Function build_scalable_vector_di_node 

fn build_scalable_vector_di_node<'ll, 'tcx>(
    cx: &GenericCx<'ll, FullCx<'ll, 'tcx>>,
    unique_type_id: UniqueTypeId<'tcx>,
    name: String,
    adt_def: AdtDef<'tcx>,
    (element_count, element_ty, number_of_vectors): (u16, Ty<'tcx>, NumScalableVectors),
    layout: Layout<'tcx>,
    def_location: Option<(&'ll Metadata, c_uint)>,
    containing_scope: &'ll Metadata,
) -> DINodeCreationResult<'ll>

Generate debuginfo for a #[rustc_scalable_vector] type.

Debuginfo for a scalable vector uses a derived type based on a composite type. The composite type has the DIFlagVector flag set and is based on the element type of the scalable vector. The composite type has a subrange from 0 to an expression that calculates the number of elements in the vector.

!1 = !DIDerivedType(tag: DW_TAG_typedef, name: "svint16_t", ..., baseType: !2, ...)
!2 = !DICompositeType(tag: DW_TAG_array_type, baseType: !3, ..., flags: DIFlagVector, elements: !4)
!3 = !DIBasicType(name: "i16", size: 16, encoding: DW_ATE_signed)
!4 = !{!5}
!5 = !DISubrange(lowerBound: 0, upperBound: !DIExpression(DW_OP_constu, 4, DW_OP_bregx, 46, 0, DW_OP_mul, DW_OP_constu, 1, DW_OP_minus))

See the CodegenType::CreateType(const BuiltinType *BT) implementation in Clang for how this is generated for C and C++.