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

[Jan Svoboda via llvm-commits]

jansvoboda11 wrote:

Another direction to explore can be making the logic in `buildLoadedInputFiles()` lazy. Currently, the amount of work it performs depends on the size of the imported modules. I think it's usually better to make it proportional to the size of the written module itself. (That holds true especially for large module graphs.) Why don't we use the same visitor+lookup pattern we already use for `HeaderFileInfo` here?

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