Re: [PATCH v2] RISC-V: Add support for 'Zacas' atomic CAS

[Nelson Chu <nelson@rivosinc.com>]

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On Tue, Oct 24, 2023 at 2:03 PM Jan Beulich <jbeulich@suse.com> wrote:

> On 24.10.2023 06:07, Tsukasa OI wrote:
> > As a single patch set, I think Gianluca's patch with a minor fix will
> > work perfectly.  But, the concept of register pairs / register groups
> > are not specific to 'Zacas', that's what I'm talking about and the
> > reason I think Gianluca's patch set's match function will not be a long
> > term solution (actually, I found Gianluca's patch set after I wrote
> > mine, but that wouldn't change my opinion).
>

As I said before, I don't know if we really need the constraint checks for
register groups in assembler or not.  Or on the other hand, I don't know if
we really need the detailed register constraint checks for assembly
syntax.  I remembered you completely unacceptable to fight back that you
don't care about hardware testing since you were doing toolchain, but for
those DV guys, they are also one of the users of toolchain.  However, for
many things, lots of users are used to using some behaviors or code in the
toolchain.  These behaviors are not wrong, maybe they are just not that
rigorous.  Even though your idea may be beneficial to some people, it can
also cause problems for others.

So, I was not rejecting your idea before, I was just trying to let you know
every change you made may cause trouble for others, especially that some
behaviors are established for many years.  Since the rvv register group
checks were argued before and removed, I will suggest we just
remove the same checks for zacas.  If other maintainers support that we
should also do these kinds of complicated constraint checks, then you can
ignore my comments.

Thanks
Nelson