[llvm] [GlobalISel] Fix volatile flag handling in memmove legalizer (PR #206025)

[Ömer Sinan Ağacan via llvm-commits]

osa1 wrote:

Would other reviewers be able to review this? Other than tests this is a tiny patch, it's basically +47/-18 in one file and one word of change in another (plus removed FIXME).

https://github.com/llvm/llvm-project/pull/206025