https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78020
ktkachov at gcc dot gnu.org changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |RESOLVED
Resolution|--- |INVALID
--- Comment #3 from ktkachov at gcc dot gnu.org ---
(In reply to Yvan Roux from comment #2)
> Christophe, Kyrill
>
> My understanding of the ARMv8-A Architecture Reference Manual is not the
> same. For me when the vectors have two elements ZIP, UZIP and TRN
> instruction give the same result.
>
> for instance if we have:
>
> + -----+------+
> Vn | A1 | A0 |
> + -----+------+
> Vm | B1 | B0 |
> + -----+------+
>
> UZIP1 reads the even-numbered elemenents of Vn (i.e A0), places it in the
> lower half of Vd and then do the same with Vm, thus we have:
>
> + -----+------+
> Vd | B0 | A0 |
> + -----+------+
>
> ZIP1 reads the first pair from Vn (which is only A0 is this case) and places
> it into the lowest element of Vd and then do same with Vm to get them
> interleaved, thus we also have:
>
> + -----+------+
> Vd | B0 | A0 |
> + -----+------+
>
> Maybe the confusion comes from the revision of the manual you looked at,
> which doesn't include detailled explanation of these instructions,
> DDI0487A_k includes figures.
>
> Kyrill, in the UZP1 figures (C7.2.346) it show that the first unzipped
> vector is from Vn ... but maybe I'm the one who misundertand the description
> ! ;)
Yes, you're right Yvan.
James just went through it with me on a board and they are indeed equivalent.
Sorry for the confusion.
