On Mon, Oct 8, 2018 at 3:57 PM Paul Koning <paulkon...@comcast.net> wrote:
>
> I have a movmem pattern in my target that pays attention to the alignment
> argument.
>
> GCC isn't passing in the expected alignment part of the time. I have this
> test case:
>
> extern int *i, *j;
> extern int iv[40], jv[40];
>
> void f1(void)
> {
> __builtin_memcpy (i, j, 32);
> }
>
> void f2(void)
> {
> __builtin_memcpy (iv, jv, 32);
> }
>
> When the movmem pattern is called for f1, alignment is 1. In f2, it is 2
> (int is 2 bytes in pdp11) as expected.
>
> The compiler clearly knows that int* points to aligned data, since it
> generates instructions that assume alignment (this is a strict-alignment
> target) when I dereference the pointer. But somehow it gets it wrong for
> block move.
>
> I also see this for the individual move operations that are generated for
> very short memcpy operations; if the count is 4, I get four move byte
> operations for f1, but two move word operations for f2.
>
> This seems like a bug. Am I missing something?
Yes, memcpy doesn't require anything bigger than byte alignment and
GCC infers alignemnt
only from actual memory references or from declarations (like iv /
jv). For i and j there
are no dereferences and thus you get alignment of 1.
Richard.
>
> paul
>
