[Libre-soc-isa] [Bug 1010] 1st Draft OPF ISA WG External RFC ls003: "bigint" operations

[bugzilla-daemon at libre-soc.org]

https://bugs.libre-soc.org/show_bug.cgi?id=1010

--- Comment #10 from Luke Kenneth Casson Leighton <lkcl at lkcl.net> ---
(In reply to Jacob Lifshay from comment #8)

> oh, why not? iirc you basically said more than 3-in/2-out was a dealbreaker

for *64-bit* datapaths. CR Fields are 4-bit.

although... yeah, a case could be made that the priority is
the Dependency Hazard Matrices, and that it's not the size
of the datapaths themselves that are the only consideration.

4-in is *definitely* not okay.  3-out (64-bit RT, 64-bit RS, 4-bit CR0)
is... dicey.  i'm happy to raise it with the ISA WG, to get
them to pass it through to IBM's Architects, to see what
they think.

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