[llvm] [X86][ISel] Improve VPTERNLOG matching for negated logic trees (PR #164863)

[Phoebe Wang via llvm-commits]

================
@@ -4740,6 +4737,35 @@ bool X86DAGToDAGISel::tryVPTERNLOG(SDNode *N) {
     return SDValue();
   };
 
+  // Identify and (optionally) peel an outer NOT that wraps a pure logic tree
+  auto tryPeelOuterNotWrappingLogic = [&](SDNode *Op) {
+    if (Op->getOpcode() == ISD::XOR && Op->hasOneUse() &&
+        ISD::isBuildVectorAllOnes(Op->getOperand(1).getNode())) {
+      SDNode *InnerN = Op->getOperand(0).getNode();
----------------
phoebewang wrote:

Use SDValue and `SDValue()` for the return, then we can use
```
if (SDValue InnerOp = tryPeelOuterNotWrappingLogic(N)) {
  PeeledOuterNot = true;
  N = InnerOp.getNode();
}
```

https://github.com/llvm/llvm-project/pull/164863