Save and restore Thread.CurrentThread._synchronizationContext for synchronous runtime async calls (#117725)

This implements the remaining handling: saving and restoring
`Thread.CurrentThread._synchronizationContext` around runtime async calls that
finish synchronously. Lots of trickiness in representing this in the JIT. We
introduce a new "suspended indicator" local that is defined by async calls and
that the front end uses when it expands IR that restores the field.

Plenty of optimization opportunities remaining, including a simple jump
threading optimization we should be able to do to make the suspension indicator
variable disappear in common cases (all cases except when resuming with an
exception).

Author: jakobbotsch

src/coreclr/System.Private.CoreLib/src/System/Runtime/CompilerServices/AsyncHelpers.CoreCLR.cs

@@ -591,19 +591,42 @@ private static ValueTask FinalizeValueTaskReturningThunk(Continuation continuati
         }
 
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        private static void RestoreExecutionContext(ExecutionContext? previousExecutionCtx)
+        private static void RestoreExecutionContext(ExecutionContext? previousExecCtx)
         {
             Thread thread = Thread.CurrentThreadAssumedInitialized;
-            ExecutionContext? currentExecutionCtx = thread._executionContext;
-            if (previousExecutionCtx != currentExecutionCtx)
+            ExecutionContext? currentExecCtx = thread._executionContext;
+            if (previousExecCtx != currentExecCtx)
             {
-                ExecutionContext.RestoreChangedContextToThread(thread, previousExecutionCtx, currentExecutionCtx);
+                ExecutionContext.RestoreChangedContextToThread(thread, previousExecCtx, currentExecCtx);
             }
         }
 
-        private static void CaptureContinuationContext(ref object context, ref CorInfoContinuationFlags flags)
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static void CaptureContexts(out ExecutionContext? execCtx, out SynchronizationContext? syncCtx)
+        {
+            Thread thread = Thread.CurrentThreadAssumedInitialized;
+            execCtx = thread._executionContext;
+            syncCtx = thread._synchronizationContext;
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static void RestoreContexts(bool suspended, ExecutionContext? previousExecCtx, SynchronizationContext? previousSyncCtx)
+        {
+            Thread thread = Thread.CurrentThreadAssumedInitialized;
+            if (!suspended && previousSyncCtx != thread._synchronizationContext)
+            {
+                thread._synchronizationContext = previousSyncCtx;
+            }
+
+            ExecutionContext? currentExecCtx = thread._executionContext;
+            if (previousExecCtx != currentExecCtx)
+            {
+                ExecutionContext.RestoreChangedContextToThread(thread, previousExecCtx, currentExecCtx);
+            }
+        }
+
+        private static void CaptureContinuationContext(SynchronizationContext syncCtx, ref object context, ref CorInfoContinuationFlags flags)
         {
-            SynchronizationContext? syncCtx = Thread.CurrentThreadAssumedInitialized._synchronizationContext;
             if (syncCtx != null && syncCtx.GetType() != typeof(SynchronizationContext))
             {
                 flags |= CorInfoContinuationFlags.CORINFO_CONTINUATION_CONTINUE_ON_CAPTURED_SYNCHRONIZATION_CONTEXT;

src/coreclr/inc/corinfo.h

@@ -1747,6 +1747,8 @@ struct CORINFO_ASYNC_INFO
     // Method handle for AsyncHelpers.RestoreExecutionContext
     CORINFO_METHOD_HANDLE restoreExecutionContextMethHnd;
     CORINFO_METHOD_HANDLE captureContinuationContextMethHnd;
+    CORINFO_METHOD_HANDLE captureContextsMethHnd;
+    CORINFO_METHOD_HANDLE restoreContextsMethHnd;
 };
 
 // Flags passed from JIT to runtime.

src/coreclr/inc/jiteeversionguid.h

@@ -37,11 +37,11 @@
 
 #include <minipal/guid.h>
 
-constexpr GUID JITEEVersionIdentifier = { /* d24a67e0-9e57-4c9e-ad31-5785df2526f2 */
-    0xd24a67e0,
-    0x9e57,
-    0x4c9e,
-    {0xad, 0x31, 0x57, 0x85, 0xdf, 0x25, 0x26, 0xf2}
+constexpr GUID JITEEVersionIdentifier = { /* 2d40ec46-2e41-4a8b-8349-3c1267b95821 */
+    0x2d40ec46,
+    0x2e41,
+    0x4a8b,
+    {0x83, 0x49, 0x3c, 0x12, 0x67, 0xb9, 0x58, 0x21}
   };
 
 #endif // JIT_EE_VERSIONING_GUID_H