[Libre-soc-isa] [Bug 1056] questions and feedback (v2) on OPF RFC ls010

[bugzilla-daemon at libre-soc.org]

https://bugs.libre-soc.org/show_bug.cgi?id=1056

--- Comment #68 from Luke Kenneth Casson Leighton <lkcl at lkcl.net> ---
(In reply to Paul Mackerras from comment #67)

> No, the adde RTL (addeo is in the adde/adde./addeo/addeo. group) should be
> fine as it is. There is no "if" in its RTL currently. The reason that addi
> has the "if" is to distinguish between addi and paddi. 

indeed.

> In the addi case, if
> you don't want to mention sv.addi you could restructure the RTL as:
> 
>   if "paddi" then
>     if R=0 then
>       ...
>     else
>       ...
>   else
>     RT <- (RA|0) + EXTS64(SI)

ahh that works really well.

> It should be only those instructions where there is an existing prefixed
> variant that would need to mention sv.xxx in the RTL

as they're mutually-exclusive (no PO9-PO1-WordInstr and no PO1-PO9-WordInstr)
that shouldn't occur

> (or where sv.xxx is actually different from xxx, of course).

the only one is sv.bc (ok and sv.bcctr etc.) and i would recommend
it be done as entirely separate RTL, otherwise it's going to get
very odd.

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