Compile runtime async versions of synchronous task-returning methods by jakobbotsch · Pull Request #128384 · dotnet/runtime

jakobbotsch · 2026-05-19T20:00:54Z

Instead of delegating from runtime async callable thunks to the original task returning methods this PR compiles a fully separate runtime async version. The JIT gets passed the IL of the synchronous task-returning method and is then responsible for adapting that to fit with the async variant. It does so by adding a (guaranteed) optimization to make tail calls in the synchronous task-returning methods into runtime async calls, and by otherwise introducing an async call to AsyncHelpers.TransparentAwaitWithResult around the task that would have otherwise been returned.

Fix #115771

Copilot

Pull request overview

This PR extends the JIT↔EE async infrastructure so the JIT can compile a dedicated “runtime async version” of synchronous Task/ValueTask-returning methods, including a tail-position optimization that turns eligible tail calls/returns into runtime-async awaits.

Changes:

Adds a new JIT↔EE interface API (getAwaitReturnCall) and plumbs it through SuperPMI and generated wrappers/shims.
Updates CoreCLR async thunk IL generation and AsyncHelpers to separate “suspend” helpers from typed TransparentAwait(...) helpers used by the JIT.
Updates the JIT importer to recognize “async-version tail await” patterns and to wrap async-version returns in an await via the new EE callback.

Reviewed changes

Copilot reviewed 33 out of 33 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
src/tests/async/reflection/reflection.cs	Disables several assertions related to reflection/stack behavior for await-on-task-returning paths.
src/coreclr/vm/prestub.cpp	Adjusts IL header retrieval logic for async variant methods.
src/coreclr/vm/method.hpp	Changes IL-header eligibility rules for async/thunk/return-dropping methods; exposes `GetAsyncThunkResultTypeSig`.
src/coreclr/vm/metasig.h	Adds metasig entries for `Task`/`ValueTask` TransparentAwait helper signatures.
src/coreclr/vm/jitinterface.h	Adds helper declarations related to runtime lookup computation for new await-return support.
src/coreclr/vm/jitinterface.cpp	Implements `getAwaitReturnCall` and runtime-lookup computation for generic await helpers; sets `CORINFO_ASYNC_VERSION` for applicable methods.
src/coreclr/vm/corelib.h	Adds/updates CoreLibBinder entries for new suspend/await AsyncHelpers methods with proper signatures.
src/coreclr/vm/asyncthunks.cpp	Switches thunk-emitted calls from `TransparentAwait` to `TransparentSuspendFor` helpers.
src/coreclr/tools/superpmi/superpmi/icorjitinfo.cpp	Records/replays the new `getAwaitReturnCall` API for SuperPMI.
src/coreclr/tools/superpmi/superpmi-shim-simple/icorjitinfo_generated.cpp	Forwards the new API in the simple shim.
src/coreclr/tools/superpmi/superpmi-shim-counter/icorjitinfo_generated.cpp	Counts/forwards the new API in the counter shim.
src/coreclr/tools/superpmi/superpmi-shim-collector/icorjitinfo.cpp	Records the new API in the collector shim.
src/coreclr/tools/superpmi/superpmi-shared/spmirecordhelper.h	Makes lookup restore helpers take `const&` and updates corresponding implementations.
src/coreclr/tools/superpmi/superpmi-shared/methodcontext.h	Adds recording/replay plumbing for `getAwaitReturnCall`.
src/coreclr/tools/superpmi/superpmi-shared/methodcontext.cpp	Implements record/dump/replay for `getAwaitReturnCall`.
src/coreclr/tools/superpmi/superpmi-shared/lwmlist.h	Registers the new lightweight-map packet for `GetAwaitReturnCall`.
src/coreclr/tools/superpmi/superpmi-shared/agnostic.h	Adds agnostic structs for `CORINFO_LOOKUP*` and the await-return result payload.
src/coreclr/tools/Common/TypeSystem/IL/Stubs/AsyncThunks.cs	Updates IL stub emitter to use `TransparentSuspendFor*` helper names.
src/coreclr/tools/Common/JitInterface/ThunkGenerator/ThunkInput.txt	Adds the new interface method to thunk generation input.
src/coreclr/tools/Common/JitInterface/CorInfoImpl.cs	Adds a stub managed implementation of `getAwaitReturnCall` for the managed JIT interface.
src/coreclr/tools/Common/JitInterface/CorInfoImpl_generated.cs	Adds unmanaged callback plumbing for `getAwaitReturnCall`.
src/coreclr/tools/aot/jitinterface/jitinterface_generated.h	Adds the new callback and wrapper method to the AOT jitinterface wrapper.
src/coreclr/System.Private.CoreLib/src/System/Runtime/CompilerServices/AsyncHelpers.CoreCLR.cs	Renames “suspend” helpers and adds typed `TransparentAwait(...)` overloads used by the JIT.
src/coreclr/jit/importercalls.cpp	Adds tail-await handling for async-version tail-await prefix and blocks inlining of async-version callees.
src/coreclr/jit/importer.cpp	Adds async-version tail-call recognition, wraps async-version returns in an await via `getAwaitReturnCall`, and introduces `impWrapTopOfStackInAwait`.
src/coreclr/jit/ICorJitInfo_wrapper_generated.hpp	Adds wrapper forwarding for `getAwaitReturnCall`.
src/coreclr/jit/ICorJitInfo_names_generated.h	Adds name entry for `getAwaitReturnCall`.
src/coreclr/jit/fginline.cpp	Minor whitespace change near async flag handling for inlinee compilation.
src/coreclr/jit/compiler.h	Introduces `PREFIX_IS_ASYNC_VERSION_TAIL_AWAIT`, `impWrapTopOfStackInAwait`, and `compIsAsyncVersion()`.
src/coreclr/jit/compiler.cpp	Adds verbose printing when compiling an async-version method.
src/coreclr/inc/jiteeversionguid.h	Updates JIT↔EE version GUID due to interface change.
src/coreclr/inc/icorjitinfoimpl_generated.h	Adds `getAwaitReturnCall` override to the generated `ICorJitInfo` impl header.
src/coreclr/inc/corinfo.h	Adds `CORINFO_ASYNC_VERSION` and the new `ICorStaticInfo::getAwaitReturnCall` method.

Copilot

Pull request overview

Copilot reviewed 32 out of 32 changed files in this pull request and generated 6 comments.

jakobbotsch · 2026-05-20T11:34:59Z

Another pattern we may want to recognize:

runtime/src/libraries/System.Linq.AsyncEnumerable/src/System/Linq/MaxAsync.cs

Lines 24 to 38 in b129b7c

    
                   public static ValueTask<TSource?> MaxAsync<TSource>( 
        
                       this IAsyncEnumerable<TSource> source, 
        
                       IComparer<TSource>? comparer = null, 
        
                       CancellationToken cancellationToken = default) 
        
                   { 
        
                       ArgumentNullException.ThrowIfNull(source); 
        
                       comparer ??= Comparer<TSource>.Default; 
        
                       // Special-case float/double/float?/double? to maintain compatibility 
        
                       // with System.Linq.Enumerable implementations. 
        
           #pragma warning disable CA2012 // Use ValueTasks correctly 
        
                       if (typeof(TSource) == typeof(float) && comparer == Comparer<TSource>.Default) 
        
                       { 
        
                           return (ValueTask<TSource?>)(object)MaxAsync((IAsyncEnumerable<float>)(object)source, cancellationToken);

Copilot

Pull request overview

Copilot reviewed 32 out of 32 changed files in this pull request and generated 3 comments.

jakobbotsch · 2026-06-15T07:58:44Z

I added the:
if (instArg.lookupKind.runtimeLookupKind == CORINFO_RUNTIME_LOOKUP_KIND.CORINFO_LOOKUP_NOT_SUPPORTED)
                    return null;
check in my commit, but maybe that's something to be handled on the RyuJIT side instead. I was hoping that would fix this, but it didn't.

Ended up removing the check and then handling this on the JIT side (it was already handled, just not checked for where we use getAwaitReturnCall)

Copilot

Pull request overview

Copilot reviewed 51 out of 51 changed files in this pull request and generated 6 comments.

jtschuster · 2026-06-15T17:59:23Z

+
+            // We allow MethodDesc so that this is usable with e.g. async variants too,
+            // but the owning module needs to be an EcmaModule.
+            _module = ((EcmaType)method.OwningType).Module;


If we should only use this on EcmaMethods and AsyncMethodVariants, could we assert that it's a method definition?

Suggested change

// We allow MethodDesc so that this is usable with e.g. async variants too,

// but the owning module needs to be an EcmaModule.

_module = ((EcmaType)method.OwningType).Module;

Debug.Assert(method.IsMethodDefinition);

// We allow MethodDesc so that this is usable with e.g. async variants too,

// but the owning module needs to be an EcmaModule.

_module = ((EcmaType)method.OwningType).Module;

jtschuster · 2026-06-15T18:05:52Z

+                MethodIL wrappedIL = asyncVariantImpl.IsAsync
+                    ? EcmaMethodIL.Create(asyncVariantImpl.Target)
+                    : GetMethodIL(asyncVariantImpl.Target);


AsyncVariantMethod.Target is an EcmaMethod, so GetMethodIL() should always return EcmaMethodIL. Could we cast here and keep AsyncMethodIL._wrappedIL as EcmaMethodIL?

Suggested change

MethodIL wrappedIL = asyncVariantImpl.IsAsync

? EcmaMethodIL.Create(asyncVariantImpl.Target)

: GetMethodIL(asyncVariantImpl.Target);

EcmaMethodIL wrappedIL = asyncVariantImpl.IsAsync

? EcmaMethodIL.Create(asyncVariantImpl.Target)

: (EcmaMethodIL)GetMethodIL(asyncVariantImpl.Target);

AsyncVariantMethod.Target is an EcmaMethod, so GetMethodIL() should always return EcmaMethodIL. Could we cast here and keep AsyncMethodIL._wrappedIL as EcmaMethodIL?

EcmaMethod can have IL that is not EcmaMethodIL. The place I hit it with is UnsafeAccessor, but there are more exotic ones too:

runtime/src/coreclr/tools/Common/TypeSystem/IL/NativeAotILProvider.cs

Lines 283 to 322 in 3d40d73

if (method is EcmaMethod ecmaMethod)

{

if (ecmaMethod.IsIntrinsic)

{

MethodIL result = TryGetIntrinsicMethodIL(ecmaMethod);

if (result != null)

return result;

}

if (ecmaMethod.IsRuntimeImplemented)

{

MethodIL result = TryGetRuntimeImplementedMethodIL(ecmaMethod);

if (result != null)

return result;

}

if (ecmaMethod.IsAsync)

{

if (ecmaMethod.Signature.ReturnsTaskOrValueTask())

{

return AsyncThunkILEmitter.EmitTaskReturningThunk(ecmaMethod, ((CompilerTypeSystemContext)ecmaMethod.Context).GetAsyncVariantMethod(ecmaMethod));

}

else

{

// We only allow non-Task returning runtime async methods in CoreLib

if (ecmaMethod.OwningType.Module != ecmaMethod.Context.SystemModule)

ThrowHelper.ThrowBadImageFormatException();

}

}

MethodIL methodIL = EcmaMethodIL.Create(ecmaMethod);

if (methodIL != null)

return methodIL;

methodIL = UnsafeAccessors.TryGetIL(ecmaMethod);

if (methodIL != null)

return methodIL;

return null;

}

jakobbotsch · 2026-06-16T13:38:16Z

I think all the failures are expected. Going to push a commit where the tests are runtime async but the libraries aren't, to get some more testing of a mix of async variants.

Copilot

Pull request overview

Copilot reviewed 50 out of 50 changed files in this pull request and generated 3 comments.

This reverts commit 54c8b3f.

jakobbotsch · 2026-06-17T12:05:52Z

Testing looked good. Reverted the disabling of runtime-async and also added handling for tail. and jmp IL instructions to JIT and interpreter.

Still looking for reviews here, @AndyAyersMS can you PTAL at the JIT side, @VSadov @jkotas at the VM/NativeAOT side (@MichalStrehovsky wrote most of that), @BrzVlad @davidwrighton at the interpreter side?

Copilot

Pull request overview

Copilot reviewed 49 out of 49 changed files in this pull request and generated 4 comments.

BrzVlad

Interpreter bits LGTM

Copilot

Pull request overview

Copilot reviewed 50 out of 50 changed files in this pull request and generated 3 comments.

+    // Get information about which await call to use to await the return type
+    // of the non-async version of an async call.
+    virtual CORINFO_METHOD_HANDLE getAwaitReturnCall(CORINFO_METHOD_HANDLE callerHandle, CORINFO_LOOKUP* instArg) = 0;
+


+    printf("GetAwaitReturnCall key %016" PRIX64 " value methodHnd-%016" PRIX64 " instArg %s",
+        key,
+        value.methodHnd,
+        SpmiDumpHelper::DumpAgnostic_CORINFO_LOOKUP(value.instArg).c_str());


+// Compute the runtime lookup for the instantiation argument for an
+// AsyncHelpers.TransparentAwait call, to be used for wrapping a return value
+// from pCallerMD for its runtime async version.
+// For example, if pCallerMD is ValueTask<List<T>> Foo<T>(), then we call this
+// for the runtime async version of Foo and it gives a runtime lookup that


jakobbotsch added 3 commits May 18, 2026 13:01

Cache Task continuation for runtime async callable task thunks

192f7ba

Compile runtime async versions of synchronous task-returning methods

74aab70

Disable some stack trace tests

5cec9e3

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github-actions Bot added the area-CodeGen-coreclr CLR JIT compiler in src/coreclr/src/jit and related components such as SuperPMI label May 19, 2026

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jakobbotsch mentioned this pull request May 19, 2026

[runtime-async] Optimize synchronous Task-returning wrappers used in async context #115771

Open

Return some code to fix crossgen2

27470b8

jakobbotsch commented May 20, 2026

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Comment thread src/coreclr/jit/importer.cpp

Run jit-format

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am11 added the runtime-async label May 20, 2026

jakobbotsch added 2 commits May 20, 2026 13:40

Call impNormStructVal on value tasks, fix some docs

514d583

Another comment

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Comment thread src/tests/async/reflection/reflection.cs

Comment thread src/coreclr/vm/asyncthunks.cpp Outdated

Comment thread src/coreclr/tools/Common/JitInterface/CorInfoImpl.cs

jakobbotsch added 3 commits May 20, 2026 14:58

Run jit-format

26c12f9

Fix bug

1cbeb65

Fix assert

e4f192a

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Run jit-format

45ef235

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jtschuster reviewed Jun 15, 2026

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Reenable runtime-async for testing

434e48e

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Comment thread src/coreclr/inc/corinfo.h

Comment thread src/coreclr/vm/jitinterface.cpp

Comment thread src/coreclr/tools/Common/JitInterface/CorInfoImpl.cs

Check canTailCall before making tail-awaits

5a3aa05

jtschuster mentioned this pull request Jun 16, 2026

[No Review] Test crossgen2 compiling runtime async versions of synchronous task-returning methods #129474

Draft

jakobbotsch added 4 commits June 17, 2026 12:17

Add tests for jmp and tail.

673f235

tail. and jmp handling for async versions

e769d56

Revert "Disable runtime async for testing"

35fa1ca

This reverts commit 54c8b3f.

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Nit

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Comment thread src/coreclr/jit/importer.cpp Outdated

Comment thread src/coreclr/jit/importer.cpp Outdated

Comment thread src/coreclr/jit/importer.cpp Outdated

Comment thread src/coreclr/inc/corinfo.h

Comment nits

5fedf9d

This was referenced Jun 17, 2026

Support inlining runtime async callable thunks #127642

Closed

Reenable compiling async variants of non-async functions in crossgen2 #129524

Open

BrzVlad approved these changes Jun 17, 2026

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Disable failing test

3d1d8ca

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	if (method is EcmaMethod ecmaMethod)
	{
	if (ecmaMethod.IsIntrinsic)
	{
	MethodIL result = TryGetIntrinsicMethodIL(ecmaMethod);
	if (result != null)
	return result;
	}

	if (ecmaMethod.IsRuntimeImplemented)
	{
	MethodIL result = TryGetRuntimeImplementedMethodIL(ecmaMethod);
	if (result != null)
	return result;
	}

	if (ecmaMethod.IsAsync)
	{
	if (ecmaMethod.Signature.ReturnsTaskOrValueTask())
	{
	return AsyncThunkILEmitter.EmitTaskReturningThunk(ecmaMethod, ((CompilerTypeSystemContext)ecmaMethod.Context).GetAsyncVariantMethod(ecmaMethod));
	}
	else
	{
	// We only allow non-Task returning runtime async methods in CoreLib
	if (ecmaMethod.OwningType.Module != ecmaMethod.Context.SystemModule)
	ThrowHelper.ThrowBadImageFormatException();
	}
	}

	MethodIL methodIL = EcmaMethodIL.Create(ecmaMethod);
	if (methodIL != null)
	return methodIL;

	methodIL = UnsafeAccessors.TryGetIL(ecmaMethod);
	if (methodIL != null)
	return methodIL;

	return null;
	}

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jakobbotsch commented May 19, 2026 •

edited

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