[Libre-soc-bugs] [Bug 558] gcc SV intrinsics concept

[bugzilla-daemon at libre-soc.org]

https://bugs.libre-soc.org/show_bug.cgi?id=558

--- Comment #57 from Luke Kenneth Casson Leighton <lkcl at lkcl.net> ---
(In reply to Jacob Lifshay from comment #56)

> So, to be clear, you're advocating for not using the scheme I proposed just
> now, or not using the scheme I proposed 18 months ago as part of the SVP for
> RISC-V spec?

i'd really like to use both (dynamically), that was what the CR8x8 matrix
concept was.  there is room to overload elwidth to do it... however the
implications for the DMs are so complex that it would be foolish to try as a
first iteration.

given that if we *don't* use vertical numbering on CRs we are forced instead to
add a 1 year delay on the critical path it is clearly unacceptable to use the
SVP scheme... for CRs

given that it is clearly unacceptable to completely cut off entire swathes of
the regfile from scalar operations forcing the use of convoluted predicated mv
operations if we *do* use vertical numbering on FP and Int operations it is
clearly unacceptable to use the vertical numbering scheme... for FP and INT.

conclusion: vertical numbering for CRs (reluctantly), horizontal numbering for
INT and FP.

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