[PATCH 06/12] RISC-V: memmove() size optimized version: Relax RAW dependency

[Kito Cheng]

LGTM

On Wed, Apr 9, 2025 at 2:57 PM m fally <marlene.fally@gmail.com> wrote:
>
> Move the instruction that increments the remaining number of
> bytes to be copied inbetween the load and store instructions.
> This is done in order to relax the RAW dependency between the
> load and store instructions.
>
> Reviewed-by: Christian Herber <christian.herber@oss.nxp.com>
> Signed-off-by: m fally <marlene.fally@gmail.com>
> ---
>  newlib/libc/machine/riscv/memmove.S | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/newlib/libc/machine/riscv/memmove.S b/newlib/libc/machine/riscv/memmove.S
> index 671a6a158..6ecad9ad6 100644
> --- a/newlib/libc/machine/riscv/memmove.S
> +++ b/newlib/libc/machine/riscv/memmove.S
> @@ -28,9 +28,9 @@ memmove:
>    add   a4, a4, a3             /* in case of source address < destination address, increment both addresses by -1 before copying any data to obtain the correct start addresses */
>    add   a1, a1, a3
>  .Lcopy:
> -  lbu a5, 0(a1)                        /* copy bytes as long as a2 (= the number of bytes to be copied) > 0 */
> +  lbu a5, 0(a1)
> +  add   a2, a2, -1             /* copy bytes as long as a2 (= the number of bytes to be copied) > 0. the increment is done here to relax the RAW dependency between load and store */
>    sb a5, 0(a4)
> -  add   a2, a2, -1
>    bnez a2, .Lincrement
>
>  .Ldone:
> --
> 2.49.0
>