[clang] [llvm] [BPF] Add load-acquire and store-release instructions under -mcpu=v5 (PR #108636)

[Peilin Ye via cfe-commits]

peilin-ye wrote:

Hi @yonghong-song,

No worries, and thanks for taking a look at this!

> So far, I suggest to stick to cpu v4.

I see, I can do that.

> is it possible to add acquire/release support in BPF_ATOMIC? We might want to reserve BPFModelModifier 7 for future use.

Sounds good, that way we also avoid the "`5` and `7` are already internally used by the verifier" problem mentioned earlier.  I'll try adding one or more new flags to the `imm` field.

> should we do sign-extension here? w0 = load_acquire((s16 *)(r1 + 0x0))?

Not sure about this one.  I'll learn about `MEMSX` and look at other backends.

https://github.com/llvm/llvm-project/pull/108636