[llvm] [SROA] Allow `llvm.launder.invariant.group` intrinsic to be splittable (PR #72056)

[Nikita Popov via llvm-commits]

nikic wrote:

> Not exactly sure if the optimized IR of `partial_use_of_struct` test is what we want.

That's not it. I'm looking for a case where the alloca is split and some parts are promoted, but others aren't, e.g. because they are accessed via volatile operations. There should still be an alloca left at the end, and the launder.invariant.group needs to be rewritten (and possibly duplicated) appropriately.

https://github.com/llvm/llvm-project/pull/72056