[llvm] VT: teach a special-case optz about samesign (PR #122590)

[Nikita Popov via llvm-commits]

nikic wrote:

Though in this particular case, the most efficient way would probably be something like `getSignedPredicate()` because then samesign doesn't have to be considered four times for four predicate comparisons.

https://github.com/llvm/llvm-project/pull/122590