[llvm] [VPlan] First step towards VPlan cost modeling. (PR #92555)

[David Blaikie via llvm-commits]

dwblaikie wrote:

Creating reduced test cases can be somewhat difficult - probably best to revert this patch for now (since https://github.com/llvm/llvm-project/pull/92555#issuecomment-2182700184 provides at least one example of a real problem) and address that reproducible issue - then check with the folks who also had problems to see if they can check whether that fix addresses their issues before recommitting? Would that be acceptable?

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