TargetRegistry.h

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//===- Support/TargetRegistry.h - Target Registration -----------*- C++ -*-===//
//
// 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 exposes the TargetRegistry interface, which tools can use to access
// the appropriate target specific classes (TargetMachine, AsmPrinter, etc.)
// which have been registered.
//
// Target specific class implementations should register themselves using the
// appropriate TargetRegistry interfaces.
//
//===----------------------------------------------------------------------===//
 
#ifndef LLVM_SUPPORT_TARGETREGISTRY_H
#define LLVM_SUPPORT_TARGETREGISTRY_H
 
#include "llvm-c/DisassemblerTypes.h"
#include "llvm/ADT/Optional.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/ADT/Triple.h"
#include "llvm/ADT/iterator_range.h"
#include "llvm/Support/CodeGen.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/FormattedStream.h"
#include <algorithm>
#include <cassert>
#include <cstddef>
#include <iterator>
#include <memory>
#include <string>
 
namespace llvm {
 
class AsmPrinter;
class MCAsmBackend;
class MCAsmInfo;
class MCAsmParser;
class MCCodeEmitter;
class MCContext;
class MCDisassembler;
class MCInstPrinter;
class MCInstrAnalysis;
class MCInstrInfo;
class MCObjectWriter;
class MCRegisterInfo;
class MCRelocationInfo;
class MCStreamer;
class MCSubtargetInfo;
class MCSymbolizer;
class MCTargetAsmParser;
class MCTargetOptions;
class MCTargetStreamer;
class raw_ostream;
class raw_pwrite_stream;
class TargetMachine;
class TargetOptions;
 
MCStreamer *createNullStreamer(MCContext &Ctx);
// Takes ownership of \p TAB and \p CE.
 
/// Create a machine code streamer which will print out assembly for the native
/// target, suitable for compiling with a native assembler.
///
/// \param InstPrint - If given, the instruction printer to use. If not given
/// the MCInst representation will be printed.  This method takes ownership of
/// InstPrint.
///
/// \param CE - If given, a code emitter to use to show the instruction
/// encoding inline with the assembly. This method takes ownership of \p CE.
///
/// \param TAB - If given, a target asm backend to use to show the fixup
/// information in conjunction with encoding information. This method takes
/// ownership of \p TAB.
///
/// \param ShowInst - Whether to show the MCInst representation inline with
/// the assembly.
MCStreamer *
createAsmStreamer(MCContext &Ctx, std::unique_ptr<formatted_raw_ostream> OS,
                  bool isVerboseAsm, bool useDwarfDirectory,
                  MCInstPrinter *InstPrint, std::unique_ptr<MCCodeEmitter> &&CE,
                  std::unique_ptr<MCAsmBackend> &&TAB, bool ShowInst);
 
MCStreamer *createELFStreamer(MCContext &Ctx,
                              std::unique_ptr<MCAsmBackend> &&TAB,
                              std::unique_ptr<MCObjectWriter> &&OW,
                              std::unique_ptr<MCCodeEmitter> &&CE,
                              bool RelaxAll);
MCStreamer *createMachOStreamer(MCContext &Ctx,
                                std::unique_ptr<MCAsmBackend> &&TAB,
                                std::unique_ptr<MCObjectWriter> &&OW,
                                std::unique_ptr<MCCodeEmitter> &&CE,
                                bool RelaxAll, bool DWARFMustBeAtTheEnd,
                                bool LabelSections = false);
MCStreamer *createWasmStreamer(MCContext &Ctx,
                               std::unique_ptr<MCAsmBackend> &&TAB,
                               std::unique_ptr<MCObjectWriter> &&OW,
                               std::unique_ptr<MCCodeEmitter> &&CE,
                               bool RelaxAll);
MCStreamer *createXCOFFStreamer(MCContext &Ctx,
                                std::unique_ptr<MCAsmBackend> &&TAB,
                                std::unique_ptr<MCObjectWriter> &&OW,
                                std::unique_ptr<MCCodeEmitter> &&CE,
                                bool RelaxAll);
 
MCRelocationInfo *createMCRelocationInfo(const Triple &TT, MCContext &Ctx);
 
MCSymbolizer *createMCSymbolizer(const Triple &TT, LLVMOpInfoCallback GetOpInfo,
                                 LLVMSymbolLookupCallback SymbolLookUp,
                                 void *DisInfo, MCContext *Ctx,
                                 std::unique_ptr<MCRelocationInfo> &&RelInfo);
 
/// Target - Wrapper for Target specific information.
///
/// For registration purposes, this is a POD type so that targets can be
/// registered without the use of static constructors.
///
/// Targets should implement a single global instance of this class (which
/// will be zero initialized), and pass that instance to the TargetRegistry as
/// part of their initialization.
class Target {
public:
  friend struct TargetRegistry;
 
  using ArchMatchFnTy = bool (*)(Triple::ArchType Arch);
 
  using MCAsmInfoCtorFnTy = MCAsmInfo *(*)(const MCRegisterInfo &MRI,
                                           const Triple &TT,
                                           const MCTargetOptions &Options);
  using MCInstrInfoCtorFnTy = MCInstrInfo *(*)();
  using MCInstrAnalysisCtorFnTy = MCInstrAnalysis *(*)(const MCInstrInfo *Info);
  using MCRegInfoCtorFnTy = MCRegisterInfo *(*)(const Triple &TT);
  using MCSubtargetInfoCtorFnTy = MCSubtargetInfo *(*)(const Triple &TT,
                                                       StringRef CPU,
                                                       StringRef Features);
  using TargetMachineCtorTy = TargetMachine
      *(*)(const Target &T, const Triple &TT, StringRef CPU, StringRef Features,
           const TargetOptions &Options, Optional<Reloc::Model> RM,
           Optional<CodeModel::Model> CM, CodeGenOpt::Level OL, bool JIT);
  // If it weren't for layering issues (this header is in llvm/Support, but
  // depends on MC?) this should take the Streamer by value rather than rvalue
  // reference.
  using AsmPrinterCtorTy = AsmPrinter *(*)(
      TargetMachine &TM, std::unique_ptr<MCStreamer> &&Streamer);
  using MCAsmBackendCtorTy = MCAsmBackend *(*)(const Target &T,
                                               const MCSubtargetInfo &STI,
                                               const MCRegisterInfo &MRI,
                                               const MCTargetOptions &Options);
  using MCAsmParserCtorTy = MCTargetAsmParser *(*)(
      const MCSubtargetInfo &STI, MCAsmParser &P, const MCInstrInfo &MII,
      const MCTargetOptions &Options);
  using MCDisassemblerCtorTy = MCDisassembler *(*)(const Target &T,
                                                   const MCSubtargetInfo &STI,
                                                   MCContext &Ctx);
  using MCInstPrinterCtorTy = MCInstPrinter *(*)(const Triple &T,
                                                 unsigned SyntaxVariant,
                                                 const MCAsmInfo &MAI,
                                                 const MCInstrInfo &MII,
                                                 const MCRegisterInfo &MRI);
  using MCCodeEmitterCtorTy = MCCodeEmitter *(*)(const MCInstrInfo &II,
                                                 const MCRegisterInfo &MRI,
                                                 MCContext &Ctx);
  using ELFStreamerCtorTy =
      MCStreamer *(*)(const Triple &T, MCContext &Ctx,
                      std::unique_ptr<MCAsmBackend> &&TAB,
                      std::unique_ptr<MCObjectWriter> &&OW,
                      std::unique_ptr<MCCodeEmitter> &&Emitter, bool RelaxAll);
  using MachOStreamerCtorTy =
      MCStreamer *(*)(MCContext &Ctx, std::unique_ptr<MCAsmBackend> &&TAB,
                      std::unique_ptr<MCObjectWriter> &&OW,
                      std::unique_ptr<MCCodeEmitter> &&Emitter, bool RelaxAll,
                      bool DWARFMustBeAtTheEnd);
  using COFFStreamerCtorTy =
      MCStreamer *(*)(MCContext &Ctx, std::unique_ptr<MCAsmBackend> &&TAB,
                      std::unique_ptr<MCObjectWriter> &&OW,
                      std::unique_ptr<MCCodeEmitter> &&Emitter, bool RelaxAll,
                      bool IncrementalLinkerCompatible);
  using WasmStreamerCtorTy =
      MCStreamer *(*)(const Triple &T, MCContext &Ctx,
                      std::unique_ptr<MCAsmBackend> &&TAB,
                      std::unique_ptr<MCObjectWriter> &&OW,
                      std::unique_ptr<MCCodeEmitter> &&Emitter, bool RelaxAll);
  using NullTargetStreamerCtorTy = MCTargetStreamer *(*)(MCStreamer &S);
  using AsmTargetStreamerCtorTy = MCTargetStreamer *(*)(
      MCStreamer &S, formatted_raw_ostream &OS, MCInstPrinter *InstPrint,
      bool IsVerboseAsm);
  using ObjectTargetStreamerCtorTy = MCTargetStreamer *(*)(
      MCStreamer &S, const MCSubtargetInfo &STI);
  using MCRelocationInfoCtorTy = MCRelocationInfo *(*)(const Triple &TT,
                                                       MCContext &Ctx);
  using MCSymbolizerCtorTy = MCSymbolizer *(*)(
      const Triple &TT, LLVMOpInfoCallback GetOpInfo,
      LLVMSymbolLookupCallback SymbolLookUp, void *DisInfo, MCContext *Ctx,
      std::unique_ptr<MCRelocationInfo> &&RelInfo);
 
private:
  /// Next - The next registered target in the linked list, maintained by the
  /// TargetRegistry.
  Target *Next;
 
  /// The target function for checking if an architecture is supported.
  ArchMatchFnTy ArchMatchFn;
 
  /// Name - The target name.
  const char *Name;
 
  /// ShortDesc - A short description of the target.
  const char *ShortDesc;
 
  /// BackendName - The name of the backend implementation. This must match the
  /// name of the 'def X : Target ...' in TableGen.
  const char *BackendName;
 
  /// HasJIT - Whether this target supports the JIT.
  bool HasJIT;
 
  /// MCAsmInfoCtorFn - Constructor function for this target's MCAsmInfo, if
  /// registered.
  MCAsmInfoCtorFnTy MCAsmInfoCtorFn;
 
  /// MCInstrInfoCtorFn - Constructor function for this target's MCInstrInfo,
  /// if registered.
  MCInstrInfoCtorFnTy MCInstrInfoCtorFn;
 
  /// MCInstrAnalysisCtorFn - Constructor function for this target's
  /// MCInstrAnalysis, if registered.
  MCInstrAnalysisCtorFnTy MCInstrAnalysisCtorFn;
 
  /// MCRegInfoCtorFn - Constructor function for this target's MCRegisterInfo,
  /// if registered.
  MCRegInfoCtorFnTy MCRegInfoCtorFn;
 
  /// MCSubtargetInfoCtorFn - Constructor function for this target's
  /// MCSubtargetInfo, if registered.
  MCSubtargetInfoCtorFnTy MCSubtargetInfoCtorFn;
 
  /// TargetMachineCtorFn - Construction function for this target's
  /// TargetMachine, if registered.
  TargetMachineCtorTy TargetMachineCtorFn;
 
  /// MCAsmBackendCtorFn - Construction function for this target's
  /// MCAsmBackend, if registered.
  MCAsmBackendCtorTy MCAsmBackendCtorFn;
 
  /// MCAsmParserCtorFn - Construction function for this target's
  /// MCTargetAsmParser, if registered.
  MCAsmParserCtorTy MCAsmParserCtorFn;
 
  /// AsmPrinterCtorFn - Construction function for this target's AsmPrinter,
  /// if registered.
  AsmPrinterCtorTy AsmPrinterCtorFn;
 
  /// MCDisassemblerCtorFn - Construction function for this target's
  /// MCDisassembler, if registered.
  MCDisassemblerCtorTy MCDisassemblerCtorFn;
 
  /// MCInstPrinterCtorFn - Construction function for this target's
  /// MCInstPrinter, if registered.
  MCInstPrinterCtorTy MCInstPrinterCtorFn;
 
  /// MCCodeEmitterCtorFn - Construction function for this target's
  /// CodeEmitter, if registered.
  MCCodeEmitterCtorTy MCCodeEmitterCtorFn;
 
  // Construction functions for the various object formats, if registered.
  COFFStreamerCtorTy COFFStreamerCtorFn = nullptr;
  MachOStreamerCtorTy MachOStreamerCtorFn = nullptr;
  ELFStreamerCtorTy ELFStreamerCtorFn = nullptr;
  WasmStreamerCtorTy WasmStreamerCtorFn = nullptr;
 
  /// Construction function for this target's null TargetStreamer, if
  /// registered (default = nullptr).
  NullTargetStreamerCtorTy NullTargetStreamerCtorFn = nullptr;
 
  /// Construction function for this target's asm TargetStreamer, if
  /// registered (default = nullptr).
  AsmTargetStreamerCtorTy AsmTargetStreamerCtorFn = nullptr;
 
  /// Construction function for this target's obj TargetStreamer, if
  /// registered (default = nullptr).
  ObjectTargetStreamerCtorTy ObjectTargetStreamerCtorFn = nullptr;
 
  /// MCRelocationInfoCtorFn - Construction function for this target's
  /// MCRelocationInfo, if registered (default = llvm::createMCRelocationInfo)
  MCRelocationInfoCtorTy MCRelocationInfoCtorFn = nullptr;
 
  /// MCSymbolizerCtorFn - Construction function for this target's
  /// MCSymbolizer, if registered (default = llvm::createMCSymbolizer)
  MCSymbolizerCtorTy MCSymbolizerCtorFn = nullptr;
 
public:
  Target() = default;
 
  /// @name Target Information
  /// @{
 
  // getNext - Return the next registered target.
  const Target *getNext() const { return Next; }
 
  /// getName - Get the target name.
  const char *getName() const { return Name; }
 
  /// getShortDescription - Get a short description of the target.
  const char *getShortDescription() const { return ShortDesc; }
 
  /// getBackendName - Get the backend name.
  const char *getBackendName() const { return BackendName; }
 
  /// @}
  /// @name Feature Predicates
  /// @{
 
  /// hasJIT - Check if this targets supports the just-in-time compilation.
  bool hasJIT() const { return HasJIT; }
 
  /// hasTargetMachine - Check if this target supports code generation.
  bool hasTargetMachine() const { return TargetMachineCtorFn != nullptr; }
 
  /// hasMCAsmBackend - Check if this target supports .o generation.
  bool hasMCAsmBackend() const { return MCAsmBackendCtorFn != nullptr; }
 
  /// hasMCAsmParser - Check if this target supports assembly parsing.
  bool hasMCAsmParser() const { return MCAsmParserCtorFn != nullptr; }
 
  /// @}
  /// @name Feature Constructors
  /// @{
 
  /// createMCAsmInfo - Create a MCAsmInfo implementation for the specified
  /// target triple.
  ///
  /// \param TheTriple This argument is used to determine the target machine
  /// feature set; it should always be provided. Generally this should be
  /// either the target triple from the module, or the target triple of the
  /// host if that does not exist.
  MCAsmInfo *createMCAsmInfo(const MCRegisterInfo &MRI, StringRef TheTriple,
                             const MCTargetOptions &Options) const {
    if (!MCAsmInfoCtorFn)
      return nullptr;
    return MCAsmInfoCtorFn(MRI, Triple(TheTriple), Options);
  }
 
  /// createMCInstrInfo - Create a MCInstrInfo implementation.
  ///
  MCInstrInfo *createMCInstrInfo() const {
    if (!MCInstrInfoCtorFn)
      return nullptr;
    return MCInstrInfoCtorFn();
  }
 
  /// createMCInstrAnalysis - Create a MCInstrAnalysis implementation.
  ///
  MCInstrAnalysis *createMCInstrAnalysis(const MCInstrInfo *Info) const {
    if (!MCInstrAnalysisCtorFn)
      return nullptr;
    return MCInstrAnalysisCtorFn(Info);
  }
 
  /// createMCRegInfo - Create a MCRegisterInfo implementation.
  ///
  MCRegisterInfo *createMCRegInfo(StringRef TT) const {
    if (!MCRegInfoCtorFn)
      return nullptr;
    return MCRegInfoCtorFn(Triple(TT));
  }
 
  /// createMCSubtargetInfo - Create a MCSubtargetInfo implementation.
  ///
  /// \param TheTriple This argument is used to determine the target machine
  /// feature set; it should always be provided. Generally this should be
  /// either the target triple from the module, or the target triple of the
  /// host if that does not exist.
  /// \param CPU This specifies the name of the target CPU.
  /// \param Features This specifies the string representation of the
  /// additional target features.
  MCSubtargetInfo *createMCSubtargetInfo(StringRef TheTriple, StringRef CPU,
                                         StringRef Features) const {
    if (!MCSubtargetInfoCtorFn)
      return nullptr;
    return MCSubtargetInfoCtorFn(Triple(TheTriple), CPU, Features);
  }
 
  /// createTargetMachine - Create a target specific machine implementation
  /// for the specified \p Triple.
  ///
  /// \param TT This argument is used to determine the target machine
  /// feature set; it should always be provided. Generally this should be
  /// either the target triple from the module, or the target triple of the
  /// host if that does not exist.
  TargetMachine *createTargetMachine(StringRef TT, StringRef CPU,
                                     StringRef Features,
                                     const TargetOptions &Options,
                                     Optional<Reloc::Model> RM,
                                     Optional<CodeModel::Model> CM = None,
                                     CodeGenOpt::Level OL = CodeGenOpt::Default,
                                     bool JIT = false) const {
    if (!TargetMachineCtorFn)
      return nullptr;
    return TargetMachineCtorFn(*this, Triple(TT), CPU, Features, Options, RM,
                               CM, OL, JIT);
  }
 
  /// createMCAsmBackend - Create a target specific assembly parser.
  MCAsmBackend *createMCAsmBackend(const MCSubtargetInfo &STI,
                                   const MCRegisterInfo &MRI,
                                   const MCTargetOptions &Options) const {
    if (!MCAsmBackendCtorFn)
      return nullptr;
    return MCAsmBackendCtorFn(*this, STI, MRI, Options);
  }
 
  /// createMCAsmParser - Create a target specific assembly parser.
  ///
  /// \param Parser The target independent parser implementation to use for
  /// parsing and lexing.
  MCTargetAsmParser *createMCAsmParser(const MCSubtargetInfo &STI,
                                       MCAsmParser &Parser,
                                       const MCInstrInfo &MII,
                                       const MCTargetOptions &Options) const {
    if (!MCAsmParserCtorFn)
      return nullptr;
    return MCAsmParserCtorFn(STI, Parser, MII, Options);
  }
 
  /// createAsmPrinter - Create a target specific assembly printer pass.  This
  /// takes ownership of the MCStreamer object.
  AsmPrinter *createAsmPrinter(TargetMachine &TM,
                               std::unique_ptr<MCStreamer> &&Streamer) const {
    if (!AsmPrinterCtorFn)
      return nullptr;
    return AsmPrinterCtorFn(TM, std::move(Streamer));
  }
 
  MCDisassembler *createMCDisassembler(const MCSubtargetInfo &STI,
                                       MCContext &Ctx) const {
    if (!MCDisassemblerCtorFn)
      return nullptr;
    return MCDisassemblerCtorFn(*this, STI, Ctx);
  }
 
  MCInstPrinter *createMCInstPrinter(const Triple &T, unsigned SyntaxVariant,
                                     const MCAsmInfo &MAI,
                                     const MCInstrInfo &MII,
                                     const MCRegisterInfo &MRI) const {
    if (!MCInstPrinterCtorFn)
      return nullptr;
    return MCInstPrinterCtorFn(T, SyntaxVariant, MAI, MII, MRI);
  }
 
  /// createMCCodeEmitter - Create a target specific code emitter.
  MCCodeEmitter *createMCCodeEmitter(const MCInstrInfo &II,
                                     const MCRegisterInfo &MRI,
                                     MCContext &Ctx) const {
    if (!MCCodeEmitterCtorFn)
      return nullptr;
    return MCCodeEmitterCtorFn(II, MRI, Ctx);
  }
 
  /// Create a target specific MCStreamer.
  ///
  /// \param T The target triple.
  /// \param Ctx The target context.
  /// \param TAB The target assembler backend object. Takes ownership.
  /// \param OW The stream object.
  /// \param Emitter The target independent assembler object.Takes ownership.
  /// \param RelaxAll Relax all fixups?
  MCStreamer *createMCObjectStreamer(const Triple &T, MCContext &Ctx,
                                     std::unique_ptr<MCAsmBackend> &&TAB,
                                     std::unique_ptr<MCObjectWriter> &&OW,
                                     std::unique_ptr<MCCodeEmitter> &&Emitter,
                                     const MCSubtargetInfo &STI, bool RelaxAll,
                                     bool IncrementalLinkerCompatible,
                                     bool DWARFMustBeAtTheEnd) const {
    MCStreamer *S = nullptr;
    switch (T.getObjectFormat()) {
    case Triple::UnknownObjectFormat:
      llvm_unreachable("Unknown object format");
    case Triple::COFF:
      assert(T.isOSWindows() && "only Windows COFF is supported");
      S = COFFStreamerCtorFn(Ctx, std::move(TAB), std::move(OW),
                             std::move(Emitter), RelaxAll,
                             IncrementalLinkerCompatible);
      break;
    case Triple::MachO:
      if (MachOStreamerCtorFn)
        S = MachOStreamerCtorFn(Ctx, std::move(TAB), std::move(OW),
                                std::move(Emitter), RelaxAll,
                                DWARFMustBeAtTheEnd);
      else
        S = createMachOStreamer(Ctx, std::move(TAB), std::move(OW),
                                std::move(Emitter), RelaxAll,
                                DWARFMustBeAtTheEnd);
      break;
    case Triple::ELF:
      if (ELFStreamerCtorFn)
        S = ELFStreamerCtorFn(T, Ctx, std::move(TAB), std::move(OW),
                              std::move(Emitter), RelaxAll);
      else
        S = createELFStreamer(Ctx, std::move(TAB), std::move(OW),
                              std::move(Emitter), RelaxAll);
      break;
    case Triple::Wasm:
      if (WasmStreamerCtorFn)
        S = WasmStreamerCtorFn(T, Ctx, std::move(TAB), std::move(OW),
                               std::move(Emitter), RelaxAll);
      else
        S = createWasmStreamer(Ctx, std::move(TAB), std::move(OW),
                               std::move(Emitter), RelaxAll);
      break;
    case Triple::GOFF:
      report_fatal_error("GOFF MCObjectStreamer not implemented yet");
    case Triple::XCOFF:
      S = createXCOFFStreamer(Ctx, std::move(TAB), std::move(OW),
                              std::move(Emitter), RelaxAll);
      break;
    }
    if (ObjectTargetStreamerCtorFn)
      ObjectTargetStreamerCtorFn(*S, STI);
    return S;
  }
 
  MCStreamer *createAsmStreamer(MCContext &Ctx,
                                std::unique_ptr<formatted_raw_ostream> OS,
                                bool IsVerboseAsm, bool UseDwarfDirectory,
                                MCInstPrinter *InstPrint,
                                std::unique_ptr<MCCodeEmitter> &&CE,
                                std::unique_ptr<MCAsmBackend> &&TAB,
                                bool ShowInst) const {
    formatted_raw_ostream &OSRef = *OS;
    MCStreamer *S = llvm::createAsmStreamer(
        Ctx, std::move(OS), IsVerboseAsm, UseDwarfDirectory, InstPrint,
        std::move(CE), std::move(TAB), ShowInst);
    createAsmTargetStreamer(*S, OSRef, InstPrint, IsVerboseAsm);
    return S;
  }
 
  MCTargetStreamer *createAsmTargetStreamer(MCStreamer &S,
                                            formatted_raw_ostream &OS,
                                            MCInstPrinter *InstPrint,
                                            bool IsVerboseAsm) const {
    if (AsmTargetStreamerCtorFn)
      return AsmTargetStreamerCtorFn(S, OS, InstPrint, IsVerboseAsm);
    return nullptr;
  }
 
  MCStreamer *createNullStreamer(MCContext &Ctx) const {
    MCStreamer *S = llvm::createNullStreamer(Ctx);
    createNullTargetStreamer(*S);
    return S;
  }
 
  MCTargetStreamer *createNullTargetStreamer(MCStreamer &S) const {
    if (NullTargetStreamerCtorFn)
      return NullTargetStreamerCtorFn(S);
    return nullptr;
  }
 
  /// createMCRelocationInfo - Create a target specific MCRelocationInfo.
  ///
  /// \param TT The target triple.
  /// \param Ctx The target context.
  MCRelocationInfo *createMCRelocationInfo(StringRef TT, MCContext &Ctx) const {
    MCRelocationInfoCtorTy Fn = MCRelocationInfoCtorFn
                                    ? MCRelocationInfoCtorFn
                                    : llvm::createMCRelocationInfo;
    return Fn(Triple(TT), Ctx);
  }
 
  /// createMCSymbolizer - Create a target specific MCSymbolizer.
  ///
  /// \param TT The target triple.
  /// \param GetOpInfo The function to get the symbolic information for
  /// operands.
  /// \param SymbolLookUp The function to lookup a symbol name.
  /// \param DisInfo The pointer to the block of symbolic information for above
  /// call
  /// back.
  /// \param Ctx The target context.
  /// \param RelInfo The relocation information for this target. Takes
  /// ownership.
  MCSymbolizer *
  createMCSymbolizer(StringRef TT, LLVMOpInfoCallback GetOpInfo,
                     LLVMSymbolLookupCallback SymbolLookUp, void *DisInfo,
                     MCContext *Ctx,
                     std::unique_ptr<MCRelocationInfo> &&RelInfo) const {
    MCSymbolizerCtorTy Fn =
        MCSymbolizerCtorFn ? MCSymbolizerCtorFn : llvm::createMCSymbolizer;
    return Fn(Triple(TT), GetOpInfo, SymbolLookUp, DisInfo, Ctx,
              std::move(RelInfo));
  }
 
  /// @}
};
 
/// TargetRegistry - Generic interface to target specific features.
struct TargetRegistry {
  // FIXME: Make this a namespace, probably just move all the Register*
  // functions into Target (currently they all just set members on the Target
  // anyway, and Target friends this class so those functions can...
  // function).
  TargetRegistry() = delete;
 
  class iterator {
    friend struct TargetRegistry;
 
    const Target *Current = nullptr;
 
    explicit iterator(Target *T) : Current(T) {}
 
  public:
    using iterator_category = std::forward_iterator_tag;
    using value_type = Target;
    using difference_type = std::ptrdiff_t;
    using pointer = value_type *;
    using reference = value_type &;
 
    iterator() = default;
 
    bool operator==(const iterator &x) const { return Current == x.Current; }
    bool operator!=(const iterator &x) const { return !operator==(x); }
 
    // Iterator traversal: forward iteration only
    iterator &operator++() { // Preincrement
      assert(Current && "Cannot increment end iterator!");
      Current = Current->getNext();
      return *this;
    }
    iterator operator++(int) { // Postincrement
      iterator tmp = *this;
      ++*this;
      return tmp;
    }
 
    const Target &operator*() const {
      assert(Current && "Cannot dereference end iterator!");
      return *Current;
    }
 
    const Target *operator->() const { return &operator*(); }
  };
 
  /// printRegisteredTargetsForVersion - Print the registered targets
  /// appropriately for inclusion in a tool's version output.
  static void printRegisteredTargetsForVersion(raw_ostream &OS);
 
  /// @name Registry Access
  /// @{
 
  static iterator_range<iterator> targets();
 
  /// lookupTarget - Lookup a target based on a target triple.
  ///
  /// \param Triple - The triple to use for finding a target.
  /// \param Error - On failure, an error string describing why no target was
  /// found.
  static const Target *lookupTarget(const std::string &Triple,
                                    std::string &Error);
 
  /// lookupTarget - Lookup a target based on an architecture name
  /// and a target triple.  If the architecture name is non-empty,
  /// then the lookup is done by architecture.  Otherwise, the target
  /// triple is used.
  ///
  /// \param ArchName - The architecture to use for finding a target.
  /// \param TheTriple - The triple to use for finding a target.  The
  /// triple is updated with canonical architecture name if a lookup
  /// by architecture is done.
  /// \param Error - On failure, an error string describing why no target was
  /// found.
  static const Target *lookupTarget(const std::string &ArchName,
                                    Triple &TheTriple, std::string &Error);
 
  /// @}
  /// @name Target Registration
  /// @{
 
  /// RegisterTarget - Register the given target. Attempts to register a
  /// target which has already been registered will be ignored.
  ///
  /// Clients are responsible for ensuring that registration doesn't occur
  /// while another thread is attempting to access the registry. Typically
  /// this is done by initializing all targets at program startup.
  ///
  /// @param T - The target being registered.
  /// @param Name - The target name. This should be a static string.
  /// @param ShortDesc - A short target description. This should be a static
  /// string.
  /// @param BackendName - The name of the backend. This should be a static
  /// string that is the same for all targets that share a backend
  /// implementation and must match the name used in the 'def X : Target ...' in
  /// TableGen.
  /// @param ArchMatchFn - The arch match checking function for this target.
  /// @param HasJIT - Whether the target supports JIT code
  /// generation.
  static void RegisterTarget(Target &T, const char *Name, const char *ShortDesc,
                             const char *BackendName,
                             Target::ArchMatchFnTy ArchMatchFn,
                             bool HasJIT = false);
 
  /// RegisterMCAsmInfo - Register a MCAsmInfo implementation for the
  /// given target.
  ///
  /// Clients are responsible for ensuring that registration doesn't occur
  /// while another thread is attempting to access the registry. Typically
  /// this is done by initializing all targets at program startup.
  ///
  /// @param T - The target being registered.
  /// @param Fn - A function to construct a MCAsmInfo for the target.
  static void RegisterMCAsmInfo(Target &T, Target::MCAsmInfoCtorFnTy Fn) {
    T.MCAsmInfoCtorFn = Fn;
  }
 
  /// RegisterMCInstrInfo - Register a MCInstrInfo implementation for the
  /// given target.
  ///
  /// Clients are responsible for ensuring that registration doesn't occur
  /// while another thread is attempting to access the registry. Typically
  /// this is done by initializing all targets at program startup.
  ///
  /// @param T - The target being registered.
  /// @param Fn - A function to construct a MCInstrInfo for the target.
  static void RegisterMCInstrInfo(Target &T, Target::MCInstrInfoCtorFnTy Fn) {
    T.MCInstrInfoCtorFn = Fn;
  }
 
  /// RegisterMCInstrAnalysis - Register a MCInstrAnalysis implementation for
  /// the given target.
  static void RegisterMCInstrAnalysis(Target &T,
                                      Target::MCInstrAnalysisCtorFnTy Fn) {
    T.MCInstrAnalysisCtorFn = Fn;
  }
 
  /// RegisterMCRegInfo - Register a MCRegisterInfo implementation for the
  /// given target.
  ///
  /// Clients are responsible for ensuring that registration doesn't occur
  /// while another thread is attempting to access the registry. Typically
  /// this is done by initializing all targets at program startup.
  ///
  /// @param T - The target being registered.
  /// @param Fn - A function to construct a MCRegisterInfo for the target.
  static void RegisterMCRegInfo(Target &T, Target::MCRegInfoCtorFnTy Fn) {
    T.MCRegInfoCtorFn = Fn;
  }
 
  /// RegisterMCSubtargetInfo - Register a MCSubtargetInfo implementation for
  /// the given target.
  ///
  /// Clients are responsible for ensuring that registration doesn't occur
  /// while another thread is attempting to access the registry. Typically
  /// this is done by initializing all targets at program startup.
  ///
  /// @param T - The target being registered.
  /// @param Fn - A function to construct a MCSubtargetInfo for the target.
  static void RegisterMCSubtargetInfo(Target &T,
                                      Target::MCSubtargetInfoCtorFnTy Fn) {
    T.MCSubtargetInfoCtorFn = Fn;
  }
 
  /// RegisterTargetMachine - Register a TargetMachine implementation for the
  /// given target.
  ///
  /// Clients are responsible for ensuring that registration doesn't occur
  /// while another thread is attempting to access the registry. Typically
  /// this is done by initializing all targets at program startup.
  ///
  /// @param T - The target being registered.
  /// @param Fn - A function to construct a TargetMachine for the target.
  static void RegisterTargetMachine(Target &T, Target::TargetMachineCtorTy Fn) {
    T.TargetMachineCtorFn = Fn;
  }
 
  /// RegisterMCAsmBackend - Register a MCAsmBackend implementation for the
  /// given target.
  ///
  /// Clients are responsible for ensuring that registration doesn't occur
  /// while another thread is attempting to access the registry. Typically
  /// this is done by initializing all targets at program startup.
  ///
  /// @param T - The target being registered.
  /// @param Fn - A function to construct an AsmBackend for the target.
  static void RegisterMCAsmBackend(Target &T, Target::MCAsmBackendCtorTy Fn) {
    T.MCAsmBackendCtorFn = Fn;
  }
 
  /// RegisterMCAsmParser - Register a MCTargetAsmParser implementation for
  /// the given target.
  ///
  /// Clients are responsible for ensuring that registration doesn't occur
  /// while another thread is attempting to access the registry. Typically
  /// this is done by initializing all targets at program startup.
  ///
  /// @param T - The target being registered.
  /// @param Fn - A function to construct an MCTargetAsmParser for the target.
  static void RegisterMCAsmParser(Target &T, Target::MCAsmParserCtorTy Fn) {
    T.MCAsmParserCtorFn = Fn;
  }
 
  /// RegisterAsmPrinter - Register an AsmPrinter implementation for the given
  /// target.
  ///
  /// Clients are responsible for ensuring that registration doesn't occur
  /// while another thread is attempting to access the registry. Typically
  /// this is done by initializing all targets at program startup.
  ///
  /// @param T - The target being registered.
  /// @param Fn - A function to construct an AsmPrinter for the target.
  static void RegisterAsmPrinter(Target &T, Target::AsmPrinterCtorTy Fn) {
    T.AsmPrinterCtorFn = Fn;
  }
 
  /// RegisterMCDisassembler - Register a MCDisassembler implementation for
  /// the given target.
  ///
  /// Clients are responsible for ensuring that registration doesn't occur
  /// while another thread is attempting to access the registry. Typically
  /// this is done by initializing all targets at program startup.
  ///
  /// @param T - The target being registered.
  /// @param Fn - A function to construct an MCDisassembler for the target.
  static void RegisterMCDisassembler(Target &T,
                                     Target::MCDisassemblerCtorTy Fn) {
    T.MCDisassemblerCtorFn = Fn;
  }
 
  /// RegisterMCInstPrinter - Register a MCInstPrinter implementation for the
  /// given target.
  ///
  /// Clients are responsible for ensuring that registration doesn't occur
  /// while another thread is attempting to access the registry. Typically
  /// this is done by initializing all targets at program startup.
  ///
  /// @param T - The target being registered.
  /// @param Fn - A function to construct an MCInstPrinter for the target.
  static void RegisterMCInstPrinter(Target &T, Target::MCInstPrinterCtorTy Fn) {
    T.MCInstPrinterCtorFn = Fn;
  }
 
  /// RegisterMCCodeEmitter - Register a MCCodeEmitter implementation for the
  /// given target.
  ///
  /// Clients are responsible for ensuring that registration doesn't occur
  /// while another thread is attempting to access the registry. Typically
  /// this is done by initializing all targets at program startup.
  ///
  /// @param T - The target being registered.
  /// @param Fn - A function to construct an MCCodeEmitter for the target.
  static void RegisterMCCodeEmitter(Target &T, Target::MCCodeEmitterCtorTy Fn) {
    T.MCCodeEmitterCtorFn = Fn;
  }
 
  static void RegisterCOFFStreamer(Target &T, Target::COFFStreamerCtorTy Fn) {
    T.COFFStreamerCtorFn = Fn;
  }
 
  static void RegisterMachOStreamer(Target &T, Target::MachOStreamerCtorTy Fn) {
    T.MachOStreamerCtorFn = Fn;
  }
 
  static void RegisterELFStreamer(Target &T, Target::ELFStreamerCtorTy Fn) {
    T.ELFStreamerCtorFn = Fn;
  }
 
  static void RegisterWasmStreamer(Target &T, Target::WasmStreamerCtorTy Fn) {
    T.WasmStreamerCtorFn = Fn;
  }
 
  static void RegisterNullTargetStreamer(Target &T,
                                         Target::NullTargetStreamerCtorTy Fn) {
    T.NullTargetStreamerCtorFn = Fn;
  }
 
  static void RegisterAsmTargetStreamer(Target &T,
                                        Target::AsmTargetStreamerCtorTy Fn) {
    T.AsmTargetStreamerCtorFn = Fn;
  }
 
  static void
  RegisterObjectTargetStreamer(Target &T,
                               Target::ObjectTargetStreamerCtorTy Fn) {
    T.ObjectTargetStreamerCtorFn = Fn;
  }
 
  /// RegisterMCRelocationInfo - Register an MCRelocationInfo
  /// implementation for the given target.
  ///
  /// Clients are responsible for ensuring that registration doesn't occur
  /// while another thread is attempting to access the registry. Typically
  /// this is done by initializing all targets at program startup.
  ///
  /// @param T - The target being registered.
  /// @param Fn - A function to construct an MCRelocationInfo for the target.
  static void RegisterMCRelocationInfo(Target &T,
                                       Target::MCRelocationInfoCtorTy Fn) {
    T.MCRelocationInfoCtorFn = Fn;
  }
 
  /// RegisterMCSymbolizer - Register an MCSymbolizer
  /// implementation for the given target.
  ///
  /// Clients are responsible for ensuring that registration doesn't occur
  /// while another thread is attempting to access the registry. Typically
  /// this is done by initializing all targets at program startup.
  ///
  /// @param T - The target being registered.
  /// @param Fn - A function to construct an MCSymbolizer for the target.
  static void RegisterMCSymbolizer(Target &T, Target::MCSymbolizerCtorTy Fn) {
    T.MCSymbolizerCtorFn = Fn;
  }
 
  /// @}
};
 
//===--------------------------------------------------------------------===//
 
/// RegisterTarget - Helper template for registering a target, for use in the
/// target's initialization function. Usage:
///
///
/// Target &getTheFooTarget() { // The global target instance.
///   static Target TheFooTarget;
///   return TheFooTarget;
/// }
/// extern "C" void LLVMInitializeFooTargetInfo() {
///   RegisterTarget<Triple::foo> X(getTheFooTarget(), "foo", "Foo
///   description", "Foo" /* Backend Name */);
/// }
template <Triple::ArchType TargetArchType = Triple::UnknownArch,
          bool HasJIT = false>
struct RegisterTarget {
  RegisterTarget(Target &T, const char *Name, const char *Desc,
                 const char *BackendName) {
    TargetRegistry::RegisterTarget(T, Name, Desc, BackendName, &getArchMatch,
                                   HasJIT);
  }
 
  static bool getArchMatch(Triple::ArchType Arch) {
    return Arch == TargetArchType;
  }
};
 
/// RegisterMCAsmInfo - Helper template for registering a target assembly info
/// implementation.  This invokes the static "Create" method on the class to
/// actually do the construction.  Usage:
///
/// extern "C" void LLVMInitializeFooTarget() {
///   extern Target TheFooTarget;
///   RegisterMCAsmInfo<FooMCAsmInfo> X(TheFooTarget);
/// }
template <class MCAsmInfoImpl> struct RegisterMCAsmInfo {
  RegisterMCAsmInfo(Target &T) {
    TargetRegistry::RegisterMCAsmInfo(T, &Allocator);
  }
 
private:
  static MCAsmInfo *Allocator(const MCRegisterInfo & /*MRI*/, const Triple &TT,
                              const MCTargetOptions &Options) {
    return new MCAsmInfoImpl(TT, Options);
  }
};
 
/// RegisterMCAsmInfoFn - Helper template for registering a target assembly info
/// implementation.  This invokes the specified function to do the
/// construction.  Usage:
///
/// extern "C" void LLVMInitializeFooTarget() {
///   extern Target TheFooTarget;
///   RegisterMCAsmInfoFn X(TheFooTarget, TheFunction);
/// }
struct RegisterMCAsmInfoFn {
  RegisterMCAsmInfoFn(Target &T, Target::MCAsmInfoCtorFnTy Fn) {
    TargetRegistry::RegisterMCAsmInfo(T, Fn);
  }
};
 
/// RegisterMCInstrInfo - Helper template for registering a target instruction
/// info implementation.  This invokes the static "Create" method on the class
/// to actually do the construction.  Usage:
///
/// extern "C" void LLVMInitializeFooTarget() {
///   extern Target TheFooTarget;
///   RegisterMCInstrInfo<FooMCInstrInfo> X(TheFooTarget);
/// }
template <class MCInstrInfoImpl> struct RegisterMCInstrInfo {
  RegisterMCInstrInfo(Target &T) {
    TargetRegistry::RegisterMCInstrInfo(T, &Allocator);
  }
 
private:
  static MCInstrInfo *Allocator() { return new MCInstrInfoImpl(); }
};
 
/// RegisterMCInstrInfoFn - Helper template for registering a target
/// instruction info implementation.  This invokes the specified function to
/// do the construction.  Usage:
///
/// extern "C" void LLVMInitializeFooTarget() {
///   extern Target TheFooTarget;
///   RegisterMCInstrInfoFn X(TheFooTarget, TheFunction);
/// }
struct RegisterMCInstrInfoFn {
  RegisterMCInstrInfoFn(Target &T, Target::MCInstrInfoCtorFnTy Fn) {
    TargetRegistry::RegisterMCInstrInfo(T, Fn);
  }
};
 
/// RegisterMCInstrAnalysis - Helper template for registering a target
/// instruction analyzer implementation.  This invokes the static "Create"
/// method on the class to actually do the construction.  Usage:
///
/// extern "C" void LLVMInitializeFooTarget() {
///   extern Target TheFooTarget;
///   RegisterMCInstrAnalysis<FooMCInstrAnalysis> X(TheFooTarget);
/// }
template <class MCInstrAnalysisImpl> struct RegisterMCInstrAnalysis {
  RegisterMCInstrAnalysis(Target &T) {
    TargetRegistry::RegisterMCInstrAnalysis(T, &Allocator);
  }
 
private:
  static MCInstrAnalysis *Allocator(const MCInstrInfo *Info) {
    return new MCInstrAnalysisImpl(Info);
  }
};
 
/// RegisterMCInstrAnalysisFn - Helper template for registering a target
/// instruction analyzer implementation.  This invokes the specified function
/// to do the construction.  Usage:
///
/// extern "C" void LLVMInitializeFooTarget() {
///   extern Target TheFooTarget;
///   RegisterMCInstrAnalysisFn X(TheFooTarget, TheFunction);
/// }
struct RegisterMCInstrAnalysisFn {
  RegisterMCInstrAnalysisFn(Target &T, Target::MCInstrAnalysisCtorFnTy Fn) {
    TargetRegistry::RegisterMCInstrAnalysis(T, Fn);
  }
};
 
/// RegisterMCRegInfo - Helper template for registering a target register info
/// implementation.  This invokes the static "Create" method on the class to
/// actually do the construction.  Usage:
///
/// extern "C" void LLVMInitializeFooTarget() {
///   extern Target TheFooTarget;
///   RegisterMCRegInfo<FooMCRegInfo> X(TheFooTarget);
/// }
template <class MCRegisterInfoImpl> struct RegisterMCRegInfo {
  RegisterMCRegInfo(Target &T) {
    TargetRegistry::RegisterMCRegInfo(T, &Allocator);
  }
 
private:
  static MCRegisterInfo *Allocator(const Triple & /*TT*/) {
    return new MCRegisterInfoImpl();
  }
};
 
/// RegisterMCRegInfoFn - Helper template for registering a target register
/// info implementation.  This invokes the specified function to do the
/// construction.  Usage:
///
/// extern "C" void LLVMInitializeFooTarget() {
///   extern Target TheFooTarget;
///   RegisterMCRegInfoFn X(TheFooTarget, TheFunction);
/// }
struct RegisterMCRegInfoFn {
  RegisterMCRegInfoFn(Target &T, Target::MCRegInfoCtorFnTy Fn) {
    TargetRegistry::RegisterMCRegInfo(T, Fn);
  }
};
 
/// RegisterMCSubtargetInfo - Helper template for registering a target
/// subtarget info implementation.  This invokes the static "Create" method
/// on the class to actually do the construction.  Usage:
///
/// extern "C" void LLVMInitializeFooTarget() {
///   extern Target TheFooTarget;
///   RegisterMCSubtargetInfo<FooMCSubtargetInfo> X(TheFooTarget);
/// }
template <class MCSubtargetInfoImpl> struct RegisterMCSubtargetInfo {
  RegisterMCSubtargetInfo(Target &T) {
    TargetRegistry::RegisterMCSubtargetInfo(T, &Allocator);
  }
 
private:
  static MCSubtargetInfo *Allocator(const Triple & /*TT*/, StringRef /*CPU*/,
                                    StringRef /*FS*/) {
    return new MCSubtargetInfoImpl();
  }
};
 
/// RegisterMCSubtargetInfoFn - Helper template for registering a target
/// subtarget info implementation.  This invokes the specified function to
/// do the construction.  Usage:
///
/// extern "C" void LLVMInitializeFooTarget() {
///   extern Target TheFooTarget;
///   RegisterMCSubtargetInfoFn X(TheFooTarget, TheFunction);
/// }
struct RegisterMCSubtargetInfoFn {
  RegisterMCSubtargetInfoFn(Target &T, Target::MCSubtargetInfoCtorFnTy Fn) {
    TargetRegistry::RegisterMCSubtargetInfo(T, Fn);
  }
};
 
/// RegisterTargetMachine - Helper template for registering a target machine
/// implementation, for use in the target machine initialization
/// function. Usage:
///
/// extern "C" void LLVMInitializeFooTarget() {
///   extern Target TheFooTarget;
///   RegisterTargetMachine<FooTargetMachine> X(TheFooTarget);
/// }
template <class TargetMachineImpl> struct RegisterTargetMachine {
  RegisterTargetMachine(Target &T) {
    TargetRegistry::RegisterTargetMachine(T, &Allocator);
  }
 
private:
  static TargetMachine *
  Allocator(const Target &T, const Triple &TT, StringRef CPU, StringRef FS,
            const TargetOptions &Options, Optional<Reloc::Model> RM,
            Optional<CodeModel::Model> CM, CodeGenOpt::Level OL, bool JIT) {
    return new TargetMachineImpl(T, TT, CPU, FS, Options, RM, CM, OL, JIT);
  }
};
 
/// RegisterMCAsmBackend - Helper template for registering a target specific
/// assembler backend. Usage:
///
/// extern "C" void LLVMInitializeFooMCAsmBackend() {
///   extern Target TheFooTarget;
///   RegisterMCAsmBackend<FooAsmLexer> X(TheFooTarget);
/// }
template <class MCAsmBackendImpl> struct RegisterMCAsmBackend {
  RegisterMCAsmBackend(Target &T) {
    TargetRegistry::RegisterMCAsmBackend(T, &Allocator);
  }
 
private:
  static MCAsmBackend *Allocator(const Target &T, const MCSubtargetInfo &STI,
                                 const MCRegisterInfo &MRI,
                                 const MCTargetOptions &Options) {
    return new MCAsmBackendImpl(T, STI, MRI);
  }
};
 
/// RegisterMCAsmParser - Helper template for registering a target specific
/// assembly parser, for use in the target machine initialization
/// function. Usage:
///
/// extern "C" void LLVMInitializeFooMCAsmParser() {
///   extern Target TheFooTarget;
///   RegisterMCAsmParser<FooAsmParser> X(TheFooTarget);
/// }
template <class MCAsmParserImpl> struct RegisterMCAsmParser {
  RegisterMCAsmParser(Target &T) {
    TargetRegistry::RegisterMCAsmParser(T, &Allocator);
  }
 
private:
  static MCTargetAsmParser *Allocator(const MCSubtargetInfo &STI,
                                      MCAsmParser &P, const MCInstrInfo &MII,
                                      const MCTargetOptions &Options) {
    return new MCAsmParserImpl(STI, P, MII, Options);
  }
};
 
/// RegisterAsmPrinter - Helper template for registering a target specific
/// assembly printer, for use in the target machine initialization
/// function. Usage:
///
/// extern "C" void LLVMInitializeFooAsmPrinter() {
///   extern Target TheFooTarget;
///   RegisterAsmPrinter<FooAsmPrinter> X(TheFooTarget);
/// }
template <class AsmPrinterImpl> struct RegisterAsmPrinter {
  RegisterAsmPrinter(Target &T) {
    TargetRegistry::RegisterAsmPrinter(T, &Allocator);
  }
 
private:
  static AsmPrinter *Allocator(TargetMachine &TM,
                               std::unique_ptr<MCStreamer> &&Streamer) {
    return new AsmPrinterImpl(TM, std::move(Streamer));
  }
};
 
/// RegisterMCCodeEmitter - Helper template for registering a target specific
/// machine code emitter, for use in the target initialization
/// function. Usage:
///
/// extern "C" void LLVMInitializeFooMCCodeEmitter() {
///   extern Target TheFooTarget;
///   RegisterMCCodeEmitter<FooCodeEmitter> X(TheFooTarget);
/// }
template <class MCCodeEmitterImpl> struct RegisterMCCodeEmitter {
  RegisterMCCodeEmitter(Target &T) {
    TargetRegistry::RegisterMCCodeEmitter(T, &Allocator);
  }
 
private:
  static MCCodeEmitter *Allocator(const MCInstrInfo & /*II*/,
                                  const MCRegisterInfo & /*MRI*/,
                                  MCContext & /*Ctx*/) {
    return new MCCodeEmitterImpl();
  }
};
 
} // end namespace llvm
 
#endif // LLVM_SUPPORT_TARGETREGISTRY_H