[llvm] [MachinePipeliner] Limit the number of stores in BB (PR #154940)

[Ryotaro Kasuga via llvm-commits]

kasuga-fj wrote:

TODO: Add some comments and tests

@aankit-ca Could you please run your benchmark with this change? I believe this is the simplest solution for #150262. If you're okay with it, I'd like to proceed with this approach. Here are some notes:

- I have confirmed that this patch resolves the specific case raised in #150262, but this change may reduce optimization opportunities for other cases.
- The default value of `SwpMaxNumStores` is arbitrary. Please let me know if you have any preferences.
- If we're very lucky, this might also improve compilation time in other cases, without causing any performance regressions.

Thanks in advance!

https://github.com/llvm/llvm-project/pull/154940