[llvm] [LoopVectorizer] Add support for partial reductions (PR #92418)

[Sam Tebbs via llvm-commits]

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@@ -7575,6 +7575,11 @@ static bool planContainsAdditionalSimplifications(VPlan &Plan,
         }
         continue;
       }
+      // A partial reduction is very differently costed compared to its
+      // underlying add instruction that the legacy cost model sees, so consider
+      // it an additional simplification.
+      if (dyn_cast<VPPartialReductionRecipe>(&R))
+        continue;
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SamTebbs33 wrote:

Yeah that's better, thank you.

https://github.com/llvm/llvm-project/pull/92418