Re: [patch] allow target config to state r18 is fixed on aarch64

[Olivier Hainque <hainque at adacore dot com>]

Hi Kyrill,

> On 16 Oct 2018, at 18:33, Kyrill Tkachov <kyrylo.tkachov@foss.arm.com> wrote:
> 
>> I'm happy to move that part to aarch64_conditional_register_usage
>> if that's considered more canonical of course.
> 
> I don't think it's more canonical, and it is a run-time thing, whereas your patch changes things
> at configure time, so there's no runtime overhead.

Ok.

>> It seems like I might need to set call_used_registers to 1 as well.
>> 
>> STATIC_CHAIN_REGNUM still needs to be adjusted directly I think.
> 
> I think so too, so you'd still need to have these configure-time changes.
> If we could make it all runtime that would be clean, but perhaps it's not worth
> splicing the two approaches.

Agreed. I also thought of triggering the effect of -ffixed-r18
from within one of the vxworks early hooks, but this wouldn't prevent
the use as a static chain AFAICS. Interesting ...

>> I wondered if we could set it to R11 unconditionally and picked
>> the way ensuring no change for !vxworks ports, especially since I
>> don't have means to test more than what I described above.
>> 
>> We're working on a transition to gcc-8 and I can certainly port this
>> and the rest rapidly to verify that we get similar results on the
>> more recent code base.
> 
> So, do you still want to make this change in current trunk? Or will you make the necessary changes
> when contributing the vxworks port?

I'm working on the port and will re propose
the change as part of that soon, hopefully in the
forthcoming days.

It was very useful to have early feedback on the approach,
thanks !

Olivier