[llvm] Fix: Distinguish CFI Metadata Checks in MergeFunctions Pass (PR #65963)

[Duncan P. N. Exon Smith via llvm-commits]

https://github.com/dexonsmith requested changes to this pull request.

This an improvement on https://reviews.llvm.org/D154119, in that it doesn't break function sorting.

However:
- It looks the performance is quadratic in the size of the function. There should be a more efficient way to do this. Especially since you have prior knowledge that the functions have sorted as equal.
- It adds a new "compare"-named and -behaving function which violates strict-weak order (since it will return both `A<B` and `B<A`). It shouldn't over-promise that it can compare `<` when it only decides "yes or no" for equivalency.

A few other comments inline.


https://github.com/llvm/llvm-project/pull/65963