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

[Teresa Johnson via llvm-commits]

https://github.com/teresajohnson requested changes to this pull request.

I don't like the approach of putting temporary analysis information in the GlobalValueSummaryInfo struct - it doesn't belong there logically, and while probably minimal, it also adds size overhead to the structure across all use cases.

I'm surprised to hear that this change took a 25 minute indexing down to 10s. We build very large apps frequently and I haven't seen anything like this, so I think we'll want to look more at why this is taking so long in your case. From the profile, is most of the time spent on the set insert, or on the set contains check?

It would be slightly better to put this in the Flags in the ValueInfo itself (where we already have the read only / write only flags being checked here), but I'd like a better understanding of why this is behaving so extreme in your app first.

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