[llvm] [VPlan] Return Max from computeCost without underlying instrs. (PR #109708)

[Florian Hahn via llvm-commits]

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@@ -315,7 +311,9 @@ InstructionCost VPRecipeBase::computeCost(ElementCount VF,
     // transform, avoid computing their cost multiple times for now.
     Ctx.SkipCostComputation.insert(UI);
   }
-  return UI ? Ctx.getLegacyCost(UI, VF) : 0;
+  // Max cost is used as a sentinel value to detect recipes without underlying
+  // instructions for which no forced target instruction cost should be applied.
+  return UI ? Ctx.getLegacyCost(UI, VF) : InstructionCost::getMax();
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fhahn wrote:

<Move the comment above to update the existing comment, thanks!

https://github.com/llvm/llvm-project/pull/109708