[llvm-branch-commits] [llvm] [LV] Only create partial reductions when profitable. (PR #181706)

[Florian Hahn via llvm-branch-commits]

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@@ -6216,10 +6195,17 @@ getScaledReductions(VPReductionPHIRecipe *RedPhiR, VPCostContext &CostCtx,
     if (!PHISize.hasKnownScalarFactor(ExtSrcSize))
       return std::nullopt;
 
+    /// Check if a partial reduction chain is supported by the target (i.e.
+    /// does not have an invalid cost) for the given VF range. Clamps the range
+    /// and returns true if feasible for any VF.
     VPPartialReductionChain Chain(
         {UpdateR, *ExtendedOp,
          static_cast<unsigned>(PHISize.getKnownScalarFactor(ExtSrcSize)), RK});
-    if (!isValidPartialReduction(Chain, PhiType, CostCtx, Range))
+    if (!LoopVectorizationPlanner::getDecisionAndClampRange(
+            [&](ElementCount VF) {
+              return getPartialReductionLinkCost(CostCtx, Chain, VF).isValid();
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fhahn wrote:

could we store the partial reduction cost as part of chain, to avid re-computing below?

https://github.com/llvm/llvm-project/pull/181706