[llvm] [DAG] Fold (umin (sub a b) a) -> (usubo a b); (select usubo.1 a usubo.0) (PR #161651)

[Matt Arsenault via llvm-commits]

================
@@ -6216,6 +6216,18 @@ SDValue DAGCombiner::visitIMINMAX(SDNode *N) {
                                         SDLoc(N), VT, N0, N1))
     return SD;
 
+  // (umin (sub a, b) a) -> (usubo a, b); (select usubo.1, a, usubo.0)
----------------
arsenm wrote:

```suggestion
  // (umin (sub a, b), a) -> (usubo a, b); (select usubo.1, a, usubo.0)
```

https://github.com/llvm/llvm-project/pull/161651