Merge pull request #13390 from stephentoub/avtmbcreate

Remove overhead from AsyncValueTaskMethodBuilder.Create

Author: stephentoub

src/mscorlib/shared/System/Runtime/CompilerServices/AsyncValueTaskMethodBuilder.cs

@@ -25,7 +25,7 @@ public struct AsyncValueTaskMethodBuilder<TResult>
         /// <summary>Creates an instance of the <see cref="AsyncValueTaskMethodBuilder{TResult}"/> struct.</summary>
         /// <returns>The initialized instance.</returns>
         public static AsyncValueTaskMethodBuilder<TResult> Create() =>
-            new AsyncValueTaskMethodBuilder<TResult>() { _methodBuilder = AsyncTaskMethodBuilder<TResult>.Create() };
+            default(AsyncValueTaskMethodBuilder<TResult>);
 
         /// <summary>Begins running the builder with the associated state machine.</summary>
         /// <typeparam name="TStateMachine">The type of the state machine.</typeparam>

src/mscorlib/src/System/Runtime/CompilerServices/AsyncMethodBuilder.cs

@@ -431,8 +431,9 @@ public struct AsyncTaskMethodBuilder<TResult>
         public static AsyncTaskMethodBuilder<TResult> Create()
         {
             return default(AsyncTaskMethodBuilder<TResult>);
-            // NOTE:  If this method is ever updated to perform more initialization,
-            //        ATMB.Create must also be updated to call this Create method.
+            // NOTE: If this method is ever updated to perform more initialization,
+            //       other Create methods like AsyncTaskMethodBuilder.Create and
+            //       AsyncValueTaskMethodBuilder.Create must be updated to call this.
         }
 
         /// <summary>Initiates the builder's execution with the associated state machine.</summary>