[llvm] [SelectionDAG] Add GET_ACTIVE_LANE_MASK to ComputeNumSignBits (PR #208977)

[Paul Walker via llvm-commits]

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@@ -17,3 +17,34 @@ entry:
   %data = call <16 x i8> @llvm.masked.load.v16i8.p0(ptr %p, i32 1, <16 x i1> %mask, <16 x i8> zeroinitializer)
   ret <16 x i8> %data
 }
+
+define void @active_lane_mask_mstore_vscaleX2(ptr %p, i64 %n) #0 {
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paulwalker-arm wrote:

```suggestion
define void @active_lane_mask_mstore_vscaleX2(ptr %p, i64 %n) vscale_range(2,2) {
```

Given this is fundamental to the test it makes it easier to understand the function in isolation.

https://github.com/llvm/llvm-project/pull/208977