[llvm] [AArch64][ISel] Add support for v8.4a RCpc `ldapur`/`stlur` (PR #67879)

[David Green via llvm-commits]

https://github.com/davemgreen commented:

I think this looks OK, is the "// If the offset is valid as a scaled immediate, don't match here." part not needed?

https://github.com/llvm/llvm-project/pull/67879