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

bugzilla-daemon at libre-soc.org bugzilla-daemon at libre-soc.org
Wed Dec 23 19:54:26 GMT 2020


--- Comment #19 from Luke Kenneth Casson Leighton <lkcl at lkcl.net> ---
(In reply to Luke Kenneth Casson Leighton from comment #18)
> jacob says VL should be allowed to be set to zero because
> then you can have a CR branch-condition test.

right: ok, so this is possible: VL can indeed be set to zero.  if the source
register RA contains zero, VL will be set to zero.  then, when that happens (as
long as you used "setvl." i.e. Rc=1 mode) the CR will indeed be set so that its
eq-to-zero flag will be raised.

however setting the *immediate* it makes no sense to me for setvli to be able
to set VL to zero.

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