Merge ThreadTasks into ThreadState, remove ThreadTasks (#127884)

`ThreadTasks` was a single-entry enum (`TT_CleanupSyncBlock`) backed by
a separate `m_ThreadTasks` field on `Thread`, even though `ThreadState`
had an unused bit (`0x00000020`) and already supported atomic set/reset
via `InterlockedOr`/`InterlockedAnd` on `m_State`. The old code even
contained a TODO noting the two should probably be merged.

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: jkotas <6668460+jkotas@users.noreply.github.com>
Co-authored-by: Jan Kotas <jkotas@microsoft.com>

Author: Copilot

src/coreclr/vm/threads.cpp

@@ -1290,11 +1290,9 @@ Thread::Thread()
     m_fHasDeadThreadBeenConsideredForGCTrigger = false;
     m_TraceCallCount = 0;
     m_ThrewControlForThread = 0;
-    m_ThreadTasks = (ThreadTasks)0;
 
-    // The state and the tasks must be 32-bit aligned for atomicity to be guaranteed.
+    // The state must be 32-bit aligned for atomicity to be guaranteed.
     _ASSERTE((((size_t) &m_State) & 3) == 0);
-    _ASSERTE((((size_t) &m_ThreadTasks) & 3) == 0);
 
     // On all callbacks, call the trap code, which we now have
     // wired to cause a GC.  Thus we will do a GC on all Transition Frame Transitions (and more).

src/coreclr/vm/threads.h

@@ -511,7 +511,7 @@ class Thread
         TS_DebugSuspendPending    = 0x00000008,    // Is the debugger suspending threads?
         TS_GCOnTransitions        = 0x00000010,    // Force a GC on stub transitions (GCStress only)
 
-        // unused                 = 0x00000020,
+        TS_SyncBlockCleanup       = 0x00000020,    // The synch block needs to be cleaned up.
 
         TS_ExecutingOnAltStack    = 0x00000040,    // Runtime is executing on an alternate stack located anywhere in the memory
 
@@ -570,17 +570,8 @@ class Thread
         TS_CatchAtSafePoint = (TS_AbortRequested | TS_DebugSuspendPending | TS_GCOnTransitions),
     };
 
-    // Thread flags that aren't really states in themselves but rather things the thread
-    // has to do.
-    enum ThreadTasks
-    {
-        TT_CleanupSyncBlock       = 0x00000001, // The synch block needs to be cleaned up.
-    };
-
     // Thread flags that have no concurrency issues (i.e., they are only manipulated by the owning thread). Use these
     // state flags when you have a new thread state that doesn't belong in the ThreadState enum above.
-    //
-    // <TODO>@TODO: its possible that the ThreadTasks from above and these flags should be merged.</TODO>
     enum ThreadStateNoConcurrency
     {
         TSNC_Unknown                    = 0x00000000, // threads are initialized this way
@@ -710,19 +701,19 @@ class Thread
     DWORD RequireSyncBlockCleanup()
     {
         LIMITED_METHOD_CONTRACT;
-        return (m_ThreadTasks & TT_CleanupSyncBlock);
+        return (m_State & TS_SyncBlockCleanup);
     }
 
     void SetSyncBlockCleanup()
     {
         LIMITED_METHOD_CONTRACT;
-        InterlockedOr((LONG*)&m_ThreadTasks, TT_CleanupSyncBlock);
+        InterlockedOr((LONG*)&m_State, TS_SyncBlockCleanup);
     }
 
     void ResetSyncBlockCleanup()
     {
         LIMITED_METHOD_CONTRACT;
-        InterlockedAnd((LONG*)&m_ThreadTasks, ~TT_CleanupSyncBlock);
+        InterlockedAnd((LONG*)&m_State, ~TS_SyncBlockCleanup);
     }
 
 #ifdef FEATURE_COMINTEROP_APARTMENT_SUPPORT
@@ -915,9 +906,6 @@ class Thread
 
     inline TypeHandle GetTHAllocContextObj() {LIMITED_METHOD_CONTRACT; return m_thAllocContextObj; }
 
-    // Flags used to indicate tasks the thread has to do.
-    ThreadTasks          m_ThreadTasks;
-
     // Flags for thread states that have no concurrency issues.
     ThreadStateNoConcurrency m_StateNC;