Emit IL for AsyncResumptionStub

src/coreclr/System.Private.CoreLib/src/System/Runtime/CompilerServices/AsyncHelpers.CoreCLR.cs

@@ -156,7 +156,8 @@ public static partial class AsyncHelpers
         //   * a continuation object if the call requires suspension.
         //     In this case the formal result of the call is undefined.
         [Intrinsic]
-        private static Continuation? AsyncCallContinuation() => throw new UnreachableException();
+        [BypassReadyToRun]
+        internal static Continuation? AsyncCallContinuation() => throw new UnreachableException(); // Unconditionally expanded intrinsic
 
         // Used during suspensions to hold the continuation chain and on what we are waiting.
         // Methods like FinalizeTaskReturningThunk will unlink the state and wrap into a Task.

src/coreclr/tools/Common/TypeSystem/IL/Stubs/AsyncResumptionStub.Sorting.cs

@@ -15,4 +15,14 @@ protected override int CompareToImpl(MethodDesc other, TypeSystemComparer compar
             return comparer.Compare(_targetMethod, ((AsyncResumptionStub)other)._targetMethod);
         }
     }
+
+    internal sealed partial class ExplicitContinuationAsyncMethod : MethodDesc
+    {
+        protected override int ClassCode => 0xd076659;
+
+        protected override int CompareToImpl(MethodDesc other, TypeSystemComparer comparer)
+        {
+            return comparer.Compare(_wrappedMethod, ((ExplicitContinuationAsyncMethod)other)._wrappedMethod);
+        }
+    }
 }

src/coreclr/tools/Common/TypeSystem/IL/Stubs/AsyncResumptionStub.cs

@@ -14,14 +14,13 @@
     public partial class AsyncResumptionStub : ILStubMethod
     {
         private readonly MethodDesc _targetMethod;
         private readonly TypeDesc _owningType;
         private MethodSignature _signature;
 
         public AsyncResumptionStub(MethodDesc targetMethod, TypeDesc owningType)
         {
             Debug.Assert(targetMethod.IsAsyncCall());
             _targetMethod = targetMethod;
-            _owningType = owningType;
         }
 
         public override ReadOnlySpan<byte> Name => _targetMethod.Name;
@@ -42,13 +41,163 @@
 
         public override MethodIL EmitIL()
         {
-            var emitter = new ILEmitter();
-            ILCodeStream codeStream = emitter.NewCodeStream();
+            ILEmitter ilEmitter = new ILEmitter();
+            ILCodeStream ilStream = ilEmitter.NewCodeStream();
 
-            // TODO: match getAsyncResumptionStub from CoreCLR VM
-            codeStream.EmitCallThrowHelper(emitter, Context.GetHelperEntryPoint("ThrowHelpers"u8, "ThrowNotSupportedException"u8));
+            // Ported from jitinterface.cpp CEEJitInfo::getAsyncResumptionStub
+            if (!_targetMethod.Signature.IsStatic)
+            {
+                if (_targetMethod.OwningType.IsValueType)
+                {
+                    ilStream.EmitLdc(0);
+                    ilStream.Emit(ILOpcode.conv_u);
+                }
+                else
+                {
+                    ilStream.Emit(ILOpcode.ldnull);
+                }
+            }
 
-            return emitter.Link(this);
+            if (Context.Target.Architecture != TargetArchitecture.X86)
+            {
+                ilStream.EmitLdArg(0);
+            }
+
+            foreach (var param in _targetMethod.Signature)
+            {
+                var local = ilEmitter.NewLocal(param);
+                ilStream.EmitLdLoca(local);
+                ilStream.Emit(ILOpcode.initobj, ilEmitter.NewToken(param));
+                ilStream.EmitLdLoc(local);
+            }
+
+            if (Context.Target.Architecture == TargetArchitecture.X86)
+            {
+                ilStream.EmitLdArg(0);
+            }
+
+            MethodDesc resumingMethod = new ExplicitContinuationAsyncMethod(_targetMethod);
+            ilStream.Emit(ILOpcode.call, ilEmitter.NewToken(resumingMethod));
+
+            bool returnsVoid = resumingMethod.Signature.ReturnType.IsWellKnownType(WellKnownType.Void);
+            Internal.IL.Stubs.ILLocalVariable resultLocal = default;
+            if (!returnsVoid)
+            {
+                resultLocal = ilEmitter.NewLocal(resumingMethod.Signature.ReturnType);
+                ilStream.EmitStLoc(resultLocal);
+            }
+
+            MethodDesc asyncCallContinuation = Context.SystemModule.GetKnownType("System.Runtime.CompilerServices"u8, "AsyncHelpers"u8)
+                .GetKnownMethod("AsyncCallContinuation"u8, null);
+            TypeDesc continuation = Context.SystemModule.GetKnownType("System.Runtime.CompilerServices"u8, "Continuation"u8);
+            var newContinuationLocal = ilEmitter.NewLocal(continuation);
+            ilStream.Emit(ILOpcode.call, ilEmitter.NewToken(asyncCallContinuation));
+            ilStream.EmitStLoc(newContinuationLocal);
+
+            if (!returnsVoid)
+            {
+                var doneResult = ilEmitter.NewCodeLabel();
+                ilStream.EmitLdLoc(newContinuationLocal);
+                ilStream.Emit(ILOpcode.brtrue, doneResult);
+                ilStream.EmitLdArg(1);
+                ilStream.EmitLdLoc(resultLocal);
+                ilStream.Emit(ILOpcode.stobj, ilEmitter.NewToken(resumingMethod.Signature.ReturnType));
+                ilStream.EmitLabel(doneResult);
+            }
+            ilStream.EmitLdLoc(newContinuationLocal);
+            ilStream.Emit(ILOpcode.ret);
+
+            return ilEmitter.Link(this);
+        }
+    }
+
+    internal sealed partial class ExplicitContinuationAsyncMethod : MethodDesc
+    {
+        private MethodSignature _signature;
+        private MethodDesc _wrappedMethod;
+
+        public ExplicitContinuationAsyncMethod(MethodDesc target)
+        {
+            _wrappedMethod = target;
+        }
+
+        public MethodDesc Target => _wrappedMethod;
+
+        private MethodSignature InitializeSignature()
+        {
+            var _methodRepresented = _wrappedMethod;
+
+            // Async methods have an implicit Continuation parameter
+            // The order of parameters depends on the architecture
+            // non-x86: this?, genericCtx?, continuation, params...
+            // x86: this?, params, continuation, genericCtx?
+            // To make the jit pass arguments in this order, we can add the continuation parameter
+            // at the end for x86 and at the beginning for other architectures.
+            // The 'this' parameter and generic context parameter (if any) can be handled by the jit.
+
+            var signature = new MethodSignatureBuilder(_wrappedMethod.Signature)
+            {
+                Length = _wrappedMethod.Signature.Length + 1,
+            };
+
+            TypeDesc continuation = Context.SystemModule.GetKnownType("System.Runtime.CompilerServices"u8, "Continuation"u8);
+            if (Context.Target.Architecture == TargetArchitecture.X86)
+            {
+                for (int i = 0; i < _methodRepresented.Signature.Length; i++)
+                    signature[i] = _methodRepresented.Signature[i];
+                signature[_methodRepresented.Signature.Length] = continuation;
+            }
+            else
+            {
+                signature[0] = continuation;
+                for (int i = 0; i < _methodRepresented.Signature.Length; i++)
+                    signature[i + 1] = _methodRepresented.Signature[i];
+            }
+            // Get the return type from the Task-returning variant
+            if (_wrappedMethod is AsyncMethodVariant variant
+                && variant.Target.Signature.ReturnType is {HasInstantiation: true } returnType)
+            {
+                signature.ReturnType = returnType.Instantiation[0];
+            }
+            else
+            {
+                signature.ReturnType = Context.GetWellKnownType(WellKnownType.Void);
+            }
+
+            return _signature = signature.ToSignature();
+        }
+
+        public override bool HasCustomAttribute(string attributeNamespace, string attributeName) => throw new NotImplementedException();
+
+        public override MethodSignature Signature
+        {
+            get
+            {
+                if (_signature is null)
+                    return InitializeSignature();
+
+                return _signature;
+            }
+        }
+
+        public override string DiagnosticName => $"ExplicitContinuationAsyncMethod({_wrappedMethod.DiagnosticName})";
+
+        public override TypeDesc OwningType => _wrappedMethod.OwningType;
+
+        public override TypeSystemContext Context => _wrappedMethod.Context;
+
+        public override bool IsInternalCall => true;
+    }
+
+    public static class AsyncResumptionStubExtensions
+    {
+        public static bool IsExplicitContinuationAsyncMethod(this MethodDesc method)
+        {
+            return method is ExplicitContinuationAsyncMethod;
+        }
+        public static MethodDesc GetExplicitContinuationAsyncMethodTarget(this MethodDesc method)
+        {
+            return ((ExplicitContinuationAsyncMethod)method).Target;
         }
     }
 }

src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/DependencyAnalysis/ILScanNodeFactory.cs

@@ -30,6 +30,10 @@ protected override IMethodNode CreateMethodEntrypointNode(MethodDesc method)
                 {
                     return MethodEntrypoint(TypeSystemContext.GetRealDefaultInterfaceMethodImplementationThunkTargetMethod(method));
                 }
+                else if (method.IsExplicitContinuationAsyncMethod())
+                {
+                    return MethodEntrypoint(method.GetExplicitContinuationAsyncMethodTarget());
+                }
                 else if (method.IsArrayAddressMethod())
                 {
                     return new ScannedMethodNode(((ArrayType)method.OwningType).GetArrayMethod(ArrayMethodKind.AddressWithHiddenArg));

src/coreclr/tools/aot/ILCompiler.ReadyToRun/ILCompiler.ReadyToRun.csproj

@@ -45,6 +45,9 @@
     <Compile Include="..\..\Common\System\FormattingHelpers.cs" Link="Common\FormattingHelpers.cs" />
     <Compile Include="..\..\Common\TypeSystem\IL\ILProvider.cs" Link="IL\ILProvider.cs" />
     <Compile Include="..\..\Common\TypeSystem\IL\ILReader.cs" Link="IL\ILReader.cs" />
+    <Compile Include="..\..\Common\TypeSystem\IL\Stubs\AsyncResumptionStub.cs" Link="IL\Stubs\AsyncResumptionStub.cs" />
+    <Compile Include="..\..\Common\TypeSystem\IL\Stubs\AsyncResumptionStub.Sorting.cs" Link="IL\Stubs\AsyncResumptionStub.Sorting.cs" />
+    <Compile Include="..\..\Common\TypeSystem\IL\Stubs\AsyncResumptionStub.Mangling.cs" Link="IL\Stubs\AsyncResumptionStub.Mangling.cs" />
     <Compile Include="..\..\Common\TypeSystem\IL\Stubs\ComparerIntrinsics.cs" Link="IL\Stubs\ComparerIntrinsics.cs" />
     <Compile Include="..\..\Common\TypeSystem\IL\Stubs\InterlockedIntrinsics.cs" Link="IL\Stubs\InterlockedIntrinsics.cs" />
     <Compile Include="..\..\Common\TypeSystem\IL\Stubs\RuntimeHelpersIntrinsics.cs" Link="IL\Stubs\RuntimeHelpersIntrinsics.cs" />

src/coreclr/tools/aot/ILCompiler.RyuJit/Compiler/DependencyAnalysis/RyuJitNodeFactory.cs

@@ -28,6 +28,10 @@ protected override IMethodNode CreateMethodEntrypointNode(MethodDesc method)
                 {
                     return MethodEntrypoint(TypeSystemContext.GetRealDefaultInterfaceMethodImplementationThunkTargetMethod(method));
                 }
+                else if (method.IsExplicitContinuationAsyncMethod())
+                {
+                    return MethodEntrypoint(method.GetExplicitContinuationAsyncMethodTarget());
+                }
                 else if (method.IsArrayAddressMethod())
                 {
                     return MethodEntrypoint(((ArrayType)method.OwningType).GetArrayMethod(ArrayMethodKind.AddressWithHiddenArg));