[llvm] [RISCV] Allow tail memcmp expansion (PR #121460)

[Philip Reames via llvm-commits]

https://github.com/preames requested changes to this pull request.

As far as I can, the reference optimization is assuming that unaligned loads are legal and fast.  This is not true for us.   As such, this optimization is not sound.  

Please, stop posting additional memcmp enable patches until you've addressed the soundness issues in that code with unaligned loads.  It a waste of your time, and a waste of reviewers time.  

https://github.com/llvm/llvm-project/pull/121460