Re: movmem pattern and missed alignment

[Paul Koning <paulkoning at comcast dot net>]

> On Oct 8, 2018, at 1:29 PM, Andrew Haley <aph@redhat.com> wrote:
> 
> On 10/08/2018 06:20 PM, Michael Matz wrote:
>> Only if you somewhere visibly add accesses to *i and *j.  Without them you 
>> only have the "accesses" via memcpy, and as Richi says, those don't imply 
>> any alignment requirements.  The i and j pointers might validly be char* 
>> pointers in disguise and hence be in fact only 1-aligned.  I.e. there's 
>> nothing in your small example program from which GCC can infer that those 
>> two global pointers are in fact 2-aligned.
> 
> So all you'd actually have to say is
> 
> void f1(void)
> {
>    *i; *j;
>    __builtin_memcpy (i, j, 32);
> }

No, that doesn't help.  Not even if I make it:

void f1(void)
{
    k = *i + *j;
    __builtin_memcpy (i, j, 4);
}

The first line does word aligned references to *i and *j, but the memcpy stubbornly remains a byte move.

	paul