https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111367
--- Comment #11 from Segher Boessenkool <segher at gcc dot gnu.org> ---
> > There really should be a comment why one alternative needs the %U{n} and the
> > other can
> > ignore it, btw. Nothing new there, but a head-scratcher :-)
>
> OK, something like: "prefixed load/store insns only have D-form but no
> update and X-form"?
Exactly. Something short is plenty, but if there is nothing there it is
surprising. Surprising is bad :-)
