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

[Richard Earnshaw (lists)]

Thanks.  I tweaked this slightly to include the compatibility header 
acle-compat.h and put this in.

R.

On 30/09/2019 18:16, Christos Gentsos wrote:
> On Mon, Sep 30 2019 at 16:37:26 +0100, Richard Earnshaw (lists) wrote:
>> On 30/09/2019 16:31, Richard Earnshaw (lists) wrote:
>>> 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).
>>>> ---
>>>>  Â  newlib/libc/machine/arm/aeabi_memmove-thumb.S | 4 +---
>>>>  Â  newlib/libc/machine/arm/aeabi_memset-thumb.SÂ  | 4 +---
>>>>  Â  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
>>>>  Â  2:
>>>> -    pop    {r4}
>>>> -    pop    {r1}
>>>> -    bx    r1
>>>> +    pop    {r4, pc}
>>>>  Â  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
>>>>  Â  9:
>>>> -    pop    {r4, r5, r6}
>>>> -    pop    {r1}
>>>> -    bx    r1
>>>> +    pop    {r4, r5, r6, pc}
>>>>  Â  10:
>>>>        movs    r3, r0
>>>>        movs    r4, r1
>>>>
>>>
>>> No.  That isn't interworking clean on armv4t, which we still need to
>>> support.
>>>
>>> Sorry.
>>>
>>> R.
>>
>> However, a patch that tests __ARM_ARCH >=5 and uses your improved
>> sequence only in that case (preserving the old code otherwise) would
>> probably be OK :-)
>>
>> R.
> 
> Oh sorry then, I wasn't aware of that, thanks for the correction. I
> re-made the patch such that it now checks for __ARM_ARCH, as per your
> suggestion. Does it look better?
> 
> Thanks,
> Christos
> ---
>   newlib/libc/machine/arm/aeabi_memmove-thumb.S | 4 ++++
>   newlib/libc/machine/arm/aeabi_memset-thumb.S  | 4 ++++
>   2 files changed, 8 insertions(+)
> 
> diff --git a/newlib/libc/machine/arm/aeabi_memmove-thumb.S b/newlib/libc/machine/arm/aeabi_memmove-thumb.S
> index 61a72581..465a5a19 100644
> --- a/newlib/libc/machine/arm/aeabi_memmove-thumb.S
> +++ b/newlib/libc/machine/arm/aeabi_memmove-thumb.S
> @@ -49,9 +49,13 @@ __aeabi_memmove:
>   	subs	r3, r3, #1
>   	bcs	1b
>   2:
> +#if __ARM_ARCH >= 5
> +	pop	{r4, pc}
> +#else
>   	pop	{r4}
>   	pop	{r1}
>   	bx	r1
> +#endif
>   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..52094a7b 100644
> --- a/newlib/libc/machine/arm/aeabi_memset-thumb.S
> +++ b/newlib/libc/machine/arm/aeabi_memset-thumb.S
> @@ -110,9 +110,13 @@ __aeabi_memset:
>   	cmp	r4, r3
>   	bne	8b
>   9:
> +#if __ARM_ARCH >= 5
> +	pop	{r4, r5, r6, pc}
> +#else
>   	pop	{r4, r5, r6}
>   	pop	{r1}
>   	bx	r1
> +#endif
>   10:
>   	movs	r3, r0
>   	movs	r4, r1
>