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

[Matt Arsenault via llvm-commits]

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@@ -6219,6 +6219,25 @@ SDValue DAGCombiner::visitIMINMAX(SDNode *N) {
                                         SDLoc(N), VT, N0, N1))
     return SD;
 
+  if (TLI.isOperationLegalOrCustom(ISD::USUBO, VT) &&
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arsenm wrote:

Mostly I'm wondering how to get this to fire in the 64-bit amdgpu case. usubo isn't legal, but expanding the 64-bit usubo is as good as expanding the min 

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