[llvm] [GlobalISel] Fix [SU]SUBO combine (PR #116998)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> The carry-out is target dependent and can lead to surprising and non-deterministic results when used as carry-in.

Can you elaborate? The carry out should be a boolean value that conforms to the target boolean content. It is not a free form value that you can just add to something. 

> Note that the carry-in participates in the addition. It must be a 0 or 1 value.

No? It's a boolean. Its value shouldn't be directly interpreted as an addend?



https://github.com/llvm/llvm-project/pull/116998