[PATCH][gas][arm] Add -mwarn-restrict-it

[Christophe Lyon]

On Mon, 9 Dec 2019 at 11:19, Wilco Dijkstra <Wilco.Dijkstra@arm.com> wrote:
>
> Hi Christophe,
>
> > So default effect of this patch is that the warning will not be
> > emitted anymore, unless the user requests it explicitly.
>
> Exactly, most people just find it annoying.

Sorry, I'd never come across this warning :-)

>
> > What is the actual performance impact of these instructions? I mean:
> > with your patch most people won't be aware of a possible future
> > problem with their code.
>
> Well you get much better performance when you use these instructions
> (https://gcc.gnu.org/ml/gcc-patches/2019-11/msg00399.html).
>
> I don't believe it's the assembler's job to warn about potentially slow code.
>

So... if the code is actually faster, do you mean that the warning is
in fact wrong? Shouldn't it be removed instead of disabled, then?
Or does it mean that these instructions with actually be forbidden in
v9 (my understanding is that things become deprecated in vN before
being removed/forbidden in vN+1) ?
In which case, I think the warning is desirable/useful.

> Cheers,
> Wilco