[llvm] [VPlan] First step towards VPlan cost modeling (LegacyCM in CostCtx) (PR #92555)

[via llvm-commits]

https://github.com/ayalz approved this pull request.

This looks good to me, thanks! Adding last few suggestions.

Would be good to rerun compilations of benchmarks before pushing, if not done so already, to ensure this is a non-degradation change, AFAWK.

https://github.com/llvm/llvm-project/pull/92555