Re: [PATCH v2] ARM: Add Cortex-A15 optimized NEON and VFP memcpy routines, with IFUNC.

[Richard Henderson <rth@twiddle.net>]

On 2013-04-16 11:25, Will Newton wrote:
>   ports/sysdeps/arm/armv7/multiarch/Makefile         |   3 +

Does this really require v7?  From a brief read I didn't see anything in the 
_arm version that didn't work since v5te (ldrd and pld).  Any reason not to put 
this into armv6 instead?

> +ENTRY(memcpy)
> +	.type	memcpy, %gnu_indirect_function
> +	ldr	r1, .Lmemcpy_arm
> +	tst	r0, #HWCAP_ARM_NEON
> +	it	ne
> +	ldrne	r1, .Lmemcpy_neon
> +	bne	1f

Swap vfp and neon tests and you don't need the branch.

> +.Lreturn:

Unused label?

> +	ldr	tmp1, [src, #-60]	/* 15 words to go.  */
> +	str	tmp1, [dst, #-60]

These negative offsets mean thumb2 doesn't work.  That's fine, but it means 
that you need care for this in the _arm case.

You have two choices: either do the swapping to arm mode by hand in the impl 
file, or force the entire memcpy.o to arm mode by using #define NO_THUMB at the 
top, before the #include <sysdep.h>.

If you chose the later, then you don't have to worry about thumb2's restriction 
on rd=rn when rm=pc, and can avoid the extra move.  And the then unnecessary it 
markup.


r~