[llvm] [LV][VPlan] Implement VPlan-based cost for exit condition. (PR #125640)

[Elvis Wang via llvm-commits]

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@@ -964,6 +964,37 @@ InstructionCost VPInstruction::computeCost(ElementCount VF,
     return Ctx.TTI.getArithmeticReductionCost(
         Instruction::Or, cast<VectorType>(VecTy), std::nullopt, Ctx.CostKind);
   }
+  case VPInstruction::BranchOnCount: {
+    Type *ValTy = Ctx.Types.inferScalarType(getOperand(0));
+
+    // If the vector loop only executed once (VF == original trip count), ignore
+    // the cost of cmp.
+    // TODO: We can remove this after hoist `unrollByUF` and
+    // `optimizeForVFandUF` which will optimize BranchOnCount out.
+    auto TC = dyn_cast_if_present<ConstantInt>(
+        getParent()->getPlan()->getTripCount()->getUnderlyingValue());
+    if (TC && VF.isFixed() && TC->getSExtValue() == VF.getFixedValue())
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ElvisWang123 wrote:

Updated, thanks!

https://github.com/llvm/llvm-project/pull/125640