[llvm] Reland "[LoopVectorizer] Add support for chaining partial reductions #120272" (PR #124282)

[Florian Hahn via llvm-commits]

================
@@ -8717,39 +8717,54 @@ void VPRecipeBuilder::collectScaledReductions(VFRange &Range) {
   }
 }
 
-std::optional<std::pair<PartialReductionChain, unsigned>>
-VPRecipeBuilder::getScaledReduction(PHINode *PHI,
-                                    const RecurrenceDescriptor &Rdx,
-                                    VFRange &Range) {
+bool VPRecipeBuilder::getScaledReductions(
+    Instruction *PHI, Instruction *RdxExitInstr, VFRange &Range,
+    SmallVector<std::pair<PartialReductionChain, unsigned>> &Chains) {
----------------
fhahn wrote:

```suggestion
    SmallVectorImpl<std::pair<PartialReductionChain, unsigned>> &Chains) {
```


https://github.com/llvm/llvm-project/pull/124282