[llvm] [X86][SelectionDAG] - Extend dag combiner to handle pow(1.5f), pow(x,2/3f) (PR #214202)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> I cross check and found that cbrt is target level requirement which can't be resolved at IR. 

Yes it can, TargetLibraryInfo already knows if cbrt/cbrtf exist and can perform the same transform. I have a very active interest in deleting all of these combines from the DAG, please only implement this in the IR 

https://github.com/llvm/llvm-project/pull/214202