[Libre-soc-isa] [Bug 1017] ISA WG RFC for binary and ternary bitops

[bugzilla-daemon at libre-soc.org]

https://bugs.libre-soc.org/show_bug.cgi?id=1017

--- Comment #13 from Jacob Lifshay <programmerjake at gmail.com> ---
(In reply to Luke Kenneth Casson Leighton from comment #11)
> (In reply to Jacob Lifshay from comment #8)
> 
> > those are true, however that doesn't change that those operations really
> > should be using GPRs for the lookup table:
> 
> no.  see comment #5.

My response already took comment #5 into account.
> 
> > GPRs are *still* much more powerful than CRs 
> 
> and more power-hungry.

doing gpr -> cr move and then crbinlut almost certainly uses *waay more power*
than just doing crbinlut with the lut in a GPR: the additional power needed by
fetch/decode/dispatch/operand-tracking for a whole separate gpr->cr move op
almost certainly dwarfs the power needed to send 64-bits instead of 4.
> 
> > all of which are operations you'd
> > generally want to run on the look-up-table,
> 
> then use binlut followed by a single crweird transfer.

that doesn't work well, i'm assuming all of the non-lut sources/dests are CRs,
hence why we're trying to use crbinlog. you'd need 4 additional instructions.

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