Function trans_aggregate

crates/rustc_codegen_spirv/src/abi.rs:600–671

FIXME(eddyb) all `ty: TyAndLayout` variables should be `layout: TyAndLayout`, the type is really more "Layout with Ty" (`.ty` field + `Deref`s to `Layout`).

(cx: &CodegenCx<'tcx>, span: Span, ty: TyAndLayout<'tcx>)

// FIXME(eddyb) all `ty: TyAndLayout` variables should be `layout: TyAndLayout`,
// the type is really more "Layout with Ty" (`.ty` field + `Deref`s to `Layout`).
fn trans_aggregate<'tcx>(cx: &CodegenCx<'tcx>, span: Span, ty: TyAndLayout<'tcx>) -> Word {
    fn create_zst<'tcx>(cx: &CodegenCx<'tcx>, span: Span, ty: TyAndLayout<'tcx>) -> Word {
        SpirvType::Adt {
            def_id: def_id_for_spirv_type_adt(ty),
            size: Some(Size::ZERO),
            align: Align::from_bytes(0).unwrap(),
            field_types: &[],
            field_offsets: &[],
            field_names: None,
        }
        .def_with_name(cx, span, TyLayoutNameKey::from(ty))
    }
    match ty.fields {
        FieldsShape::Primitive => span_bug!(
            span,
            "trans_aggregate called for FieldsShape::Primitive layout {:#?}",
            ty
        ),
        FieldsShape::Union(_) => {
            assert!(!ty.is_unsized(), "{ty:#?}");

            // Represent the `union` with its largest case, which should work
            // for at least `MaybeUninit<T>` (which is between `T` and `()`),
            // but also potentially some other ones as well.
            // NOTE(eddyb) even if long-term this may become a byte array, that
            // only works for "data types" and not "opaque handles" (images etc.).
            let largest_case = (0..ty.fields.count())
                .map(|i| ty.field(cx, i))
                .max_by_key(|case| case.size);

            if let Some(case) = largest_case {
                assert_eq!(ty.size, case.size);
                case.spirv_type(span, cx)
            } else {
                assert_eq!(ty.size, Size::ZERO);
                create_zst(cx, span, ty)
            }
        }
        FieldsShape::Array { stride, count } => {
            let element_type = ty.field(cx, 0).spirv_type(span, cx);
            if ty.is_unsized() {
                // There's a potential for this array to be sized, but the element to be unsized, e.g. `[[u8]; 5]`.
                // However, I think rust disallows all these cases, so assert this here.
                assert_eq!(count, 0);
                SpirvType::RuntimeArray {
                    element: element_type,
                }
                .def(span, cx)
            } else if count == 0 {
                // spir-v doesn't support zero-sized arrays
                create_zst(cx, span, ty)
            } else {
                let count_const = cx.constant_u32(span, count as u32);
                let element_spv = cx.lookup_type(element_type);
                let stride_spv = element_spv
                    .sizeof(cx)
                    .expect("Unexpected unsized type in sized FieldsShape::Array")
                    .align_to(element_spv.alignof(cx));