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

[David Sherwood via llvm-commits]

david-arm wrote:

Hi @fhahn, could you clarify what you mean by passing in `CostCtx`? I have addressed most of your review comments downstream, but it's not clear whether you want me to just pass it into `calculateEarlyExitCost` and create it in `isOutsideLoopWorkProfitable`, or pass it to `isOutsideLoopWorkProfitable`. Once I know your preference I can upload a new version - thanks!

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