[Libre-soc-bugs] [Bug 751] idea for reducing dependency matrixes in 6600-derived architecture with register renaming

[bugzilla-daemon at libre-soc.org]

https://bugs.libre-soc.org/show_bug.cgi?id=751

--- Comment #11 from Jacob Lifshay <programmerjake at gmail.com> ---
(In reply to Luke Kenneth Casson Leighton from comment #9)
> now, it so happens that only the Function Unit itself can determine,
> itself, whether things such as XER.SO actually need to be written,
> because writing to XER.SO is determined from the *input*, which
> is, clearly, NOT YET EVEN AVAILABLE at the time that the instruction is
> actually issued.

well, I'm approaching it from the perspective of: the instruction is fully
known at decode time, if the instruction is an addi, then it never writes SO,
and any successive instructions that read SO ignore the addi, not waiting for
it. if it's addo, then it *always* writes SO, writing 0 if necessary, and any
successive instructions that need SO will *always* wait for the addo. it never
*maybe* writes anything, cuz that has questionable benefits and requires
additional logic, it's always completely determined at decode time.

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