diff mbox series

[02/12] RISC-V: memmove() size optimized version: Use compressed registers only

Message ID 20250409064701.3435-3-marlene.fally@gmail.com
State New
Headers
Series newlib: RISC-V: Optimize memory and string functions for code size |

Commit Message

m fally April 9, 2025, 6:46 a.m. UTC 
  Change register t1 to register a4, so that the affected instructions
can be compressed. Since now we have less registers available, the
following changes need to be made:
In the previous version of this function, a4 was used to hold the offset
that needs to be added to source and destination addresses before copying
any data in the case of source address > destination address.
Since a4 now holds the destination address, this offset is not calculated
anymore. Instead, the value in a2 (the number of bytes to be copied) is added
to the source and destination addresses. Therefore, in the case of
source address > destination adress, a value of 1 needs to be subtracted
from both addresses before starting the copying process.

Reviewed-by: Christian Herber <christian.herber@oss.nxp.com>
Signed-off-by: m fally <marlene.fally@gmail.com>
---
 newlib/libc/machine/riscv/memmove.S | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

Comments

Kito Cheng April 9, 2025, 8 a.m. UTC | #1 
LGTM

On Wed, Apr 9, 2025 at 2:55 PM m fally <marlene.fally@gmail.com> wrote:
>
> Change register t1 to register a4, so that the affected instructions
> can be compressed. Since now we have less registers available, the
> following changes need to be made:
> In the previous version of this function, a4 was used to hold the offset
> that needs to be added to source and destination addresses before copying
> any data in the case of source address > destination address.
> Since a4 now holds the destination address, this offset is not calculated
> anymore. Instead, the value in a2 (the number of bytes to be copied) is added
> to the source and destination addresses. Therefore, in the case of
> source address > destination adress, a value of 1 needs to be subtracted
> from both addresses before starting the copying process.
>
> Reviewed-by: Christian Herber <christian.herber@oss.nxp.com>
> Signed-off-by: m fally <marlene.fally@gmail.com>
> ---
>  newlib/libc/machine/riscv/memmove.S | 16 ++++++++--------
>  1 file changed, 8 insertions(+), 8 deletions(-)
>
> diff --git a/newlib/libc/machine/riscv/memmove.S b/newlib/libc/machine/riscv/memmove.S
> index 0f7216a68..123ab3834 100644
> --- a/newlib/libc/machine/riscv/memmove.S
> +++ b/newlib/libc/machine/riscv/memmove.S
> @@ -16,22 +16,22 @@
>  memmove:
>    beqz a2, 2f
>
> -  mv t1, a0
> +  mv a4, a0
>    li a3, 1
>    bgtu  a1, a0, 1f
>
>    li a3, -1
> -  addi  a4, a2 , -1
> -  add t1, t1, a4
> -  add a1, a1, a4
> +  add   a4, a4, a2
> +  add   a1, a1, a2
>
> +3:
> +  add   a4, a4, a3
> +  add   a1, a1, a3
>  1:
>    lb a5, 0(a1)
> -  sb a5, 0(t1)
> +  sb a5, 0(a4)
>    add   a2, a2, -1
> -  add   t1, t1, a3
> -  add   a1, a1, a3
> -  bnez a2, 1b
> +  bnez a2, 3b
>
>  2:
>    ret
> --
> 2.49.0
>
diff mbox series

Patch

diff --git a/newlib/libc/machine/riscv/memmove.S b/newlib/libc/machine/riscv/memmove.S
index 0f7216a68..123ab3834 100644
--- a/newlib/libc/machine/riscv/memmove.S
+++ b/newlib/libc/machine/riscv/memmove.S
@@ -16,22 +16,22 @@ 
 memmove:
   beqz a2, 2f
 
-  mv t1, a0
+  mv a4, a0
   li a3, 1
   bgtu  a1, a0, 1f
 
   li a3, -1
-  addi  a4, a2 , -1
-  add t1, t1, a4
-  add a1, a1, a4
+  add   a4, a4, a2
+  add   a1, a1, a2
 
+3:
+  add   a4, a4, a3
+  add   a1, a1, a3
 1:
   lb a5, 0(a1)
-  sb a5, 0(t1)
+  sb a5, 0(a4)
   add   a2, a2, -1
-  add   t1, t1, a3
-  add   a1, a1, a3
-  bnez a2, 1b
+  bnez a2, 3b
 
 2:
   ret