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Re: gcc optimises out test of value in register-only loop
Andrew Haley <aph@redhat.com> writes:
> On 10/14/2011 05:41 AM, Ian Lance Taylor wrote:
>> MikeW <mw_phil@yahoo.co.uk> writes:
>>
>>> volatile register int stop_loop __asm("r5")__;
>>
>> gcc does not support volatile register variables. I think it could be
>> meaningful, but it has never worked.
>
> It would be really nasty to implement: we'd have to check for volatility
> on every access to a hard register. The benefits don't seem worth it,
> IMO.
No, it's not that bad. At the tree level, we would only have to check
on every reference to a DECL for which DECL_REGISTER is true. When
expanding to RTL, we would replace each reference with a special
UNSPEC_VOLATILE which we handle specially when generating asm code. Or
perhaps simply expand each reference to a specially handled asm
statement.
Ian