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

[Teresa Johnson via llvm-commits]

https://github.com/teresajohnson approved this pull request.

@nikic nice find!

This could presumably help other places that use a DenseSet/Map of ValueInfo. Perhaps the description should be about improving the hashing of ValueInfo and note the massive improvement to propagateAttributes in your case in the summary.

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