Re: arm memcpy of aligned data

[Kyrill Tkachov <kyrylo dot tkachov at foss dot arm dot com>]

On 16/08/15 20:01, Mike Stump wrote:
> On Jun 15, 2015, at 7:30 AM, Kyrill Tkachov <kyrylo.tkachov@arm.com> wrote:
> > On 29/05/15 11:15, Kyrill Tkachov wrote:
> > > On 29/05/15 10:08, Kyrill Tkachov wrote:
> > > > Hi Mike,
> > > >
> > > > On 28/05/15 22:15, Mike Stump wrote:
> > > > > So, the arm memcpy code of aligned data isn’t as good as it can be.
> > > > >
> > > > > void *memcpy(void *dest, const void *src, unsigned int n);
> > > > >
> > > > > void foo(char *dst, int i) {
> > > > >      memcpy (dst, &i, sizeof (i));
> > > > > }
> > > > >
> > > > > generates horrible code, but, it we are willing to notice the src or the destination are aligned, we can do much better:
> > > > >
> > > > > $ ./cc1 -fschedule-fusion -fdump-tree-all-all -da -march=armv7ve -mcpu=cortex-m4 -fomit-frame-pointer -quiet -O2 /tmp/t.c -o t.s
> > > > > $ cat t.s
> > > > > [ … ]
> > > > > foo:
> > > > > 	@ args = 0, pretend = 0, frame = 4
> > > > > 	@ frame_needed = 0, uses_anonymous_args = 0
> > > > > 	@ link register save eliminated.
> > > > > 	sub	sp, sp, #4
> > > > > 	str	r1, [r0]	@ unaligned
> > > > > 	add	sp, sp, #4
> > > > I think there's something to do with cpu tuning here as well.
> > > That being said, I do think this is a good idea.
> > > I'll give it a test.
> > The patch passes bootstrap and testing ok and I've seen it
> > improve codegen in a few places in SPEC.
> > I've added a testcase all marked up.
> >
> > Mike, I'll commit the attached patch in 24 hours unless somebody objects.
> Was this ever applied?

Sorry, slipped through the cracks.
Committed with r226935.

Thanks,
Kyrill