[llvm] [SDAGBuilder] Fix incorrect fcmp+select to minnum/maxnum transform (PR #184590)

[Nikita Popov via llvm-commits]

nikic wrote:

> > we must convert to minimumnum/maximumnum instead.
> 
> Even that can still alter NaN payloads as per the usual NaN rules, whereas select exactly returns one of the operands, doesn't it? So this still seems like an incorrect transform?

Yes, that's correct. The goal should still be to remove this transform entirely (https://github.com/llvm/llvm-project/pull/93575), but it will need more work.

https://github.com/llvm/llvm-project/pull/184590