[llvm] [RISCV] Split regalloc between RVV and other (PR #72096)

[Piyou Chen via llvm-commits]

BeMg wrote:

Here is the SPEC2k17 benchmark result to measure the impact after implementing this patch.

with O3 and enable V extension

| Name                  | Instruction count Diff % |
| ------------------ | ---------- |
| 500.perlbench_r  | -0.03%   |
| 502.gcc_r             | -0.01%   |
| 505.mcf_r            | 0% |
| 520.omnetpp_r   | 0% |
| 523.xalancbmk_r | -0.04 % |
| 525.x264_r          | 0%|
| 531.deepsjeng_r | 0% |
| 541.leela_r          | 0% |
| 548.exchange2_r | 0% |
| 557.xz_r               | 0% |

https://github.com/llvm/llvm-project/pull/72096