[lld-macho] Remove old macho darwin lld

During the llvm round table it was generally agreed that the newer macho
lld implementation is feature complete enough to replace the old
implementation entirely. This will reduce confusion for new users who
aren't aware of the history.

Differential Revision: https://reviews.llvm.org/D114842

4 files changed, 1 insertions, 554 deletions

diff --git a/lld/include/lld/Common/Driver.h b/lld/include/lld/Common/Driver.h
index eb5bc7b82b9b..0e505a16463e 100644
--- a/lld/include/lld/Common/Driver.h
+++ b/lld/include/lld/Common/Driver.h
@@ -42,11 +42,6 @@ bool link(llvm::ArrayRef<const char *> args, bool canExitEarly,
           llvm::raw_ostream &stdoutOS, llvm::raw_ostream &stderrOS);
 }
 
-namespace mach_o {
-bool link(llvm::ArrayRef<const char *> args, bool canExitEarly,
-          llvm::raw_ostream &stdoutOS, llvm::raw_ostream &stderrOS);
-}
-
 namespace macho {
 bool link(llvm::ArrayRef<const char *> args, bool canExitEarly,
           llvm::raw_ostream &stdoutOS, llvm::raw_ostream &stderrOS);
diff --git a/lld/include/lld/Core/Reference.h b/lld/include/lld/Core/Reference.h
index b104f8495474..7a6c36aecfc5 100644
--- a/lld/include/lld/Core/Reference.h
+++ b/lld/include/lld/Core/Reference.h
@@ -42,9 +42,8 @@ class Reference {
 public:
   /// Which universe defines the kindValue().
   enum class KindNamespace {
-    all     = 0,
+    all = 0,
     testing = 1,
-    mach_o  = 2,
   };
 
   KindNamespace kindNamespace() const { return (KindNamespace)_kindNamespace; }
diff --git a/lld/include/lld/ReaderWriter/MachOLinkingContext.h b/lld/include/lld/ReaderWriter/MachOLinkingContext.h
deleted file mode 100644
index 974f323bc612..000000000000
--- a/lld/include/lld/ReaderWriter/MachOLinkingContext.h
+++ /dev/null
@@ -1,505 +0,0 @@
-//===- lld/ReaderWriter/MachOLinkingContext.h -----------------------------===//
-//
-// 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
-//
-//===----------------------------------------------------------------------===//
-
-#ifndef LLD_READER_WRITER_MACHO_LINKING_CONTEXT_H
-#define LLD_READER_WRITER_MACHO_LINKING_CONTEXT_H
-
-#include "lld/Core/LinkingContext.h"
-#include "lld/Core/Reader.h"
-#include "lld/Core/Writer.h"
-#include "llvm/ADT/STLExtras.h"
-#include "llvm/ADT/StringMap.h"
-#include "llvm/ADT/StringSet.h"
-#include "llvm/BinaryFormat/MachO.h"
-#include "llvm/Support/ErrorHandling.h"
-#include <set>
-
-using llvm::MachO::HeaderFileType;
-
-namespace lld {
-
-namespace mach_o {
-class ArchHandler;
-class MachODylibFile;
-class MachOFile;
-class SectCreateFile;
-}
-
-class MachOLinkingContext : public LinkingContext {
-public:
-  MachOLinkingContext();
-  ~MachOLinkingContext() override;
-
-  enum Arch {
-    arch_unknown,
-    arch_ppc,
-    arch_x86,
-    arch_x86_64,
-    arch_armv6,
-    arch_armv7,
-    arch_armv7s,
-    arch_arm64,
-  };
-
-  enum class OS {
-    unknown,
-    macOSX,
-    iOS,
-    iOS_simulator
-  };
-
-  enum class ExportMode {
-    globals,    // Default, all global symbols exported.
-    exported,   // -exported_symbol[s_list], only listed symbols exported.
-    unexported  // -unexported_symbol[s_list], no listed symbol exported.
-  };
-
-  enum class DebugInfoMode {
-    addDebugMap,    // Default
-    noDebugMap      // -S option
-  };
-
-  enum class UndefinedMode {
-    error,
-    warning,
-    suppress,
-    dynamicLookup
-  };
-
-  enum ObjCConstraint {
-    objc_unknown = 0,
-    objc_supports_gc = 2,
-    objc_gc_only = 4,
-    // Image optimized by dyld = 8
-    // GC compaction = 16
-    objc_retainReleaseForSimulator = 32,
-    objc_retainRelease
-  };
-
-  /// Initializes the context to sane default values given the specified output
-  /// file type, arch, os, and minimum os version.  This should be called before
-  /// other setXXX() methods.
-  void configure(HeaderFileType type, Arch arch, OS os, uint32_t minOSVersion,
-                 bool exportDynamicSymbols);
-
-  void addPasses(PassManager &pm) override;
-  bool validateImpl() override;
-  std::string demangle(StringRef symbolName) const override;
-
-  void createImplicitFiles(std::vector<std::unique_ptr<File>> &) override;
-
-  /// Creates a new file which is owned by the context.  Returns a pointer to
-  /// the new file.
-  template <class T, class... Args>
-  typename std::enable_if<!std::is_array<T>::value, T *>::type
-  make_file(Args &&... args) const {
-    auto file = std::unique_ptr<T>(new T(std::forward<Args>(args)...));
-    auto *filePtr = file.get();
-    auto *ctx = const_cast<MachOLinkingContext *>(this);
-    ctx->getNodes().push_back(std::make_unique<FileNode>(std::move(file)));
-    return filePtr;
-  }
-
-  uint32_t getCPUType() const;
-  uint32_t getCPUSubType() const;
-
-  bool addEntryPointLoadCommand() const;
-  bool addUnixThreadLoadCommand() const;
-  bool outputTypeHasEntry() const;
-  bool is64Bit() const;
-
-  virtual uint64_t pageZeroSize() const { return _pageZeroSize; }
-  virtual uint64_t pageSize() const { return _pageSize; }
-
-  mach_o::ArchHandler &archHandler() const;
-
-  HeaderFileType outputMachOType() const { return _outputMachOType; }
-
-  Arch arch() const { return _arch; }
-  StringRef archName() const { return nameFromArch(_arch); }
-  OS os() const { return _os; }
-
-  ExportMode exportMode() const { return _exportMode; }
-  void setExportMode(ExportMode mode) { _exportMode = mode; }
-  void addExportSymbol(StringRef sym);
-  bool exportRestrictMode() const { return _exportMode != ExportMode::globals; }
-  bool exportSymbolNamed(StringRef sym) const;
-
-  DebugInfoMode debugInfoMode() const { return _debugInfoMode; }
-  void setDebugInfoMode(DebugInfoMode mode) {
-    _debugInfoMode = mode;
-  }
-
-  void appendOrderedSymbol(StringRef symbol, StringRef filename);
-
-  bool keepPrivateExterns() const { return _keepPrivateExterns; }
-  void setKeepPrivateExterns(bool v) { _keepPrivateExterns = v; }
-  bool demangleSymbols() const { return _demangle; }
-  void setDemangleSymbols(bool d) { _demangle = d; }
-  bool mergeObjCCategories() const { return _mergeObjCCategories; }
-  void setMergeObjCCategories(bool v) { _mergeObjCCategories = v; }
-  /// Create file at specified path which will contain a binary encoding
-  /// of all input and output file paths.
-  std::error_code createDependencyFile(StringRef path);
-  void addInputFileDependency(StringRef path) const;
-  void addInputFileNotFound(StringRef path) const;
-  void addOutputFileDependency(StringRef path) const;
-
-  bool minOS(StringRef mac, StringRef iOS) const;
-  void setDoNothing(bool value) { _doNothing = value; }
-  bool doNothing() const { return _doNothing; }
-  bool printAtoms() const { return _printAtoms; }
-  bool testingFileUsage() const { return _testingFileUsage; }
-  const StringRefVector &searchDirs() const { return _searchDirs; }
-  const StringRefVector &frameworkDirs() const { return _frameworkDirs; }
-  void setSysLibRoots(const StringRefVector &paths);
-  const StringRefVector &sysLibRoots() const { return _syslibRoots; }
-  bool PIE() const { return _pie; }
-  void setPIE(bool pie) { _pie = pie; }
-  bool generateVersionLoadCommand() const {
-    return _generateVersionLoadCommand;
-  }
-  void setGenerateVersionLoadCommand(bool v) {
-    _generateVersionLoadCommand = v;
-  }
-
-  bool generateFunctionStartsLoadCommand() const {
-    return _generateFunctionStartsLoadCommand;
-  }
-  void setGenerateFunctionStartsLoadCommand(bool v) {
-    _generateFunctionStartsLoadCommand = v;
-  }
-
-  bool generateDataInCodeLoadCommand() const {
-    return _generateDataInCodeLoadCommand;
-  }
-  void setGenerateDataInCodeLoadCommand(bool v) {
-    _generateDataInCodeLoadCommand = v;
-  }
-
-  uint64_t stackSize() const { return _stackSize; }
-  void setStackSize(uint64_t stackSize) { _stackSize = stackSize; }
-
-  uint64_t baseAddress() const { return _baseAddress; }
-  void setBaseAddress(uint64_t baseAddress) { _baseAddress = baseAddress; }
-
-  ObjCConstraint objcConstraint() const { return _objcConstraint; }
-
-  uint32_t osMinVersion() const { return _osMinVersion; }
-
-  uint32_t sdkVersion() const { return _sdkVersion; }
-  void setSdkVersion(uint64_t v) { _sdkVersion = v; }
-
-  uint64_t sourceVersion() const { return _sourceVersion; }
-  void setSourceVersion(uint64_t v) { _sourceVersion = v; }
-
-  uint32_t swiftVersion() const { return _swiftVersion; }
-
-  /// Checks whether a given path on the filesystem exists.
-  ///
-  /// When running in -test_file_usage mode, this method consults an
-  /// internally maintained list of files that exist (provided by -path_exists)
-  /// instead of the actual filesystem.
-  bool pathExists(StringRef path) const;
-
-  /// Like pathExists() but only used on files - not directories.
-  bool fileExists(StringRef path) const;
-
-  /// Adds any library search paths derived from the given base, possibly
-  /// modified by -syslibroots.
-  ///
-  /// The set of paths added consists of approximately all syslibroot-prepended
-  /// versions of libPath that exist, or the original libPath if there are none
-  /// for whatever reason. With various edge-cases for compatibility.
-  void addModifiedSearchDir(StringRef libPath, bool isSystemPath = false);
-
-  /// Determine whether -lFoo can be resolve within the given path, and
-  /// return the filename if so.
-  ///
-  /// The -lFoo option is documented to search for libFoo.dylib and libFoo.a in
-  /// that order, unless Foo ends in ".o", in which case only the exact file
-  /// matches (e.g. -lfoo.o would only find foo.o).
-  llvm::Optional<StringRef> searchDirForLibrary(StringRef path,
-                                                StringRef libName) const;
-
-  /// Iterates through all search path entries looking for libName (as
-  /// specified by -lFoo).
-  llvm::Optional<StringRef> searchLibrary(StringRef libName) const;
-
-  /// Add a framework search path.  Internally, this method may be prepended
-  /// the path with syslibroot.
-  void addFrameworkSearchDir(StringRef fwPath, bool isSystemPath = false);
-
-  /// Iterates through all framework directories looking for
-  /// Foo.framework/Foo (when fwName = "Foo").
-  llvm::Optional<StringRef> findPathForFramework(StringRef fwName) const;
-
-  /// The dylib's binary compatibility version, in the raw uint32 format.
-  ///
-  /// When building a dynamic library, this is the compatibility version that
-  /// gets embedded into the result. Other Mach-O binaries that link against
-  /// this library will store the compatibility version in its load command. At
-  /// runtime, the loader will verify that the binary is compatible with the
-  /// installed dynamic library.
-  uint32_t compatibilityVersion() const { return _compatibilityVersion; }
-
-  /// The dylib's current version, in the raw uint32 format.
-  ///
-  /// When building a dynamic library, this is the current version that gets
-  /// embedded into the result. Other Mach-O binaries that link against
-  /// this library will store the compatibility version in its load command.
-  uint32_t currentVersion() const { return _currentVersion; }
-
-  /// The dylib's install name.
-  ///
-  /// Binaries that link against the dylib will embed this path into the dylib
-  /// load command. When loading the binaries at runtime, this is the location
-  /// on disk that the loader will look for the dylib.
-  StringRef installName() const { return _installName; }
-
-  /// Whether or not the dylib has side effects during initialization.
-  ///
-  /// Dylibs marked as being dead strippable provide the guarantee that loading
-  /// the dylib has no side effects, allowing the linker to strip out the dylib
-  /// when linking a binary that does not use any of its symbols.
-  bool deadStrippableDylib() const { return _deadStrippableDylib; }
-
-  /// Whether or not to use flat namespace.
-  ///
-  /// MachO usually uses a two-level namespace, where each external symbol
-  /// referenced by the target is associated with the dylib that will provide
-  /// the symbol's definition at runtime. Using flat namespace overrides this
-  /// behavior: the linker searches all dylibs on the command line and all
-  /// dylibs those original dylibs depend on, but does not record which dylib
-  /// an external symbol came from. At runtime dyld again searches all images
-  /// and uses the first definition it finds. In addition, any undefines in
-  /// loaded flat_namespace dylibs must be resolvable at build time.
-  bool useFlatNamespace() const { return _flatNamespace; }
-
-  /// How to handle undefined symbols.
-  ///
-  /// Options are:
-  ///  * error: Report an error and terminate linking.
-  ///  * warning: Report a warning, but continue linking.
-  ///  * suppress: Ignore and continue linking.
-  ///  * dynamic_lookup: For use with -twolevel namespace: Records source dylibs
-  ///    for symbols that are defined in a linked dylib at static link time.
-  ///    Undefined symbols are handled by searching all loaded images at
-  ///    runtime.
-  UndefinedMode undefinedMode() const { return _undefinedMode; }
-
-  /// The path to the executable that will load the bundle at runtime.
-  ///
-  /// When building a Mach-O bundle, this executable will be examined if there
-  /// are undefined symbols after the main link phase. It is expected that this
-  /// binary will be loading the bundle at runtime and will provide the symbols
-  /// at that point.
-  StringRef bundleLoader() const { return _bundleLoader; }
-
-  void setCompatibilityVersion(uint32_t vers) { _compatibilityVersion = vers; }
-  void setCurrentVersion(uint32_t vers) { _currentVersion = vers; }
-  void setInstallName(StringRef name) { _installName = name; }
-  void setDeadStrippableDylib(bool deadStrippable) {
-    _deadStrippableDylib = deadStrippable;
-  }
-  void setUseFlatNamespace(bool flatNamespace) {
-    _flatNamespace = flatNamespace;
-  }
-
-  void setUndefinedMode(UndefinedMode undefinedMode) {
-    _undefinedMode = undefinedMode;
-  }
-
-  void setBundleLoader(StringRef loader) { _bundleLoader = loader; }
-  void setPrintAtoms(bool value=true) { _printAtoms = value; }
-  void setTestingFileUsage(bool value = true) {
-    _testingFileUsage = value;
-  }
-  void addExistingPathForDebug(StringRef path) {
-    _existingPaths.insert(path);
-  }
-
-  void addRpath(StringRef rpath);
-  const StringRefVector &rpaths() const { return _rpaths; }
-
-  /// Add section alignment constraint on final layout.
-  void addSectionAlignment(StringRef seg, StringRef sect, uint16_t align);
-
-  /// Add a section based on a command-line sectcreate option.
-  void addSectCreateSection(StringRef seg, StringRef sect,
-                            std::unique_ptr<MemoryBuffer> content);
-
-  /// Returns true if specified section had alignment constraints.
-  bool sectionAligned(StringRef seg, StringRef sect, uint16_t &align) const;
-
-  StringRef dyldPath() const { return "/usr/lib/dyld"; }
-
-  /// Stub creation Pass should be run.
-  bool needsStubsPass() const;
-
-  // GOT creation Pass should be run.
-  bool needsGOTPass() const;
-
-  /// Pass to add TLV sections.
-  bool needsTLVPass() const;
-
-  /// Pass to transform __compact_unwind into __unwind_info should be run.
-  bool needsCompactUnwindPass() const;
-
-  /// Pass to add shims switching between thumb and arm mode.
-  bool needsShimPass() const;
-
-  /// Pass to add objc image info and optimized objc data.
-  bool needsObjCPass() const;
-
-  /// Magic symbol name stubs will need to help lazy bind.
-  StringRef binderSymbolName() const;
-
-  /// Used to keep track of direct and indirect dylibs.
-  void registerDylib(mach_o::MachODylibFile *dylib, bool upward) const;
-
-  // Reads a file from disk to memory. Returns only a needed chunk
-  // if a fat binary.
-  ErrorOr<std::unique_ptr<MemoryBuffer>> getMemoryBuffer(StringRef path);
-
-  /// Used to find indirect dylibs. Instantiates a MachODylibFile if one
-  /// has not already been made for the requested dylib.  Uses -L and -F
-  /// search paths to allow indirect dylibs to be overridden.
-  mach_o::MachODylibFile* findIndirectDylib(StringRef path);
-
-  uint32_t dylibCurrentVersion(StringRef installName) const;
-
-  uint32_t dylibCompatVersion(StringRef installName) const;
-
-  ArrayRef<mach_o::MachODylibFile*> allDylibs() const {
-    return _allDylibs;
-  }
-
-  /// Creates a copy (owned by this MachOLinkingContext) of a string.
-  StringRef copy(StringRef str) { return str.copy(_allocator); }
-
-  /// If the memoryBuffer is a fat file with a slice for the current arch,
-  /// this method will return the offset and size of that slice.
-  bool sliceFromFatFile(MemoryBufferRef mb, uint32_t &offset, uint32_t &size);
-
-  /// Returns if a command line option specified dylib is an upward link.
-  bool isUpwardDylib(StringRef installName) const;
-
-  static bool isThinObjectFile(StringRef path, Arch &arch);
-  static Arch archFromCpuType(uint32_t cputype, uint32_t cpusubtype);
-  static Arch archFromName(StringRef archName);
-  static StringRef nameFromArch(Arch arch);
-  static uint32_t cpuTypeFromArch(Arch arch);
-  static uint32_t cpuSubtypeFromArch(Arch arch);
-  static bool is64Bit(Arch arch);
-  static bool isHostEndian(Arch arch);
-  static bool isBigEndian(Arch arch);
-
-  /// Construct 32-bit value from string "X.Y.Z" where
-  /// bits are xxxx.yy.zz.  Largest number is 65535.255.255
-  static bool parsePackedVersion(StringRef str, uint32_t &result);
-
-  /// Construct 64-bit value from string "A.B.C.D.E" where
-  /// bits are aaaa.bb.cc.dd.ee.  Largest number is 16777215.1023.1023.1023.1023
-  static bool parsePackedVersion(StringRef str, uint64_t &result);
-
-  void finalizeInputFiles() override;
-
-  llvm::Error handleLoadedFile(File &file) override;
-
-  bool customAtomOrderer(const DefinedAtom *left, const DefinedAtom *right,
-                         bool &leftBeforeRight) const;
-
-  /// Return the 'flat namespace' file. This is the file that supplies
-  /// atoms for otherwise undefined symbols when the -flat_namespace or
-  /// -undefined dynamic_lookup options are used.
-  File* flatNamespaceFile() const { return _flatNamespaceFile; }
-
-private:
-  Writer &writer() const override;
-  mach_o::MachODylibFile* loadIndirectDylib(StringRef path);
-  struct ArchInfo {
-    StringRef                 archName;
-    MachOLinkingContext::Arch arch;
-    bool                      littleEndian;
-    uint32_t                  cputype;
-    uint32_t                  cpusubtype;
-  };
-
-  struct SectionAlign {
-    StringRef segmentName;
-    StringRef sectionName;
-    uint16_t  align;
-  };
-
-  struct OrderFileNode {
-    StringRef fileFilter;
-    unsigned  order;
-  };
-
-  static bool findOrderOrdinal(const std::vector<OrderFileNode> &nodes,
-                             const DefinedAtom *atom, unsigned &ordinal);
-
-  static ArchInfo _s_archInfos[];
-
-  std::set<StringRef> _existingPaths; // For testing only.
-  StringRefVector _searchDirs;
-  StringRefVector _syslibRoots;
-  StringRefVector _frameworkDirs;
-  HeaderFileType _outputMachOType = llvm::MachO::MH_EXECUTE;
-  bool _outputMachOTypeStatic = false; // Disambiguate static vs dynamic prog
-  bool _doNothing = false;             // for -help and -v which just print info
-  bool _pie = false;
-  Arch _arch = arch_unknown;
-  OS _os = OS::macOSX;
-  uint32_t _osMinVersion = 0;
-  uint32_t _sdkVersion = 0;
-  uint64_t _sourceVersion = 0;
-  uint64_t _pageZeroSize = 0;
-  uint64_t _pageSize = 4096;
-  uint64_t _baseAddress = 0;
-  uint64_t _stackSize = 0;
-  uint32_t _compatibilityVersion = 0;
-  uint32_t _currentVersion = 0;
-  ObjCConstraint _objcConstraint = objc_unknown;
-  uint32_t _swiftVersion = 0;
-  StringRef _installName;
-  StringRefVector _rpaths;
-  bool _flatNamespace = false;
-  UndefinedMode _undefinedMode = UndefinedMode::error;
-  bool _deadStrippableDylib = false;
-  bool _printAtoms = false;
-  bool _testingFileUsage = false;
-  bool _keepPrivateExterns = false;
-  bool _demangle = false;
-  bool _mergeObjCCategories = true;
-  bool _generateVersionLoadCommand = false;
-  bool _generateFunctionStartsLoadCommand = false;
-  bool _generateDataInCodeLoadCommand = false;
-  StringRef _bundleLoader;
-  mutable std::unique_ptr<mach_o::ArchHandler> _archHandler;
-  mutable std::unique_ptr<Writer> _writer;
-  std::vector<SectionAlign> _sectAligns;
-  mutable llvm::StringMap<mach_o::MachODylibFile*> _pathToDylibMap;
-  mutable std::vector<mach_o::MachODylibFile*> _allDylibs;
-  mutable std::set<mach_o::MachODylibFile*> _upwardDylibs;
-  mutable std::vector<std::unique_ptr<File>> _indirectDylibs;
-  mutable std::mutex _dylibsMutex;
-  ExportMode _exportMode = ExportMode::globals;
-  llvm::StringSet<> _exportedSymbols;
-  DebugInfoMode _debugInfoMode = DebugInfoMode::addDebugMap;
-  std::unique_ptr<llvm::raw_fd_ostream> _dependencyInfo;
-  llvm::StringMap<std::vector<OrderFileNode>> _orderFiles;
-  unsigned _orderFileEntries = 0;
-  File *_flatNamespaceFile = nullptr;
-  mach_o::SectCreateFile *_sectCreateFile = nullptr;
-};
-
-} // end namespace lld
-
-#endif // LLD_READER_WRITER_MACHO_LINKING_CONTEXT_H
diff --git a/lld/include/lld/ReaderWriter/YamlContext.h b/lld/include/lld/ReaderWriter/YamlContext.h
deleted file mode 100644
index dc133e3627de..000000000000
--- a/lld/include/lld/ReaderWriter/YamlContext.h
+++ /dev/null
@@ -1,42 +0,0 @@
-//===- lld/ReaderWriter/YamlContext.h - object used in YAML I/O context ---===//
-//
-// 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
-//
-//===----------------------------------------------------------------------===//
-
-#ifndef LLD_READER_WRITER_YAML_CONTEXT_H
-#define LLD_READER_WRITER_YAML_CONTEXT_H
-
-#include "lld/Common/LLVM.h"
-#include <functional>
-#include <memory>
-#include <vector>
-
-namespace lld {
-class File;
-class LinkingContext;
-class Registry;
-namespace mach_o {
-namespace normalized {
-struct NormalizedFile;
-}
-}
-
-using lld::mach_o::normalized::NormalizedFile;
-
-/// When YAML I/O is used in lld, the yaml context always holds a YamlContext
-/// object.  We need to support hetergenous yaml documents which each require
-/// different context info.  This struct supports all clients.
-struct YamlContext {
-  const LinkingContext *_ctx = nullptr;
-  const Registry *_registry = nullptr;
-  File *_file = nullptr;
-  NormalizedFile *_normalizeMachOFile = nullptr;
-  StringRef _path;
-};
-
-} // end namespace lld
-
-#endif // LLD_READER_WRITER_YAML_CONTEXT_H