[llvm] [llvm][CodeGen] Fix the empty interval issue in Window Scheduler(#128714) (PR #129204)

[Hua Tian via llvm-commits]

huaatian wrote:

This patch is to add the newly generated MIs  into slot index map in ModuloScheduleExpander, then recalculates the LiveIntervals for these new registers, rather than producing empty ones.

https://github.com/llvm/llvm-project/pull/129204