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 "COFFLinkerContext.h"
11 #include "Config.h"
12 #include "InputFiles.h"
13 #include "Symbols.h"
14 #include "lld/Common/Args.h"
15 #include "lld/Common/CommonLinkerContext.h"
16 #include "lld/Common/Filesystem.h"
17 #include "lld/Common/Strings.h"
18 #include "lld/Common/TargetOptionsCommandFlags.h"
19 #include "llvm/ADT/STLExtras.h"
20 #include "llvm/ADT/SmallString.h"
21 #include "llvm/ADT/StringRef.h"
22 #include "llvm/ADT/Twine.h"
23 #include "llvm/Bitcode/BitcodeWriter.h"
24 #include "llvm/IR/DiagnosticPrinter.h"
25 #include "llvm/LTO/Config.h"
26 #include "llvm/LTO/LTO.h"
27 #include "llvm/Object/SymbolicFile.h"
28 #include "llvm/Support/Caching.h"
29 #include "llvm/Support/CodeGen.h"
30 #include "llvm/Support/Error.h"
31 #include "llvm/Support/FileSystem.h"
32 #include "llvm/Support/MemoryBuffer.h"
33 #include "llvm/Support/raw_ostream.h"
34 #include <algorithm>
35 #include <cstddef>
36 #include <memory>
37 #include <string>
38 #include <system_error>
39 #include <vector>
40
41 using namespace llvm;
42 using namespace llvm::object;
43 using namespace lld;
44 using namespace lld::coff;
45
getThinLTOOutputFile(StringRef path)46 std::string BitcodeCompiler::getThinLTOOutputFile(StringRef path) {
47 return lto::getThinLTOOutputFile(path, ctx.config.thinLTOPrefixReplaceOld,
48 ctx.config.thinLTOPrefixReplaceNew);
49 }
50
createConfig()51 lto::Config BitcodeCompiler::createConfig() {
52 lto::Config c;
53 c.Options = initTargetOptionsFromCodeGenFlags();
54 c.Options.EmitAddrsig = true;
55 for (StringRef C : ctx.config.mllvmOpts)
56 c.MllvmArgs.emplace_back(C.str());
57
58 // Always emit a section per function/datum with LTO. LLVM LTO should get most
59 // of the benefit of linker GC, but there are still opportunities for ICF.
60 c.Options.FunctionSections = true;
61 c.Options.DataSections = true;
62
63 // Use static reloc model on 32-bit x86 because it usually results in more
64 // compact code, and because there are also known code generation bugs when
65 // using the PIC model (see PR34306).
66 if (ctx.config.machine == COFF::IMAGE_FILE_MACHINE_I386)
67 c.RelocModel = Reloc::Static;
68 else
69 c.RelocModel = Reloc::PIC_;
70 #ifndef NDEBUG
71 c.DisableVerify = false;
72 #else
73 c.DisableVerify = true;
74 #endif
75 c.DiagHandler = diagnosticHandler;
76 c.DwoDir = ctx.config.dwoDir.str();
77 c.OptLevel = ctx.config.ltoo;
78 c.CPU = getCPUStr();
79 c.MAttrs = getMAttrs();
80 std::optional<CodeGenOptLevel> optLevelOrNone = CodeGenOpt::getLevel(
81 ctx.config.ltoCgo.value_or(args::getCGOptLevel(ctx.config.ltoo)));
82 assert(optLevelOrNone && "Invalid optimization level!");
83 c.CGOptLevel = *optLevelOrNone;
84 c.AlwaysEmitRegularLTOObj = !ctx.config.ltoObjPath.empty();
85 c.DebugPassManager = ctx.config.ltoDebugPassManager;
86 c.CSIRProfile = std::string(ctx.config.ltoCSProfileFile);
87 c.RunCSIRInstr = ctx.config.ltoCSProfileGenerate;
88 c.PGOWarnMismatch = ctx.config.ltoPGOWarnMismatch;
89 c.SampleProfile = ctx.config.ltoSampleProfileName;
90 c.TimeTraceEnabled = ctx.config.timeTraceEnabled;
91 c.TimeTraceGranularity = ctx.config.timeTraceGranularity;
92
93 if (ctx.config.emit == EmitKind::LLVM) {
94 c.PreCodeGenModuleHook = [this](size_t task, const Module &m) {
95 if (std::unique_ptr<raw_fd_ostream> os =
96 openLTOOutputFile(ctx.config.outputFile))
97 WriteBitcodeToFile(m, *os, false);
98 return false;
99 };
100 } else if (ctx.config.emit == EmitKind::ASM) {
101 c.CGFileType = CodeGenFileType::AssemblyFile;
102 c.Options.MCOptions.AsmVerbose = true;
103 }
104
105 if (ctx.config.saveTemps)
106 checkError(c.addSaveTemps(std::string(ctx.config.outputFile) + ".",
107 /*UseInputModulePath*/ true));
108 return c;
109 }
110
BitcodeCompiler(COFFLinkerContext & c)111 BitcodeCompiler::BitcodeCompiler(COFFLinkerContext &c) : ctx(c) {
112 // Initialize indexFile.
113 if (!ctx.config.thinLTOIndexOnlyArg.empty())
114 indexFile = openFile(ctx.config.thinLTOIndexOnlyArg);
115
116 // Initialize ltoObj.
117 lto::ThinBackend backend;
118 if (ctx.config.thinLTOIndexOnly) {
119 auto OnIndexWrite = [&](StringRef S) { thinIndices.erase(S); };
120 backend = lto::createWriteIndexesThinBackend(
121 std::string(ctx.config.thinLTOPrefixReplaceOld),
122 std::string(ctx.config.thinLTOPrefixReplaceNew),
123 std::string(ctx.config.thinLTOPrefixReplaceNativeObject),
124 ctx.config.thinLTOEmitImportsFiles, indexFile.get(), OnIndexWrite);
125 } else {
126 backend = lto::createInProcessThinBackend(
127 llvm::heavyweight_hardware_concurrency(ctx.config.thinLTOJobs));
128 }
129
130 ltoObj = std::make_unique<lto::LTO>(createConfig(), backend,
131 ctx.config.ltoPartitions);
132 }
133
134 BitcodeCompiler::~BitcodeCompiler() = default;
135
undefine(Symbol * s)136 static void undefine(Symbol *s) { replaceSymbol<Undefined>(s, s->getName()); }
137
add(BitcodeFile & f)138 void BitcodeCompiler::add(BitcodeFile &f) {
139 lto::InputFile &obj = *f.obj;
140 unsigned symNum = 0;
141 std::vector<Symbol *> symBodies = f.getSymbols();
142 std::vector<lto::SymbolResolution> resols(symBodies.size());
143
144 if (ctx.config.thinLTOIndexOnly)
145 thinIndices.insert(obj.getName());
146
147 // Provide a resolution to the LTO API for each symbol.
148 for (const lto::InputFile::Symbol &objSym : obj.symbols()) {
149 Symbol *sym = symBodies[symNum];
150 lto::SymbolResolution &r = resols[symNum];
151 ++symNum;
152
153 // Ideally we shouldn't check for SF_Undefined but currently IRObjectFile
154 // reports two symbols for module ASM defined. Without this check, lld
155 // flags an undefined in IR with a definition in ASM as prevailing.
156 // Once IRObjectFile is fixed to report only one symbol this hack can
157 // be removed.
158 r.Prevailing = !objSym.isUndefined() && sym->getFile() == &f;
159 r.VisibleToRegularObj = sym->isUsedInRegularObj;
160 if (r.Prevailing)
161 undefine(sym);
162
163 // We tell LTO to not apply interprocedural optimization for wrapped
164 // (with -wrap) symbols because otherwise LTO would inline them while
165 // their values are still not final.
166 r.LinkerRedefined = !sym->canInline;
167 }
168 checkError(ltoObj->add(std::move(f.obj), resols));
169 }
170
171 // Merge all the bitcode files we have seen, codegen the result
172 // and return the resulting objects.
compile()173 std::vector<InputFile *> BitcodeCompiler::compile() {
174 unsigned maxTasks = ltoObj->getMaxTasks();
175 buf.resize(maxTasks);
176 files.resize(maxTasks);
177 file_names.resize(maxTasks);
178
179 // The /lldltocache option specifies the path to a directory in which to cache
180 // native object files for ThinLTO incremental builds. If a path was
181 // specified, configure LTO to use it as the cache directory.
182 FileCache cache;
183 if (!ctx.config.ltoCache.empty())
184 cache = check(localCache("ThinLTO", "Thin", ctx.config.ltoCache,
185 [&](size_t task, const Twine &moduleName,
186 std::unique_ptr<MemoryBuffer> mb) {
187 files[task] = std::move(mb);
188 file_names[task] = moduleName.str();
189 }));
190
191 checkError(ltoObj->run(
192 [&](size_t task, const Twine &moduleName) {
193 buf[task].first = moduleName.str();
194 return std::make_unique<CachedFileStream>(
195 std::make_unique<raw_svector_ostream>(buf[task].second));
196 },
197 cache));
198
199 // Emit empty index files for non-indexed files
200 for (StringRef s : thinIndices) {
201 std::string path = getThinLTOOutputFile(s);
202 openFile(path + ".thinlto.bc");
203 if (ctx.config.thinLTOEmitImportsFiles)
204 openFile(path + ".imports");
205 }
206
207 // ThinLTO with index only option is required to generate only the index
208 // files. After that, we exit from linker and ThinLTO backend runs in a
209 // distributed environment.
210 if (ctx.config.thinLTOIndexOnly) {
211 if (!ctx.config.ltoObjPath.empty())
212 saveBuffer(buf[0].second, ctx.config.ltoObjPath);
213 if (indexFile)
214 indexFile->close();
215 return {};
216 }
217
218 if (!ctx.config.ltoCache.empty())
219 pruneCache(ctx.config.ltoCache, ctx.config.ltoCachePolicy, files);
220
221 std::vector<InputFile *> ret;
222 bool emitASM = ctx.config.emit == EmitKind::ASM;
223 const char *Ext = emitASM ? ".s" : ".obj";
224 for (unsigned i = 0; i != maxTasks; ++i) {
225 StringRef bitcodeFilePath;
226 // Get the native object contents either from the cache or from memory. Do
227 // not use the cached MemoryBuffer directly, or the PDB will not be
228 // deterministic.
229 StringRef objBuf;
230 if (files[i]) {
231 objBuf = files[i]->getBuffer();
232 bitcodeFilePath = file_names[i];
233 } else {
234 objBuf = buf[i].second;
235 bitcodeFilePath = buf[i].first;
236 }
237 if (objBuf.empty())
238 continue;
239
240 // If the input bitcode file is path/to/a.obj, then the corresponding lto
241 // object file name will look something like: path/to/main.exe.lto.a.obj.
242 StringRef ltoObjName;
243 if (bitcodeFilePath == "ld-temp.o") {
244 ltoObjName =
245 saver().save(Twine(ctx.config.outputFile) + ".lto" +
246 (i == 0 ? Twine("") : Twine('.') + Twine(i)) + Ext);
247 } else {
248 StringRef directory = sys::path::parent_path(bitcodeFilePath);
249 StringRef baseName = sys::path::stem(bitcodeFilePath);
250 StringRef outputFileBaseName = sys::path::filename(ctx.config.outputFile);
251 SmallString<64> path;
252 sys::path::append(path, directory,
253 outputFileBaseName + ".lto." + baseName + Ext);
254 sys::path::remove_dots(path, true);
255 ltoObjName = saver().save(path.str());
256 }
257 if (ctx.config.saveTemps || emitASM)
258 saveBuffer(buf[i].second, ltoObjName);
259 if (!emitASM)
260 ret.push_back(make<ObjFile>(ctx, MemoryBufferRef(objBuf, ltoObjName)));
261 }
262
263 return ret;
264 }
265