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 "Symbols.h"
13 #include "lld/Common/Args.h"
14 #include "lld/Common/CommonLinkerContext.h"
15 #include "lld/Common/Strings.h"
16 #include "lld/Common/TargetOptionsCommandFlags.h"
17 #include "llvm/ADT/STLExtras.h"
18 #include "llvm/ADT/SmallString.h"
19 #include "llvm/ADT/StringRef.h"
20 #include "llvm/ADT/Twine.h"
21 #include "llvm/Bitcode/BitcodeWriter.h"
22 #include "llvm/IR/DiagnosticPrinter.h"
23 #include "llvm/LTO/Config.h"
24 #include "llvm/LTO/LTO.h"
25 #include "llvm/Object/SymbolicFile.h"
26 #include "llvm/Support/Caching.h"
27 #include "llvm/Support/CodeGen.h"
28 #include "llvm/Support/Error.h"
29 #include "llvm/Support/FileSystem.h"
30 #include "llvm/Support/MemoryBuffer.h"
31 #include "llvm/Support/raw_ostream.h"
32 #include <algorithm>
33 #include <cstddef>
34 #include <memory>
35 #include <string>
36 #include <system_error>
37 #include <vector>
38
39 using namespace llvm;
40 using namespace llvm::object;
41 using namespace lld;
42 using namespace lld::coff;
43
44 // Creates an empty file to and returns a raw_fd_ostream to write to it.
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
getThinLTOOutputFile(StringRef path)56 static std::string getThinLTOOutputFile(StringRef path) {
57 return lto::getThinLTOOutputFile(
58 std::string(path), std::string(config->thinLTOPrefixReplace.first),
59 std::string(config->thinLTOPrefixReplace.second));
60 }
61
createConfig()62 static lto::Config createConfig() {
63 lto::Config c;
64 c.Options = initTargetOptionsFromCodeGenFlags();
65 c.Options.EmitAddrsig = true;
66
67 // Always emit a section per function/datum with LTO. LLVM LTO should get most
68 // of the benefit of linker GC, but there are still opportunities for ICF.
69 c.Options.FunctionSections = true;
70 c.Options.DataSections = true;
71
72 // Use static reloc model on 32-bit x86 because it usually results in more
73 // compact code, and because there are also known code generation bugs when
74 // using the PIC model (see PR34306).
75 if (config->machine == COFF::IMAGE_FILE_MACHINE_I386)
76 c.RelocModel = Reloc::Static;
77 else
78 c.RelocModel = Reloc::PIC_;
79 c.DisableVerify = true;
80 c.DiagHandler = diagnosticHandler;
81 c.OptLevel = config->ltoo;
82 c.CPU = getCPUStr();
83 c.MAttrs = getMAttrs();
84 c.CGOptLevel = args::getCGOptLevel(config->ltoo);
85 c.AlwaysEmitRegularLTOObj = !config->ltoObjPath.empty();
86 c.DebugPassManager = config->ltoDebugPassManager;
87 c.CSIRProfile = std::string(config->ltoCSProfileFile);
88 c.RunCSIRInstr = config->ltoCSProfileGenerate;
89 c.PGOWarnMismatch = config->ltoPGOWarnMismatch;
90
91 if (config->saveTemps)
92 checkError(c.addSaveTemps(std::string(config->outputFile) + ".",
93 /*UseInputModulePath*/ true));
94 return c;
95 }
96
BitcodeCompiler()97 BitcodeCompiler::BitcodeCompiler() {
98 // Initialize indexFile.
99 if (!config->thinLTOIndexOnlyArg.empty())
100 indexFile = openFile(config->thinLTOIndexOnlyArg);
101
102 // Initialize ltoObj.
103 lto::ThinBackend backend;
104 if (config->thinLTOIndexOnly) {
105 auto OnIndexWrite = [&](StringRef S) { thinIndices.erase(S); };
106 backend = lto::createWriteIndexesThinBackend(
107 std::string(config->thinLTOPrefixReplace.first),
108 std::string(config->thinLTOPrefixReplace.second),
109 config->thinLTOEmitImportsFiles, indexFile.get(), OnIndexWrite);
110 } else {
111 backend = lto::createInProcessThinBackend(
112 llvm::heavyweight_hardware_concurrency(config->thinLTOJobs));
113 }
114
115 ltoObj = std::make_unique<lto::LTO>(createConfig(), backend,
116 config->ltoPartitions);
117 }
118
119 BitcodeCompiler::~BitcodeCompiler() = default;
120
undefine(Symbol * s)121 static void undefine(Symbol *s) { replaceSymbol<Undefined>(s, s->getName()); }
122
add(BitcodeFile & f)123 void BitcodeCompiler::add(BitcodeFile &f) {
124 lto::InputFile &obj = *f.obj;
125 unsigned symNum = 0;
126 std::vector<Symbol *> symBodies = f.getSymbols();
127 std::vector<lto::SymbolResolution> resols(symBodies.size());
128
129 if (config->thinLTOIndexOnly)
130 thinIndices.insert(obj.getName());
131
132 // Provide a resolution to the LTO API for each symbol.
133 for (const lto::InputFile::Symbol &objSym : obj.symbols()) {
134 Symbol *sym = symBodies[symNum];
135 lto::SymbolResolution &r = resols[symNum];
136 ++symNum;
137
138 // Ideally we shouldn't check for SF_Undefined but currently IRObjectFile
139 // reports two symbols for module ASM defined. Without this check, lld
140 // flags an undefined in IR with a definition in ASM as prevailing.
141 // Once IRObjectFile is fixed to report only one symbol this hack can
142 // be removed.
143 r.Prevailing = !objSym.isUndefined() && sym->getFile() == &f;
144 r.VisibleToRegularObj = sym->isUsedInRegularObj;
145 if (r.Prevailing)
146 undefine(sym);
147
148 // We tell LTO to not apply interprocedural optimization for wrapped
149 // (with -wrap) symbols because otherwise LTO would inline them while
150 // their values are still not final.
151 r.LinkerRedefined = !sym->canInline;
152 }
153 checkError(ltoObj->add(std::move(f.obj), resols));
154 }
155
156 // Merge all the bitcode files we have seen, codegen the result
157 // and return the resulting objects.
compile(COFFLinkerContext & ctx)158 std::vector<InputFile *> BitcodeCompiler::compile(COFFLinkerContext &ctx) {
159 unsigned maxTasks = ltoObj->getMaxTasks();
160 buf.resize(maxTasks);
161 files.resize(maxTasks);
162
163 // The /lldltocache option specifies the path to a directory in which to cache
164 // native object files for ThinLTO incremental builds. If a path was
165 // specified, configure LTO to use it as the cache directory.
166 FileCache cache;
167 if (!config->ltoCache.empty())
168 cache =
169 check(localCache("ThinLTO", "Thin", config->ltoCache,
170 [&](size_t task, std::unique_ptr<MemoryBuffer> mb) {
171 files[task] = std::move(mb);
172 }));
173
174 checkError(ltoObj->run(
175 [&](size_t task) {
176 return std::make_unique<CachedFileStream>(
177 std::make_unique<raw_svector_ostream>(buf[task]));
178 },
179 cache));
180
181 // Emit empty index files for non-indexed files
182 for (StringRef s : thinIndices) {
183 std::string path = getThinLTOOutputFile(s);
184 openFile(path + ".thinlto.bc");
185 if (config->thinLTOEmitImportsFiles)
186 openFile(path + ".imports");
187 }
188
189 // ThinLTO with index only option is required to generate only the index
190 // files. After that, we exit from linker and ThinLTO backend runs in a
191 // distributed environment.
192 if (config->thinLTOIndexOnly) {
193 if (!config->ltoObjPath.empty())
194 saveBuffer(buf[0], config->ltoObjPath);
195 if (indexFile)
196 indexFile->close();
197 return {};
198 }
199
200 if (!config->ltoCache.empty())
201 pruneCache(config->ltoCache, config->ltoCachePolicy);
202
203 std::vector<InputFile *> ret;
204 for (unsigned i = 0; i != maxTasks; ++i) {
205 // Assign unique names to LTO objects. This ensures they have unique names
206 // in the PDB if one is produced. The names should look like:
207 // - foo.exe.lto.obj
208 // - foo.exe.lto.1.obj
209 // - ...
210 StringRef ltoObjName =
211 saver().save(Twine(config->outputFile) + ".lto" +
212 (i == 0 ? Twine("") : Twine('.') + Twine(i)) + ".obj");
213
214 // Get the native object contents either from the cache or from memory. Do
215 // not use the cached MemoryBuffer directly, or the PDB will not be
216 // deterministic.
217 StringRef objBuf;
218 if (files[i])
219 objBuf = files[i]->getBuffer();
220 else
221 objBuf = buf[i];
222 if (objBuf.empty())
223 continue;
224
225 if (config->saveTemps)
226 saveBuffer(buf[i], ltoObjName);
227 ret.push_back(make<ObjFile>(ctx, MemoryBufferRef(objBuf, ltoObjName)));
228 }
229
230 return ret;
231 }
232