[llvm] Clean up strange uses of getAnalysisIfAvailable (PR #65729)

[Nikita Popov via llvm-commits]

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

LGTM

GVN seems to have different behavior regarding LoopInfo in the LegacyPM and NewPM, but that's an orthogonal issue. I'll check whether always requiring LoopInfo in GVN has any compile-time impact, as I don't think this is supposed to be an optional analysis there (otherwise loop load PRE is not going to work reliably).

https://github.com/llvm/llvm-project/pull/65729