[llvm] [CVP] Improve the value solving of select at use (PR #76700)

[Nikita Popov via llvm-commits]

nikic wrote:

This issue is on my todo list for next week, as it's also needed for https://github.com/llvm/llvm-project/pull/73662#issuecomment-1853634553. My tentative plan was to add a new value lattice state to represent cycles, which will mostly get treated as overdefined, but can be preserved for pass-through operations.

https://github.com/llvm/llvm-project/pull/76700