[llvm] [TBAA] Do not rewrite TBAA tag in `adjustForAccess` if already exists (PR #96483)

[Antonio Frighetto via llvm-commits]

antoniofrighetto wrote:

> > > Is there any reason that clang shouldn't emit struct-path tags for !tbaa.struct?
> > 
> > That seems to be the case, AFAICT, though this should be orthogonal wrt the above, if I'm not mistaken.
>
> I am not sure, have inconsistent/conflicting `tbaa` and `tbaa.struct` nodes seems like it could cause other problems as well. If `tbaa.struct` nodes would be consistent with the `!tbaa` nodes, this patch shouldn't be needed?

May there exist a specific reason why NewStructPathTBAA directly favours !tbaa metadata? This is at least what it seems to be from https://reviews.llvm.org/D41394. Maybe cc/ @kosarev?

https://github.com/llvm/llvm-project/pull/96483