[llvm] [DA] runtime predicates for delinearization bounds checks (PR #170713)

[Nikita Popov via llvm-commits]

nikic wrote:

Just as a high-level question: Do we want to introduce more runtime predicates at this point in time? Given that there is a lot of active ongoing work on correctness issues in DA/Delinearization, it may be better to delay this until a later time, just to make it easier to do further code changes, without also having to maintain the predicates along the way.

I've been out for a while and am not up to date on the DA/Delinearization work, but IIRC these runtime predicates are not yet used anywhere, right? They only appear in the analysis output for now? I expect that actually making use of them will be quite challenging, because of the need to trade off the value of the transform with the probability of passing the runtime check and the code size increase of performing loop versioning. Having a lot of runtime checks implemented will probably make this harder than introducing them gradually and evaluating which of them are actually valuable in practice.

On the other hand, I could see value in doing this now if this helps with testing somehow, e.g. because it allows us to easily test situations in DA that would otherwise be hard to test because of delinearization failures. Is something like this the case?

https://github.com/llvm/llvm-project/pull/170713