JIT: Null out exceptions in reused continuations and reenable continuation reuse

src/coreclr/jit/async.cpp

@@ -2871,6 +2871,16 @@ BasicBlock* AsyncTransformation::RethrowExceptionOnResumption(BasicBlock*
     GenTree* storeException  = m_compiler->gtNewStoreLclVarNode(exceptionLclNum, exceptionInd);
     LIR::AsRange(resumeBB).InsertAtEnd(LIR::SeqTree(m_compiler, storeException));
 
+    if (ReuseContinuations())
+    {
+        // If we may reuse this continuation later then make sure we don't see the same exception again.
+        GenTree* continuation    = m_compiler->gtNewLclvNode(m_compiler->lvaAsyncContinuationArg, TYP_REF);
+        unsigned exceptionOffset = OFFSETOF__CORINFO_Continuation__data + layout.ExceptionOffset;
+        GenTree* null            = m_compiler->gtNewNull();
+        GenTree* nullException   = StoreAtOffset(continuation, exceptionOffset, null, TYP_REF);
+        LIR::AsRange(resumeBB).InsertAtEnd(LIR::SeqTree(m_compiler, nullException));
+    }
+
     GenTree* exception = m_compiler->gtNewLclVarNode(exceptionLclNum, TYP_REF);
     GenTree* null      = m_compiler->gtNewNull();
     GenTree* neNull    = m_compiler->gtNewOperNode(GT_NE, TYP_INT, exception, null);
@@ -3244,6 +3254,16 @@ void AsyncTransformation::CreateResumptionsAndSuspensions()
 //
 bool AsyncTransformation::ReuseContinuations()
 {
+#ifdef DEBUG
+    static ConfigMethodRange s_range;
+    s_range.EnsureInit(JitConfig.JitAsyncReuseContinuationsRange());
+
+    if (!s_range.Contains(m_compiler->info.compMethodHash()))
+    {
+        return false;
+    }
+#endif
+
     return JitConfig.JitAsyncReuseContinuations() != 0;
 }
 

src/coreclr/jit/jitconfigvalues.h

@@ -592,9 +592,11 @@ OPT_CONFIG_INTEGER(JitDoOptimizeMaskConversions, "JitDoOptimizeMaskConversions",
 OPT_CONFIG_INTEGER(JitOptimizeAwait, "JitOptimizeAwait", 1) // Perform optimization of Await intrinsics
 OPT_CONFIG_STRING(JitAsyncDefaultValueAnalysisRange,
                   "JitAsyncDefaultValueAnalysisRange") // Enable async default value analysis based on method hash range
+// Enable continuation reuse based on method hash range
+OPT_CONFIG_STRING(JitAsyncReuseContinuationsRange, "JitAsyncReuseContinuationsRange")
 // Save and reuse continuation instances in runtime async functions. Also
 // implies use of shared continuation layouts for all suspension points.
-RELEASE_CONFIG_INTEGER(JitAsyncReuseContinuations, "JitAsyncReuseContinuations", 0)
+RELEASE_CONFIG_INTEGER(JitAsyncReuseContinuations, "JitAsyncReuseContinuations", 1)
 
 RELEASE_CONFIG_INTEGER(JitEnableOptRepeat, "JitEnableOptRepeat", 1) // If zero, do not allow JitOptRepeat
 RELEASE_CONFIG_METHODSET(JitOptRepeat, "JitOptRepeat")            // Runs optimizer multiple times on specified methods

src/tests/async/regression/125805.cs

@@ -0,0 +1,51 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Runtime.CompilerServices;
+using System.Threading.Tasks;
+using Xunit;
+
+public class Runtime_125805
+{
+    [Fact]
+    public static void TestEntryPoint()
+    {
+        ExceptionReuse().GetAwaiter().GetResult();
+    }
+
+    private static async Task ExceptionReuse()
+    {
+        try
+        {
+            await Throws();
+            Assert.Fail("Expected throw");
+        }
+        catch (NullReferenceException)
+        {
+        }
+
+        try
+        {
+            await NoThrow();
+        }
+        catch (Exception ex)
+        {
+            Assert.Fail("Did not expect throw: " + ex);
+        }
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private static async Task Throws()
+    {
+        await Task.Yield();
+        throw new NullReferenceException();
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private static async Task NoThrow()
+    {
+        await Task.Yield();
+    }
+}
+

src/tests/async/regression/125805.csproj

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