[llvm] [ThinLTO] optimize propagateAttributes performance (PR #132917)

[Teresa Johnson via llvm-commits]

https://github.com/teresajohnson commented:

A couple ideas for improving the efficiency of this code below. I'm curious as to what the index graph looks like in your case. This isn't a recursive algorithm, so there presumably are just an extreme number of references for it to take so long. But then I'm surprised that improving this would drop the indexing time so dramatically to complete in 10s, as the rest of the indexing contains other graph traversals such as computing imports, and those aren't free.

https://github.com/llvm/llvm-project/pull/132917