From 95e693609c24954b043a2d9e40388af6e798b23d Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Wed, 27 May 2026 06:56:50 +0000
Subject: [PATCH 1/4] Remove BypassReadyToRun attributes from AsyncHelpers
 files

Co-authored-by: jakobbotsch <7887810+jakobbotsch@users.noreply.github.com>
---
 .../Runtime/CompilerServices/AsyncHelpers.CoreCLR.cs |  8 --------
 .../System/Runtime/CompilerServices/AsyncHelpers.cs  | 12 ------------
 2 files changed, 20 deletions(-)

diff --git a/src/coreclr/System.Private.CoreLib/src/System/Runtime/CompilerServices/AsyncHelpers.CoreCLR.cs b/src/coreclr/System.Private.CoreLib/src/System/Runtime/CompilerServices/AsyncHelpers.CoreCLR.cs
index 64169a699065f4..5cd0a8e4298491 100644
--- a/src/coreclr/System.Private.CoreLib/src/System/Runtime/CompilerServices/AsyncHelpers.CoreCLR.cs
+++ b/src/coreclr/System.Private.CoreLib/src/System/Runtime/CompilerServices/AsyncHelpers.CoreCLR.cs
@@ -349,7 +349,6 @@ private static unsafe Continuation AllocContinuationClass(Continuation prevConti
         }
 #endif
 
-        [BypassReadyToRun]
         [MethodImpl(MethodImplOptions.NoInlining | MethodImplOptions.Async)]
         private static unsafe void AwaitTask(Task task, ConfigureAwaitOptions options)
         {
@@ -384,7 +383,6 @@ private static unsafe void AwaitTask(Task task, ConfigureAwaitOptions options)
             AsyncSuspend(taskCont);
         }
 
-        [BypassReadyToRun]
         [MethodImpl(MethodImplOptions.NoInlining | MethodImplOptions.Async)]
         private static unsafe T AwaitTask<T>(Task<T> task, ConfigureAwaitOptions options)
         {
@@ -430,7 +428,6 @@ private static unsafe T AwaitTask<T>(Task<T> task, ConfigureAwaitOptions options
         /// awaiting a completion of an underlying Task or ValueTaskSource.
         /// </summary>
         /// <param name="valueTask">ValueTask whose completion we are awaiting.</param>
-        [BypassReadyToRun]
         [MethodImpl(MethodImplOptions.NoInlining | MethodImplOptions.Async)]
         private static unsafe void TransparentAwaitValueTask(ValueTask valueTask)
         {
@@ -479,7 +476,6 @@ private static unsafe void TransparentAwaitValueTask(ValueTask valueTask)
             AsyncSuspend(nextCont);
         }
 
-        [BypassReadyToRun]
         [MethodImpl(MethodImplOptions.NoInlining | MethodImplOptions.Async)]
         private static unsafe void AwaitValueTaskSource(IValueTaskSource source, short token, bool continueOnCapturedContext)
         {
@@ -516,7 +512,6 @@ private static unsafe void AwaitValueTaskSource(IValueTaskSource source, short t
             AsyncSuspend(vtsCont);
         }
 
-        [BypassReadyToRun]
         [MethodImpl(MethodImplOptions.NoInlining | MethodImplOptions.Async)]
         private static unsafe T TransparentAwaitValueTaskOfT<T>(ValueTask<T> valueTask)
         {
@@ -565,7 +560,6 @@ private static unsafe T TransparentAwaitValueTaskOfT<T>(ValueTask<T> valueTask)
             return default!;
         }
 
-        [BypassReadyToRun]
         [MethodImpl(MethodImplOptions.NoInlining | MethodImplOptions.Async)]
         private static unsafe T AwaitValueTaskSource<T>(IValueTaskSource<T> source, short token, bool continueOnCapturedContext)
         {
@@ -607,7 +601,6 @@ private static unsafe T AwaitValueTaskSource<T>(IValueTaskSource<T> source, shor
         /// Used by internal thunks that implement awaiting on Task.
         /// </summary>
         /// <param name="task">Task whose completion we are awaiting.</param>
-        [BypassReadyToRun]
         [MethodImpl(MethodImplOptions.NoInlining | MethodImplOptions.Async)]
         private static unsafe void TransparentAwait(Task task)
         {
@@ -637,7 +630,6 @@ private static unsafe void TransparentAwait(Task task)
         /// Used by internal thunks that implement awaiting on Task.
         /// </summary>
         /// <param name="task">Task whose completion we are awaiting.</param>
-        [BypassReadyToRun]
         [MethodImpl(MethodImplOptions.NoInlining | MethodImplOptions.Async)]
         private static unsafe T TransparentAwaitOfT<T>(Task<T> task)
         {
diff --git a/src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/AsyncHelpers.cs b/src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/AsyncHelpers.cs
index daa89fb6a7a225..63212fdfe6f07e 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/AsyncHelpers.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/AsyncHelpers.cs
@@ -14,7 +14,6 @@ namespace System.Runtime.CompilerServices
     public static partial class AsyncHelpers
     {
 #if CORECLR || NATIVEAOT
-        // "BypassReadyToRun" is until AOT/R2R typesystem has support for MethodImpl.Async
         // Must be NoInlining because we use AsyncSuspend to manufacture an explicit suspension point.
         // It will not capture/restore any local state that is live across it.
 
@@ -23,7 +22,6 @@ public static partial class AsyncHelpers
         /// </summary>
         /// <typeparam name="TAwaiter">The awaiter type.</typeparam>
         /// <param name="awaiter">The awaiter to await.</param>
-        [BypassReadyToRun]
         [MethodImpl(MethodImplOptions.NoInlining | MethodImplOptions.Async)]
         [StackTraceHidden]
         public static unsafe void AwaitAwaiter<TAwaiter>(TAwaiter awaiter) where TAwaiter : INotifyCompletion
@@ -43,7 +41,6 @@ public static unsafe void AwaitAwaiter<TAwaiter>(TAwaiter awaiter) where TAwaite
         /// </summary>
         /// <typeparam name="TAwaiter">The awaiter type.</typeparam>
         /// <param name="awaiter">The awaiter to await.</param>
-        [BypassReadyToRun]
         [MethodImpl(MethodImplOptions.NoInlining | MethodImplOptions.Async)]
         [StackTraceHidden]
         public static unsafe void UnsafeAwaitAwaiter<TAwaiter>(TAwaiter awaiter) where TAwaiter : ICriticalNotifyCompletion
@@ -61,7 +58,6 @@ public static unsafe void UnsafeAwaitAwaiter<TAwaiter>(TAwaiter awaiter) where T
         /// <typeparam name="T">The result type produced by the task.</typeparam>
         /// <param name="task">The task to await.</param>
         [Intrinsic]
-        [BypassReadyToRun]
         [MethodImpl(MethodImplOptions.Async)]
         [StackTraceHidden]
         public static T Await<T>(Task<T> task)
@@ -81,7 +77,6 @@ public static T Await<T>(Task<T> task)
         /// </summary>
         /// <param name="task">The task to await.</param>
         [Intrinsic]
-        [BypassReadyToRun]
         [MethodImpl(MethodImplOptions.Async)]
         [StackTraceHidden]
         public static void Await(Task task)
@@ -102,7 +97,6 @@ public static void Await(Task task)
         /// <typeparam name="T">The result type produced by the value task.</typeparam>
         /// <param name="task">The value task to await.</param>
         [Intrinsic]
-        [BypassReadyToRun]
         [MethodImpl(MethodImplOptions.Async)]
         [StackTraceHidden]
         public static T Await<T>(ValueTask<T> task)
@@ -141,7 +135,6 @@ public static T Await<T>(ValueTask<T> task)
         /// </summary>
         /// <param name="task">The value task to await.</param>
         [Intrinsic]
-        [BypassReadyToRun]
         [MethodImpl(MethodImplOptions.Async)]
         [StackTraceHidden]
         public static void Await(ValueTask task)
@@ -182,7 +175,6 @@ public static void Await(ValueTask task)
         /// </summary>
         /// <param name="configuredAwaitable">The configured awaitable to await.</param>
         [Intrinsic]
-        [BypassReadyToRun]
         [MethodImpl(MethodImplOptions.Async)]
         [StackTraceHidden]
         public static void Await(ConfiguredTaskAwaitable configuredAwaitable)
@@ -206,7 +198,6 @@ public static void Await(ConfiguredTaskAwaitable configuredAwaitable)
         }
 
         [Intrinsic]
-        [BypassReadyToRun]
         [MethodImpl(MethodImplOptions.Async | MethodImplOptions.NoInlining)]
         [StackTraceHidden]
         private static void AwaitTaskWithRareOptions(ConfiguredTaskAwaitable.ConfiguredTaskAwaiter awaiter)
@@ -224,7 +215,6 @@ private static void AwaitTaskWithRareOptions(ConfiguredTaskAwaitable.ConfiguredT
         /// </summary>
         /// <param name="configuredAwaitable">The configured value task awaitable to await.</param>
         [Intrinsic]
-        [BypassReadyToRun]
         [MethodImpl(MethodImplOptions.Async)]
         [StackTraceHidden]
         public static void Await(ConfiguredValueTaskAwaitable configuredAwaitable)
@@ -267,7 +257,6 @@ public static void Await(ConfiguredValueTaskAwaitable configuredAwaitable)
         /// <typeparam name="T">The result type produced by the awaitable.</typeparam>
         /// <param name="configuredAwaitable">The configured awaitable to await.</param>
         [Intrinsic]
-        [BypassReadyToRun]
         [MethodImpl(MethodImplOptions.Async)]
         [StackTraceHidden]
         public static T Await<T>(ConfiguredTaskAwaitable<T> configuredAwaitable)
@@ -292,7 +281,6 @@ public static T Await<T>(ConfiguredTaskAwaitable<T> configuredAwaitable)
         /// <typeparam name="T">The result type produced by the awaitable.</typeparam>
         /// <param name="configuredAwaitable">The configured awaitable to await.</param>
         [Intrinsic]
-        [BypassReadyToRun]
         [MethodImpl(MethodImplOptions.Async)]
         [StackTraceHidden]
         public static T Await<T>(ConfiguredValueTaskAwaitable<T> configuredAwaitable)

From d8f73a3332c3bb35be4c66ae96aba9010e4a85de Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Wed, 27 May 2026 18:20:09 +0000
Subject: [PATCH 2/4] Fix crossgen2 assertion for non-task-returning async
 methods

Co-authored-by: jtschuster <36744439+jtschuster@users.noreply.github.com>
---
 .../tools/Common/Compiler/AsyncMethodVariant.cs      | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/src/coreclr/tools/Common/Compiler/AsyncMethodVariant.cs b/src/coreclr/tools/Common/Compiler/AsyncMethodVariant.cs
index 78b0c9c76b174b..ad0c94de6626d7 100644
--- a/src/coreclr/tools/Common/Compiler/AsyncMethodVariant.cs
+++ b/src/coreclr/tools/Common/Compiler/AsyncMethodVariant.cs
@@ -152,9 +152,20 @@ public static bool IsReturnDroppingAsyncThunk(this MethodDesc method)
 
         public static bool IsAsyncThunk(this MethodDesc method)
         {
+            if (method.IsNonTaskReturningAsyncMethod())
+                return false;
+
             return (method.IsAsyncVariant() ^ method.IsAsync) || method.IsReturnDroppingAsyncThunk();
         }
 
+        public static bool IsNonTaskReturningAsyncMethod(this MethodDesc method)
+        {
+            bool isNonTaskReturningAsyncMethod = method.GetTypicalMethodDefinition() is EcmaMethod && method.IsAsync && !method.Signature.ReturnsTaskOrValueTask();
+            // non-task-returning async methods should only be in corelib
+            Debug.Assert(!isNonTaskReturningAsyncMethod || (method.GetTypicalMethodDefinition() is EcmaMethod methodDef && methodDef.Context.SystemModule == methodDef.Module));
+            return isNonTaskReturningAsyncMethod;
+        }
+
         public static bool IsCompilerGeneratedILBodyForAsync(this MethodDesc method)
         {
             return method.IsAsyncThunk() || method is AsyncResumptionStub;
@@ -163,6 +174,7 @@ public static bool IsCompilerGeneratedILBodyForAsync(this MethodDesc method)
         public static MethodDesc GetAsyncVariant(this MethodDesc method)
         {
             Debug.Assert(!method.IsAsyncVariant());
+            Debug.Assert(!method.IsNonTaskReturningAsyncMethod());
             return ((CompilerTypeSystemContext)method.Context).GetAsyncVariantMethod(method);
         }
 

From e51d2f4f6aab34a29798a1d8af186dc2f8bb7a0a Mon Sep 17 00:00:00 2001
From: Jackson Schuster <36744439+jtschuster@users.noreply.github.com>
Date: Fri, 29 May 2026 13:33:32 -0700
Subject: [PATCH 3/4] Gate BypassReadyToRun on AsyncHelpers by runtime-async
 support

Removing [BypassReadyToRun] crashed crossgen2 on browser-wasm:
REG_ASYNC_CONTINUATION_RET == REG_NA there, so zeroing the continuation
register on a synchronous return tripped genIsValidIntOrFakeReg
(instr.cpp). Keep the attributes on platforms that don't support
runtime-async, and remove them where it is supported.

Mirror the RuntimeAsyncSupported predicate (from
src/libraries/Directory.Build.targets, which the corelib build does not
import) into both corelib csprojs and define RUNTIME_ASYNC_SUPPORTED when
it is true. Wrap each [BypassReadyToRun] in #if !RUNTIME_ASYNC_SUPPORTED.

Verified by building clr.corelib for browser/wasm (attributes retained)
and linux/x64 (attributes removed) and inspecting the emitted metadata.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
---
 .../System.Private.CoreLib.csproj             | 14 ++++++++
 .../CompilerServices/AsyncHelpers.CoreCLR.cs  | 24 +++++++++++++
 .../src/System.Private.CoreLib.csproj         | 14 ++++++++
 .../Runtime/CompilerServices/AsyncHelpers.cs  | 36 +++++++++++++++++++
 4 files changed, 88 insertions(+)

diff --git a/src/coreclr/System.Private.CoreLib/System.Private.CoreLib.csproj b/src/coreclr/System.Private.CoreLib/System.Private.CoreLib.csproj
index 9e02584f4c34f1..6f15ca9dd88e85 100644
--- a/src/coreclr/System.Private.CoreLib/System.Private.CoreLib.csproj
+++ b/src/coreclr/System.Private.CoreLib/System.Private.CoreLib.csproj
@@ -54,6 +54,20 @@
     <DocumentationFile>$(OutputPath)$(MSBuildProjectName).xml</DocumentationFile>
   </PropertyGroup>
 
+  <!-- Mirror the runtime-async support predicate from src/libraries/Directory.Build.targets so the
+       BypassReadyToRun attributes on the MethodImpl.Async helpers can be conditioned on it. -->
+  <PropertyGroup Condition="'$(RuntimeAsyncSupported)' == ''">
+    <RuntimeAsyncSupported Condition="'$(TargetOS)' != 'browser'
+      and '$(TargetOS)' != 'wasi'
+      and '$(TargetOS)' != 'android'
+      and '$(TargetsAppleMobile)' != 'true'
+      and '$(RuntimeFlavor)' != 'Mono'">true</RuntimeAsyncSupported>
+  </PropertyGroup>
+
+  <PropertyGroup>
+    <DefineConstants Condition="'$(RuntimeAsyncSupported)' == 'true'">$(DefineConstants);RUNTIME_ASYNC_SUPPORTED</DefineConstants>
+  </PropertyGroup>
+
   <!-- Platform specific properties -->
   <PropertyGroup Condition="'$(Platform)' == 'x64'">
     <DefineConstants>$(DefineConstants);TARGET_AMD64</DefineConstants>
diff --git a/src/coreclr/System.Private.CoreLib/src/System/Runtime/CompilerServices/AsyncHelpers.CoreCLR.cs b/src/coreclr/System.Private.CoreLib/src/System/Runtime/CompilerServices/AsyncHelpers.CoreCLR.cs
index 5cd0a8e4298491..edcedc14c4ef43 100644
--- a/src/coreclr/System.Private.CoreLib/src/System/Runtime/CompilerServices/AsyncHelpers.CoreCLR.cs
+++ b/src/coreclr/System.Private.CoreLib/src/System/Runtime/CompilerServices/AsyncHelpers.CoreCLR.cs
@@ -349,6 +349,9 @@ private static unsafe Continuation AllocContinuationClass(Continuation prevConti
         }
 #endif
 
+#if !RUNTIME_ASYNC_SUPPORTED
+        [BypassReadyToRun]
+#endif
         [MethodImpl(MethodImplOptions.NoInlining | MethodImplOptions.Async)]
         private static unsafe void AwaitTask(Task task, ConfigureAwaitOptions options)
         {
@@ -383,6 +386,9 @@ private static unsafe void AwaitTask(Task task, ConfigureAwaitOptions options)
             AsyncSuspend(taskCont);
         }
 
+#if !RUNTIME_ASYNC_SUPPORTED
+        [BypassReadyToRun]
+#endif
         [MethodImpl(MethodImplOptions.NoInlining | MethodImplOptions.Async)]
         private static unsafe T AwaitTask<T>(Task<T> task, ConfigureAwaitOptions options)
         {
@@ -428,6 +434,9 @@ private static unsafe T AwaitTask<T>(Task<T> task, ConfigureAwaitOptions options
         /// awaiting a completion of an underlying Task or ValueTaskSource.
         /// </summary>
         /// <param name="valueTask">ValueTask whose completion we are awaiting.</param>
+#if !RUNTIME_ASYNC_SUPPORTED
+        [BypassReadyToRun]
+#endif
         [MethodImpl(MethodImplOptions.NoInlining | MethodImplOptions.Async)]
         private static unsafe void TransparentAwaitValueTask(ValueTask valueTask)
         {
@@ -476,6 +485,9 @@ private static unsafe void TransparentAwaitValueTask(ValueTask valueTask)
             AsyncSuspend(nextCont);
         }
 
+#if !RUNTIME_ASYNC_SUPPORTED
+        [BypassReadyToRun]
+#endif
         [MethodImpl(MethodImplOptions.NoInlining | MethodImplOptions.Async)]
         private static unsafe void AwaitValueTaskSource(IValueTaskSource source, short token, bool continueOnCapturedContext)
         {
@@ -512,6 +524,9 @@ private static unsafe void AwaitValueTaskSource(IValueTaskSource source, short t
             AsyncSuspend(vtsCont);
         }
 
+#if !RUNTIME_ASYNC_SUPPORTED
+        [BypassReadyToRun]
+#endif
         [MethodImpl(MethodImplOptions.NoInlining | MethodImplOptions.Async)]
         private static unsafe T TransparentAwaitValueTaskOfT<T>(ValueTask<T> valueTask)
         {
@@ -560,6 +575,9 @@ private static unsafe T TransparentAwaitValueTaskOfT<T>(ValueTask<T> valueTask)
             return default!;
         }
 
+#if !RUNTIME_ASYNC_SUPPORTED
+        [BypassReadyToRun]
+#endif
         [MethodImpl(MethodImplOptions.NoInlining | MethodImplOptions.Async)]
         private static unsafe T AwaitValueTaskSource<T>(IValueTaskSource<T> source, short token, bool continueOnCapturedContext)
         {
@@ -601,6 +619,9 @@ private static unsafe T AwaitValueTaskSource<T>(IValueTaskSource<T> source, shor
         /// Used by internal thunks that implement awaiting on Task.
         /// </summary>
         /// <param name="task">Task whose completion we are awaiting.</param>
+#if !RUNTIME_ASYNC_SUPPORTED
+        [BypassReadyToRun]
+#endif
         [MethodImpl(MethodImplOptions.NoInlining | MethodImplOptions.Async)]
         private static unsafe void TransparentAwait(Task task)
         {
@@ -630,6 +651,9 @@ private static unsafe void TransparentAwait(Task task)
         /// Used by internal thunks that implement awaiting on Task.
         /// </summary>
         /// <param name="task">Task whose completion we are awaiting.</param>
+#if !RUNTIME_ASYNC_SUPPORTED
+        [BypassReadyToRun]
+#endif
         [MethodImpl(MethodImplOptions.NoInlining | MethodImplOptions.Async)]
         private static unsafe T TransparentAwaitOfT<T>(Task<T> task)
         {
diff --git a/src/coreclr/nativeaot/System.Private.CoreLib/src/System.Private.CoreLib.csproj b/src/coreclr/nativeaot/System.Private.CoreLib/src/System.Private.CoreLib.csproj
index ffa900b4b08198..fd996d3adf5658 100644
--- a/src/coreclr/nativeaot/System.Private.CoreLib/src/System.Private.CoreLib.csproj
+++ b/src/coreclr/nativeaot/System.Private.CoreLib/src/System.Private.CoreLib.csproj
@@ -46,6 +46,20 @@
     <Features>$(Features);runtime-async=on</Features>
   </PropertyGroup>
 
+  <!-- Mirror the runtime-async support predicate from src/libraries/Directory.Build.targets so the
+       BypassReadyToRun attributes on the MethodImpl.Async helpers can be conditioned on it. -->
+  <PropertyGroup Condition="'$(RuntimeAsyncSupported)' == ''">
+    <RuntimeAsyncSupported Condition="'$(TargetOS)' != 'browser'
+      and '$(TargetOS)' != 'wasi'
+      and '$(TargetOS)' != 'android'
+      and '$(TargetsAppleMobile)' != 'true'
+      and '$(RuntimeFlavor)' != 'Mono'">true</RuntimeAsyncSupported>
+  </PropertyGroup>
+
+  <PropertyGroup>
+    <DefineConstants Condition="'$(RuntimeAsyncSupported)' == 'true'">$(DefineConstants);RUNTIME_ASYNC_SUPPORTED</DefineConstants>
+  </PropertyGroup>
+
   <!-- Sources -->
   <ItemGroup>
     <Compile Include="$(CompilerCommonPath)\Internal\Runtime\DehydratedData.cs">
diff --git a/src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/AsyncHelpers.cs b/src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/AsyncHelpers.cs
index 63212fdfe6f07e..c38f104620d8dc 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/AsyncHelpers.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/AsyncHelpers.cs
@@ -14,6 +14,9 @@ namespace System.Runtime.CompilerServices
     public static partial class AsyncHelpers
     {
 #if CORECLR || NATIVEAOT
+        // "BypassReadyToRun" keeps these MethodImpl.Async helpers out of AOT/R2R images on platforms
+        // that don't support runtime-async (RUNTIME_ASYNC_SUPPORTED is not defined there). On those
+        // platforms the JIT cannot emit code for runtime-async returns, so the helpers must be JITted.
         // Must be NoInlining because we use AsyncSuspend to manufacture an explicit suspension point.
         // It will not capture/restore any local state that is live across it.
 
@@ -22,6 +25,9 @@ public static partial class AsyncHelpers
         /// </summary>
         /// <typeparam name="TAwaiter">The awaiter type.</typeparam>
         /// <param name="awaiter">The awaiter to await.</param>
+#if !RUNTIME_ASYNC_SUPPORTED
+        [BypassReadyToRun]
+#endif
         [MethodImpl(MethodImplOptions.NoInlining | MethodImplOptions.Async)]
         [StackTraceHidden]
         public static unsafe void AwaitAwaiter<TAwaiter>(TAwaiter awaiter) where TAwaiter : INotifyCompletion
@@ -41,6 +47,9 @@ public static unsafe void AwaitAwaiter<TAwaiter>(TAwaiter awaiter) where TAwaite
         /// </summary>
         /// <typeparam name="TAwaiter">The awaiter type.</typeparam>
         /// <param name="awaiter">The awaiter to await.</param>
+#if !RUNTIME_ASYNC_SUPPORTED
+        [BypassReadyToRun]
+#endif
         [MethodImpl(MethodImplOptions.NoInlining | MethodImplOptions.Async)]
         [StackTraceHidden]
         public static unsafe void UnsafeAwaitAwaiter<TAwaiter>(TAwaiter awaiter) where TAwaiter : ICriticalNotifyCompletion
@@ -58,6 +67,9 @@ public static unsafe void UnsafeAwaitAwaiter<TAwaiter>(TAwaiter awaiter) where T
         /// <typeparam name="T">The result type produced by the task.</typeparam>
         /// <param name="task">The task to await.</param>
         [Intrinsic]
+#if !RUNTIME_ASYNC_SUPPORTED
+        [BypassReadyToRun]
+#endif
         [MethodImpl(MethodImplOptions.Async)]
         [StackTraceHidden]
         public static T Await<T>(Task<T> task)
@@ -77,6 +89,9 @@ public static T Await<T>(Task<T> task)
         /// </summary>
         /// <param name="task">The task to await.</param>
         [Intrinsic]
+#if !RUNTIME_ASYNC_SUPPORTED
+        [BypassReadyToRun]
+#endif
         [MethodImpl(MethodImplOptions.Async)]
         [StackTraceHidden]
         public static void Await(Task task)
@@ -97,6 +112,9 @@ public static void Await(Task task)
         /// <typeparam name="T">The result type produced by the value task.</typeparam>
         /// <param name="task">The value task to await.</param>
         [Intrinsic]
+#if !RUNTIME_ASYNC_SUPPORTED
+        [BypassReadyToRun]
+#endif
         [MethodImpl(MethodImplOptions.Async)]
         [StackTraceHidden]
         public static T Await<T>(ValueTask<T> task)
@@ -135,6 +153,9 @@ public static T Await<T>(ValueTask<T> task)
         /// </summary>
         /// <param name="task">The value task to await.</param>
         [Intrinsic]
+#if !RUNTIME_ASYNC_SUPPORTED
+        [BypassReadyToRun]
+#endif
         [MethodImpl(MethodImplOptions.Async)]
         [StackTraceHidden]
         public static void Await(ValueTask task)
@@ -175,6 +196,9 @@ public static void Await(ValueTask task)
         /// </summary>
         /// <param name="configuredAwaitable">The configured awaitable to await.</param>
         [Intrinsic]
+#if !RUNTIME_ASYNC_SUPPORTED
+        [BypassReadyToRun]
+#endif
         [MethodImpl(MethodImplOptions.Async)]
         [StackTraceHidden]
         public static void Await(ConfiguredTaskAwaitable configuredAwaitable)
@@ -198,6 +222,9 @@ public static void Await(ConfiguredTaskAwaitable configuredAwaitable)
         }
 
         [Intrinsic]
+#if !RUNTIME_ASYNC_SUPPORTED
+        [BypassReadyToRun]
+#endif
         [MethodImpl(MethodImplOptions.Async | MethodImplOptions.NoInlining)]
         [StackTraceHidden]
         private static void AwaitTaskWithRareOptions(ConfiguredTaskAwaitable.ConfiguredTaskAwaiter awaiter)
@@ -215,6 +242,9 @@ private static void AwaitTaskWithRareOptions(ConfiguredTaskAwaitable.ConfiguredT
         /// </summary>
         /// <param name="configuredAwaitable">The configured value task awaitable to await.</param>
         [Intrinsic]
+#if !RUNTIME_ASYNC_SUPPORTED
+        [BypassReadyToRun]
+#endif
         [MethodImpl(MethodImplOptions.Async)]
         [StackTraceHidden]
         public static void Await(ConfiguredValueTaskAwaitable configuredAwaitable)
@@ -257,6 +287,9 @@ public static void Await(ConfiguredValueTaskAwaitable configuredAwaitable)
         /// <typeparam name="T">The result type produced by the awaitable.</typeparam>
         /// <param name="configuredAwaitable">The configured awaitable to await.</param>
         [Intrinsic]
+#if !RUNTIME_ASYNC_SUPPORTED
+        [BypassReadyToRun]
+#endif
         [MethodImpl(MethodImplOptions.Async)]
         [StackTraceHidden]
         public static T Await<T>(ConfiguredTaskAwaitable<T> configuredAwaitable)
@@ -281,6 +314,9 @@ public static T Await<T>(ConfiguredTaskAwaitable<T> configuredAwaitable)
         /// <typeparam name="T">The result type produced by the awaitable.</typeparam>
         /// <param name="configuredAwaitable">The configured awaitable to await.</param>
         [Intrinsic]
+#if !RUNTIME_ASYNC_SUPPORTED
+        [BypassReadyToRun]
+#endif
         [MethodImpl(MethodImplOptions.Async)]
         [StackTraceHidden]
         public static T Await<T>(ConfiguredValueTaskAwaitable<T> configuredAwaitable)

From 0d320a2d04389ba0b86a3ff63d523de86b1edf69 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Wed, 17 Jun 2026 15:17:33 +0000
Subject: [PATCH 4/4] Revert runtime-async gating and disable crossgen for
 InvalidCSharp

Co-authored-by: jakobbotsch <7887810+jakobbotsch@users.noreply.github.com>
---
 .../System.Private.CoreLib.csproj             | 14 --------
 .../CompilerServices/AsyncHelpers.CoreCLR.cs  | 24 -------------
 .../src/System.Private.CoreLib.csproj         | 14 --------
 .../Runtime/CompilerServices/AsyncHelpers.cs  | 36 -------------------
 .../UnmanagedCallersOnly/InvalidCSharp.ilproj |  2 ++
 5 files changed, 2 insertions(+), 88 deletions(-)

diff --git a/src/coreclr/System.Private.CoreLib/System.Private.CoreLib.csproj b/src/coreclr/System.Private.CoreLib/System.Private.CoreLib.csproj
index 6f15ca9dd88e85..9e02584f4c34f1 100644
--- a/src/coreclr/System.Private.CoreLib/System.Private.CoreLib.csproj
+++ b/src/coreclr/System.Private.CoreLib/System.Private.CoreLib.csproj
@@ -54,20 +54,6 @@
     <DocumentationFile>$(OutputPath)$(MSBuildProjectName).xml</DocumentationFile>
   </PropertyGroup>
 
-  <!-- Mirror the runtime-async support predicate from src/libraries/Directory.Build.targets so the
-       BypassReadyToRun attributes on the MethodImpl.Async helpers can be conditioned on it. -->
-  <PropertyGroup Condition="'$(RuntimeAsyncSupported)' == ''">
-    <RuntimeAsyncSupported Condition="'$(TargetOS)' != 'browser'
-      and '$(TargetOS)' != 'wasi'
-      and '$(TargetOS)' != 'android'
-      and '$(TargetsAppleMobile)' != 'true'
-      and '$(RuntimeFlavor)' != 'Mono'">true</RuntimeAsyncSupported>
-  </PropertyGroup>
-
-  <PropertyGroup>
-    <DefineConstants Condition="'$(RuntimeAsyncSupported)' == 'true'">$(DefineConstants);RUNTIME_ASYNC_SUPPORTED</DefineConstants>
-  </PropertyGroup>
-
   <!-- Platform specific properties -->
   <PropertyGroup Condition="'$(Platform)' == 'x64'">
     <DefineConstants>$(DefineConstants);TARGET_AMD64</DefineConstants>
diff --git a/src/coreclr/System.Private.CoreLib/src/System/Runtime/CompilerServices/AsyncHelpers.CoreCLR.cs b/src/coreclr/System.Private.CoreLib/src/System/Runtime/CompilerServices/AsyncHelpers.CoreCLR.cs
index edcedc14c4ef43..5cd0a8e4298491 100644
--- a/src/coreclr/System.Private.CoreLib/src/System/Runtime/CompilerServices/AsyncHelpers.CoreCLR.cs
+++ b/src/coreclr/System.Private.CoreLib/src/System/Runtime/CompilerServices/AsyncHelpers.CoreCLR.cs
@@ -349,9 +349,6 @@ private static unsafe Continuation AllocContinuationClass(Continuation prevConti
         }
 #endif
 
-#if !RUNTIME_ASYNC_SUPPORTED
-        [BypassReadyToRun]
-#endif
         [MethodImpl(MethodImplOptions.NoInlining | MethodImplOptions.Async)]
         private static unsafe void AwaitTask(Task task, ConfigureAwaitOptions options)
         {
@@ -386,9 +383,6 @@ private static unsafe void AwaitTask(Task task, ConfigureAwaitOptions options)
             AsyncSuspend(taskCont);
         }
 
-#if !RUNTIME_ASYNC_SUPPORTED
-        [BypassReadyToRun]
-#endif
         [MethodImpl(MethodImplOptions.NoInlining | MethodImplOptions.Async)]
         private static unsafe T AwaitTask<T>(Task<T> task, ConfigureAwaitOptions options)
         {
@@ -434,9 +428,6 @@ private static unsafe T AwaitTask<T>(Task<T> task, ConfigureAwaitOptions options
         /// awaiting a completion of an underlying Task or ValueTaskSource.
         /// </summary>
         /// <param name="valueTask">ValueTask whose completion we are awaiting.</param>
-#if !RUNTIME_ASYNC_SUPPORTED
-        [BypassReadyToRun]
-#endif
         [MethodImpl(MethodImplOptions.NoInlining | MethodImplOptions.Async)]
         private static unsafe void TransparentAwaitValueTask(ValueTask valueTask)
         {
@@ -485,9 +476,6 @@ private static unsafe void TransparentAwaitValueTask(ValueTask valueTask)
             AsyncSuspend(nextCont);
         }
 
-#if !RUNTIME_ASYNC_SUPPORTED
-        [BypassReadyToRun]
-#endif
         [MethodImpl(MethodImplOptions.NoInlining | MethodImplOptions.Async)]
         private static unsafe void AwaitValueTaskSource(IValueTaskSource source, short token, bool continueOnCapturedContext)
         {
@@ -524,9 +512,6 @@ private static unsafe void AwaitValueTaskSource(IValueTaskSource source, short t
             AsyncSuspend(vtsCont);
         }
 
-#if !RUNTIME_ASYNC_SUPPORTED
-        [BypassReadyToRun]
-#endif
         [MethodImpl(MethodImplOptions.NoInlining | MethodImplOptions.Async)]
         private static unsafe T TransparentAwaitValueTaskOfT<T>(ValueTask<T> valueTask)
         {
@@ -575,9 +560,6 @@ private static unsafe T TransparentAwaitValueTaskOfT<T>(ValueTask<T> valueTask)
             return default!;
         }
 
-#if !RUNTIME_ASYNC_SUPPORTED
-        [BypassReadyToRun]
-#endif
         [MethodImpl(MethodImplOptions.NoInlining | MethodImplOptions.Async)]
         private static unsafe T AwaitValueTaskSource<T>(IValueTaskSource<T> source, short token, bool continueOnCapturedContext)
         {
@@ -619,9 +601,6 @@ private static unsafe T AwaitValueTaskSource<T>(IValueTaskSource<T> source, shor
         /// Used by internal thunks that implement awaiting on Task.
         /// </summary>
         /// <param name="task">Task whose completion we are awaiting.</param>
-#if !RUNTIME_ASYNC_SUPPORTED
-        [BypassReadyToRun]
-#endif
         [MethodImpl(MethodImplOptions.NoInlining | MethodImplOptions.Async)]
         private static unsafe void TransparentAwait(Task task)
         {
@@ -651,9 +630,6 @@ private static unsafe void TransparentAwait(Task task)
         /// Used by internal thunks that implement awaiting on Task.
         /// </summary>
         /// <param name="task">Task whose completion we are awaiting.</param>
-#if !RUNTIME_ASYNC_SUPPORTED
-        [BypassReadyToRun]
-#endif
         [MethodImpl(MethodImplOptions.NoInlining | MethodImplOptions.Async)]
         private static unsafe T TransparentAwaitOfT<T>(Task<T> task)
         {
diff --git a/src/coreclr/nativeaot/System.Private.CoreLib/src/System.Private.CoreLib.csproj b/src/coreclr/nativeaot/System.Private.CoreLib/src/System.Private.CoreLib.csproj
index fd996d3adf5658..ffa900b4b08198 100644
--- a/src/coreclr/nativeaot/System.Private.CoreLib/src/System.Private.CoreLib.csproj
+++ b/src/coreclr/nativeaot/System.Private.CoreLib/src/System.Private.CoreLib.csproj
@@ -46,20 +46,6 @@
     <Features>$(Features);runtime-async=on</Features>
   </PropertyGroup>
 
-  <!-- Mirror the runtime-async support predicate from src/libraries/Directory.Build.targets so the
-       BypassReadyToRun attributes on the MethodImpl.Async helpers can be conditioned on it. -->
-  <PropertyGroup Condition="'$(RuntimeAsyncSupported)' == ''">
-    <RuntimeAsyncSupported Condition="'$(TargetOS)' != 'browser'
-      and '$(TargetOS)' != 'wasi'
-      and '$(TargetOS)' != 'android'
-      and '$(TargetsAppleMobile)' != 'true'
-      and '$(RuntimeFlavor)' != 'Mono'">true</RuntimeAsyncSupported>
-  </PropertyGroup>
-
-  <PropertyGroup>
-    <DefineConstants Condition="'$(RuntimeAsyncSupported)' == 'true'">$(DefineConstants);RUNTIME_ASYNC_SUPPORTED</DefineConstants>
-  </PropertyGroup>
-
   <!-- Sources -->
   <ItemGroup>
     <Compile Include="$(CompilerCommonPath)\Internal\Runtime\DehydratedData.cs">
diff --git a/src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/AsyncHelpers.cs b/src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/AsyncHelpers.cs
index c38f104620d8dc..63212fdfe6f07e 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/AsyncHelpers.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/AsyncHelpers.cs
@@ -14,9 +14,6 @@ namespace System.Runtime.CompilerServices
     public static partial class AsyncHelpers
     {
 #if CORECLR || NATIVEAOT
-        // "BypassReadyToRun" keeps these MethodImpl.Async helpers out of AOT/R2R images on platforms
-        // that don't support runtime-async (RUNTIME_ASYNC_SUPPORTED is not defined there). On those
-        // platforms the JIT cannot emit code for runtime-async returns, so the helpers must be JITted.
         // Must be NoInlining because we use AsyncSuspend to manufacture an explicit suspension point.
         // It will not capture/restore any local state that is live across it.
 
@@ -25,9 +22,6 @@ public static partial class AsyncHelpers
         /// </summary>
         /// <typeparam name="TAwaiter">The awaiter type.</typeparam>
         /// <param name="awaiter">The awaiter to await.</param>
-#if !RUNTIME_ASYNC_SUPPORTED
-        [BypassReadyToRun]
-#endif
         [MethodImpl(MethodImplOptions.NoInlining | MethodImplOptions.Async)]
         [StackTraceHidden]
         public static unsafe void AwaitAwaiter<TAwaiter>(TAwaiter awaiter) where TAwaiter : INotifyCompletion
@@ -47,9 +41,6 @@ public static unsafe void AwaitAwaiter<TAwaiter>(TAwaiter awaiter) where TAwaite
         /// </summary>
         /// <typeparam name="TAwaiter">The awaiter type.</typeparam>
         /// <param name="awaiter">The awaiter to await.</param>
-#if !RUNTIME_ASYNC_SUPPORTED
-        [BypassReadyToRun]
-#endif
         [MethodImpl(MethodImplOptions.NoInlining | MethodImplOptions.Async)]
         [StackTraceHidden]
         public static unsafe void UnsafeAwaitAwaiter<TAwaiter>(TAwaiter awaiter) where TAwaiter : ICriticalNotifyCompletion
@@ -67,9 +58,6 @@ public static unsafe void UnsafeAwaitAwaiter<TAwaiter>(TAwaiter awaiter) where T
         /// <typeparam name="T">The result type produced by the task.</typeparam>
         /// <param name="task">The task to await.</param>
         [Intrinsic]
-#if !RUNTIME_ASYNC_SUPPORTED
-        [BypassReadyToRun]
-#endif
         [MethodImpl(MethodImplOptions.Async)]
         [StackTraceHidden]
         public static T Await<T>(Task<T> task)
@@ -89,9 +77,6 @@ public static T Await<T>(Task<T> task)
         /// </summary>
         /// <param name="task">The task to await.</param>
         [Intrinsic]
-#if !RUNTIME_ASYNC_SUPPORTED
-        [BypassReadyToRun]
-#endif
         [MethodImpl(MethodImplOptions.Async)]
         [StackTraceHidden]
         public static void Await(Task task)
@@ -112,9 +97,6 @@ public static void Await(Task task)
         /// <typeparam name="T">The result type produced by the value task.</typeparam>
         /// <param name="task">The value task to await.</param>
         [Intrinsic]
-#if !RUNTIME_ASYNC_SUPPORTED
-        [BypassReadyToRun]
-#endif
         [MethodImpl(MethodImplOptions.Async)]
         [StackTraceHidden]
         public static T Await<T>(ValueTask<T> task)
@@ -153,9 +135,6 @@ public static T Await<T>(ValueTask<T> task)
         /// </summary>
         /// <param name="task">The value task to await.</param>
         [Intrinsic]
-#if !RUNTIME_ASYNC_SUPPORTED
-        [BypassReadyToRun]
-#endif
         [MethodImpl(MethodImplOptions.Async)]
         [StackTraceHidden]
         public static void Await(ValueTask task)
@@ -196,9 +175,6 @@ public static void Await(ValueTask task)
         /// </summary>
         /// <param name="configuredAwaitable">The configured awaitable to await.</param>
         [Intrinsic]
-#if !RUNTIME_ASYNC_SUPPORTED
-        [BypassReadyToRun]
-#endif
         [MethodImpl(MethodImplOptions.Async)]
         [StackTraceHidden]
         public static void Await(ConfiguredTaskAwaitable configuredAwaitable)
@@ -222,9 +198,6 @@ public static void Await(ConfiguredTaskAwaitable configuredAwaitable)
         }
 
         [Intrinsic]
-#if !RUNTIME_ASYNC_SUPPORTED
-        [BypassReadyToRun]
-#endif
         [MethodImpl(MethodImplOptions.Async | MethodImplOptions.NoInlining)]
         [StackTraceHidden]
         private static void AwaitTaskWithRareOptions(ConfiguredTaskAwaitable.ConfiguredTaskAwaiter awaiter)
@@ -242,9 +215,6 @@ private static void AwaitTaskWithRareOptions(ConfiguredTaskAwaitable.ConfiguredT
         /// </summary>
         /// <param name="configuredAwaitable">The configured value task awaitable to await.</param>
         [Intrinsic]
-#if !RUNTIME_ASYNC_SUPPORTED
-        [BypassReadyToRun]
-#endif
         [MethodImpl(MethodImplOptions.Async)]
         [StackTraceHidden]
         public static void Await(ConfiguredValueTaskAwaitable configuredAwaitable)
@@ -287,9 +257,6 @@ public static void Await(ConfiguredValueTaskAwaitable configuredAwaitable)
         /// <typeparam name="T">The result type produced by the awaitable.</typeparam>
         /// <param name="configuredAwaitable">The configured awaitable to await.</param>
         [Intrinsic]
-#if !RUNTIME_ASYNC_SUPPORTED
-        [BypassReadyToRun]
-#endif
         [MethodImpl(MethodImplOptions.Async)]
         [StackTraceHidden]
         public static T Await<T>(ConfiguredTaskAwaitable<T> configuredAwaitable)
@@ -314,9 +281,6 @@ public static T Await<T>(ConfiguredTaskAwaitable<T> configuredAwaitable)
         /// <typeparam name="T">The result type produced by the awaitable.</typeparam>
         /// <param name="configuredAwaitable">The configured awaitable to await.</param>
         [Intrinsic]
-#if !RUNTIME_ASYNC_SUPPORTED
-        [BypassReadyToRun]
-#endif
         [MethodImpl(MethodImplOptions.Async)]
         [StackTraceHidden]
         public static T Await<T>(ConfiguredValueTaskAwaitable<T> configuredAwaitable)
diff --git a/src/tests/Interop/UnmanagedCallersOnly/InvalidCSharp.ilproj b/src/tests/Interop/UnmanagedCallersOnly/InvalidCSharp.ilproj
index b7b8b4d7665382..046255dbd56116 100644
--- a/src/tests/Interop/UnmanagedCallersOnly/InvalidCSharp.ilproj
+++ b/src/tests/Interop/UnmanagedCallersOnly/InvalidCSharp.ilproj
@@ -1,6 +1,8 @@
 <Project Sdk="Microsoft.NET.Sdk.IL">
   <PropertyGroup>
     <OutputType>library</OutputType>
+    <!-- crossgen2 cannot handle non-task-returning runtime-async methods that are not in CoreLib -->
+    <CrossGenTest>false</CrossGenTest>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="InvalidCallbacks.il" />