[llvm] [TargetLowering] Prevent expandVectorFindLastActive from creating illegal vector types during vector op legalization. (PR #190914)

[Luke Lau via llvm-commits]

================
@@ -10139,6 +10145,44 @@ SDValue TargetLowering::expandVectorFindLastActive(SDNode *N,
   SDLoc DL(N);
   auto [Mask, StepVec] = getLegalMaskAndStepVector(
       N->getOperand(0), /*ZeroIsPoison=*/true, DL, DAG);
+
+  // If StepVec is empty, the stepvector would require splitting.
+  // Split the operation instead and let it be recursively legalized.
+  if (!StepVec) {
+    EVT MaskVT = N->getOperand(0).getValueType();
+    EVT ResVT = N->getValueType(0);
+
+    // Split the mask
+    auto [LoVT, HiVT] = DAG.GetSplitDestVTs(MaskVT);
+    std::pair<SDValue, SDValue> SplitMask =
+        DAG.SplitVector(N->getOperand(0), DL);
+    SDValue MaskLo = SplitMask.first;
+    SDValue MaskHi = SplitMask.second;
----------------
lukel97 wrote:

Use destructuring?

```suggestion
    auto [MaskLo, MaskHi] = DAG.SplitVector(N->getOperand(0), DL);
```

https://github.com/llvm/llvm-project/pull/190914