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Re: [PATCH][gas][arm] Add -mwarn-restrict-it
On Mon, 9 Dec 2019 at 14:41, Wilco Dijkstra <Wilco.Dijkstra@arm.com> wrote:
>
> Hi Christophe,
>
> >> Exactly, most people just find it annoying.
> >
> > Sorry, I'd never come across this warning :-)
>
> You will see it a lot if you assemble existing Thumb-2 code for ARMv8-A...
>
> >> 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) ?
>
> The warning is useless indeed, and we could remove it in the future (but
> that is more work since hundreds of gas tests would fail).
OK, thanks for the clarification, the patch LGTM, although I can't approve it.
Christophe
>
> The instructions are not actually deprecated. It just explicitly allows an
> implementation to execute them slowly if so desired. No implementation
> has done so since it would slow down existing code.
>
> Cheers,
> Wilco
>