[llvm] [BasicBlockSections] Propose a staleness detection method, checking the func cfg node num (PR #133244)

[Jinjie Huang via llvm-commits]

Jinjie-Huang wrote:

> CFG hash like This PR is much preferred.

Thanks for response, and I also appreciate Fengxiang's related work in this area. 
Using node count and hashing the entire function may not be mutually exclusive. At this stage, adding this feature facilitates quick implementation, providing Propeller with a "last resort" 
 of staleness detection capability. 
In the future, when CFG hash-related features are well-supported (which might involve significant changes), users can choose to use either cfg_hash for verification (or directly incorporate the node count into the hash calculation).

https://github.com/llvm/llvm-project/pull/133244