[llvm] IndVarSimplify/test: replace undef with poison (PR #126069)

[Nikita Popov via llvm-commits]

https://github.com/nikic commented:

If possible, please replace these with non-undef/poison values instead. The store can be 0 and the sdiv operand should be an argument.

https://github.com/llvm/llvm-project/pull/126069