[llvm] Zext sext undef in sdag (PR #115451)

[via llvm-commits]

fengfeng09 wrote:

> This optimization is not correct for 'undef'. I think it would be correct for 'poison', but SelectionDAG doesn't have 'poison' today.
> 
> See also https://blog.regehr.org/archives/1837

I see. Thanks for your explanation, so zext undef to a zero is by designed, is this right?

https://github.com/llvm/llvm-project/pull/115451