[clang] [compiler-rt] [UBSan] Add -fsanitize=uninitialized-read check (ISO C 6.3.2.1p2) (PR #207529)

[Yanzuo Liu via llvm-commits]

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

IIUC `memcpy` stuff is not handled correctly.

> **Known limitations (future work):**
> 
> ...
> 
> - Whole-function existence check, not path-sensitive — misses conditionally-initialized variables

Please implement it in this PR. This is the core part of `-fsanitize=uninitialized-read`. This check will be a duplicate of `-Wuninitialized` if it's not path-sensitive.

https://github.com/llvm/llvm-project/pull/207529