https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113134
--- Comment #17 from JuzheZhong <juzhe.zhong at rivai dot ai> ---
(In reply to Tamar Christina from comment #16)
> >
> > I wonder whether ARM SVE can also use this approach VEC_EXTRACT with index =
> > 0.
>
> Perhaps, I'll look into it thanks. though this is ofcourse only applicable
> when the mask comes from whilelo.
>
> In the future when we get to loops such as:
>
> for (int i = ..;;)
> {
> if (a)
> {
> ....
> if (b)
> return i;
> }
> }
>
> the reduction would come from the first active element of the mask created
> by the condition a and not the whilelo.
If the mask comes from a condition, VEC_EXTRACT approach is definitely
incorrect.
However, look into vectorizable_live_operation_1:
The mask should always come from whilo instruction (or say it is always loop
mask):
tree mask = vect_get_loop_mask (loop_vinfo, &gsi,
&LOOP_VINFO_MASKS (loop_vinfo),
1, vectype, 0);
So I think it should be correct using VEC_EXTRACT with index = 0.
But if we look into vectorizable_early_break which will handle mask come from
condition, that is another story.
