https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116855
--- Comment #5 from Feng Xue <fxue at os dot amperecomputing.com> ---
(In reply to Tamar Christina from comment #4)
> (In reply to Richard Biener from comment #3)
> > I would suggest to add a STMT_VINFO_ENSURE_NOTRAP or so and delay actual
> > verification to vectorizable_load when both vector type and VF are fixed.
> > We'd then likely need a LOOP_VINFO_MUST_USE_PARTIAL_VECTORS_P set
> > conservatively the other way around from
> > LOOP_VINFO_CAN_USE_PARTIAL_VECTORS_P.
> > Alignment peeling could then peel if STMT_VINFO_ENSURE_NOTRAP and the target
> > cannot do full loop masking.
>
>
> Yeah the original reported testcase is fine as the alignment makes it safe.
> For the manually misaligned case that Andrew posted it makes sense to delay
> and re-evaluate later on.
>
> I don't think we should bother peeling though, I don't think they're that
> common and alignment peeling breaks some dominators and exposes some
> existing vectorizer bugs, which is being fixed in Alex's patch.
>
> So at least alignment peeling I'll defer to a later point and instead just
> reject loops that are loading from structures the user misaligned wrt to the
> vector mode.
>
>
> So mine..
Actually, what I wish is that we could allow vectorization on early break case
for arbitrary address pointer (knowing nothing about alignment and bound) based
on some sort of assumption specified via command option under -Ofast, as the
mentioned example:
char * find(char *string, size_t n, char c)
{
for (size_t i = 0; i < n; i++) {
if (string[i] == c)
return &string[i];
}
return 0;
}
and example for which there is no way to do peeling to align more than one
address pointers:
int compare(char *string1, char *string2, size_t n)
{
for (size_t i = 0; i < n; i++) {
if (string1[i] != string2[i])
return string1[i] - string2[i];
}
return 0;
}
