[clang] [Serialization] Storing DeclID separately (PR #95897)

[Ilya Biryukov via cfe-commits]

ilya-biryukov wrote:

Thanks for this patch, I will try it on our codebase to see the effects of it and report back to you.
I am also trying to understand in which cases this would be a win and when not.
IIUC, this is always a win when `ModuleFileIndex != 0`  and a pessimization otherwise.

When is `ModuleFileIndex == 0`? Does this only happen for predefined decls (that we never deserialize) or also for the declarations owned by the currently written module?


https://github.com/llvm/llvm-project/pull/95897