llvm-project

5f3b40ec - [mlir][Interfaces][NFC] Simplify and align `RegionSuccessor` design / API (#174945)

[mlir][Interfaces][NFC] Simplify and align `RegionSuccessor` design / API (#174945) Simplify the design of `RegionSuccessor`. There is no need to store the `Operation *` pointer when branching out of the region branch op (to the parent). There is no API to even access the `Operation *` pointer. Add a new helper function `RegionSuccessor::parent` to construct a region successor that points to the parent. This aligns the `RegionSuccessor` design and API with `RegionBranchPoint`: * Both classes now have a `parent()` helper function. `ClassName::parent()` can be used in documentation to precisely describe the source/target of a region branch. * Both classes now use `nullptr` internally to represent "parent". This API change also protects against incorrect API usage: users can no longer pass an incorrect parent op. If a region successor is not a region of the region branch op, it *must* branch out of region branch op itself ("parent"). However, the previous API allowed passing other operations. There was one such API violation in a [test case](https://github.com/llvm/llvm-project/pull/174945/files#diff-d5717e4a8d7344b2ff77762b8fa480bcfec0eeee97a86195c787d791a6217e13L71). Also clean up the documentation to use the correct terminology (such as "successor operands", "successor inputs") consistently. Note: This PR effectively rolls back some changes from #161575. That PR introduced `llvm::PointerUnion<Region *, Operation *> successor{nullptr};`. It is unclear from the commit message why that change was made. Note for LLVM integration: You may have to slightly modify `getSuccessorRegion` implementations: Replace `RegionSuccessor(getOperation(), getOperation()->getResults())` with `RegionSuccessor::parent(getResults())`.