[llvm] [LV] Simplify the chain traversal in `getScaledReductions()` (NFCI) (PR #184830)

[Florian Hahn via llvm-commits]

================
@@ -6159,33 +6131,71 @@ getScaledReductions(VPReductionPHIRecipe *RedPhiR, VPValue *PrevValue,
 
     if (!BinOp || !Instruction::isBinaryOp(BinOp->getOpcode()) ||
         !MatchExtends(BinOp->operands()))
-      return false;
+      return std::nullopt;
   } else if (match(UpdateR, m_Add(m_VPValue(), m_VPValue())) ||
              match(UpdateR, m_FAdd(m_VPValue(), m_VPValue()))) {
-    // We already know the operands for Update are Op and PhiOp.
+    // We already know Op is an operand of UpdateR.
     if (!MatchExtends({Op}))
-      return false;
+      return std::nullopt;
     BinOp = UpdateR;
   } else {
-    return false;
+    return std::nullopt;
   }
 
+  return ExtendedReductionOperand{BinOp, CastRecipes};
+}
+
+/// Examines reduction operations to see if the target can use a cheaper
----------------
fhahn wrote:

```suggestion
/// Examines reduction operations of \p RedPhiR to see if the target can use a cheaper
```

or something like that to clarify this looks for the operations that are part of the `RedPhiR` reduction cycle

https://github.com/llvm/llvm-project/pull/184830