[llvm] [ADT,CodeGen] Remove stable_hash_combine_string (PR #100668)

[Kyungwoo Lee via llvm-commits]

kyulee-com wrote:

`stable` is designed to be consistent across different versions or builds for safe entity matching. How consistent is `xxh3_64bits` across versions?

This change seems conflicting with my upcoming changes detailed in https://github.com/llvm/llvm-project/pull/90074/commits/b5d7f5f918ff250763e916865e0ee5bc5c160474#diff-56094e62599ca13f28f0857547a76c2387917badcb618eda3ee1547c915888ce, based on https://discourse.llvm.org/t/rfc-enhanced-machine-outliner-part-2-thinlto-nolto/78753. However, optimistic transformations using stable hashes should not depend solely on hash stability, although it affects efficiency. I believe there's no upstream dependency yet, pending the RFC's implementation. So, I think updating the hash implementation now might be okay if it remains stable across versions, but continuous updates pose a risk as it will impact the effectiveness of these optimizations.


https://github.com/llvm/llvm-project/pull/100668