Re: [PATCH] Optimize epilogue in thumb __aeabi_{memmove,memset} implementations

["Richard Earnshaw (lists)" <Richard dot Earnshaw at arm dot com>]

On 30/09/2019 15:55, Christos Gentsos wrote:
> The same pop instruction that is used to restore registers can be used
> to return from the function (as it is already done in other function
> implementations).
> ---
>   newlib/libc/machine/arm/aeabi_memmove-thumb.S | 4 +---
>   newlib/libc/machine/arm/aeabi_memset-thumb.S  | 4 +---
>   2 files changed, 2 insertions(+), 6 deletions(-)
>
> diff --git a/newlib/libc/machine/arm/aeabi_memmove-thumb.S b/newlib/libc/machine/arm/aeabi_memmove-thumb.S
> index 61a72581..a0aad852 100644
> --- a/newlib/libc/machine/arm/aeabi_memmove-thumb.S
> +++ b/newlib/libc/machine/arm/aeabi_memmove-thumb.S
> @@ -49,9 +49,7 @@ __aeabi_memmove:
>   	subs	r3, r3, #1
>   	bcs	1b
>   2:
> -	pop	{r4}
> -	pop	{r1}
> -	bx	r1
> +	pop	{r4, pc}
>   3:
>   	movs	r3, #0
>   	cmp	r2, #0
> diff --git a/newlib/libc/machine/arm/aeabi_memset-thumb.S b/newlib/libc/machine/arm/aeabi_memset-thumb.S
> index aa8f2719..5bb80b20 100644
> --- a/newlib/libc/machine/arm/aeabi_memset-thumb.S
> +++ b/newlib/libc/machine/arm/aeabi_memset-thumb.S
> @@ -110,9 +110,7 @@ __aeabi_memset:
>   	cmp	r4, r3
>   	bne	8b
>   9:
> -	pop	{r4, r5, r6}
> -	pop	{r1}
> -	bx	r1
> +	pop	{r4, r5, r6, pc}
>   10:
>   	movs	r3, r0
>   	movs	r4, r1

No.  That isn't interworking clean on armv4t, which we still need to 
support.

Sorry.

R.