[llvm] [RISCV] Shrink vslideup's LMUL when lowering fixed insert_subvector (PR #65997)

[Jay Foad via llvm-commits]

jayfoad wrote:

> This is somewhat dependent on #66211 , since it introduces a subregister copy that triggers a crash with -early-live-intervals in one of the tests.

I think #65916 and #66211 are two different fixes for the same problem. Do you #65916 also fix the crash? Or do you really need #66211?

https://github.com/llvm/llvm-project/pull/65997