llvm-project

48a6157e - [mlir][Interfaces][NFC] Document that `RegionBranchTerminatorOpInterface` is mandatory (#174978)

[mlir][Interfaces][NFC] Document that `RegionBranchTerminatorOpInterface` is mandatory (#174978) Document that implementing the `RegionBranchTerminatorOpInterface` is mandatory. Omitting this interface on a block terminator that models region branching may lead to invalid/incomplete analyses and transformations. This commit does not change the op/interface semantics. It just puts in writing an assumption that is made throughout the code base. For example: - It is baked into the API design of the `RegionBranchOpInterface`. You cannot query the region successors of block terminators that do not implement the `RegionBranchTerminatorOpInterface`: `RegionBranchOpInterface::getSuccessors()` takes a `RegionBranchPoint` parameter, and such region branch points can be constructed only from `RegionBranchTerminatorOpInterface` and not arbitrary `Operation *`. - Helper functions + default interface method implementations enumerate region branch points by looking for `RegionBranchTerminatorOpInterface` and ignoring other operations. E.g., `RegionBranchOpInterface::getAllRegionBranchPoints`, default implementation of `RegionBranchOpInterface::getSuccessorRegions(Region &)`, default implementation of `RegionBranchOpInterface::getPredecessorValues`. - Core analyses such as `DeadCodeAnalysis` look for `RegionBranchTerminatorOpInterface` and misbehave when the interface is not implemented. The analysis does not (and cannot) query region successors of a region branching terminator that does not implement the `RegionBranchTerminatorOpInterface`. In practice, this means that forgetting to implement the `RegionBranchTerminatorOpInterface` may incorrectly classify regions as dead. - Other analyses / transformations that look for and depend on the implementation of `RegionBranchTerminatorOpInterface`: `mlir::getControlFlowPredecessors`, `AbstractDenseBackwardDataFlowAnalysis`, ownership-based buffer deallocation pass.