JIT: Fix reordering of inlinee return expression with async save/restore

src/coreclr/jit/fgbasic.cpp

@@ -3583,8 +3583,11 @@ void Compiler::fgFindBasicBlocks()
         }
 
         // Use a spill temp for the return value if there are multiple return blocks,
-        // or if the inlinee has GC ref locals.
-        if ((info.compRetNativeType != TYP_VOID) && ((fgReturnCount > 1) || impInlineInfo->HasGcRefLocals()))
+        // if the inlinee has GC ref locals, or if async contexts need save/restore.
+        // In the latter cases we will need to insert IR after the return.
+        if ((info.compRetNativeType != TYP_VOID) &&
+            ((fgReturnCount > 1) || impInlineInfo->HasGcRefLocals() ||
+             ((info.compMethodInfo->options & CORINFO_ASYNC_SAVE_CONTEXTS) != 0)))
         {
             // If we've spilled the ret expr to a temp we can reuse the temp
             // as the inlinee return spill temp.

src/coreclr/jit/importer.cpp

@@ -11254,8 +11254,7 @@ bool Compiler::impReturnInstruction(int prefixFlags, OPCODE& opcode)
 
                 if (fgNeedReturnSpillTemp())
                 {
-                    assert(info.compRetNativeType != TYP_VOID &&
-                           (fgMoreThanOneReturnBlock() || impInlineInfo->HasGcRefLocals()));
+                    assert(info.compRetNativeType != TYP_VOID);
 
                     // If this method returns a ref type, track the actual types seen in the returns.
                     if (info.compRetType == TYP_REF)
@@ -11331,7 +11330,6 @@ bool Compiler::impReturnInstruction(int prefixFlags, OPCODE& opcode)
                     // in this case we have to insert multiple struct copies to the temp
                     // and the retexpr is just the temp.
                     assert(info.compRetNativeType != TYP_VOID);
-                    assert(fgMoreThanOneReturnBlock() || impInlineInfo->HasGcRefLocals());
 
                     impStoreToTemp(lvaInlineeReturnSpillTemp, op2, CHECK_SPILL_ALL);
                 }

src/tests/async/regression/125042.cs

@@ -0,0 +1,55 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+// Generated by Fuzzlyn v3.3 on 2026-03-01 17:28:06
+// Run on Arm64 Linux
+// Seed: 17604030292119785473-async,runtimeasync,vectort,vector64,vector128,armadvsimd,armadvsimdarm64,armaes,armarmbase,armarmbasearm64,armcrc32,armcrc32arm64,armdp,armrdm,armrdmarm64,armsha1,armsha256,armsve,armsve2
+// Reduced from 44.5 KiB to 0.8 KiB in 00:00:29
+// Release: Runs successfully
+// Release with Runtime Async: Throws 'System.InvalidOperationException'
+
+using System.Runtime.CompilerServices;
+using System.Runtime.Intrinsics;
+using System.Threading;
+using System.Threading.Tasks;
+using Xunit;
+
+// When an async method that modifies an AsyncLocal is inlined with runtime async,
+// the "Save contexts around async calls" phase wraps the body in a try/fault that
+// restores the execution context on exit. The return value expression
+// (GetAsyncLocal1) must be evaluated inside the try block before the context is
+// restored; otherwise the AsyncLocal read sees a null value and throws.
+
+public class Runtime_125042
+{
+    public static AsyncLocal<bool?> s_asyncLocal1 = new AsyncLocal<bool?>();
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    public static bool GetAsyncLocal1()
+    {
+        return s_asyncLocal1.Value.Value;
+    }
+
+    [Fact]
+    public static void TestEntryPoint()
+    {
+        M0().GetAwaiter().GetResult();
+    }
+
+    private static async Task M0()
+    {
+        var vr3 = (sbyte)0;
+        var vr2 = Vector128.CreateScalar(vr3);
+        var vr1 = await M1(true, vr2);
+        var vr5 = (sbyte)-1;
+        var vr4 = Vector128.CreateScalar(vr5);
+        bool vr0 = await M1(vr1, vr4);
+    }
+
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    private static async Task<bool> M1(bool arg1, Vector128<sbyte> arg2)
+    {
+        s_asyncLocal1.Value = arg1;
+        return GetAsyncLocal1();
+    }
+}

src/tests/async/regression/125042.csproj

@@ -0,0 +1,5 @@
+<Project Sdk="Microsoft.NET.Sdk.IL">
+  <ItemGroup>
+    <Compile Include="$(MSBuildProjectName).cs" />
+  </ItemGroup>
+</Project>