[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 18:48:44 GMT 2020


--- Comment #11 from Jacob Lifshay <programmerjake at gmail.com> ---
(In reply to Luke Kenneth Casson Leighton from comment #8)
> the answer to that is in the form of the two Compressed instructions i added
> 1hr ago:
>    * setmvli immed
>    * setvl rt, ra

Now, that's a good reason to keep a mvl spr.

> > 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.

> > For setvli, since the value VL is set to is a constant, having a destination
> > register is much less important.
> no, it's critical.  without it, loops are forced to read VL after the setvl
> instruction.

your talking about setvl, not setvli. setvli sets both VL and MVL to a known
constant for use with fixed-length vectors, no need to loop.

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