[llvm] [SelectionDAG] Legalize non-divisible scalable vector widening (PR #218777)

[Paul Walker via llvm-commits]

================
@@ -9242,6 +9242,32 @@ SDValue DAGTypeLegalizer::ModifyToType(SDValue InOp, EVT NVT,
   if (InEC.hasKnownScalarFactor(WidenEC))
     return DAG.getExtractSubvector(dl, NVT, InOp, 0);
 
+  if (InVT.isScalableVector()) {
----------------
paulwalker-arm wrote:

```suggestion
  if (NVT.isScalableVector() && InVT.isScalableVector()) {
```
The functionality also works when both types are fixed length, but that might be looking for trouble so I'm happy enough with the scalable vector restriction. We can revisit later to see if there's value in relaxing it.

https://github.com/llvm/llvm-project/pull/218777