text: //===-LTOCodeGenerator.cpp - LLVM Link Time Optimizer ---------------------===//
  //
  //                     The LLVM Compiler Infrastructure
  //
  // This file is distributed under the University of Illinois Open Source
  // License. See LICENSE.TXT for details.
  //
  //===----------------------------------------------------------------------===//
  //
  // This file implements the Link Time Optimization library. This library is
  // intended to be used by linker to optimize code at link time.
  //
  //===----------------------------------------------------------------------===//
  
  #include "llvm/LTO/LTOCodeGenerator.h"
  #include "llvm/ADT/StringExtras.h"
  #include "llvm/Analysis/Passes.h"
  #include "llvm/Analysis/TargetLibraryInfo.h"
  #include "llvm/Analysis/TargetTransformInfo.h"
  #include "llvm/Bitcode/ReaderWriter.h"
  #include "llvm/CodeGen/ParallelCG.h"
  #include "llvm/CodeGen/RuntimeLibcalls.h"
  #include "llvm/Config/config.h"
  #include "llvm/IR/Constants.h"
  #include "llvm/IR/DataLayout.h"
  #include "llvm/IR/DerivedTypes.h"
  #include "llvm/IR/DiagnosticInfo.h"
  #include "llvm/IR/DiagnosticPrinter.h"
  #include "llvm/IR/LLVMContext.h"
  #include "llvm/IR/LegacyPassManager.h"
  #include "llvm/IR/Mangler.h"
  #include "llvm/IR/Module.h"
  #include "llvm/IR/Verifier.h"
  #include "llvm/InitializePasses.h"
  #include "llvm/LTO/LTOModule.h"
  #include "llvm/Linker/Linker.h"
  #include "llvm/MC/MCAsmInfo.h"
  #include "llvm/MC/MCContext.h"
  #include "llvm/MC/SubtargetFeature.h"
  #include "llvm/Support/CommandLine.h"
  #include "llvm/Support/FileSystem.h"
  #include "llvm/Support/Host.h"
  #include "llvm/Support/MemoryBuffer.h"
  #include "llvm/Support/Signals.h"
  #include "llvm/Support/TargetRegistry.h"
  #include "llvm/Support/TargetSelect.h"
  #include "llvm/Support/ToolOutputFile.h"
  #include "llvm/Support/raw_ostream.h"
  #include "llvm/Target/TargetLowering.h"
  #include "llvm/Target/TargetOptions.h"
  #include "llvm/Target/TargetRegisterInfo.h"
  #include "llvm/Target/TargetSubtargetInfo.h"
  #include "llvm/Transforms/IPO.h"
  #include "llvm/Transforms/IPO/PassManagerBuilder.h"
  #include "llvm/Transforms/ObjCARC.h"
  #include <system_error>
  using namespace llvm;
  
  const char* LTOCodeGenerator::getVersionString() {
  #ifdef LLVM_VERSION_INFO
    return PACKAGE_NAME " version " PACKAGE_VERSION ", " LLVM_VERSION_INFO;
  #else
    return PACKAGE_NAME " version " PACKAGE_VERSION;
  #endif
  }
  
  LTOCodeGenerator::LTOCodeGenerator()
      : Context(getGlobalContext()),
        MergedModule(new Module("ld-temp.o", Context)),
        IRLinker(MergedModule.get()) {
    initializeLTOPasses();
  }
  
  LTOCodeGenerator::LTOCodeGenerator(std::unique_ptr<LLVMContext> Context)
      : OwnedContext(std::move(Context)), Context(*OwnedContext),
        MergedModule(new Module("ld-temp.o", *OwnedContext)),
        IRLinker(MergedModule.get()) {
    initializeLTOPasses();
  }
  
  LTOCodeGenerator::~LTOCodeGenerator() {}
  
  // Initialize LTO passes. Please keep this function in sync with
  // PassManagerBuilder::populateLTOPassManager(), and make sure all LTO
  // passes are initialized.
  void LTOCodeGenerator::initializeLTOPasses() {
    PassRegistry &R = *PassRegistry::getPassRegistry();
  
    initializeInternalizePassPass(R);
    initializeIPSCCPPass(R);
    initializeGlobalOptPass(R);
    initializeConstantMergePass(R);
    initializeDAHPass(R);
    initializeInstructionCombiningPassPass(R);
    initializeSimpleInlinerPass(R);
    initializePruneEHPass(R);
    initializeGlobalDCEPass(R);
    initializeArgPromotionPass(R);
    initializeJumpThreadingPass(R);
    initializeSROALegacyPassPass(R);
    initializeSROA_DTPass(R);
    initializeSROA_SSAUpPass(R);
    initializeFunctionAttrsPass(R);
    initializeGlobalsAAWrapperPassPass(R);
    initializeLICMPass(R);
    initializeMergedLoadStoreMotionPass(R);
    initializeGVNPass(R);
    initializeMemCpyOptPass(R);
    initializeDCEPass(R);
    initializeCFGSimplifyPassPass(R);
  }
  
  bool LTOCodeGenerator::addModule(LTOModule *Mod) {
    assert(&Mod->getModule().getContext() == &Context &&
           "Expected module in same context");
  
    bool ret = IRLinker.linkInModule(&Mod->getModule());
  
    const std::vector<const char *> &undefs = Mod->getAsmUndefinedRefs();
    for (int i = 0, e = undefs.size(); i != e; ++i)
      AsmUndefinedRefs[undefs[i]] = 1;
  
    return !ret;
  }
  
  void LTOCodeGenerator::setModule(std::unique_ptr<LTOModule> Mod) {
    assert(&Mod->getModule().getContext() == &Context &&
           "Expected module in same context");
  
    AsmUndefinedRefs.clear();
  
    MergedModule = Mod->takeModule();
    IRLinker.setModule(MergedModule.get());
  
    const std::vector<const char*> &Undefs = Mod->getAsmUndefinedRefs();
    for (int I = 0, E = Undefs.size(); I != E; ++I)
      AsmUndefinedRefs[Undefs[I]] = 1;
  }
  
  void LTOCodeGenerator::setTargetOptions(TargetOptions Options) {
    this->Options = Options;
  }
  
  void LTOCodeGenerator::setDebugInfo(lto_debug_model Debug) {
    switch (Debug) {
    case LTO_DEBUG_MODEL_NONE:
      EmitDwarfDebugInfo = false;
      return;
  
    case LTO_DEBUG_MODEL_DWARF:
      EmitDwarfDebugInfo = true;
      return;
    }
    llvm_unreachable("Unknown debug format!");
  }
  
  void LTOCodeGenerator::setOptLevel(unsigned Level) {
    OptLevel = Level;
    switch (OptLevel) {
    case 0:
      CGOptLevel = CodeGenOpt::None;
      break;
    case 1:
      CGOptLevel = CodeGenOpt::Less;
      break;
    case 2:
      CGOptLevel = CodeGenOpt::Default;
      break;
    case 3:
      CGOptLevel = CodeGenOpt::Aggressive;
      break;
    }
  }
  
  bool LTOCodeGenerator::writeMergedModules(const char *Path) {
    if (!determineTarget())
      return false;
  
    // mark which symbols can not be internalized
    applyScopeRestrictions();
  
    // create output file
    std::error_code EC;
    tool_output_file Out(Path, EC, sys::fs::F_None);
    if (EC) {
      std::string ErrMsg = "could not open bitcode file for writing: ";
      ErrMsg += Path;
      emitError(ErrMsg);
      return false;
    }
  
    // write bitcode to it
    WriteBitcodeToFile(MergedModule.get(), Out.os(), ShouldEmbedUselists);
    Out.os().close();
  
    if (Out.os().has_error()) {
      std::string ErrMsg = "could not write bitcode file: ";
      ErrMsg += Path;
      emitError(ErrMsg);
      Out.os().clear_error();
      return false;
    }
  
    Out.keep();
    return true;
  }
  
  bool LTOCodeGenerator::compileOptimizedToFile(const char **Name) {
    // make unique temp output file to put generated code
    SmallString<128> Filename;
    int FD;
  
    const char *Extension =
        (FileType == TargetMachine::CGFT_AssemblyFile ? "s" : "o");
  
    std::error_code EC =
        sys::fs::createTemporaryFile("lto-llvm", Extension, FD, Filename);
    if (EC) {
      emitError(EC.message());
      return false;
    }
  
    // generate object file
    tool_output_file objFile(Filename.c_str(), FD);
  
    bool genResult = compileOptimized(&objFile.os());
    objFile.os().close();
    if (objFile.os().has_error()) {
      objFile.os().clear_error();
      sys::fs::remove(Twine(Filename));
      return false;
    }
  
    objFile.keep();
    if (!genResult) {
      sys::fs::remove(Twine(Filename));
      return false;
    }
  
    NativeObjectPath = Filename.c_str();
    *Name = NativeObjectPath.c_str();
    return true;
  }
  
  std::unique_ptr<MemoryBuffer>
  LTOCodeGenerator::compileOptimized() {
    const char *name;
    if (!compileOptimizedToFile(&name))
      return nullptr;
  
    // read .o file into memory buffer
    ErrorOr<std::unique_ptr<MemoryBuffer>> BufferOrErr =
        MemoryBuffer::getFile(name, -1, false);
    if (std::error_code EC = BufferOrErr.getError()) {
      emitError(EC.message());
      sys::fs::remove(NativeObjectPath);
      return nullptr;
    }
  
    // remove temp files
    sys::fs::remove(NativeObjectPath);
  
    return std::move(*BufferOrErr);
  }
  
  bool LTOCodeGenerator::compile_to_file(const char **Name, bool DisableVerify,
                                         bool DisableInline,
                                         bool DisableGVNLoadPRE,
                                         bool DisableVectorization) {
    if (!optimize(DisableVerify, DisableInline, DisableGVNLoadPRE,
                  DisableVectorization))
      return false;
  
    return compileOptimizedToFile(Name);
  }
  
  std::unique_ptr<MemoryBuffer>
  LTOCodeGenerator::compile(bool DisableVerify, bool DisableInline,
                            bool DisableGVNLoadPRE, bool DisableVectorization) {
    if (!optimize(DisableVerify, DisableInline, DisableGVNLoadPRE,
                  DisableVectorization))
      return nullptr;
  
    return compileOptimized();
  }
  
  bool LTOCodeGenerator::determineTarget() {
    if (TargetMach)
      return true;
  
    std::string TripleStr = MergedModule->getTargetTriple();
    if (TripleStr.empty()) {
      TripleStr = sys::getDefaultTargetTriple();
      MergedModule->setTargetTriple(TripleStr);
    }
    llvm::Triple Triple(TripleStr);
  
    // create target machine from info for merged modules
    std::string ErrMsg;
    const Target *march = TargetRegistry::lookupTarget(TripleStr, ErrMsg);
    if (!march) {
      emitError(ErrMsg);
      return false;
    }
  
    // Construct LTOModule, hand over ownership of module and target. Use MAttr as
    // the default set of features.
    SubtargetFeatures Features(MAttr);
    Features.getDefaultSubtargetFeatures(Triple);
    FeatureStr = Features.getString();
    // Set a default CPU for Darwin triples.
    if (MCpu.empty() && Triple.isOSDarwin()) {
      if (Triple.getArch() == llvm::Triple::x86_64)
        MCpu = "core2";
      else if (Triple.getArch() == llvm::Triple::x86)
        MCpu = "yonah";
      else if (Triple.getArch() == llvm::Triple::aarch64)
        MCpu = "cyclone";
    }
  
    TargetMach.reset(march->createTargetMachine(TripleStr, MCpu, FeatureStr,
                                                Options, RelocModel,
                                                CodeModel::Default, CGOptLevel));
    return true;
  }
  
  void LTOCodeGenerator::
  applyRestriction(GlobalValue &GV,
                   ArrayRef<StringRef> Libcalls,
                   std::vector<const char*> &MustPreserveList,
                   SmallPtrSetImpl<GlobalValue*> &AsmUsed,
                   Mangler &Mangler) {
    // There are no restrictions to apply to declarations.
    if (GV.isDeclaration())
      return;
  
    // There is nothing more restrictive than private linkage.
    if (GV.hasPrivateLinkage())
      return;
  
    SmallString<64> Buffer;
    TargetMach->getNameWithPrefix(Buffer, &GV, Mangler);
  
    if (MustPreserveSymbols.count(Buffer))
      MustPreserveList.push_back(GV.getName().data());
    if (AsmUndefinedRefs.count(Buffer))
      AsmUsed.insert(&GV);
  
    // Conservatively append user-supplied runtime library functions to
    // llvm.compiler.used.  These could be internalized and deleted by
    // optimizations like -globalopt, causing problems when later optimizations
    // add new library calls (e.g., llvm.memset => memset and printf => puts).
    // Leave it to the linker to remove any dead code (e.g. with -dead_strip).
    if (isa<Function>(GV) &&
        std::binary_search(Libcalls.begin(), Libcalls.end(), GV.getName()))
      AsmUsed.insert(&GV);
  }
  
  static void findUsedValues(GlobalVariable *LLVMUsed,
                             SmallPtrSetImpl<GlobalValue*> &UsedValues) {
    if (!LLVMUsed) return;
  
    ConstantArray *Inits = cast<ConstantArray>(LLVMUsed->getInitializer());
    for (unsigned i = 0, e = Inits->getNumOperands(); i != e; ++i)
      if (GlobalValue *GV =
          dyn_cast<GlobalValue>(Inits->getOperand(i)->stripPointerCasts()))
        UsedValues.insert(GV);
  }
  
  // Collect names of runtime library functions. User-defined functions with the
  // same names are added to llvm.compiler.used to prevent them from being
  // deleted by optimizations.
  static void accumulateAndSortLibcalls(std::vector<StringRef> &Libcalls,
                                        const TargetLibraryInfo& TLI,
                                        const Module &Mod,
                                        const TargetMachine &TM) {
    // TargetLibraryInfo has info on C runtime library calls on the current
    // target.
    for (unsigned I = 0, E = static_cast<unsigned>(LibFunc::NumLibFuncs);
         I != E; ++I) {
      LibFunc::Func F = static_cast<LibFunc::Func>(I);
      if (TLI.has(F))
        Libcalls.push_back(TLI.getName(F));
    }
  
    SmallPtrSet<const TargetLowering *, 1> TLSet;
  
    for (const Function &F : Mod) {
      const TargetLowering *Lowering =
          TM.getSubtargetImpl(F)->getTargetLowering();
  
      if (Lowering && TLSet.insert(Lowering).second)
        // TargetLowering has info on library calls that CodeGen expects to be
        // available, both from the C runtime and compiler-rt.
        for (unsigned I = 0, E = static_cast<unsigned>(RTLIB::UNKNOWN_LIBCALL);
             I != E; ++I)
          if (const char *Name =
                  Lowering->getLibcallName(static_cast<RTLIB::Libcall>(I)))
            Libcalls.push_back(Name);
    }
  
    array_pod_sort(Libcalls.begin(), Libcalls.end());
    Libcalls.erase(std::unique(Libcalls.begin(), Libcalls.end()),
                   Libcalls.end());
  }
  
  void LTOCodeGenerator::applyScopeRestrictions() {
    if (ScopeRestrictionsDone || !ShouldInternalize)
      return;
  
    // Start off with a verification pass.
    legacy::PassManager passes;
    passes.add(createVerifierPass());
  
    // mark which symbols can not be internalized
    Mangler Mangler;
    std::vector<const char*> MustPreserveList;
    SmallPtrSet<GlobalValue*, 8> AsmUsed;
    std::vector<StringRef> Libcalls;
    TargetLibraryInfoImpl TLII(Triple(TargetMach->getTargetTriple()));
    TargetLibraryInfo TLI(TLII);
  
    accumulateAndSortLibcalls(Libcalls, TLI, *MergedModule, *TargetMach);
  
    for (Function &f : *MergedModule)
      applyRestriction(f, Libcalls, MustPreserveList, AsmUsed, Mangler);
    for (GlobalVariable &v : MergedModule->globals())
      applyRestriction(v, Libcalls, MustPreserveList, AsmUsed, Mangler);
    for (GlobalAlias &a : MergedModule->aliases())
      applyRestriction(a, Libcalls, MustPreserveList, AsmUsed, Mangler);
  
    GlobalVariable *LLVMCompilerUsed =
      MergedModule->getGlobalVariable("llvm.compiler.used");
    findUsedValues(LLVMCompilerUsed, AsmUsed);
    if (LLVMCompilerUsed)
      LLVMCompilerUsed->eraseFromParent();
  
    if (!AsmUsed.empty()) {
      llvm::Type *i8PTy = llvm::Type::getInt8PtrTy(Context);
      std::vector<Constant*> asmUsed2;
      for (auto *GV : AsmUsed) {
        Constant *c = ConstantExpr::getBitCast(GV, i8PTy);
        asmUsed2.push_back(c);
      }
  
      llvm::ArrayType *ATy = llvm::ArrayType::get(i8PTy, asmUsed2.size());
      LLVMCompilerUsed =
        new llvm::GlobalVariable(*MergedModule, ATy, false,
                                 llvm::GlobalValue::AppendingLinkage,
                                 llvm::ConstantArray::get(ATy, asmUsed2),
                                 "llvm.compiler.used");
  
      LLVMCompilerUsed->setSection("llvm.metadata");
    }
  
    passes.add(createInternalizePass(MustPreserveList));
  
    // apply scope restrictions
    passes.run(*MergedModule);
  
    ScopeRestrictionsDone = true;
  }
  
  /// Optimize merged modules using various IPO passes
  bool LTOCodeGenerator::optimize(bool DisableVerify, bool DisableInline,
                                  bool DisableGVNLoadPRE,
                                  bool DisableVectorization) {
    if (!this->determineTarget())
      return false;
  
    // Mark which symbols can not be internalized
    this->applyScopeRestrictions();
  
    // Instantiate the pass manager to organize the passes.
    legacy::PassManager passes;
  
    // Add an appropriate DataLayout instance for this module...
    MergedModule->setDataLayout(TargetMach->createDataLayout());
  
    passes.add(
        createTargetTransformInfoWrapperPass(TargetMach->getTargetIRAnalysis()));
  
    Triple TargetTriple(TargetMach->getTargetTriple());
    PassManagerBuilder PMB;
    PMB.DisableGVNLoadPRE = DisableGVNLoadPRE;
    PMB.LoopVectorize = !DisableVectorization;
    PMB.SLPVectorize = !DisableVectorization;
    if (!DisableInline)
      PMB.Inliner = createFunctionInliningPass();
    PMB.LibraryInfo = new TargetLibraryInfoImpl(TargetTriple);
    PMB.OptLevel = OptLevel;
    PMB.VerifyInput = !DisableVerify;
    PMB.VerifyOutput = !DisableVerify;
  
    PMB.populateLTOPassManager(passes);
  
    // Run our queue of passes all at once now, efficiently.
    passes.run(*MergedModule);
  
    return true;
  }
  
  bool LTOCodeGenerator::compileOptimized(ArrayRef<raw_pwrite_stream *> Out) {
    if (!this->determineTarget())
      return false;
  
    legacy::PassManager preCodeGenPasses;
  
    // If the bitcode files contain ARC code and were compiled with optimization,
    // the ObjCARCContractPass must be run, so do it unconditionally here.
    preCodeGenPasses.add(createObjCARCContractPass());
    preCodeGenPasses.run(*MergedModule);
  
    // Do code generation. We need to preserve the module in case the client calls
    // writeMergedModules() after compilation, but we only need to allow this at
    // parallelism level 1. This is achieved by having splitCodeGen return the
    // original module at parallelism level 1 which we then assign back to
    // MergedModule.
    MergedModule =
        splitCodeGen(std::move(MergedModule), Out, MCpu, FeatureStr, Options,
                     RelocModel, CodeModel::Default, CGOptLevel, FileType);
  
    return true;
  }
  
  /// setCodeGenDebugOptions - Set codegen debugging options to aid in debugging
  /// LTO problems.
  void LTOCodeGenerator::setCodeGenDebugOptions(const char *Options) {
    for (std::pair<StringRef, StringRef> o = getToken(Options); !o.first.empty();
         o = getToken(o.second))
      CodegenOptions.push_back(o.first);
  }
  
  void LTOCodeGenerator::parseCodeGenDebugOptions() {
    // if options were requested, set them
    if (!CodegenOptions.empty()) {
      // ParseCommandLineOptions() expects argv[0] to be program name.
      std::vector<const char *> CodegenArgv(1, "libLLVMLTO");
      for (std::string &Arg : CodegenOptions)
        CodegenArgv.push_back(Arg.c_str());
      cl::ParseCommandLineOptions(CodegenArgv.size(), CodegenArgv.data());
    }
  }
  
  void LTOCodeGenerator::DiagnosticHandler(const DiagnosticInfo &DI,
                                           void *Context) {
    ((LTOCodeGenerator *)Context)->DiagnosticHandler2(DI);
  }
  
  void LTOCodeGenerator::DiagnosticHandler2(const DiagnosticInfo &DI) {
    // Map the LLVM internal diagnostic severity to the LTO diagnostic severity.
    lto_codegen_diagnostic_severity_t Severity;
    switch (DI.getSeverity()) {
    case DS_Error:
      Severity = LTO_DS_ERROR;
      break;
    case DS_Warning:
      Severity = LTO_DS_WARNING;
      break;
    case DS_Remark:
      Severity = LTO_DS_REMARK;
      break;
    case DS_Note:
      Severity = LTO_DS_NOTE;
      break;
    }
    // Create the string that will be reported to the external diagnostic handler.
    std::string MsgStorage;
    raw_string_ostream Stream(MsgStorage);
    DiagnosticPrinterRawOStream DP(Stream);
    DI.print(DP);
    Stream.flush();
  
    // If this method has been called it means someone has set up an external
    // diagnostic handler. Assert on that.
    assert(DiagHandler && "Invalid diagnostic handler");
    (*DiagHandler)(Severity, MsgStorage.c_str(), DiagContext);
  }
  
  void
  LTOCodeGenerator::setDiagnosticHandler(lto_diagnostic_handler_t DiagHandler,
                                         void *Ctxt) {
    this->DiagHandler = DiagHandler;
    this->DiagContext = Ctxt;
    if (!DiagHandler)
      return Context.setDiagnosticHandler(nullptr, nullptr);
    // Register the LTOCodeGenerator stub in the LLVMContext to forward the
    // diagnostic to the external DiagHandler.
    Context.setDiagnosticHandler(LTOCodeGenerator::DiagnosticHandler, this,
                                 /* RespectFilters */ true);
  }
  
  namespace {
  class LTODiagnosticInfo : public DiagnosticInfo {
    const Twine &Msg;
  public:
    LTODiagnosticInfo(const Twine &DiagMsg, DiagnosticSeverity Severity=DS_Error)
        : DiagnosticInfo(DK_Linker, Severity), Msg(DiagMsg) {}
    void print(DiagnosticPrinter &DP) const override { DP << Msg; }
  };
  }
  
  void LTOCodeGenerator::emitError(const std::string &ErrMsg) {
    if (DiagHandler)
      (*DiagHandler)(LTO_DS_ERROR, ErrMsg.c_str(), DiagContext);
    else
      Context.diagnose(LTODiagnosticInfo(ErrMsg));
  }
  