[llvm] [LoopInfo] Derive Loop::contains(BlockT*) from the block-to-loop map (PR #207613)

[Nikita Popov via llvm-commits]

nikic wrote:

An alternative that does not change asymptotic complexity would be to replace the block set with a child loop set (which, presumably, is usually much smaller).

Though I'm not really opposed to this. In practice, I don't think we see a lot of IR with very deeply nested loops. (Usually what we see is IR with a lot of sibling loops...)

https://github.com/llvm/llvm-project/pull/207613