runtime: Test failure: XmlSerializerTests.XmlMembersMapping_With_ChoiceIdentifier, XmlSerializerTests.XmlMembersMapping_IntArray

pipeline: runtime-coreclr libraries-jitstressregs

win-arm64, JitStressRegs=1 or JitStressRegs=8

https://dev.azure.com/dnceng/public/_build/results?buildId=1735202&view=ms.vss-test-web.build-test-results-tab&runId=46975904&resultId=193080&paneView=debug

D:\h\w\AFED094C\w\AE650933\e>set COMPlus 
COMPlus_JitStressRegs=8
COMPlus_TieredCompilation=0

D:\h\w\AFED094C\w\AE650933\e>call RunTests.cmd --runtime-path D:\h\w\AFED094C\p 
----- start Sun 04/24/2022  6:38:34.80 ===============  To repro directly: ===================================================== 
pushd D:\h\w\AFED094C\w\AE650933\e\
"D:\h\w\AFED094C\p\dotnet.exe" exec --runtimeconfig System.Xml.XmlSerializer.Tests.runtimeconfig.json --depsfile System.Xml.XmlSerializer.Tests.deps.json xunit.console.dll System.Xml.XmlSerializer.Tests.dll -xml testResults.xml -nologo -nocolor -notrait category=IgnoreForCI -notrait category=OuterLoop -notrait category=failing 
popd
===========================================================================================================

D:\h\w\AFED094C\w\AE650933\e>"D:\h\w\AFED094C\p\dotnet.exe" exec --runtimeconfig System.Xml.XmlSerializer.Tests.runtimeconfig.json --depsfile System.Xml.XmlSerializer.Tests.deps.json xunit.console.dll System.Xml.XmlSerializer.Tests.dll -xml testResults.xml -nologo -nocolor -notrait category=IgnoreForCI -notrait category=OuterLoop -notrait category=failing  
  Discovering: System.Xml.XmlSerializer.Tests (method display = ClassAndMethod, method display options = None)
  Discovered:  System.Xml.XmlSerializer.Tests (found 242 of 243 test cases)
  Starting:    System.Xml.XmlSerializer.Tests (parallel test collections = on, max threads = 8)
    XmlSerializerTests.XmlMembersMapping_With_ChoiceIdentifier [FAIL]
      System.InvalidOperationException : There is an error in XML document (1, 176).
      ---- System.NullReferenceException : Object reference not set to an instance of an object.
      Stack Trace:
        /_/src/libraries/System.Private.Xml/src/System/Xml/Serialization/XmlSerializer.cs(495,0): at System.Xml.Serialization.XmlSerializer.Deserialize(XmlReader xmlReader, String encodingStyle, XmlDeserializationEvents events)
        /_/src/libraries/System.Private.Xml/src/System/Xml/Serialization/XmlSerializer.cs(427,0): at System.Xml.Serialization.XmlSerializer.Deserialize(Stream stream)
        /_/src/libraries/System.Private.Xml/tests/XmlSerializer/XmlSerializerTests.cs(2043,0): at XmlSerializerTests.RoundTripWithXmlMembersMapping(Object[] value, String baseline, Boolean skipStringCompare, XmlReflectionMember[] members, String ns, String wrapperName, Boolean rpc)
        /_/src/libraries/System.Private.Xml/tests/XmlSerializer/XmlSerializerTests.RuntimeOnly.cs(2438,0): at XmlSerializerTests.XmlMembersMapping_With_ChoiceIdentifier()
           at System.RuntimeMethodHandle.InvokeMethod(Object target, Void** arguments, Signature sig, Boolean isConstructor)
        /_/src/coreclr/System.Private.CoreLib/src/System/Reflection/RuntimeMethodInfo.CoreCLR.cs(383,0): at System.Reflection.RuntimeMethodInfo.InvokeNonEmitUnsafe(Object obj, IntPtr* arguments, Span`1 argsForTemporaryMonoSupport, BindingFlags invokeAttr)
        ----- Inner Stack Trace -----
        /_/src/coreclr/System.Private.CoreLib/src/System/Array.CoreCLR.cs(307,0): at System.Array.GetLowerBound(Int32 dimension)
        /_/src/coreclr/System.Private.CoreLib/src/System/Array.CoreCLR.cs(51,0): at System.Array.Copy(Array sourceArray, Array destinationArray, Int32 length)
           at Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationReader1.Read2_wrapper()
        /_/src/libraries/System.Private.Xml/src/System/Xml/Serialization/XmlSerializer.cs(480,0): at System.Xml.Serialization.XmlSerializer.Deserialize(XmlReader xmlReader, String encodingStyle, XmlDeserializationEvents events)
    XmlSerializerTests.XmlMembersMapping_IntArray [FAIL]
      System.InvalidOperationException : There is an error in XML document (1, 176).
      ---- System.NullReferenceException : Object reference not set to an instance of an object.
      Stack Trace:
        /_/src/libraries/System.Private.Xml/src/System/Xml/Serialization/XmlSerializer.cs(495,0): at System.Xml.Serialization.XmlSerializer.Deserialize(XmlReader xmlReader, String encodingStyle, XmlDeserializationEvents events)
        /_/src/libraries/System.Private.Xml/src/System/Xml/Serialization/XmlSerializer.cs(427,0): at System.Xml.Serialization.XmlSerializer.Deserialize(Stream stream)
        /_/src/libraries/System.Private.Xml/tests/XmlSerializer/XmlSerializerTests.cs(2043,0): at XmlSerializerTests.RoundTripWithXmlMembersMapping(Object[] value, String baseline, Boolean skipStringCompare, XmlReflectionMember[] members, String ns, String wrapperName, Boolean rpc)
        /_/src/libraries/System.Private.Xml/tests/XmlSerializer/XmlSerializerTests.RuntimeOnly.cs(2194,0): at XmlSerializerTests.XmlMembersMapping_IntArray()
           at System.RuntimeMethodHandle.InvokeMethod(Object target, Void** arguments, Signature sig, Boolean isConstructor)
        /_/src/coreclr/System.Private.CoreLib/src/System/Reflection/RuntimeMethodInfo.CoreCLR.cs(383,0): at System.Reflection.RuntimeMethodInfo.InvokeNonEmitUnsafe(Object obj, IntPtr* arguments, Span`1 argsForTemporaryMonoSupport, BindingFlags invokeAttr)
        ----- Inner Stack Trace -----
        /_/src/coreclr/System.Private.CoreLib/src/System/Array.CoreCLR.cs(307,0): at System.Array.GetLowerBound(Int32 dimension)
        /_/src/coreclr/System.Private.CoreLib/src/System/Array.CoreCLR.cs(51,0): at System.Array.Copy(Array sourceArray, Array destinationArray, Int32 length)
           at Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationReader1.Read1_wrapper()
        /_/src/libraries/System.Private.Xml/src/System/Xml/Serialization/XmlSerializer.cs(480,0): at System.Xml.Serialization.XmlSerializer.Deserialize(XmlReader xmlReader, String encodingStyle, XmlDeserializationEvents events)
  Finished:    System.Xml.XmlSerializer.Tests
=== TEST EXECUTION SUMMARY ===
   System.Xml.XmlSerializer.Tests  Total: 242, Errors: 0, Failed: 2, Skipped: 0, Time: 22.740s
----- end Sun 04/24/2022  6:39:02.17 ----- exit code 1 ----------------------------------------------------------

I verified that the failure does not occur without JitStressRegs=1 or JitStressRegs=8.

@kunalspathak @dotnet/jit-contrib