[PATCH v2 3/3] riscv: memcpy_noalignment: Reorder to store via a3, then bump a3

[Peter Bergner]

On 9/3/25 4:45 AM, Yao Zihong wrote:
> Rewrite the copy micro-step from:
> 
>     REG_L  a4, 0(a5)
>     addi   a3, a3, SZREG
>     addi   a5, a5, SZREG
>     REG_S  a4, -SZREG(a3)
> 
> to:
> 
>     REG_L  a4, 0(a5)
>     addi   a5, a5, SZREG
>     REG_S  a4, 0(a3)
>     addi   a3, a3, SZREG
> 
> Semantics are unchanged: both read *(a5_old), write *(a3_old), and then
> increment a3/a5 by SZREG. memcpy assumes non-overlapping regions, so the
> reordering preserves correctness.

LGTM and bonus, the REG_S insn is converted to a compressed form too.

Reviewed-by: Peter Bergner <bergner@tenstorrent.com>

Peter