[llvm] [DAGCombine]Fold (fadd A, Splat(fneg(B))) -> (fsub A, Splat(B)) (PR #173967)

[Simon Pilgrim via llvm-commits]

RKSimon wrote:

@ChunyuLiao Sorry I don't quite understand, why don't you want to use the existing getCheaperNegatedExpression call? I don't like the idea that we end up with duplicated folds for splat cases everywhere.

https://github.com/llvm/llvm-project/pull/173967