[llvm] [VPlan] Construct initial once and pass clones to tryToBuildVPlan (NFC). (PR #141363)

[Florian Hahn via llvm-commits]

fhahn wrote:

Thanks for the heads-up, it is a bit surprising. There was at least one case where we now are doing unnecessary work which should be fixed by ad58ea3ba8b9ab60a3b31316cb2010034f6257e3. 

This recovers some of the impact, but not yet all of it: http://llvm-compile-time-tracker.com/compare.php?from=3033f202f6707937cd28c2473479db134993f96f&to=1a0b9e5834f7fd4abf058864e656f8e26b7a26ff&stat=instructions:u

Will check if there's anything else to improve.

https://github.com/llvm/llvm-project/pull/141363