[llvm] [IndVarSimplify][NFC] Add precommit test for umax subset ule folding (PR #213295)

[Antonio Frighetto via llvm-commits]

https://github.com/antoniofrighetto commented:

Maybe I'm missing something here, but isn't umax(a, b) <= umax(a, b, c) always true already handled by InstCombine?

https://github.com/llvm/llvm-project/pull/213295