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 "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.
  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 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
  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.UseNewPM = config->ltoNewPassManager;
  87   c.DebugPassManager = config->ltoDebugPassManager;
  88   c.CSIRProfile = std::string(config->ltoCSProfileFile);
  89   c.RunCSIRInstr = config->ltoCSProfileGenerate;
  90   c.PGOWarnMismatch = config->ltoPGOWarnMismatch;
  91
  92   if (config->saveTemps)
  93     checkError(c.addSaveTemps(std::string(config->outputFile) + ".",
  94                               /*UseInputModulePath*/ true));
  95   return c;
  96 }
  97
  98 BitcodeCompiler::BitcodeCompiler() {
  99   // Initialize indexFile.
 100   if (!config->thinLTOIndexOnlyArg.empty())
 101     indexFile = openFile(config->thinLTOIndexOnlyArg);
 102
 103   // Initialize ltoObj.
 104   lto::ThinBackend backend;
 105   if (config->thinLTOIndexOnly) {
 106     auto OnIndexWrite = [&](StringRef S) { thinIndices.erase(S); };
 107     backend = lto::createWriteIndexesThinBackend(
 108         std::string(config->thinLTOPrefixReplace.first),
 109         std::string(config->thinLTOPrefixReplace.second),
 110         config->thinLTOEmitImportsFiles, indexFile.get(), OnIndexWrite);
 111   } else {
 112     backend = lto::createInProcessThinBackend(
 113         llvm::heavyweight_hardware_concurrency(config->thinLTOJobs));
 114   }
 115
 116   ltoObj = std::make_unique<lto::LTO>(createConfig(), backend,
 117                                        config->ltoPartitions);
 118 }
 119
 120 BitcodeCompiler::~BitcodeCompiler() = default;
 121
 122 static void undefine(Symbol *s) { replaceSymbol<Undefined>(s, s->getName()); }
 123
 124 void BitcodeCompiler::add(BitcodeFile &f) {
 125   lto::InputFile &obj = *f.obj;
 126   unsigned symNum = 0;
 127   std::vector<Symbol *> symBodies = f.getSymbols();
 128   std::vector<lto::SymbolResolution> resols(symBodies.size());
 129
 130   if (config->thinLTOIndexOnly)
 131     thinIndices.insert(obj.getName());
 132
 133   // Provide a resolution to the LTO API for each symbol.
 134   for (const lto::InputFile::Symbol &objSym : obj.symbols()) {
 135     Symbol *sym = symBodies[symNum];
 136     lto::SymbolResolution &r = resols[symNum];
 137     ++symNum;
 138
 139     // Ideally we shouldn't check for SF_Undefined but currently IRObjectFile
 140     // reports two symbols for module ASM defined. Without this check, lld
 141     // flags an undefined in IR with a definition in ASM as prevailing.
 142     // Once IRObjectFile is fixed to report only one symbol this hack can
 143     // be removed.
 144     r.Prevailing = !objSym.isUndefined() && sym->getFile() == &f;
 145     r.VisibleToRegularObj = sym->isUsedInRegularObj;
 146     if (r.Prevailing)
 147       undefine(sym);
 148
 149     // We tell LTO to not apply interprocedural optimization for wrapped
 150     // (with -wrap) symbols because otherwise LTO would inline them while
 151     // their values are still not final.
 152     r.LinkerRedefined = !sym->canInline;
 153   }
 154   checkError(ltoObj->add(std::move(f.obj), resols));
 155 }
 156
 157 // Merge all the bitcode files we have seen, codegen the result
 158 // and return the resulting objects.
 159 std::vector<InputFile *> BitcodeCompiler::compile(COFFLinkerContext &ctx) {
 160   unsigned maxTasks = ltoObj->getMaxTasks();
 161   buf.resize(maxTasks);
 162   files.resize(maxTasks);
 163
 164   // The /lldltocache option specifies the path to a directory in which to cache
 165   // native object files for ThinLTO incremental builds. If a path was
 166   // specified, configure LTO to use it as the cache directory.
 167   FileCache cache;
 168   if (!config->ltoCache.empty())
 169     cache =
 170         check(localCache("ThinLTO", "Thin", config->ltoCache,
 171                          [&](size_t task, std::unique_ptr<MemoryBuffer> mb) {
 172                            files[task] = std::move(mb);
 173                          }));
 174
 175   checkError(ltoObj->run(
 176       [&](size_t task) {
 177         return std::make_unique<CachedFileStream>(
 178             std::make_unique<raw_svector_ostream>(buf[task]));
 179       },
 180       cache));
 181
 182   // Emit empty index files for non-indexed files
 183   for (StringRef s : thinIndices) {
 184     std::string path = getThinLTOOutputFile(s);
 185     openFile(path + ".thinlto.bc");
 186     if (config->thinLTOEmitImportsFiles)
 187       openFile(path + ".imports");
 188   }
 189
 190   // ThinLTO with index only option is required to generate only the index
 191   // files. After that, we exit from linker and ThinLTO backend runs in a
 192   // distributed environment.
 193   if (config->thinLTOIndexOnly) {
 194     if (!config->ltoObjPath.empty())
 195       saveBuffer(buf[0], config->ltoObjPath);
 196     if (indexFile)
 197       indexFile->close();
 198     return {};
 199   }
 200
 201   if (!config->ltoCache.empty())
 202     pruneCache(config->ltoCache, config->ltoCachePolicy);
 203
 204   std::vector<InputFile *> ret;
 205   for (unsigned i = 0; i != maxTasks; ++i) {
 206     // Assign unique names to LTO objects. This ensures they have unique names
 207     // in the PDB if one is produced. The names should look like:
 208     // - foo.exe.lto.obj
 209     // - foo.exe.lto.1.obj
 210     // - ...
 211     StringRef ltoObjName =
 212         saver().save(Twine(config->outputFile) + ".lto" +
 213                      (i == 0 ? Twine("") : Twine('.') + Twine(i)) + ".obj");
 214
 215     // Get the native object contents either from the cache or from memory.  Do
 216     // not use the cached MemoryBuffer directly, or the PDB will not be
 217     // deterministic.
 218     StringRef objBuf;
 219     if (files[i])
 220       objBuf = files[i]->getBuffer();
 221     else
 222       objBuf = buf[i];
 223     if (objBuf.empty())
 224       continue;
 225
 226     if (config->saveTemps)
 227       saveBuffer(buf[i], ltoObjName);
 228     ret.push_back(make<ObjFile>(ctx, MemoryBufferRef(objBuf, ltoObjName)));
 229   }
 230
 231   return ret;
 232 }