[llvm] [DAGCombiner] Fold subtraction if above a constant threshold to `umin` (PR #135194)

[Mikael Holmén via llvm-commits]

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@@ -12074,6 +12078,17 @@ SDValue DAGCombiner::visitSELECT(SDNode *N) {
 
     if (SDValue NewSel = SimplifySelect(DL, N0, N1, N2))
       return NewSel;
+
+    // (select (ugt x, C), (add x, ~C), x) -> (umin (add x, ~C), x)
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mikaelholmen wrote:

@pfusik: What if the add results in poison?
select blocks poison but umin doesn't(?). We've seen a downstream miscompile that we think is because of this.

https://github.com/llvm/llvm-project/pull/135194