[llvm] [AArch64] Mark Armv8.4-a LDAPUR* instructions as mayLoad (PR #171142)

[Cullen Rhodes via llvm-commits]

c-rhodes wrote:

> I presume the other instructions get this from the patterns? 

ah ok, I didnt realise this until I saw your comment but seems so, when I remove https://github.com/llvm/llvm-project/blob/614fe6da145e883cb0aa1b1406bbd5e5d103747b/llvm/lib/Target/AArch64/AArch64InstrAtomics.td#L602-L633 

all of these instructions then just have `HasSideEffects`.

> They should have atomic side-effects but from the other instructions that I believe that usually comes from the MMO. HasSideEffects should be stronger so wouldn't make it incorrect to keep.

ok thanks for the context, I think I can see that now https://github.com/llvm/llvm-project/blob/614fe6da145e883cb0aa1b1406bbd5e5d103747b/llvm/lib/Target/AArch64/AArch64InstrAtomics.td#L40

This isn't set on the instruction so I guess `HasSideEffects` is best we can do for `ldapurs[bhw]`? 

https://github.com/llvm/llvm-project/pull/171142