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

[Grigory Pastukhov via cfe-commits]

grigorypas wrote:

> What exactly is the motivation for this?
> 
> This also kind of changes the semantics of `alwaysinline`, which states the functions should be inlined always unless illegal. I guess this can be viewed as making inlining illegal in such circumstances, but a LangRef update would probably be good either way.

Can you please elaborate what do you mean by it "changes the semantics of alwaysinline"? I am introducing a new attribute flatten_deep both on clang side and LLVM side. `alwaysinline` should still mean the same thing.


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