[llvm] AMDGPU: Combine nnan fminimum/fmaximum to fminnum_ieee/fmaxnum_ieee (PR #142217)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> I'm not sure this plays well with the generic DAGCombiner. It prefers fminimum/fmaximum over the others when available; it might be better to just add this as an alternative pattern based on the flag

The DAGCombiner doesn't directly do any transforms between the different min/maxes, but it should. The preference is only applied when matching the compare and select patterns into one of these 

https://github.com/llvm/llvm-project/pull/142217