On Fri, Dec 15, 2023 at 1:38 PM Jeff Law <jeffreya...@gmail.com> wrote:
>
>
>
> On 12/12/23 20:54, Palmer Dabbelt wrote:
> > I can't actually find anything in the ISA manual that makes Ztso imply
> > A. In theory the memory ordering is just a different thing that the set
> > of availiable instructions (ie, Ztso without A would still imply TSO for
> > loads and stores). It also seems like a configuration that could be
> > sane to build: without A it's all but impossible to write any meaningful
> > multi-core code, and TSO is really cheap for a single core.
> >
> > That said, I think it's kind of reasonable to provide A to users asking
> > for Ztso. So maybe even if this was a mistake it's the right thing to
> > do?
> >
> > gcc/ChangeLog:
> >
> > * common/config/riscv/riscv-common.cc (riscv_implied_info):
> > Remove {"ztso", "a"}.
> I'd tend to think step #1 is to determine what the ISA intent is,
> meaning engagement with RVI.
>
> We've got time for that engagement and to adjust based on the result.
> So I'd tend to defer until we know if Ztso should imply A or not.
Palmer is correct. There is no coupling between Ztso and A. (And
there are uncontrived examples of such systems: e.g. embedded
processors without caches that don't support the LR/SC instructions,
but happen to be TSO.)
>
> jeff
