[llvm] [SDAG] (setcc (add nsw a, b), zero, s??) -> (setcc a, b, s??) (PR #175459)

[Craig Topper via llvm-commits]

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@@ -13893,6 +13893,13 @@ SDValue DAGCombiner::visitSETCC(SDNode *N) {
     return Combined;
   }
 
+  // (setcc (sub n?w a, b), zero, ?lt) -> (setcc a, b, ?lt)
+  if (isZeroOrZeroSplat(N1) && N0.getOpcode() == ISD::SUB) {
+    if ((N0->getFlags().hasNoSignedWrap() && ISD::isSignedIntSetCC(Cond)) ||
+        (N0->getFlags().hasNoUnsignedWrap() && ISD::isUnsignedIntSetCC(Cond)))
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topperc wrote:

An unsigned comparison with zero is probably going to be written to true/false or eq/ne before we get here.

https://github.com/llvm/llvm-project/pull/175459