[clang] [llvm] [clang][Modules][serialization] Deduplicate source location entries across loaded modules (PR #209795)

[Vassil Vassilev via cfe-commits]

vgvassilev wrote:

> > Can you measure the file stat count before and after?
> 
> Done. Added the table to the gist linked in the description.

Can you summarize the before and after file stat counts in the description of this PR?

Also, 40% is the max empirical finding, however, what's our theoretical expectation? Nominally one would think that if a pcm is dominated by copied content the reuse will yield much higher numbers...

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