[llvm] [LoopInterchange] Hoist isCompuatableLoopNest() in the control flow (PR #124247)

[Madhur Amilkanthwar via llvm-commits]

madhur13490 wrote:

I am not sure how to test this. One possible option is to add an optimization remark before `DependenceInfo` and CHECK-NOT the message for the case which exits from `isComputableLoopNest()`. I tried this locally but requires changes to 5 other tests. I just want to check on what is suitable before I make the change to the tests.
Looking forward to suggestions!

https://github.com/llvm/llvm-project/pull/124247