Before this commit, the DLA code made very strong assumptions about
Functions that returned struct types.
In particular, calls to such Functions were expected to have at most a
number of uses equal to the number of fields of the returned struct.
Moreover, such uses were only expected to be ExtractValueInst.
Now, we still assume that such uses are ExtractValueInst, but we don't
make any strong assumption on their number anymore.
This makes the DLA code less reliant on specific form of LLVM IR, so we
can also drop -gvn-hoist from the decompilation test pipeline.
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