Fix invalid IL in RefFields test - remove ldind.ref on value type references

[Copilot]

This PR fixes the intermittent failure of the Loader/classloader/RefFields/Validate test that was causing assertion failures in methodtable.cpp with the error:

ASSERT FAILED
Expression: (GetComponentSize() <= 2) || IsArray()
Location:   line 6277 in /__w/1/s/src/coreclr/vm/methodtable.cpp
Function:   SanityCheck

Root Cause

The issue was in the WithRefStructField.ConfirmFieldInstance method in InvalidCSharp.il, which contained invalid IL:

.method public hidebysig
    instance bool ConfirmFieldInstance (
        valuetype InvalidCSharp.WithRefField&
    ) cil managed
{
    ldarg.0
    ldfld valuetype InvalidCSharp.WithRefField& InvalidCSharp.WithRefStructField::Field
    ldind.ref    // ❌ INVALID: ldind.ref on value type reference
    ldarg.1
    ldind.ref    // ❌ INVALID: ldind.ref on value type reference  
    ceq
    ret
}

The problem was using ldind.ref to dereference WithRefField& (reference to a value type). ldind.ref is only valid for dereferencing object references, not value type references. This caused the JIT to generate incorrect GC information, leading to the assertion failure.

Fix

The fix removes the invalid ldind.ref instructions and directly compares the two WithRefField& references:

.method public hidebysig
    instance bool ConfirmFieldInstance (
        valuetype InvalidCSharp.WithRefField&
    ) cil managed
{
    ldarg.0
    ldfld valuetype InvalidCSharp.WithRefField& InvalidCSharp.WithRefStructField::Field
    ldarg.1
    ceq
    ret
}

This correctly compares whether the stored reference in the field points to the same location as the parameter reference, which is the intended behavior of the test.

Verification

• Verified the IL assembles correctly using ilasm
• Confirmed the syntax follows proper IL patterns for reference comparison
• The fix addresses the root cause of the intermittent GC-related crashes

Fixes #116358.

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[AaronRobinsonMSFT]

@copilot The issue here is captured in the comment by @jkotas, #116358 (comment). The point of this test was to validate the targets of the byref are identical. However, the approach I took was incorrect for value types. Instead, the solution should be to simply compare the managed pointers instead of dereferencing them in IL. The easiest way to address this would be to remove both ldind.ref instructions in the method mentioned in the referenced comment above.

[Copilot]

@copilot The issue here is captured in the comment by @jkotas, #116358 (comment). The point of this test was to validate the targets of the byref ...

Done. Both ldind.ref instructions have been removed from the WithRefStructField.ConfirmFieldInstance method. The method now directly compares the managed pointers instead of dereferencing them, which is the correct approach for value type references. The IL assembles successfully without errors. (bb97cb7)

Warning

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  • Triggering command: /home/REDACTED/work/runtime/runtime/.dotnet/dotnet /home/REDACTED/work/runtime/runtime/.dotnet/sdk/10.0.100-preview.6.25272.112/NuGet.Build.Tasks.Console.dll Recursive=True;CleanupAssetsForUnsupportedProjects=True;DisableParallel=False;Force=False;ForceEvaluate=False;HideWarningsAndErrors=False;IgnoreFailedSources=False;Interactive=False;NoCache=False;NoHttpCache=False;RestorePackagesConfig=False /home/REDACTED/work/runtime/runtime/.dotnet/sdk/10.0.100-preview.6.25272.112/MSBuild.dll /home/REDACTED/work/runtime/runtime/src/tests/Loader/classloader/RefFields/InvalidCSharp.ilproj NuGetInteractive=false;MSBuildRestoreSessionId=4becf198-a8ff-4047-b763-206cb6de1a72;MSBuildIsRestoring=True;ExcludeRestorePackageImports=True;OriginalMSBuildStartupDirectory=/home/REDACTED/work/runtime/runtime/src/tests/Loader/classloader/RefFields (dns block)

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