[llvm] [LoopVectorize] Further improve cost model for early exit loops (PR #126235)

[Florian Hahn via llvm-commits]

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@@ -726,6 +726,19 @@ InstructionCost VPInstruction::computeCost(ElementCount VF,
     return Ctx.TTI.getArithmeticReductionCost(
         Instruction::Or, cast<VectorType>(VecTy), std::nullopt, Ctx.CostKind);
   }
+  case VPInstruction::ExtractFirstActive: {
+    // Calculate the cost of determining the lane index.
+    auto *PredTy = toVectorTy(Ctx.Types.inferScalarType(getOperand(1)), VF);
+    IntrinsicCostAttributes Attrs(
+        Intrinsic::experimental_cttz_elts, Type::getInt64Ty(Ctx.LLVMCtx),
+        {PoisonValue::get(PredTy), ConstantInt::getTrue(Ctx.LLVMCtx)});
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fhahn wrote:

Are the arguments here only used to pass the type? Is there a variant of `IntrinsicCostAttributes` that just takes the argument types?

https://github.com/llvm/llvm-project/pull/126235