V2 [PATCH] x86-64: Avoid rep movsb with short distance [BZ #27130]

[Florian Weimer]

* H. J. Lu via Libc-alpha:

>  1:
> +# if AVOID_SHORT_DISTANCE_REP_MOVSB
> +	movq	%rsi, %rcx
> +	subq	%rdi, %rcx
> +2:
> +/* Avoid "rep movsb" if RCX, the distance between source and destination,
> +   is N*4GB + [1..63] with N >= 0.  */
> +	cmpl	$63, %ecx
> +	jbe	L(more_2x_vec)	/* Avoid "rep movsb" if ECX <= 63.  */
> +# endif
>  	mov	%RDX_LP, %RCX_LP
>  	rep movsb
>  L(nop):

Why not use _LP names here?  I think the %ecx comparison at least can
give false results on x86-64 (64-bit).

Thanks,
Florian
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