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/ErrorHandler.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/IR/DiagnosticPrinter.h" 22 #include "llvm/LTO/Caching.h" 23 #include "llvm/LTO/Config.h" 24 #include "llvm/LTO/LTO.h" 25 #include "llvm/Object/SymbolicFile.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 "llvm/Support/raw_ostream.h" 31 #include <algorithm> 32 #include <cstddef> 33 #include <memory> 34 #include <string> 35 #include <system_error> 36 #include <vector> 37 38 using namespace llvm; 39 40 namespace lld { 41 namespace wasm { 42 static std::unique_ptr<lto::LTO> createLTO() { 43 lto::Config c; 44 c.Options = initTargetOptionsFromCodeGenFlags(); 45 46 // Always emit a section per function/data with LTO. 47 c.Options.FunctionSections = true; 48 c.Options.DataSections = true; 49 50 c.DisableVerify = config->disableVerify; 51 c.DiagHandler = diagnosticHandler; 52 c.OptLevel = config->ltoo; 53 c.MAttrs = getMAttrs(); 54 c.CGOptLevel = args::getCGOptLevel(config->ltoo); 55 56 if (config->relocatable) 57 c.RelocModel = None; 58 else if (config->isPic) 59 c.RelocModel = Reloc::PIC_; 60 else 61 c.RelocModel = Reloc::Static; 62 63 if (config->saveTemps) 64 checkError(c.addSaveTemps(config->outputFile.str() + ".", 65 /*UseInputModulePath*/ true)); 66 67 lto::ThinBackend backend; 68 if (config->thinLTOJobs != -1U) 69 backend = lto::createInProcessThinBackend(config->thinLTOJobs); 70 return std::make_unique<lto::LTO>(std::move(c), backend, 71 config->ltoPartitions); 72 } 73 74 BitcodeCompiler::BitcodeCompiler() : ltoObj(createLTO()) {} 75 76 BitcodeCompiler::~BitcodeCompiler() = default; 77 78 static void undefine(Symbol *s) { 79 if (auto f = dyn_cast<DefinedFunction>(s)) 80 replaceSymbol<UndefinedFunction>(f, f->getName(), "", "", 0, f->getFile(), 81 f->signature); 82 else if (isa<DefinedData>(s)) 83 replaceSymbol<UndefinedData>(s, s->getName(), 0, s->getFile()); 84 else 85 llvm_unreachable("unexpected symbol kind"); 86 } 87 88 void BitcodeCompiler::add(BitcodeFile &f) { 89 lto::InputFile &obj = *f.obj; 90 unsigned symNum = 0; 91 ArrayRef<Symbol *> syms = f.getSymbols(); 92 std::vector<lto::SymbolResolution> resols(syms.size()); 93 94 // Provide a resolution to the LTO API for each symbol. 95 for (const lto::InputFile::Symbol &objSym : obj.symbols()) { 96 Symbol *sym = syms[symNum]; 97 lto::SymbolResolution &r = resols[symNum]; 98 ++symNum; 99 100 // Ideally we shouldn't check for SF_Undefined but currently IRObjectFile 101 // reports two symbols for module ASM defined. Without this check, lld 102 // flags an undefined in IR with a definition in ASM as prevailing. 103 // Once IRObjectFile is fixed to report only one symbol this hack can 104 // be removed. 105 r.Prevailing = !objSym.isUndefined() && sym->getFile() == &f; 106 r.VisibleToRegularObj = config->relocatable || sym->isUsedInRegularObj || 107 sym->isNoStrip() || 108 (r.Prevailing && sym->isExported()); 109 if (r.Prevailing) 110 undefine(sym); 111 112 // We tell LTO to not apply interprocedural optimization for wrapped 113 // (with --wrap) symbols because otherwise LTO would inline them while 114 // their values are still not final. 115 r.LinkerRedefined = !sym->canInline; 116 } 117 checkError(ltoObj->add(std::move(f.obj), resols)); 118 } 119 120 // Merge all the bitcode files we have seen, codegen the result 121 // and return the resulting objects. 122 std::vector<StringRef> BitcodeCompiler::compile() { 123 unsigned maxTasks = ltoObj->getMaxTasks(); 124 buf.resize(maxTasks); 125 files.resize(maxTasks); 126 127 // The --thinlto-cache-dir option specifies the path to a directory in which 128 // to cache native object files for ThinLTO incremental builds. If a path was 129 // specified, configure LTO to use it as the cache directory. 130 lto::NativeObjectCache cache; 131 if (!config->thinLTOCacheDir.empty()) 132 cache = check( 133 lto::localCache(config->thinLTOCacheDir, 134 [&](size_t task, std::unique_ptr<MemoryBuffer> mb) { 135 files[task] = std::move(mb); 136 })); 137 138 checkError(ltoObj->run( 139 [&](size_t task) { 140 return std::make_unique<lto::NativeObjectStream>( 141 std::make_unique<raw_svector_ostream>(buf[task])); 142 }, 143 cache)); 144 145 if (!config->thinLTOCacheDir.empty()) 146 pruneCache(config->thinLTOCacheDir, config->thinLTOCachePolicy); 147 148 std::vector<StringRef> ret; 149 for (unsigned i = 0; i != maxTasks; ++i) { 150 if (buf[i].empty()) 151 continue; 152 if (config->saveTemps) { 153 if (i == 0) 154 saveBuffer(buf[i], config->outputFile + ".lto.o"); 155 else 156 saveBuffer(buf[i], config->outputFile + Twine(i) + ".lto.o"); 157 } 158 ret.emplace_back(buf[i].data(), buf[i].size()); 159 } 160 161 for (std::unique_ptr<MemoryBuffer> &file : files) 162 if (file) 163 ret.push_back(file->getBuffer()); 164 165 return ret; 166 } 167 168 } // namespace wasm 169 } // namespace lld 170