[llvm] [LV] Handle partial reductions with predication (PR #194859)

[Sander de Smalen via llvm-commits]

================
@@ -6355,6 +6355,9 @@ struct VPPartialReductionChain {
   /// is `1 - AccumulatorOpIdx`.
   unsigned AccumulatorOpIdx;
   unsigned ScaleFactor;
+
+  /// Optional blend guarding the reduction.
----------------
sdesmalen-arm wrote:

```suggestion
  /// Optional blend to represent predication for the block that updates the reduction.
```

https://github.com/llvm/llvm-project/pull/194859