[llvm] [RISCV] Fold subtraction if above threshold to Zbb `minu` (PR #134235)

[Piotr Fusik via llvm-commits]

================
@@ -14895,6 +14895,19 @@ static SDValue performSUBCombine(SDNode *N, SelectionDAG &DAG,
   if (SDValue V = combineSubShiftToOrcB(N, DAG, Subtarget))
     return V;
 
+  if (Subtarget.hasStdExtZbb()) {
+    // fold (sub x, (select (ult x, y), 0, y)) -> (umin x, (sub x, y))
----------------
pfusik wrote:

That's three differences:
- ult vs uge
- x, y vs y, x
- 0, y vs y, 0

Any two would form a different spelling of the same pattern. I can add more tests. Is there some canonical form or shortcuts to match different spellings?
All three at once (or one) is a different pattern.

https://github.com/llvm/llvm-project/pull/134235