[llvm] [RISCV] Set AllocationPriority in line with LMUL (PR #131176)

[Luke Lau via llvm-commits]

lukel97 wrote:

> Thanks for looking at this! I tried this before but I can't remember why I dropped it (maybe it was simply because setting `AllocationPriority` couldn't fix #113489). I do see some improvements and regressions but I don't think they are significant, this PR locates in improving compile-time since it avoids the later eviction? @lukel97 Can you also evaluate the performance please?

I've kicked off a run on a banana pi now, it should be done over the weekend

https://github.com/llvm/llvm-project/pull/131176