This assertion was conceived to check that DLADeduplicateUnionFields was
doing its job, ensuring that we never created a union with only one
field.
However, the assertion is too strict, and there are situation that union
deduplication cannot handle and that still generate a union with one
single field. Here's an example
Node A, with Interfering Children
Instance Edge -> Node B
Offset 12 Edge -> Node C
Node C
Offset 12 Edge -> Node D
Node C: uint32_t
Node D: uint32_t
Hence we need to remove the assertion.
Since in the model a FunctionPrototype can be shared among different
functions or indirect calls, we should take into account this fact when
initializing the DLA.
In particular, if the aforementioned case happens, we want to add
equality edges between the return value(s) and the arguments of all the
functions that have the same prototype. These will then be merged by
later steps in the middle-end, and the resulting information will be
shared among all the merged nodes.
Add `MakeModelTypes` and `UpdateFuncPrototypes` to the DLA backend:
* `MakeModelTypes` adds to the model all the types recovered by the DLA
* `UpdateFuncPrototypes` updates function prototypes in the model that
have generic return values or arguments to use the types recovered by
the DLA
* Changes to the `LayoutTypeSystem` graph
Pointers are identified in the TypeSystem graph as leaf nodes which
have a new type of edge (PointerEdge) that connects them to another
node of the graph. The destination of the edge represents the layout of
the pointed type.
* Changes to the Front-end
Pointer edges, and their destination nodes, are created by the DLA
front-end (`DLACreateIntraProceduralTypes`) whenever an access node has
a size that is compatible with the size of a pointer in the current
Architecture.
Successors might then be added to the newly generated node, if any,
by looking up the llvm::Value it is attached to.
* Changes to the Middle-end
Most of the DLA passes should ignore Pointer Edges, so they are modified
accordingly. Most notably, nodes that represent pointed layouts should
never be merged/pruned-off.
* Changes to the Back-end
The `TypeDeclCreationAction` of the decompiler and the `DLAMakeLayouts`
step of the DLA back-end are modified to take into account the new
information about pointers.
⚠️ There is a known issue with this version of the decompiler,
namely the fact that type loops are not detected and can cause the
emitter to enter an infinite loop.
When deduplicating unions, for each union we compare each successor
with all other successors. However, the same successor node might be
reachable by more than one edge from the parent.
This can cause problems when a node gets merged while the comparison is
still ongoing. In particular, since the comparison is done using a copy
of the successor list, to avoid iterator invalidation, the links in
the worklist are not updated when a node gets merged, causing links to
the merged node to have an invalid destination.
The fix here is to keep a list of **nodes** to visit, and a list of
**edges** that have already been visited, so that, if a node is merged
through one of its links, we are not visiting other links connected to
the same node after the merge.
Add a step that recognizes if two subtrees of a union node are
topologically equivalent and merges them. This corresponds to removing
duplicate fields in unions.
This deduplication was prevously done while emitting layouts.
A check is inserted into DLAMakeLayouts to assert that, after
constructing unions, no union has only one child, which could be the
case if we didn't deduplicate union fields in the graph.
Since the reasoning behind single child collapsing can be reused in
other points of the DLA pipeline, move the logic that acts on a single
node in a static function out of the CollapseSingleChild step.
* Inheritance straight lines are now collapsed by CollapseSingleChild
* Don't collapse if parent has more than one parent or if the child has
more than one parent
* Allow the possibility to construct single-member struct: if this
struct is inherited by many other structs, "flattening" the struct is not
the most sensible thing to do, since inheritance information is something
we want to preserve in these cases.
While doing thie, also drop `printAccessNode()` from DLA DebugPrinter.
The information about which LLVM instruction originated a given access
node is already available in the csv generated by the `dla-accesses-log`
logger.
Until now, in makeLayout, inheritance edges were ignored when the
children were interfering.
Now the inheritance edges are treated as if they were instance edges at
offset 0.
Pietro Fezzardi