[llvm] [AArch64] Tighten conditions for expanding GET_ACTIVE_LANE_MASK (PR #208962)

[Paul Walker via llvm-commits]

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@@ -34374,15 +34374,21 @@ SDValue
 AArch64TargetLowering::LowerGET_ACTIVE_LANE_MASK(SDValue Op,
                                                  SelectionDAG &DAG) const {
   EVT VT = Op.getValueType();
-  assert(VT.isFixedLengthVector() && "Expected fixed length vector type!");
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paulwalker-arm wrote:

Up to you but I would just move the existing assert just after the "There are no dedicated fixed-length instructions..." comment.

https://github.com/llvm/llvm-project/pull/208962