[llvm] [IA]: Construct (de)interleave4 out of (de)interleave2 (PR #89276)

[Paul Walker via llvm-commits]

================
@@ -16958,40 +17079,94 @@ bool AArch64TargetLowering::lowerDeinterleaveIntrinsicToLoad(
         LdN = Builder.CreateCall(LdNFunc, {Pred, Address}, "ldN");
       else
         LdN = Builder.CreateCall(LdNFunc, Address, "ldN");
-
       Value *Idx =
           Builder.getInt64(I * LdTy->getElementCount().getKnownMinValue());
-      Left = Builder.CreateInsertVector(
-          VTy, Left, Builder.CreateExtractValue(LdN, 0), Idx);
-      Right = Builder.CreateInsertVector(
-          VTy, Right, Builder.CreateExtractValue(LdN, 1), Idx);
+      for (unsigned J = 0; J < Factor; ++J) {
+        WideValues[J] = Builder.CreateInsertVector(
+            VTy, WideValues[J], Builder.CreateExtractValue(LdN, J), Idx);
+      }
+    }
+    if (Factor == 2)
+      Result = PoisonValue::get(StructType::get(VTy, VTy));
+    else
+      Result = PoisonValue::get(StructType::get(VTy, VTy, VTy, VTy));
----------------
paulwalker-arm wrote:

Would the following work?

```
SmallVector<Type *, 4> ResultFieldTys(Factor, VTy);
Result = PoisonValue::get(StructType::create(ResultFieldTys));
```


https://github.com/llvm/llvm-project/pull/89276