lld/COFF/LTO.cpp

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