[clang] [llvm] [clang][Modules][Serialization] Avoid serializing duplicate source location entries for shared input files (PR #209795)

[Chuanqi Xu via llvm-commits]

ChuanqiXu9 wrote:

> > Tested in our internal workload and the result looks not bad (no crash). This is not a LGTM and I want to take a close look for this. Thanks for your patience in ahead.
> 
> Can you provide maybe some performance numbers, too?
> 
> @ayokunle321, the other thing I was thinking about is that now when we can detect duplicates maybe we can issue better diagnostics advising users how to avoid such duplications.

I didn't observe significant change.

https://github.com/llvm/llvm-project/pull/209795