JIT: Add support for async variant delegate GDV

src/coreclr/jit/gentree.cpp

@@ -1784,6 +1784,39 @@ CallArg* CallArgs::InsertInstParam(Compiler* comp, GenTree* node)
     }
 }
 
+//---------------------------------------------------------------
+// InsertAsyncContinuation: Insert async continuation argument.
+//
+// Parameters:
+//   comp         - The compiler.
+//   node         - The IR node for the async continuation argument.
+//
+// Returns:
+//   The created representative for the argument.
+//
+CallArg* CallArgs::InsertAsyncContinuation(Compiler* comp, GenTree* node)
+{
+    NewCallArg newArg = NewCallArg::Primitive(node).WellKnown(WellKnownArg::AsyncContinuation);
+    assert(FindWellKnownArg(WellKnownArg::InstParam) == nullptr);
+
+    if (Target::g_tgtArgOrder == Target::ARG_ORDER_R2L)
+    {
+        CallArg* retBufferArg = GetRetBufferArg();
+        if (retBufferArg != nullptr)
+        {
+            return InsertAfter(comp, retBufferArg, newArg);
+        }
+        else
+        {
+            return InsertAfterThisOrFirst(comp, newArg);
+        }
+    }
+    else
+    {
+        return PushBack(comp, newArg);
+    }
+}
+
 //---------------------------------------------------------------
 // InsertAfterThisOrFirst: Insert an argument after 'this' if the call has a
 //                         'this' argument, or otherwise first.

src/coreclr/jit/gentree.h

@@ -4992,6 +4992,7 @@ class CallArgs
     CallArg* InsertAfter(Compiler* comp, CallArg* after, const NewCallArg& arg);
     CallArg* InsertAfterUnchecked(Compiler* comp, CallArg* after, const NewCallArg& arg);
     CallArg* InsertInstParam(Compiler* comp, GenTree* node);
+    CallArg* InsertAsyncContinuation(Compiler* comp, GenTree* node);
     CallArg* InsertAfterThisOrFirst(Compiler* comp, const NewCallArg& arg);
     void     PushLateBack(CallArg* arg);
     void     Remove(CallArg* arg);

src/coreclr/jit/importercalls.cpp

@@ -7049,24 +7049,10 @@ void Compiler::impSetupAsyncCall(GenTreeCall* call, OPCODE opcode, unsigned pref
 // Arguments:
 //    call - The call
 //
-// Remarks:
-//   Should be called before the 'this' arg is inserted, but after other IL args
-//   have been inserted.
-//
 void Compiler::impInsertAsyncContinuationForLdvirtftnCall(GenTreeCall* call)
 {
-    assert(call->AsCall()->IsAsync());
-
-    if (Target::g_tgtArgOrder == Target::ARG_ORDER_R2L)
-    {
-        call->AsCall()->gtArgs.PushFront(this, NewCallArg::Primitive(gtNewNull(), TYP_REF)
-                                                   .WellKnown(WellKnownArg::AsyncContinuation));
-    }
-    else
-    {
-        call->AsCall()->gtArgs.PushBack(this, NewCallArg::Primitive(gtNewNull(), TYP_REF)
-                                                  .WellKnown(WellKnownArg::AsyncContinuation));
-    }
+    assert(call->IsAsync());
+    call->gtArgs.InsertAsyncContinuation(this, gtNewNull());
 }
 
 //------------------------------------------------------------------------