[flang-commits] [flang] [mlir] [MLIR][LLVM] Fix inlining of a single block ending with unreachable (PR #122615)

[Tobias Gysi via flang-commits]

gysit wrote:

> LLVM is similar: https://godbolt.org/z/ncM7enGh6

LLVM seems to split the callee block into a first block terminated by an unreachable operation and a second block that returns poison. This has the advantage that the unreachable is inlined and not lost (I believe the PR deletes the poison?). I wonder if we could implement the same behavior? 

One approach may be to overwrite `processInlinedBlocks` to detect if the inlined blocks contain one block terminated with an unreachable. In this case, we could split the single block and have a separate block that returns poison to avoid the code path in the inliner that optimizes the single-block case. I am not entirely sure if this works though.

https://github.com/llvm/llvm-project/pull/122615