[llvm] [LoopUnswitch] Improve algorithm of unswitch cost estimation (PR #106544)

[Sergey Kachkov via llvm-commits]

skachkov-sc wrote:

@nikic I have some concerns about affecting compilation time with this new algorithm; my local measurements on test-suite haven't shown any noticeable difference, but the results were quite noisy to be sure of this; so I'd appreciate you for measurements with llvm-compile-time-tracker.

https://github.com/llvm/llvm-project/pull/106544