Remove the ThreadLocal template from LLVM.

[resistor]

Summary

This has been obsoleted by C++ thread_local for a long time.
As far as I know, Xcode was the last supported toolchain to add
support for C++ thread_local in 2016.

As a precaution, use LLVM_THREAD_LOCAL which provides even greater
backwards compatibility, allowing this to function even pre-C++11
versions of GCC.

[resistor]

Incorporated build fixes for GCC. Waiting for buildbots to complete.

[nikic]

LGTM

As a precaution, use LLVM_THREAD_LOCAL which provides even greater
backwards compatibility, allowing this to function even pre-C++11
versions of GCC.

I don't think backwards compatibility is still relevant given our minimum version requirements. We can probably drop the __thread fallback. What LLVM_THREAD_LOCAL does though is fall back to a normal variable if !LLVM_ENABLE_THREADS.

clang-tools-extra/clangd/support/ThreadCrashReporter.cpp

 //===--- ThreadCrashReporter.cpp - Thread local signal handling --*- 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
 //
 //===----------------------------------------------------------------------===//
 
 #include "support/ThreadCrashReporter.h"
-#include "llvm/Support/ThreadLocal.h"
 #include <atomic>
 
 namespace clang {
 namespace clangd {
 
 static thread_local ThreadCrashReporter *CurrentReporter = nullptr;
 
 void ThreadCrashReporter::runCrashHandlers() {

llvm/include/llvm/Support/ThreadLocal.h

-//===- llvm/Support/ThreadLocal.h - Thread Local Data ------------*- 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 declares the llvm::sys::ThreadLocal class.
-//
-//===----------------------------------------------------------------------===//
-
-#ifndef LLVM_SUPPORT_THREADLOCAL_H
-#define LLVM_SUPPORT_THREADLOCAL_H
-
-#include "llvm/Support/DataTypes.h"
-#include "llvm/Support/Threading.h"
-#include <cassert>
-
-namespace llvm {
-  namespace sys {
-    // ThreadLocalImpl - Common base class of all ThreadLocal instantiations.
-    // YOU SHOULD NEVER USE THIS DIRECTLY.
-    class ThreadLocalImpl {
-      typedef uint64_t ThreadLocalDataTy;
-      /// Platform-specific thread local data.
-      ///
-      /// This is embedded in the class and we avoid malloc'ing/free'ing it,
-      /// to make this class more safe for use along with CrashRecoveryContext.
-      union {
-        char data[sizeof(ThreadLocalDataTy)];
-        ThreadLocalDataTy align_data;
-      };
-    public:
-      ThreadLocalImpl();
-      virtual ~ThreadLocalImpl();
-      void setInstance(const void* d);
-      void *getInstance();
-      void removeInstance();
-    };
-
-    /// ThreadLocal - A class used to abstract thread-local storage.  It holds,
-    /// for each thread, a pointer a single object of type T.
-    template<class T>
-    class ThreadLocal : public ThreadLocalImpl {
-    public:
-      ThreadLocal() : ThreadLocalImpl() { }
-
-      /// get - Fetches a pointer to the object associated with the current
-      /// thread.  If no object has yet been associated, it returns NULL;
-      T* get() { return static_cast<T*>(getInstance()); }
-
-      // set - Associates a pointer to an object with the current thread.
-      void set(T* d) { setInstance(d); }
-
-      // erase - Removes the pointer associated with the current thread.
-      void erase() { removeInstance(); }
-    };
-  }
-}
-
-#endif

llvm/lib/Support/CMakeLists.txt

# System
   DynamicLibrary.cpp
   Errno.cpp
   Memory.cpp
   Path.cpp
   Process.cpp
   Program.cpp
   RWMutex.cpp
   Signals.cpp
-  ThreadLocal.cpp
   Threading.cpp
   Valgrind.cpp
   Watchdog.cpp
 
   ADDITIONAL_HEADER_DIRS
   Unix
   Windows
   ${LLVM_MAIN_INCLUDE_DIR}/llvm/ADT

llvm/lib/Support/CrashRecoveryContext.cpp

 //===--- CrashRecoveryContext.cpp - Crash Recovery ------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "llvm/Support/CrashRecoveryContext.h"
 #include "llvm/Config/llvm-config.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/ExitCodes.h"
 #include "llvm/Support/Signals.h"
-#include "llvm/Support/ThreadLocal.h"
 #include "llvm/Support/thread.h"
+#include <cassert>
 #include <mutex>
 #include <setjmp.h>
 
 using namespace llvm;
 
 namespace {
 
 struct CrashRecoveryContextImpl;
-
-sys::ThreadLocal<const CrashRecoveryContextImpl> &getCurrentContext() {
-  static sys::ThreadLocal<const CrashRecoveryContextImpl> CurrentContext;
-  return CurrentContext;
-}
+static LLVM_THREAD_LOCAL const CrashRecoveryContextImpl *CurrentContext;
 
 struct CrashRecoveryContextImpl {
   // When threads are disabled, this links up all active
   // CrashRecoveryContextImpls.  When threads are enabled there's one thread
   // per CrashRecoveryContext and CurrentContext is a thread-local, so only one
   // CrashRecoveryContextImpl is active per thread and this is always null.
   const CrashRecoveryContextImpl *Next;
 
   CrashRecoveryContext *CRC;
   ::jmp_buf JumpBuffer;
   volatile unsigned Failed : 1;
   unsigned SwitchedThread : 1;
   unsigned ValidJumpBuffer : 1;
 
 public:
   CrashRecoveryContextImpl(CrashRecoveryContext *CRC) noexcept
       : CRC(CRC), Failed(false), SwitchedThread(false), ValidJumpBuffer(false) {
-    Next = getCurrentContext().get();
-    getCurrentContext().set(this);
+    Next = CurrentContext;
+    CurrentContext = this;
   }
   ~CrashRecoveryContextImpl() {
     if (!SwitchedThread)
-      getCurrentContext().set(Next);
+      CurrentContext = Next;
   }
 
   /// Called when the separate crash-recovery thread was finished, to
   /// indicate that we don't need to clear the thread-local CurrentContext.
   void setSwitchedThread() {
 #if defined(LLVM_ENABLE_THREADS) && LLVM_ENABLE_THREADS != 0
     SwitchedThread = true;
 #endif
   }
 
   // If the function ran by the CrashRecoveryContext crashes or fails, then
   // 'RetCode' represents the returned error code, as if it was returned by a
   // process. 'Context' represents the signal type on Unix; on Windows, it is
   // the ExceptionContext.
   void HandleCrash(int RetCode, uintptr_t Context) {
     // Eliminate the current context entry, to avoid re-entering in case the
     // cleanup code crashes.
-    getCurrentContext().set(Next);
+    CurrentContext = Next;
 
     assert(!Failed && "Crash recovery context already failed!");
     Failed = true;
 
     if (CRC->DumpStackAndCleanupOnFailure)
       sys::CleanupOnSignal(Context);
 
     CRC->RetCode = RetCode;

 
 std::mutex &getCrashRecoveryContextMutex() {
   static std::mutex CrashRecoveryContextMutex;
   return CrashRecoveryContextMutex;
 }
 
 static bool gCrashRecoveryEnabled = false;
 
-sys::ThreadLocal<const CrashRecoveryContext> &getIsRecoveringFromCrash() {
-  static sys::ThreadLocal<const CrashRecoveryContext> IsRecoveringFromCrash;
-  return IsRecoveringFromCrash;
-}
+static LLVM_THREAD_LOCAL const CrashRecoveryContext *IsRecoveringFromCrash;
 
 } // namespace
 
 static void installExceptionOrSignalHandlers();
 static void uninstallExceptionOrSignalHandlers();
 
 CrashRecoveryContextCleanup::~CrashRecoveryContextCleanup() = default;
 
 CrashRecoveryContext::CrashRecoveryContext() {
   // On Windows, if abort() was previously triggered (and caught by a previous
   // CrashRecoveryContext) the Windows CRT removes our installed signal handler,
   // so we need to install it again.
   sys::DisableSystemDialogsOnCrash();
 }
 
 CrashRecoveryContext::~CrashRecoveryContext() {
   // Reclaim registered resources.
   CrashRecoveryContextCleanup *i = head;
-  const CrashRecoveryContext *PC = getIsRecoveringFromCrash().get();
-  getIsRecoveringFromCrash().set(this);
+  const CrashRecoveryContext *PC = IsRecoveringFromCrash;
+  IsRecoveringFromCrash = this;
   while (i) {
     CrashRecoveryContextCleanup *tmp = i;
     i = tmp->next;
     tmp->cleanupFired = true;
     tmp->recoverResources();
     delete tmp;
   }
-  getIsRecoveringFromCrash().set(PC);
+  IsRecoveringFromCrash = PC;
 
   CrashRecoveryContextImpl *CRCI = (CrashRecoveryContextImpl *) Impl;
   delete CRCI;
 }
 
 bool CrashRecoveryContext::isRecoveringFromCrash() {
-  return getIsRecoveringFromCrash().get() != nullptr;
+  return IsRecoveringFromCrash != nullptr;
 }
 
 CrashRecoveryContext *CrashRecoveryContext::GetCurrent() {
   if (!gCrashRecoveryEnabled)
     return nullptr;
 
-  const CrashRecoveryContextImpl *CRCI = getCurrentContext().get();
+  const CrashRecoveryContextImpl *CRCI = CurrentContext;
   if (!CRCI)
     return nullptr;
 
   return CRCI->CRC;
 }
 
 void CrashRecoveryContext::Enable() {
   std::lock_guard<std::mutex> L(getCrashRecoveryContextMutex());

 
 static void installExceptionOrSignalHandlers() {}
 static void uninstallExceptionOrSignalHandlers() {}
 
 // We need this function because the call to GetExceptionInformation() can only
 // occur inside the __except evaluation block
 static int ExceptionFilter(_EXCEPTION_POINTERS *Except) {
   // Lookup the current thread local recovery object.
-  const CrashRecoveryContextImpl *CRCI = getCurrentContext().get();
+  const CrashRecoveryContextImpl *CRCI = CurrentContext;
 
   if (!CRCI) {
     // Something has gone horribly wrong, so let's just tell everyone
     // to keep searching
     CrashRecoveryContext::Disable();
     return EXCEPTION_CONTINUE_SEARCH;
   }
 
static LONG CALLBACK ExceptionHandler(PEXCEPTION_POINTERS ExceptionInfo)
   {
   case DBG_PRINTEXCEPTION_C:
   case DbgPrintExceptionWideC:
   case 0x406D1388:  // set debugger thread name
     return EXCEPTION_CONTINUE_EXECUTION;
   }
 
   // Lookup the current thread local recovery object.
-  const CrashRecoveryContextImpl *CRCI = getCurrentContext().get();
+  const CrashRecoveryContextImpl *CRCI = CurrentContext;
 
   if (!CRCI) {
     // Something has gone horribly wrong, so let's just tell everyone
     // to keep searching
     CrashRecoveryContext::Disable();
     return EXCEPTION_CONTINUE_SEARCH;
   }
 

 
 static const int Signals[] =
     { SIGABRT, SIGBUS, SIGFPE, SIGILL, SIGSEGV, SIGTRAP };
 static const unsigned NumSignals = std::size(Signals);
 static struct sigaction PrevActions[NumSignals];
 
 static void CrashRecoverySignalHandler(int Signal) {
   // Lookup the current thread local recovery object.
-  const CrashRecoveryContextImpl *CRCI = getCurrentContext().get();
+  const CrashRecoveryContextImpl *CRCI = CurrentContext;
 
   if (!CRCI) {
     // We didn't find a crash recovery context -- this means either we got a
     // signal on a thread we didn't expect it on, the application got a signal
     // outside of a crash recovery context, or something else went horribly
     // wrong.
     //
     // Disable crash recovery and raise the signal again. The assumption here is

llvm/lib/Support/ThreadLocal.cpp

-//===- ThreadLocal.cpp - Thread Local Data ----------------------*- 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 implements the llvm::sys::ThreadLocal class.
-//
-//===----------------------------------------------------------------------===//
-
-#include "llvm/Support/ThreadLocal.h"
-#include "llvm/Config/llvm-config.h"
-#include "llvm/Support/Compiler.h"
-
-//===----------------------------------------------------------------------===//
-//=== WARNING: Implementation here must contain only TRULY operating system
-//===          independent code.
-//===----------------------------------------------------------------------===//
-
-#if !defined(LLVM_ENABLE_THREADS) || LLVM_ENABLE_THREADS == 0
-// Define all methods as no-ops if threading is explicitly disabled
-namespace llvm {
-using namespace sys;
-ThreadLocalImpl::ThreadLocalImpl() : data() { }
-ThreadLocalImpl::~ThreadLocalImpl() { }
-void ThreadLocalImpl::setInstance(const void* d) {
-  static_assert(sizeof(d) <= sizeof(data), "size too big");
-  void **pd = reinterpret_cast<void**>(&data);
-  *pd = const_cast<void*>(d);
-}
-void *ThreadLocalImpl::getInstance() {
-  void **pd = reinterpret_cast<void**>(&data);
-  return *pd;
-}
-void ThreadLocalImpl::removeInstance() {
-  setInstance(nullptr);
-}
-}
-#elif defined(LLVM_ON_UNIX)
-#include "Unix/ThreadLocal.inc"
-#elif defined( _WIN32)
-#include "Windows/ThreadLocal.inc"
-#else
-#warning Neither LLVM_ON_UNIX nor _WIN32 set in Support/ThreadLocal.cpp
-#endif

llvm/lib/Support/Unix/ThreadLocal.inc

-//=== llvm/Support/Unix/ThreadLocal.inc - Unix Thread Local Data -*- 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 implements the Unix specific (non-pthread) ThreadLocal class.
-//
-//===----------------------------------------------------------------------===//
-
-//===----------------------------------------------------------------------===//
-//=== WARNING: Implementation here must contain only generic UNIX code that
-//===          is guaranteed to work on *all* UNIX variants.
-//===----------------------------------------------------------------------===//
-
-#include "llvm/Config/config.h"
-
-#include <cassert>
-#include <pthread.h>
-#include <stdlib.h>
-
-namespace llvm {
-using namespace sys;
-
-ThreadLocalImpl::ThreadLocalImpl() : data() {
-  static_assert(sizeof(pthread_key_t) <= sizeof(data), "size too big");
-  pthread_key_t *key = reinterpret_cast<pthread_key_t *>(&data);
-  int errorcode = pthread_key_create(key, nullptr);
-  assert(errorcode == 0);
-  (void)errorcode;
-}
-
-ThreadLocalImpl::~ThreadLocalImpl() {
-  pthread_key_t *key = reinterpret_cast<pthread_key_t *>(&data);
-  int errorcode = pthread_key_delete(*key);
-  assert(errorcode == 0);
-  (void)errorcode;
-}
-
-void ThreadLocalImpl::setInstance(const void *d) {
-  pthread_key_t *key = reinterpret_cast<pthread_key_t *>(&data);
-  int errorcode = pthread_setspecific(*key, d);
-  assert(errorcode == 0);
-  (void)errorcode;
-}
-
-void *ThreadLocalImpl::getInstance() {
-  pthread_key_t *key = reinterpret_cast<pthread_key_t *>(&data);
-  return pthread_getspecific(*key);
-}
-
-void ThreadLocalImpl::removeInstance() { setInstance(nullptr); }
-
-} // namespace llvm

llvm/lib/Support/Windows/ThreadLocal.inc

-//= llvm/Support/Win32/ThreadLocal.inc - Win32 Thread Local Data -*- 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 implements the Win32 specific (non-pthread) ThreadLocal class.
-//
-//===----------------------------------------------------------------------===//
-
-//===----------------------------------------------------------------------===//
-//=== WARNING: Implementation here must contain only generic Win32 code that
-//===          is guaranteed to work on *all* Win32 variants.
-//===----------------------------------------------------------------------===//
-
-#include "llvm/Support/ThreadLocal.h"
-#include "llvm/Support/Windows/WindowsSupport.h"
-
-namespace llvm {
-
-sys::ThreadLocalImpl::ThreadLocalImpl() : data() {
-  static_assert(sizeof(DWORD) <= sizeof(data), "size too big");
-  DWORD *tls = reinterpret_cast<DWORD *>(&data);
-  *tls = TlsAlloc();
-  assert(*tls != TLS_OUT_OF_INDEXES);
-}
-
-sys::ThreadLocalImpl::~ThreadLocalImpl() {
-  DWORD *tls = reinterpret_cast<DWORD *>(&data);
-  TlsFree(*tls);
-}
-
-void *sys::ThreadLocalImpl::getInstance() {
-  DWORD *tls = reinterpret_cast<DWORD *>(&data);
-  return TlsGetValue(*tls);
-}
-
-void sys::ThreadLocalImpl::setInstance(const void *d) {
-  DWORD *tls = reinterpret_cast<DWORD *>(&data);
-  int errorcode = TlsSetValue(*tls, const_cast<void *>(d));
-  assert(errorcode != 0);
-  (void)errorcode;
-}
-
-void sys::ThreadLocalImpl::removeInstance() { setInstance(0); }
-
-} // namespace llvm

llvm/unittests/Support/CMakeLists.txt

add_llvm_unittest(SupportTests
   SHA256.cpp
   SourceMgrTest.cpp
   SpecialCaseListTest.cpp
   SuffixTreeTest.cpp
   SwapByteOrderTest.cpp
   SymbolRemappingReaderTest.cpp
   TarWriterTest.cpp
   TaskQueueTest.cpp
-  ThreadLocalTest.cpp
   ThreadPool.cpp
   Threading.cpp
   TimerTest.cpp
   TimeProfilerTest.cpp
   ToolOutputFileTest.cpp
   TypeNameTest.cpp
   TypeSizeTest.cpp
   TypeTraitsTest.cpp

llvm/unittests/Support/ThreadLocalTest.cpp

-//===- llvm/unittest/Support/ThreadLocalTest.cpp - ThreadLocal tests ------===//
-//
-// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
-// See https://llvm.org/LICENSE.txt for license information.
-// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-//
-//===----------------------------------------------------------------------===//
-
-#include "llvm/Support/ThreadLocal.h"
-#include "gtest/gtest.h"
-#include <type_traits>
-
-using namespace llvm;
-using namespace sys;
-
-namespace {
-
-class ThreadLocalTest : public ::testing::Test {
-};
-
-struct S {
-  int i;
-};
-
-TEST_F(ThreadLocalTest, Basics) {
-  ThreadLocal<const S> x;
-
-  static_assert(std::is_const_v<std::remove_pointer_t<decltype(x.get())>>,
-                "ThreadLocal::get didn't return a pointer to const object");
-
-  EXPECT_EQ(nullptr, x.get());
-
-  S s;
-  x.set(&s);
-  EXPECT_EQ(&s, x.get());
-
-  x.erase();
-  EXPECT_EQ(nullptr, x.get());
-
-  ThreadLocal<S> y;
-
-  static_assert(!std::is_const_v<std::remove_pointer_t<decltype(y.get())>>,
-                "ThreadLocal::get returned a pointer to const object");
-
-  EXPECT_EQ(nullptr, y.get());
-
-  y.set(&s);
-  EXPECT_EQ(&s, y.get());
-
-  y.erase();
-  EXPECT_EQ(nullptr, y.get());
-}
-
-}

mlir/include/mlir/Support/ThreadLocalCache.h

 
 #ifndef MLIR_SUPPORT_THREADLOCALCACHE_H
 #define MLIR_SUPPORT_THREADLOCALCACHE_H
 
 #include "mlir/Support/LLVM.h"
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/Support/ManagedStatic.h"
 #include "llvm/Support/Mutex.h"
-#include "llvm/Support/ThreadLocal.h"
 
 namespace mlir {
 /// This class provides support for defining a thread local object with non
 /// static storage duration. This is very useful for situations in which a data
 /// cache has very large lock contention.
 template <typename ValueT>
 class ThreadLocalCache {
   /// The type used for the static thread_local cache. This is a map between an