On Wed, Jan 29, 2020 at 02:58:44PM +1000, Nicholas Piggin wrote:
> Adhemerval Zanella's on January 29, 2020 3:26 am:
> > __asm__ __volatile__ \
> > ("sc\n\t" \
> > "bns+ 1f\n\t" \
> > "neg %1, %1\n\t" \
> > "1:\n\t" \
> True, but the taken branch would be a 1 cycle bubble in fetch. Could
> avoid that by branching out of line then back for the error case. But
> mfocrf is fine (only sources one register), that's what should be used
> here I think.
neg %9,%1 ; isel %1,%9,%1,so
> That probably makes the performance argument for avoiding CR[SO] for
> error return indication less significant. Commonality with other
> architectures is probably the bigger reason for it.
Yes, and to have the syscall calling convention closer to the normal
function calling convention would be good, too.
Segher
