This is a flag used to mark a given `LayoutTypeSystemNode`.
It represents the fact that the children nodes are either all
interfering with each other, non-interfering with each other, or
unknown.
This information will be filled-in by the
`ComputeNonInterferingComponents` step, and will be used from the
`MakeLayouts` step to decide if the children of the node will be emitted
as fields of a union (interfering) or fields of a struct
(non-interfering).
This method allows to create artificial layouts that are not directly
associated to `llvm::Value`s.
Because of this missing association with `Value`s, the artificial
layouts are not retrievable by using the public `getOrCreateLayoutType`
and `getLayoutType` methods of `LayoutTypeSystem`, but they will be
accessible only by walking the graph.
The capability to add layouts that are not associated to `llvm::Value`s
is necessary for the future implementation of the DLA Step:
`ComputeNonInterferingComponents`.
The step will add artificial layouts to represent non-intefering
components.
Pietro Fezzardi