[llvm] [DropUnnecessaryAssumes] Make the ephemeral value check more precise (PR #160700)

[Nikita Popov via llvm-commits]

nikic wrote:

> > Interestingly, this doesn't seem to actually matter in practice (no difference on llvm-opt-benchmark).
> 
> Not sure how I feel about this. I've personally abandoned patches in the past due to zero-diff (or even small diff) on llvm-opt-benchmark. The patch is certainly nice for completeness though?

Generally agreed. I do think it's valuable to have this to make sure the pass behavior is consistent (i.e. the pass shouldn't break just because we added a second dead assume).

https://github.com/llvm/llvm-project/pull/160700