JIT incorrectly reorders constrained call 'this' indirections with other arguments

[jakobbotsch]

Small example:

using InlineIL;
using System;
using System.Runtime.CompilerServices;

public class Program
{
    public static void Main()
    {
        Foo(new C("A"));
    }

    [MethodImpl(MethodImplOptions.NoInlining)]
    private static void Foo(C arg)
    {
        IL.Emit.Ldarga(nameof(arg));
        IL.Emit.Ldarga(nameof(arg));
        IL.Emit.Call(new MethodRef(typeof(Program), nameof(Bar)));
        IL.Emit.Constrained<C>();
        IL.Emit.Callvirt(new MethodRef(typeof(C), nameof(arg.Baz)));
    }

    [MethodImpl(MethodImplOptions.NoInlining)]
    private static int Bar(ref C o)
    {
        o = new C("B");
        return 0;
    }
}

public record class C(string Name)
{
    public void Baz(int arg)
    {
        Console.WriteLine(Name);
    }
}

Expected: B
Actual: A

Seen in #73606 (comment)

category:correctness
theme:importer
skill-level:intermediate
cost:small
impact:small

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Issue Details

---

Small example:

using InlineIL;
using System;

public class Program
{
    public static void Main()
    {
        Foo(new C("A"));
    }

    private static void Foo(C arg)
    {
        IL.Emit.Ldarga(nameof(arg));
        IL.Emit.Ldarga(nameof(arg));
        IL.Emit.Call(new MethodRef(typeof(Program), nameof(Bar)));
        IL.Emit.Constrained<C>();
        IL.Emit.Callvirt(new MethodRef(typeof(C), nameof(arg.Baz)));
    }

    private static int Bar(ref C o)
    {
        o = new C("B");
        return 0;
    }
}

public record class C(string Name)
{
    public void Baz(int arg)
    {
        Console.WriteLine(Name);
    }
}

Expected: B
Actual: A

Seen in #73606 (comment)

Author:	jakobbotsch
Assignees:	-
Labels:	area-CodeGen-coreclr
Milestone:	-

[jakobbotsch]

This needs to wait for dotnet/roslyn#63221 for a runtime side fix. As of writing this the C# compiler has been fixed, but not the VB.NET compiler.

[jakobbotsch]

I'm going to move this to 9.0 since it's blocked waiting for a Roslyn VB.NET fix.

[AlekseyTs]

@jakobbotsch FYI, the fix for dotnet/roslyn#63221 for VB got merged into Roslyn.