[Support] Use newer thread naming API if available on Windows.

[scotttodd]

Summary

See https://learn.microsoft.com/en-us/visualstudio/debugger/how-to-set-a-thread-name-in-native-code. The newer API allows for performance analysis tools (such as Tracy) that don't use the debugger API to still view thread names.

[scotttodd]

llvm/lib/Support/Windows/Threading.inc

120–128

Ah, looks like there is a matching new API for getting the thread name: https://learn.microsoft.com/en-us/windows/win32/api/processthreadsapi/nf-processthreadsapi-getthreaddescription

llvm/lib/Support/Windows/Threading.inc

 
 } // namespace llvm
 
 uint64_t llvm::get_threadid() { return uint64_t(::GetCurrentThreadId()); }
 
 uint32_t llvm::get_max_thread_name_length() { return 0; }
 
 #if defined(_MSC_VER)
-static void SetThreadName(DWORD Id, LPCSTR Name) {
+static void SetThreadName(DWORD Id, StringRef Name) {
+  // https://learn.microsoft.com/en-us/visualstudio/debugger/how-to-set-a-thread-name-in-native-code
+
+  // Try first to use the modern SetThreadDescription API.
+  // This will work even if a debugger is not attached meaning that tools that
+  // don't use the debugger API can still query thread names. It's only
+  // available on Win10+.
+  typedef HRESULT(WINAPI * SetThreadDescriptionFn)(HANDLE hThread,
+                                                   PCWSTR lpThreadDescription);
+  SetThreadDescriptionFn ProcSetThreadDescription =
+      (SetThreadDescriptionFn)GetProcAddress(GetModuleHandleW(L"Kernel32.dll"),
+                                             "SetThreadDescription");
+  if (ProcSetThreadDescription) {
+    wchar_t NameWide[16] = {0};
+    MultiByteToWideChar(CP_UTF8, MB_ERR_INVALID_CHARS, Name.data(), -1,
+                        NameWide, 16 - 1);
+    ProcSetThreadDescription(::GetCurrentThread(), NameWide);
+    return;
+  }
+
+  // Fallback to throwing a specially-configured exception. This will only work
+  // if a debugger is attached - thread names will not be available in dumps or
+  // performance analysis tools.
   constexpr DWORD MS_VC_EXCEPTION = 0x406D1388;
 
 #pragma pack(push, 8)
   struct THREADNAME_INFO {
     DWORD dwType;     // Must be 0x1000.
     LPCSTR szName;    // Pointer to thread name
     DWORD dwThreadId; // Thread ID (-1 == current thread)
     DWORD dwFlags;    // Reserved.  Do not use.
   };
 #pragma pack(pop)
 
   THREADNAME_INFO info;
   info.dwType = 0x1000;
-  info.szName = Name;
+  info.szName = Name.data();
   info.dwThreadId = Id;
   info.dwFlags = 0;
 
   __try {
     ::RaiseException(MS_VC_EXCEPTION, 0, sizeof(info) / sizeof(ULONG_PTR),
                      (ULONG_PTR *)&info);
   } __except (EXCEPTION_EXECUTE_HANDLER) {
   }
 }
 #endif
 
 void llvm::set_thread_name(const Twine &Name) {
 #if defined(_MSC_VER)
   // Make sure the input is null terminated.
   SmallString<64> Storage;
   StringRef NameStr = Name.toNullTerminatedStringRef(Storage);
-  SetThreadName(::GetCurrentThreadId(), NameStr.data());
+  SetThreadName(::GetCurrentThreadId(), NameStr);
 #endif
 }
 
 void llvm::get_thread_name(SmallVectorImpl<char> &Name) {
   // "Name" is not an inherent property of a thread on Windows.  In fact, when
   // you "set" the name, you are only firing a one-time message to a debugger
   // which it interprets as a program setting its threads' name.  We may be
   // able to get fancy by creating a TLS entry when someone calls
   // set_thread_name so that subsequent calls to get_thread_name return this
   // value.
   Name.clear();
 }
 
 SetThreadPriorityResult llvm::set_thread_priority(ThreadPriority Priority) {
   // https://docs.microsoft.com/en-us/windows/desktop/api/processthreadsapi/nf-processthreadsapi-setthreadpriority
   // Begin background processing mode. The system lowers the resource scheduling
   // priorities of the thread so that it can perform background work without
   // significantly affecting activity in the foreground.
   // End background processing mode. The system restores the resource scheduling
   // priorities of the thread as they were before the thread entered background