We weren't properly visiting region successors when the terminator wasn't return like, which could create incorrect results in the analysis. This revision ensures that we properly visit region successors, to avoid optimistically assuming a value is constant when it isn't.
Differential Revision: https://reviews.llvm.org/D101783
Explicitly check for uninitialized to prevent crashes in edge cases where the derived analysis creates a lattice element for a value that hasn't been visited yet.
This revision takes the forward value propagation engine in SCCP and refactors it into a more generalized forward dataflow analysis framework. This framework allows for propagating information about values across the various control flow constructs in MLIR, and removes the need for users to reinvent the traversal (often not as completely). There are a few aspects of the traversal, that were conservative for SCCP, that should be relaxed to support the needs of different value analyses. To keep this revision simple, these conservative behaviors will be left in (Note that this won't produce an incorrect result, but may produce more conservative results than necessary in certain edge cases. e.g. region entry arguments for non-region branch interface operations). The framework also only focuses on computing lattices for values, given the SCCP origins, but this is something to relax as needed in the future.
Given that this logic is already in SCCP, a majority of this commit is NFC. The more interesting parts are the interface glue that clients interact with.
Differential Revision: https://reviews.llvm.org/D100915
River Riddle