text: //===- LTO.cpp ------------------------------------------------------------===//
  //
  // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
  // See https://llvm.org/LICENSE.txt for license information.
  // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
  //
  //===----------------------------------------------------------------------===//
  
  #include "LTO.h"
  #include "Config.h"
  #include "InputFiles.h"
  #include "Symbols.h"
  #include "lld/Common/Args.h"
  #include "lld/Common/CommonLinkerContext.h"
  #include "lld/Common/Strings.h"
  #include "lld/Common/TargetOptionsCommandFlags.h"
  #include "llvm/ADT/STLExtras.h"
  #include "llvm/ADT/SmallString.h"
  #include "llvm/ADT/StringRef.h"
  #include "llvm/ADT/Twine.h"
  #include "llvm/Bitcode/BitcodeWriter.h"
  #include "llvm/IR/DiagnosticPrinter.h"
  #include "llvm/LTO/Config.h"
  #include "llvm/LTO/LTO.h"
  #include "llvm/Object/SymbolicFile.h"
  #include "llvm/Support/Caching.h"
  #include "llvm/Support/CodeGen.h"
  #include "llvm/Support/Error.h"
  #include "llvm/Support/FileSystem.h"
  #include "llvm/Support/MemoryBuffer.h"
  #include "llvm/Support/raw_ostream.h"
  #include <algorithm>
  #include <cstddef>
  #include <memory>
  #include <string>
  #include <system_error>
  #include <vector>
  
  using namespace llvm;
  using namespace llvm::object;
  using namespace lld;
  using namespace lld::coff;
  
  // Creates an empty file to and returns a raw_fd_ostream to write to it.
  static std::unique_ptr<raw_fd_ostream> openFile(StringRef file) {
    std::error_code ec;
    auto ret =
        std::make_unique<raw_fd_ostream>(file, ec, sys::fs::OpenFlags::OF_None);
    if (ec) {
      error("cannot open " + file + ": " + ec.message());
      return nullptr;
    }
    return ret;
  }
  
  static std::string getThinLTOOutputFile(StringRef path) {
    return lto::getThinLTOOutputFile(
        std::string(path), std::string(config->thinLTOPrefixReplace.first),
        std::string(config->thinLTOPrefixReplace.second));
  }
  
  static lto::Config createConfig() {
    lto::Config c;
    c.Options = initTargetOptionsFromCodeGenFlags();
    c.Options.EmitAddrsig = true;
  
    // Always emit a section per function/datum with LTO. LLVM LTO should get most
    // of the benefit of linker GC, but there are still opportunities for ICF.
    c.Options.FunctionSections = true;
    c.Options.DataSections = true;
  
    // Use static reloc model on 32-bit x86 because it usually results in more
    // compact code, and because there are also known code generation bugs when
    // using the PIC model (see PR34306).
    if (config->machine == COFF::IMAGE_FILE_MACHINE_I386)
      c.RelocModel = Reloc::Static;
    else
      c.RelocModel = Reloc::PIC_;
    c.DisableVerify = true;
    c.DiagHandler = diagnosticHandler;
    c.OptLevel = config->ltoo;
    c.CPU = getCPUStr();
    c.MAttrs = getMAttrs();
    c.CGOptLevel = args::getCGOptLevel(config->ltoo);
    c.AlwaysEmitRegularLTOObj = !config->ltoObjPath.empty();
    c.UseNewPM = config->ltoNewPassManager;
    c.DebugPassManager = config->ltoDebugPassManager;
    c.CSIRProfile = std::string(config->ltoCSProfileFile);
    c.RunCSIRInstr = config->ltoCSProfileGenerate;
    c.PGOWarnMismatch = config->ltoPGOWarnMismatch;
  
    if (config->saveTemps)
      checkError(c.addSaveTemps(std::string(config->outputFile) + ".",
                                /*UseInputModulePath*/ true));
    return c;
  }
  
  BitcodeCompiler::BitcodeCompiler() {
    // Initialize indexFile.
    if (!config->thinLTOIndexOnlyArg.empty())
      indexFile = openFile(config->thinLTOIndexOnlyArg);
  
    // Initialize ltoObj.
    lto::ThinBackend backend;
    if (config->thinLTOIndexOnly) {
      auto OnIndexWrite = [&](StringRef S) { thinIndices.erase(S); };
      backend = lto::createWriteIndexesThinBackend(
          std::string(config->thinLTOPrefixReplace.first),
          std::string(config->thinLTOPrefixReplace.second),
          config->thinLTOEmitImportsFiles, indexFile.get(), OnIndexWrite);
    } else {
      backend = lto::createInProcessThinBackend(
          llvm::heavyweight_hardware_concurrency(config->thinLTOJobs));
    }
  
    ltoObj = std::make_unique<lto::LTO>(createConfig(), backend,
                                         config->ltoPartitions);
  }
  
  BitcodeCompiler::~BitcodeCompiler() = default;
  
  static void undefine(Symbol *s) { replaceSymbol<Undefined>(s, s->getName()); }
  
  void BitcodeCompiler::add(BitcodeFile &f) {
    lto::InputFile &obj = *f.obj;
    unsigned symNum = 0;
    std::vector<Symbol *> symBodies = f.getSymbols();
    std::vector<lto::SymbolResolution> resols(symBodies.size());
  
    if (config->thinLTOIndexOnly)
      thinIndices.insert(obj.getName());
  
    // Provide a resolution to the LTO API for each symbol.
    for (const lto::InputFile::Symbol &objSym : obj.symbols()) {
      Symbol *sym = symBodies[symNum];
      lto::SymbolResolution &r = resols[symNum];
      ++symNum;
  
      // Ideally we shouldn't check for SF_Undefined but currently IRObjectFile
      // reports two symbols for module ASM defined. Without this check, lld
      // flags an undefined in IR with a definition in ASM as prevailing.
      // Once IRObjectFile is fixed to report only one symbol this hack can
      // be removed.
      r.Prevailing = !objSym.isUndefined() && sym->getFile() == &f;
      r.VisibleToRegularObj = sym->isUsedInRegularObj;
      if (r.Prevailing)
        undefine(sym);
  
      // We tell LTO to not apply interprocedural optimization for wrapped
      // (with -wrap) symbols because otherwise LTO would inline them while
      // their values are still not final.
      r.LinkerRedefined = !sym->canInline;
    }
    checkError(ltoObj->add(std::move(f.obj), resols));
  }
  
  // Merge all the bitcode files we have seen, codegen the result
  // and return the resulting objects.
  std::vector<InputFile *> BitcodeCompiler::compile(COFFLinkerContext &ctx) {
    unsigned maxTasks = ltoObj->getMaxTasks();
    buf.resize(maxTasks);
    files.resize(maxTasks);
  
    // The /lldltocache option specifies the path to a directory in which to cache
    // native object files for ThinLTO incremental builds. If a path was
    // specified, configure LTO to use it as the cache directory.
    FileCache cache;
    if (!config->ltoCache.empty())
      cache =
          check(localCache("ThinLTO", "Thin", config->ltoCache,
                           [&](size_t task, std::unique_ptr<MemoryBuffer> mb) {
                             files[task] = std::move(mb);
                           }));
  
    checkError(ltoObj->run(
        [&](size_t task) {
          return std::make_unique<CachedFileStream>(
              std::make_unique<raw_svector_ostream>(buf[task]));
        },
        cache));
  
    // Emit empty index files for non-indexed files
    for (StringRef s : thinIndices) {
      std::string path = getThinLTOOutputFile(s);
      openFile(path + ".thinlto.bc");
      if (config->thinLTOEmitImportsFiles)
        openFile(path + ".imports");
    }
  
    // ThinLTO with index only option is required to generate only the index
    // files. After that, we exit from linker and ThinLTO backend runs in a
    // distributed environment.
    if (config->thinLTOIndexOnly) {
      if (!config->ltoObjPath.empty())
        saveBuffer(buf[0], config->ltoObjPath);
      if (indexFile)
        indexFile->close();
      return {};
    }
  
    if (!config->ltoCache.empty())
      pruneCache(config->ltoCache, config->ltoCachePolicy);
  
    std::vector<InputFile *> ret;
    for (unsigned i = 0; i != maxTasks; ++i) {
      // Assign unique names to LTO objects. This ensures they have unique names
      // in the PDB if one is produced. The names should look like:
      // - foo.exe.lto.obj
      // - foo.exe.lto.1.obj
      // - ...
      StringRef ltoObjName =
          saver().save(Twine(config->outputFile) + ".lto" +
                       (i == 0 ? Twine("") : Twine('.') + Twine(i)) + ".obj");
  
      // Get the native object contents either from the cache or from memory.  Do
      // not use the cached MemoryBuffer directly, or the PDB will not be
      // deterministic.
      StringRef objBuf;
      if (files[i])
        objBuf = files[i]->getBuffer();
      else
        objBuf = buf[i];
      if (objBuf.empty())
        continue;
  
      if (config->saveTemps)
        saveBuffer(buf[i], ltoObjName);
      ret.push_back(make<ObjFile>(ctx, MemoryBufferRef(objBuf, ltoObjName)));
    }
  
    return ret;
  }
  