[Bug target/43814] gcc failed to inline memcpy

[mkuvyrkov at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43814

--- Comment #9 from Maxim Kuvyrkov <mkuvyrkov at gcc dot gnu.org> 2010-12-04 18:09:15 UTC ---
(In reply to comment #8)

> In the end we _should_ be able to use alignment information of the
> types used at the access (that's also more reliable as compared to
> use alignment information from pointer argument types).
> 
> But we already do that in MEM_REF expansion:
> 
>         align = MAX (TYPE_ALIGN (TREE_TYPE (exp)),
>                      get_object_alignment (exp, BIGGEST_ALIGNMENT));

Indeed.  SRC will be considered 4-byte aligned in
==
unsigned long long get_ull(const unsigned int *src)
{
    unsigned long long tmp;

    tmp = src[0];
    return tmp;
}
==
, but only 1-byte aligned in
==
unsigned long long get_ull(const unsigned int *src)
{
    unsigned long long tmp;

    __builtin_memcpy(&tmp, &src[0], 8);
    return tmp;
}
==

It seems we should really use for MEM_REFs
==
align = get_pointer_alignment (exp, BIGGEST_ALIGNMENT);
==
without relying on type alignment.  Unfortunately, that will worsen code
generation even more.