I wouldn't learn C++ by learning LLVM if that's what you mean, or at least have one of (say) Stroustrup's books on the shelf.
I think I did Stroustrup's "Principles and Practice Using C++" for about 12 chapters a while ago; I might revisit it later thanks to your comment.
I advise you to at least read Tour of C++ 2nd edition.
Projects like LLVM are one of the reasons C++ will stay around for decades to come, and they make use of many features that you won't find explained how they work on a book describing LLVM APIs.