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

[Philip Reames via llvm-commits]

preames wrote:

> What are the soundness issues? I thought we only had costing issues?
> 
> The code in `RISCVTTIImpl::enableMemCmpExpansion` currently checks `ST->enableUnalignedScalarMem()` before enabling any expansion.

Gah, you're correct!  I read the check code too fast and apparently mentally placed the negate in the wrong place.  Please ignore my comment on this review entirely. 

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