[llvm] [DAGCombiner] add fold (xor (smin(x, C), C)) and fold (xor (smax(x, C), C)) (PR #155141)

[guan jian via llvm-commits]

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@@ -10086,6 +10086,48 @@ SDValue DAGCombiner::visitXOR(SDNode *N) {
   if (SDValue Combined = combineCarryDiamond(DAG, TLI, N0, N1, N))
     return Combined;
 
+  // fold (xor (smin(x, C), C)) -> select (x < C), xor(x, C), 0
+  // fold (xor (smin(C, x), C)) -> select (x < C), xor(x, C), 0
+  if (N0.getOpcode() == ISD::SMIN && N0.hasOneUse()) {
+    SDValue Op0 = N0.getOperand(0);
+    SDValue Op1 = N0.getOperand(1);
+
+    if (Op1 != N1) {
+      std::swap(Op0, Op1);
+    }
+
+    if (Op1 == N1) {
+      if (isa<ConstantSDNode>(N1)) {
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rez5427 wrote:

Well, I added some logic to handle vector types and wrote a few tests. The vector instruction set doesn’t have parallel instructions like csinv, so the optimization only perform better when the constant C is 0 nor -1.

https://github.com/llvm/llvm-project/pull/155141