[llvm] [LV]: Teach LV to recursively (de)interleave. (PR #89018)

[Paul Walker via llvm-commits]

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@@ -2773,10 +2773,22 @@ static Value *interleaveVectors(IRBuilderBase &Builder, ArrayRef<Value *> Vals,
   // Scalable vectors cannot use arbitrary shufflevectors (only splats), so
   // must use intrinsics to interleave.
   if (VecTy->isScalableTy()) {
-    VectorType *WideVecTy = VectorType::getDoubleElementsVectorType(VecTy);
-    return Builder.CreateIntrinsic(WideVecTy, Intrinsic::vector_interleave2,
-                                   Vals,
-                                   /*FMFSource=*/nullptr, Name);
+    unsigned InterleaveFactor = Vals.size();
+    SmallVector<Value *> InterleavingValues(Vals);
+    // As we are interleaving, the values sz will be shrinked until we have the
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paulwalker-arm wrote:

```suggestion
    // When interleaving, the number of values will be shrunk until we have the
```

https://github.com/llvm/llvm-project/pull/89018