[llvm] [MachinePipeliner] Fix store-store dependences (#72508) (PR #72575)

[via llvm-commits]

bcahoon wrote:

Hi @ytmukai, thanks for providing an example. The case you provide is an interesting one, but an additional case to consider. The original case already has an order dependence, so we need to make sure that the second store isn't scheduled too far way from the first (such that the overlap when the final pipelined scheduled is formed). I also don't fully understand why the order dependence is needed since I would have thought that the first store is dead. I just assumed it's a valid case and it made sense to make sure that the stores aren't scheduled more than MII cycles apart.

https://github.com/llvm/llvm-project/pull/72575