[PATCH, AARCH64] Optimized memset

[pinskia@gmail.com]

> On Jul 8, 2015, at 8:05 AM, Wilco Dijkstra <wdijkstr@arm.com> wrote:
> 
> This is an optimized memset for AArch64. Memset is split into 4 main cases: small sets of up to 16
> bytes, medium of 16..96 bytes which are fully unrolled. Large memsets of more than 96 bytes align
> the destination and use an unrolled loop processing 64 bytes per iteration. Memsets of zero of more
> than 256 use the dc zva instruction, and there are faster versions for the common ZVA sizes 64 or
> 128. STP of Q registers is used to reduce codesize without loss of performance.

Since you are using the vector register already, why not avoid using the multiply and just do:
dup followed by a fmov?  At least for thunderX, this will be faster than doing the dup and the mult. That is thunderX has a cheap fmov between vector and gprs (2 cycles). 

Thanks,
Andrew


> 
> ChangeLog:
> 2015-07-08  Wilco Dijkstra  <wdijkstr@arm.com>
> 
>    * newlib/libc/machine/aarch64/memset.S (memset): 
>    Rewrite of optimized memset.
> 
> OK for commit?
> <0003-Optimized-memset.txt>