[llvm-branch-commits] [llvm] [LoongArch][DAGCombiner] Combine vxor (vand ..) to vandn (PR #161037)

[via llvm-branch-commits]

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@@ -4939,6 +4939,86 @@ void LoongArchTargetLowering::ReplaceNodeResults(
   }
 }
 
+// Helper to attempt to return a cheaper, bit-inverted version of \p V.
+static SDValue isNOT(SDValue V, SelectionDAG &DAG) {
+  // TODO: don't always ignore oneuse constraints.
+  V = peekThroughBitcasts(V);
+  EVT VT = V.getValueType();
+
+  // Match not(xor X, -1) -> X.
+  if (V.getOpcode() == ISD::XOR &&
+      (ISD::isBuildVectorAllOnes(V.getOperand(1).getNode()) ||
+       isAllOnesConstant(V.getOperand(1))))
+    return V.getOperand(0);
+
+  // Match not(extract_subvector(not(X)) -> extract_subvector(X).
+  if (V.getOpcode() == ISD::EXTRACT_SUBVECTOR &&
+      (isNullConstant(V.getOperand(1)) || V.getOperand(0).hasOneUse())) {
+    if (SDValue Not = isNOT(V.getOperand(0), DAG)) {
+      Not = DAG.getBitcast(V.getOperand(0).getValueType(), Not);
+      return DAG.getNode(ISD::EXTRACT_SUBVECTOR, SDLoc(Not), VT, Not,
+                         V.getOperand(1));
+    }
+  }
+
+  // Match not(SplatVector(not(X)) -> SplatVector(X).
+  if (V.getOpcode() == ISD::BUILD_VECTOR) {
+    if (SDValue SplatValue =
+            cast<BuildVectorSDNode>(V.getNode())->getSplatValue()) {
+      if (!V->isOnlyUserOf(SplatValue.getNode()))
+        return SDValue();
+
+      if (SDValue Not = isNOT(SplatValue, DAG)) {
+        Not = DAG.getBitcast(V.getOperand(0).getValueType(), Not);
+        return DAG.getSplat(VT, SDLoc(Not), Not);
+      }
+    }
+  }
+
+  // Match not(or(not(X),not(Y))) -> and(X, Y).
+  if (V.getOpcode() == ISD::OR && DAG.getTargetLoweringInfo().isTypeLegal(VT) &&
+      V.getOperand(0).hasOneUse() && V.getOperand(1).hasOneUse()) {
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heiher wrote:

and this one.

https://github.com/llvm/llvm-project/pull/161037