[llvm] [UTC] Record TBAA semantics when autogenerating check lines (PR #147670)

[Antonio Frighetto via llvm-commits]

antoniofrighetto wrote:

> > Hit an assert in a few tests that are using the `new-struct-path-tbaa` option, while testing locally. Relaxed the assert and left a TODO for now, as I couldn't find description of the new TBAA format in the LangRef, and I'm not sure if adoption to the new format is still an open work.
> 
> Hopefully the following links will help: [04e1d01](https://github.com/llvm/llvm-project/commit/04e1d01736d3368fd491d4bdb99a52452e9e83e1) https://lists.llvm.org/pipermail/llvm-dev/2017-November/118748.html

IIUC the 2017 thread discusses moving away from !tbaa.struct, currently expected to be attached to aggregate-accessing instructions like memcpy, towards a more refined !tbaa, also encoding the struct size and field size, among others. However, Clang is still defaulting to the classic TBAA format. Likewise, the number of tests (both in Clang and LLVM) using the old format by far exceeds the number of tests using the new-struct-path-tbaa format. Perhaps, for the time being, supporting the new format may be left behind.

Follow-up PRs updating tests: https://github.com/llvm/llvm-project/pull/154347, https://github.com/llvm/llvm-project/pull/154354. @rjmccall Kindly know anyone who could take another look at this? 

https://github.com/llvm/llvm-project/pull/147670