache native object files for ThinLTO incremental builds. If a path was
328 // specified, configure LTO to use it as the cache directory.
329 FileCache cache;
330 if (!config->thinLTOCacheDir.empty())
331 cache = check(localCache("ThinLTO", "Thin", config->thinLTOCacheDir,
332 [&](size_t task, const Twine &moduleName,
333 std::unique_ptr<MemoryBuffer> mb) {
334 files[task] = std::move(mb);
335 }));
336
337 if (!ctx.bitcodeFiles.empty())
338 checkError(ltoObj->run(
339 [&](size_t task, const Twine &moduleName) {
340 return std::make_unique<CachedFileStream>(
341 std::make_unique<raw_svector_ostream>(buf[task]));
342 },
343 cache));
344
345 // Emit empty index files for non-indexed files but not in single-module mode.
346 if (config->thinLTOModulesToCompile.empty()) {
347 for (StringRef s : thinIndices) {
348 std::string path = getThinLTOOutputFile(s);
349 openFile(path + ".thinlto.bc");
350 if (config->thinLTOEmitImportsFiles)
351 openFile(path + ".imports");
352 }
353 }
354
355 if (config->thinLTOEmitIndexFiles)
356 thinLTOCreateEmptyIndexFiles();
357
358 if (config->thinLTOIndexOnly) {
359 if (!config->ltoObjPath.empty())
360 saveBuffer(buf[0], config->ltoObjPath);
361
362 // ThinLTO with index only option is required to generate only the index
363 // files. After that, we exit from linker and ThinLTO backend runs in a
364 // distributed environment.
365 if (indexFile)
366 indexFile->close();
367 return {};
368 }
369
370 if (!config->thinLTOCacheDir.empty())
371 pruneCache(config->thinLTOCacheDir, config->thinLTOCachePolicy, files);
372
373 if (!config->ltoObjPath.empty()) {
374 saveBuffer(buf[0], config->ltoObjPath);
375 for (unsigned i = 1; i != maxTasks; ++i)
376 saveBuffer(buf[i], config->ltoObjPath + Twine(i));
377 }
378
379 if (config->saveTempsArgs.contains("prelink")) {
380 if (!buf[0].empty())
381 saveBuffer(buf[0], config->outputFile + ".lto.o");
382 for (unsigned i = 1; i != maxTasks; ++i)
383 saveBuffer(buf[i], config->outputFile + Twine(i) + ".lto.o");
384 }
385
386 if (config->ltoEmitAsm) {
387 saveBuffer(buf[0], config->outputFile);
388 for (unsigned i = 1; i != maxTasks; ++i)
389 saveBuffer(buf[i], config->outputFile + Twine(i));
390 return {};
391 }
392
393 std::vector<InputFile *> ret;
394 for (unsigned i = 0; i != maxTasks; ++i)
395 if (!buf[i].empty())
396 ret.push_back(createObjFile(MemoryBufferRef(buf[i], "lto.tmp")));
397
398 for (std::unique_ptr<MemoryBuffer> &file : files)
399 if (file)
400 ret.push_back(createObjFile(*file));
401 return ret;
402 }
403