[OpenPOWER-HDL-Cores] [Libre-soc-dev] GPR-to-FPR and FPR-to-GPR move operations

Jacob Lifshay programmerjake at gmail.com
Sun May 30 05:44:18 UTC 2021


On Sat, May 29, 2021, 02:05 Luke Kenneth Casson Leighton <lkcl at lkcl.net>
wrote:

> links:
> https://bugs.libre-soc.org/show_bug.cgi?id=230#c71
> https://libre-soc.org/openpower/sv/int_fp_mv/
>
> Lauri is kindly investigating MP3 in SVP64 assembler and it's turning out
> to
> be a good test of what opcodes are needed.  in the bi-weekly meeting last
> week, Paul, we mentioned briefly the need for GPR-to-FPR and FPR-to-GPR
> mv operations (straight bit-wise) given that VSX/SIMD will not be added to
> Libre-SOC as a GPU / VPU.
>

If we're going to add bitwise FPR <-> GPR move instructions, it is also
very important to also add the combined integer <-> fp conversion + move
instructions, since those are easily >90% of FPR <-> GPR moves, converting
a common 2 instruction sequence to a 1 instruction sequence, as explained
in more detail here:
https://bugs.libre-soc.org/show_bug.cgi?id=230#c74

Jacob

>
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