Remove boxing for awaited custom awaiters

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

@@ -223,6 +223,8 @@ private ref struct RuntimeAsyncStackState
             public INotifyCompletion? Notifier;
             public ValueTaskSourceContinuation? ValueTaskSourceContinuation;
             public RuntimeAsyncTaskContinuation? TaskContinuation;
+            public delegate*<Continuation, int, Action, void> AwaiterContinuation;
+            public int AwaiterOffset;
 
             // When we suspend in the leaf, the contexts are captured into these fields.
             public ExecutionContext? LeafExecutionContext;
@@ -265,6 +267,8 @@ public void CaptureContexts()
             [NonVersionable]
             public void Push(RuntimeAsyncStackState* stackState)
             {
+                stackState->AwaiterContinuation = null;
+                stackState->AwaiterOffset = 0;
                 stackState->Next = StackState;
                 StackState = stackState;
                 CurrentThread ??= Thread.CurrentThread;
@@ -805,7 +809,15 @@ internal unsafe bool HandleSuspended(ref RuntimeAsyncAwaitState state)
 
                 try
                 {
-                    if (stackState->CriticalNotifier is { } critNotifier)
+                    if (stackState->AwaiterContinuation != null)
+                    {
+                        // The awaiter is stored in the continuation for the caller of
+                        // AwaitAwaiterInContinuation or UnsafeAwaitAwaiterInContinuation.
+                        Debug.Assert((headContinuation.Flags & ContinuationFlags.AllContinuationFlags) == 0);
+                        stackState->AwaiterContinuation(
+                            headContinuation, stackState->AwaiterOffset, GetContinuationAction());
+                    }
+                    else if (stackState->CriticalNotifier is { } critNotifier)
                     {
                         // Result of async call to AwaitAwaiter or UnsafeAwaitAwaiter.
                         // These never have special continuation context handling.

src/coreclr/inc/corinfo.h

@@ -3154,6 +3154,14 @@ class ICorStaticInfo
     // instantiation argument that must be passed to the await call.
     virtual CORINFO_METHOD_HANDLE getAwaitReturnCall(CORINFO_METHOD_HANDLE callerHandle, CORINFO_CONTEXT_HANDLE* contextHandle, CORINFO_LOOKUP* instArg) = 0;
 
+    virtual CORINFO_METHOD_HANDLE getAwaitAwaiterInContinuationCall(
+        CORINFO_METHOD_HANDLE callerHandle,
+        CORINFO_SIG_INFO* callSig,
+        bool isUnsafe,
+        CORINFO_CONTEXT_HANDLE* contextHandle,
+        CORINFO_LOOKUP* instArg
+    ) = 0;
+
     /*********************************************************************************/
     //
     // Diagnostic methods

src/coreclr/inc/icorjitinfoimpl_generated.h

@@ -503,6 +503,13 @@ CORINFO_METHOD_HANDLE getAwaitReturnCall(
           CORINFO_CONTEXT_HANDLE* contextHandle,
           CORINFO_LOOKUP* instArg) override;
 
+CORINFO_METHOD_HANDLE getAwaitAwaiterInContinuationCall(
+          CORINFO_METHOD_HANDLE callerHandle,
+          CORINFO_SIG_INFO* callSig,
+          bool isUnsafe,
+          CORINFO_CONTEXT_HANDLE* contextHandle,
+          CORINFO_LOOKUP* instArg) override;
+
 mdMethodDef getMethodDefFromMethod(
           CORINFO_METHOD_HANDLE hMethod) override;
 

src/coreclr/inc/jiteeversionguid.h

@@ -37,11 +37,11 @@
 
 #include <minipal/guid.h>
 
-constexpr GUID JITEEVersionIdentifier = { /* 5bb9b1e5-9941-4762-a195-351b6a736588 */
-    0x5bb9b1e5,
-    0x9941,
-    0x4762,
-    {0xa1, 0x95, 0x35, 0x1b, 0x6a, 0x73, 0x65, 0x88}
+constexpr GUID JITEEVersionIdentifier = { /* 364f7f40-1feb-4b18-bc70-a3cb6481665b */
+    0x364f7f40,
+    0x1feb,
+    0x4b18,
+    {0xbc, 0x70, 0xa3, 0xcb, 0x64, 0x81, 0x66, 0x5b}
   };
 
 #endif // JIT_EE_VERSIONING_GUID_H

src/coreclr/jit/ICorJitInfo_names_generated.h

@@ -125,6 +125,7 @@ DEF_CLR_API(runWithSPMIErrorTrap)
 DEF_CLR_API(getEEInfo)
 DEF_CLR_API(getAsyncInfo)
 DEF_CLR_API(getAwaitReturnCall)
+DEF_CLR_API(getAwaitAwaiterInContinuationCall)
 DEF_CLR_API(getMethodDefFromMethod)
 DEF_CLR_API(printMethodName)
 DEF_CLR_API(getMethodNameFromMetadata)

src/coreclr/jit/ICorJitInfo_wrapper_generated.hpp

@@ -1190,6 +1190,19 @@ CORINFO_METHOD_HANDLE WrapICorJitInfo::getAwaitReturnCall(
     return temp;
 }
 
+CORINFO_METHOD_HANDLE WrapICorJitInfo::getAwaitAwaiterInContinuationCall(
+          CORINFO_METHOD_HANDLE callerHandle,
+          CORINFO_SIG_INFO* callSig,
+          bool isUnsafe,
+          CORINFO_CONTEXT_HANDLE* contextHandle,
+          CORINFO_LOOKUP* instArg)
+{
+    API_ENTER(getAwaitAwaiterInContinuationCall);
+    CORINFO_METHOD_HANDLE temp = wrapHnd->getAwaitAwaiterInContinuationCall(callerHandle, callSig, isUnsafe, contextHandle, instArg);
+    API_LEAVE(getAwaitAwaiterInContinuationCall);
+    return temp;
+}
+
 mdMethodDef WrapICorJitInfo::getMethodDefFromMethod(
           CORINFO_METHOD_HANDLE hMethod)
 {