[PATCH][AArch64] Add optimized memchr

[Wilco Dijkstra]

> Ondřej Bílka wrote:
> On Fri, Sep 25, 2015 at 02:21:13PM +0100, Wilco Dijkstra wrote:
> > An optimized memchr was missing for AArch64. This version is similar to strchr and is
> significantly
> > faster than the C version. Passes GLIBC tests.
> >
> > OK for commit?
> >
> > ChangeLog:
> > 2015-09-25  Wilco Dijkstra  <wdijkstr@arm.com>
> > 2015-09-25  Kevin Petit  <kevin.petit@arm.com>
> >
> > 	* sysdeps/aarch64/memchr.S (__memchr): New file.
> 
> How you tested performance. I think that also here loading first 32
> bytes unaligned should be better. Could you use dryrun to verify?
> 
> Also same optimization could be used for memrchr.

I haven't tuned this at all, this is an existing implementation that
was added to Newlib last year but not yet ported to GLIBC.

For maximum performance doing the first 16/32 bytes unaligned will likely 
be fastest just like it was for strlen.

Wilco