[llvm] [VPlan] Don't use the legacy cost model for loop conditions (PR #156864)

[John Brawn via llvm-commits]

================
@@ -1117,6 +1117,29 @@ InstructionCost VPInstruction::computeCost(ElementCount VF,
     return Ctx.TTI.getIndexedVectorInstrCostFromEnd(Instruction::ExtractElement,
                                                     VecTy, Ctx.CostKind, 0);
   }
+  case VPInstruction::BranchOnCount: {
----------------
john-brawn-arm wrote:

BranchOnCond doesn't cause a compare instruction to be generated, it uses the condition generated by another instruction.

https://github.com/llvm/llvm-project/pull/156864