[llvm] [LV] NFCI: Add RecurKind to VPPartialReductionChain (PR #181705)

[Benjamin Maxwell via llvm-commits]

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@@ -5964,14 +5968,11 @@ getScaledReductions(VPSingleDefRecipe *RedPhiR, VPValue *PrevValue,
   // If one is found, we use the discovered reduction instruction in
   // place of the accumulator for costing.
   if (getScaledReductions(RedPhiR, Op, Chains, CostCtx, Range)) {
-    RedPhiR = Chains.rbegin()->ReductionBinOp;
     Op = UpdateR->getOperand(0);
     PhiOp = UpdateR->getOperand(1);
-    if (Op == RedPhiR)
+    if (Op == Chains.rbegin()->ReductionBinOp)
       std::swap(Op, PhiOp);
   }
-  if (RedPhiR != PhiOp)
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MacDue wrote:

> if it doesn't go into this if() block, then RedPhiR == PhiOp is always true as per these two statements on lines 5944-5945

This does not seem to be the case. If you simply replace the `if (RedPhiR != PhiOp) return false;` with `assert(RedPhiR == PhiOp);` that fails in a bunch of tests that are not intended to match partial reductions when the `if (getScaledReductions(...))` block is not entered. I guess they're still rejected by some other matching though. 

https://github.com/llvm/llvm-project/pull/181705