[Libre-soc-isa] [Bug 535] setvl/setvli encoding & future reg file expansion

bugzilla-daemon at libre-soc.org bugzilla-daemon at libre-soc.org
Tue Dec 1 19:31:21 GMT 2020


--- Comment #14 from Jacob Lifshay <programmerjake at gmail.com> ---
(In reply to Luke Kenneth Casson Leighton from comment #12)
> in *compressed*, do we want a separate setvli? mmm... maayyybeee... although
> i don't think there's space.

sounds like the perfect place to do some immediate reencoding to just use
common values, giving us 1 bit for setvli vs. setmvli

> (In reply to Jacob Lifshay from comment #11)
> > > > We can even include setting CR0 (if Rc = 1) to allow jumps on VL == 0
> > > > immediately after setvl.
> > > 
> > > awesome, isn't it? :)  i love CRs.  see comment #4 i put Rc support in.  i
> > > mean, it's part of XO-form so why not.
> > 
> > yup, that's what I was referencing.
> ok,ok, this is hilarious: if we allow setvl to be an SV-P48 prefixable
> instruction, it *might* be possible (stress: might) to get CR0 retargetted
> at an alternative CR.
> one downside of Rc=1 is you can't doecify an alternative CR, end result you
> have to move it to another CR then the bc can use that alternative target.

can't bc just use cr0 as-is?

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