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

[Nikita Popov via llvm-commits]

https://github.com/nikic commented:

I don't think that this is a good IR level canonicalization. The new form is more complex and less analyzable -- e.g. it would require teaching code about this specific pattern to recognize that the result is >= 0. And the need for correlated values make it incorrect for undef values.

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