[llvm] [InstCombine] Canonicalize `abs(sub(ext(X),ext(Y)))` -> `ext(sub(max(X,Y),min(X,Y)))` (PR #162296)

[David Green via llvm-commits]

davemgreen wrote:

Maybe something like #161224 but for abd? That was just a test/prototype to show @rj-jesus who was asking about something similar. It would need some way for the backend to tell the vectorizer that this thing is cheap (or an intrinsic for it). It is useful for cases like i32 abd/mulh/hadd with MVE, where the i64 costs are otherwise very high.

https://github.com/llvm/llvm-project/pull/162296