Bug Calling .GetHashCode() on instances of empty structs doesn't return the same value in il2cpp builds

Hey there, I just encounter something that feels like a bug.

Let's say we have an empty struct :

Code (CSharp):

1. public struct EmptyStruct
2. {
3. }

If we create two instances of this struct and store them in two different variables :

Code (CSharp):

1. var emptyStruct1 = new EmptyStruct();
2. var emptyStruct2 = new EmptyStruct();

I would expect .Equals to be true between them and thus .GetHashCode() returning the same value :

Code (CSharp):

1. Debug.Log($"Are Empty StructGetHashCode the same ? {emptyStruct1.GetHashCode() == emptyStruct2.GetHashCode()}");
2. Debug.Log($"Are EmptyStruct Equals ? {emptyStruct1.Equals(emptyStruct2)}");

It turns out everything is fine in Editor and in Mono Build.

Code (CSharp):

1. Are EmptyStruct GetHashCode the same ? True
2. Are EmptyStruct Equals ? True

But ..

When I build the project with IL2CPP, .Equals() still is true, but their .GetHashCode() returns different values, which seems contradictory to the classic Equals/GetHashCode usage.

Code (CSharp):

1. Are EmptyStruct GetHashCode the same ? False
2. Are EmptyStruct Equals ? True

This behaviour is observed in Unity 2020.3.28f1 and also Unity 2021.2.15f1 on Android IL2CPP builds (and I think in all IL2CPP builds).

Ugly ways to 'fix' this involve overriding .GetHashCode() in the empty struct or just adding an unused field.

Is there something I miss ?

Just in case I created a bug report (https://fogbugz.unity3d.com/default.asp?1411455_rs5538034dq74a9l) and a colleague of mine recommended me to tag @JoshPeterson

Thank you all for your insights

 

Update : it has been accepted in the Unity Issue Tracker, you can vote for it now
https://issuetracker.unity3d.com/is...es-not-return-the-same-value-in-il2cpp-builds