xref: /freebsd/contrib/llvm-project/lld/ELF/LTO.cpp (revision e32fecd0c2c3ee37c47ee100f169e7eb0282a873)
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.
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.
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 
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 
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.RelaxELFRelocations = true;
81   c.Options.EmitAddrsig = true;
82 
83   // Always emit a section per function/datum with LTO.
84   c.Options.FunctionSections = true;
85   c.Options.DataSections = true;
86 
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;
98     } else {
99       ErrorOr<std::unique_ptr<MemoryBuffer>> MBOrErr =
100           MemoryBuffer::getFile(config->ltoBasicBlockSections.str());
101       if (!MBOrErr) {
102         error("cannot open " + config->ltoBasicBlockSections + ":" +
103               MBOrErr.getError().message());
104       } else {
105         c.Options.BBSectionsFuncListBuf = std::move(*MBOrErr);
106       }
107       c.Options.BBSections = BasicBlockSection::List;
108     }
109   }
110 
111   c.Options.UniqueBasicBlockSectionNames =
112       config->ltoUniqueBasicBlockSectionNames;
113 
114   if (auto relocModel = getRelocModelFromCMModel())
115     c.RelocModel = *relocModel;
116   else if (config->relocatable)
117     c.RelocModel = None;
118   else if (config->isPic)
119     c.RelocModel = Reloc::PIC_;
120   else
121     c.RelocModel = Reloc::Static;
122 
123   c.CodeModel = getCodeModelFromCMModel();
124   c.DisableVerify = config->disableVerify;
125   c.DiagHandler = diagnosticHandler;
126   c.OptLevel = config->ltoo;
127   c.CPU = getCPUStr();
128   c.MAttrs = getMAttrs();
129   c.CGOptLevel = args::getCGOptLevel(config->ltoo);
130 
131   c.PTO.LoopVectorization = c.OptLevel > 1;
132   c.PTO.SLPVectorization = c.OptLevel > 1;
133 
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);
137 
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);
144 
145   // Set up output file to emit statistics.
146   c.StatsFile = std::string(config->optStatsFilename);
147 
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);
153 
154   c.HasWholeProgramVisibility = config->ltoWholeProgramVisibility;
155   c.AlwaysEmitRegularLTOObj = !config->ltoObjPath.empty();
156 
157   for (const llvm::StringRef &name : config->thinLTOModulesToCompile)
158     c.ThinLTOModulesToCompile.emplace_back(name);
159 
160   c.TimeTraceEnabled = config->timeTraceEnabled;
161   c.TimeTraceGranularity = config->timeTraceGranularity;
162 
163   c.CSIRProfile = std::string(config->ltoCSProfileFile);
164   c.RunCSIRInstr = config->ltoCSProfileGenerate;
165   c.PGOWarnMismatch = config->ltoPGOWarnMismatch;
166 
167   c.OpaquePointers = config->opaquePointers;
168 
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);
174       return false;
175     };
176   }
177 
178   if (config->ltoEmitAsm)
179     c.CGFileType = CGFT_AssemblyFile;
180 
181   if (!config->saveTempsArgs.empty())
182     checkError(c.addSaveTemps(config->outputFile.str() + ".",
183                               /*UseInputModulePath*/ true,
184                               config->saveTempsArgs));
185   return c;
186 }
187 
188 BitcodeCompiler::BitcodeCompiler() {
189   // Initialize indexFile.
190   if (!config->thinLTOIndexOnlyArg.empty())
191     indexFile = openFile(config->thinLTOIndexOnlyArg);
192 
193   // Initialize ltoObj.
194   lto::ThinBackend backend;
195   auto onIndexWrite = [&](StringRef s) { thinIndices.erase(s); };
196   if (config->thinLTOIndexOnly) {
197     backend = lto::createWriteIndexesThinBackend(
198         std::string(config->thinLTOPrefixReplace.first),
199         std::string(config->thinLTOPrefixReplace.second),
200         config->thinLTOEmitImportsFiles, indexFile.get(), onIndexWrite);
201   } else {
202     backend = lto::createInProcessThinBackend(
203         llvm::heavyweight_hardware_concurrency(config->thinLTOJobs),
204         onIndexWrite, config->thinLTOEmitIndexFiles,
205         config->thinLTOEmitImportsFiles);
206   }
207 
208   ltoObj = std::make_unique<lto::LTO>(createConfig(), backend,
209                                        config->ltoPartitions);
210 
211   // Initialize usedStartStop.
212   if (ctx->bitcodeFiles.empty())
213     return;
214   for (Symbol *sym : symtab->symbols()) {
215     if (sym->isPlaceholder())
216       continue;
217     StringRef s = sym->getName();
218     for (StringRef prefix : {"__start_", "__stop_"})
219       if (s.startswith(prefix))
220         usedStartStop.insert(s.substr(prefix.size()));
221   }
222 }
223 
224 BitcodeCompiler::~BitcodeCompiler() = default;
225 
226 void BitcodeCompiler::add(BitcodeFile &f) {
227   lto::InputFile &obj = *f.obj;
228   bool isExec = !config->shared && !config->relocatable;
229 
230   if (config->thinLTOEmitIndexFiles)
231     thinIndices.insert(obj.getName());
232 
233   ArrayRef<Symbol *> syms = f.getSymbols();
234   ArrayRef<lto::InputFile::Symbol> objSyms = obj.symbols();
235   std::vector<lto::SymbolResolution> resols(syms.size());
236 
237   // Provide a resolution to the LTO API for each symbol.
238   for (size_t i = 0, e = syms.size(); i != e; ++i) {
239     Symbol *sym = syms[i];
240     const lto::InputFile::Symbol &objSym = objSyms[i];
241     lto::SymbolResolution &r = resols[i];
242 
243     // Ideally we shouldn't check for SF_Undefined but currently IRObjectFile
244     // reports two symbols for module ASM defined. Without this check, lld
245     // flags an undefined in IR with a definition in ASM as prevailing.
246     // Once IRObjectFile is fixed to report only one symbol this hack can
247     // be removed.
248     r.Prevailing = !objSym.isUndefined() && sym->file == &f;
249 
250     // We ask LTO to preserve following global symbols:
251     // 1) All symbols when doing relocatable link, so that them can be used
252     //    for doing final link.
253     // 2) Symbols that are used in regular objects.
254     // 3) C named sections if we have corresponding __start_/__stop_ symbol.
255     // 4) Symbols that are defined in bitcode files and used for dynamic
256     //    linking.
257     // 5) Symbols that will be referenced after linker wrapping is performed.
258     r.VisibleToRegularObj = config->relocatable || sym->isUsedInRegularObj ||
259                             sym->referencedAfterWrap ||
260                             (r.Prevailing && sym->includeInDynsym()) ||
261                             usedStartStop.count(objSym.getSectionName());
262     // Identify symbols exported dynamically, and that therefore could be
263     // referenced by a shared library not visible to the linker.
264     r.ExportDynamic =
265         sym->computeBinding() != STB_LOCAL &&
266         (config->exportDynamic || sym->exportDynamic || sym->inDynamicList);
267     const auto *dr = dyn_cast<Defined>(sym);
268     r.FinalDefinitionInLinkageUnit =
269         (isExec || sym->visibility != STV_DEFAULT) && dr &&
270         // Skip absolute symbols from ELF objects, otherwise PC-rel relocations
271         // will be generated by for them, triggering linker errors.
272         // Symbol section is always null for bitcode symbols, hence the check
273         // for isElf(). Skip linker script defined symbols as well: they have
274         // no File defined.
275         !(dr->section == nullptr && (!sym->file || sym->file->isElf()));
276 
277     if (r.Prevailing)
278       sym->replace(
279           Undefined{nullptr, StringRef(), STB_GLOBAL, STV_DEFAULT, sym->type});
280 
281     // We tell LTO to not apply interprocedural optimization for wrapped
282     // (with --wrap) symbols because otherwise LTO would inline them while
283     // their values are still not final.
284     r.LinkerRedefined = sym->scriptDefined;
285   }
286   checkError(ltoObj->add(std::move(f.obj), resols));
287 }
288 
289 // If LazyObjFile has not been added to link, emit empty index files.
290 // This is needed because this is what GNU gold plugin does and we have a
291 // distributed build system that depends on that behavior.
292 static void thinLTOCreateEmptyIndexFiles() {
293   for (BitcodeFile *f : ctx->lazyBitcodeFiles) {
294     if (!f->lazy)
295       continue;
296     std::string path = replaceThinLTOSuffix(getThinLTOOutputFile(f->getName()));
297     std::unique_ptr<raw_fd_ostream> os = openFile(path + ".thinlto.bc");
298     if (!os)
299       continue;
300 
301     ModuleSummaryIndex m(/*HaveGVs*/ false);
302     m.setSkipModuleByDistributedBackend();
303     writeIndexToFile(m, *os);
304     if (config->thinLTOEmitImportsFiles)
305       openFile(path + ".imports");
306   }
307 }
308 
309 // Merge all the bitcode files we have seen, codegen the result
310 // and return the resulting ObjectFile(s).
311 std::vector<InputFile *> BitcodeCompiler::compile() {
312   unsigned maxTasks = ltoObj->getMaxTasks();
313   buf.resize(maxTasks);
314   files.resize(maxTasks);
315 
316   // The --thinlto-cache-dir option specifies the path to a directory in which
317   // to cache native object files for ThinLTO incremental builds. If a path was
318   // specified, configure LTO to use it as the cache directory.
319   FileCache cache;
320   if (!config->thinLTOCacheDir.empty())
321     cache =
322         check(localCache("ThinLTO", "Thin", config->thinLTOCacheDir,
323                          [&](size_t task, std::unique_ptr<MemoryBuffer> mb) {
324                            files[task] = std::move(mb);
325                          }));
326 
327   if (!ctx->bitcodeFiles.empty())
328     checkError(ltoObj->run(
329         [&](size_t task) {
330           return std::make_unique<CachedFileStream>(
331               std::make_unique<raw_svector_ostream>(buf[task]));
332         },
333         cache));
334 
335   // Emit empty index files for non-indexed files but not in single-module mode.
336   if (config->thinLTOModulesToCompile.empty()) {
337     for (StringRef s : thinIndices) {
338       std::string path = getThinLTOOutputFile(s);
339       openFile(path + ".thinlto.bc");
340       if (config->thinLTOEmitImportsFiles)
341         openFile(path + ".imports");
342     }
343   }
344 
345   if (config->thinLTOEmitIndexFiles)
346     thinLTOCreateEmptyIndexFiles();
347 
348   if (config->thinLTOIndexOnly) {
349     if (!config->ltoObjPath.empty())
350       saveBuffer(buf[0], config->ltoObjPath);
351 
352     // ThinLTO with index only option is required to generate only the index
353     // files. After that, we exit from linker and ThinLTO backend runs in a
354     // distributed environment.
355     if (indexFile)
356       indexFile->close();
357     return {};
358   }
359 
360   if (!config->thinLTOCacheDir.empty())
361     pruneCache(config->thinLTOCacheDir, config->thinLTOCachePolicy);
362 
363   if (!config->ltoObjPath.empty()) {
364     saveBuffer(buf[0], config->ltoObjPath);
365     for (unsigned i = 1; i != maxTasks; ++i)
366       saveBuffer(buf[i], config->ltoObjPath + Twine(i));
367   }
368 
369   if (config->saveTempsArgs.contains("prelink")) {
370     if (!buf[0].empty())
371       saveBuffer(buf[0], config->outputFile + ".lto.o");
372     for (unsigned i = 1; i != maxTasks; ++i)
373       saveBuffer(buf[i], config->outputFile + Twine(i) + ".lto.o");
374   }
375 
376   if (config->ltoEmitAsm) {
377     saveBuffer(buf[0], config->outputFile);
378     for (unsigned i = 1; i != maxTasks; ++i)
379       saveBuffer(buf[i], config->outputFile + Twine(i));
380     return {};
381   }
382 
383   std::vector<InputFile *> ret;
384   for (unsigned i = 0; i != maxTasks; ++i)
385     if (!buf[i].empty())
386       ret.push_back(createObjFile(MemoryBufferRef(buf[i], "lto.tmp")));
387 
388   for (std::unique_ptr<MemoryBuffer> &file : files)
389     if (file)
390       ret.push_back(createObjFile(*file));
391   return ret;
392 }
393