[Libre-soc-bugs] [Bug 238] POWER Compressed Formal Standard writeup

bugzilla-daemon at libre-soc.org bugzilla-daemon at libre-soc.org
Sun Nov 29 22:41:34 GMT 2020


https://bugs.libre-soc.org/show_bug.cgi?id=238

--- Comment #98 from Jacob Lifshay <programmerjake at gmail.com> ---
(In reply to Alexandre Oliva from comment #96)
> I'm surprised/confused by some proposed encodings in
> https://libre-soc.org/openpower/sv/16_bit_compressed/ that affect my attempt
> at implementing an accurate compression estimator.
> 
> - is it really the case that an operation as common as 'mr' can only be
> encoded in compressed mode using an 16-bit + 16-bit immediate encoding?  (I
> gather it is, because all of the Immediate opcodes have the N and M bits set
> to 1)

The proposed instructions there are an initial guess, IIRC we plan to
rearrange/modify the supported compressed instructions to actually follow the
observed instruction statistics. as part of that, `mr` is highly likely to be
included in the final instruction set.

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