[llvm] [RISCV][MRI] Account for fixed registers when determining callee saved regs (PR #115756)

[Craig Topper via llvm-commits]

topperc wrote:

> LLVM + this patch:
> 
> ```
>         addi    sp, sp, -16
>         sd      s0, 8(sp)                       # 8-byte Folded Spill
>         sd      s1, 0(sp)                       # 8-byte Folded Spill
>         li      s0, 321
>         li      a0, 0
>         ld      s0, 8(sp)                       # 8-byte Folded Reload
>         ld      s1, 0(sp)                       # 8-byte Folded Reload
>         addi    sp, sp, 16
>         ret
> ```

Shouldn't this patch prevent the save/restore of s0?

https://github.com/llvm/llvm-project/pull/115756