text: //===- llvm/CodeGen/TargetLoweringObjectFileImpl.cpp - Object File Info ---===//
  //
  // 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
  //
  //===----------------------------------------------------------------------===//
  //
  // This file implements classes used to handle lowerings specific to common
  // object file formats.
  //
  //===----------------------------------------------------------------------===//
  
  #include "llvm/CodeGen/TargetLoweringObjectFileImpl.h"
  #include "llvm/ADT/SmallString.h"
  #include "llvm/ADT/SmallVector.h"
  #include "llvm/ADT/StringExtras.h"
  #include "llvm/ADT/StringRef.h"
  #include "llvm/ADT/Triple.h"
  #include "llvm/BinaryFormat/COFF.h"
  #include "llvm/BinaryFormat/Dwarf.h"
  #include "llvm/BinaryFormat/ELF.h"
  #include "llvm/BinaryFormat/MachO.h"
  #include "llvm/CodeGen/MachineModuleInfo.h"
  #include "llvm/CodeGen/MachineModuleInfoImpls.h"
  #include "llvm/IR/Comdat.h"
  #include "llvm/IR/Constants.h"
  #include "llvm/IR/DataLayout.h"
  #include "llvm/IR/DerivedTypes.h"
  #include "llvm/IR/Function.h"
  #include "llvm/IR/GlobalAlias.h"
  #include "llvm/IR/GlobalObject.h"
  #include "llvm/IR/GlobalValue.h"
  #include "llvm/IR/GlobalVariable.h"
  #include "llvm/IR/Mangler.h"
  #include "llvm/IR/Metadata.h"
  #include "llvm/IR/Module.h"
  #include "llvm/IR/Type.h"
  #include "llvm/MC/MCAsmInfo.h"
  #include "llvm/MC/MCContext.h"
  #include "llvm/MC/MCExpr.h"
  #include "llvm/MC/MCSectionCOFF.h"
  #include "llvm/MC/MCSectionELF.h"
  #include "llvm/MC/MCSectionMachO.h"
  #include "llvm/MC/MCSectionWasm.h"
  #include "llvm/MC/MCSectionXCOFF.h"
  #include "llvm/MC/MCStreamer.h"
  #include "llvm/MC/MCSymbol.h"
  #include "llvm/MC/MCSymbolELF.h"
  #include "llvm/MC/MCValue.h"
  #include "llvm/MC/SectionKind.h"
  #include "llvm/ProfileData/InstrProf.h"
  #include "llvm/Support/Casting.h"
  #include "llvm/Support/CodeGen.h"
  #include "llvm/Support/Format.h"
  #include "llvm/Support/ErrorHandling.h"
  #include "llvm/Support/raw_ostream.h"
  #include "llvm/Target/TargetMachine.h"
  #include <cassert>
  #include <string>
  
  using namespace llvm;
  using namespace dwarf;
  
  static void GetObjCImageInfo(Module &M, unsigned &Version, unsigned &Flags,
                               StringRef &Section) {
    SmallVector<Module::ModuleFlagEntry, 8> ModuleFlags;
    M.getModuleFlagsMetadata(ModuleFlags);
  
    for (const auto &MFE: ModuleFlags) {
      // Ignore flags with 'Require' behaviour.
      if (MFE.Behavior == Module::Require)
        continue;
  
      StringRef Key = MFE.Key->getString();
      if (Key == "Objective-C Image Info Version") {
        Version = mdconst::extract<ConstantInt>(MFE.Val)->getZExtValue();
      } else if (Key == "Objective-C Garbage Collection" ||
                 Key == "Objective-C GC Only" ||
                 Key == "Objective-C Is Simulated" ||
                 Key == "Objective-C Class Properties" ||
                 Key == "Objective-C Image Swift Version") {
        Flags |= mdconst::extract<ConstantInt>(MFE.Val)->getZExtValue();
      } else if (Key == "Objective-C Image Info Section") {
        Section = cast<MDString>(MFE.Val)->getString();
      }
    }
  }
  
  //===----------------------------------------------------------------------===//
  //                                  ELF
  //===----------------------------------------------------------------------===//
  
  void TargetLoweringObjectFileELF::Initialize(MCContext &Ctx,
                                               const TargetMachine &TgtM) {
    TargetLoweringObjectFile::Initialize(Ctx, TgtM);
    TM = &TgtM;
  
    CodeModel::Model CM = TgtM.getCodeModel();
  
    switch (TgtM.getTargetTriple().getArch()) {
    case Triple::arm:
    case Triple::armeb:
    case Triple::thumb:
    case Triple::thumbeb:
      if (Ctx.getAsmInfo()->getExceptionHandlingType() == ExceptionHandling::ARM)
        break;
      // Fallthrough if not using EHABI
      LLVM_FALLTHROUGH;
    case Triple::ppc:
    case Triple::x86:
      PersonalityEncoding = isPositionIndependent()
                                ? dwarf::DW_EH_PE_indirect |
                                      dwarf::DW_EH_PE_pcrel |
                                      dwarf::DW_EH_PE_sdata4
                                : dwarf::DW_EH_PE_absptr;
      LSDAEncoding = isPositionIndependent()
                         ? dwarf::DW_EH_PE_pcrel | dwarf::DW_EH_PE_sdata4
                         : dwarf::DW_EH_PE_absptr;
      TTypeEncoding = isPositionIndependent()
                          ? dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel |
                                dwarf::DW_EH_PE_sdata4
                          : dwarf::DW_EH_PE_absptr;
      break;
    case Triple::x86_64:
      if (isPositionIndependent()) {
        PersonalityEncoding = dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel |
          ((CM == CodeModel::Small || CM == CodeModel::Medium)
           ? dwarf::DW_EH_PE_sdata4 : dwarf::DW_EH_PE_sdata8);
        LSDAEncoding = dwarf::DW_EH_PE_pcrel |
          (CM == CodeModel::Small
           ? dwarf::DW_EH_PE_sdata4 : dwarf::DW_EH_PE_sdata8);
        TTypeEncoding = dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel |
          ((CM == CodeModel::Small || CM == CodeModel::Medium)
           ? dwarf::DW_EH_PE_sdata8 : dwarf::DW_EH_PE_sdata4);
      } else {
        PersonalityEncoding =
          (CM == CodeModel::Small || CM == CodeModel::Medium)
          ? dwarf::DW_EH_PE_udata4 : dwarf::DW_EH_PE_absptr;
        LSDAEncoding = (CM == CodeModel::Small)
          ? dwarf::DW_EH_PE_udata4 : dwarf::DW_EH_PE_absptr;
        TTypeEncoding = (CM == CodeModel::Small)
          ? dwarf::DW_EH_PE_udata4 : dwarf::DW_EH_PE_absptr;
      }
      break;
    case Triple::hexagon:
      PersonalityEncoding = dwarf::DW_EH_PE_absptr;
      LSDAEncoding = dwarf::DW_EH_PE_absptr;
      TTypeEncoding = dwarf::DW_EH_PE_absptr;
      if (isPositionIndependent()) {
        PersonalityEncoding |= dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel;
        LSDAEncoding |= dwarf::DW_EH_PE_pcrel;
        TTypeEncoding |= dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel;
      }
      break;
    case Triple::aarch64:
    case Triple::aarch64_be:
    case Triple::aarch64_32:
      // The small model guarantees static code/data size < 4GB, but not where it
      // will be in memory. Most of these could end up >2GB away so even a signed
      // pc-relative 32-bit address is insufficient, theoretically.
      if (isPositionIndependent()) {
        PersonalityEncoding = dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel |
          dwarf::DW_EH_PE_sdata8;
        LSDAEncoding = dwarf::DW_EH_PE_pcrel | dwarf::DW_EH_PE_sdata8;
        TTypeEncoding = dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel |
          dwarf::DW_EH_PE_sdata8;
      } else {
        PersonalityEncoding = dwarf::DW_EH_PE_absptr;
        LSDAEncoding = dwarf::DW_EH_PE_absptr;
        TTypeEncoding = dwarf::DW_EH_PE_absptr;
      }
      break;
    case Triple::lanai:
      LSDAEncoding = dwarf::DW_EH_PE_absptr;
      PersonalityEncoding = dwarf::DW_EH_PE_absptr;
      TTypeEncoding = dwarf::DW_EH_PE_absptr;
      break;
    case Triple::mips:
    case Triple::mipsel:
    case Triple::mips64:
    case Triple::mips64el:
      // MIPS uses indirect pointer to refer personality functions and types, so
      // that the eh_frame section can be read-only. DW.ref.personality will be
      // generated for relocation.
      PersonalityEncoding = dwarf::DW_EH_PE_indirect;
      // FIXME: The N64 ABI probably ought to use DW_EH_PE_sdata8 but we can't
      //        identify N64 from just a triple.
      TTypeEncoding = dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel |
                      dwarf::DW_EH_PE_sdata4;
      // We don't support PC-relative LSDA references in GAS so we use the default
      // DW_EH_PE_absptr for those.
  
      // FreeBSD must be explicit about the data size and using pcrel since it's
      // assembler/linker won't do the automatic conversion that the Linux tools
      // do.
      if (TgtM.getTargetTriple().isOSFreeBSD()) {
        PersonalityEncoding |= dwarf::DW_EH_PE_pcrel | dwarf::DW_EH_PE_sdata4;
        LSDAEncoding = dwarf::DW_EH_PE_pcrel | dwarf::DW_EH_PE_sdata4;
      }
      break;
    case Triple::ppc64:
    case Triple::ppc64le:
      PersonalityEncoding = dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel |
        dwarf::DW_EH_PE_udata8;
      LSDAEncoding = dwarf::DW_EH_PE_pcrel | dwarf::DW_EH_PE_udata8;
      TTypeEncoding = dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel |
        dwarf::DW_EH_PE_udata8;
      break;
    case Triple::sparcel:
    case Triple::sparc:
      if (isPositionIndependent()) {
        LSDAEncoding = dwarf::DW_EH_PE_pcrel | dwarf::DW_EH_PE_sdata4;
        PersonalityEncoding = dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel |
          dwarf::DW_EH_PE_sdata4;
        TTypeEncoding = dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel |
          dwarf::DW_EH_PE_sdata4;
      } else {
        LSDAEncoding = dwarf::DW_EH_PE_absptr;
        PersonalityEncoding = dwarf::DW_EH_PE_absptr;
        TTypeEncoding = dwarf::DW_EH_PE_absptr;
      }
      CallSiteEncoding = dwarf::DW_EH_PE_udata4;
      break;
    case Triple::riscv32:
    case Triple::riscv64:
      LSDAEncoding = dwarf::DW_EH_PE_pcrel | dwarf::DW_EH_PE_sdata4;
      PersonalityEncoding = dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel |
                            dwarf::DW_EH_PE_sdata4;
      TTypeEncoding = dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel |
                      dwarf::DW_EH_PE_sdata4;
      CallSiteEncoding = dwarf::DW_EH_PE_udata4;
      break;
    case Triple::sparcv9:
      LSDAEncoding = dwarf::DW_EH_PE_pcrel | dwarf::DW_EH_PE_sdata4;
      if (isPositionIndependent()) {
        PersonalityEncoding = dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel |
          dwarf::DW_EH_PE_sdata4;
        TTypeEncoding = dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel |
          dwarf::DW_EH_PE_sdata4;
      } else {
        PersonalityEncoding = dwarf::DW_EH_PE_absptr;
        TTypeEncoding = dwarf::DW_EH_PE_absptr;
      }
      break;
    case Triple::systemz:
      // All currently-defined code models guarantee that 4-byte PC-relative
      // values will be in range.
      if (isPositionIndependent()) {
        PersonalityEncoding = dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel |
          dwarf::DW_EH_PE_sdata4;
        LSDAEncoding = dwarf::DW_EH_PE_pcrel | dwarf::DW_EH_PE_sdata4;
        TTypeEncoding = dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel |
          dwarf::DW_EH_PE_sdata4;
      } else {
        PersonalityEncoding = dwarf::DW_EH_PE_absptr;
        LSDAEncoding = dwarf::DW_EH_PE_absptr;
        TTypeEncoding = dwarf::DW_EH_PE_absptr;
      }
      break;
    default:
      break;
    }
  }
  
  void TargetLoweringObjectFileELF::emitModuleMetadata(MCStreamer &Streamer,
                                                       Module &M) const {
    auto &C = getContext();
  
    if (NamedMDNode *LinkerOptions = M.getNamedMetadata("llvm.linker.options")) {
      auto *S = C.getELFSection(".linker-options", ELF::SHT_LLVM_LINKER_OPTIONS,
                                ELF::SHF_EXCLUDE);
  
      Streamer.SwitchSection(S);
  
      for (const auto &Operand : LinkerOptions->operands()) {
        if (cast<MDNode>(Operand)->getNumOperands() != 2)
          report_fatal_error("invalid llvm.linker.options");
        for (const auto &Option : cast<MDNode>(Operand)->operands()) {
          Streamer.EmitBytes(cast<MDString>(Option)->getString());
          Streamer.EmitIntValue(0, 1);
        }
      }
    }
  
    if (NamedMDNode *DependentLibraries = M.getNamedMetadata("llvm.dependent-libraries")) {
      auto *S = C.getELFSection(".deplibs", ELF::SHT_LLVM_DEPENDENT_LIBRARIES,
                                ELF::SHF_MERGE | ELF::SHF_STRINGS, 1, "");
  
      Streamer.SwitchSection(S);
  
      for (const auto &Operand : DependentLibraries->operands()) {
        Streamer.EmitBytes(
            cast<MDString>(cast<MDNode>(Operand)->getOperand(0))->getString());
        Streamer.EmitIntValue(0, 1);
      }
    }
  
    unsigned Version = 0;
    unsigned Flags = 0;
    StringRef Section;
  
    GetObjCImageInfo(M, Version, Flags, Section);
    if (!Section.empty()) {
      auto *S = C.getELFSection(Section, ELF::SHT_PROGBITS, ELF::SHF_ALLOC);
      Streamer.SwitchSection(S);
      Streamer.EmitLabel(C.getOrCreateSymbol(StringRef("OBJC_IMAGE_INFO")));
      Streamer.EmitIntValue(Version, 4);
      Streamer.EmitIntValue(Flags, 4);
      Streamer.AddBlankLine();
    }
  
    SmallVector<Module::ModuleFlagEntry, 8> ModuleFlags;
    M.getModuleFlagsMetadata(ModuleFlags);
  
    MDNode *CFGProfile = nullptr;
  
    for (const auto &MFE : ModuleFlags) {
      StringRef Key = MFE.Key->getString();
      if (Key == "CG Profile") {
        CFGProfile = cast<MDNode>(MFE.Val);
        break;
      }
    }
  
    if (!CFGProfile)
      return;
  
    auto GetSym = [this](const MDOperand &MDO) -> MCSymbol * {
      if (!MDO)
        return nullptr;
      auto V = cast<ValueAsMetadata>(MDO);
      const Function *F = cast<Function>(V->getValue());
      return TM->getSymbol(F);
    };
  
    for (const auto &Edge : CFGProfile->operands()) {
      MDNode *E = cast<MDNode>(Edge);
      const MCSymbol *From = GetSym(E->getOperand(0));
      const MCSymbol *To = GetSym(E->getOperand(1));
      // Skip null functions. This can happen if functions are dead stripped after
      // the CGProfile pass has been run.
      if (!From || !To)
        continue;
      uint64_t Count = cast<ConstantAsMetadata>(E->getOperand(2))
                           ->getValue()
                           ->getUniqueInteger()
                           .getZExtValue();
      Streamer.emitCGProfileEntry(
          MCSymbolRefExpr::create(From, MCSymbolRefExpr::VK_None, C),
          MCSymbolRefExpr::create(To, MCSymbolRefExpr::VK_None, C), Count);
    }
  }
  
  MCSymbol *TargetLoweringObjectFileELF::getCFIPersonalitySymbol(
      const GlobalValue *GV, const TargetMachine &TM,
      MachineModuleInfo *MMI) const {
    unsigned Encoding = getPersonalityEncoding();
    if ((Encoding & 0x80) == DW_EH_PE_indirect)
      return getContext().getOrCreateSymbol(StringRef("DW.ref.") +
                                            TM.getSymbol(GV)->getName());
    if ((Encoding & 0x70) == DW_EH_PE_absptr)
      return TM.getSymbol(GV);
    report_fatal_error("We do not support this DWARF encoding yet!");
  }
  
  void TargetLoweringObjectFileELF::emitPersonalityValue(
      MCStreamer &Streamer, const DataLayout &DL, const MCSymbol *Sym) const {
    SmallString<64> NameData("DW.ref.");
    NameData += Sym->getName();
    MCSymbolELF *Label =
        cast<MCSymbolELF>(getContext().getOrCreateSymbol(NameData));
    Streamer.EmitSymbolAttribute(Label, MCSA_Hidden);
    Streamer.EmitSymbolAttribute(Label, MCSA_Weak);
    unsigned Flags = ELF::SHF_ALLOC | ELF::SHF_WRITE | ELF::SHF_GROUP;
    MCSection *Sec = getContext().getELFNamedSection(".data", Label->getName(),
                                                     ELF::SHT_PROGBITS, Flags, 0);
    unsigned Size = DL.getPointerSize();
    Streamer.SwitchSection(Sec);
    Streamer.EmitValueToAlignment(DL.getPointerABIAlignment(0).value());
    Streamer.EmitSymbolAttribute(Label, MCSA_ELF_TypeObject);
    const MCExpr *E = MCConstantExpr::create(Size, getContext());
    Streamer.emitELFSize(Label, E);
    Streamer.EmitLabel(Label);
  
    Streamer.EmitSymbolValue(Sym, Size);
  }
  
  const MCExpr *TargetLoweringObjectFileELF::getTTypeGlobalReference(
      const GlobalValue *GV, unsigned Encoding, const TargetMachine &TM,
      MachineModuleInfo *MMI, MCStreamer &Streamer) const {
    if (Encoding & DW_EH_PE_indirect) {
      MachineModuleInfoELF &ELFMMI = MMI->getObjFileInfo<MachineModuleInfoELF>();
  
      MCSymbol *SSym = getSymbolWithGlobalValueBase(GV, ".DW.stub", TM);
  
      // Add information about the stub reference to ELFMMI so that the stub
      // gets emitted by the asmprinter.
      MachineModuleInfoImpl::StubValueTy &StubSym = ELFMMI.getGVStubEntry(SSym);
      if (!StubSym.getPointer()) {
        MCSymbol *Sym = TM.getSymbol(GV);
        StubSym = MachineModuleInfoImpl::StubValueTy(Sym, !GV->hasLocalLinkage());
      }
  
      return TargetLoweringObjectFile::
        getTTypeReference(MCSymbolRefExpr::create(SSym, getContext()),
                          Encoding & ~DW_EH_PE_indirect, Streamer);
    }
  
    return TargetLoweringObjectFile::getTTypeGlobalReference(GV, Encoding, TM,
                                                             MMI, Streamer);
  }
  
  static SectionKind getELFKindForNamedSection(StringRef Name, SectionKind K) {
    // N.B.: The defaults used in here are not the same ones used in MC.
    // We follow gcc, MC follows gas. For example, given ".section .eh_frame",
    // both gas and MC will produce a section with no flags. Given
    // section(".eh_frame") gcc will produce:
    //
    //   .section   .eh_frame,"a",@progbits
  
    if (Name == getInstrProfSectionName(IPSK_covmap, Triple::ELF,
                                        /*AddSegmentInfo=*/false))
      return SectionKind::getMetadata();
  
    if (Name.empty() || Name[0] != '.') return K;
  
    // Default implementation based on some magic section names.
    if (Name == ".bss" ||
        Name.startswith(".bss.") ||
        Name.startswith(".gnu.linkonce.b.") ||
        Name.startswith(".llvm.linkonce.b.") ||
        Name == ".sbss" ||
        Name.startswith(".sbss.") ||
        Name.startswith(".gnu.linkonce.sb.") ||
        Name.startswith(".llvm.linkonce.sb."))
      return SectionKind::getBSS();
  
    if (Name == ".tdata" ||
        Name.startswith(".tdata.") ||
        Name.startswith(".gnu.linkonce.td.") ||
        Name.startswith(".llvm.linkonce.td."))
      return SectionKind::getThreadData();
  
    if (Name == ".tbss" ||
        Name.startswith(".tbss.") ||
        Name.startswith(".gnu.linkonce.tb.") ||
        Name.startswith(".llvm.linkonce.tb."))
      return SectionKind::getThreadBSS();
  
    return K;
  }
  
  static unsigned getELFSectionType(StringRef Name, SectionKind K) {
    // Use SHT_NOTE for section whose name starts with ".note" to allow
    // emitting ELF notes from C variable declaration.
    // See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77609
    if (Name.startswith(".note"))
      return ELF::SHT_NOTE;
  
    if (Name == ".init_array")
      return ELF::SHT_INIT_ARRAY;
  
    if (Name == ".fini_array")
      return ELF::SHT_FINI_ARRAY;
  
    if (Name == ".preinit_array")
      return ELF::SHT_PREINIT_ARRAY;
  
    if (K.isBSS() || K.isThreadBSS())
      return ELF::SHT_NOBITS;
  
    return ELF::SHT_PROGBITS;
  }
  
  static unsigned getELFSectionFlags(SectionKind K) {
    unsigned Flags = 0;
  
    if (!K.isMetadata())
      Flags |= ELF::SHF_ALLOC;
  
    if (K.isText())
      Flags |= ELF::SHF_EXECINSTR;
  
    if (K.isExecuteOnly())
      Flags |= ELF::SHF_ARM_PURECODE;
  
    if (K.isWriteable())
      Flags |= ELF::SHF_WRITE;
  
    if (K.isThreadLocal())
      Flags |= ELF::SHF_TLS;
  
    if (K.isMergeableCString() || K.isMergeableConst())
      Flags |= ELF::SHF_MERGE;
  
    if (K.isMergeableCString())
      Flags |= ELF::SHF_STRINGS;
  
    return Flags;
  }
  
  static const Comdat *getELFComdat(const GlobalValue *GV) {
    const Comdat *C = GV->getComdat();
    if (!C)
      return nullptr;
  
    if (C->getSelectionKind() != Comdat::Any)
      report_fatal_error("ELF COMDATs only support SelectionKind::Any, '" +
                         C->getName() + "' cannot be lowered.");
  
    return C;
  }
  
  static const MCSymbolELF *getAssociatedSymbol(const GlobalObject *GO,
                                                const TargetMachine &TM) {
    MDNode *MD = GO->getMetadata(LLVMContext::MD_associated);
    if (!MD)
      return nullptr;
  
    const MDOperand &Op = MD->getOperand(0);
    if (!Op.get())
      return nullptr;
  
    auto *VM = dyn_cast<ValueAsMetadata>(Op);
    if (!VM)
      report_fatal_error("MD_associated operand is not ValueAsMetadata");
  
    auto *OtherGV = dyn_cast<GlobalValue>(VM->getValue());
    return OtherGV ? dyn_cast<MCSymbolELF>(TM.getSymbol(OtherGV)) : nullptr;
  }
  
  static unsigned getEntrySizeForKind(SectionKind Kind) {
    if (Kind.isMergeable1ByteCString())
      return 1;
    else if (Kind.isMergeable2ByteCString())
      return 2;
    else if (Kind.isMergeable4ByteCString())
      return 4;
    else if (Kind.isMergeableConst4())
      return 4;
    else if (Kind.isMergeableConst8())
      return 8;
    else if (Kind.isMergeableConst16())
      return 16;
    else if (Kind.isMergeableConst32())
      return 32;
    else {
      // We shouldn't have mergeable C strings or mergeable constants that we
      // didn't handle above.
      assert(!Kind.isMergeableCString() && "unknown string width");
      assert(!Kind.isMergeableConst() && "unknown data width");
      return 0;
    }
  }
  
  MCSection *TargetLoweringObjectFileELF::getExplicitSectionGlobal(
      const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
    StringRef SectionName = GO->getSection();
  
    // Check if '#pragma clang section' name is applicable.
    // Note that pragma directive overrides -ffunction-section, -fdata-section
    // and so section name is exactly as user specified and not uniqued.
    const GlobalVariable *GV = dyn_cast<GlobalVariable>(GO);
    if (GV && GV->hasImplicitSection()) {
      auto Attrs = GV->getAttributes();
      if (Attrs.hasAttribute("bss-section") && Kind.isBSS()) {
        SectionName = Attrs.getAttribute("bss-section").getValueAsString();
      } else if (Attrs.hasAttribute("rodata-section") && Kind.isReadOnly()) {
        SectionName = Attrs.getAttribute("rodata-section").getValueAsString();
      } else if (Attrs.hasAttribute("relro-section") && Kind.isReadOnlyWithRel()) {
        SectionName = Attrs.getAttribute("relro-section").getValueAsString();
      } else if (Attrs.hasAttribute("data-section") && Kind.isData()) {
        SectionName = Attrs.getAttribute("data-section").getValueAsString();
      }
    }
    const Function *F = dyn_cast<Function>(GO);
    if (F && F->hasFnAttribute("implicit-section-name")) {
      SectionName = F->getFnAttribute("implicit-section-name").getValueAsString();
    }
  
    // Infer section flags from the section name if we can.
    Kind = getELFKindForNamedSection(SectionName, Kind);
  
    StringRef Group = "";
    unsigned Flags = getELFSectionFlags(Kind);
    if (const Comdat *C = getELFComdat(GO)) {
      Group = C->getName();
      Flags |= ELF::SHF_GROUP;
    }
  
    // A section can have at most one associated section. Put each global with
    // MD_associated in a unique section.
    unsigned UniqueID = MCContext::GenericSectionID;
    const MCSymbolELF *AssociatedSymbol = getAssociatedSymbol(GO, TM);
    if (AssociatedSymbol) {
      UniqueID = NextUniqueID++;
      Flags |= ELF::SHF_LINK_ORDER;
    }
  
    MCSectionELF *Section = getContext().getELFSection(
        SectionName, getELFSectionType(SectionName, Kind), Flags,
        getEntrySizeForKind(Kind), Group, UniqueID, AssociatedSymbol);
    // Make sure that we did not get some other section with incompatible sh_link.
    // This should not be possible due to UniqueID code above.
    assert(Section->getAssociatedSymbol() == AssociatedSymbol &&
           "Associated symbol mismatch between sections");
    return Section;
  }
  
  /// Return the section prefix name used by options FunctionsSections and
  /// DataSections.
  static StringRef getSectionPrefixForGlobal(SectionKind Kind) {
    if (Kind.isText())
      return ".text";
    if (Kind.isReadOnly())
      return ".rodata";
    if (Kind.isBSS())
      return ".bss";
    if (Kind.isThreadData())
      return ".tdata";
    if (Kind.isThreadBSS())
      return ".tbss";
    if (Kind.isData())
      return ".data";
    assert(Kind.isReadOnlyWithRel() && "Unknown section kind");
    return ".data.rel.ro";
  }
  
  static MCSectionELF *selectELFSectionForGlobal(
      MCContext &Ctx, const GlobalObject *GO, SectionKind Kind, Mangler &Mang,
      const TargetMachine &TM, bool EmitUniqueSection, unsigned Flags,
      unsigned *NextUniqueID, const MCSymbolELF *AssociatedSymbol) {
  
    StringRef Group = "";
    if (const Comdat *C = getELFComdat(GO)) {
      Flags |= ELF::SHF_GROUP;
      Group = C->getName();
    }
  
    // Get the section entry size based on the kind.
    unsigned EntrySize = getEntrySizeForKind(Kind);
  
    SmallString<128> Name;
    if (Kind.isMergeableCString()) {
      // We also need alignment here.
      // FIXME: this is getting the alignment of the character, not the
      // alignment of the global!
      unsigned Align = GO->getParent()->getDataLayout().getPreferredAlignment(
          cast<GlobalVariable>(GO));
  
      std::string SizeSpec = ".rodata.str" + utostr(EntrySize) + ".";
      Name = SizeSpec + utostr(Align);
    } else if (Kind.isMergeableConst()) {
      Name = ".rodata.cst";
      Name += utostr(EntrySize);
    } else {
      Name = getSectionPrefixForGlobal(Kind);
    }
  
    if (const auto *F = dyn_cast<Function>(GO)) {
      const auto &OptionalPrefix = F->getSectionPrefix();
      if (OptionalPrefix)
        Name += *OptionalPrefix;
    }
  
    unsigned UniqueID = MCContext::GenericSectionID;
    if (EmitUniqueSection) {
      if (TM.getUniqueSectionNames()) {
        Name.push_back('.');
        TM.getNameWithPrefix(Name, GO, Mang, true /*MayAlwaysUsePrivate*/);
      } else {
        UniqueID = *NextUniqueID;
        (*NextUniqueID)++;
      }
    }
    // Use 0 as the unique ID for execute-only text.
    if (Kind.isExecuteOnly())
      UniqueID = 0;
    return Ctx.getELFSection(Name, getELFSectionType(Name, Kind), Flags,
                             EntrySize, Group, UniqueID, AssociatedSymbol);
  }
  
  MCSection *TargetLoweringObjectFileELF::SelectSectionForGlobal(
      const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
    unsigned Flags = getELFSectionFlags(Kind);
  
    // If we have -ffunction-section or -fdata-section then we should emit the
    // global value to a uniqued section specifically for it.
    bool EmitUniqueSection = false;
    if (!(Flags & ELF::SHF_MERGE) && !Kind.isCommon()) {
      if (Kind.isText())
        EmitUniqueSection = TM.getFunctionSections();
      else
        EmitUniqueSection = TM.getDataSections();
    }
    EmitUniqueSection |= GO->hasComdat();
  
    const MCSymbolELF *AssociatedSymbol = getAssociatedSymbol(GO, TM);
    if (AssociatedSymbol) {
      EmitUniqueSection = true;
      Flags |= ELF::SHF_LINK_ORDER;
    }
  
    MCSectionELF *Section = selectELFSectionForGlobal(
        getContext(), GO, Kind, getMangler(), TM, EmitUniqueSection, Flags,
        &NextUniqueID, AssociatedSymbol);
    assert(Section->getAssociatedSymbol() == AssociatedSymbol);
    return Section;
  }
  
  MCSection *TargetLoweringObjectFileELF::getSectionForJumpTable(
      const Function &F, const TargetMachine &TM) const {
    // If the function can be removed, produce a unique section so that
    // the table doesn't prevent the removal.
    const Comdat *C = F.getComdat();
    bool EmitUniqueSection = TM.getFunctionSections() || C;
    if (!EmitUniqueSection)
      return ReadOnlySection;
  
    return selectELFSectionForGlobal(getContext(), &F, SectionKind::getReadOnly(),
                                     getMangler(), TM, EmitUniqueSection,
                                     ELF::SHF_ALLOC, &NextUniqueID,
                                     /* AssociatedSymbol */ nullptr);
  }
  
  bool TargetLoweringObjectFileELF::shouldPutJumpTableInFunctionSection(
      bool UsesLabelDifference, const Function &F) const {
    // We can always create relative relocations, so use another section
    // that can be marked non-executable.
    return false;
  }
  
  /// Given a mergeable constant with the specified size and relocation
  /// information, return a section that it should be placed in.
  MCSection *TargetLoweringObjectFileELF::getSectionForConstant(
      const DataLayout &DL, SectionKind Kind, const Constant *C,
      unsigned &Align) const {
    if (Kind.isMergeableConst4() && MergeableConst4Section)
      return MergeableConst4Section;
    if (Kind.isMergeableConst8() && MergeableConst8Section)
      return MergeableConst8Section;
    if (Kind.isMergeableConst16() && MergeableConst16Section)
      return MergeableConst16Section;
    if (Kind.isMergeableConst32() && MergeableConst32Section)
      return MergeableConst32Section;
    if (Kind.isReadOnly())
      return ReadOnlySection;
  
    assert(Kind.isReadOnlyWithRel() && "Unknown section kind");
    return DataRelROSection;
  }
  
  static MCSectionELF *getStaticStructorSection(MCContext &Ctx, bool UseInitArray,
                                                bool IsCtor, unsigned Priority,
                                                const MCSymbol *KeySym) {
    std::string Name;
    unsigned Type;
    unsigned Flags = ELF::SHF_ALLOC | ELF::SHF_WRITE;
    StringRef COMDAT = KeySym ? KeySym->getName() : "";
  
    if (KeySym)
      Flags |= ELF::SHF_GROUP;
  
    if (UseInitArray) {
      if (IsCtor) {
        Type = ELF::SHT_INIT_ARRAY;
        Name = ".init_array";
      } else {
        Type = ELF::SHT_FINI_ARRAY;
        Name = ".fini_array";
      }
      if (Priority != 65535) {
        Name += '.';
        Name += utostr(Priority);
      }
    } else {
      // The default scheme is .ctor / .dtor, so we have to invert the priority
      // numbering.
      if (IsCtor)
        Name = ".ctors";
      else
        Name = ".dtors";
      if (Priority != 65535)
        raw_string_ostream(Name) << format(".%05u", 65535 - Priority);
      Type = ELF::SHT_PROGBITS;
    }
  
    return Ctx.getELFSection(Name, Type, Flags, 0, COMDAT);
  }
  
  MCSection *TargetLoweringObjectFileELF::getStaticCtorSection(
      unsigned Priority, const MCSymbol *KeySym) const {
    return getStaticStructorSection(getContext(), UseInitArray, true, Priority,
                                    KeySym);
  }
  
  MCSection *TargetLoweringObjectFileELF::getStaticDtorSection(
      unsigned Priority, const MCSymbol *KeySym) const {
    return getStaticStructorSection(getContext(), UseInitArray, false, Priority,
                                    KeySym);
  }
  
  const MCExpr *TargetLoweringObjectFileELF::lowerRelativeReference(
      const GlobalValue *LHS, const GlobalValue *RHS,
      const TargetMachine &TM) const {
    // We may only use a PLT-relative relocation to refer to unnamed_addr
    // functions.
    if (!LHS->hasGlobalUnnamedAddr() || !LHS->getValueType()->isFunctionTy())
      return nullptr;
  
    // Basic sanity checks.
    if (LHS->getType()->getPointerAddressSpace() != 0 ||
        RHS->getType()->getPointerAddressSpace() != 0 || LHS->isThreadLocal() ||
        RHS->isThreadLocal())
      return nullptr;
  
    return MCBinaryExpr::createSub(
        MCSymbolRefExpr::create(TM.getSymbol(LHS), PLTRelativeVariantKind,
                                getContext()),
        MCSymbolRefExpr::create(TM.getSymbol(RHS), getContext()), getContext());
  }
  
  MCSection *TargetLoweringObjectFileELF::getSectionForCommandLines() const {
    // Use ".GCC.command.line" since this feature is to support clang's
    // -frecord-gcc-switches which in turn attempts to mimic GCC's switch of the
    // same name.
    return getContext().getELFSection(".GCC.command.line", ELF::SHT_PROGBITS,
                                      ELF::SHF_MERGE | ELF::SHF_STRINGS, 1, "");
  }
  
  void
  TargetLoweringObjectFileELF::InitializeELF(bool UseInitArray_) {
    UseInitArray = UseInitArray_;
    MCContext &Ctx = getContext();
    if (!UseInitArray) {
      StaticCtorSection = Ctx.getELFSection(".ctors", ELF::SHT_PROGBITS,
                                            ELF::SHF_ALLOC | ELF::SHF_WRITE);
  
      StaticDtorSection = Ctx.getELFSection(".dtors", ELF::SHT_PROGBITS,
                                            ELF::SHF_ALLOC | ELF::SHF_WRITE);
      return;
    }
  
    StaticCtorSection = Ctx.getELFSection(".init_array", ELF::SHT_INIT_ARRAY,
                                          ELF::SHF_WRITE | ELF::SHF_ALLOC);
    StaticDtorSection = Ctx.getELFSection(".fini_array", ELF::SHT_FINI_ARRAY,
                                          ELF::SHF_WRITE | ELF::SHF_ALLOC);
  }
  
  //===----------------------------------------------------------------------===//
  //                                 MachO
  //===----------------------------------------------------------------------===//
  
  TargetLoweringObjectFileMachO::TargetLoweringObjectFileMachO()
    : TargetLoweringObjectFile() {
    SupportIndirectSymViaGOTPCRel = true;
  }
  
  void TargetLoweringObjectFileMachO::Initialize(MCContext &Ctx,
                                                 const TargetMachine &TM) {
    TargetLoweringObjectFile::Initialize(Ctx, TM);
    if (TM.getRelocationModel() == Reloc::Static) {
      StaticCtorSection = Ctx.getMachOSection("__TEXT", "__constructor", 0,
                                              SectionKind::getData());
      StaticDtorSection = Ctx.getMachOSection("__TEXT", "__destructor", 0,
                                              SectionKind::getData());
    } else {
      StaticCtorSection = Ctx.getMachOSection("__DATA", "__mod_init_func",
                                              MachO::S_MOD_INIT_FUNC_POINTERS,
                                              SectionKind::getData());
      StaticDtorSection = Ctx.getMachOSection("__DATA", "__mod_term_func",
                                              MachO::S_MOD_TERM_FUNC_POINTERS,
                                              SectionKind::getData());
    }
  
    PersonalityEncoding =
        dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel | dwarf::DW_EH_PE_sdata4;
    LSDAEncoding = dwarf::DW_EH_PE_pcrel;
    TTypeEncoding =
        dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel | dwarf::DW_EH_PE_sdata4;
  }
  
  void TargetLoweringObjectFileMachO::emitModuleMetadata(MCStreamer &Streamer,
                                                         Module &M) const {
    // Emit the linker options if present.
    if (auto *LinkerOptions = M.getNamedMetadata("llvm.linker.options")) {
      for (const auto &Option : LinkerOptions->operands()) {
        SmallVector<std::string, 4> StrOptions;
        for (const auto &Piece : cast<MDNode>(Option)->operands())
          StrOptions.push_back(cast<MDString>(Piece)->getString());
        Streamer.EmitLinkerOptions(StrOptions);
      }
    }
  
    unsigned VersionVal = 0;
    unsigned ImageInfoFlags = 0;
    StringRef SectionVal;
  
    GetObjCImageInfo(M, VersionVal, ImageInfoFlags, SectionVal);
  
    // The section is mandatory. If we don't have it, then we don't have GC info.
    if (SectionVal.empty())
      return;
  
    StringRef Segment, Section;
    unsigned TAA = 0, StubSize = 0;
    bool TAAParsed;
    std::string ErrorCode =
      MCSectionMachO::ParseSectionSpecifier(SectionVal, Segment, Section,
                                            TAA, TAAParsed, StubSize);
    if (!ErrorCode.empty())
      // If invalid, report the error with report_fatal_error.
      report_fatal_error("Invalid section specifier '" + Section + "': " +
                         ErrorCode + ".");
  
    // Get the section.
    MCSectionMachO *S = getContext().getMachOSection(
        Segment, Section, TAA, StubSize, SectionKind::getData());
    Streamer.SwitchSection(S);
    Streamer.EmitLabel(getContext().
                       getOrCreateSymbol(StringRef("L_OBJC_IMAGE_INFO")));
    Streamer.EmitIntValue(VersionVal, 4);
    Streamer.EmitIntValue(ImageInfoFlags, 4);
    Streamer.AddBlankLine();
  }
  
  static void checkMachOComdat(const GlobalValue *GV) {
    const Comdat *C = GV->getComdat();
    if (!C)
      return;
  
    report_fatal_error("MachO doesn't support COMDATs, '" + C->getName() +
                       "' cannot be lowered.");
  }
  
  MCSection *TargetLoweringObjectFileMachO::getExplicitSectionGlobal(
      const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
    // Parse the section specifier and create it if valid.
    StringRef Segment, Section;
    unsigned TAA = 0, StubSize = 0;
    bool TAAParsed;
  
    checkMachOComdat(GO);
  
    std::string ErrorCode =
      MCSectionMachO::ParseSectionSpecifier(GO->getSection(), Segment, Section,
                                            TAA, TAAParsed, StubSize);
    if (!ErrorCode.empty()) {
      // If invalid, report the error with report_fatal_error.
      report_fatal_error("Global variable '" + GO->getName() +
                         "' has an invalid section specifier '" +
                         GO->getSection() + "': " + ErrorCode + ".");
    }
  
    // Get the section.
    MCSectionMachO *S =
        getContext().getMachOSection(Segment, Section, TAA, StubSize, Kind);
  
    // If TAA wasn't set by ParseSectionSpecifier() above,
    // use the value returned by getMachOSection() as a default.
    if (!TAAParsed)
      TAA = S->getTypeAndAttributes();
  
    // Okay, now that we got the section, verify that the TAA & StubSize agree.
    // If the user declared multiple globals with different section flags, we need
    // to reject it here.
    if (S->getTypeAndAttributes() != TAA || S->getStubSize() != StubSize) {
      // If invalid, report the error with report_fatal_error.
      report_fatal_error("Global variable '" + GO->getName() +
                         "' section type or attributes does not match previous"
                         " section specifier");
    }
  
    return S;
  }
  
  MCSection *TargetLoweringObjectFileMachO::SelectSectionForGlobal(
      const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
    checkMachOComdat(GO);
  
    // Handle thread local data.
    if (Kind.isThreadBSS()) return TLSBSSSection;
    if (Kind.isThreadData()) return TLSDataSection;
  
    if (Kind.isText())
      return GO->isWeakForLinker() ? TextCoalSection : TextSection;
  
    // If this is weak/linkonce, put this in a coalescable section, either in text
    // or data depending on if it is writable.
    if (GO->isWeakForLinker()) {
      if (Kind.isReadOnly())
        return ConstTextCoalSection;
      if (Kind.isReadOnlyWithRel())
        return ConstDataCoalSection;
      return DataCoalSection;
    }
  
    // FIXME: Alignment check should be handled by section classifier.
    if (Kind.isMergeable1ByteCString() &&
        GO->getParent()->getDataLayout().getPreferredAlignment(
            cast<GlobalVariable>(GO)) < 32)
      return CStringSection;
  
    // Do not put 16-bit arrays in the UString section if they have an
    // externally visible label, this runs into issues with certain linker
    // versions.
    if (Kind.isMergeable2ByteCString() && !GO->hasExternalLinkage() &&
        GO->getParent()->getDataLayout().getPreferredAlignment(
            cast<GlobalVariable>(GO)) < 32)
      return UStringSection;
  
    // With MachO only variables whose corresponding symbol starts with 'l' or
    // 'L' can be merged, so we only try merging GVs with private linkage.
    if (GO->hasPrivateLinkage() && Kind.isMergeableConst()) {
      if (Kind.isMergeableConst4())
        return FourByteConstantSection;
      if (Kind.isMergeableConst8())
        return EightByteConstantSection;
      if (Kind.isMergeableConst16())
        return SixteenByteConstantSection;
    }
  
    // Otherwise, if it is readonly, but not something we can specially optimize,
    // just drop it in .const.
    if (Kind.isReadOnly())
      return ReadOnlySection;
  
    // If this is marked const, put it into a const section.  But if the dynamic
    // linker needs to write to it, put it in the data segment.
    if (Kind.isReadOnlyWithRel())
      return ConstDataSection;
  
    // Put zero initialized globals with strong external linkage in the
    // DATA, __common section with the .zerofill directive.
    if (Kind.isBSSExtern())
      return DataCommonSection;
  
    // Put zero initialized globals with local linkage in __DATA,__bss directive
    // with the .zerofill directive (aka .lcomm).
    if (Kind.isBSSLocal())
      return DataBSSSection;
  
    // Otherwise, just drop the variable in the normal data section.
    return DataSection;
  }
  
  MCSection *TargetLoweringObjectFileMachO::getSectionForConstant(
      const DataLayout &DL, SectionKind Kind, const Constant *C,
      unsigned &Align) const {
    // If this constant requires a relocation, we have to put it in the data
    // segment, not in the text segment.
    if (Kind.isData() || Kind.isReadOnlyWithRel())
      return ConstDataSection;
  
    if (Kind.isMergeableConst4())
      return FourByteConstantSection;
    if (Kind.isMergeableConst8())
      return EightByteConstantSection;
    if (Kind.isMergeableConst16())
      return SixteenByteConstantSection;
    return ReadOnlySection;  // .const
  }
  
  const MCExpr *TargetLoweringObjectFileMachO::getTTypeGlobalReference(
      const GlobalValue *GV, unsigned Encoding, const TargetMachine &TM,
      MachineModuleInfo *MMI, MCStreamer &Streamer) const {
    // The mach-o version of this method defaults to returning a stub reference.
  
    if (Encoding & DW_EH_PE_indirect) {
      MachineModuleInfoMachO &MachOMMI =
        MMI->getObjFileInfo<MachineModuleInfoMachO>();
  
      MCSymbol *SSym = getSymbolWithGlobalValueBase(GV, "$non_lazy_ptr", TM);
  
      // Add information about the stub reference to MachOMMI so that the stub
      // gets emitted by the asmprinter.
      MachineModuleInfoImpl::StubValueTy &StubSym = MachOMMI.getGVStubEntry(SSym);
      if (!StubSym.getPointer()) {
        MCSymbol *Sym = TM.getSymbol(GV);
        StubSym = MachineModuleInfoImpl::StubValueTy(Sym, !GV->hasLocalLinkage());
      }
  
      return TargetLoweringObjectFile::
        getTTypeReference(MCSymbolRefExpr::create(SSym, getContext()),
                          Encoding & ~DW_EH_PE_indirect, Streamer);
    }
  
    return TargetLoweringObjectFile::getTTypeGlobalReference(GV, Encoding, TM,
                                                             MMI, Streamer);
  }
  
  MCSymbol *TargetLoweringObjectFileMachO::getCFIPersonalitySymbol(
      const GlobalValue *GV, const TargetMachine &TM,
      MachineModuleInfo *MMI) const {
    // The mach-o version of this method defaults to returning a stub reference.
    MachineModuleInfoMachO &MachOMMI =
      MMI->getObjFileInfo<MachineModuleInfoMachO>();
  
    MCSymbol *SSym = getSymbolWithGlobalValueBase(GV, "$non_lazy_ptr", TM);
  
    // Add information about the stub reference to MachOMMI so that the stub
    // gets emitted by the asmprinter.
    MachineModuleInfoImpl::StubValueTy &StubSym = MachOMMI.getGVStubEntry(SSym);
    if (!StubSym.getPointer()) {
      MCSymbol *Sym = TM.getSymbol(GV);
      StubSym = MachineModuleInfoImpl::StubValueTy(Sym, !GV->hasLocalLinkage());
    }
  
    return SSym;
  }
  
  const MCExpr *TargetLoweringObjectFileMachO::getIndirectSymViaGOTPCRel(
      const GlobalValue *GV, const MCSymbol *Sym, const MCValue &MV,
      int64_t Offset, MachineModuleInfo *MMI, MCStreamer &Streamer) const {
    // Although MachO 32-bit targets do not explicitly have a GOTPCREL relocation
    // as 64-bit do, we replace the GOT equivalent by accessing the final symbol
    // through a non_lazy_ptr stub instead. One advantage is that it allows the
    // computation of deltas to final external symbols. Example:
    //
    //    _extgotequiv:
    //       .long   _extfoo
    //
    //    _delta:
    //       .long   _extgotequiv-_delta
    //
    // is transformed to:
    //
    //    _delta:
    //       .long   L_extfoo$non_lazy_ptr-(_delta+0)
    //
    //       .section        __IMPORT,__pointers,non_lazy_symbol_pointers
    //    L_extfoo$non_lazy_ptr:
    //       .indirect_symbol        _extfoo
    //       .long   0
    //
    // The indirect symbol table (and sections of non_lazy_symbol_pointers type)
    // may point to both local (same translation unit) and global (other
    // translation units) symbols. Example:
    //
    // .section __DATA,__pointers,non_lazy_symbol_pointers
    // L1:
    //    .indirect_symbol _myGlobal
    //    .long 0
    // L2:
    //    .indirect_symbol _myLocal
    //    .long _myLocal
    //
    // If the symbol is local, instead of the symbol's index, the assembler
    // places the constant INDIRECT_SYMBOL_LOCAL into the indirect symbol table.
    // Then the linker will notice the constant in the table and will look at the
    // content of the symbol.
    MachineModuleInfoMachO &MachOMMI =
      MMI->getObjFileInfo<MachineModuleInfoMachO>();
    MCContext &Ctx = getContext();
  
    // The offset must consider the original displacement from the base symbol
    // since 32-bit targets don't have a GOTPCREL to fold the PC displacement.
    Offset = -MV.getConstant();
    const MCSymbol *BaseSym = &MV.getSymB()->getSymbol();
  
    // Access the final symbol via sym$non_lazy_ptr and generate the appropriated
    // non_lazy_ptr stubs.
    SmallString<128> Name;
    StringRef Suffix = "$non_lazy_ptr";
    Name += MMI->getModule()->getDataLayout().getPrivateGlobalPrefix();
    Name += Sym->getName();
    Name += Suffix;
    MCSymbol *Stub = Ctx.getOrCreateSymbol(Name);
  
    MachineModuleInfoImpl::StubValueTy &StubSym = MachOMMI.getGVStubEntry(Stub);
  
    if (!StubSym.getPointer())
      StubSym = MachineModuleInfoImpl::StubValueTy(const_cast<MCSymbol *>(Sym),
                                                   !GV->hasLocalLinkage());
  
    const MCExpr *BSymExpr =
      MCSymbolRefExpr::create(BaseSym, MCSymbolRefExpr::VK_None, Ctx);
    const MCExpr *LHS =
      MCSymbolRefExpr::create(Stub, MCSymbolRefExpr::VK_None, Ctx);
  
    if (!Offset)
      return MCBinaryExpr::createSub(LHS, BSymExpr, Ctx);
  
    const MCExpr *RHS =
      MCBinaryExpr::createAdd(BSymExpr, MCConstantExpr::create(Offset, Ctx), Ctx);
    return MCBinaryExpr::createSub(LHS, RHS, Ctx);
  }
  
  static bool canUsePrivateLabel(const MCAsmInfo &AsmInfo,
                                 const MCSection &Section) {
    if (!AsmInfo.isSectionAtomizableBySymbols(Section))
      return true;
  
    // If it is not dead stripped, it is safe to use private labels.
    const MCSectionMachO &SMO = cast<MCSectionMachO>(Section);
    if (SMO.hasAttribute(MachO::S_ATTR_NO_DEAD_STRIP))
      return true;
  
    return false;
  }
  
  void TargetLoweringObjectFileMachO::getNameWithPrefix(
      SmallVectorImpl<char> &OutName, const GlobalValue *GV,
      const TargetMachine &TM) const {
    bool CannotUsePrivateLabel = true;
    if (auto *GO = GV->getBaseObject()) {
      SectionKind GOKind = TargetLoweringObjectFile::getKindForGlobal(GO, TM);
      const MCSection *TheSection = SectionForGlobal(GO, GOKind, TM);
      CannotUsePrivateLabel =
          !canUsePrivateLabel(*TM.getMCAsmInfo(), *TheSection);
    }
    getMangler().getNameWithPrefix(OutName, GV, CannotUsePrivateLabel);
  }
  
  //===----------------------------------------------------------------------===//
  //                                  COFF
  //===----------------------------------------------------------------------===//
  
  static unsigned
  getCOFFSectionFlags(SectionKind K, const TargetMachine &TM) {
    unsigned Flags = 0;
    bool isThumb = TM.getTargetTriple().getArch() == Triple::thumb;
  
    if (K.isMetadata())
      Flags |=
        COFF::IMAGE_SCN_MEM_DISCARDABLE;
    else if (K.isText())
      Flags |=
        COFF::IMAGE_SCN_MEM_EXECUTE |
        COFF::IMAGE_SCN_MEM_READ |
        COFF::IMAGE_SCN_CNT_CODE |
        (isThumb ? COFF::IMAGE_SCN_MEM_16BIT : (COFF::SectionCharacteristics)0);
    else if (K.isBSS())
      Flags |=
        COFF::IMAGE_SCN_CNT_UNINITIALIZED_DATA |
        COFF::IMAGE_SCN_MEM_READ |
        COFF::IMAGE_SCN_MEM_WRITE;
    else if (K.isThreadLocal())
      Flags |=
        COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
        COFF::IMAGE_SCN_MEM_READ |
        COFF::IMAGE_SCN_MEM_WRITE;
    else if (K.isReadOnly() || K.isReadOnlyWithRel())
      Flags |=
        COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
        COFF::IMAGE_SCN_MEM_READ;
    else if (K.isWriteable())
      Flags |=
        COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
        COFF::IMAGE_SCN_MEM_READ |
        COFF::IMAGE_SCN_MEM_WRITE;
  
    return Flags;
  }
  
  static const GlobalValue *getComdatGVForCOFF(const GlobalValue *GV) {
    const Comdat *C = GV->getComdat();
    assert(C && "expected GV to have a Comdat!");
  
    StringRef ComdatGVName = C->getName();
    const GlobalValue *ComdatGV = GV->getParent()->getNamedValue(ComdatGVName);
    if (!ComdatGV)
      report_fatal_error("Associative COMDAT symbol '" + ComdatGVName +
                         "' does not exist.");
  
    if (ComdatGV->getComdat() != C)
      report_fatal_error("Associative COMDAT symbol '" + ComdatGVName +
                         "' is not a key for its COMDAT.");
  
    return ComdatGV;
  }
  
  static int getSelectionForCOFF(const GlobalValue *GV) {
    if (const Comdat *C = GV->getComdat()) {
      const GlobalValue *ComdatKey = getComdatGVForCOFF(GV);
      if (const auto *GA = dyn_cast<GlobalAlias>(ComdatKey))
        ComdatKey = GA->getBaseObject();
      if (ComdatKey == GV) {
        switch (C->getSelectionKind()) {
        case Comdat::Any:
          return COFF::IMAGE_COMDAT_SELECT_ANY;
        case Comdat::ExactMatch:
          return COFF::IMAGE_COMDAT_SELECT_EXACT_MATCH;
        case Comdat::Largest:
          return COFF::IMAGE_COMDAT_SELECT_LARGEST;
        case Comdat::NoDuplicates:
          return COFF::IMAGE_COMDAT_SELECT_NODUPLICATES;
        case Comdat::SameSize:
          return COFF::IMAGE_COMDAT_SELECT_SAME_SIZE;
        }
      } else {
        return COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE;
      }
    }
    return 0;
  }
  
  MCSection *TargetLoweringObjectFileCOFF::getExplicitSectionGlobal(
      const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
    int Selection = 0;
    unsigned Characteristics = getCOFFSectionFlags(Kind, TM);
    StringRef Name = GO->getSection();
    StringRef COMDATSymName = "";
    if (GO->hasComdat()) {
      Selection = getSelectionForCOFF(GO);
      const GlobalValue *ComdatGV;
      if (Selection == COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE)
        ComdatGV = getComdatGVForCOFF(GO);
      else
        ComdatGV = GO;
  
      if (!ComdatGV->hasPrivateLinkage()) {
        MCSymbol *Sym = TM.getSymbol(ComdatGV);
        COMDATSymName = Sym->getName();
        Characteristics |= COFF::IMAGE_SCN_LNK_COMDAT;
      } else {
        Selection = 0;
      }
    }
  
    return getContext().getCOFFSection(Name, Characteristics, Kind, COMDATSymName,
                                       Selection);
  }
  
  static StringRef getCOFFSectionNameForUniqueGlobal(SectionKind Kind) {
    if (Kind.isText())
      return ".text";
    if (Kind.isBSS())
      return ".bss";
    if (Kind.isThreadLocal())
      return ".tls$";
    if (Kind.isReadOnly() || Kind.isReadOnlyWithRel())
      return ".rdata";
    return ".data";
  }
  
  MCSection *TargetLoweringObjectFileCOFF::SelectSectionForGlobal(
      const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
    // If we have -ffunction-sections then we should emit the global value to a
    // uniqued section specifically for it.
    bool EmitUniquedSection;
    if (Kind.isText())
      EmitUniquedSection = TM.getFunctionSections();
    else
      EmitUniquedSection = TM.getDataSections();
  
    if ((EmitUniquedSection && !Kind.isCommon()) || GO->hasComdat()) {
      SmallString<256> Name = getCOFFSectionNameForUniqueGlobal(Kind);
  
      unsigned Characteristics = getCOFFSectionFlags(Kind, TM);
  
      Characteristics |= COFF::IMAGE_SCN_LNK_COMDAT;
      int Selection = getSelectionForCOFF(GO);
      if (!Selection)
        Selection = COFF::IMAGE_COMDAT_SELECT_NODUPLICATES;
      const GlobalValue *ComdatGV;
      if (GO->hasComdat())
        ComdatGV = getComdatGVForCOFF(GO);
      else
        ComdatGV = GO;
  
      unsigned UniqueID = MCContext::GenericSectionID;
      if (EmitUniquedSection)
        UniqueID = NextUniqueID++;
  
      if (!ComdatGV->hasPrivateLinkage()) {
        MCSymbol *Sym = TM.getSymbol(ComdatGV);
        StringRef COMDATSymName = Sym->getName();
  
        // Append "$symbol" to the section name *before* IR-level mangling is
        // applied when targetting mingw. This is what GCC does, and the ld.bfd
        // COFF linker will not properly handle comdats otherwise.
        if (getTargetTriple().isWindowsGNUEnvironment())
          raw_svector_ostream(Name) << '$' << ComdatGV->getName();
  
        return getContext().getCOFFSection(Name, Characteristics, Kind,
                                           COMDATSymName, Selection, UniqueID);
      } else {
        SmallString<256> TmpData;
        getMangler().getNameWithPrefix(TmpData, GO, /*CannotUsePrivateLabel=*/true);
        return getContext().getCOFFSection(Name, Characteristics, Kind, TmpData,
                                           Selection, UniqueID);
      }
    }
  
    if (Kind.isText())
      return TextSection;
  
    if (Kind.isThreadLocal())
      return TLSDataSection;
  
    if (Kind.isReadOnly() || Kind.isReadOnlyWithRel())
      return ReadOnlySection;
  
    // Note: we claim that common symbols are put in BSSSection, but they are
    // really emitted with the magic .comm directive, which creates a symbol table
    // entry but not a section.
    if (Kind.isBSS() || Kind.isCommon())
      return BSSSection;
  
    return DataSection;
  }
  
  void TargetLoweringObjectFileCOFF::getNameWithPrefix(
      SmallVectorImpl<char> &OutName, const GlobalValue *GV,
      const TargetMachine &TM) const {
    bool CannotUsePrivateLabel = false;
    if (GV->hasPrivateLinkage() &&
        ((isa<Function>(GV) && TM.getFunctionSections()) ||
         (isa<GlobalVariable>(GV) && TM.getDataSections())))
      CannotUsePrivateLabel = true;
  
    getMangler().getNameWithPrefix(OutName, GV, CannotUsePrivateLabel);
  }
  
  MCSection *TargetLoweringObjectFileCOFF::getSectionForJumpTable(
      const Function &F, const TargetMachine &TM) const {
    // If the function can be removed, produce a unique section so that
    // the table doesn't prevent the removal.
    const Comdat *C = F.getComdat();
    bool EmitUniqueSection = TM.getFunctionSections() || C;
    if (!EmitUniqueSection)
      return ReadOnlySection;
  
    // FIXME: we should produce a symbol for F instead.
    if (F.hasPrivateLinkage())
      return ReadOnlySection;
  
    MCSymbol *Sym = TM.getSymbol(&F);
    StringRef COMDATSymName = Sym->getName();
  
    SectionKind Kind = SectionKind::getReadOnly();
    StringRef SecName = getCOFFSectionNameForUniqueGlobal(Kind);
    unsigned Characteristics = getCOFFSectionFlags(Kind, TM);
    Characteristics |= COFF::IMAGE_SCN_LNK_COMDAT;
    unsigned UniqueID = NextUniqueID++;
  
    return getContext().getCOFFSection(
        SecName, Characteristics, Kind, COMDATSymName,
        COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE, UniqueID);
  }
  
  void TargetLoweringObjectFileCOFF::emitModuleMetadata(MCStreamer &Streamer,
                                                        Module &M) const {
    if (NamedMDNode *LinkerOptions = M.getNamedMetadata("llvm.linker.options")) {
      // Emit the linker options to the linker .drectve section.  According to the
      // spec, this section is a space-separated string containing flags for
      // linker.
      MCSection *Sec = getDrectveSection();
      Streamer.SwitchSection(Sec);
      for (const auto &Option : LinkerOptions->operands()) {
        for (const auto &Piece : cast<MDNode>(Option)->operands()) {
          // Lead with a space for consistency with our dllexport implementation.
          std::string Directive(" ");
          Directive.append(cast<MDString>(Piece)->getString());
          Streamer.EmitBytes(Directive);
        }
      }
    }
  
    unsigned Version = 0;
    unsigned Flags = 0;
    StringRef Section;
  
    GetObjCImageInfo(M, Version, Flags, Section);
    if (Section.empty())
      return;
  
    auto &C = getContext();
    auto *S = C.getCOFFSection(
        Section, COFF::IMAGE_SCN_CNT_INITIALIZED_DATA | COFF::IMAGE_SCN_MEM_READ,
        SectionKind::getReadOnly());
    Streamer.SwitchSection(S);
    Streamer.EmitLabel(C.getOrCreateSymbol(StringRef("OBJC_IMAGE_INFO")));
    Streamer.EmitIntValue(Version, 4);
    Streamer.EmitIntValue(Flags, 4);
    Streamer.AddBlankLine();
  }
  
  void TargetLoweringObjectFileCOFF::Initialize(MCContext &Ctx,
                                                const TargetMachine &TM) {
    TargetLoweringObjectFile::Initialize(Ctx, TM);
    const Triple &T = TM.getTargetTriple();
    if (T.isWindowsMSVCEnvironment() || T.isWindowsItaniumEnvironment()) {
      StaticCtorSection =
          Ctx.getCOFFSection(".CRT$XCU", COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
                                             COFF::IMAGE_SCN_MEM_READ,
                             SectionKind::getReadOnly());
      StaticDtorSection =
          Ctx.getCOFFSection(".CRT$XTX", COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
                                             COFF::IMAGE_SCN_MEM_READ,
                             SectionKind::getReadOnly());
    } else {
      StaticCtorSection = Ctx.getCOFFSection(
          ".ctors", COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
                        COFF::IMAGE_SCN_MEM_READ | COFF::IMAGE_SCN_MEM_WRITE,
          SectionKind::getData());
      StaticDtorSection = Ctx.getCOFFSection(
          ".dtors", COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
                        COFF::IMAGE_SCN_MEM_READ | COFF::IMAGE_SCN_MEM_WRITE,
          SectionKind::getData());
    }
  }
  
  static MCSectionCOFF *getCOFFStaticStructorSection(MCContext &Ctx,
                                                     const Triple &T, bool IsCtor,
                                                     unsigned Priority,
                                                     const MCSymbol *KeySym,
                                                     MCSectionCOFF *Default) {
    if (T.isWindowsMSVCEnvironment() || T.isWindowsItaniumEnvironment()) {
      // If the priority is the default, use .CRT$XCU, possibly associative.
      if (Priority == 65535)
        return Ctx.getAssociativeCOFFSection(Default, KeySym, 0);
  
      // Otherwise, we need to compute a new section name. Low priorities should
      // run earlier. The linker will sort sections ASCII-betically, and we need a
      // string that sorts between .CRT$XCA and .CRT$XCU. In the general case, we
      // make a name like ".CRT$XCT12345", since that runs before .CRT$XCU. Really
      // low priorities need to sort before 'L', since the CRT uses that
      // internally, so we use ".CRT$XCA00001" for them.
      SmallString<24> Name;
      raw_svector_ostream OS(Name);
      OS << ".CRT$X" << (IsCtor ? "C" : "T") <<
          (Priority < 200 ? 'A' : 'T') << format("%05u", Priority);
      MCSectionCOFF *Sec = Ctx.getCOFFSection(
          Name, COFF::IMAGE_SCN_CNT_INITIALIZED_DATA | COFF::IMAGE_SCN_MEM_READ,
          SectionKind::getReadOnly());
      return Ctx.getAssociativeCOFFSection(Sec, KeySym, 0);
    }
  
    std::string Name = IsCtor ? ".ctors" : ".dtors";
    if (Priority != 65535)
      raw_string_ostream(Name) << format(".%05u", 65535 - Priority);
  
    return Ctx.getAssociativeCOFFSection(
        Ctx.getCOFFSection(Name, COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
                                     COFF::IMAGE_SCN_MEM_READ |
                                     COFF::IMAGE_SCN_MEM_WRITE,
                           SectionKind::getData()),
        KeySym, 0);
  }
  
  MCSection *TargetLoweringObjectFileCOFF::getStaticCtorSection(
      unsigned Priority, const MCSymbol *KeySym) const {
    return getCOFFStaticStructorSection(getContext(), getTargetTriple(), true,
                                        Priority, KeySym,
                                        cast<MCSectionCOFF>(StaticCtorSection));
  }
  
  MCSection *TargetLoweringObjectFileCOFF::getStaticDtorSection(
      unsigned Priority, const MCSymbol *KeySym) const {
    return getCOFFStaticStructorSection(getContext(), getTargetTriple(), false,
                                        Priority, KeySym,
                                        cast<MCSectionCOFF>(StaticDtorSection));
  }
  
  void TargetLoweringObjectFileCOFF::emitLinkerFlagsForGlobal(
      raw_ostream &OS, const GlobalValue *GV) const {
    emitLinkerFlagsForGlobalCOFF(OS, GV, getTargetTriple(), getMangler());
  }
  
  void TargetLoweringObjectFileCOFF::emitLinkerFlagsForUsed(
      raw_ostream &OS, const GlobalValue *GV) const {
    emitLinkerFlagsForUsedCOFF(OS, GV, getTargetTriple(), getMangler());
  }
  
  const MCExpr *TargetLoweringObjectFileCOFF::lowerRelativeReference(
      const GlobalValue *LHS, const GlobalValue *RHS,
      const TargetMachine &TM) const {
    const Triple &T = TM.getTargetTriple();
    if (T.isOSCygMing())
      return nullptr;
  
    // Our symbols should exist in address space zero, cowardly no-op if
    // otherwise.
    if (LHS->getType()->getPointerAddressSpace() != 0 ||
        RHS->getType()->getPointerAddressSpace() != 0)
      return nullptr;
  
    // Both ptrtoint instructions must wrap global objects:
    // - Only global variables are eligible for image relative relocations.
    // - The subtrahend refers to the special symbol __ImageBase, a GlobalVariable.
    // We expect __ImageBase to be a global variable without a section, externally
    // defined.
    //
    // It should look something like this: @__ImageBase = external constant i8
    if (!isa<GlobalObject>(LHS) || !isa<GlobalVariable>(RHS) ||
        LHS->isThreadLocal() || RHS->isThreadLocal() ||
        RHS->getName() != "__ImageBase" || !RHS->hasExternalLinkage() ||
        cast<GlobalVariable>(RHS)->hasInitializer() || RHS->hasSection())
      return nullptr;
  
    return MCSymbolRefExpr::create(TM.getSymbol(LHS),
                                   MCSymbolRefExpr::VK_COFF_IMGREL32,
                                   getContext());
  }
  
  static std::string APIntToHexString(const APInt &AI) {
    unsigned Width = (AI.getBitWidth() / 8) * 2;
    std::string HexString = AI.toString(16, /*Signed=*/false);
    transform(HexString.begin(), HexString.end(), HexString.begin(), tolower);
    unsigned Size = HexString.size();
    assert(Width >= Size && "hex string is too large!");
    HexString.insert(HexString.begin(), Width - Size, '0');
  
    return HexString;
  }
  
  static std::string scalarConstantToHexString(const Constant *C) {
    Type *Ty = C->getType();
    if (isa<UndefValue>(C)) {
      return APIntToHexString(APInt::getNullValue(Ty->getPrimitiveSizeInBits()));
    } else if (const auto *CFP = dyn_cast<ConstantFP>(C)) {
      return APIntToHexString(CFP->getValueAPF().bitcastToAPInt());
    } else if (const auto *CI = dyn_cast<ConstantInt>(C)) {
      return APIntToHexString(CI->getValue());
    } else {
      unsigned NumElements;
      if (isa<VectorType>(Ty))
        NumElements = Ty->getVectorNumElements();
      else
        NumElements = Ty->getArrayNumElements();
      std::string HexString;
      for (int I = NumElements - 1, E = -1; I != E; --I)
        HexString += scalarConstantToHexString(C->getAggregateElement(I));
      return HexString;
    }
  }
  
  MCSection *TargetLoweringObjectFileCOFF::getSectionForConstant(
      const DataLayout &DL, SectionKind Kind, const Constant *C,
      unsigned &Align) const {
    if (Kind.isMergeableConst() && C &&
        getContext().getAsmInfo()->hasCOFFComdatConstants()) {
      // This creates comdat sections with the given symbol name, but unless
      // AsmPrinter::GetCPISymbol actually makes the symbol global, the symbol
      // will be created with a null storage class, which makes GNU binutils
      // error out.
      const unsigned Characteristics = COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
                                       COFF::IMAGE_SCN_MEM_READ |
                                       COFF::IMAGE_SCN_LNK_COMDAT;
      std::string COMDATSymName;
      if (Kind.isMergeableConst4()) {
        if (Align <= 4) {
          COMDATSymName = "__real@" + scalarConstantToHexString(C);
          Align = 4;
        }
      } else if (Kind.isMergeableConst8()) {
        if (Align <= 8) {
          COMDATSymName = "__real@" + scalarConstantToHexString(C);
          Align = 8;
        }
      } else if (Kind.isMergeableConst16()) {
        // FIXME: These may not be appropriate for non-x86 architectures.
        if (Align <= 16) {
          COMDATSymName = "__xmm@" + scalarConstantToHexString(C);
          Align = 16;
        }
      } else if (Kind.isMergeableConst32()) {
        if (Align <= 32) {
          COMDATSymName = "__ymm@" + scalarConstantToHexString(C);
          Align = 32;
        }
      }
  
      if (!COMDATSymName.empty())
        return getContext().getCOFFSection(".rdata", Characteristics, Kind,
                                           COMDATSymName,
                                           COFF::IMAGE_COMDAT_SELECT_ANY);
    }
  
    return TargetLoweringObjectFile::getSectionForConstant(DL, Kind, C, Align);
  }
  
  
  //===----------------------------------------------------------------------===//
  //                                  Wasm
  //===----------------------------------------------------------------------===//
  
  static const Comdat *getWasmComdat(const GlobalValue *GV) {
    const Comdat *C = GV->getComdat();
    if (!C)
      return nullptr;
  
    if (C->getSelectionKind() != Comdat::Any)
      report_fatal_error("WebAssembly COMDATs only support "
                         "SelectionKind::Any, '" + C->getName() + "' cannot be "
                         "lowered.");
  
    return C;
  }
  
  static SectionKind getWasmKindForNamedSection(StringRef Name, SectionKind K) {
    // If we're told we have function data, then use that.
    if (K.isText())
      return SectionKind::getText();
  
    // Otherwise, ignore whatever section type the generic impl detected and use
    // a plain data section.
    return SectionKind::getData();
  }
  
  MCSection *TargetLoweringObjectFileWasm::getExplicitSectionGlobal(
      const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
    // We don't support explict section names for functions in the wasm object
    // format.  Each function has to be in its own unique section.
    if (isa<Function>(GO)) {
      return SelectSectionForGlobal(GO, Kind, TM);
    }
  
    StringRef Name = GO->getSection();
  
    Kind = getWasmKindForNamedSection(Name, Kind);
  
    StringRef Group = "";
    if (const Comdat *C = getWasmComdat(GO)) {
      Group = C->getName();
    }
  
    MCSectionWasm* Section =
        getContext().getWasmSection(Name, Kind, Group,
                                    MCContext::GenericSectionID);
  
    return Section;
  }
  
  static MCSectionWasm *selectWasmSectionForGlobal(
      MCContext &Ctx, const GlobalObject *GO, SectionKind Kind, Mangler &Mang,
      const TargetMachine &TM, bool EmitUniqueSection, unsigned *NextUniqueID) {
    StringRef Group = "";
    if (const Comdat *C = getWasmComdat(GO)) {
      Group = C->getName();
    }
  
    bool UniqueSectionNames = TM.getUniqueSectionNames();
    SmallString<128> Name = getSectionPrefixForGlobal(Kind);
  
    if (const auto *F = dyn_cast<Function>(GO)) {
      const auto &OptionalPrefix = F->getSectionPrefix();
      if (OptionalPrefix)
        Name += *OptionalPrefix;
    }
  
    if (EmitUniqueSection && UniqueSectionNames) {
      Name.push_back('.');
      TM.getNameWithPrefix(Name, GO, Mang, true);
    }
    unsigned UniqueID = MCContext::GenericSectionID;
    if (EmitUniqueSection && !UniqueSectionNames) {
      UniqueID = *NextUniqueID;
      (*NextUniqueID)++;
    }
  
    return Ctx.getWasmSection(Name, Kind, Group, UniqueID);
  }
  
  MCSection *TargetLoweringObjectFileWasm::SelectSectionForGlobal(
      const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
  
    if (Kind.isCommon())
      report_fatal_error("mergable sections not supported yet on wasm");
  
    // If we have -ffunction-section or -fdata-section then we should emit the
    // global value to a uniqued section specifically for it.
    bool EmitUniqueSection = false;
    if (Kind.isText())
      EmitUniqueSection = TM.getFunctionSections();
    else
      EmitUniqueSection = TM.getDataSections();
    EmitUniqueSection |= GO->hasComdat();
  
    return selectWasmSectionForGlobal(getContext(), GO, Kind, getMangler(), TM,
                                      EmitUniqueSection, &NextUniqueID);
  }
  
  bool TargetLoweringObjectFileWasm::shouldPutJumpTableInFunctionSection(
      bool UsesLabelDifference, const Function &F) const {
    // We can always create relative relocations, so use another section
    // that can be marked non-executable.
    return false;
  }
  
  const MCExpr *TargetLoweringObjectFileWasm::lowerRelativeReference(
      const GlobalValue *LHS, const GlobalValue *RHS,
      const TargetMachine &TM) const {
    // We may only use a PLT-relative relocation to refer to unnamed_addr
    // functions.
    if (!LHS->hasGlobalUnnamedAddr() || !LHS->getValueType()->isFunctionTy())
      return nullptr;
  
    // Basic sanity checks.
    if (LHS->getType()->getPointerAddressSpace() != 0 ||
        RHS->getType()->getPointerAddressSpace() != 0 || LHS->isThreadLocal() ||
        RHS->isThreadLocal())
      return nullptr;
  
    return MCBinaryExpr::createSub(
        MCSymbolRefExpr::create(TM.getSymbol(LHS), MCSymbolRefExpr::VK_None,
                                getContext()),
        MCSymbolRefExpr::create(TM.getSymbol(RHS), getContext()), getContext());
  }
  
  void TargetLoweringObjectFileWasm::InitializeWasm() {
    StaticCtorSection =
        getContext().getWasmSection(".init_array", SectionKind::getData());
  
    // We don't use PersonalityEncoding and LSDAEncoding because we don't emit
    // .cfi directives. We use TTypeEncoding to encode typeinfo global variables.
    TTypeEncoding = dwarf::DW_EH_PE_absptr;
  }
  
  MCSection *TargetLoweringObjectFileWasm::getStaticCtorSection(
      unsigned Priority, const MCSymbol *KeySym) const {
    return Priority == UINT16_MAX ?
           StaticCtorSection :
           getContext().getWasmSection(".init_array." + utostr(Priority),
                                       SectionKind::getData());
  }
  
  MCSection *TargetLoweringObjectFileWasm::getStaticDtorSection(
      unsigned Priority, const MCSymbol *KeySym) const {
    llvm_unreachable("@llvm.global_dtors should have been lowered already");
    return nullptr;
  }
  
  //===----------------------------------------------------------------------===//
  //                                  XCOFF
  //===----------------------------------------------------------------------===//
  MCSection *TargetLoweringObjectFileXCOFF::getExplicitSectionGlobal(
      const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
    report_fatal_error("XCOFF explicit sections not yet implemented.");
  }
  
  MCSection *TargetLoweringObjectFileXCOFF::SelectSectionForGlobal(
      const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
    assert(!TM.getFunctionSections() && !TM.getDataSections() &&
           "XCOFF unique sections not yet implemented.");
  
    // Common symbols go into a csect with matching name which will get mapped
    // into the .bss section.
    if (Kind.isBSSLocal() || Kind.isCommon()) {
      SmallString<128> Name;
      getNameWithPrefix(Name, GO, TM);
      XCOFF::StorageClass SC =
          TargetLoweringObjectFileXCOFF::getStorageClassForGlobal(GO);
      return getContext().getXCOFFSection(
          Name, Kind.isBSSLocal() ? XCOFF::XMC_BS : XCOFF::XMC_RW, XCOFF::XTY_CM,
          SC, Kind, /* BeginSymbolName */ nullptr);
    }
  
    if (Kind.isText())
      return TextSection;
  
    if (Kind.isData())
      return DataSection;
  
    // Zero initialized data must be emitted to the .data section because external
    // linkage control sections that get mapped to the .bss section will be linked
    // as tentative defintions, which is only appropriate for SectionKind::Common.
    if (Kind.isBSS())
      return DataSection;
  
    if (Kind.isReadOnly() && !Kind.isMergeableConst() &&
        !Kind.isMergeableCString())
      return ReadOnlySection;
  
    report_fatal_error("XCOFF other section types not yet implemented.");
  }
  
  bool TargetLoweringObjectFileXCOFF::shouldPutJumpTableInFunctionSection(
      bool UsesLabelDifference, const Function &F) const {
    report_fatal_error("TLOF XCOFF not yet implemented.");
  }
  
  void TargetLoweringObjectFileXCOFF::Initialize(MCContext &Ctx,
                                                 const TargetMachine &TgtM) {
    TargetLoweringObjectFile::Initialize(Ctx, TgtM);
    TTypeEncoding = 0;
    PersonalityEncoding = 0;
    LSDAEncoding = 0;
  }
  
  MCSection *TargetLoweringObjectFileXCOFF::getStaticCtorSection(
      unsigned Priority, const MCSymbol *KeySym) const {
    report_fatal_error("XCOFF ctor section not yet implemented.");
  }
  
  MCSection *TargetLoweringObjectFileXCOFF::getStaticDtorSection(
      unsigned Priority, const MCSymbol *KeySym) const {
    report_fatal_error("XCOFF dtor section not yet implemented.");
  }
  
  const MCExpr *TargetLoweringObjectFileXCOFF::lowerRelativeReference(
      const GlobalValue *LHS, const GlobalValue *RHS,
      const TargetMachine &TM) const {
    report_fatal_error("XCOFF not yet implemented.");
  }
  
  XCOFF::StorageClass TargetLoweringObjectFileXCOFF::getStorageClassForGlobal(
      const GlobalObject *GO) {
    switch (GO->getLinkage()) {
    case GlobalValue::InternalLinkage:
      return XCOFF::C_HIDEXT;
    case GlobalValue::ExternalLinkage:
    case GlobalValue::CommonLinkage:
      return XCOFF::C_EXT;
    case GlobalValue::ExternalWeakLinkage:
      return XCOFF::C_WEAKEXT;
    default:
      report_fatal_error(
          "Unhandled linkage when mapping linkage to StorageClass.");
    }
  }
  