[llvm] Windows: use EcoQoS for ThreadPriority::Background (PR #148797)

[Alexandre Ganea via llvm-commits]

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@@ -107,6 +107,35 @@ void llvm::get_thread_name(SmallVectorImpl<char> &Name) {
 }
 
 SetThreadPriorityResult llvm::set_thread_priority(ThreadPriority Priority) {
+
+  // SetThreadInformation is only available on Windows 8 and later. Since we still
+  // support compilation on Windows 7, we load the function dynamically.
+  typedef BOOL(WINAPI * SetThreadInformation_t)(
+      HANDLE hThread, THREAD_INFORMATION_CLASS ThreadInformationClass,
+      _In_reads_bytes_(ThreadInformationSize) PVOID ThreadInformation,
+      ULONG ThreadInformationSize);
+  static const auto pfnSetThreadInformation =
+      (SetThreadInformation_t)GetProcAddress(
+          GetModuleHandle(TEXT("kernel32.dll")), "SetThreadInformation");
+
+  if (pfnSetThreadInformation) {
+    auto setThreadInformation = [](ULONG ControlMaskAndStateMask) {
+      THREAD_POWER_THROTTLING_STATE state{};
+      state.Version = THREAD_POWER_THROTTLING_CURRENT_VERSION;
+      state.ControlMask = ControlMask;
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aganea wrote:

You need to change `ControlMask` for `ControlMaskAndStateMask` and same below, `StateMask` for `ControlMaskAndStateMask`.

https://github.com/llvm/llvm-project/pull/148797