>On 8/5/25 19:43, Richard Henderson wrote:
>> That said, I'm a little confused
>> why we'd want to use SUBS+B.{EQ,NE} instead of SUB+CB{Z,NZ}.
>
> The answer to that is that B.{EQ,NE} converts easily to CSEL/CSINC/CSINV.
I did it originally because that works out best - CBZ has a shorter branch
range and was not efficient on all micro architectures at the time.
It's possible that doing it differently works out better today - immediate
generation is far more advanced now, CBZ is fast on all microarchitectures,
and it may be that eg. something like:
mov x0, imm16
cmp x1, x0, lsl 4
could be used in many cases.
Interestingly I don't see it trigger even in basic examples, so the pattern may
have bitrotted already...
Cheers,
Wilco
