[NativeAOT] don't generate __GetFieldHelper if struct is never boxed?

[NinoFloris]

I'm unsure how feasible this is but it would be helpful if the helper isn't emitted if the struct is never boxed (and never gets a constrained call on Equals/GetHashCode either).

I understand the difficulty of tracking whether a struct is 'boxed', as generics (and (T)(object)value casts etc) significantly complicate the analysis. Though with struct types forcing specialization it should not be impossible to get some certainty?

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[MichalStrehovsky]

Do you have an example where the struct is not boxed but we still generate the helper? We do not generate the helper unless the compiler thinks it could be boxed.

For example:

using System.Runtime.CompilerServices;

Consume(default, new Bar[1]);

[MethodImpl(MethodImplOptions.NoInlining)]
static void Consume(Foo f, Bar[] b) { }

struct Foo { double d; }

struct Bar { double d; }

Sizoscope reports:

Notice Foo is gone.

Bar is there even though not boxed, but there are easy ways to get it as boxed. For example: call Array.GetValue. Or cast to non-generic IEnumerable and enumerate. Etc. The compiler doesn't track what exact object instance the interface methods get called on and these foundational interfaces are pretty much guaranteed to get called somewhere.

[NinoFloris]

This is the repro, not great.

var action = (Struct _) => { };
struct Struct;