[clang] [llvm] [clang/LLVM] Add flatten_deep attribute for depth-limited inlining (1/2) (PR #165777)

[via llvm-commits]

WenleiHe wrote:

alwaysinline can't always meet the needs -- it causes a particular function to be inlined into all callers, which is not selective based on calling context. What this does is make inlining happen under a particular call tree, and fully flatten a call tree. 

+ at mtrofin hope you can see the merit of the extension -- we have real use case for it in our internal codebase where we don't want any calls for some paths and this is a simple, natural extension for existing flatten attribute. 

https://github.com/llvm/llvm-project/pull/165777