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

[Vassil Vassilev via llvm-commits]

vgvassilev wrote:

Thank you @qiongsiwu for the detailed analysis. It aligns with my expectation -- the size benefits are marginal for apple because they spent significant time to modularize the entire toolchain bottom up by reducing the header duplication as much as possible. 

I am a bit surprised that we saw a regression in scanning and writing -- @ayokunle321, any ideas what we can do? Do you need artifacts such as a flamegraph, etc?

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