From 450541bbd97095e162b0d88b50ba3c53bcd0a3b4 Mon Sep 17 00:00:00 2001
From: Ben Adams <thundercat@illyriad.co.uk>
Date: Thu, 30 May 2019 15:55:07 +0100
Subject: [PATCH] Code improves

---
 .../AsyncIteratorMethodBuilder.cs             |  6 ++--
 .../AsyncValueTaskMethodBuilder.cs            | 28 ++++++++-----------
 2 files changed, 15 insertions(+), 19 deletions(-)

diff --git a/src/System.Private.CoreLib/shared/System/Runtime/CompilerServices/AsyncIteratorMethodBuilder.cs b/src/System.Private.CoreLib/shared/System/Runtime/CompilerServices/AsyncIteratorMethodBuilder.cs
index 42df1078e71f..fee9d40cdfcf 100644
--- a/src/System.Private.CoreLib/shared/System/Runtime/CompilerServices/AsyncIteratorMethodBuilder.cs
+++ b/src/System.Private.CoreLib/shared/System/Runtime/CompilerServices/AsyncIteratorMethodBuilder.cs
@@ -13,10 +13,10 @@ namespace System.Runtime.CompilerServices
     public struct AsyncIteratorMethodBuilder
     {
         // AsyncIteratorMethodBuilder is used by the language compiler as part of generating
-        // async iterators. For now, the implementation just wraps AsyncTaskMethodBuilder, as
-        // most of the logic is shared.  However, in the future this could be changed and
+        // async iterators. For now, the implementation just forwards to AsyncMethodBuilderCore, 
+        // as most of the logic is shared.  However, in the future this could be changed and
         // optimized.  For example, we do need to allocate an object (once) to flow state like
-        // ExecutionContext, which AsyncTaskMethodBuilder handles, but it handles it by
+        // ExecutionContext, which AsyncMethodBuilderCore handles, but it handles it by
         // allocating a Task-derived object.  We could optimize this further by removing
         // the Task from the hierarchy, but in doing so we'd also lose a variety of optimizations
         // related to it, so we'd need to replicate all of those optimizations (e.g. storing
diff --git a/src/System.Private.CoreLib/shared/System/Runtime/CompilerServices/AsyncValueTaskMethodBuilder.cs b/src/System.Private.CoreLib/shared/System/Runtime/CompilerServices/AsyncValueTaskMethodBuilder.cs
index 6fe1dab75d5d..065bce7ec94e 100644
--- a/src/System.Private.CoreLib/shared/System/Runtime/CompilerServices/AsyncValueTaskMethodBuilder.cs
+++ b/src/System.Private.CoreLib/shared/System/Runtime/CompilerServices/AsyncValueTaskMethodBuilder.cs
@@ -63,17 +63,15 @@ public ValueTask Task
         {
             get
             {
-                if (ReferenceEquals(m_task, System.Threading.Tasks.Task.s_cachedCompleted))
-                {
-                    return default;
-                }
-                else
-                {
-                    return new ValueTask(m_task ?? AsyncMethodBuilderCore.InitializeTaskAsPromise(ref m_task!)); // TODO-NULLABLE: Remove ! when nullable attributes are respected
-                }
+                return ReferenceEquals(m_task, System.Threading.Tasks.Task.s_cachedCompleted) ? 
+                    default : 
+                    CreateValueTask(ref m_task);
             }
         }
 
+        [MethodImpl(MethodImplOptions.NoInlining)]
+        private static ValueTask CreateValueTask(ref Task<VoidTaskResult> task) => new ValueTask(task ?? AsyncMethodBuilderCore.InitializeTaskAsPromise(ref task!)); // TODO-NULLABLE: Remove ! when nullable attributes are respected
+
         /// <summary>Schedules the state machine to proceed to the next action when the specified awaiter completes.</summary>
         /// <typeparam name="TAwaiter">The type of the awaiter.</typeparam>
         /// <typeparam name="TStateMachine">The type of the state machine.</typeparam>
@@ -158,17 +156,15 @@ public ValueTask<TResult> Task
         {
             get
             {
-                if (ReferenceEquals(s_haveResultSentinel, m_task))
-                {
-                    return new ValueTask<TResult>(_result);
-                }
-                else
-                {
-                    return new ValueTask<TResult>(m_task ?? AsyncMethodBuilderCore.InitializeTaskAsPromise(ref m_task!)); // TODO-NULLABLE: Remove ! when nullable attributes are respected
-                }
+                return ReferenceEquals(s_haveResultSentinel, m_task) ?
+                    new ValueTask<TResult>(_result) :
+                    CreateValueTask(ref m_task);
             }
         }
 
+        [MethodImpl(MethodImplOptions.NoInlining)]
+        private static ValueTask<TResult> CreateValueTask(ref Task<TResult> task) => new ValueTask<TResult>(task ?? AsyncMethodBuilderCore.InitializeTaskAsPromise(ref task!)); // TODO-NULLABLE: Remove ! when nullable attributes are respected
+
         /// <summary>Schedules the state machine to proceed to the next action when the specified awaiter completes.</summary>
         /// <typeparam name="TAwaiter">The type of the awaiter.</typeparam>
         /// <typeparam name="TStateMachine">The type of the state machine.</typeparam>