[llvm] [AArch64] Emit ST<OP> instruction when the return value has no use. (PR #72887)

[via llvm-commits]

ktkachov-arm wrote:

> > Using LDADD here is a conscious decision by compilers (GCC also generates the same code). See the thread at https://gcc.gnu.org/pipermail/gcc-patches/2018-October/509550.html
> 
> Thanks for the useful information. But maybe we can add a special handling for the LD with acquire semantics?

It's tempting to do this translation to STADD only for the relaxed memory model, but apparently that's not legal either:
https://gcc.gnu.org/pipermail/gcc-patches/2018-October/509632.html

https://github.com/llvm/llvm-project/pull/72887