[clang] [CIR] Upstream initial TBAA implementation (PR #169226)

[Hendrik Hübner via cfe-commits]

HendrikHuebner wrote:

> > Might be a good moment to check whether this is the best approach (cc @andykaylor @xlauko). Others raised the question if we really need to map them into CIR this early or whether it makes sense to only generate them during lowering time. TBH I don't remember the full discussion we had couple years back in the incubator (cc @Lancern @PikachuHyA), but this has been discussed before. Might be related to the fact that we need to keep some information around to distinguish some of the types, and instead of changing the types themselves it made sense at the time to have TBAA populated as side information, "only pay for what you use" kinda thing.
> > My personal take is that this is fine as an initial approach, once the lowering part gets upstreamed we'll have good test coverage to simplify CIRGen if needed.
> 
> @bcardosolopes I’m afraid I don’t really remember the details, and I don’t have time to look them up right now.
> 
> could you clarify what the CIR merge policy is, especially regarding authorship/attribution? I’m a bit concerned whether names from previous work might get dropped in the process.

Depending on whether or not we end up merging this I could add you as a co-author, since this PR is mostly a duplicate from your work on the incubator repo.

https://github.com/llvm/llvm-project/pull/169226