[llvm] [LoopInterchange] Defer CacheCost calculation until needed (PR #146874)

[Ryotaro Kasuga via llvm-commits]

https://github.com/kasuga-fj commented:

Though out of the scope of this PR, [this message](https://github.com/llvm/llvm-project/blob/23771cad96d74123362883c03129caaa4ba0bf03/llvm/lib/Transforms/Scalar/LoopInterchange.cpp#L1882-L1887) appears somewhat misleading, as constructing DependenceInfo itself doesn’t involve any expensive computation.

https://github.com/llvm/llvm-project/pull/146874