[llvm] [LV] Vectorize histogram operations (PR #99851)

[Florian Hahn via llvm-commits]

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@@ -274,6 +276,10 @@ static Instruction *getInstructionForCost(const VPRecipeBase *R) {
     return IG->getInsertPos();
   if (auto *WidenMem = dyn_cast<VPWidenMemoryRecipe>(R))
     return &WidenMem->getIngredient();
+  // FIXME: Override the cost method properly to take gather/scatter cost
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fhahn wrote:

Histogram cost computation looks self contained, can we instead directly implement `VPHistogramRecipe::computeCost` instead falling back?

https://github.com/llvm/llvm-project/pull/99851